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Article

Comprehensive Two-Dimensional Gas Chromatography as a Powerful Strategy for the Exploration of Broas Volatile Composition

by
Andreia Bento-Silva
1,2,3,4,
Noélia Duarte
2,3,
Magda Santos
5,
Carina Pedrosa Costa
5,
Maria Carlota Vaz Patto
4,
Sílvia M. Rocha
5 and
Maria Rosário Bronze
2,3,4,6,*
1
FCT NOVA, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal
2
iMed.ULisboa, Instituto de Investigação do Medicamento, Faculdade de Farmácia, Universidade de Lisboa, Avenida Prof. Gama Pinto, 1649-003 Lisboa, Portugal
3
DCFM, Departamento de Ciências Farmacêuticas e do Medicamento, Faculdade de Farmácia da Universidade de Lisboa, Av. das Forças Armadas, 1649-003 Lisboa, Portugal
4
ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Avenida da República, 2780-157 Oeiras, Portugal
5
Department of Chemistry & LAQV-REQUIMTE, Universidade de Aveiro, Campus Universitário Santiago, 3810-193 Aveiro, Portugal
6
iBET, Instituto de Biologia Experimental e Tecnológica, Avenida da República, Quinta do Marquês, Estação Agronómica Nacional, Apartado 12, 2780-157 Oeiras, Portugal
*
Author to whom correspondence should be addressed.
Molecules 2022, 27(9), 2728; https://doi.org/10.3390/molecules27092728
Submission received: 27 March 2022 / Accepted: 18 April 2022 / Published: 23 April 2022
(This article belongs to the Special Issue Volatile Compounds in Food Chemistry)
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Abstract

:
Broa is a Portuguese maize bread with characteristic sensory attributes that can only be achieved using traditional maize varieties. This study intends to disclose the volatile compounds that are mainly associated with the baking process of broas, which can be important contributors to their aroma. Twelve broas were prepared from twelve maize flours (eleven traditional maize varieties and one commercial hybrid). Their volatile compounds were analyzed by GC×GC–ToFMS (two-dimensional gas chromatography coupled with time-of-flight mass spectrometry) for an untargeted screening of the chemical compounds mainly formed during baking. It was possible to identify 128 volatiles that belonged to the main chemical families formed during this stage. Among these, only 16 had been previously detected in broas. The most abundant were furans, furanones, and pyranones, but the most relevant for the aroma of broas were ascribed to sulfur-containing compounds, in particular dimethyl trisulfide and methanethiol. Pyrazines might contribute negatively to the aroma of broas since they were present in higher amounts in the commercial broa. This work constitutes the most detailed study of the characterization of broas volatile compounds, particularly those formed during the Maillard reaction. These findings may contribute to the characterization of other maize-based foodstuffs, ultimately improving the production of foods with better sensory features.

1. Introduction

Bread is considered one of the most important foodstuffs worldwide [1]. In Portugal, whole maize flour is used to produce a traditional bread known as broa [2], considered one of the 50 world’s best breads by CNN Travel in 2019 [3]. Over the last centuries, several traditional open-pollinated maize varieties have been developed to produce high-quality broas with improved flavors and aromas that are not possible to achieve using the presently available more productive commercial maize hybrids [2,4].
The aroma of bread plays a key role in its acceptance by consumers [1,5,6]. The nature of aroma is very complex [7,8], and the contribution of an individual compound to the overall aroma depends on several factors, such as its odor description and threshold (the intensity perceived by olfaction), adsorption to the food matrices, content, and interactions with other volatiles [5,7,9,10,11]. In addition, the sensory description of a volatile may change depending on its concentration, therefore influencing, positively or negatively, the overall food aroma [12]. Only a small portion of the volatile compounds contribute to the overall aroma of bread [5,7,8,10,11,12]. These volatiles are often referred to as “key” or “character-impact” compounds [11,13,14] and are generally present at trace levels [5,15], while other compounds present in high concentrations are only scarcely perceived by the human nose [5]. Frequently, many potent aroma compounds must blend to give the integrated aroma and flavor perception of a certain food [16].
The origin of bread volatiles is difficult to determine [17] once they result from lipid oxidation, fermentation and baking reactions [1,11]. However, at the baking stage, some of the most valuable aroma impact compounds are generated since they generally have low odor thresholds [18] and desirable sensory characteristics [7,9,15,19,20,21]. These reactions are often quoted as nonenzymatic browning reactions [21] and include mainly the Maillard reaction and, to a lower extent, the caramelization reactions [7,11]. Around 2 to 3% of sugars present in the dough undergo caramelization [22], giving rise to carbonyl compounds, furans, and brown-colored complex polymers [5,7,11,14,21,22]. The more relevant Maillard reaction occurs between carbonyls (most often reducing sugars) and free amino groups of amino acids, peptides, or proteins [5,7,9,18,20,23]. The main steps of this reaction are summarized in Figure 1. In the initial stage, free amino groups and reducing sugars condense and originate the Amadori or Heyns products [20,24]. Then, at the intermediate stage, furans, furanones, pyrans and pyranones are formed [20,24], following by amino acid degradation (Strecker reaction), when volatile compounds are formed without the need for sugars [25]. Ultimately, condensation and polymerization occur, leading to highly colored melanoidins and several aroma compounds, including pyrazines, pyrroles, pyridines, furans, oxazoles, thiazoles and thiophenes [7,11,15,20,21,26]. A previous study on broas has suggested that the volatiles produced at the baking stage, special pyranones, may positively contribute to the taste and aroma of this ethnical bread [27].
The volatile composition of bread has been usually characterized by HS-SPMS-GC-MS techniques (1D-GC) [27]. However, taking into account the complexity of bread aroma and the presence of very low amounts of important key volatiles [5,7,8,10,11], an analysis with a highly sensitive technique, such as comprehensive two-dimensional gas chromatography (GC×GC) [13,28], may allow the detection of important Maillard volatiles, which would be otherwise difficult or even impossible to identify. GC×GC employs two independent columns to separate sample analytes, and, therefore, the separation potential is greatly enhanced. ToFMS (time-of-flight mass spectrometry) detects unambiguous identification and ensures high selectivity throughout the chromatogram [28]. GC×GC–ToFMS has been recently used for untargeted food analyses, such as fruits, rice, hazelnuts, coffee and beverages [29,30]. To the best of our knowledge, this technique was only employed for targeted analysis of 2-acetyl-1-pyrroline in wheat and gluten-free bread [31] and has never been used to characterize the volatile composition of bread comprehensively.
Taking advantage of the powerful GC×GC–ToFMS technique, the present research involved an in-depth investigation of the volatile compounds of broas, aiming at the disclosure of those that might be important contributors to the typical aroma of this ethnic bread. The knowledge of broas volatiles may also be useful for identifying relevant compounds in other foods, which currently remain unidentified. Ultimately, the data obtained in this work can be explored to fingerprint [29] broas prepared from traditional varieties and contribute to a better knowledge of the Maillard reaction, which is essential to design foods that present sensory attributes demanded by the consumers [15,31].

2. Results and Discussion

Eleven broas (B1 to B11) prepared from eleven traditional maize varieties and one broa (B12) prepared from commercial hybrid maize flour were studied (Table S1 and Figure S2) [27]. A contour plot of the total ion current chromatogram of a broa sample (B1) under study is presented in Figure 2. In a first approach, the presence of volatiles belonging to the chemical families mostly associated with baking was identified in the chromatograms of all studied samples (n = 12). A total number of 128 volatile compounds belonging to these families were detected and are described in Table 1. More than 80% of the compounds have been identified according to the criteria described in Section 3.3.
The peak areas corresponding to the studied volatiles were measured, and their average in the twelve studied broas is presented in Table 1. The ratio of the peak area to odor threshold values in water (OT, in the Log10 form) was used as a screening method to identify the most relevant volatiles to the aroma of broas. Calculation of the odor activity value (OAV, ratio of the concentration to OT) is often carried out to evaluate the most aroma-active compounds in a food product. A compound might be sensed when OAV > 1 (or >0, when the Log10 form is considered) [18,30,32,33]. Although differences in peak areas among different compounds do not give direct information about their relative concentration, they greatly varied (sometimes more than 10.000-fold), suggesting they were present in very distinct concentrations. Thus, the higher the ratio, the higher the probability of a compound contributing to the aroma of this bread. The table also includes some examples of foods where the compounds have been detected (visually represented in Figure S1 from Supplementary Materials).
The results will be presented as follows: firstly, the advantages of the analysis of broas volatile compounds by GC×GC–ToFMS will be discussed by providing examples that allow the identification of unreported compounds. Secondly, the compounds will be explored according to their chemical families, and those which may be more relevant to the aroma of broas will be suggested. Finally, the results from the analyzed samples will be compared, and the correlations among their volatiles will be studied to elucidate which compounds may be responsible for the differences in their aroma.

2.1. The potentialities of GC×GC–ToFMS in the Identification of Broas Volatile Compounds

In a previous study on broas volatile composition by GC-MS (1D) [27], only 16 out of the 128 volatiles described in the present work were detected (Table 1), which confirms that GC×GC–ToFMS provides a much higher potential for the detection and identification of food volatiles [63,64]. It should also be noted that, in this work, a relatively high signal-to-noise (S/N) threshold (100) was used, which limited the number of detected compounds. Figure 2 and Figure 3 illustrate the advantages of GC×GC–ToFMS, which allowed the separation of analytes with similar volatility and common product ions through the secondary 2D column. Considering the set of columns used (non-polar/polar), the decrease in volatility (high 1tR) is mainly related to the increase in the number of carbons [64,65]. In contrast, the increase in the 2tR corresponds to increasing polarity [64,65]. For instance, 2-butyl-tetrahydrofuran (F31) was not detected in the previous study [27]. This compound was co-eluted with 2-nonanone (1tR: 715 s), and both presented similar mass spectra, with identical product ions at m/z 71 and 43 (Figure 3). However, since they present different polarities, their separation was achieved through the 2D column. 2-Butyl-tetrahydrofuran (F31) exhibits a slightly lower Log P than 2-nonanone (Log P: 2.93 and 3.08, respectively), which supports its relatively high polarity, and, therefore, the higher retention time in the 2D (2tR: 0.77 vs. 0.56 s). Thus, despite the high similarity index of 2-nonanone with the library spectra (89%) obtained in the previous analysis by GC-MS [27], the compound 2-butyl-tetrahydrofuran also contributed to the peak area considered for 2-nonanone. Without the high resolving power of GC×GC, the separation, identification, and relative quantitation of these two compounds would have been a challenge.
Another example is the identification of methylpentylfuran (F27). This compound was not commonly detected in foods but was previously tentatively identified in broas by GC-MS [27]. The results obtained in the present work corroborate this earlier identification. The mass spectrum of F27 showed a high similarity index with the spectra from methylpentylfuran from the Wiley database (Table 1). Furthermore, this compound showed a very low retention time of 0.50 s in the 2D column (Figure 4), suggesting its low polarity, which was confirmed by its calculated Log P of 4.43. Although methylpentylfuran usually refers to 3-methyl-2-pentylfuran, F27 can also correspond to other isomers, such as 2-methyl-5-pentylfuran or 4-methyl-2-pentylfuran. In addition, several other volatiles belonging to chemical families, which usually arise during baking, were eluted at this 1tR (705 s), namely furfurylfuran (F28), 2-formyl-3-methylthiophene (Tp4), 2-acetylthiophene (Tp5) and furaneol (Fo20). Since they show different polarities (Log P of 2.52, 1.38, 1.28 and –0.33, respectively), they were separated through the 2D column (2tR: 0.95, 1.31, 1.56 and 4.02, respectively). As shown in Figure 4A, the peak intensities of methylpentylfuran (F27) and 3-nonanone were much higher than F28, Tp4, Tp5 and Fo20. Thus, it would not have been possible to identify these compounds without the orthogonal separation through the 2D column [64,65]. The identification of volatile sulfur compounds (Figure 4B) is particularly relevant since they are typically present in foods at extremely low levels, often at sub-parts-per-billion concentrations, but provide background sensory nuances to the flavor and are often considered “character-impact compounds” [13].
These results show the potentialities of GC×GC–ToFMS for the characterization of food volatiles and demonstrate the complexity of the volatile composition of broas. Moreover, this technique also allowed the identification of several compounds belonging to the characteristic chemical classes of the baking process, which have not been commonly described either in bread or maize-based foods.

2.2. Exploring the Volatile Compounds Associated with Baking

The most relevant compounds of broas, selected based on their abundance and, more importantly, their OTs, will be discussed below.

2.2.1. Furans and Furanones

Furan and furanone derivatives are among the most common volatiles of heated foods [20,66], and give burnt, savory, sweet and caramel aroma to foods [9,15,20]. The major furans included 2-pentylfuran (F20) and 2-butylfuran (F14), which have been previously detected in broas [27]. 2-Pentylfuran (F20) was particularly abundant, and it is a potent odorant [48], giving floral-fruity notes [60], which may significantly contribute to their aroma. It has been reported as the most common aroma-active furan in wheat bread crumb [60] and a likely contributor to the total aroma and flavor of maize tortilla chips [43] and popcorn [33].
Several furans with oxygenated substituents, such as furfurals and furanones, were also identified in broas. Among all the compounds described in the present work, the highest peak areas were obtained for 2-furanmethanol (F13). Although it is not a very strong odorant [32,48], this compound may also be relevant for the aroma of broas due to its abundance. It is usually associated with pleasant, creamy and caramel notes [41] and may be relevant to the aroma of popcorn [33]. Other oxygenated furans include 5-methyl-2-furanmethanol (F19), 3-furfural (F10), and isomaltol (F22), which had not been previously reported in broas [27]. Among these, 5-methyl-2-furanmethanol showed a relatively low OT and was confirmed as a key aroma compound of Chinese white bread [49]. It was not possible to confirm the OTs of 3-furfural and isomaltol, but they have been considered important compounds to the aroma of popcorn [33] and wheat bread [5,21], respectively.
Only two out of the twenty-six furanones detected in the present work have been previously detected in broas, namely N-caprolactone (Fo19) and γ-nonalactone (Fo26). Both are possible contributors to broa’s sweet aroma [5,41] since they were present in high amounts in broas and are potent odorants [44,47]. γ-Octalactone (Fo23), detected in broas for the first time, may also contribute to their aroma, considering its abundance and low OT.

2.2.2. Pyrans and Pyranones

Pyrans have not been described in similar food products, but some may also be important odorants, specially tetrahydropyrans [48]. In contrast, pyranones occur in the volatiles of all heated foods [20], conferring sweet, burnt, pungent and caramel-like flavors and aromas [15]. The most relevant pyranones were maltol (Po7) and 3-hydroxy-2,3-dihydromaltol (Po8). These compounds have been previously described as possible positive contributors to the ‘taste and aroma’ of broas [27]. Maltol imparts desirable, caramel-like, sweet and fruity characteristics to foods [14,20,21]. It can mask bitter flavors [14] and is considered a key odorant in cereal products [67]. Although it has a relatively high OT of 2500–9000 µg L−1 [14,43], it may be important for the aroma of broas due to its abundance.

2.2.3. Pyrazines

In the present study, twelve pyrazines were identified in broas, although only 2-methyl pyrazine (Pz2) had been previously described [27]. Pyrazines are considered impact odorants, with characteristic pleasant nutty and roasted odor notes [7,11,20,59,68]. They significantly contribute to the flavor of baked products [11], such as bread [5,7,31], popcorn, rye crisp bread [68] and maize products [24]. Broas appear to have a lack of pyrazines when compared to similar foods. Recent studies have shown that the amount of pyrazines varies greatly between different cereal bread [31,56,69].
Although the OT values of alkylpyrazines are relatively high (above 1000 µg L−1) [20,68], replacing one or more methyl groups with ethyl can give a marked decrease in the OT. Some ethyl-substituted pyrazines have sufficiently low threshold values to be important in the roast aroma of cooked foods [20]. Taking into account the OTs described for pyrazines and their amount in broas, 2-methylpyrazine (Pz2), 2,6-dimethylpyrazine (Pz3) and, especially, 2-ethyl-dimethylpyrazine (Pz9), may be relevant for their overall aroma. The former shows nutty, cocoa, and roasted meat aromas [68]; however, it was described as a possible off-volatile popcorn [33]. 2,6-Dimethylpyrazine was also considered an important volatile in maize meal extruded product with whey protein [24]. Lastly, Pz9 was tentatively identified as 2-ethyl-3,6-dimethylpyrazine or 2-ethyl-3,5-dimethyl-pyrazine since they show similar SI and LRI (Table 1). Both compounds are potent odorants and contribute to cocoa, nutty, potato and roasted notes [51]. 2-Ethyl-3,5-dimethylpyrazine is a key odorant of maize tortilla chips, popcorn and rye bread crust [7,43,70], whilst 2-ethyl-3,6-dimethylpyrazine is a key odorant of maize tortilla chips, taco shell [32,43] and popcorn [33].
Some pyrazines, such as 2-acetyl-3-methylpyrazine (Pz10), 5H-5-methyl-6,7-dihydrocyclopentapyrazine (Pz11) and 2-(2′-furyl)-pyrazine (Pz12), have not been detected in related food products, but may still be relevant to the aroma of broas, since Pz10 and Pz11 may give maize-like aromas to foods [51].

2.2.4. Pyridines and Pyrimidines

Pyridines and pyrimidines were detected in broas for the first time. Although they were not present in high amounts, they might still be relevant to the overall aroma due to their low OTs. Pyridines give roasted and popcorn odors to foods [14,43].
2-Acetyltetrahydropyridines (or 6-acetyltetrahydropyridines) are possibly the most common pyridines in similar foodstuffs. They are potent Maillard flavor compounds that contribute substantially to caramel, roasty, and bready aromas [51,71] in several bakery products [14,16,32,71], and are formed by the degradation of proline and hydroxyproline [20]. However, these compounds were not detected in broas. Instead, 1-acetyl-1,2,3,4-tetrahydropyridine (Pd8) was identified as the main pyridine. Although it exhibits a similar mass spectrum to 2-acetyltetrahydropyridine, Pd8 showed a very intense peak at m/z 68 (Figure S3), which is not expected in 2-acetyltetrahydropyridine [72]. This compound has also been identified in the crusts of wheat bread [42] and lupin protein isolate-enriched wheat bread as an important contributor to its aroma profile [42]. Thus, it might also be an important broa volatile, contributing to a nutty odor [42].
2-Pentylpyridine (Pd9) may also be relevant for broas aroma, contributing to roasted and nutty odors [51]. Although it was present in lower amounts than other pyridines, it shows a very low OT [48]. This compound has not been described in similar foods, probably due to its low concentration, but it has been described in several fried foods [73].
4-Methylpyrimidine (Pd2) was the only pyrimidine detected in broas. This compound has not been described either in bread or in other maize-based foods, and it was not possible to obtain any information regarding its odor characteristics.

2.2.5. Pyrroles, Pyrrolines and Oxazoles

Pyrrole derivatives are responsible for roasted odors [14]. Skatole (Py12) has a very low OT of 0.2 µg L−1 [16] and may be relevant to the aroma of broas. It is usually described as an off-flavor. However, in low concentrations, it may introduce a natural note of ‘overmature flower’ [51].
One of the most striking results to emerge from this study was the absence of pyrrolines in broas. These compounds are abundant bread volatiles, significantly contributing to their flavor [5,7]. Pyrrolines have been described as character impact odorants of the ‘roasted’ and ‘popcorn-like’ notes [7]. Important pyrrolidines described in cereal bread and maize-based foods are 2-acetyl-1-pyrroline and its precursor 1-pyrroline [7,14,20,59]. However, recent studies have shown that 2-acetyl-1-pyrroline varies greatly among different cereal bread [69]. For instance, 2-acetyl-1-pyrroline seems not to be so relevant to the aroma properties of rye bread [7], and it was not detected in gluten-free bread, which was analyzed by GC×GC [31]. By contrast, other authors have found that 2-acetyl-1-pyrroline was higher in gluten-free bread [56]. These differences can be explained by the presence or absence of precursors or interferents in the cereal flours. For instance, differences in the ornithine content of yeasts may play a role in forming pyrrolines since this amino acid has been ascribed as the most important precursor for forming 2-acetyl-1-pyrroline during baking [7,11,20]. 2-Acetylpyrroline may also be formed by the degradation of proline and hydroxyproline, similar to 2-acetyl-tetrahydropyridines [20], which were also not found in broas, as previously discussed. Thus, differences in the amounts of proline and hydroxyproline may also influence the production of 2-acetylpyrroline and 2-acetyl-tetrahydropyridines. In addition, phenolic acids may inhibit the production of 2-acetyl-1-pyrroline [74], and whole maize flours were used to prepare broas, which have higher amounts of phenolic compounds compared to other cereals or with refined maize flours [75]. Lastly, 2-acetyl-1-pyrroline is highly volatile and can be oxidized to 2-acetylpyrrole [14,20], one of the major volatile compounds detected in the present work.
Three oxazoles were detected in broas, but they probably have a low impact on their overall aroma, as reported for other foods [20]. They were present in broas in very low amounts compared to other compounds.

2.2.6. Sulfur-Containing Compounds

Sulfur compounds had not been previously reported in broas [27], possibly due to their low concentrations. Usually, foods from cereals show very low contents in sulfur-containing compounds due to the low amounts of sulfur amino acids [20]. However, sulfur-containing Maillard odorants constitute the most powerful aroma compounds of foods, even though they are present at trace levels [14,15]. These compounds have traditionally been associated with unpleasant and noxious off-flavors [13,14]. Still, they contribute to positive flavor characteristics at low concentrations (<1 µg kg−1), giving tropical, fruity, and savory aromas to foods [13]. They are considered “character-impact compounds” of bread crust, popcorn and toasted cereal grains [13,15].
Dimethyl sulfide (S2), dimethyl disulfide (S3), and, in particular, dimethyl trisulfide (S8) may be extremely relevant for the aroma of broas. At low levels, they all show positive aroma characteristics. Dimethyl trisulfide (S8) has an extremely low OT of 0.01 µg L−1 [43] and, when present at low concentrations, is associated with tropical fruit and grapefruit aromas [13]. The most abundant sulfur compound detected in broas was dimethyl disulfide (S3), an important contributor to maize flavor [24]. Dimethyl sulfide (S2) is considered a flavor impact compound of sweet maize and conveys the typical flavor impression of canned maize when present at reduced levels [13]. Methanethiol (S1) was the second most abundant sulfur-containing compound and may also significantly impact the aroma of broas. It has been described as a possible contributor to the aroma of sweet maize [13].
Another sulfur-containing compound detected in broas was the very well-known methional (S7) [68], possibly also one of the most relevant volatiles for the aroma of broas. It is a potent [5] and desired odorant [21], with a characteristic potato-like aroma [7,59]. It has been considered a key odorant of fried foods [43], wheat, rye [7] and Chinese white [49] bread. It may be responsible in part for typical popcorn [33], maize tortilla chips [43] and taco shell [32] aroma characteristics. Furthermore, it has flavor-modifying characteristics since it has been shown to suppress flavor and aroma [59]. Other aliphatic sulfur compounds detected in broas were 1-methylthiopropane (S4) and methylthio-2-propanone (S5). These compounds have not been described in similar foods, and their impact on the overall aroma of broas is unknown.
Regarding aromatic sulfur heterocycles derivatives, it was possible to detect three thiazoles and six thiophenes. Thiazoles usually confer green, vegetable-like, cocoa and nutty aromas to foods [20], while thiophenes contribute to sulfurous, nutty and fatty aromas [51]. Among them, 2-acetylthiazole (Tz2) may have high importance in the aroma of broas. It has been described as a key volatile of popcorn and maize flour extrudates [40]. It was possible to detect six thiophenes in broas. Still, they have not been so commonly described in similar foods, and it was not possible to find information regarding their OTs in the literature.
Another sulfur heterocycle compound detected in broas was an oxathiane derivative (S6), which may refer to 1,2-, 1,3- or 1,4-oxathiane. However, considering their polarities (Log P of 1.14, 0.43 and 0.36, respectively) and the 2tR of S6 (1.10 s), it was tentatively identified as 1,2-oxathiane. This compound has not been described in foods, but oxathiane derivatives have been ascribed as important aroma compounds. The most relevant example is 2-methyl-4-propyl-1,3-oxathiane, a key aroma compound of passion fruit, with a low OT of 3 µg L−1 [13]. Recently, this compound and 2,4,4,6-tetramethyl-1,3-oxathiane have been detected in wines [76]. Although the impact of oxathiane on the aroma of foods is currently unknown, it may impact the aroma of broas, and this compound is worth further study.

2.3. An Overall View of the Volatiles Associated with Baking in Broas

Sensory analysis in a previous study [77] revealed that the broa prepared from the available commercial maize hybrid variety (B12) showed the lowest scores for ‘smell and odor’ and ‘taste and aroma’. In contrast, the traditional broas (obtained from the traditional open-pollinated varieties) were poorly discriminated among them [77]. A subsequent study revealed that these differences could at least be partially explained by their volatile composition [27]. Thus, a PCA (principal component analysis) was performed to explore further these differences for an easy, rapid and global assessment of the main differences in the volatile composition among the studied broas. Figure 5 shows the projection of samples and variables in the space defined by the two principal components, corresponding to 59.2% of the total variance. A hierarchical cluster analysis combined with a heatmap representation was also constructed and shown in Figure S4.
Since all broas were prepared following the same procedure and submitted to the same temperature of kneading and baking, it can be stated that the differences observed among the different broas were caused by differences in the corresponding maize flours, which affect the Maillard reaction. A matrix correlation analysis was conducted and represented by a heatmap to shed some light on the volatile compounds which might have been formed from the same precursors (Figure 6 and Tables S4 and S5).
The volatiles that strongly contributed to differentiating the samples along PC2 (Figure 5) are represented in group A of the correlation matrix (Figure 6) and highlighted in Tables S4 and S5. This group is characterized by a simple pattern of strong and positive correlations amongst several furans and furanones. In low-moisture starchy foods, such as broas, the Maillard reaction seems to be the main route of their formation [78,79]. Thus, higher amounts of the Maillard reaction precursors, such as amino acids and sugars, may have generated broas with higher amounts in furans. Alternatively, the presence of interferents, for instance, phenolic compounds [27], may explain these correlations since they may promote [27,80] or inhibit [74,80] the reaction. In particular, very strong correlations (R > 0.85, p < 0.05) were observed among 2-methylfuran (F2), 5-methyl-2-furanmethanol (F19) and 2-acetyl-5-methylfuran (F25), which are usually produced by caramelization reactions and by the breakdown of the Amadori or Heyns intermediates in the early stages of the Maillard reaction (Figure 1) [14,19,20]. Strong and positive (R > 0.7, p < 0.05) correlations were also found between dihydro-2-methyl-3-(2H)-furanone (Fo2) and sulfur-containing heterocycles. Higher amounts in dihydro-2-methyl-3-(2H)-furanone, which reacts with ammonia and hydrogen sulfide (produced from cysteine by hydrolysis or by Strecker degradation) [19,20,24,81], may directly cause higher amounts of thiazoles and thiophenes.
The volatile compounds that strongly contributed to differentiating the samples along PC1 (Figure 5) are placed in group B of the correlation heatmap (Figure 6 and Tables S4 and S5) and consisted, among others, of several pyrazines. The major route for the formation of pyrazines is thought to be from α-aminoketones, which are products of the condensation of a dicarbonyl with an amino compound via Strecker degradation during the Maillard reaction [20,24]. Very strong and positive correlations were found between Pz7 (2-methyl-5-vinylpyrazine) and Pz3 (2,6-dimethylpyrazine), both products from the reaction between leucine and fructose [59]. The broa prepared from the available commercial hybrid variety maize flour (B12) showed a higher content in pyrazines (p < 0.05) than all the traditional varieties (Table S2 and Figure 7), especially in 2-methylpyrazine (Pz2) and 3-dimethylpyrazine (Pz5) (Table S3). The higher amounts of total ferulic acid in the traditional maize varieties [82] might have inhibited the formation of pyrazines [80] in the corresponding broas.
Lastly, the volatiles which negatively contributed to PC1 and PC2 are located in group C (Figure 6). These volatiles show strong and negative correlations with several of the volatiles which belong to groups A and B. Furfural (F12) was strongly and negatively correlated to both benzofuran (F21) and furfurylfuran (F28). Thus, broas with higher amounts of furfural also showed lower amounts of benzofuran and furfurylfuran, and vice versa. Furfural is mainly generated in the initial stages of the Maillard reaction and participates in further reactions [14,24,83]; thus, differences in the precursors which reacted with furfural and generated benzofuran and furfurylfuran, or the presence of interferents of this reaction [27,80], may have influenced its extent. Similarly, negative correlations were found among several sulfur compounds and both furans and furanones, which have been described as important precursors of thiazoles and thiophenes [24], and between oxathiane (S6) and sulfur-containing compounds, such as dimethyl disulfide (S3), dimethyl trisulfide (S8), 2-acetylthiophene (Tp5) and benzothiazole (Tz3), which might have been precursors of the formation of oxathiane. A recent study in wines has proposed that thiols act as precursors of the formation of oxathiane [76].
Taken together, these results suggest that the main differences among the volatile compounds of the studied broas are likely due to the presence of specific precursors or interferents which affect the extent of some reaction pathways of the Maillard reaction, as the formation of pyrazines and oxathiane, rather than the overall Maillard reaction. These results can partially explain the contradictory reports on the effect of phenolic compounds on the Maillard reaction [27,74,80]. Differences in precursors or interferents of certain pathways of this reaction in maize varieties can cause differences in broas aroma.
As previously stated, the analyzed commercial hybrid variety sample (B12) showed lower scores in a sensory analysis [77]. The results from the present study have shown that this sample showed a higher content in pyrazines (Figure 7), particularly in 2-methylpyrazine (p < 0.05). These results were somewhat surprising since pyrazines are strong odorants usually associated with positive sensorial characteristics, giving roasted and nutty aromas to bread [5,51]. However, pyrazines may contribute to aroma characteristics in broas that are not typical of this type of bread, giving rise to some of the negative comments associated with B12, such as a ‘weak typical flavor’, ‘wheat bread flavor’, ‘with a weak maize flavor’ and ‘no history’ [27]. Similarly, it has been reported that most pyrazines contributed negatively to the aroma of popcorn [33]. Besides the higher amount in pyrazines, a closer examination of Table S3 also showed that 2-butyltetrahydrofuran (F31) was present in B12 in higher (p < 0.05) amounts. However, this compound has not been described in similar foods, and it was not possible to infer its impact on broas aroma. Therefore, these data should be further explored for the characterization of broas aroma and fingerprinting [29], since both 2-butyltetrahydrofuran and 2-methylpyrazine may be potential biomarkers of the authenticity of broas prepared from traditional maize varieties.
Other compounds can contribute to the lower sensory attributes of B12, namely the higher contents in some pyridines and pyrroles, including the powerful skatole (Py12), often associated with off-aromas [51], and lower contents in maltol (Po7), associated with higher ‘taste and aroma’ [27]. Although the ANOVA showed that these results were not statistically different from some traditional varieties (p > 0.05) (Table S3), combinations of volatiles can yield different characteristics than those expected from individual compounds [12,30], and therefore contribute to the lower sensory attributes of broas prepared from the commercial maize hybrid variety under study.

3. Materials and Methods

3.1. Samples

Eleven broas (B1 to B11) were prepared from eleven traditional open-pollinated maize varieties, described in Table S1. The traditional samples were chosen as representative of the Portuguese maize germplasm variability, taking into account their agronomic performance in field trials, basic nutritional quality and genetic diversity evaluated under the scope of the FP7 SOLIBAM European project. One broa (B12) prepared from a commercial maize hybrid variety was also studied.
Broas was prepared following a traditional recipe, as previously described [27]. The ingredients included 70% maize flour, 20% commercial rye flour (Concordia type 70, Portugal) and 10% commercial wheat flour (National type 65, Portugal). The dough was manually molded into 400 g balls and baked in a gas oven (Matador; Werner & Pfleiderer) at 270 °C for 40 min.

3.2. HS-SPME Methodology

The HS-SPME methodology was based on the previous work developed by Bento-Silva et al., 2021 [27]. Briefly, 4 g of broas (whole bread, including crumb and crust) were smashed manually and placed in a 20 mL vial. A 50/30 µm DVB/CAR/PDMS (divinylbenzene/carboxen/polydimethylsiloxane) fiber purchased from Supelco (Sigma-Aldrich, St. Louis, MO, USA) was used to concentrate the volatile compounds present in the headspace. Samples were extracted for 40 min in a thermostated bath adjusted to 60.0 ± 0.1 °C at 250 rpm. All samples were extracted in duplicate.

3.3. GC×GC–ToFMS Analysis

The GC×GC–ToFMS experimental parameters were adapted from Costa et al. (2020) [65]. The equipment used was a LECO Pegasus 4D GC×GC–ToFMS system (LECO, St. Joseph, MI, USA) consisting of an Agilent GC 7890A gas chromatograph (Agilent Technologies, Inc., Wilmington, DE, USA) with a dual-stage jet cryogenic modulator (licensed from Zoex) and a secondary oven, and a mass spectrometer equipped with a time-of-flight (ToF) analyzer.
The SPME fiber was manually introduced into the port at 250 °C for analyte desorption. The injection port was lined with a 0.75 mm I.D. glass liner. Splitless conditions (30 s) were used. An Equity-5 30 m × 0.32 mm I.D., 0.25 μm film thickness (Supelco, Bellefonte, PA, USA) was used as a first-dimension column (1D), and a DB-FFAP 0.79 m × 0.25 mm I.D., 0.25 μm film thickness (J&W Scientific Inc., Folsom, CA, USA) was used as a second-dimension column (2D). The carrier gas was helium at a constant flow rate of 2.50 mL min−1. The primary oven temperature was programmed from 35 °C (5 min) to 230 °C (2 min) at 10 °C min−1, and the secondary oven program was 30 °C offset above the primary one. The MS transfer line and MS source temperatures were set at 250 °C. The modulation period was 5 s, keeping the modulator at 20 °C offset above the primary oven, with hot and cold pulses by 0.80 and 1.70 s, respectively. The mass spectrometer ran in the EI mode at 70 eV and detector voltage of –1530 V, using an m/z range of 35–350.
In an initial approach, the total ion chromatograms were processed using the automated data processing software ChromaTOF (LECO) at the S/N threshold of 100. The obtained GC×GC total ion chromatogram contour plots exhibited more than 1200 peaks. As the present study focused on the compounds mainly produced during baking, in a second approach, all the compounds belonging to the characteristic chemical families associated with the Maillard and caramelization reactions were selected. In addition, the volatile compounds described in the literature as key aromas of bread or maize-based foods and which were not detected using the automated data processing (S/N < 100) were searched on the chromatograms based on extracted ion chromatogram contour plots of the characteristic ions, and the corresponding peak areas were also included.
For identification purposes, the mass spectrum and retention times (1D and 2D) of the analytes were compared with the mass spectral libraries, namely an in-house library of standards and two commercial databases (Wiley 275 and US National Institute of Science and Technology (NIST) V. 2.0–Mainlib and Replib). Additionally, the linear retention index (LRI) was experimentally determined according to the van den Dool and Kratz LRI equation [84]. A C8-C20 n-alkane series was used for LRI determination (the solvent n-hexane was used as the C6 standard). These values were compared with those reported in the literature for chromatographic columns similar to the 1D column mentioned above. A positive identification was considered when the experimental spectra shared at least an 80% similarity with spectra from the software libraries and the LRI deviation was less than 5%. This difference in LRI takes into account that (i) the literature data are obtained from a large range of GC stationary phases (several commercial GC columns are composed of 5% phenylpolysilphenylene-siloxane or equivalent stationary phases), and (ii) the modulation causes some inaccuracy in the first dimension retention time, and the majority of the values reported in the literature were determined in a 1D-GC separation system [64]. The Log p values were calculated using ALOGPS 2.1 to confirm the identification of some compounds which did not match all the criteria described above [85].
The DTIC (deconvoluted total ion current) GC×GC peak area data were used to estimate the relative content of each volatile component in the different samples.

3.4. Statistical Analysis

The peak area data of all studied compounds were extracted from the chromatograms and used to build the full data matrix consisting of 12 broas samples and 128 variables. After data normalization, hierarchical cluster analysis (HCA) and Pearson’s coefficient correlations, both combined with heatmap visualizations, were applied for this dataset using the MetaboAnalyst 3.0 (web software, The Metabolomics Innovation Centre (TMIC), Edmonton, AB, Canada). Independent sample t-tests, ANOVA followed by post hoc Tukey tests and principal component analyses (PCA) were obtained using the software SPSS version 21 (IBM, Armonk, NY, USA). The limit of significance was set at p < 0.05.

4. Conclusions

This study aimed to extend previous research on the volatile compounds of broas, focusing on those mainly associated with the baking process. Almost 90% of the compounds identified in this work have not been previously detected in broas. One of the most relevant study findings was the absence of pyrrolidines and the lack of pyrazines in broas, especially when prepared from traditional open-pollinated maize varieties. Thus, the absence of pyrrolidines may contribute to the distinctive aroma of broas, and the high amounts of pyrazines may confer negative characteristics associated with the commercial hybrid maize broa analyzed. Sulfur compounds, such as dimethyl trisulfide and methanethiol, were identified as the most likely contributors to the aroma of this ethnic bread. Some volatiles, such as oxathiane, have not been previously reported in similar foods, and their relevance to the overall aroma of foods is currently unknown. The data obtained in this study can be further explored for the purpose of fingerprinting traditional broas since some compounds (2-methylpyrazine and 2-butyltetrahydrofuran) were present in significantly higher amounts in the broa prepared from the analyzed commercial maize hybrid variety. In conclusion, this work represents the most detailed study on the volatile composition of broas. It may contribute to disclosing possible volatiles of other bread and maize-based foods. These findings may have a number of important implications for future practice since better knowledge of the volatile compounds produced along the Maillard reaction may help to achieve the production of foods with sensory characteristics more appreciated by consumers.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/molecules27092728/s1; Figure S1: Visual representation of the volatile baking compounds reported in the literature for several bread and maize-based foods (nodes), Figure S2: Picture of broas, Figure S3: Electron ionization mass of Pd8 (1-acetyl-1,2,3,4-tetrahydropyridine) and mass spectra of 1-acetyl-1,2,3,4-tetrahydropyridine and 2-acetyl-1,4,5,6-tetrahydropyridine from the Wiley library, Figure S4: Heatmap and hierarchical cluster analysis representation of the 128 volatiles identified in broas. The content of each metabolite is illustrated through a chromatic scale, Table S1: Maize flours and broas identification and description., Table S2: Average total peak areas and % of chromatogram area for the families of chemical compounds studied in broas, Table S3: Peak areas obtained for each sample (average of duplicates) and considered for the statistical analysis, Tables S4 and S5: Spearman correlation coefficients among the 128 studied broas volatile compounds.

Author Contributions

Conceptualization, A.B.-S. and M.R.B.; methodology, A.B.-S., M.S. and S.M.R.; software, A.B.-S., M.S. and C.P.C.; validation, A.B.-S., N.D., M.C.V.P., S.M.R. and M.R.B.; formal analysis, A.B.-S.; investigation, A.B.-S., M.S. and S.M.R.; resources, M.C.V.P., S.M.R. and M.R.B.; data curation, A.B.-S., M.S. and C.P.C.; writing—original draft preparation, A.B.-S.; writing—review and editing, A.B.-S., N.D., M.C.V.P., S.M.R. and M.R.B.; visualization, A.B.-S.; supervision, S.M.R. and M.R.B.; project administration, M.C.V.P., S.M.R. and M.R.B.; funding acquisition, M.C.V.P. and M.R.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement number 245058, by Fundação para a Ciência e Tecnologia through GREEN-IT - Bioresources for Sustainability R&D Unit (UIDB/04551/2020, UIDP/04551/2020) and LS4FUTURE Associated Laboratory (LA/P/0087/2020).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data supporting the findings of this study are available within the article and its Supplementary Material.

Acknowledgments

The authors are grateful to Pedro Moreira from ESAC for providing the maize samples and to Carla Brites and Bruna Carbas from INIAV for their assistance with broas preparation.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Sample Availability

Not available.

References

  1. Pico, J.; Gómez, M.; Bernal, J.; Bernal, J.L. Analytical Methods for Volatile Compounds in Wheat Bread. J. Chromatogr. A 2016, 1428, 55–71. [Google Scholar] [CrossRef] [PubMed]
  2. Vaz Patto, M.C.; Alves, M.L.; Almeida, N.F.; Santos, C.; Moreira, P.M.; Satovic, Z.; Brites, C.; Patto, V.; Alves, N.F.; Almeida, C.S.; et al. Is the Bread Making Technological Ability of Portuguese Traditional Maize Landraces Associated with Their Genetic Diversity? Maydica 2009, 54, 297–311. [Google Scholar]
  3. Smith, J.R. 50 of the World’s Best Breads. Available online: https://edition.cnn.com/travel/article/world-50-best-breads/index.html (accessed on 26 March 2022).
  4. Vaz Patto, M.C.; Mendes-Moreira, P.M.; Alves, M.L.; Mecha, E.; Brites, C.; Bronze, R.; Pego, S. Participatory Plant Quality Breeding: An Ancient Art Revisited by Knowledge Sharing. The Portuguese Experience. In Plant Breeding from Laboratories to Fields; InTechOpen: London, UK, 2013; pp. 255–288. [Google Scholar]
  5. Pico, J.; Bernal, J.; Gómez, M. Wheat Bread Aroma Compounds in Crumb and Crust: A Review. Food Res. Int. 2015, 75, 200–215. [Google Scholar] [CrossRef] [PubMed]
  6. Lasekan, O.; Dabaj, F.; Muniandy, M.; Juhari, N.H.; Lasekan, A. Characterization of the Key Aroma Compounds in Three Types of Bagels by Means of the Sensomics Approach. BMC Chem. 2021, 15, 16. [Google Scholar] [CrossRef] [PubMed]
  7. Cho, I.H.; Peterson, D.G. Chemistry of Bread Aroma: A Review. Food Sci. Biotechnol. 2010, 19, 575–582. [Google Scholar] [CrossRef]
  8. Raffo, A.; Carcea, M.; Castagna, C.; Magrì, A. Improvement of a Headspace Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry Method for the Analysis of Wheat Bread Volatile Compounds. J. Chromatogr. A 2015, 1406, 266–278. [Google Scholar] [CrossRef] [PubMed]
  9. Starowicz, M.; Zieliński, H. How Maillard Reaction Influences Sensorial Properties (Color, Flavor and Texture) of Food Products? Food Rev. Int. 2019, 35, 707–725. [Google Scholar] [CrossRef]
  10. Pétel, C.; Onno, B.; Prost, C. Sourdough Volatile Compounds and Their Contribution to Bread: A Review. Trends Food Sci. Technol. 2017, 59, 105–123. [Google Scholar] [CrossRef]
  11. Pozo-Bayón, M.A.; Guichard, E.; Cayot, N. Flavor Control in Baked Cereal Products; Taylor & Francis Group: Philadelphia, PA, USA, 2006; Volume 22, ISBN 8755912060. [Google Scholar]
  12. Chambers, E., IV; Koppel, K. Associations of Volatile Compounds with Sensory Aroma and Flavor: The Complex Nature of Flavor. Molecules 2013, 18, 4887–4905. [Google Scholar] [CrossRef]
  13. McGorrin, R.J. The Significance of Volatile Sulfur Compounds in Food Flavors. ACS Symp. Ser. 2011, 1068, 3–31. [Google Scholar] [CrossRef]
  14. Belitz, H.-D.; Grosch, W.; Schieberle, P. Cereals and Cereal Products. In Food Chemistry; Springer: Berlin/Heidelberg, Germany, 2009; pp. 670–745. [Google Scholar]
  15. Bastos, D.M.; Monaro, É.; Siguemoto, É.; Séfora, M.; Markowicz, D.; Monaro, E.; Siguemoto, E.; Sefor, M. Maillard Reaction Products in Processed Food: Pros and Cons. In Food Industrial Processes – Methods and Equipment; Benjamin, V., Ed.; InTechOpen: London, UK, 2012. [Google Scholar] [CrossRef] [Green Version]
  16. Buttery, R.G.; Ling, L.C.; Stern, D.J. Studies on Popcorn Aroma and Flavor Volatiles. J. Agric. Food Chem. 1997, 45, 837–843. [Google Scholar] [CrossRef]
  17. Martins, S.I.F.S.; Jongen, W.M.F.; Van Boekel, M.A.J.S. A Review of Maillard Reaction in Food and Implications to Kinetic Modelling. Trends Food Sci. Technol. 2000, 11, 364–373. [Google Scholar] [CrossRef]
  18. Birch, A.N.; Petersen, M.A.; Hansen, Å.S. REVIEW: Aroma of Wheat Bread Crumb. Cereal Chem. 2014, 91, 105–114. [Google Scholar] [CrossRef]
  19. Hellwig, M.; Henle, T. Baking, Ageing, Diabetes: A Short History of the Maillard Reaction. Angew. Chemie Int. Ed. 2014, 53, 10316–10329. [Google Scholar] [CrossRef]
  20. Berger, R.G. Flavours and Fragrances: Chemistry, Bioprocessing and Sustainability; Springer Science & Business Media: Berlin, Germany, 2007; ISBN 3540493395. [Google Scholar]
  21. Purlis, E. Browning Development in Bakery Products—A Review. J. Food Eng. 2010, 99, 239–249. [Google Scholar] [CrossRef]
  22. Cauvain, S.P. Bread Making: Improving Quality; Woodhead Publishing Limited: Cambridge, UK, 2003; ISBN 0-203-49500-4. [Google Scholar]
  23. Tamanna, N.; Mahmood, N. Food Processing and Maillard Reaction Products: Effect on Human Health and Nutrition. Int. J. Food Sci. 2015, 2015, 526762. [Google Scholar] [CrossRef]
  24. Bailey, M.E.; Gutheil, R.A.; Hsieh, F.-H.; Cheng, C.-W.; Gerhardt, K.O. Maillard Reaction Volatile Compounds and Color Quality of a Whey Protein Concentrate—Corn Meal Extruded Product; ACS Publications: Washington, DC, USA, 1994; ISBN 1947-5918. [Google Scholar]
  25. Seok, Y.-J.; Kim, Y.-G.; Jeong, S.Y.; Lee, J.; Yoon, H.-J. Furan in Thermally Processed Foods—A Review. Toxicol. Res. 2015, 31, 241. [Google Scholar] [CrossRef]
  26. Rizzi, G.P. The Strecker Degradation of Amino Acids: Newer Avenues for Flavor Formation. Food Rev. Int. 2008, 24, 416–435. [Google Scholar] [CrossRef]
  27. Bento-Silva, A.; Duarte, N.; Belo, M.; Mecha, E.; Carbas, B.; Brites, C.; Vaz Patto, M.C.; Bronze, M.R. Shedding Light on the Volatile Composition of Broa, a Traditional Portuguese Maize Bread. Biomolecules 2021, 11, 1396. [Google Scholar] [CrossRef]
  28. Adahchour, M.; Beens, J.; Brinkman, U.A.T. Recent Developments in the Application of Comprehensive Two-Dimensional Gas Chromatography. J. Chromatogr. A 2008, 1186, 67–108. [Google Scholar] [CrossRef]
  29. Tranchida, P.Q.; Purcaro, G.; Maimone, M.; Mondello, L. Impact of Comprehensive Two-Dimensional Gas Chromatography with Mass Spectrometry on Food Analysis. J. Sep. Sci. 2016, 39, 149–161. [Google Scholar] [CrossRef] [PubMed]
  30. Rocha, S.M.; Costa, C.P.; Martins, C. Aroma Clouds of Foods: A Step Forward to Unveil Food Aroma Complexity Using GC×GC. Front. Chem. 2022, 10, 820749. [Google Scholar] [CrossRef] [PubMed]
  31. Pacyński, M.; Wojtasiak, R.Z.; Mildner-Szkudlarz, S. Improving the Aroma of Gluten-Free Bread. Lebensm. -Wiss. Und-Technol. 2015, 63, 706–713. [Google Scholar] [CrossRef]
  32. Buttery, R.G.; Ling, L.C. Volatile Flavor Components of Corn Tortillas and Related Products. J. Agric. Food Chem. 1995, 43, 1878–1882. [Google Scholar] [CrossRef]
  33. Park, D.; Maga, J.A. Identification of Key Volatiles Responsible for Odour Quality Differences in Popped Popcorn of Selected Hybrids. Food Chem. 2006, 99, 538–545. [Google Scholar] [CrossRef]
  34. Linstrom, P.J.; Mallard, W.G. NIST Chemistry Webbook; NIST Standard Reference Database No. 69. Available online: http://webbook.nist.gov/chemistry/ (accessed on 26 March 2022).
  35. Lee, J.; Hong, S.J.; Cho, J.-J.; Boo, C.G.; And, D.-S.K.; Shin, E.-C. Peanut Coffee: Enhancement of Nutritional, Physicochemical, and Sensory Characteristics in Coffee Brewed with Conventional and High-Oleic Peanut Extracts. Foods 2020, 9, 1664. [Google Scholar] [CrossRef]
  36. Wang, Z.; Xiao, Q.; Zhuang, J.; Feng, T.; Ho, C.T.; Song, S. Characterization of Aroma-Active Compounds in Four Yeast Extracts Using Instrumental and Sensory Techniques. J. Agric. Food Chem. 2020, 68, 267–278. [Google Scholar] [CrossRef]
  37. Elmore, J.S.; Mottram, D.S.; Hierro, E. Two-Fibre Solid-Phase Microextraction Combined with Gas Chromatography-Mass Spectrometry for the Analysis of Volatile Aroma Compounds in Cooked Pork. J. Chromatogr. A 2001, 905, 233–240. [Google Scholar] [CrossRef]
  38. Mildner-Szkudlarz, S.; Różańska, M.; Gaca, A.; Jeleń, H.H. Changes in Volatile Compound Profiles of Cold-Pressed Berry Seed Oils Induced by Roasting. LWT 2021, 148, 111718. [Google Scholar] [CrossRef]
  39. Farag, M.A.; Otify, A.M.; El-sayed, A.M.; Michel, C.G.; ElShebiney, S.A.; Ehrlich, A.; Wessjohann, L.A. Sensory Metabolite Profiling in a Date Pit Based Coffee Substitute and in Response to Roasting as Analyzed via Mass Spectrometry Based Metabolomics. Molecules 2019, 24, 3377. [Google Scholar] [CrossRef] [Green Version]
  40. Bredie, W.L.P.; Mottram, D.S.; Guy, R.C.E. Aroma Volatiles Generated during Extrusion Cooking of Maize Flour. J. Agric. Food Chem. 1998, 46, 1479–1487. [Google Scholar] [CrossRef]
  41. El-Sayed, A.M. The Pherobase: Database of Insect Pheromones and Semiochemicals. Available online: http://www.pherobase.com (accessed on 22 March 2022).
  42. Paraskevopoulou, A.; Chrysanthou, A.; Koutidou, M. Characterisation of Volatile Compounds of Lupin Protein Isolate-enriched Wheat Flour Bread. Food Res. Int. 2012, 48, 568–577. [Google Scholar] [CrossRef]
  43. Buttery, R.G.; Ling, L.C. Additional Studies on Flavor Components of Corn Tortilla Chips. J. Agric. Food Chem. 1998, 46, 2764–2769. [Google Scholar] [CrossRef]
  44. Miller, G.H. Whisky Science—A Condensed Distillation; Springer Nature: Cham, Switzerland, 2019; ISBN 978-3-030-13732-8. [Google Scholar]
  45. Vázquez-Araújo, L.; Enguix, L.; Verdú, A.E.G.-G.; Carbonell-Barrachina, A.A. Investigation of Aromatic Compounds in Toasted Almonds Used for the Manufacture of Turrón. Eur. Food Res. Technol. 2008, 227, 243–254. [Google Scholar] [CrossRef]
  46. Ruth, J. Odor Thresholds and Irritation Levels of Several Chemical Substances: A Review. Am. Ind. Hyg. Assoc. J. 1986, 47, A142–A151. [Google Scholar] [CrossRef]
  47. Buttery, R.G.; Orts, W.J.; Takeoka, G.R.; Nam, Y. Volatile Flavor Components of Rice Cakes. J. Agric. Food Chem. 1999, 47, 4353–4356. [Google Scholar] [CrossRef]
  48. Leffingwell, J.C.; Leffingwell, D. GRAS Flavor Chemicals Detection Thresholds. Perfum. Flavorist 1991, 16, 1–13. [Google Scholar]
  49. Pu, D.; Zhang, H.; Zhang, Y.; Sun, B.; Ren, F.; Chen, H. Characterization of the Key Aroma Compounds in White Bread by Aroma Extract Dilution Analysis, Quantitation, and Sensory Evaluation Experiments. J. Food Process. Preserv. 2019, 43, e13933. [Google Scholar] [CrossRef]
  50. de Lerma, N.L.; Martínez, T.G.; Moreno, J.; Mauricio, J.C.; Peinado, R.A. Sweet Wines with Great Aromatic Complexity Obtained by Partial Fermentation of Must from Tempranillo Dried Grapes. Eur. Food Res. Technol. 2012, 234, 695–701. [Google Scholar] [CrossRef]
  51. The Good Scents Company. TGSC Information System. Available online: http://www.thegoodscentscompany.com/search2.html (accessed on 17 January 2022).
  52. Laukaleja, I.; Koppel, K. Aroma Active Compound Perception in Differently Roasted and Brewed Coffees by Gas Chromatography–Olfactometry. J. Sens. Stud. 2021, 36, e12708. [Google Scholar] [CrossRef]
  53. Oertling, H.; Gomann, C.; Vom Ende, M. Dihydrobenzofuran Derivatives as Fragrance and/or Flavoring Materials. U.S. Patent 2013024 3716A1, 2 June 2015. [Google Scholar]
  54. Acree, T.; Arn, H. Flavornet and Human Odor Space. Available online: http://www.flavornet.org/ (accessed on 5 March 2022).
  55. Peinado, R.A.; Moreno, J.; Medina, M.; Mauricio, J.C. Changes in Volatile Compounds and Aromatic Series in Sherry Wine with High Gluconic Acid Levels Subjected to Aging by Submerged Flor Yeast Cultures. Biotechnol. Lett. 2004, 26, 757–762. [Google Scholar] [CrossRef] [PubMed]
  56. Drakula, S.; Mustač, N.Č.; Novotni, D.; Voučko, B.; Krpan, M.; Hruškar, M.; Ćurić, D. Optimization and Validation of a HS-SPME/GC–MS Method for the Analysis of Gluten-Free Bread Volatile Flavor Compounds. Food Anal. Methods 2021. [Google Scholar] [CrossRef]
  57. Feng, X.; Pan, L.; Wang, Q.; Liao, Z.; Wang, X.; Zhang, X.; Guo, W.; Hu, E.; Li, J.; Xu, J.; et al. Nutritional and Physicochemical Characteristics of Purple Sweet Corn Juice before and after Boiling. PLoS ONE 2020, 15, e0233094. [Google Scholar] [CrossRef] [PubMed]
  58. Galoburda, R.; Straumite, E.; Sabovics, M.; Kruma, Z. Dynamics of Volatile Compounds in Triticale Bread with Sourdough: From Flour to Bread. Foods 2020, 9, 1837. [Google Scholar] [CrossRef] [PubMed]
  59. Karahadian, C.; Johnson, K.A. Analysis of Headspace Volatiles and Sensory Characteristics of Fresh Corn Tortillas Made from Fresh Masa Dough and Spray-Dried Masa Flour. J. Agric. Food Chem. 1993, 41, 791–799. [Google Scholar] [CrossRef]
  60. Pico, J.; Martinez, M.M.; Bernal, J.; Gomez, M. Evolution of Volatile Compounds in Gluten-Free Bread: From Dough to Crumb. Food Chem. 2017, 227, 179–186. [Google Scholar] [CrossRef]
  61. Pico, J.; Antolín, B.; Román, L.; Bernal, J.; Gómez, M. Selection of the Most Suitable Mixture of Flours and Starches for the Improvement of Gluten-Free Breads through Their Volatile Profiles. Eur. Food Res. Technol. 2019, 245, 1755–1766. [Google Scholar] [CrossRef]
  62. Hussein, A.M.S.; Ibrahim, G.E. Effects of Various Brans on Quality and Volatile Compounds of Bread. Foods Raw Mater. 2019, 7, 42–50. [Google Scholar] [CrossRef]
  63. Rocha, S.M.; Coelho, E.; Zrostlíková, J.; Delgadillo, I.; Coimbra, M.A. Comprehensive Two-Dimensional Gas Chromatography with Time-of-Flight Mass Spectrometry of Monoterpenoids as a Powerful Tool for Grape Origin Traceability. J. Chromatogr. A 2007, 1161, 292–299. [Google Scholar] [CrossRef]
  64. Rocha, S.M.; Freitas, R.; Cardoso, P.; Santos, M.; Martins, R.; Figueira, E. Exploring the Potentialities of Comprehensive Two-Dimensional Gas Chromatography Coupled to Time of Flight Mass Spectrometry to Distinguish Bivalve Species: Comparison of Two Clam Species (Venerupis decussata and Venerupis philippinarum). J. Chromatogr. A 2013, 1315, 152–161. [Google Scholar] [CrossRef] [PubMed]
  65. Costa, C.P.; Bezerra, A.R.; Almeida, A.; Rocha, S.M. Candida Species (Volatile) Metabotyping through Advanced Comprehensive Two-Dimensional Gas Chromatography. Microorganisms 2020, 8, 1911. [Google Scholar] [CrossRef] [PubMed]
  66. Vranová, J.; Ciesarová, Z. Furan in Food—A Review. Czech J. Food Sci. 2009, 27, 1–10. [Google Scholar] [CrossRef]
  67. Mohsen, S.M.; Ammar, A.S.M. Total Phenolic Contents and Antioxidant Activity of Corn Tassel Extracts. Food Chem. 2009, 112, 595–598. [Google Scholar] [CrossRef]
  68. Starowicz, M. Analysis of Volatiles in Food Products. Separations 2021, 8, 157. [Google Scholar] [CrossRef]
  69. Pico, J.; Antolín, B.; Román, L.; Gómez, M.; Bernal, J. Analysis of Volatile Compounds in Gluten-Free Bread Crusts with an Optimised and Validated SPME-GC/QTOF Methodology. Food Res. Int. 2018, 106, 686–695. [Google Scholar] [CrossRef]
  70. Obuchowski, W.; Makowska, A.; Mildner-Szkudlarz, S.; Szwengiel, A.; Majcher, M.; Remiszewski, M. Effect of Triticale Grain Characteristics, Scouring, and Extrusion Conditions on Physico-Chemical Properties, Antioxidant Activity, and Volatile Compounds of Flat Bread. Acta Aliment. 2015, 44, 511–519. [Google Scholar] [CrossRef] [Green Version]
  71. Deblander, J.; Van Aeken, S.; Adams, A.; De Kimpe, N.; Abbaspour Tehrani, K. New Short and General Synthesis of Three Key Maillard Flavour Compounds: 2-Acetyl-1-Pyrroline, 6-Acetyl-1,2,3,4-Tetrahydropyridine and 5-Acetyl-2,3-Dihydro-4H-1,4-Thiazine. Food Chem. 2015, 168, 327–331. [Google Scholar] [CrossRef]
  72. Sanders, R.A.; Zyzak, D.V.; Morsch, T.R.; Rizzi, G.P. Elucidation of Tautomer Structures of 2-Acetyltetrahydropyridine Using Gas Chromatography/Mass Spectrometry and Gas Chromatography/Infrared Spectroscopy. Eur. J. Mass Spectrom. 2005, 11, 217–220. [Google Scholar] [CrossRef]
  73. Zhang, Q.; Wan, C.; Wang, C.; Chen, H.; Liu, Y.; Li, S.; Lin, D.; Wu, D.; Qin, W. Evaluation of the Non-Aldehyde Volatile Compounds Formed during Deep-Fat Frying Process. Food Chem. 2018, 243, 151–161. [Google Scholar] [CrossRef]
  74. Moskowitz, M.R.; Bin, Q.; Elias, R.J.; Peterson, D.G. Influence of Endogenous Ferulic Acid in Whole Wheat Flour on Bread Crust Aroma. J. Agric. Food Chem. 2012, 60, 11245–11252. [Google Scholar] [CrossRef] [PubMed]
  75. Bento-Silva, A.; Patto, M.C.V.; do Rosário Bronze, M.; Vaz Patto, M.C.; do Rosário Bronze, M.; Patto, M.C.V.; do Rosário Bronze, M. Relevance, Structure and Analysis of Ferulic Acid in Maize Cell Walls. Food Chem. 2017, 246, 360–378. [Google Scholar] [CrossRef] [PubMed]
  76. Wang, X.; Capone, D.L.; Roland, A.; Jeffery, D.W. Chiral Analysis of Cis-2-Methyl-4-Propyl-1,3-Oxathiane and Identification of Cis-2,4,4,6-Tetramethyl-1,3-Oxathiane in Wine. Food Chem. 2021, 357, 129406. [Google Scholar] [CrossRef] [PubMed]
  77. Carbas, B.; Vaz-Patto, M.C.; Bronze, M.R.; Bento-Da-Silva, A.; Trigo, M.J.; Brites, C. Maize Flour Parameters That Are Related to the Consumer Perceived Quality of ‘Broa’ Specialty Bread. Food Sci. Technol. 2016, 36, 259–267. [Google Scholar] [CrossRef] [Green Version]
  78. Mariotti, M.; Granby, K.; Fromberg, A.; Risum, J.; Agosin, E.; Pedreschi, F. Furan Occurrence in Starchy Food Model Systems Processed at High Temperatures: Effect of Ascorbic Acid and Heating Conditions. J. Agric. Food Chem. 2012, 60, 10162–10169. [Google Scholar] [CrossRef]
  79. Van Lancker, F.; Adams, A.; Owczarek-Fendor, A.; De Meulenaer, B.; De Kimpe, N. Mechanistic Insights into Furan Formation in Maillard Model Systems. J. Agric. Food Chem. 2011, 59, 229–235. [Google Scholar] [CrossRef]
  80. Zhao, Q.; Yao, S.; Ou, S.Y. Maillard Volatiles in Baked Products as Affected by Feruloylated Oligosaccharides from Maize Bran. Int. J. Food Prop. 2017, 20, 3266–3273. [Google Scholar] [CrossRef]
  81. Frankel, E. Lipid Oxidation; Elsevier: Amsterdam, The Netherlands, 2014; ISBN 9780953194988. [Google Scholar]
  82. Bento-Silva, A.; Duarte, N.; Mecha, E.; Belo, M.; Serra, A.T.; Vaz Patto, M.C.; Bronze, M.R. Broa, an Ethnic Maize Bread, as a Source of Phenolic Compounds. Antioxidants 2021, 10, 672. [Google Scholar] [CrossRef]
  83. Ozolina, V.; Kunkulberga, D.; Cieslak, B.; Obiedzinski, M. Furan Derivatives Dynamic in Rye Bread Processing. Procedia Food Sci. 2011, 1, 1158–1164. [Google Scholar] [CrossRef] [Green Version]
  84. Van den Dool, H.; Kratz, P.D. A Generalization of the Retention Index System Including Linear Temperature Programmed Gas—Liquid Partition Chromatography. J. Chromatogr. A 1963, 11, 463–471. [Google Scholar] [CrossRef]
  85. Tetko, I.V.; Tanchuk, V.Y. Application of Associative Neural Networks for Prediction of Lipophilicity in ALOGPS 2.1 Program. J. Chem. Inf. Comput. Sci. 2002, 42, 1136–1145. [Google Scholar] [CrossRef] [PubMed]
Molecules 27 02728 g001 550
Figure 1. Representative scheme of the Maillard reaction [7,10,15,20,21,24,25,26].
Figure 1. Representative scheme of the Maillard reaction [7,10,15,20,21,24,25,26].
Molecules 27 02728 g001
Molecules 27 02728 g002 550
Figure 2. Contour plot of the total ion current GC×GC chromatogram of a broa sample (B1) under study. The highlighted volatiles have been previously detected in broas by GC-MS (1D) [27].
Figure 2. Contour plot of the total ion current GC×GC chromatogram of a broa sample (B1) under study. The highlighted volatiles have been previously detected in broas by GC-MS (1D) [27].
Molecules 27 02728 g002
Molecules 27 02728 g003 550
Figure 3. A blow-up of a part of a contour plot extracted ion chromatogram at m/z 71 from a broa sample, showing the separation, through the 2D column, of 2-nonanone and 2-butyl-tetrahydrofuran, which showed the same retention time in the 1D column and shared similar mass spectra.
Figure 3. A blow-up of a part of a contour plot extracted ion chromatogram at m/z 71 from a broa sample, showing the separation, through the 2D column, of 2-nonanone and 2-butyl-tetrahydrofuran, which showed the same retention time in the 1D column and shared similar mass spectra.
Molecules 27 02728 g003
Molecules 27 02728 g004 550
Figure 4. A blow-up of (A) total ion GC×GC chromatogram and (B) extracted ion chromatogram at m/z 126 and 128, through the 2D column from a broa sample, showing the separation of methylpentylfuran (F27), furfurylfuran (F28), 2-formyl-3-methylthiophene (Tp4), 2-acetylthiophene (Tp5) and furaneol (Fo20).
Figure 4. A blow-up of (A) total ion GC×GC chromatogram and (B) extracted ion chromatogram at m/z 126 and 128, through the 2D column from a broa sample, showing the separation of methylpentylfuran (F27), furfurylfuran (F28), 2-formyl-3-methylthiophene (Tp4), 2-acetylthiophene (Tp5) and furaneol (Fo20).
Molecules 27 02728 g004
Molecules 27 02728 g005 550
Figure 5. Projection of broas (coloured dots) and variables (grey) (Table 1) in the plane defined by PC1 and PC2, corresponding to 59.2% of the total variance. The volatiles that strongly (PC > 0.85) contributed to differentiating the samples along the two PCs are represented in black.
Figure 5. Projection of broas (coloured dots) and variables (grey) (Table 1) in the plane defined by PC1 and PC2, corresponding to 59.2% of the total variance. The volatiles that strongly (PC > 0.85) contributed to differentiating the samples along the two PCs are represented in black.
Molecules 27 02728 g005
Molecules 27 02728 g006 550
Figure 6. Correlation heatmap of the 128 volatile compounds in broas. The correlation coefficients of volatiles are represented through a chromatic scale from deep blue (−1), corresponding to negative correlations, to red (1), corresponding to positive correlations. The letters correspond to volatiles that (A) strongly contributed to differentiating the samples along PC2; (B) strongly contributed to differentiating the samples along PC1 and (C) negatively contributed to PC1 and PC2.
Figure 6. Correlation heatmap of the 128 volatile compounds in broas. The correlation coefficients of volatiles are represented through a chromatic scale from deep blue (−1), corresponding to negative correlations, to red (1), corresponding to positive correlations. The letters correspond to volatiles that (A) strongly contributed to differentiating the samples along PC2; (B) strongly contributed to differentiating the samples along PC1 and (C) negatively contributed to PC1 and PC2.
Molecules 27 02728 g006
Molecules 27 02728 g007 550
Figure 7. Representation of the percentage of chromatogram area for the families of chemical compounds studied in broas prepared from traditional maize varieties (n = 11) and commercial maize flour.
Figure 7. Representation of the percentage of chromatogram area for the families of chemical compounds studied in broas prepared from traditional maize varieties (n = 11) and commercial maize flour.
Molecules 27 02728 g007
Table
Table 1. Volatile characteristics from browning reactions identified in broas, including their average peak areas, odor and taste descriptors, and odor thresholds; and examples of foods where the compounds have been detected.
Table 1. Volatile characteristics from browning reactions identified in broas, including their average peak areas, odor and taste descriptors, and odor thresholds; and examples of foods where the compounds have been detected.
ID1tR2tRCompoundOdor and Taste
Descriptors		CASFormulam/zSI LRIcLRIlitPAOT (ppb)Log10
PA/OT		Foods
Furans
F1950.382,3-DihydrofuranPungent1191-99-7C4H6O70, 41, 39, 29891600n/f3,100,662
± 2,605,740		n/fn/aWRB
F21000.402-Methylfuran or
3-Methylfuran (TI)		Ethereal, acetone, chocolate
n/f		534-22-5
930-27-8		C5H6O82, 53, 39, 27912
900		606605
611		3,101,036
± 1,363,010		90,450
n/f		1.5
n/a		P, RSB, TB, WB, WRB
RSB, WB
F31300.432,3-Dihydro-5-methylfurann/f1487-15-6C5H8O43, 84, 39, 27, 69872641n/f1,630,190
± 846,164		n/fn/an/i
F41400.40TetrahydrofuranEthereal109-99-9C4H8O42, 72, 2794264763315,225,039
± 4,244,701		7375–177,0001.9–3.3WB, WP
F51550.472-EthylfuranRubbery, pungent, acid, sweet3208-16-0C6H8O81, 53, 96, 399756626892,595,043
± 621,119		n/fn/aP, RS, WB
F61600.472,5-DimethylfuranChemical, ethereal, meaty, gravy, juicy, bacon625-86-5C6H8O43, 96, 53, 81, 27, 39916667667843,893
± 397,252		n/fn/aWRB
F72700.582-Propylfuran n/f4229-91-8C7H10O81, 53, 110, 39, 27973780792613,397
± 229,105		n/fn/aWB
F82950.592-Ethyl-5-methylfuranFresh, gassy, burnt1703-52-2C7H10O95, 110, 43877803803357,713
± 172,466		n/fn/an/i
F93250.602,3,5-Trimethylfurann/f10504-04-8C7H10O110, 109, 43, 95, 6789681981764,938
± 50,557		n/fn/aWB
F103253.653-Furfural
(3-furancarboxaldehyde)		Almond-like498-60-2C5H4O295, 39, 67, 299428208324,539,412
± 1,121,048		n/fn/aGFB, NSB, P, RSB, WB
F113550.802-Vinyl-5-methylfurann/f10504-13-9C7H8O108, 65, 43, 79, 56, 93889835826295,635
± 120,061		n/fn/an/i
F123603.43Furfural
(2-furancarboxaldehyde)		Woody, almond, sweet, fruity, flowery98-01-1C5H4O296, 39, 29966839843200,344,626
± 78,855,174		3000–23,0003.9–4.8B, BAG, CWB, ME, GFB, NSB, P, T, TB, TC, S, WB, WSB
F134251.70Furfuryl alcohol
(2-furanmethanol)		Weak, fermented, creamy, caramel98-00-0C5H6O239, 41, 53, 81, 70, 98949872865404,124,163
± 136,284,119		20005.3B, CWB, ME, GFB, NSB, P, RSB, T, TB, TC, TF, TS, WB, WP, WSB
F144650.562-n-Butyl furanGreen4466-24-4C8H12O81, 53, 39, 27951892898 5,012,989
± 1,768,099		50,8002.0B, RS, WB
F154901.77Furfuryl formateEthereal13493-97-5C6H6O381, 53, 39, 44918909902 643,862
± 233,472		n/fn/aWB
F164951.772-Acetylfuran
(1-(2-furanyl)-ethanone)		Smoky, roasty1192-62-7C6H6O295, 39, 43, 67921912915 49,074,458
± 10,718,656		10,0003.7B, CWB, ME, GFB, P, RSB, T, TC, TF, WB, WP, WSB
F175551.371-(2-Furyl)-2-propanone
(2-furyl acetone)		Herbal, caramel, fruity, spicy, radish, green, burnt6975-60-6C7H8O281, 43, 53, 1249159579542,719,968
± 2,692,555		n/fn/aWB
F185651.615-Methyl furfural
(5-methyl-2-furancarboxaldehyde)		Almond, sweet, bitter620-02-0C6H6O2110, 53, 39, 43, 8197996496633,471,223
± 8,857,491		5004.8B, ME, GFB, NSB, P, RSB, TB, WB
F195652.985-methyl-2-furanmethanol
(5-methylfurfuryl alcohol)		Bread-like, honey, sweet3857-25-8C6H8O295, 112, 43, 69, 53913965966 8,379,336
± 4,226,245		11.95.8BAG, CWB, WB
F206000.532-PentylfuranButter, green bean, floral, fruity, mushroom, raw nuts3777-69-3C9H14O81, 53, 39934989993 55,139,336
± 14,203,476		67.0B, BAG, ME, GFB, MF, MJ, NSB, P, RS, TC, TF, TS, WB, WP, WRB
F216051.05BenzofuranStyrene, aromatic271-89-6C8H6O118, 89, 63, 39, 51, 45892993996470,358
± 286,276		n/fn/an/i
F226051.53Isomaltol
(2-acetyl-3-hydroxyfuran)		Caramel-like3420-59-5C6H6O3111, 126, 43, 55, 84918994989 392,890
± 417,850		n/fn/an/i
F236101.12Furfuryl acetate
(2-furanmethanol acetate)		Sweet, fruity, banana-like, horseradish, ethereal, green623-17-6C7H8O381, 98, 43, 52, 1409209979985,202,352
± 2,702,948		n/fn/aWB
F246251.211-(2-Furanyl)-1-propanoneFruity3194-15-8C7H8O295, 39, 45, 74, 67, 57872101110162,589,462
± 1,364,329		n/fn/aWP
F256451.222-Acetyl-5-methylfuranSweet, nutty with a caramel nuance, cocoa-like with a toasted bready nuance1193-79-9C7H8O2109, 124, 43, 53928103010427,472,295
± 7,428,702		n/fn/an/i
F266551.132,2′-Bifuran
(2-(2-furanyl)furan)		Vegetable, garlic5905-00-0C8H6O2134, 78, 105, 51, 3989310391047998,680
± 662,678		n/fn/aWB
F277050.50Methylpentylfurann/f-C10H20O95, 152, 43, 67892108610833,099,292
± 2,322,514		n/fn/aB
F287050.952-Furfurylfuran
(2,2′-Methylenebisfuran)		Rich, roasted, aromatic1197-40-6C9H8O291, 148, 120, 39, 6586310871086451,285
± 232,810		n/fn/an/i
F297103.245-Formylfurfural
(2,5-furandicarboxaldehyde)		n/f823-82-5C6H4O3124, 77879109410845,731,606
± 2,639,042		n/fn/aWB
F307150.512-Hexylfurann/f3777-70-6C10H16O81, 53, 39, 41, 95, 12390510961096463,776
± 178,720		n/fn/an/i
F317150.772-Butyl-tetrahydrofurann/f1004-29-1C8H16O71, 41, 55864109610963,919,696
± 3,110,078		n/fn/an/i
F327153.29Furyl hydroxymethyl ketone
(1-(2-furanyl)-2-hydroxyethanone)		n/f17678-19-2C6H6O395, 39, 126, 29, 679481098108821,691,749
± 9,667,403		n/fn/an/i
F338051.321-(5-Methyl-2-furanyl)-2-hydroxyethanonen/f-C7H8O3109, 56, 69, 43, 1408331191n/f1,550,219
± 734,005		n/fn/an/i
F348654.972,3-DihydrobenzofuranMusky notes496-16-2C8H8O120, 91, 65, 51911126512222,807,760
± 735,738		n/fn/aB, BMJ
F359051.17Difurfuryl ether
(2,2′-[oxybis(methylene)]bis-furan)		Coffee, mushroom-like, nutty, earthy4437-22-3C10H10O381, 56, 27, 39, 97, 11094413081305240,009
± 95,353		n/fn/an/i
F369354.45Hydroxymethylfurfural
(5-(Hydroxymethyl)furfural)		Fatty, buttery, musty, waxy, caramel, herbal, tobacco67-47-0C6H6O397, 126, 41, 69, 539071325126622,784,687
± 12,185,059		1,000,0001.4P, RSB, WSB
Furanones
Fo12453.322-Furanone (TI)
(2(3H)-furanone) 		n/f20825-71-2C4H4O255, 84, 27, 53, 39, 44873757914
(DB-1)		2,079,421
± 625,998		n/fn/an/i
Fo23051.58Dihydro-2-methyl-3-(2H)-furanone
(2-methyltetrahydro-3-furanone)		Spicy, rancid, butter3188-00-9C5H8O243, 72, 10097480981219,616,932
± 16,891,970		n/fn/aWB, WP
Fo34203.115-Methyl-2(3H)-furanoneSweet, oily, coconut, tobacco, creamy, vanilla, hay591-12-8C5H6O255, 98, 43, 27, 70851870869235,195
± 69,497		n/fn/an/i
Fo44800.835-Methyl-5-furfuryl-2(5H)-furanone
(5-(2-furanylmethyl)-5-methyl-2(5H)-furanone) (TI)		n/f31969-27-4C10H10O381, 53, 39, 69751901n/f1,263,633
± 1,567,577		n/fn/aWB
Fo55054.882(5H)-Furanone
(2,5-dihydrofuranone)		n/f497-23-4C4H4O255, 84, 27, 29, 3994092291843,176,086
± 16,137,613		n/fn/aWB, CWB
Fo65402.775-Methyl-2(5H)-furanonen/f591-11-7C5H6O269, 41, 39, 98942943938 6,155,177
± 2,897,005		n/fn/aWB
Fo75501.313-Methyl-2,5-furandione or
2,5-Dimethyl-3(2H)-furanone (TI)		n/f
n/f		616-02-4
14400-67-0		C5H4O339, 68, 40, 28, 53, 112706
926		953949
924
(DB-1)		1,818,359
± 629,312		n/fn/aWB
n/i
Fo85551.93γ-Valerolactone
(dihydro-5-methyl-2(3H)-furanone)		Herbal, sweet, warm, tobacco, cocoa, woody, coconut108-29-2C5H8O256, 85, 41, 439589569563,864,613
± 1,759,554		n/fn/aWB, CWB
Fo95551.915,5-Dimethyl-2(5H)-furanonen/f20019-64-1C6H8O297, 69, 43, 54, 26, 112891957958250,199
± 71,863		n/fn/an/i
Fo105601.90Dihydro-3-methyl-2(3H)-furanone or
Dihydro-4-methyl-2(3H)-furanone
(3-methylbutyrolactone) (TI)		n/f


n/f		1679-47-6


1679-49-8		C5H8O241, 56, 27, 100910


917		961958


919		2,130,675
± 842,009		n/f


n/f		n/a


n/a		n/i


n/i
Fo115651.84Dihydro-3-methyl-2(3H)-furanone or
Dihydro-4-methyl-2(3H)-furanone
(3-methylbutyrolactone) (TI)		n/f
n/f		1679-47-6
1679-49-8		C5H8O256, 85, 41, 43, 100895
891		964958
919		502,907
± 283,902		n/f
n/f		n/a
n/a		n/
n/i
Fo125701.87n/in/a-C6H8O297, 69, 43, 26, 54n/a968n/a183,534
± 115,610		n/an/an/a
Fo135751.245-Ethyl-(3H)-furan-2-one
(2-ethylbutenolide)		Spicy2313-01-1C6H8O255, 112, 83, 97910971954612,612
± 196,297		n/fn/aWB
Fo146151.642,5-Dihydro-3,5-dimethyl 2-furanonen/f5584-69-0C6H8O269, 41, 115, 978841002993973,653
± 442,005		n/fn/an/i
Fo156551.955-Ethyl-2(5H)-Furanone (TI)Spicy2407-43-4C6H8O228, 83, 18, 55, 448971040984
(DB-1)		5,650,222
± 2,621,703		n/fn/aWB
Fo166551.793,4-Dimethyl-2,5-furandione
(2,3-dimethyl maleic anhydride)		n/f766-39-2C6H6O339, 54, 82, 126882104010383,343,389
± 1,471,465		n/fn/an/i
Fo176654.90R-PantolactoneCotton candy, licorice, smoky, toasted bread599-04-2C6H10O371, 43, 29, 57951104710432,268,814
± 1,125,826		504.7MF
Fo186702.824-Methyl-2(5H)-furanonen/f6124-79-4C5H6O269, 41, 39, 989241055n/f2,855,095
± 885,123		n/fn/an/i
Fo196751.45γ-N-Caprolactone
(γ-hexalactone,
5-ethyldihydro-2(3H)-furanone)		Coumarin-like, sweet695-06-7C6H10O285, 42, 56, 70, 1149421059105815,427,139
± 6,696,866		505.5B, CWB
Fo207054.02Furaneol (2,5-dimethyl-4-hydroxy-3(2H)-furanone)Caramel, strawberry3658-77-3C6H8O343, 57, 128, 8591810901090 3,801,345
± 2,827,164		604.8WB, BAG, CWB, GFB, NSB, P, RS, TC
Fo217653.00Solerone (TI)
(5-acetyldihydro-2(3H)-furanone)		n/f29393-32-6C6H8O385, 29, 43, 57, 12893711511299
(SE-54)		2,040,510
± 929,704		n/fn/an/i
Fo227751.26γ-Heptalactone
(dihydro-5-propyl-2(3H)-furanone)		Sweet, coconut, nutty, caramel, creamy, milky, tobacco105-21-5C7H12O285, 29, 56, 4194811591163833,364
± 298,059		4993.2n/i
Fo238701.17γ-Octalactone
(5-butyldihydro-2(3H)-furanone)		Sweet, coconut, waxy, creamy, milky, soapy, fruity104-50-7C8H14O285, 41, 56, 100955126612641,318,130
± 558,277		85.2CWB, TC
Fo248750.895-Pentyl-2(3H)-furanone
(3-nonen-4-olide)		Tropical, fruity, milky, dairy51352-68-2C9H14O298, 111, 55, 83, 70, 154840127212733,499,672
± 1,292,082		n/fn/an/i
Fo259401.295-Pentyl-2(5H)-furanone
(4-hydroxy-2-nonenoic acid lactone)		Minty, fruity21963-26-8C9H14O229, 28, 45, 57, 100, 113, 126, 85, 728231352135810,012,186
± 4,179,765		n/fn/an/i
Fo269551.10γ-Nonalactone
(dihydro-5-pentyl-2(3H)-furanone)		Coconut-like, sweet, fruity104-61-0C9H16O285, 114, 41, 55, 99, 137946137013639,304,844
± 4,182,379		9.7–275.5–6.0B, BMJ, CWB, MJ, WSB
Pyrans
Pn12400.533,4-Dihydro-6-methyl-2H-pyrann/f16015-11-5C6H10O43, 55, 98, 83913749n/f134,400
± 30,229		n/fn/an/i
Pn26751.505,6-Dihydro-2H-pyran-2-carboxaldehyde or
3,4-Dihydro-2H-pyran-2-carboxaldehyde (TI)		n/f

n/f		53897-26-0

100-73-2		C6H8O283, 55, 29, 112, 39867

860		1059n/f

853
(OV-101)		1,444,173
± 653,900		n/f

n/f		n/a

n/a		n/i
Pn39151.022-(1-Butenyl)-tetrahydropyrann/f95652-24-7C9H16O111, 140, 83, 98, 1258011320n/f129,456
± 54,493		n/fn/an/i
Pyranones
Po14501.47Dihydro-2H-pyran-3(4H)-one (TI)n/f23462-75-1C5H8O242, 27, 71, 559478851439
(HP-Wax)		54,028
± 25,761		n/fn/an/i
Po25853.052H-Pyran-2-one
(α-pyrone)		Herbal504-31-4C5H4O239, 68, 9687798097834,118
± 13,808		n/fn/aWP
Po36501.58n/in/an/an/a68, 39, 98, 53801
756		1035n/a5,592,787
± 4,970,053		n/a
n/a		n/a
n/a		n/i
Po46552.745,6-Dihydro-2H-pyran-2-one (TI) n/f3393-45-1C5H6O268, 39, 98, 5392910411838
(DB-Wax)		1,621,497
± 558,094		n/fn/an/i
Po56752.03δ-Valerolactone (TI)
(tetrahydro-2H-pyran-2-one) 		n/f542-28-9C5H8O242, 41, 27, 56, 100, 709471059965916,387
± 142,550		n/fn/an/i
Po67151.60δ-Hexalactone
(tetrahydro-6-methyl-2H-pyran-2-one, δ-caprolactone) 		Creamy, fruity, coconut, spicy823-22-3C6H10O242, 70, 55, 9994410971084 840,593
± 226,566		n/fn/aWB
Po77402.64Maltol
(3-hydroxy-2-methyl-4H-pyran-4-one)		Warmy-fruity, caramel-sweet118-71-8C6H6O3126, 71, 43, 55, 9797411241113117,672,149
± 40,223,031		25004.7B, P, TB, TC, WB
Po87950.203-Hydroxy-2,3-dihydromaltol
(2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one)		Caramelized28564-83-2C6H8O443, 144, 101, 73, 559721179114429,961,549
± 16,035,481		n/fn/aB, P, WB
Po99752.402-Hydroxy-3-methyl-4H-pyran-4-onen/f61892-88-4C6H6O3126, 71, 43, 55, 978181397n/f37,421
± 25,172		n/fn/an/i
Pyrazines
Pz11901.25PyrazineRoasted290-37-9C4H4N280, 26, 539607047391,631,354
± 797,679		180,0001.0WB, ME, GFB, NSB, P, TC, TS, WP
Pz23451.342-MethylpyrazineRoasted, burnt, sweet109-08-0C5H6N294, 67, 39, 26, 5397483084015,773,787
± 11,169,354		60–105,0002.2–5.4B, WB, BAG, ME, GFB, NSB, P, T, TC, TS, WFB, WP, WRB
Pz34950.902,6-DimethylpyrazineRoasted108-50-9C6H8N242, 108, 39, 40, 28, 1897291291523,375,159
± 12,540,414		200–90003.4–5.1WB, CWB, GFB, NSB, P, T, TC, WFB, WP, WRB
Pz45000.912-EthylpyrazinePopcorn, nutty13925-00-3C6H8N2107, 108, 80, 53, 39, 289269159152,149,106
± 1,864,070		6000–22,0002.0–2.6WB, ME, GFB, NSB, P, RSB, T, TC, TS, WRB
Pz55050.932,3-DimethylpyrazinePopcorn, roasted5910-89-4C6H8N2108, 67, 429299199192,413,964
± 1,493,485		2500–35,0001.8–3.0WB, ME, GFB, NSB, P, T, TC, TS
Pz66150.752-Ethyl-3-methylpyrazine
or
2,3,5-trimethylpyrazine (TI)		Potato-like, earthy
Nutty, roasted, sweet		15707-23-0

14667-55-1		C7H10N242, 122, 81, 39954

936		10011001

1005		5,256,433
± 2,326,845		400–1800
130		4.6
3.5–4.1		WB, ME, GFB, NSB, P, RSB, TC, WFB, WP, WRB
WB, BAG, ME, GFB, TC
Pz76300.902-Ethenyl-6-methylpyrazine
(2-methyl-6-vinylpyrazine)		Coffee13925-09-2C7H8N2120, 52, 39, 9483410151023918,205
± 550,329		n/fn/aWB, ME, P, T, WP
Pz86401.35AcetylpyrazineBiscuit, cracker-like, crust-like, sweet, roasted22047-25-2C6H6N2O43, 52, 80, 122, 94, 28, 1596510251031418,788
± 223,595		623.8WB, GFB, NSB, RSB, WRB
Pz97000.652-Ethyl-3,6-dimethylpyrazine
(3-ethyl-2,5-dimethyl-pyrazine) or
2-Ethyl-3,5-dimethyl-pyrazine
(3-ethyl-2,6-dimethylpyrazine)		Potato, cocoa, roasted, nutty

Burnt, roasted, nutty, coffee, caramel, cocoa, maize		13360-65-1


13925-07-0		C8H12N2135, 136, 42, 39, 56, 108918

885		10821082

1082		749,792
± 503,023		8.6

0.04–1		4.9

5.9–7.3		WB, ME, P, RSB

WB, ME, P, T, TC, WRB, WSB
Pz107401.072-Acetyl-3-methylpyrazineNutty, roasted, hazelnut, corn chip, caramel, potato chip23787-80-6C7H8N2O43, 93, 136, 94, 42, 67, 5286411221128207,115
± 107,124		n/fn/an/i
Pz117600.835H-5-Methyl-6,7-dihydrocyclopentapyrazineEarthy, baked potato, sweet, roasted, corn with savory23747-48-0C8H10N2119, 13490711431149 511,503
± 176,711		n/fn/an/i
Pz128751.402-(2′-Furyl)-pyrazine (TI)
(2-(furan-2-yl)pyrazine)		n/f32736-95-1C8H6N2O146, 93, 63, 38, 3981612721255
(DB-1)		293,650
± 139,715		n/fn/an/i
Pyridines and Pyrimidines
Pd13501.052-MethylpyridineSweat, astringent, hazelnut, nutty109-06-8C6H7N93, 66, 39, 78, 51958832824349,470
± 195,878		n/fn/an/i
Pd24200.984-Methylpyrimidinen/f3438-46-8C5H6N294, 40, 53, 67, 798028698539105
± 6947		n/fn/an/i
Pd34600.792,6-Dimethylpyridine
(2,6-lutidine)		Nutty, ammoniacal, woody, bready, cocoa, coffee, musty108-48-5C7H9N107, 106, 39, 66, 79, 93924890890306,301
± 109,246		n/fn/an/i
Pd44900.792-Ethylpyridine (TI)Green, grassy100-71-0C7H9N106, 107, 79, 52, 66, 39702908906135,706
± 64,908		n/fn/aT
Pd55500.832,3-Dimethylpyridine
(2,3-lutidine)		Coffee, caramel583-61-9C7H9N107, 106, 39, 66, 79, 9293795295229,778
± 9134		n/fn/an/i
Pd66050.712,4,6-TrimethylpyridineAromatic odor108-75-8C8H11N121, 79, 39, 106842993993167,322
± 96,358		n/fn/an/i
Pd76501.182-Acetylpyridine
(1-(2-pyridinyl)-ethanone)		Biscuit-like, toasted, cracker-like, crust-like, roasted1122-62-9C7H7NO79, 121, 93, 43, 51939103510501,141,684
± 1,282,175		194.8ME, P, T, TC
Pd88101.131-Acetyl-1,2,3,4-tetrahydropyridineNutty19615-27-1C7H11NO85, 125, 83, 68, 43, 54882119611891,504,556
± 534,232		n/fn/an/i
Pd98150.652-Pentylpyridine
(2-propylpyridine)		Green, fatty, roasted, tobacco, nutty622-39-9C8H11N93, 106, 120, 79, 65, 398501201120289,596
± 34,399		0.65.2n/i
Pyrroles
Py13151.041-Ethyl-1H-pyrroleBurnt617-92-5C6H9N80, 95, 67, 39, 27, 5387981481568,416
± 27,880		n/fn/aME
Py26151.48N-Methyl-2-formylpyrrole
(1-methyl-1H-pyrrole-2-carboxaldehyde)		Roasted, nutty1192-58-1C6H7NO109, 108, 53, 80, 3992010041010848,932
± 340,434		374.4P
Py36651.141-Ethyl-2-formyl-1H-pyrrole
(1-ethyl-1H-pyrrole-2-carboxaldehyde)		Burnt, roasted, smoky2167-14-8C7H9NO123, 94, 39, 108, 66, 53, 8081610471046664,513
± 343,483		n/fn/aME
Py46650.142-Formyl-1H-pyrrole
(1H-pyrrole-2-carboxaldehyde)		Musty1003-29-8C5H5NO95, 94, 66, 39949104810472,142,059
± 1,055,032		n/fn/aME, P, WB
Py56701.381-Methyl-2-pyrrolidinoneFishlike872-50-4C5H9NO44, 42, 99, 98, 2884910571046331,816
± 211,791		n/fn/an/i
Py66903.462-Acetylpyrrole
(1-(1H-pyrrol-2-yl)-ethanone)		Musty1072-83-9C6H7NO94, 109, 66, 39, 43, 539541076106921,389,485
± 7,698,915		170,0002.1B, BAG, CWB, GFB, NSB, P, TC, WB
Py77351.141-Ethyl-2-pyrrolidinone (TI)Slight amine2687-91-4C6H11NO98, 113, 70, 41, 2890711171856 (FFAP)209,715
± 147,230		n/fn/an/i
Py87401.42Ethyl pyrrole 1-acetate (TI)n/f5145-67-5C8H11NO280, 153, 53, 57, 717181123n/f995,860
± 1,013,831		n/fn/an/i
Py98001.20N-Furfurylpyrrole
(1-(2-furanylmethyl)-1H-pyrrole)		Vegetable, plastic, waxy, fruity, cereal, bready, potato1438-94-4C9H9NO81, 147, 53, 27, 3995511861179775,590
± 358,385		1003.9B, ME, P, WB, WRB
Py109104.10Indole
(benzopyrrole)		Animal, naphthyl, fecal, pungent, musty; in low concentrations: powerful floral notes and pleasant radiation120-72-9C8H7N117, 90, 63, 39, 50954131812956,532,212
± 1,981,606		1404.7B, WB
Py119801.185-Acetyl-2,3-dihydro-1H-pyrrolizine (TI)Amine, grass, hay, smoky55041-85-5C9H11NO134, 149, 106, 79, 5191014021382
(DB-1)		807,263
± 424,045		n/fn/aP
Py129853.01Skatole
(3-methyl-1H-indole)		Animal, fecal, warm, sweet, over-ripe fruit; in low concentrations: may give a note of ‘overmature flower’83-34-1C9H9N130, 131, 77, 51, 65, 103, 399401411141050,749
± 33,736		0.25.4P
Py1310001.491-Furfuryl-2-formyl pyrrole (1-methyl-1H-pyrrole-2-carboxaldehyde) Slightly burnt taste, acid
n/f		19377-82-3C10H9NO281, 175, 53, 39, 14785114291384284,459
± 165,711		973.5P, WRB
Oxazoles
Ox12350.934,5-Dimethyloxazolen/f7064-40-6C5H7NO97, 43, 5582174575029,777
± 23,570		n/fn/an/i
Ox24100.77TrimethyloxazoleNutty, roasted, shellfish, mustard burnt, oily, mushroom20662-84-4C6H9NO111, 43, 68, 55868864863109,136
± 176,271		n/fn/aWP
Ox37351.34Benzoxazole (TI)n/f273-53-0C7H5NO119, 64, 9185311171067
(DB-1)		182,454
± 98,420		n/fn/an/i
Thiazoles
Tz11951.49ThiazoleFishy, nutty, meaty288-47-1C3H3NS85, 58, 45967704694294,112
± 230,369		n/fn/aWB
Tz26351.462-AcetylthiazoleRoasty24295-03-2C5H5NOS43, 127, 99, 58, 85944102010181,155,525
± 300,637		105.1WB, ME
Tz38401.45BenzothiazoleSulfurous95-16-9C7H5NS135, 108, 69, 45956123112311,124,234
± 601,368		804.1WB
Thiophenes
Tp12350.723-MethylthiopheneFatty, winey616-44-4C5H6S97, 98, 4596874477022,399
± 9459		n/fn/an/i
Tp26001.973-Thiophenecarboxaldehyden/f498-62-4C5H4OS111, 112, 83, 398479901003252,769
± 141,357		n/fn/an/i
Tp36101.982-Thiophenecarboxaldehyde
(2-formylthiophene, thenaldehyde)		Sulfurous, almond, bitter, cherry98-03-3C5H4OS111, 112, 83, 589529981001762,146
± 260,839		n/fn/aME
Tp47051.312-Formyl-3-methylthiophene
(3-methyl-2-thiophenecarboxaldehyde)		Saffron, camphoreous5834-16-2C6H6OS125, 126, 97, 4584510871109123,821
± 40,906		n/fn/an/i
Tp57051.562-Acetylthiophene
(1-(2-thienyl)-ethanone)		Sulfurous, nutty, hazelnut, onion88-15-3C6H6OS111, 1268291087108570,861
± 22,816		n/fn/aWB
Tp67451.482-Formyl-5-methylthiophene (TI)
(5-methyl-2-thiophenecarboxaldehyde)		Rancid, fatty, grass13679-70-4C6H6OS125, 126, 97, 457601128112490,000
± 35,587		n/fn/aWP, ME
Other sulfur-containing compounds
S1700.32MethanethiolRotting cabbage; in low concentrations: tropical fruit, may contribute for the aroma of sweet maize74-93-1CH4S47, 45, 48991575<5006,115,559
± 1,459,463		0.04–824.9–8.2WB, CB
S2800.35Dimethyl sulfideCabbage-like, in low concentrations: canned maize75-18-3C2H6S47, 62, 359785855651,689,726
± 724,639		0.3–16.2–6.8WB, CB, P, RS
S31950.69Dimethyl disulfideGarlic; in low concentrations: contributes to maize flavor624-92-0C2H6S294, 45, 79, 619737037189,175,781
± 4,840,433		125.9WB, CB, ME, GFB, P, RS, TC, WP
S42201.561-Methylthiopropane (TI)
(methyl propyl sulfide) 		Alliceous, creamy, green, leek3877-15-4C4H10S61, 90, 48714730715100,912
± 2,3581		n/fn/an/i
S53751.58Methylthio-2-propanone
(acetonyl methyl sulfide)		Melon, cabbage, garlic14109-72-9C4H8OS43, 61, 10492384686317,904
± 16,085		n/fn/an/i
S64801.101,4-Oxathiane, or
1,3-Oxathiane, or
1,2-Oxathiane
(thioxane) (TI)		Characteristic
n/f
Green, grassy, leafy, cortex, foliage, aromatic, vegetable, floral, juicy mango, tropical		15980-15-1
646-12-8 57917-36-9		C4H8OS46, 104, 74, 61811

863

n/a		901885

n/f

n/f		57,599
± 47,389		n/f

n/f

n/f		n/a

n/a

n/a		n/i

n/i

n/i
S74851.52Methional
(3-methylthiopropanal)		Boiled-potato, cooked-potato, malty, waxy3268-49-3C4H8OS48, 104, 61, 76930905903806,522
± 660,313		0.26.6WB, CB, CWB, NSB, P, T, TC, TS, WP
S85650.85Dimethyl trisulfideCabbage-like, in low concentrations: tropical fruit/grapefruit3658-80-8C2H6S3126, 79, 45, 1119479649642,195,136
± 1,508,373		0.018.3WB, ME, GFB, P, TC, WFB
ID: Peak identification;1tR: retention time for the first dimension (seconds); 2tR: retention time for the second dimension (seconds); CAS: Chemical Abstracts Service registry number; m/z: mass-to-charge ratio (ions are ordered according to their decreasing intensities); SI: similarity index (‰); LRIc: linear retention index obtained through the modulated chromatogram; LRIlit: linear retention index reported in the literature for Equity-5 column or equivalents [27,34,35,36,37,38,39,40,41,42]; OT: Odor threshold values in water [16,32,43,44,45,46,47,48,49,50]; PA: average peak area (n = 12); PA/OT: ratio between PA and OT; TI: tentatively identified; n/a: not applicable; n/f: not found; n/i: not identified. Aroma and taste descriptors were obtained from the literature [5,6,13,24,41,42,49,51,52,53,54,55]. Abbreviations used for other maize-based foods or breads where the compounds have been detected [5,6,7,10,16,18,24,27,31,32,33,40,43,49,56,57,58,59,60,61,62]: MF: maize flour; B: broa (compounds highlighted in bold); WB: wheat bread; WSB: wheat sourdough bread; WRB: wheat-rye bread; RSB: rye sourdough bread; GFB: gluten-free bread; MSB: maize starch bread; CWB: Chinese white bread; BAG: bagels; WFB: whole fino bread; TB: triticale bread; CB: crisp bread; ME: maize extrudates; P: popcorn; T: maize tortilla; TC: tortilla chips; TS: taco shell; WP: maize meal extruded product with whey protein; MJ: maize juice; BMJ: boiled maize juice; RS: rye sourdough; TF: tortilla flour.
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Bento-Silva, A.; Duarte, N.; Santos, M.; Costa, C.P.; Vaz Patto, M.C.; Rocha, S.M.; Bronze, M.R. Comprehensive Two-Dimensional Gas Chromatography as a Powerful Strategy for the Exploration of Broas Volatile Composition. Molecules 2022, 27, 2728. https://doi.org/10.3390/molecules27092728

AMA Style

Bento-Silva A, Duarte N, Santos M, Costa CP, Vaz Patto MC, Rocha SM, Bronze MR. Comprehensive Two-Dimensional Gas Chromatography as a Powerful Strategy for the Exploration of Broas Volatile Composition. Molecules. 2022; 27(9):2728. https://doi.org/10.3390/molecules27092728

Chicago/Turabian Style

Bento-Silva, Andreia, Noélia Duarte, Magda Santos, Carina Pedrosa Costa, Maria Carlota Vaz Patto, Sílvia M. Rocha, and Maria Rosário Bronze. 2022. "Comprehensive Two-Dimensional Gas Chromatography as a Powerful Strategy for the Exploration of Broas Volatile Composition" Molecules 27, no. 9: 2728. https://doi.org/10.3390/molecules27092728

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