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Article

The Volatile Compounds and Aroma Description in Various Rhizopus oligosporus Solid-State Fermented and Nonfermented Rice Bran

by
Retno Dwi Astuti
1,
Dwi Larasatie Nur Fibri
1,
Dody Dwi Handoko
2,
Wahyudi David
3,
Slamet Budijanto
4,
Hitoshi Shirakawa
5,6 and
Ardiansyah
3,*
1
Department of Food Science and Technology, Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta 55281, Indonesia
2
Indonesian Center for Rice Research, Indonesian Agency for Agricultural Research and Development, Ministry of Agriculture, Subang 41256, Indonesia
3
Department of Food Technology, Universitas Bakrie, Jakarta 12920, Indonesia
4
Department of Food Science and Technology, Faculty of Agricultural Engineering and Technology, IPB University, Bogor 16680, Indonesia
5
Laboratory of Nutrition, Graduate School of Agricultural Science, Tohoku University, Sendai 980-8572, Japan
6
International Education and Research Center for Food Agricultural Immunology, Graduate School of Agricultural Science, Tohoku University, Sendai 980-8572, Japan
*
Author to whom correspondence should be addressed.
Fermentation 2022, 8(3), 120; https://doi.org/10.3390/fermentation8030120
Submission received: 21 January 2022 / Revised: 27 February 2022 / Accepted: 4 March 2022 / Published: 10 March 2022
(This article belongs to the Section Fermentation for Food and Beverages)
Browse Figures
Versions Notes

Abstract

:
Rice bran is known to have beneficial nutrients. Current studies suggest that solid-state fermentation affects the rice bran’s volatile profile. The aim of this study is to identify the volatile compounds and aroma description of fermented and nonfermented rice bran (FRB and NFRB) of Ciherang, Inpari30, IR64 and Inpari42. The fermentation was conducted using Rhizopus oligosporus solid-state fermentation. Headspace-solid phase microextraction coupled with GC/MS was performed, and the aroma was translated by 10 trained panelists through quantitative descriptive analysis (QDA). The result showed that 72 and 68 compounds were identified in FRB and NFRB, respectively. They are aldehydes, ketones, alcohols, acids, esters, fatty acid, phenol, benzenes, furan, thiazole, pyrazines, pyridine, lactones, terpenes, and hydrocarbons. The PCA showed that FRB was dominated by alcohols, whereas NFRB was dominated by aldehydes. The QDA described nine aromas, i.e., rancid, smoky, musty, grassy, green, earthy, cereal, and sweet in NFRB. The fermentation process added fermented attributes to the aroma description to FRB and enhanced the rancid, smoky, and musty aromas. These studies indicated that fermented rice bran might increase the volatile compound of rice bran. Thus, it may provide opportunities to develop the production of fermented rice bran as a functional ingredient.

1. Introduction

Rice bran (RB) is a by-product of milling rice that is produced in an estimated million tons per year. This high production has a great potential to be developed as functional ingredients, due to its high nutritional and bioactive compounds such as dietary fiber, vitamins, minerals, lipids, protein, γ-oryzanol, ferulic acid, and tocopherol [1].
The sensory profiles of RB odor are the most decisive in terms of acceptance. Volatile compounds are chemical compounds that play an essential role in regulating odors in food. The volatile compounds of RB have been detailed by a few investigators utilizing GC-MS to identify the compounds. The main volatiles of RB are aldehydes, ketones, acids, esters, hydrocarbons, alcohols, and alkanes, among which hydrocarbons, acids, and aldehydes contribute to the off-flavor [2]. These compounds have an unacceptable odor that makes them difficult to consume.
Rancidity in RB is created by lipid oxidation and by the lipase and lipoxygenase in free fatty acids (FFA) such as oleic and linoleic acids which produce the off-flavor in RB [2,3,4]. The degradation of lipid results in an aldehyde group, one of which is hexanal as a marker that comes from linoleic acid degradation [3]. This is used as a degradation indicator in rice bran flavor quality.
Rice-based products that are fermented by variety of microorganisms are capable of producing various volatile compounds such as alcohol and acids in RB [4]. The fermentation process can remove the hexanal, reduce alcohol, and oxidize it into acid by microorganisms [5]. Fermentation has been shown to improve the bioactivities of RB in recent studies. There is an increase in the total phenolic compound and antioxidant activity of RB using Rhizopus oryzae [6] and R. oligosporus [7] in fermented rice bran (FRB).
In recent studies, 55 volatile compounds were identified in fermented rice bran (FRB) and nonfermented rice bran (NFRB) in the Indonesian popular cultivars IPR30 and Cempo Ireng [8]. They were categorized within aldehydes, ketones, acids, alcohols, esters, benzene, pyrazines, furans, phenols, terpenes, thiazoles lactone, and pyridines. Solid-state fermentation, performed by implementing R. oligosporus, can enhance the acceptance of RB [8].
Ciherang (C), Inpari30 (IPR30), Setra Ramos (IR64), and Inpari42 (IPR42) were the most widely circulated rice types in the Indonesian market because of their affordable price and relative suitability to the tastes of urban communities [9]. These four varieties were considered for use in this study because their accessibility ensured that the bran obtained was also abundant.
The descriptive analysis approach was recognized as a great and optimal measurement tool in assessing sensory attributes in various food products [10], especially fermented food products [11] and Indian milk products such as cham cham [10]. The training panelists measure product-specific quality attributes to produce product descriptions that could be statistically analyzed, which is a key principle of qualitative descriptive analysis (QDA) [10].
In comparison with our group in the previous study [8], these studies aimed to come up with novel information about the relationship between volatile compounds and aroma description in C, IPR30, IR64, and IPR42 fermented and nonfermented RB varieties.

2. Materials and Methods

2.1. Materials

This research used the superior seed quality of four varieties of rice: Ciherang (C), Inpari30 (IPR30), Setra Ramos (IR64), and Inpari42 (IPR42). The IPR30 was obtained from the Indonesian Center for Rice Research, Subang, West Java, Indonesia. C, IR64, IPR42 were purchased from rice collectors in Bantul, Yogyakarta, Indonesia. The culture R. oligosporus 6010 was purchased from the Center for Food and Nutrition Studies, Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta, Indonesia. The alkane C8-28 was obtained from Sigma-Aldrich (St. Louis, MO, USA) as used by authentic standards.

2.2. Rice Bran Preparation

The samples of C, IPR30, IR64, and IPR42 rice varieties were milled using a grinder LM 24 (Bantul, Yogyakarta, Indonesia) to remove the husks and epidermis, carried out for approximately one minute, and grinder N50 inch (Bantul, Yogyakarta, Indonesia) for less than one minute to get the bran. The method used for RB preparation was carried out as in previous studies [7], followed by 40 mesh sieving. all samples were stored in a dark zipper pouch at 5 °C before being sterilized at 121 °C for 15 min in an autoclave. The purpose of sterilization is stabilization. All bran treatments were the same, both NFRB and FRB were sterilized for stabilization purposes as in previous studies [7].

2.3. Rice Bran Fermentation

The preparation of the culture and fermentation process followed the method used in a previous study [7] with slight modifications. Each nine grams sterilized RB and 20% (v/v) of distilled water were mixed and inoculated with 15% (v/w) of R. oligosporus (106 spore/mL) in a petri dish on sterile Potato Dextrose Agar (PDA) and incubated for 72 h at 30 °C. Following the mycelium growth evenly distributed, all samples of FRB and NFRB were dried by freeze-drying at BenchTop Pro with Omnitronics (Ipswich, UK) at −20 °C for 48 h.

2.4. Headspace Solid Phase Microextraction (HS-SPME)/GC-MS Analysis

HS-SPME was also used by referring to the previous study [12] with slight modifications. Fiber 50/30 µm DVB/CAR/PDMS 2 cm was used in this study from SUPELCO Bellefonte, PA (USA). The FRB and NFRB weighed as much as 3 g and were put into the SPME Agilent 22 mL vial then closed using a Septa PTFE/Silicon. Furthermore, in an 80 °C water bath for 30 min, the fiber DVB/CAR/PDMS was laid onto the headspace of a vial in a water bath. Afterward, the fiber was removed from the vial and injected into the GC-MS/Olfactometry injector at 250 °C desorption for 10 min. The SPME was carried out cleaning procedure after absorption.
Gas Chromatography-Mass Spectra (GC-MS) (Agilent Technologies, Palo Alto, CA, USA) 7890 A and MS Agilent 5975 C with triple exist detector XL EI/CI) was used to analyze the volatile compounds in RB. The GC-MS system was equipped with a splitless injection port at 250 °C. DB-WAX was (30 m × 250 µm × 0.25 µm) used as column. Initially, the oven temperature was set at 40 °C, which was later increased to 110 °C by the speed 5 °C/min and up again to 230 °C by the speed of 8 °C/min and then maintained for 5 min. The interface temperature was set at 250 °C. The carrier gas was helium with a flow rate of 0.8 mL/min.
The comparison of mass spectra with the NIST05A database was used to identify volatile compounds. In addition, further confirmation was carried out by comparing the retention index with the existing reference. Retention data of linear alkane solution (C8C28) in hexane were used to calculate linear retention index (LRI). Peak area percentage was obtained from the quantification of the comparison of the peak area to the sample weight and expressed in peak area percentage.
peak   area   percentage = peak   area   peak   area   of   total   compound   × 100 %

2.5. Aroma Description

The aroma of FRB and NFRB was analyzed by QDA in a focus group discussion (FGD) [13] with 10 trained panelists (7 females and 3 males). The panels were trained based on ISO 8586-2012 for 3 h. The performance panel was carried out 3 times based on ISO 11132 followed by final evaluations. All panelists supplied informed consents before the examination.
Panelists were asked to provide an assessment of the aroma attributes contained in the sample. Eight samples consisting of four FRB and four NFRB were presented individually at room temperature by using a trivial code to avoid bias during testing. Then the panels were asked to inhale the aroma of the sample for 5 s and neutralize it with the aroma of coffee.

2.6. Statistical Analysis

The principal component analysis (PCA) was used to analyze the FRB and NFRB volatile compounds based on their peak area percentage and aroma description by trained panels. Pearson’s correlation was applied for the mapping of cultivars based on volatile compounds using XLSTAT 2021 software.

3. Results and Discussion

3.1. Volatiles of Fermented and Nonfermented Rice Bran

The FRB and NFRB volatile compounds are listed in Table 1. Totals of 69 and 65 compounds were identified in FRB and NFRB volatile compounds, respectively. FRB included 10 alcohols, 8 aldehydes, 8 ketones, 7 acids, 7 esters, 6 naphthalene, 4 phenol, 2 furan, 1 benzene, 2 thiazole, 2 pyrazines, 2 pyridine, 2 lactones, 4 terpenes, and 4 hydrocarbons. NFRB included 12 aldehydes, 6 ketones, 8 alcohols, 9 acids, 3 esters, 4 phenols, 7 naphthalene, 1 benzene, 2 furans, 2 thiazoles, 1 pyridine, 2 lactone, 3 terpenes, and 4 hydrocarbons. As seen in Table 1, it could be concluded that the volatile compounds of FRB were more distinctive than NFRB, including increased peak area percentages. These results are relevant to previous results [3] that the fermentation process is the crucial way to improve the volatile compounds.
Regarding the sample, these compounds are generally considered to be derived from carbohydrates, triglycerides, protein, free amino acids, and their derivatives [14]. As shown in Figure 1, among these varieties, aldehydes were the dominant volatile, followed by alcohol, benzene, and acid, especially in FRB. The aldehyde group was formed through lipid oxidation, with the greatest contribution to the aroma in all categories, due to the comparatively lower odor threshold. The aldehyde content such as hexanal, heptanal, and nonanal increase during the storage. This was due to the increase in lipoxygenase and lipase activity [15]. Consequent to all the above-mentioned factors, the rancidity increased.
Table
Table 1. Volatile compounds of fermented and nonfermented rice bran.
Table 1. Volatile compounds of fermented and nonfermented rice bran.
NoVolatile
Compounds		CodeLRI aLRI Ref dIdentifi Cation ePeak Area PercentageOdor Description
FermentedNonfermented
CFIPR30FIR64FIPR42FCNFIPR30NFIR64NFIPR42NF
Aldehyde
1HexanalAd101065 [16]MS + LRInd2403.09ndnd0.63632550.6460.176grass, tallow, fat b
2HeptanalAd211841186 [17]MS + LRIndndndnd0.4430.3880.3290.431fat, citrus, rancid b
3OctanalAd312871286 [18]MS + LRInd0.001ndnd0.2770.1460.4170.473fat, soap, lemon, green b
4NonanalAd413911392 [17]MS + LRIndndndnd3.748186023751214fat, citrus, green b
53-FuraldehydeAd51425naMSnd0.002ndnd0.3510.7300.3420.254-
6FurfuralAd614481448 [18]MS + LRI0.0560.0040.0060.3830.4680.7460.5210.605bread, nutty, roasted, almond, sweet b
7DecanalAd714951484 [17]MS + LRIndndndnd0.7490.7610.6150.800soap, orange peel, tallow b
8BenzaldehydeAd815171513 [17]MS + LRIndndnd0.25111110.7640.6390.745almond, nutty, burnt sugar b
9Benzene acetaldehydeAd916361643 [17]MS + LRIndndndnd0.3090.3770.3700.425green, honey, alcoholic, chemical, sweet, caramel, bread, coffee, mosty c
103-methylbenzaldehydeAd101644naMSndndnd0.3020.5400.4730.3700.763sweet fruity c
11CinnamaldehydeAd1120462045 [19]MS + LRIndndnd0.6630.0620.2090.1510.394cinnamon, paint c
12VanillinAd1225762578 [20]MS + LRIndndndnd0.1530.2610.1350.288vanilla b
Ketone
133-Penten-2-oneKt11120naMS0.546ndndndndndndndfruity c
143-Octen-2-oneKt213881435 [21]MS + LRI0.0560.001ndnd0.220ndndndherbal c
155-ethyldihydro-5-methyl-2(3H)-furanone Kt316671684 [22]MS + LRIndndnd0.392ndnd0.245ndcreamy c
166,10-dimethyl (E) -5,9-undecadien-2-oneKt418571865 [17]MS + LRIndndnd1612ndndnd0.275-
171-(1H-pyrrol-2-yl)-ethanoneKt519771967 [23]MS + LRIndnd0.0040.404ndnd0.1890.363musty c
18dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanoneKt62037naMSndndnd0.288ndndndndcotton candy c
196,10,14-trimethyl-2-Pentadecanone,Kt721302110 [24]MS + LRI0.0300.0050.0050.3240.2580.3790.3930.330green, fat, floral
205,6,7,7a-tetrahydro-4,4,7a-trimethyl-2(4H)-benzofuranoneKt82368naMS0.1080.0010.0010.0490.1280.1860.1180.106fruity c
Alcohol
21EthanolAl10913 [25]MS + LRIndndnd2058ndndndndsweet b
222-methyl-1 propanol Al21101093 [26]MS + LRInd0.0100.01715270.499ndndndethereal c
233-methyl-1-butanolAl312121220 [25]MS + LRInd0.014ndndndndndndfermented c
241-Octen-3-olAl414531456 [27]MS + LRIndndndnd0.338ndndndmushroom-like odor c
252,3-ButanediolAl515461494 [28]MS + LRI11220.0100.02419330.420ndndndcreamy c
274-ethyl-1,3-benzenediolAl61572naMS + LRIndndndnd0.2210.2470.130nd-
282-FuranmethanolAl716621686 [25]MS + LRIndndnd0.3070.206nd0.7890.330bready c
292-hexadecanolAl81745naMSndndnd0.262nd0.152ndnd-
30benzyl alcoholAl918821879 [17]MS + LRIndndnd0.397ndndndndsweet, floral b
31phenylethyl alcoholAl1019201920 [29]MS + LRI0.4300.0010.0060.6530.1420.1380.1130.252floral, slightly rose, sweet, clove-like c
32Nicotinyl alcoholAl112236naMS0.9060.0090.01010900.2610.3710.2740.424green c
Acid
33Acetic acidAs114491450 [16]MS + LRIndndndnd0.6480.1210.8451630sour b
34Butanoic acidAs216281628 [17]MS + LRIndndnd0.9490.171ndnd0.129cheesy, buttery c
35Hexanoic acidAs318471846 [26]MS + LRI0.273nd0.0040.5590.56818230.3731260fatty, sour fatty cheesy c
36Heptanoic acidAs419551954 [30]MS + LRIndndnd0.1480.1050.3230.1161641cheesy, rancid, sour c
37Octanoic acidAs520642065 [17]MS + LRI0.2440.0020.0030.2760.1020.4500.1390.340sweet, cheese b
38Nonanoic acidAs621632177 [17]MS + LRI0.053ndnd0.0550.6530.5080.4390.259green, fat b
39Dodecanoic acidAs724922502 [26]MS + LRIndndndndnd0.0660.1150.062-
40Tetradecanoic acidAs827042706 [26]MS + LRI0.083ndnd0.1090.2610.3510.5020.137waxy, fatty, soapy, coconut c
Ester
41Ethyl hexanoateEs112331230 [31]MS + LRI0.367ndnd0.286ndndndndapple peel, fruity b
42Methyl tetradecanoatEs220151994 [18]MS + LRI0.4480.0040.0050.247ndnd0.122ndorris
43Isobutyl palmitatEs32374naMSnd0.0350.03735870.081ndndndgrape b
449-Octadecenoic acid methyl esterEs42452naMS0.042ndnd0.148ndndndnd-
45ethyl oleatEs520522044 [32]MS + LRI12330.0070.0063081ndndndndfatty, fruity, oily c
469,12-Octadecadienoic acid (Z,Z)-, methyl esterEs62502naMS0.047ndnd25710.089nd0.1130.075fatty c
47Ethyl linoleate Es725352491 [18]MS + LRInd0.0050.0041954ndndndndfatty, fruity, oily c
Phenol
482-methoxyphenol Ph118621872 [17]MS + LRI17430.0080.0170.983nd0.6060.2070.114phenolic c
49Butylated HydroxytoluenePh219121912 [23]MS + LRIndnd0.0030.2560.0700.1470.1010.121phenolic c
50phenolPh320082002 [33]MS + LRI18050.0050.00813250.050nd0.2170.434phenol b
512-Methoxy-4-vinylphenolPh422022200 [34]MS + LRI0.070nd0.0070.7101030150217540.771woody c
Benzene
52StyreneBz112541250 [35]MS + LRI0.3060.003nd0.5921094nd0.4130.524balsamic, gasoline b
Naphthalene
53NaphthaleneNa117381734 [17]MS + LRI10780.0090.01212200.68613900.9781862tar b
542-methylnaphthalene Na218531877 [36]MS + LRI0.3830.0020.0020.3260.1120.2560.1100.153floral c
551-methylnaphthalene Na31889naMS0.3810.0020.0040.4840.1780.3710.274ndnaphthyl c
562,6-dimethylnaphthaleneNa41998naMS0.0670.0010.001ndndnd0.123ndgrass b
572,7-dimethylnaphthaleneNa520062012 [36]MS + LRI0.1060.001ndndndnd0.129nd-
582,3-dimethylnaphthaleneNa620732122 [37]MS + LRIndndnd0.102nd0.0630.000ndearthy c
591,6,7-trimethylnaphthaleneNa721122122 [37]MS + LRIndndndndnd0.0750.040ndfruity strawberry
Furan
602-PentylfuranFr112291230 [38]MS + LRI0.0620.0010.001nd0.2080.1570.2420.114fruity, green, nutty, earthy, beany, vegetable c
612,3-dihydro-BenzofuranFr223982392 [39]MS + LRI0.092nd0.0010.0890.1000.1250.1050.134musky odor
Thiazole
62ThiazoleTh11804naMS ndndnd0.178nd0.151ndndfishy c
63BenzothiazoleTh219641950 [39]MS + LRI0.154nd0.0020.3710.2380.3150.3350.366gasoline, rubber-like b
Pyrazine
642,6-dimethylpyrazine Pz113181308 [40]MS + LRIndndnd0.179ndndndnd-
65trimethyl pyrazinePz213871433 [25]MS + LRIndndnd0.064ndndndndroast, potato, must b
Pyridine
66trimethyl-pyridinePr11373naMS0.2070.0020.0030.1640.4500.1820.3920.359nutty
672-piperidinonePr21586naMSndndnd1308ndndndnd-
Lactone
68ButyrolactoneLc11623naMSndndnd0.3510.1000.1590.1220.230creamy-milk, oily, fatty c
69PantolactoneLc220372033 [41]MS + LRIndndnd0.162nd0.7460.416ndcotton candy b
Terpene
703-CareneTp111401138 [18]MS + LRI0.3900.0040.0050.3550.7940.5770.7011079lemon, resin b
71D-LimoneneTp211971190 [23]MS + LRI0.9790.0090.04014154755186924043384lemon, orange b
72CaryophylleneTp315931593 [42]MS + LRIndnd0.0251344nd23710.4780.614spicy c
73EpizonareneTp41758naMSndndnd0.434ndndndnd-
Hydrocarbon
74o-XyleneHd111341174 [18]MS + LRIndndnd0.280ndndnd6674,91geranium b
75o-CymeneHd212661260 [42]MS + LRIndndnd0.254ndndnd6048,25-
76TetradecaneHd313961400 [43]MS + LRI0.1850.0020.0050.2160.6710.876nd0.393alkane b
77cyclodecanoneHd41815naMSndndndnd0.1560.180ndnd-
782-PentadecanoneHd520251998 [44]MS + LRIndndndnd0.0210.0000.0660.095floral c
79IndoleHd624542450 [42]MS + LRIndndnd0.2802371.57ndndndburnt, mothball b
a Retention index was determined using n-alkane C8 to C28; b Flavornet.org https://www.flavornet.org/flavornet.html (accessed on 1 November 2021).; c The Good Scents Company Information System http://www.thegoodscentscompany.com/search2.html (accessed on 1 November 2021). d Linear Retention Index (LRI) Reference is obtained from journal references were analyzed by DB-WAX column; e Identification methods: retention index (RI) and mass spectra data (MS); nd (no detection); na (not available).
In this study, D-limonene and nonanal had the highest peak area percentage with 4755 and 3748 in CNF. This is in accordance with the physical characteristics of its color, which is more yellowish than other varieties. In addition, according to a previous study in 2013 [45], RB had a rich bioactive component: β-carotene [11], so that it gives a citrus aroma and spices that are generally associated with terpenes [46]. Nonanal, contributing fatty, citrus, and green aroma has a low odor threshold of one ppb. Other than that, benzaldehyde is found to be an important fragrance for wild rice [47] as it supplies an almond and nutty-like odor. The uniqueness of the type of nutty and roasted aroma mainly results from various volatile active compounds, 2-pentylfuran, benzaldehyde, and furfural [47].
Generally, the results of heating processes such as the Maillard reaction and lipid oxidation are reported to produce volatile compounds that are unique to grain products [2]. The Maillard reaction, which forms the main volatile heterocyclic compounds, includes furan, pyridine pyrazine, thiophene, thiazole, pyrrole, imidazole, etc. [15]. Amino acids and reducing sugars are present in the Maillard reaction during heat treatment, resulting from lipid degradation as aldehydes and ketones [48].
Alcohols are considered inferior products from the oxidation of unsaturated fatty acids [15]. The second plentiful volatile in FRB were alcohols, consisting of ethanol and 2,3-Butanediol 2058 and 1933 which had the highest peak area percentage, respectively, in IPR42F. The formation of 2,3-Butanediol was from the catabolism of glucose to pyruvate via the glycolysis pathway. This gives it a characteristic buttery and creamy aroma. Although alcohol such as 1-octen-3-ol has relatively high odor thresholds, most of the phenol has relatively low odor thresholds which contribute to the rice flavor. In addition, 1-octen-3-ol (mushroom-like odor) is also one of the most plentiful volatiles in rice [15].
The highest peak area percentage of phenol was found in CF with 1805. During heating, the products produced from the decarboxylation of p-coumaric acid and ferulic acid in plants can be classified as phenol [15]. The most plentiful phenolic acid in RB is 2-methoxy-4-vinyl phenol, gained from ferulic acid, which is thermally decarboxylated. This produces a spicy or clove-like aroma. Those derived from lignin degradation and formed by thermal degradation of ferulic acid are vanillin (vanilla) [49].
Fat oxidation reactions are formed through the process of free radicals. These include oxygenated fats, primary oxidation products (hydroperoxides), and degraded and volatile oxides such as aldehydes, acids, esters, hydrocarbons, and ketones [48]. Ketone is mainly derived from amino acid degradation and beta-oxidation of saturated fatty acids during the fermentation process [50]. Esterification reaction between fatty acid and alcohol, resulting from carbohydrate fermentation or amino acid catabolism, forms an ester group [46]. This reaction is catalyzed by an esterase, wherein the formation of esters by one of the acetic acid precursors during fermentation produces fruity and floral notes.
Among these compounds, the aldehyde is the greatest aroma compound in the NFRB, followed by alcohols, acids, esters, benzenes, ketones, phenols, hydrocarbons, terpenes, furans, fatty acid, thiazoles, pyrazines, pyridines, lactones, and alkaloids. These group compounds dominated the FRB. Most of these are in higher content than NFRB, derived from rice fatty acids during fermentation. The large amount of FFA in RB is responsible for the level of lipid degradation products during fermentation [4].

3.2. Principal Component Analysis of Fermented and Nonfermented Rice Bran

PCA was applied to compare the volatile compounds of FRB and NFRB. The PCA of FRB, NFRB, and a combination of both is shown in Figure 2. In Figure 2a, the volatile compounds in FRB are located in a quadrant different from NFRB, thus indicating that fermentation influenced volatile compound production. The alcohol group was generally found in FRB, such as 2-methyl-1 propanol, 2,3-butanediol, phenylethyl alcohol, and nicotinyl alcohol. Furthermore, octanoic acid, ethyl oleate; 6,10,14-trimethyl-2-pentadecanone, 2-methoxyphenol, phenol, and 9-octadecenoic acid methyl ester were also identified. This could be due to the fermentation process which increases the alcohol content. NFRB included hexanal, nonanal, furfural, and decanal aldehydes, benzaldehyde, 3-methylbenzaldehyde, butanoic acid, heptanoic acid, octanoic acid, 2-methoxy-4-vinylphenol, 3-carene, D-limonene, and caryophyllene.
During fermentation, the fungal active enzyme produced alcohol [51] from microbial metabolites that can increase the volatile compound. Hydrolyzing starch to glucose via glycolysis produced the desired fermentation product such as ethanol. Other alcohol compounds identified in FRB were benzyl alcohol and phenyl ethyl alcohol indicating a slightly sweet aroma. This is following the origination from the degradation of carbohydrates [52].
The PCA volatile compound FRB (Figure 2b) showed that CF is in contrast from others, in which 2-methoxyphenol, phenol, benzyl alcohol, phenylethyl alcohol, nicotinyl alcohol, D-limonene, ethyl oleate, 1-methylnaphthalene, hexanoic acid, and 9-octadecenoic acid methyl ester were dominant. PCA in NFRB (Figure 2c), IPR30, and IPR42 have more volatile dominants such as hexanal, heptanal, 3-furaldehyde, furfural, benzaldehyde, benzene acetaldehyde, 3-methylbenzaldehyde, hexanoic, heptanoic, octanoic, nonanoic, and tetradecanoic acid, 3-carene, caryophyllene, 2-methoxy-4-vinylphenol, and a different quadrant from IR64 and C.
The acid produced from the aldehyde group is appropriate during the continuous oxidation process, and this acid had other aromas such as cheesy, sweet, sour, and fatty. The storage process can increase the intensity of the odor-active compound. In addition, acid aromas can be formed through the oxidation of aldehydes such as hexanoic acid, which was detected most abundantly in RB. The increase in levels may be the result of hexanal oxidation.
This difference in position is shown in addition to the different treatments. The characteristics of each variety are also different, even though the C and IPR30 varieties came from the IR64 selection. These different characteristics show the aroma profile, and the fermentation shows changes. This is the novel finding of this research.

3.3. Aroma Description of Fermented and Nonfermented Rice Bran

The QDA determined the effects of changes in the rice bran samples, including the fermentation process. Figure 3 represents the distinction of aroma description in FRB and NFRB. No panelist mentioned any fermented or alcohol odor in NFRB (Figure 3a). The PCA results of dominant aroma description in various RB are given in Figure 3c. These results showed the same grouping of volatile compounds, starting with different FRBs and NFRB quadrants.
On PCA the volatile compounds indicated that the alcohol group is the dominant group in the FRB. This is following the description of the aroma stated by the panelists of the presence of fermented, rancid, and musty aromas. On the other hand, the NFRB quadrant was dominated by the aldehyde group, where the aldehyde contributes to the fat, green, and rancid aroma. Uniquely, IPR30 and IR64 are stated to have a dominant aroma of sweet and green, while C and IPR42 are cereals, nuts, and grassy. The PCA biplot Figure 3c shows that the diversity in the first and second components is not much different, indicating that the distribution of the aroma description data stated by the panelists is evenly distributed.

3.4. Correlation Analysis between Volatile Compounds with Aroma Description (QDA)

To determine the relationship between volatile compounds and the aroma, which is descriptive in this study, testing was carried out using Pearson’s correlation. There was a positive correlation between volatile compounds and aroma description as seen in Table 2. Furfural (0.801), benzaldehyde (0.760), benzene acetaldehyde (0.650), 3-methylbenzaldehyde (0.747), and pantolactone (0.792) have a correlation with sweet aroma. It implies that an increase in peak area percentage of these volatile compounds is highly correlated with the sweet aroma in FRB and NFRB. The results showed that 3-methyl-1-butanol (0.657) and octanoic acid (0.703 and 0.693) were related to fermented and rancid flavors that were produced by aldehyde oxidation and lipid hydrolysis, especial during storage. Moreover, the off-flavor of RB occurs lipid hydrolysis by lipase, and the RB is stabilized by autoclaving to inactive lipase and lipoxygenase. Therefore, the off-flavor of rice bran will not be produced during storage unless the rice bran is not enough stabilized by 15 min autoclaving.

4. Conclusions

The study detected volatile compounds in FRB and 66 in NFRB, including aldehydes, ketones, alcohols, acids, esters, fatty acid, phenol, benzenes, furan, thiazole, pyrazines, pyridine, lactones, terpenes, and hydrocarbons. Volatile compounds from the fermentation process showed more diverse compounds than NFRB. The QDA define nine aromas, i.e., rancid, smoky, musty, green, earthy, cereal, and sweet in NFRB. The PCA plot showed that the volatile compound and aroma description of FRB is in the different quadrant with NFRB. The solid-state fermentation method added fermented attributes to the aroma description in FRB and enhanced the rancid, smoky, and musty aromas. The alcohol group was dominant in FRB, while the aldehyde group dominated NFRB. There was a positive correlation between volatile compounds and aroma description. Consequently, the relationship between volatile compounds and aroma description can be used as a characteristic aroma in various fermented and nonfermented RB varieties.

Author Contributions

Conceptualization, D.L.N.F., D.D.H., W.D. and A.; Investigation, R.D.A. and D.D.H.; Supervision, D.L.N.F., D.D.H. and A.; Project administration, A.; Writing—original draft, R.D.A.; Writing—review & editing, D.L.N.F., D.D.H., W.D., S.B., H.S. and A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Education, Culture, Research and Technology, Indonesia with contract No. 124/SPK/LPP-UB/VII/2021.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Acknowledgments

The author would like to thank Anang Juni Yustanto, Yuda, and Desi for laboratory assistance.

Conflicts of Interest

The authors declare no conflict of interest.

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Fermentation 08 00120 g001 550
Figure 1. Number of volatile compounds in Ciherang fermented (CF), Inpari42 fermented (IPR42F), Inpari30 fermented (IPR30F), IR64 fermented (IR64F) Ciherang nonfermented (CNF), Inpari42 nonfermented (IPR42NF), Inpari30 nonfermented (IPR30NF) and IR64 nonfermented (IR64NF) rice bran.
Figure 1. Number of volatile compounds in Ciherang fermented (CF), Inpari42 fermented (IPR42F), Inpari30 fermented (IPR30F), IR64 fermented (IR64F) Ciherang nonfermented (CNF), Inpari42 nonfermented (IPR42NF), Inpari30 nonfermented (IPR30NF) and IR64 nonfermented (IR64NF) rice bran.
Fermentation 08 00120 g001
Fermentation 08 00120 g002 550
Figure 2. Volatile compound: (a) FRB and NFRB; (b) Ciherang fermented; (CF), Inpari42 fermented (IPR42F), Inpari30 fermented (IPR30F), IR64 fermented (IR64F) rice bran; (c) Ciherang nonfermented (CNF), Inpari42 nonfermented (IPR42NF), Inpari30 nonfermented (IPR30NF), and IR64 nonfermented (IR64NF) rice bran.
Figure 2. Volatile compound: (a) FRB and NFRB; (b) Ciherang fermented; (CF), Inpari42 fermented (IPR42F), Inpari30 fermented (IPR30F), IR64 fermented (IR64F) rice bran; (c) Ciherang nonfermented (CNF), Inpari42 nonfermented (IPR42NF), Inpari30 nonfermented (IPR30NF), and IR64 nonfermented (IR64NF) rice bran.
Fermentation 08 00120 g002
Fermentation 08 00120 g003 550
Figure 3. PCA of aroma description: (a) Ciherang nonfermented (CNF), Inpari42 nonfermented (IPR42NF), Inpari30 nonfermented (IPR30NF) and IR64 nonfermented (IR64NF) rice bran; (b) Ciherang fermented (CF), Inpari42 fermented (IPR42F), Inpari30 fermented (IPR30F), IR64 fermented (IR64F) rice bran; (c) FRB and NFRB.
Figure 3. PCA of aroma description: (a) Ciherang nonfermented (CNF), Inpari42 nonfermented (IPR42NF), Inpari30 nonfermented (IPR30NF) and IR64 nonfermented (IR64NF) rice bran; (b) Ciherang fermented (CF), Inpari42 fermented (IPR42F), Inpari30 fermented (IPR30F), IR64 fermented (IR64F) rice bran; (c) FRB and NFRB.
Fermentation 08 00120 g003
Table
Table 2. Pearson’s correlation volatile compounds and aroma description in various fermented and nonfermented rice bran.
Table 2. Pearson’s correlation volatile compounds and aroma description in various fermented and nonfermented rice bran.
VariablesFurfuralBenzaldehydeBenzene Acetaldehyde3-methylbenzaldehyde3-methyl-1-butanolOctanoic AcidPantolactone
Sweet0.8010.7600.6500.7470.000−0.4460.792
Cereal0.4930.575−0.0860.691−0.309−0.471−0.143
Earthy−0.293−0.265−0.358−0.1920.128−0.1250.044
Green−0.350−0.429−0.574−0.229−0.0510.1380.415
Grassy−0.0700.0110.026−0.0270.061−0.395−0.493
Nutty0.2410.2810.3810.120−0.286−0.306−0.267
Musty−0.583−0.462−0.401−0.5390.2610.842−0.216
Smoky0.0490.1930.2670.0240.0000.674−0.703
Fermented−0.569−0.471−0.153−0.6200.6570.703−0.203
Rancid−0.495−0.555−0.318−0.5100.3940.6930.428
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Astuti, R.D.; Fibri, D.L.N.; Handoko, D.D.; David, W.; Budijanto, S.; Shirakawa, H.; Ardiansyah. The Volatile Compounds and Aroma Description in Various Rhizopus oligosporus Solid-State Fermented and Nonfermented Rice Bran. Fermentation 2022, 8, 120. https://doi.org/10.3390/fermentation8030120

AMA Style

Astuti RD, Fibri DLN, Handoko DD, David W, Budijanto S, Shirakawa H, Ardiansyah. The Volatile Compounds and Aroma Description in Various Rhizopus oligosporus Solid-State Fermented and Nonfermented Rice Bran. Fermentation. 2022; 8(3):120. https://doi.org/10.3390/fermentation8030120

Chicago/Turabian Style

Astuti, Retno Dwi, Dwi Larasatie Nur Fibri, Dody Dwi Handoko, Wahyudi David, Slamet Budijanto, Hitoshi Shirakawa, and Ardiansyah. 2022. "The Volatile Compounds and Aroma Description in Various Rhizopus oligosporus Solid-State Fermented and Nonfermented Rice Bran" Fermentation 8, no. 3: 120. https://doi.org/10.3390/fermentation8030120

APA Style

Astuti, R. D., Fibri, D. L. N., Handoko, D. D., David, W., Budijanto, S., Shirakawa, H., & Ardiansyah. (2022). The Volatile Compounds and Aroma Description in Various Rhizopus oligosporus Solid-State Fermented and Nonfermented Rice Bran. Fermentation, 8(3), 120. https://doi.org/10.3390/fermentation8030120

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