Sensory and Nutritional Characteristics of Organic Italian Hazelnuts from the Lazio Region

Abstract

Currently, there is an ever-increasing demand for organic food from consumers who are convinced that it is healthier and more nutritious. The purpose of our research was to carry out an evaluation of the nutritional and sensory characteristics of organic and conventional hazelnuts of Tonda Gentile Romana cv. To this end, volatile composition, total phenolics, antioxidant capacity, and sensory profile of organic and conventional hazelnuts were identified. In comparison to conventional hazelnuts, organic hazelnuts had a greater amount of total phenols and antioxidants. Furthermore, organic hazelnuts had a different sensory profile, with more crunchiness (6.722 vs. 4.056 for raw and 8.389 vs. 4.667 for roasted) and sweetness (7.667 vs. 4.867 for raw and 7.089 vs. 3.889 for roasted), accompanied by distinct hazelnut, almond, walnut, popcorn, coffee, and roasty notes, present in much higher amounts than conventional hazelnuts. One of our key findings is that organic hazelnuts have a higher nutritional value due to their higher antioxidant capacity. Promoting organic hazelnuts helps to encourage consumers to use these products, which have a high nutritional value, thus contributing to public health.

1. Introduction

Hazelnuts (Corylus avellana) are cultivated worldwide, especially in Turkey, with a production of 765,000 tonnes, followed by Italy in second place with 98,670 tonnes [1]. In central Italy, Lazio, with 28,410 tonnes, is the leading producer among the Italian regions [2]. In Lazio, hazelnut plantations are mainly located in the Cimini Mountain areas of Viterbo province. The most widely grown variety is Tonda Gentile Romana (TGR). The growing demand from the food industry for high-quality hazelnuts is the main reason for the recent increase in production. Indeed, hazelnuts are a key ingredient in sweetened spreads, confectionery, chocolate, and biscuits [3]. A recent review [4] highlighted hazelnuts as a valuable resource from nutritional and sustainability perspectives. In addition, the nutritional and health benefits of hazelnuts have been the subject of numerous studies [5,6,7], which have shown that the presence of bioactive antioxidant molecules inhibits oxidative damage to LDL cholesterol, and thereby the likelihood of developing coronary heart disease is diminished, as well as several other types of cancer [8]. The specific fatty acid composition of hazelnuts is also noteworthy, as they are rich in monounsaturated fatty acids and have the ability to protect the product from lipid oxidation. This oxidation must be avoided, as it could lead to changes in sensory characteristics and nutritional value, thus negatively affecting the health benefits of hazelnut consumption [9]. Moreover, hazelnut shells are a rich source of dietary fibre, and hazelnut skins have functional properties that are very important for human health [10,11]. In this context, Karaosmanoğlu [5] has shown that the different cultivation systems, organic and conventional, have an impact on the chemical composition of Turkish hazelnuts. It is well known that the popularity of organic food is on the rise. The growing demand is primarily driven by consumer concerns about the adverse environmental and health implications of traditional farming methods. In fact, the majority of consumers believe that organic food is safer and healthier than food produced using conventional methods [12]. In this regard, there is a lot of research on the nutritional content of organic and conventional foods. However, few studies have been carried out on organic hazelnuts [13]. On the other hand, studies on the sensory characteristics of Italian organic hazelnuts compared to conventional hazelnuts are not available in the literature. Anyway, the hazelnut’s sensory properties play an important role for consumers who value its high quality [14,15]. Sensory analysis can therefore help to characterize the quality of organic hazelnuts and to identify processing chains that can make full use of them. From this point of view, and as an exploratory study, our research aimed to determine the sensory characteristics, along with the antioxidant capacity and the volatile component of Italian organic hazelnuts compared to conventional hazelnuts. All of this is in light of the fact that organic hazelnut production has been growing steadily in Italy and currently represents 17.5% of the total harvest [16]. There is also the practical application of evaluating whether sensory analysis can reveal differences in attributes that can help consumers make the best choice. The purpose of this investigation was the comparison of sensorial and nutraceutical properties of Italian hazelnuts from organic and conventional production systems. To this end, we analyzed organic and conventional roasted and raw hazelnuts. For our experiment, we chose the Tonda Gentile Romana cultivar, which originates from central Italy and has a Protected Designation of Origin (“Nocciola Romana” [17]). This cultivar is also important in the production of high-quality confectionery.

2. Materials and Methods

2.1. Samples

Hazelnuts of the ‘Tonda Gentile Romana’ cultivar were purchased from Assofrutti SRL, Loc. San Valentino s.n.c., Caprarola (Province of Viterbo, Lazio, Italy) (latitude: 42°19’23.09” N; longitude: 12°14′18.53″ E), grown on volcanic soil at an elevation of about 450 m (1480 ft) above sea level. Two 1 kg vacuum-packed bags of each type (raw and roasted, both organic and conventional) were supplied for a total of 8 kg. It is worth noting that the hazelnut in our study has been awarded the Protected Designation of Origin ‘Nocciola Romana’. The sampling area corresponds to the total surface area of hazelnut groves, equal to 7675 hectares. The samples analyzed were taken from the same geographical region and are subject to the same climatic conditions. The same cultural treatments were applied to both organic and conventional orchards, excluding fertilizing.

The organic hazelnuts were produced in certified organic orchards. Liquid foliar fertilizer and micronutrients (boron and zinc) were used for fertilization, as well as solid fertilizers (compost and animal manure). Liquid sulphur was used for pest control. The roasted hazelnuts have been toasted at a temperature of 140 °C for 30 min. The testing process involved samples of organically and conventionally grown produce, in both raw and roasted forms (see Figure 1). All samples (2 kg of each type) were stored cool and dark (at 5 °C).

2.2. Physical Features

The fruits (50) were randomly selected from all samples and physically evaluated. Weight, length, width, thickness, mean diameter, sphericity, volume, and area were measured [18,19]. The length (L), width (W), and thickness (T) of each fruit were determined using a digital calliper (precision 0.01 mm). As described by Mohsenin [20], the geometric mean diameter (Dg), sphericity (Ø), arithmetic mean diameter (Da), area (A), and volume (V) were determined.

2.3. Sensory Analysis

The sensory test was conducted in accordance with ISO 8589 [21] and UNI EN ISO13299 [22] by the Nocciola Romana DOP Tasting Panel, set up and officially recognized by the Ministry of Agriculture, Food Sovereignty and Forestry at the Order of Agronomists of Viterbo (Italy). This panel has a great deal of experience as it is specific to the sensory analyses of hazelnuts. In a lab with the necessary equipment for sensory studies, the sensory assessment was conducted by a panel of authorized sensory panellists under the direction of a panel leader. The temperature in the sensory lab was kept at 20 °C. The lighting, both solar and electric (e.g., a tube lamp of the ‘sunlight’ type), was kept uniform. Samples of hazelnuts, three whole nuts, were placed in white Pyrex dishes. The samples were coded and presented in a random manner. Each sample was analyzed in two replicates for statistical analysis. The judges were provided with water to wash their mouths between analyses. A training session was conducted for the judges with the objective of establishing a shared lexicon of descriptors. The session was concluded with the selection of appropriate descriptors to be used (

Table 1. Hazelnut sensory descriptors and related reference standards.

Descriptors	Sensory Attribute Definitions	Standards and Reference Materials
ease of peeling	ease of peeling the shell and pellicle away from the nut	different level of adherence of shell/pellicle to the nut (value 0 corresponds to hard, while value 10 corresponds to easy)
seed colour	external colour of the seed, after removing the pellicle	seed colour with a degree of darkness (value 0 corresponds to a light colour seed, while value 10 corresponds to dark)
crunchiness	amount of noise generated when the sample is chewed at a fast rate with the back teeth	value 0 corresponds to a dried apple piece, while 10 corresponds to a fresh celery piece
astringent	sensation of drying, drawing-up, or puckering of any of the mouth surfaces	diluted tannic acid solution (0.06–2 mg/mL)
sweetness	basic taste associated with sugar (sucrose)	diluted sucrose solution (0.5–6 g/L)
bitterness	basic taste associated with caffeine	diluted caffeine solution (0.03–0.2 g/L)
hazelnut aroma	intensity of aroma of hazelnut products	taste of hazelnut
oily aroma	oily taste	taste of hazelnut or vegetable oils
almond aroma	Sweet cherry pit-like nutty aromatic associated with almonds	taste of almond
butter aroma	aromatics commonly associated with natural, slightly salted butter	taste of butter
caramel aroma	aromatics associated with caramel	taste of caramel
walnut aroma	aromatics associated with walnuts	taste of walnut
woody	aromatics associated with woody	taste of wood
malty	aromatics associated with malty	taste of malt
popcorn-like	aromatics associated with popcorn-like	taste of popcorn
coffee-like	aromatics associated with coffee-like	taste of coffee
roasty	aromatics associated with roasty	taste of roasted
aromatic intensity	characteristic flavour of hazelnut at the seed break	aromatics commonly associated with hazelnut

), which also had reference to evidence from the literature [23,24,25,26]. The descriptors were scored from 0 (no descriptor) to 10 (maximum descriptor) [27,28,29]. On the basis of the chosen attributes, a quantitative descriptive analysis (QDA) was performed. Using the same scale of 0–10, the overall satisfaction rating of each panel member was then assessed.

2.4. Antioxidant Activity

2.4.1. Extract Preparation for Polyphenol Compounds and Antioxidant Activity Determination

The extractions for polyphenol compounds and antioxidant activity were performed following the method described by Costantini et al. [30]. The samples were ground using a laboratory mill (IKA^® A11 basic Analytical mill (IKA^®-Werke GmbH & CO., KG, Staufen im Breisgau, Germany). The powdered edible roasted samples were then extracted overnight in the dark using 80% aqueous methanol at a ratio of 1:25 (w/v). Following extraction, the samples were centrifuged at 10,000 rpm (ALC PK121R centrifuge; Bodanchimica s.r.l., Cagliari, Italy) for 10 min at 4 °C. The resulting supernatants were collected for subsequent analysis.

2.4.2. Total Phenolic Compounds (TPCs)

The TPC was determined using the Folin–Ciocalteu method, as modified by Costantini et al. [28], and adapted for use with 96-well plates and an automatic microplate reader (Infinite 2000, Tecan, Salzburg, Austria). Briefly, 10 µL of ethanolic extract was mixed with 30 µL of deionized water, 10 µL of Folin–Ciocalteu reagent, and 200 µL of 30% Na₂CO₃. The absorbance of the reaction mixture was then measured at 725 nm using a plate reader (Infinite F200, TECAN, Männedorf, Switzerland). A standard calibration curve was generated using gallic acid, and the results were expressed as milligrams of gallic acid equivalents (GAE) per gram of sample.

2.4.3. Total Antioxidant Capacity (TAC) Determination

The TAC was assessed using two complementary assays: the ferric-reducing antioxidant power (FRAP), and 2,2-azino-bis (3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS^•+) radical scavenging activity assay, as detailed below. The FRAP assay was performed according to Benzie and Strain [31], with modifications for use in 96-well plates and analysis via an automated reader (Infinite 2000, Tecan, Salzburg, Austria). This assay measures the reduction of the Fe³⁺-2,4,6-tripyridyl-s-triazine (TPTZ) complex to its ferrous form under acid conditions. Briefly, 160 µL of freshly prepared FRAP reagent—comprising 20 mM ferric chloride solution, 10 mM TPTZ solution, and 0.3 M acetate buffer at pH 3.6—was mixed with 10 µL of the sample, standard, or blank. The mixture was incubated at 37 °C for 30 min, after which the absorbance was measured at 595 nm. Results were expressed as mmol Fe²⁺ equivalents per gram of sample. The ABTS^•+ radical scavenging activity was evaluated by the OxiSelect^TM Trolox Equivalent Antioxidant Capacity (TEAC) Assay Kit (ABTS) (Cell Biolabs INC. San Diego, CA, USA) following the manufacturer’s instructions. The absorbance was measured at 405 nm using the same microplate reader as above. A Trolox standard curve was prepared, and results were reported as mmol of Trolox equivalents (TE) per gram of sample.

2.5. HS-SPME/GC-MS Determination of Volatile Chemical Composition

The hazelnuts investigated were first deshelled by cracking on the ground, and then a NaCl solution was added to help extract the volatiles. The volatile chemical profiles of hazelnuts were described by employing the SPME extraction method, followed by GC/MS analysis. Approximately 1 mg of each sample was placed inside a 7 mL glass vial with a PTFE-coated silicone septum. To adsorb the volatile components, a SPME device from Supelco (Bellefonte, PA, USA) with 1 cm fibre coated with 50/30 μm DVB/CAR/PDMS (divinylbenzene/carboxen/polydimethylsiloxane) was used. Before using it, the fibre was conditioned at 270 °C for 30 min. The equilibration time was obtained by heating to 40 °C for 10 min. For the sampling phase, the fibre was exposed to the headspace for 30 min at 40 °C and then, to complete the desorption phase, it was inserted into the GC injector maintained at 250 °C in splitless mode. The analyses were performed using a gas chromatograph coupled with a mass spectrometer Clarus 500 model Perkin Elmer (Waltham, MA, USA), equipped with a FID (flame detector ionization). The capillary column used for the chromatographic separation of the components was a Varian Factor Four VF-5. The operative terms were the following: The injector was set to 250 °C, and the programmer set the oven temperature from 35 °C, held for 0.5 min and then increased, at a rate of 6 °C/min, to 220 °C for 10 min. The mass spectrometer was operated at 70 eV (EI) in full scan mode in the range 35–450 m/z. The ion source and the connection parts temperature were set 180 °C and 200 °C, respectively. Volatiles were identified by analyzing their mass spectra and comparing them to spectra in the Wiley 2.2 and NIST 11 databases. Linear retention indices (LRIs) were calculated using a series of alkane standards. The obtained LRIs were then matched with the literature data. For the quantification of the analytes, the peak areas of the FID signal were determined. The concentrations were expressed as percentages. This was conducted without the use of an internal standard. It was also conducted without any factor correction. Each analysis was performed in triplicate.

2.6. Statistical Analyses

The statistical investigation was carried out using XLSTAT 2024.1.1 software, developed by Addinsoft SARL, a New York-based company (New York, NY, USA). Fisher’s least significant difference test was used for the description of statistical differences between means at a significance level of p < 0.05. Principal component analysis (PCA) was employed to gain a better understanding of the differences in the sensory attributes and overall scores of the hazelnuts under study. The GC/MS results were expressed as means ± standard deviation (SD), and the Anova test (one-way analysis of variance test), followed by Tukey’s HSD test, was used to analyze significant differences among means (p < 0.01; p < 0.05). Each analysis was performed in triplicate.

3. Results and Discussion

3.1. Physical Characteristics

Table 2. Measurements of the physical characteristics of organic Tonda Gentile Romana hazelnuts (both roasted and raw) compared to conventional ones.

Samples	Weight (g)	Length (mm)	Width (mm)	Thickness (mm)	Geometric Mean Diameter (mm)	Arithmetic Mean Diameter (mm)	Surface Area (mm2)	Sphericity (%)	Volume (mm3)
OF	1.27 ± 0.17 a	14.25 ± 1.98 a	16.87 ± 1.72 a	12.50 ± 1.21 a	14.22 ± 0.89 a	14.54 ± 0.92 a	636.13 ± 76.27 a	1.03 ± 0.09 a	1523.89 ± 261.1 a
OR	1.18 ± 0.17 a	13.25 ± 1.98 a	16.00 ± 1.78 a	12.87 ± 1.21 a	13.91 ± 0.89 ab	14.04 ± 0.92 ab	609.26 ± 76.27 ab	1.05 ± 0.09 a	1429.65 ± 261.1 a
CR	1.26 ± 0.17 a	12.12 ± 1.98 a	15.00 ± 1.72 a	11.75 ± 1.21 a	12.83 ± 0.89 ab	12.95 ± 0.92 b	518.53 ± 76.27 ab	1.05 ± 0.09 a	1121.83 ± 261.1 a
CF	1.20 ± 0.17 a	12.37 ± 1.98 a	14.50 ± 1.72 a	11.75 ± 1.21 a	1.78 ± 0.89 b	12.87 ± 0.92 b	513.98 ± 76.27 b	1.03 ± 0.09 a	1106.73 ± 261.1 a
Pr > F(Model)	0.89	0.45	0.21	0.50	0.02	0.01	0.02	0.98	0.02
Significant	No	No	No	No	Yes	Yes	Yes	No	Yes

Legend: OF: organic raw hazelnuts; OR: organic roasted hazelnuts; CF: conventional raw hazelnuts; CR: conventional roasted hazelnuts. Note: means that show different letters are significantly different (p < 0.05).

shows the physical traits of the hazelnuts analyzed. As can be seen, no significant differences were observed for weight, length, width, thickness, and sphericity between organic and conventional samples, nor between roasted and raw. These findings on the organic and conventional samples of the Tonda Gentile Romana cultivar are supported by previous researchers [15,18] who found that differences in morphological traits were directly related to different cultivars. The noteworthy parameter is the sphericity of the analyzed hazelnuts, both organic and conventional (raw and roasted), with values ranging from 1.034 to 1.059 (Table 2).

In this regard, as spherical nuts are highly desirable for industrial processing, sphericity is an important quality characteristic of hazelnut kernels [32]. Morphological characteristics are also important when selecting cultivars for specific food products. For example, whole hazelnut products require spherical hazelnut varieties, such as Tonda Gentile Romana, which also have sensory characteristics, such as increased kernel hardness, to remain intact during production.

3.2. Sensory Analysis

The sensory attributes of organic and conventional Tonda Gentile Romana cv hazelnuts, both raw and toasted, are presented in

Table 3. Least squares means of the sensory attributes and the overall judgment of the hazelnuts studied.

Sample	Ease of Peeling	Seed Colour	Crunchiness	Sweetness	Bitterness	Astringent	Hazelnut Aroma	Oily Aroma	Almond Aroma	Butter Aroma	Caramel Aroma	Walnut Aroma	Woody	Malty	Popcorn-Like	Coffee-Like	Roasty	Aromatic Intensity	Overall Judgment
OR	8.0 a	6.0 a	8.3 a	7.0 b	1.2 a	0.0 b	8.8 a	1.8 a	3.0 a	1.2 b	1.0 b	4.2 b	1.4 b	2.0 a	2.8 a	5.1 a	8.3 a	8.5 a	8.6 a
OF	1.1 b	5.0 b	6.7 b	7.6 a	0.7 a	0.0 b	8.3 b	1.2 b	2.9 a	3.0 a	1.9 a	4.6 a	2.9 a	0.0 b	0.0 c	0.0 c	0.0 c	8.2 ab	7.9 b
CR	8.0 a	5.8 a	4.6 c	3.8 d	1.0 a	0.0 b	7.4 c	1.7 a	2.0 b	1.2 c	0.9 b	3.0 c	1.4 b	1.8 a	2.6 b	4.6 b	7.6 b	7.8 b	6.9 c
CF	0.6 c	3.8 c	4.0 c	4.8 c	0.9 a	0.2 a	7.1 c	1.0 b	0.0 c	2.9 a	2.0 a	3.0 c	2.9 a	0.0 b	0.0 c	0.0 c	0.0 c	6.9 c	6.9 c
Pr > F(Model)	<0.0001	<0.0001	<0.0001	<0.0001	0.927	0.002	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001
Significant	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes

Legend: OF: organic raw hazelnuts; OR: organic roasted hazelnuts; CF: conventional raw hazelnuts; CR: conventional roasted hazelnuts. Note: means that show different letters are significantly different (p < 0.05).

. Overall, butter, caramel aroma, and wood were predominant sensory attributes in raw hazelnuts, whereas oily, malty, popcorn-like, coffee-like, and roasty were predominant in roasted hazelnuts. These results are consistent with those of previous researchers [33,34]. A particularly important aspect is that the contribution of the sensory attributes of popcorn-like, coffee-like, and roasty in roasted hazelnuts appears to be more significantly pronounced in organic samples than in conventional ones (Table 3). An important parameter among the descriptors is crunchiness, which is higher in organic hazelnuts than in conventional ones (6.722 vs. 4.056 for raw and 8.389 vs. 4.667 for roasted). Indeed, higher crunchiness is considered a positive element, as the noise experienced is perceived by consumers as synonymous with quality [35]. With regard to crunchiness, a line of research was followed that is common to other studies in the literature [35,36], in which sensory analyses include the crunchiness descriptor without necessarily assessing texture instrumentally. In fact, there are specific works that have carried out only the instrumental assessment of texture without combining it with a sensory study [37,38]. This confirms that the two lines of research can be carried out independently.

The aromatic profile of organic hazelnuts is dominated by an intense hazelnut aroma (8.333 for raw and 8.833 for roasted), followed by a walnut and almond aroma that strongly characterizes organic hazelnuts compared to conventional ones (Table 3). In this respect, the difference between the sensory characteristics of organic and conventional hazelnuts of the same variety is a novelty effect. Sweetness was also significantly higher in organic hazelnuts, both raw and roasted, with values almost double those of conventional hazelnuts (7.667 vs. 4.867 for raw and 7.089 vs. 3.889 for roasted). In addition, a higher aromatic intensity was found in the organic hazelnuts, both raw and roasted (8.278 and 8.556, respectively), compared to the aromatic intensity of conventional hazelnuts. The hazelnuts examined showed a significant difference in the panel’s subjective judgement scores (Figure 2).

The roasted organic sample had the highest score (8.678), followed by the raw organic sample (7.989). For the conventional hazelnuts, there was no significant difference between the raw and roasted samples (6.978 vs. 6.956). Furthermore, Principal Component Analysis (PCA) was performed on sensory differences between organic and conventional hazelnuts, both raw and roasted, as well as on panellists’ total ratings. The sensory differences between organic and conventional hazelnuts are clear, as seen in Figure 3, where the first two components explain 84.67% of the total variability, with F1 contributing 56.42% and F2 28.25%. According to the PCA results, it can be stated that the organic and conventional hazelnut samples, raw and roasted, are positioned in different quadrants of the graph: the organic roasted hazelnuts (OR) are located in the upper right quadrant of the PCA projection and are characterized by crunchiness, sweetness, hazelnut aroma, almond aroma, and walnut aroma; the conventional roasted hazelnuts (CR) are located in the lower right quadrant of the PCA projection and are characterized by popcorn, coffee, malt and roasted; in the lower left quadrant of the PCA projection are the conventional raw hazelnuts (CF), which, together with the organic raw hazelnuts (OF), are distinguished by the presence of butter, caramel aroma, and wood.

This allows us to see that the samples formed two different clusters: organic and conventional. The plots provide evidence that organic and conventional hazelnuts can be discriminated by sensory descriptors. The diagram was created using median attribute values for organic and conventional hazelnuts. Figure 4 shows that there is a notable difference in the sensory profiles between organic and conventional hazelnuts, which distinguishes each of them like a fingerprint.

As sensory characteristics play an important role for all food companies producing hazelnuts, our results are of great importance.

3.3. Total Phenolic Compounds (TPCs) and Total Antioxidant Capacity (TAC)

Hazelnuts are rich in phenolics and flavonoids [5], making them a powerful source of natural antioxidants, which are very effective and potent scavengers of dangerous free radicals. Figure 5 shows the results of our study, highlighting that the amounts of total phenolic compounds (TPCs) are significantly higher in organic hazelnuts than in conventional ones, both roasted and raw (8.29 and 7.58 vs. 6.68 and 6.56 mg GAE/g). This could be due to the exposure, in organic farming where chemical pesticides are not used, to pathogen attacks, which may lead to an increase in the biosynthesis of phenolic compounds. Our results are in agreement with those of other researchers on Turkish hazelnuts [5], but with considerably higher levels of TPCs found in Tonda Gentile Romana hazelnuts. Regarding total polyphenols in roasted versus raw samples, our data agrees with Lucchetti et al.’s [39] results. Indeed, roasted hazelnuts slightly increased total phenolic compounds compared to raw (Figure 5). The total antioxidant capacity of organic and conventional hazelnuts in roasted form was determined to be 0.97 and 0.75 mmol TE/g, respectively, according to the ABTS test (Figure 5). Organic raw hazelnuts also had higher antioxidant capacity than conventional hazelnuts (0.88 vs. 0.70 mmol TE/g). In this respect, it can be hypothesized that the difference in antioxidant capacity between organic and conventional hazelnuts is closely related to the reducing effect that pesticides used in conventional agriculture exert on the total phenol content and consequently also on the antioxidant capacity. Indeed, previous evidence has demonstrated an increase in total phenolic content and total antioxidant capacity in organic fruits and vegetables compared to conventional ones [40,41]. However, to the best of our knowledge, no study has investigated the contribution of organic agriculture to polyphenol contents and antioxidant capacity in nuts.

3.4. Volatile Compounds

The chemical analyses allowed the detection and identification of a series of volatile compounds belonging to different chemical classes. In particular, aldehydes, ketones, and acids were the most numerous (

Table 4. Volatiles content (percentage mean value ± standard deviation) of organic and conventional hazelnuts, as determined by HS-SPME/GC–MS.

N°	COMPONENT 1	LRI 2	LRI 3	CF (%)	CR (%)	OF (%)	OR (%)
1	2-pentanol	660	664	8.4 ± 0.07 a	6.5 ± 0.06 b	7.2 ± 0.05 c	9.1 ± 0.10 d
2	2-hexanol	800	801	10.2 ± 0.09 a	9.4 ± 0.10 b	12.2 ± 0.14 c	10.5 ± 1.60 da
3	hexanal	808	804	2.4 ± 0.02 a	1.2 ± 0.02 b	1.9 ± 0.03 cb	0.9 ± 0.03 d
4	4-heptanone	872	869	2.6 ± 0.02 a	3.1 ± 0.02 b	4.5 ± 0.02 c	2.0 ± 0.02 da
5	2-furfurylthiol	893	883	0.2 ± 0.02 a	5.1 ± 0.04 b	Tr	4.2 ± 0.05 c
6	2(3H)-furanone	904	914	1.5 ± 0.04 a	9.1 ± 0.09 b	Tr	5.2 ± 0.05 c
7	3-methyl-4-heptanone	927	932	6.3 ± 0.05 a	4.2 ± 0.02 b	2.5 ± 0.02 c	3.2 ± 0.02 d
8	hexanoic acid	970	978	18.5 ± 0.20 a	15.5 ± 0.15 b	20.7 ± 0.15 c	22.7 ± 0.34 d
9	1,8-cineole	1028	1035	Tr	2.4 ± 0.02 a	0.9 ± 0.05 b	2.2 ± 0.03 ca
10	4-hydroxy-2,5-dimethyl-3(2H)-furanone	1040	1055	0.9 ± 0.03 a	3.6 ± 0.05 b	Tr	2.1 ± 0.02 c
11	2-nonanone	1089	1091	4.1 ± 0.06 a	2.1 ± 0.02 b	3.6 ± 0.03 c	4.0 ± 0.03 da
12	octanoic acid	1169	1178	2.3 ± 0.05 a	3.3 ± 0.03 b	0.5 ± 0.02 c	2.1 ± 0.07 da
13	2-hexenal, (E)-	1200	1205	2.2 ± 0.07 a	1.8 ± 0.05 b	2.5 ± 0.03 ca	1.9 ± 0.12 db
14	decanal	1207	1217	1.9 ± 0.03 a	2.2 ± 0.04 b	2.1 ± 0.04 cb	3.3 ± 0.02 d
15	1-pentanol	1230	1233	6.2 ± 0.05 a	5.5 ± 0.07 b	9.3 ± 0.11 c	4.1 ± 0.05 d
16	nonanoic acid	1271	1276	3.4 ± 0.03 a	4.2 ± 0.03 b	2.1 ± 0.02 c	5.5 ± 0.06 d
17	octanal	1285	1278	6.5 ± 0.10 a	4.3 ± 0.08 b	5.5 ± 0.04 c	3.2 ± 0.02 d
18	2-heptanol	1333	1325	14.5 ± 0.14 a	12.3 ± 0.11 b	20.1 ± 0.24 c	10.9 ± 0.22 d
19	nonanal	1387	1390	4.5 ± 0.03 a	2.8 ± 0.07 b	3.2 ± 0.05 c	2.0 ± 0.03 d
20	acetic acid	1420	1427	3.3 ± 0.03 a	1.3 ± 0.02 b	0.9 ± 0.06 c	1.2 ± 0.02 db
	SUM			99.9	99.9	99.7	100.0

Legend: ¹ The components are reported according to their elution order on apolar column; ² Linear retention indices measured on apolar column; ³ Linear retention indices from the literature; data are means ± standard deviation of three (n = 3) replicates. Means with different letters, among columns, indicate significant differences (p ≤ 0.01), according to one-way ANOVA with post hoc Tukey HSD. CF: conventional raw hazelnuts; CR: conventional roasted hazelnuts; OF: organic raw hazelnuts; OR: organic roasted hazelnuts; Tr: percentage mean values < 0.1%.

). The profiles of volatiles found between conventional and organic raw hazelnuts showed significant differences. The presence of 4-heptanone was 4.5% in OF compared to 2.6% in CF. As in organic hazelnuts (OF), the average percentages of volatiles such as hexanoic acid (20.7 and 18.5%), decanal (2.1 and 1.9%), 1-pentanol (9.3 vs. 6.2%), and 2-heptanol (20.1 vs. 14.5%) were higher in OF than in conventional hazelnuts (CF). Several previous studies [34,42] have highlighted that hazelnuts can have their own odour depending on the volatile compounds. Specifically, 4-heptanone and 2-heptanol for fruity; 1-pentanol for balsamic; decanal for flowery. Hence, there could be a link between the results of the sensory evaluation and those of the volatile chemical composition analysis. Indeed, the higher presence of the volatile compounds 4-heptanone and 2-heptanol, 1-pentanol and decanal in raw organic hazelnuts corresponds to a higher aromatic intensity and more fruity notes found in the sensory analysis (Table 3). This issue will be investigated in a forthcoming study. The authors also reported that the volatiles of hazelnut vary significantly depending on the ecological conditions and the stage of ripeness. Moreover, the presence of volatile compounds in hazelnuts is influenced by a variety of factors, including the variety of the nut, the soil’s structure, the prevailing climate, the time of harvest, the cultivation method, the drying method, the season, the geographical origin of the nut, environmental factors, storage conditions and the level of maturity [42].

Our study adds that organic farming has a significant impact on these compounds compared to conventional. Differences between organic and conventional hazelnuts were also observed in the roasted samples (Table 4).

In particular, the roasted aroma developed in both CR and OR samples showed higher levels in conventional hazelnuts with 2-furfurylthiol (5.1% vs. 4.2%); 4-hydroxy-2,5-dimethyl-3(2H)-furanone (3.6% vs. 2.1%). A final observation is the presence of 1,8-cineole in both CR and OR with non-significantly different percentages (2.2 vs. 2.4%).

4. Conclusions

In this study, the sensory characteristics, the antioxidant activities and the volatile profiles of hazelnuts organically and conventionally produced were investigated, and significant differences were found. In particular, organic hazelnuts had a higher antioxidant capacity than conventional hazelnuts. This suggests that perhaps higher resistance to oxidation and nutritional value may be possessed by organic hazelnuts than conventional hazelnuts. One new finding was the significant difference in sensory profiles between organic and conventional hazelnuts of the same variety. Organic hazelnuts showed more sensory notes of hazelnut, walnut, and almond than conventional hazelnuts. Organic hazelnuts also scored higher on the panel’s overall judgment in comparison with the conventional ones. Significant differences were also found in the volatile profiles of conventional and organic raw hazelnuts. In detail, 4-heptanone and 2-heptanol for the fruity notes, 1-pentanol for the balsamic notes, and decanal for the floral notes characterized the organic hazelnuts. As well as encouraging consumer consumption of these nutritious foods and improving public health, the promotion of organic hazelnuts is very important for environmental sustainability. Based on the knowledge gained from our results, an important recommendation for producers is to be able to cope with the greater effort required for organic hazelnut production compared to conventional production. Future research is needed to assess the challenges associated with organic products, as well as to determine the most effective strategies for overcoming them.