Abstract
As an essential flavor condiment in Sichuan cuisine, Pixian Douban (PXDB) is usually produced by open fermentation process in strip pools or ceramic vats. In this study, an experiment of PXDB fermentation was conducted for 90 days in a closed system of gradient steady‐state temperature field (GSTF). To investigate the characterization of volatile compounds of PXDB in the closed system, the volatiles in three kinds of samples including samples of GSTF (SGT), samples of constant temperature (SCT), and samples of traditional fermentation (STF) were analyzed. The results showed that 75, 67, and 68 volatile compounds were detected in SGT, SCT, and STF, respectively. Compared with the traditional fermentation, the process in the closed system of GSTF was conducive to produce more kinds of esters and alcohols. A total of 22 major aroma active compounds were identified in three samples by combination analyses of gas chromatography‐olfactometry (GC‐O) and odor activity value (OAV). The appearance, smell, texture, and taste of the three different samples had shown different changes, but the sensory characteristics of the SGT were more similar to those of the STF by quantitative descriptive analysis (QDA) and principal component analysis (PCA). This study indicated that the closed system of GSTF could be applied in PXDB fermentation to obtain higher quality products, which brought a bright prospect of replacing the traditional fermentation process to realize the controllable industrialized production of PXDB.
Keywords: aroma active compounds, gas chromatography‐olfactometry, gradient steady‐state temperature field, odor activity value, Pixian Douban
The results showed that flavor characteristics of SGT were similar to those of the STF. This study indicated that the closed system of GSTF could be applied in PXDB fermentation to obtain higher quality products, which brought a bright prospect of replacing the traditional fermentation process to realize the controllable industrialized production of PXDB.
1. INTRODUCTION
As a traditional fermented food produced from a small town named Pixian County in Sichuan Province of China, Pixian Douban (PXDB) is an essential condiment in preparing Sichuan cuisine, which is honored as the spirit of Sichuan Cuisine and famous for its fascinating flavor globally. The production process of PXDB employed in most factories is traditional process, which has a history of hundreds of years. However, this process has many drawbacks, such as lower mechanization and automatization, lower productivity, higher labor and production cost, less quality and higher risks of food safety, which have seriously hindered the development of the industry (Ding et al., 2020). Therefore, with the development of fermentation technologies, it has become an urgent requirement to upgrade this industry by using advanced technologies and equipment.
In recent two years, the production of PXDB in tank fermenter has been proposed and carried out in some factories. However, compared with traditional fermentation, this new process which just changed the equipment from strip pool or ceramic vat to tank fermenter without any other improvement is still dependent on the weather heavily (Figure 1). Moreover, the new process was not verified by the strict tests before it was amplified, which caused that the defects of the traditional process has not been overcome although the occupancy area of the factory had been greatly reduced by the new process (Ding et al., 2020). Therefore, as a new process with the most potential to replace the traditional fermentation, the PXDB process of tank fermenter should be further studied deeply to overcome the defects of traditional process and obtain high‐quality products before it was used in the factory.
FIGURE 1.
Process diagram of PXDB production
Besides, aroma is a key indicator in evaluating the product quality of PXDB as the same other fermented foods such as soy sauces and vinegars (Al‐Dalali et al., 2019; Feng et al., 2014). Therefore, the new process should be developed based on the study of traditional fermentation process to obtain high‐quality product with good aroma. In the literatures, many studies about the volatile compositions of PXDB have been conducted, and many valuable results were obtained (Li et al., 2016, 2018, 2019; Lin et al., 2019). In Lu's study, 22 key volatile compounds were identified in PXDB fermented with traditional process (Lu et al., 2019). The microbial communities, flavors, and their relationships in PXDB were studied in Liu's study, which revealed that the flavor compounds would accumulate significantly with the prolonging of the fermentation period, especially for umami‐taste amino acids, organic acids, and volatile compounds (Liu et al., 2020). In Lin's study, 21 aroma active compounds were detected with flavor dilution factor ranging from 2 to 16 in PXDB (Lin et al., 2019). Those researches were benefit of revealing the aroma of the traditional fermentation products and provided the foundation for the studies of new process.
In this study, a closed system of PXDB fermentation under gradient steady‐state temperature field (GSTF) was constructed based on the results of our previous research (Ding et al., 2020). Then, three experiments of PXDB fermentation were conducted in the closed system of GSTF, closed system of constant temperature, and traditional fermentation system, respectively. The volatiles of the product fermented in the new system were characterized by comparing with those of the products from the closed system of constant temperature and the traditional fermentation system in order to clarify the volatile compounds of the three products and improve the new process to produce high‐quality products.
2. MATERIALS AND METHODS
2.1. Procedures of three different fermentation processes
The schematic apparatus of fermentation processes of PXDB is shown in Figure 2. As shown in Figure 2, the apparatus of the new closed system was mainly constructed from two tank fermenters of 50 L, an air supply system, and a thermostat. The fermentation of PXDB in closed system was conducted with the fermenters of a filling coefficient of 0.8 at constant temperature of 30°C and at GSTF, respectively. It should be noted that the GSTF in the fermenter was designed and achieved by keeping the temperature of jacket at 27°C and the propeller temperature between 45°C and 52°C. The traditional fermentation was carried out in an open ceramic vat of 30 L following the traditional operation. The meju and red peppers purchased from Sichuan PXDB Co., LTD. were first mixed at a ratio of 1:3 before starting the fermentation and then transfer into the fermenters and the ceramic vats. The PXDB in the tank fermenters was stirred once every 6 hr at a rate of 35 rpm for 3 min and ventilated every 4 hr at a rate of 5 L/min for 5 min. The experiment was carried out for 90 days from August to October.
FIGURE 2.
Schematic apparatus of three fermentation systems for PXDB. (1) pump; (2) solenoid valve; (3) air dryer; (4) air filter; (5) gas rotameter; (6) constant temperature fermenter; (7) temperature control unit; (8) GSTF fermenter; (9) temperature detected unit; (10) ceramic vat; (11) timing socket; (12) intelligent temperature controller
2.2. Extraction of volatile compounds
The HS‐SPME sampling was carried out according to previously described method with some modifications (Lu et al., 2019). Sample was mashed into homogenized paste, and 5.0‐g mashed sample was put into a 15‐ml solid‐phase micro‐extraction (SPME) vial, where 10 μl of 1,2‐dichlorobenzene (10 μg/ml in methanol) was used as the internal standard. Then, the vial was sealed and equilibrated at 55°C for 30 min. Afterwards, a carboxen‐polydimethylsiloxane fused silica (CAR/PDMS, 75 μm)‐coating fiber (Anpel Inc.) was exposed to the headspace of the sample to absorb the volatiles at 55°C for 40 min and the coating fiber was quickly inserted into a GC injection port and desorbed at 250°C for 5 min.
2.3. Gas chromatography‐mass spectrometer analysis
GC‐MS analysis was performed on a Shimadzu gas chromatograph (Shimadzu). Separation of volatile components was performed on a DB‐5MS column (Agilent). Helium was used as a carrier gas at a constant flow rate of 1 ml/min. Oven temperature was maintained at 40°C for 1 min, programmed at 5°C/min to 100°C and held for 1 min, programmed at 7°C/min to 150°C and held for 4 min, thereafter programmed at 5°C/min to 185°C and held for 5 min, finally programmed at 10°C/min to 200°C. The mass spectrometer was operated in electron impact mode with the electron energy set at 70 eV and a scan range of 35–500 m/z. The temperature of MS source was set at 200°C. A mixture of n‐alkanes (C6–C20) was injected directly into GC‐MS under the same condition as that for the samples to calculate the retention indices (RIs). Each volatile compound was identified using the National Institute of Standards and Technology (NIST17) library. The content of each compound is obtained by comparing it with the internal standard.
2.4. Gas chromatography‐olfactometry analysis
The samples were analyzed by using a gas chromatograph equipped with an olfactory detector (Shimadzu). The sample was injected in the splitless mode at 200°C for 5 min. The oven temperature was adjusted to the same condition as that of GC‐MS. Retention times and descriptions of aromas were recorded by three trained assessors (replaced at 10 min intervals) after the sample injection. Each trained assessor sniffed each sample in three replicates.
2.5. Qualification and quantification of volatile compounds
The qualification of the volatile compounds was done of the following methods. The compounds were tentatively identified by comparing their mass spectra with those which were found in the National Institute of Standards and Technology library (NIST17), and by comparing their RIs with those reported in the previous literature. Quantitative analysis of volatile compounds was conducted under the same condition as that of GC‐MS. The chemical quantities were calculated based on the relative peak area to the area of 1,2‐dichlorobenzene, which was used as the internal standard.
2.6. Calculation of odor activity values
Although GC‐O analysis is an effective method for odorant identification, it could not indicate a final importance of the odorant to the overall aroma (Gao et al., 2014). Therefore, the ultimate contribution of a particular compound to the overall aroma of PXDB mainly determined its odor threshold and the odor activity value (OAV) (Giri et al., 2010). If the OAV of the compound calculated as the ratio of its concentration to odor threshold was larger than or equal to 1, it could be considered to contribute to the overall aroma (Zhao et al., 2020).
2.7. Sensory evaluation
2.7.1. Establishment of flavor descriptors
The sensory characteristics of the three kinds of samples were evaluated by the quantitative descriptive analysis (QDA). According to the methods previously described (Chen et al., 2013; Gao et al., 2018; Zhao et al., 2020), the sensory characteristics of samples were characterized by the sensory team, which was composed of 10 students (five males and five females, aged 23–26) with rich sensory evaluation experience from Xihua University. Firstly, the evaluators discussed the aroma characteristics and put forward the descriptors of PXDB. Then, a flavor description table was obtained according to the descriptors proposed by the evaluators and in the literature. Finally, the evaluator tasted three kinds of samples and retained the flavor descriptors with a pass rate of more than 50% to establish the final sensory description vocabulary.
2.7.2. Evaluation method
10 g PXDB was taken into a 30‐ml plastic cup and coded randomly. The intensity range of aromas were 0–9 scale (0 represented none, 9 represented very strong). The sensory evaluation of each sample was tested three times and the results were averaged.
2.8. Statistical analysis
All data were presented as means ± SD for at least three replicates. The graph presentations were generated using Origin version 8.5 (OriginLab Inc.). Principal component analysis (PCA) was performed using the Simca version 14.1 (Simca Inc.).
3. RESULTS AND DISCUSSION
3.1. Identification and quantification of volatile compounds by GC‐MS
The volatile compounds in the samples of gradient temperature of steady‐state (SGT), samples of constant temperature (SCT), and samples of traditional fermentation (STF) were identified by GC‐MS. As a result, a total of 103 volatiles were identified in the three samples (Table 1), which could be categorized into 10 different groups, including alcohols, aldehydes, acids, esters, hydrocarbons, ketones, phenols, heterocyclics, and others. As shown in Figure 3, alcohols, acids, esters, and phenols were the largest four groups in SGT accounting for approximately 6.1%, 2.9%, 4.4%, and 4.0% of the total volatiles, respectively. For SCT, alcohols, esters, and phenols were the three largest groups accounting for approximately 10.0%, 8.6%, and 7.1% of the total volatiles, respectively. For STF, alcohols, aldehydes, acids, esters, and phenols were the dominant classes, and accounted for 12.8%, 11.3%, 8.2%, and 8.4% of the total volatiles, respectively.
TABLE 1.
Identification and quantification of volatile compounds in three samples
| No. | Compounds | CAS | Concentration (µg/kg)a | Previously reported | ||
|---|---|---|---|---|---|---|
| SGT | STF | SCT | ||||
| Alcohols | ||||||
| 1 | Phenethyl alcohol | 60–12–8 | 1,162.2 ± 1.04 | 1564.3 ± 0.12 | 2,808.3 ± 1.44 | 1,2,5–7 |
| 2 | Furfuryl alcohol | 98–00–0 | 977.7 ± 0.06 | 1821.8 ± 0.11 | 1,294.0 ± 0.80 | 1,7 |
| 3 | Linalool | 78–70–6 | 125.7 ± 0.03 | 375.7 ± 0.04 | 191.5 ± 0.1 | 1,6 |
| 4 | Benzyl alcohol | 100–51–6 | 146.2 ± 0.08 | 214.8 ± 0.03 | 165.8 ± 0.09 | 1,6,7 |
| 5 | 1‐Hexanol | 111–27–3 | 149.8 ± 0.04 | 720.0 ± 0.05 | 186.6 ± 0.11 | 4,7 |
| 6 | 2,3‐Butanediol | 513–85–9 | 53.1 ± 0.06 | 635.2 ± 0.08 | 7.8 ± 0.06 | 3 |
| 7 | (‐)‐Alpha‐terpineol | 10482–56–1 | nd | 223.2 ± 0.004 | nd | 1 |
| 8 | 3‐Methylthiopropanol | 505–10–2 | 186.7 ± 0.07 | 458.5 ± 0.16 | 287.2 ± 0.13 | 3 |
| 9 | 2‐Heptanol | 543–49–7 | 27.0 ± 0.07 | 81.3 ± 0.013 | 28.8 ± 0.06 | b |
| 10 | 1‐Octen−3‐ol | 3391–86–4 | nd | 165.4 ± 0.05 | nd | b |
| 11 | 1‐Heptanol | 111–70–6 | nd | 80.9 ± 0.07 | nd | b |
| 12 | Trans−2‐octen−1‐ol | 18409–17–1 | nd | 32.9 ± 0.06 | nd | b |
| 13 | 2‐Phenyl−2‐propanol | 617–94–7 | 139.4 ± 0.05 | nd | nd | b |
| 14 | 3‐Methyl−1‐pentanol | 589–35–5 | 24.6 ± 0.04 | nd | nd | b |
| 15 | 2‐(4‐Methylphenyl) propan−2‐ol | 1197–01–9 | 14.9 ± 0.03 | nd | nd | b |
| 16 | (5‐Methyl−2‐furyl) methanol | 3857–25–8 | 13.2 ± 0.06 | nd | nd | b |
| 17 | Beta‐ethylphenethyl alcohol 98 | 2035–94–1 | 12.0 ± 0.05 | nd | nd | b |
| 18 | (‐)‐Verbenone | 1196–01–6 | 10.7 ± 0.04 | nd | nd | b |
| 19 | Diisobutylcarbinol | 108–82–7 | nd | nd | 18.1 ± 0.06 | b |
| Aldehydes | ||||||
| 20 | Phenylacetaldehyde | 122–78–1 | 459.0 ± 0.03 | 1815.4 ± 0.06 | 482.8 ± 0.05 | 1–3,5–7 |
| 21 | Benzaldehyde | 100–52–7 | 83.7 ± 0.04 | 1979.5 ± 0.9 | 94.1 ± 0.06 | 1,3,6,7 |
| 22 | Furfural | 98–01–1 | 34.6 ± 0.08 | 411.6 ± 0.03 | 34.4 ± 0.03 | 1,3,6 |
| 23 | 3‐(Methylthio)propionaldehyde | 3268–49–3 | 90.7 ± 0.09 | 369.4 ± 0.05 | 77.5 ± 0.07 | 8 |
| 24 | 1‐Nonanal | 124–19–6 | 36.6 ± 0.06 | 252.6 ± 0.03 | 68.1 ± 0.08 | 3,5,6 |
| 25 | 3‐Methyl−2‐butenal | 107–86–8 | nd | 185.0 ± 0.07 | 23 ± 0.04 | b |
| 26 | Octanal | 124–13–0 | nd | 44.7 ± 0.05 | nd | b |
| 27 | Decanal | 112–31–2 | nd | 39.6 ± 0.06 | nd | 5 |
| 28 | Trans−2‐heptenal | 18829–55–5 | nd | 149.9 ± 0.07 | nd | b |
| 29 | Heptaldehyde | 111–71–7 | nd | 137.9 ± 0.11 | nd | b |
| 30 | 2‐Phenyl−2‐butenal | 4411–89–6 | nd | 127.5 ± 0.05 | nd | 10 |
| 31 | (e)−2‐Octenal | 2548–87–0 | nd | 64.9 ± 0.04 | nd | b |
| 32 | Cocal | 21834–92–4 | nd | 36.6 ± 0.06 | nd | b |
| 33 | Trans−2‐methyl−2‐butenal | 497–03–0 | 17.9 ± 0.004 | nd | nd | b |
| Acids | ||||||
| 34 | Isovaleric acid | 503–74–2 | 567.0 ± 0.04 | 1,002.9 ± 0.04 | nd | 1 |
| 35 | Butyric acid | 107–92–6 | 311.3 ± 0.03 | 954.6 ± 0.05 | nd | 2,7 |
| 36 | Hexanoic acid | 142–62–1 | 192.1 ± 0.02 | 681.8 ± 0.06 | 133 ± 0.03 | 2,7 |
| 37 | 4‐Methylvaleric acid | 646–07–1 | 27.8 ± 0.04 | nd | nd | 2,7 |
| 38 | Octanoic acid | 124–07–2 | 15.4 ± 0.06 | nd | nd | 2 |
| 39 | 2‐Methyl butyric acid | 116–53–0 | 214.8 ± 0.07 | 517 ± 0.03 | 201.7 ± 0.04 | 11 |
| 40 | Isobutyric acid | 79–31–2 | 125.7 ± 0.12 | 371.5 ± 0.08 | 61.9 ± 0.06 | 1 |
| Esters | ||||||
| 41 | Ethyl hexanoate | 123–66–0 | 165.8 ± 0.04 | 210.0 ± 0.06 | 373.1 ± 0.06 | 2,4,5,7 |
| 42 | Ethyl butyrate | 105–54–4 | 168.8 ± 0.06 | 672.0 ± 0.04 | 325.5 ± 0.05 | 2,7 |
| 43 | Ethyl laurate | 106–33–2 | 265.4 ± 0.08 | 161.0 ± 0.06 | 662.3 ± 0.07 | 5 |
| 44 | Methyl palmitate | 112–39–0 | 170.9 ± 0.05 | 383 ± 0.05 | 178.2 ± 0.02 | 2,5 |
| 45 | Ethyl myristate | 124–06–1 | 182.5 ± 0.04 | 142.3 ± 0.11 | 415.9 ± 0.08 | 2,5–7 |
| 46 | Methyl salicylate | 119–36–8 | 102.8 ± 0.05 | 305.0 ± 0.08 | 172.7 ± 0.03 | 6 |
| 47 | Ethyl isovalerate | 108–64–5 | 143.8 ± 0.04 | 294.9 ± 0,003 | 205.7 ± 0.05 | 7 |
| 48 | Ethyl phenylacetate | 101–97–3 | 117.0 ± 0.08 | 264.9 ± 0.1 | 319.0 ± 0.13 | 1,3–7 |
| 49 | Methyl laurate | 111–82–0 | 117.7 ± 0.07 | 209.1 ± 0.06 | 158.7 ± 0.05 | 5 |
| 50 | Ethyl 2‐methylbutyrate | 7452–79–1 | 75.6 ± 0.07 | 135.2 ± 0.09 | 155.3 ± 0.05 | 2,7 |
| 51 | Isoamyl acetate | 123–92–2 | 56.6 ± 0.08 | 144.2 ± 0.03 | 61.8 ± 0.04 | 7 |
| 52 | Ethyl trans−4‐decenoate | 76649–16–6 | 42.8 ± 0.05 | 58.0 ± 0.03 | 153.9 ± 0.04 | 5 |
| 53 | Ethyl linoleate | 544–35–4 | nd | 168.5 ± 0.05 | nd | 2,3,5,6 |
| 54 | Ethyl valerate | 539–82–2 | nd | nd | 58.8 ± 0.05 | 2,7 |
| 55 | Ethyl nonanoate | 123–29–5 | 17.3 ± 0.05 | nd | 42.6 ± 0.06 | 7 |
| 56 | Ethyl heptanoate | 106–30–9 | 13.0 ± 0.03 | nd | 38.4 ± 0.08 | 7 |
| 57 | N‐pentadecanoic acid ethyl ester | 41114–00–5 | 12.1 ± 0.02 | nd | 33.7 ± 0.04 | 7 |
| 58 | Ethyl caprylate | 106–32–1 | nd | nd | 221.7 ± 0.02 | 2,5,7 |
| 59 | Diethyl succinate | 123–25–1 | nd | nd | 23.0 ± 0.03 | 2,7 |
| 60 | Methyl nonanoate | 1731–84–6 | nd | nd | 9.8 ± 0.02 | b |
| 61 | Ethyl methacrylate | 7493–69–8 | 81.2 ± 0.05 | nd | nd | b |
| 62 | Methyl phenylacetate | 101–41–7 | 17.9 ± 0.02 | nd | nd | b |
| 63 | Gamma‐butyrolactone(gbl) | 96–48–0 | 7.5 ± 0.04 | nd | nd | b |
| 64 | Allyl 2‐ethylbutyrate | 7493–69–8 | 8.0 ± 0.05 | 100.9 ± 0.02 | nd | b |
| 65 | Ethyl L (‐)‐lactate | 687–47–8 | 45.0 ± 0.05 | 201.2 ± 0.05 | 74.7 ± 0.04 | b |
| 66 | Methyl myristate | 124–10–7 | 93.2 ± 0.12 | 165.1 ± 0.08 | 99.5 ± 0.06 | b |
| 67 | Caprylic acid methyl ester | 111–11–5 | 50.2 ± 0.07 | 120.3 ± 0.05 | 37.5 ± 0.04 | b |
| 68 | Methyl hexanoate | 106–70–7 | 28.4 ± 0.05 | 111.2 ± 0.05 | 30.9 ± 0.03 | b |
| 69 | Ethyl isobutyrate | 97–62–1 | 31.4 ± 0.05 | 45.6 ± 0.04 | 59.8 ± 0.05 | b |
| 70 | Dihydro−5‐methyl−5‐vinylfuran−2(3h)‐one | 1073–11–6 | 25.4 ± 0.04 | 60.2 ± 0.05 | 24.2 ± 0.02 | b |
| 71 | Ethyl crotonate | 623–70–1 | 16.3 ± 0.03 | 68.4 ± 0.05 | 38.4 ± 0.02 | b |
| 72 | Methyl decanoate | 110–42–9 | 13.5 ± 0.04 | 47.9 ± 0.05 | 30.7 ± 0.05 | b |
| 73 | 2‐Methylbutyl acetate | 624–41–9 | 17.7 ± 0.13 | 43.3 ± 0.11 | 24.8 ± 0.04 | b |
| 74 | Ethyl caprate | 110–38–3 | 46.3 ± 0.12 | nd | 66.5 ± 0.02 | 5,11,12 |
| 75 | Phenethyl acetate | 103–45–7 | 20.8 ± 0.05 | nd | 36.9 ± 0.12 | b |
| 76 | Gamma‐nonanolactone | 104–61–0 | 19.0 ± 0.09 | nd | 17.5 ± 0.005 | 11 |
| 77 | Ethyl undecanoate | 627–90–7 | 13.8 ± 0.03 | nd | 124.1 ± 0.04 | b |
| 78 | Palmitoleic acid methyl ester | 1120–25–8 | 15.7 ± 0.11 | nd | 25.8 ± 0.01 | b |
| Hydrocarbons | ||||||
| 79 | Tetradecane | 629–59–4 | 66.7 ± 0.06 | nd | 47.3 ± 0.05 | 2 |
| 80 | N‐hexadecane | 544–76–3 | 61.9 ± 0.04 | 39.9 ± 0.03 | 56.3 ± 0.04 | b |
| 81 | Octadecane | 593–45–3 | nd | 127.0 ± 0.05 | nd | b |
| 82 | 1‐Chloropentane | 543–59–9 | nd | 19.1 ± 0.04 | nd | b |
| 83 | N‐hexacosane | 630–01–3 | nd | 15.1 ± 0.06 | nd | b |
| 84 | 1‐Chlorooctadecane | 3386–33–2 | nd | 88.3 ± 0.08 | 42.2 ± 0.06 | b |
| 85 | 1‐Chloro−3‐methylbutane | 107–84–6 | nd | nd | 37.8 ± 0.06 | b |
| 86 | 1‐Iodododecane | 4292–19–7 | nd | nd | 23.3 ± 0.05 | b |
| 87 | N‐heptadecane | 629–78–7 | 15.2 ± 0.13 | nd | nd | b |
| Ketones | ||||||
| 88 | 2‐Heptanone | 110–43–0 | 17.8 ± 0.11 | 74.9 ± 0.12 | 23.7 ± 0.04 | 7 |
| 89 | 2‐Nonanone | 821–55–6 | nd | 26.4 ± 0.05 | 16.4 ± 0.08 | 7 |
| 90 | 2,6,6‐Trimethyl−2‐cyclohexene−1,4‐dione | 1125–21–9 | nd | 53.4 ± 0.11 | nd | b |
| 91 | Isophorone | 78–59–1 | 9.5 ± 0.08 | 25.6 ± 0.07 | nd | b |
| Phenols | ||||||
| 92 | 4‐Ethyl−2‐methoxyphenol | 2785–89–9 | 1,082.9 ± 0.2 | 2,299.6 ± 0.38 | 2020.6 ± 0.3 | 1,2,5–7 |
| 93 | 4‐Ethylphenol | 123–07–9 | 823.7 ± 0.13 | 1759.6 ± 0.15 | 1,402.4 ± 0.11 | 1,2,5–7 |
| 94 | Guaiacol | 90–05–1 | 63.4 ± 0.06 | 121.1 ± 0.05 | 76.4 ± 0.04 | 8 |
| 95 | P‐cresol | 106–44–5 | 45.3 ± 0.04 | nd | 55.3 ± 0.05 | 4 |
| Heterocyclics | ||||||
| 96 | 2‐Acetyl pyrrole | 1072–83–9 | 350.4 ± 0.02 | 837.7 ± 0.12 | 278.2 ± 0.04 | 7 |
| 97 | 2‐Acetylfuran | 1192–62–7 | 15.2 ± 0.05 | nd | 16.8 ± 0.05 | 5,7 |
| 98 | 2,6‐Dimethylpyrazine | 108–50–9 | 15.2 ± 0.04 | nd | 6.7 ± 0.03 | 1–3,5,7 |
| 99 | 2‐Propionylfuran | 3194–15–8 | 13.4 ± 0.05 | nd | nd | b |
| Others | ||||||
| 100 | Toluene | 108–88–3 | 38.9 ± 0.04 | 29.3 ± 0.05 | 8.5 ± 0.02 | 2 |
| 101 | M‐xylene | 108–38–3 | nd | 79.8 ± 0.005 | nd | 2 |
| 102 | Borneol | 507–70–0 | nd | nd | 28.1 ± 0.07 | b |
| 103 | Tetramethylthiourea | 2782–91–4 | 22.2 ± 0.06 | nd | nd | b |
Values expressed as average (n = 3) ± standard deviation.
Abbreviation: GSTF, gradient steady‐state temperature field; nd, not detected; SCT, samples of constant temperature; STF, samples of traditional fermentation; SGT, samples including samples of GSTF.
Relative peak area to that of internal standard (10 μl of 10 μg/ml 1,2‐dichlorobenzene in methanol) using DB‐5MS column.
Compounds by identified in fermented soybean products.
Zhang et al. (2020).
Jo, et al. (2011).
Zhao et al. (2011).
Inoue et al. (2016).
Li et al. (2018).
Li et al. (2016).
Lee and Ahn (2009).
Lu et al. (2019).
Giri et al. (2010).
Al‐Dalali et al. (2019).
Lu et al. (2020).
FIGURE 3.
Total concentrations of volatile compounds in three samples
As shown in Figure 4, there were 75, 67, and 68 kinds of volatile compounds in SGT, SCT, and STF, respectively. Compared with traditional fermentation, the number of esters in SGT and SCT was larger while the number of aldehydes was smaller, which implied that SGT and SCT both had an advantage of producing esters rather than aldehydes. Besides, more kinds of esters and acids were included in the SGT but there were more kinds of aldehydes in the STF. The reasons for this phenomenon might be that the traditional fermentation process could provide more various fermentation conditions, which were conducive to the oxidation of alcohols to aldehydes, while the closed system of tank fermenter with stable temperature could provide more energy for some biochemical reactions among small molecules, which would promote more alcohols to participate in the esterification reaction of producing more esters. Notably, alcohols were easily formed in the SGT and STF probably because the complexion of temperature in the GSTF was more similar with that in the traditional fermentation. Meanwhile, alcohols have played important roles in the flavor characteristics of PXDB (Li et al., ,2016, 2018; Lu et al., 2020).
FIGURE 4.
Number of volatile compounds in three samples
Esters are highly important indicators for the quality grade of fermentation products (Moy et al., 2012), which might mainly be formed by alcohol fermentation or esterification between acids and alcohols during the aging technology (Charles et al., 2000; Li et al., 2018). In this work, ester was also the largest group of all the volatiles as reported in other studies of fermented foods, in which 38 volatile esters were identified in a concentration ranging from 7.5 to 672 µg/kg (Table 1). Totally, 33, 33, and 23 volatile esters were contained in SGT, SCT, and STF, respectively, indicating that the fermentation processes of closed system were beneficial to the formation of ester species. Nineteen of the 38 identified volatile esters in this study were also found previously in other fermented soybean products as marked in Table 1. Among the identified 38 volatile esters, 21 esters were shared in those three samples and the other 17 esters were identified in one or two samples suggesting that these compounds were unique for PXDB. For example, ethyl valerate, ethyl linoleate, and ethyl methacrylate only existed in SCT, STF, and SGT, respectively, but nonanoate in SCT and SGT and allyl 2‐ethylbutyrate in STF and SGT. Besides, the top four esters in these three samples are different showing that those in SCT were ethy laurate, ethy myristate, ethy hexanoate, and ethy butyrate but ethy butyrate, methyl palmitate, methyl salicylate, ethy isovalerate, and ethy phenylacetate in STF and ethy laurate, ethy myristate, ethy butyrate, and ethy hexanoate in STG. In addition, it has been reported that many lactones have an aroma of pleasant and a low threshold (Zhou et al., 2017). Therefore, gamma‐nonanolactone which was detected in SGT (19.0 µg/kg) and SCT (17.5 µg/kg) could make a positive contribution to the overall aroma of the samples although its concentration was not high.
A total of 19 volatile alcohols that might mainly come from alcohol fermentation were identified becoming the second largest group of the volatile compounds, in which seven of them had been reported in the literatures. Besides, eight alcohols were shared in those three samples, in which concentrations were the lowest in SGT but highest in STF. The three samples showed different quantities and concentrations of volatile alcohols. In total, 14, 8 and 12 volatile alcohols were found in SGT, SCT, and STF with their concentrations ranging from 10.7 to 1,162.2 µg/kg, 7.8 to 2,808.3 µg/kg, and 32.9 to 1,821.8 µg/kg, respectively. Among the alcohols, phenethyl alcohol showed the highest concentration in SGT and SCT, but furfuryl alcohol in STF. Particularly, fusel alcohols, such as 2‐phenyl‐1‐propanol, 3‐methyl‐1‐pentanol, and (5‐methyl‐2‐furyl) methanol, were identified in appreciable abundance in SGT in this study, which were not appeared in other two samples. The changes of alcohol compounds might be attributed to the complicated metabolism of some microorganisms. For instance, Lactobacillus plantarum was potential to hydrolyze proteins and generate phenylethyl alcohol (Wang et al., 2017).
Fourteen volatile aldehydes were obtained in the three samples becoming the third largest group of the identified volatiles, which might be resulted from alcohol oxidation (Chinnici et al., 2009). Among the identified aldehydes, 13 were found in STF much larger than 6 in SGT and SCT. Five of the 14 volatile aldehydes identified in this work were reported in the literatures including phenylacetaldehyde, benzaldehyde, furfural, 1‐nonanal, and decanal. Besides, as shown in Table 1, the volatiles of benzaldehyde, phenylacetaldehyde, and 3‐(methylthio) propionaldehyde were the most three abundant aldehydes in SGT and SCT, while benzaldehyde, phenylacetaldehyde, and furfural were the most three abundant aldehydes in STF. The phenylacetaldehyde was generally considered to be produced by a series of biochemical reactions such as the oxidation of phenethyl alcohol (Wang et al., 2017), of which concentration was determined at 459, 482.8, and 1,815.4 µg/kg in SGT, SCT, and STF, respectively. From above analysis, it could be knew that the quantities and concentrations of volatile aldehydes in STF were both higher than those in the other two samples.
Seven, three, and five acid volatiles were identified in SGT, SCT, and STF, respectively, ranked as the fourth largest group, in which five of them had been reported previously. The concentrations of the acids in SGT, SCT, and STF were in a range from 15.4 to 567 µg/kg, 61.9 to 132.6 µg/kg, and 371.5 to 1,002.9 µg/kg, respectively. The volatile acid of the highest concentration was isovaleric acid both in SGT and STF but 2‐methyl butyric acid in SCT. It was worth mentioning that isovaleric acid and butyric acid both appeared in SGT and STF while 4‐methylvaleric acid and octanoic acid were only found in SGT, and the other acids were all detected in the three samples. This phenomenon indicated that, in terms of species, SGT is more similar to STF than SCT.
Four phenols were detected in all the samples, of which the phenol compounds of the highest and lowest concentration were 4‐ethyl‐2‐methoxyphenol and p‐cresol, respectively. Three phenols were detected in STF, which concentrations were ranged from 121.1 µg/kg to 2,299.6 µg/kg. P‐cresol was only found both in SGT and SCT, but the other three phenols were identified in all the three samples. According to the reports, the phenolic compounds might mainly come from the lignin degradation (Lu et al., 2019; NATERA et al., 2003). Besides, guaiacol and 4‐ethylphenol also existed naturally in the PXDB (Lu et al., 2019). 4, 3, and 1 heterocyclic compounds were identified in SGT, SCT, and STF, respectively, of which the concentration of 2‐acetyl pyrrole was the highest in the three samples. Furthermore, the concentration of 2,6‐dimethylpyrazine in SGT was twice as that in SCT. 2‐acetylfuran and 2,6‐dimethylpyrazine were found both in SGT and SCT, while 2‐propionylfuran only appeared in SGT.
For hydrocarbons, five compounds were obtained in SCT and STF but three in SGT. n‐hexadecane was found in all the three samples, while the other hydrocarbons were detected only in one or two samples. Table 1 showed that the concentrations of five hydrocarbons were ranged from 15.2 to 66.7 µg/kg, 23.3 to 56.3 µg/kg, and 15.1 to 127 µg/kg in SGT, SCT, and STF, respectively. For ketones, two compounds were obtained in SGT and SCT but four in STF, of which the concentration of 2‐heptanone was the highest in the three samples.
Therefore, compared with the traditional fermentation, more kinds of esters and alcohols were easily formed in the SGT, which might account for the aroma differences between these two samples. To characterize the aroma of the SGT, it was necessary to screen the aroma active compounds of the three kinds of samples by GC‐O.
3.2. Characterization of the aroma active compounds by GC‐O
In order to further characterize the important volatile components in the three kinds of samples, the aroma extracts obtained by HS‐SPME were subjected to GC‐O analysis. As shown in Figures 5 and 6, alcohols, esters, and aldehydes were the three largest major volatile compounds in the three samples, which were consistent with the results of the previous study (Wu et al., 2018). As shown in Table 2, a total of 27 active compounds detected by HS‐SPME/GC‐O could be grouped into sweet, burnt, sour, honey, bread, fruity, floral, green leaves, almonds, pickles, baked potatoes, sweat, mint, and nuts, which were associated with different chemical groups such as alcohols, aldehydes, acids, esters, phenols, pyrroles, and pyrazines. Among the active aromas, the compound of the highest concentration was phenethyl alcohol (honey‐like) in the SGT and SCT but 4‐Ethyl‐2‐methoxyphenol (burnt, spicy) in the STF. Besides, there were 20 aroma active volatiles that were shared in the three samples, while the other volatiles were found only in one or two samples. For example, the aroma‐active compounds including alpha‐terpineol (oil, anise, and mint), 1‐octen‐3‐ol (earthy), decanal (floral, sweet), and ethyl linoleate (grease) were considered to be the unique aroma compounds of the STF.
FIGURE 5.
Concentrations of each class of aroma‐active compounds in three samples
FIGURE 6.
Number of aroma active compounds in three samples
TABLE 2.
Odor description of aroma‐active compounds in three samples
| No. | Compounds | RIs a | Odor description b | Previously reported |
|---|---|---|---|---|
| 1 | Phenethyl alcohol | 1,163 | Honey‐like | 2 |
| 2 | Furfuryl alcohol | 853 | Burnt | 2 |
| 3 | Benzyl alcohol | 1,124 | Sweet, flower | 1 |
| 4 | Linalool | 951 | Flower, lavender | 2 |
| 5 | 1‐Hexanol | 836 | Floral | 2 |
| 6 | 2,3‐Butanediol | 743 | Burning | 2 |
| 7 | Alpha‐terpineol | 1,220 | Oil, anise, mint | 1 |
| 8 | 1‐Octen‐3‐ol | 1,093 | Earthy | 9 |
| 9 | Phenylacetaldehyde | 1,129 | Honey‐like | 9 |
| 10 | Benzaldehyde | 976 | Almond, burnt sugar | 3 |
| 11 | Furfural | 846 | Bread, almond, sweet | 4 |
| 12 | 3(Methylthio)propionaldehyde | 943 | Sauce, cooked potato | 4 |
| 13 | 1‐Nonanal | 1,158 | Floral | 4 |
| 14 | Decanal | 1,235 | Floral, sweet | 4 |
| 15 | Isovaleric acid | 880 | Sweat | 5 |
| 16 | Butyric Acid | 823 | Rancid, cheese, sweat | 2 |
| 17 | Ethyl Hexanoate | 1,059 | Apple peel, fruit | 5 |
| 18 | Ethyl laurate | 2,134 | Leaf | 2 |
| 19 | Methyl salicylate | 1,211 | Peppermint | 2 |
| 20 | Ethyl phenylacetate | 1,444 | Rosy, honey | 7 |
| 21 | Ethyl linoleate | 2,193 | Grease | 7 |
| 22 | Ethyl nonanoate | 1,519 | Coconut | 4 |
| 23 | Methyl decanoate | 1,504 | Grape | 5 |
| 24 | 4‐Ethylphenol | 1,192 | Spicy | 6 |
| 25 | 4‐Ethyl‐2‐methoxyphenol | 1,442 | Burnt, spicy | 5 |
| 26 | 2‐Acetyl pyrrole | 1,145 | Bread, walnut, licorice | 8 |
| 27 | 2,6‐Dimethylpyrazine | 988 | Nutty, coffee, green | 8 |
Abbreviation: nd, not detected.
RIs: Calculated in HP‐5 column in GC‐O.
Odor description at the olfactory detection port.
Intensity of odorants: 1 (very weak), 2 (weak), 3 (medium), 4 (strong).
Adedeji et al. (1991).
Beaulieu and Stein‐Chisholm (2016).
Triqui and Reineccius (1995).
Lee and Noble (2003).
Schnermann and Schieberle (1997).
Feng et al. (2014).
Feng et al. (2015).
Perez‐Boada et al. (2005).
Morales‐Valle et al. (2011).
Fanaro et al. (2012).
Zhao et al. (2011).
Al‐Dalali et al. (2019).
Lin et al. (2019).
Inoue et al. (2016).
As reported in the literatures, the production of fruit aroma is related to ester compounds (Al‐Dalali et al., 2019). Isovaleric acid was found in different foods with a sweaty, strong pungent, and cheesy taste (Zhou et al., 2017). Moreover, the studies had shown that the spiciness was caused by some phenolic compounds such as 4‐ethylphenol and 4‐ethyl‐2‐methoxyphenol in PXDB (Zhang et al., 2020).
3.3. OAV analysis of aroma active compounds
As shown in Table 3, the concentrations of 22 volatile compounds exceeded their odor threshold, namely, their OAVs ≥ 1. Among them, the 14 aroma compounds with OAVs > 1 in the three samples were phenyl alcohol, linalool, 1‐hexanol, phenylacetaldehyde, 3‐(methylthio) propionaldehyde, 1‐nonanal, ethyl hexanoate, ethyl laurate, methyl salicylate, ethyl phenylacetate, methyl decanoate, 4‐ethylphenol, and 4‐ethyl‐2‐methoxyphenyl. As reported in the literatures, phenylacetaldehyde known as main volatiles were found to come from free amino acids formed during fermentation (Lin et al., 2019). 3‐methylthiopropanal was a sulfur‐containing compound with a cooked potato, which was also found in other fermented products, such as Korean soy sauce, high‐salt soy sauce, and yeast extraction (Zhao et al., 2011). 4‐ethyl‐2‐methoxyphenol with burnt and spicy aroma was considered as a dominant odor impression of PXDB, which had been reported to be related to the metabolic activity of yeast (Lin et al., 2019). Moreover, esters also played an important role in the aroma profile of PXDB due to their low odor threshold and desirable fruity and sweet odor. The other volatiles with OAVs > 1 are only detected in one or two kinds of samples. For example, five aroma compounds which presented OAVs > 1 only were found in the STF, including 2,3‐butanediol, alpha terpineol, 1‐octen‐3‐ol, benzaldehyde, and ethyl linoleate. But butyric acid with OAV > 1 is only detected in the SGT and STF.
TABLE 3.
OAV analysis of aroma compounds in three samples
| No | Compounds | Odor threshold (µg/kg) | OAV | ||
|---|---|---|---|---|---|
| SGT | STF | SCT | |||
| 1 | Phenethyl alcohol | 390 1 | 2.980 | 4.011 | 7.201 |
| 2 | Furfuryl alcohol | 4,500.6 2 | <1 | <1 | <1 |
| 3 | Benzyl alcohol | 900 3 | <1 | <1 | <1 |
| 4 | Linalool | 37 4 | 3.397 | 10.154 | 5.176 |
| 5 | 1‐Hexanol | 9 5 | 16.644 | 80.000 | 20.733 |
| 6 | 2,3‐Butanediol | 95.1 2 | <1 | 6.679 | <1 |
| 7 | alpha‐Terpineol | 0.3 6 | nd | 744.000 | nd |
| 8 | 1‐Octen‐3‐ol | 1 1 | nd | 165.400 | nd |
| 9 | Phenylacetaldehyde | 4 1 | 114.750 | 453.850 | 120.700 |
| 10 | Benzaldehyde | 350 1 | <1 | 5.656 | <1 |
| 11 | Furfural | 3000 1 | <1 | <1 | <1 |
| 12 | 3‐(Methylthio)propionaldehyde | 1.4 2 | 64.786 | 263.857 | 55.357 |
| 13 | 1‐Nonanal | 8 1 | 4.575 | 31.575 | 8.513 |
| 14 | Decanal | 70.8 7 | nd | <1 | nd |
| 15 | Isovaleric acid | 1200 2 | <1 | <1 | nd |
| 16 | Butyric Acid | 3.19 8 | 97.586 | 299.248 | nd |
| 17 | Ethyl Hexanoate | 2.3 2 | 72.087 | 91.304 | 162.217 |
| 18 | Ethyl laurate | 3.5 8 | 75.829 | 46.000 | 189.229 |
| 19 | Methyl salicylate | 0.06 8 | 1713.333 | 5,083.333 | 2,878.333 |
| 20 | Ethyl phenylacetate | 1 8 | 117.000 | 264.900 | 319.000 |
| 21 | Ethyl linoleate | 4 8 | nd | 42.125 | nd |
| 22 | Ethyl nonanoate | 1.2 8 | 14.417 | nd | 35.500 |
| 23 | Methyl decanoate | 1 8 | 13.500 | 47.900 | 30.700 |
| 24 | 4‐Ethylphenol | 140 3 | 5.884 | 12.569 | 10.017 |
| 25 | 4‐Ethyl‐2‐methoxyphenol | 50 1 | 21.658 | 45.992 | 40.412 |
| 26 | 2‐Acetyl pyrrole | 19 1 | 18.442 | 44.089 | 14.642 |
| 27 | 2,6‐Dimethylpyrazine | 10 8 | 1.520 | nd | <1 |
Abbreviations: GSTF, gradient steady‐state temperature field; OAV, odor activity value; SCT, samples of constant temperature; STF, samples of traditional fermentation; SGT, samples including samples of GSTF.
Orthonasal odor thresholds in water determined and taken from the literature:
Lin et al. (2019).
Giri et al. (2010).
Chen et al. (2013).
Frauendorfer and Schieberle (2006).
Zhao et al. (2020).
Gernert (2011).
Gao et al. (2014).
Tieman et al. (2006).
Besides, the four aroma compounds with OAVs < 1 in the three samples were furfuryl alcohol, benzyl alcohol, furfural, and decanal. Among them, furfural had the lowest OAV in three samples, which result from its high odor threshold. But the roles of furfural in soy sauce could not be underestimated for furfural could interact with other flavor substances and enhance the taste of soy sauce although furfural had a high threshold (Feng et al., 2014).
3.4. Principal component analysis
Principal component analysis (PCA) is an unsupervised clustering method that does not require any knowledge of the data set, which reduces the dimensionality of multivariate data while preserving most of the variance therein (Lee & Ahn, 2009). Therefore, the relationships among the 22 major aroma‐active compounds were clarified by PCA as shown in Figure 7. The first principal component (PC‐1) explained 85.7% of the variation across the samples, while the second component (PC‐2) revealed 13.7% of the variation, which represented 99.4% of the total variation. Furthermore, the samples produced by the three fermentation processes had different positions in different loading areas. As shown in Figure 7, the SGT was closer to the STF on the coordinate axis, so the three samples could be divided into two groups in which SCT was divided into a group but SGT and STF were divided into another group indicating that the odor characteristics of the SGT were similar to that of the STF. This PCA results were most partly in accordance with those of aroma‐active compounds analysis and OAV analysis.
FIGURE 7.
Principal component analysis of major aroma active compounds in three samples
3.5. Sensory analysis of three kinds of PXDB products
The sensory quality of the three samples was identified by QDA. The description categories were divided into appearance (reddish brown, moisture, graininess, and pepper size), smell (soy sauce‐like, mellow, pungent, sour, musty, coordination, durability, and intensity), texture (hardness, viscosity, elasticity, and adhesiveness), and taste (salty, delicate taste, spicy, and citric acid‐like). It could be seen from Figure 8, for the appearance, the reddish brown and the moisture score of SGT were closer to those of the STF than those of the SCT, which probably caused by the variable temperature in the GSTF that was closer to that in the traditional fermentation process, resulting in some similarity in color and moisture between the two products. In terms of smell, soy sauce‐like odor scored the highest, indicating that soy sauce‐like odor was the characteristic smell of PXDB. Compared with the SCT, the results showed that the mellow, soy sauce‐like and sour odor of the SGT was closer to the STF, which could be related to some alcohols, aldehydes, and acids, such as 3‐(methylthio)propionaldehyde, isovaleric acid, butyric acid, and phenylethanol. In addition, the scores of coordination, durability, and intensity of the three kinds of PXDB were similar. In terms of texture, the score of the SGT was more similar to the STF, which might be caused by the differences of moisture. In terms of taste, the evaluation results of salty taste, delicate taste, and citric acid‐like taste in the SGT were more similar to those of the STF. In conclusion, compared with the SCT, the sensory characteristics of SGT were more similar to those of the STF, which were consistent with the analyses of OAV and PCA.
FIGURE 8.
Sensory characteristics of three samples
The sensory scores for the three samples were analyzed by the PCA as shown in Figure 9. The sensory scores for the three samples given by the 10 evaluators were relatively concentrated, indicating that the consistency and repeatability of the evaluation results were good and the results could truly reflect the sensory characteristics of the three types of products. According to the positions of the three samples, they could be divided into two groups, in which SCT was divided into a group but STF and SGT were divided into another group. The results were consistent with those in Figure 8 and the sensory quality of the SGT was closer to the STF than that of the SCT.
FIGURE 9.
Principal component analysis on sensory evaluation of three samples
4. CONCLUSION
This study focused on the characteristics of the volatile compounds in PXDB produced from different three fermentation processes. A total of 103 volatile compounds were detected in the three samples, of which 75, 67, and 68 volatiles were detected in SGT, SCT, and STF, respectively. Compared with STF, more kinds of esters and alcohols were obtained in SGT by analyzing with GC‐MS although the total concentrations of volatiles in the SGT were smaller, which suggested that the process in the closed system of GSTF was conducive to produce more kinds of esters and alcohols compared with traditional fermentation. A total of 27 active compounds including eight alcohols, six aldehydes, two acids, seven esters, two phenols, and two heterocyclics were detected in the three kinds of samples by GC‐O analysis, of which the three largest major compounds were alcohols, esters, and aldehydes. A total of 22 major aroma‐active compounds were identified in the three samples by the combination analysis with GC‐O and OAV. The PCA results of 22 major aroma‐active compounds had shown that SGT and STF could be divided into a group indicating that the odor characteristics of the SGT were similar to those of the STF. This PCA results were most partly in accordance with those of aroma‐active compounds analysis and OAV analysis. The appearance (reddish brown and moisture), smell (soy‐sauce‐like mellow and sour), texture, and taste (salty, delicate, and citric acid) of sensory index in the SGT exhibited a more similar profile with the STF by the sensory evaluation of QDA and PCA, which had shown that the sensory characteristics of the SGT were more similar to those of the STF. The closed system of GSTF could be applied in PXDB fermentation to obtain higher quality products, which brought a bright prospect of replacing the traditional fermentation process to realize the controllable industrialized production of PXDB.
CONFLICTS OF INTEREST
The authors declare no conflict of interest.
ETHICAL APPROVAL
In this research, there are no studies involving animal or human subjects.
ACKNOWLEDGEMENTS
This work was supported by the Applied Basic Research Programs of Science and Technology Department of Sichuan Province (2019YJ0390), the young plant project of Science and Technology Department of Sichuan Province (2021JDRC0130), the Spring Sunshine Plan of the Ministry of Education of China (Z2017058), the Key Project of Xihua University of China (z1420523), the Department of Education of Sichuan Province of China (15ZB0126), the Key Laboratory program of Grain and Oil Processing and Food Safety of Xihua University of China (szjj2015‐001), the Science and Technology Department of Sichuan Province：2020YFN0151, 2020JDRC0095, 2019JDRC120.
Ding W, Liu Y, Zhao X, et al. Characterization of volatile compounds of Pixian Douban fermented in closed system of gradient steady‐state temperature field. Food Sci Nutr. 2021;9:2862–2876. 10.1002/fsn3.2242
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are not shared.
REFERENCES
- Adedeji, J. , Hartman, T. G. , Rosen, R. T. , & Ho, C.‐T. (1991). Free and glycosidically bound aroma compounds in hog plum (Spondias mombins L.). Journal Agricultural and Food Chemistry, 39, 1494–1497. 10.1021/jf00008a025 [DOI] [Google Scholar]
- Al‐Dalali, S. , Zheng, F. , Li, H. , Huang, M. , & Chen, F. (2019). Characterization of volatile compounds in three commercial Chinese vinegars by SPME‐GC‐MS and GC‐O. Lwt‐Food Science and Technology, 112, 108264. 10.1016/j.lwt.2019.108264 [DOI] [Google Scholar]
- Beaulieu, J. C. , & Stein‐Chisholm, R. E. (2016). HS‐GC‐MS volatile compounds recovered in freshly pressed ‘Wonderful’ cultivar and commercial pomegranate juices. Food Chemistry, 190, 643–656. 10.1016/j.foodchem.2015.06.005 [DOI] [PubMed] [Google Scholar]
- Charles, M. , Martin, B. , Ginies, C. , Etievant, P. , Coste, G. , & Guichard, E. (2000). Potent aroma compounds of two red wine vinegars. Journal Agricultural and Food Chemistry, 48, 70–77. 10.1021/jf9905424 [DOI] [PubMed] [Google Scholar]
- Chen, S. , Xu, Y. , & Qian, M. C. (2013). Aroma characterization of Chinese rice wine by gas chromatography‐olfactometry, chemical quantitative analysis, and aroma reconstitution. Journal of Agricultural and Food Chemistry, 61(47), 11295–11302. 10.1021/jf4030536 [DOI] [PubMed] [Google Scholar]
- Chinnici, F. , Duran Guerrero, E. , Sonni, F. , Natali, N. , Natera Marin, R. , & Riponi, C. (2009). Gas chromatography‐mass spectrometry (GC‐MS) characterization of volatile compounds in quality vinegars with protected European geographical indication. Journal Agricultural and Food Chemistry, 57(11), 4784–4792. 10.1021/jf804005w [DOI] [PubMed] [Google Scholar]
- Ding, W. , Zhao, X. , Xie, S. I. , Liu, Y. , Zhang, M. , Che, Z. , Liu, Y. I. , Liu, P. , & Lin, H. (2020). Dynamics and correlation of microbial community and flavor in Pixian Douban fermented with closed process of constant temperature. Journal of the Science of Food and Agriculture. 10.1002/jsfa.11050 [DOI] [PubMed] [Google Scholar]
- Fanaro, G. B. , Duarte, R. C. , Santillo, A. G. , Pinto e Silva, M. , Purgatto, E. , & Villavicencio, A. (2012). Evaluation of γ‐radiation on oolong tea odor volatiles. Radiation Physics and Chemistry, 81(8), 1152–1156. 10.1016/j.radphyschem.2011.11.061 [DOI] [Google Scholar]
- Feng, Y. , Cai, Y. , Su, G. , Zhao, H. , Wang, C. , & Zhao, M. (2014). Evaluation of aroma differences between high‐salt liquid‐state fermentation and low‐salt solid‐state fermentation soy sauces from China. Food Chemistry, 145, 126–134. 10.1016/j.foodchem.2013.07.072 [DOI] [PubMed] [Google Scholar]
- Feng, Y. , Cai, Y. , Sun‐Waterhouse, D. , Cui, C. , Su, G. , Lin, L. , & Zhao, M. (2015). Approaches of aroma extraction dilution analysis (AEDA) for headspace solid phase microextraction and gas chromatography‐olfactometry (HS‐SPME‐GC‐O): Altering sample amount, diluting the sample or adjusting split ratio. Food Chemistry, 187, 44–52. 10.1016/j.foodchem.2015.03.138 [DOI] [PubMed] [Google Scholar]
- Frauendorfer, F. , & Schieberle, P. (2006). Identification of the key aroma compounds in cocoa powder based on molecular sensory correlations. Journal of Agricultural and Food Chemistry, 54(15), 5521–5529. 10.1021/jf060728k [DOI] [PubMed] [Google Scholar]
- Gao, W. , Fan, W. , & Xu, Y. (2014). Characterization of the key odorants in light aroma type Chinese liquor by gas chromatography‐olfactometry, quantitative measurements, aroma recombination, and omission studies. Journal of Agricultural and Food Chemistry, 62(25), 5796–5804. 10.1021/jf501214c [DOI] [PubMed] [Google Scholar]
- Gao, X. L. , Zhang, J. K. , Regenstein, J. M. , Yin, Y. Y. , & Zhou, C. S. (2018). Characterization of taste and aroma compounds in Tianyou, a traditional fermented wheat flour condiment. Food Research International, 106(25), 156–163. 10.1016/j.foodres.2017.12.063 [DOI] [PubMed] [Google Scholar]
- Giri, A. , Osako, K. , Okamoto, A. , & Ohshima, T. (2010). Olfactometric characterization of aroma active compounds in fermented fish paste in comparison with fish sauce, fermented soy paste and sauce products. Food Research International, 43(4), 1027–1040. 10.1016/j.foodres.2010.01.012 [DOI] [Google Scholar]
- Inoue, Y. , Kato, S. , Saikusa, M. , Suzuki, C. , Otsubo, Y. , Tanaka, Y. , Watanabe, H. , & Hayase, F. (2016). Analysis of the cooked aroma and odorants that contribute to umami aftertaste of soy miso (Japanese soybean paste). Food Chemistry, 213, 521–528. 10.1016/j.foodchem.2016.06.106 [DOI] [PubMed] [Google Scholar]
- Jo, Y. J. , Cho, I. H. , Song, C. K. , Shin, H. W. , & Kim, Y. S. (2011). Comparison of fermented soybean paste (Doenjang) prepared by different methods based on profiling of volatile compounds. Journal of Food Science, 76(3), C368–C379. 10.1111/j.1750-3841.2011.02068.x [DOI] [PubMed] [Google Scholar]
- Lee, S. , & Ahn, B. (2009). Comparison of volatile components in fermented soybean pastes using simultaneous distillation and extraction (SDE) with sensory characterisation. Food Chemistry, 114(2), 600–609. 10.1016/j.foodchem.2008.09.091 [DOI] [Google Scholar]
- Lee, S. J. , & Noble, A. C. (2003). Characterization of odor‐active compounds in californian chardonnay wines using GC‐olfactometry and GC‐mass spectrometry. Journal of Agricultural and Food Chemistry, 51(27), 8036–8044. 10.1021/jf034747v [DOI] [PubMed] [Google Scholar]
- Li, X. Y. , Zhao, C. S. , Zheng, C. , Liu, J. , Vu, V. H. , Wang, X. D. , & Sun, Q. (2018). Characteristics of microbial community and aroma compounds in traditional fermentation of Pixian broad bean paste as compared to industrial fermentation. International Journal of Food Properties, 20, S2520–S2531. 10.1080/10942912.2017.1373358 [DOI] [Google Scholar]
- Li, Z. , Dong, L. , Huang, Q. , & Wang, X. (2016). Bacterial communities and volatile compounds in Doubanjiang, a Chinese traditional red pepper paste. Journal of Applied Microbiology, 120(6), 1585–1594. 10.1111/jam.13130 [DOI] [PubMed] [Google Scholar]
- Li, Z. , Dong, L. , Jeon, J. , Kwon, S. Y. , Zhao, C. , & Baek, H. H. (2019). Characterization and evaluation of aroma quality in Doubanjiang, a Chinese traditional fermented red pepper paste, using aroma extract dilution analysis and a sensory profile. Molecules, 24(17), 3107. 10.3390/molecules24173107 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lin, H. , Liu, Y. , He, Q. , Liu, P. , Che, Z. , Wang, X. , & Huang, J. (2019). Characterization of odor components of Pixian Douban (broad bean paste) by aroma extract dilute analysis and odor activity values. International Journal of Food Properties, 22(1), 1223–1234. 10.1080/10942912.2019.1636816 [DOI] [Google Scholar]
- Liu, P. , Xiang, Q. , Sun, W. , Wang, X. , Lin, J. , Che, Z. , & Ma, P. (2020). Correlation between microbial communities and key flavors during post‐fermentation of Pixian broad bean paste. Food Research International, 137, 109513. 10.1016/j.foodres.2020.109513 [DOI] [PubMed] [Google Scholar]
- Lu, Y. , Chi, Y. , Lv, Y. , Yang, G. , & He, Q. (2019). Evolution of the volatile flavor compounds of Chinese horse bean‐chili‐paste. Lwt‐Food Science and Technology, 102, 131–135. 10.1016/j.lwt.2018.12.035 [DOI] [Google Scholar]
- Lu, Y. , Tan, X. , Lv, Y. , Yang, G. , Chi, Y. , & He, Q. (2020). Flavor volatiles evolution of Chinese horse bean‐chili‐paste during ripening, accessed by GC×GC‐TOF/MS and GC‐MS‐olfactometry. International Journal of Food Properties, 23(1), 570–581. 10.1080/10942912.2020.1749066 [DOI] [Google Scholar]
- Morales‐Valle, H. , Silva, L. C. , Paterson, R. R. , Venancio, A. , & Lima, N. (2011). Effects of the origins of Botrytis cinerea on earthy aromas from grape broth media further inoculated with Penicillium expansum. Food Microbiology, 28(5), 1048–1053. 10.1016/j.fm.2011.02.005 [DOI] [PubMed] [Google Scholar]
- Moy, Y. S. , Lu, T. J. , & Chou, C. C. (2012). Volatile components of the enzyme‐ripened sufu, a Chinese traditional fermented product of soy bean. Journal of Bioscience and Bioengineering, 113(2), 196–201. 10.1016/j.jbiosc.2011.09.021 [DOI] [PubMed] [Google Scholar]
- Natera, R. , Caetro, R. , Garcia‐Moreno, M. D. V. , Hernandez, M. J. , & Garcia‐Barroso, C. (2003). Chemometric studies of vinegars from different raw materials and processes of production. Journal of Agricultural and Food Chemistry, 51(11), 3345–3351. 10.1021/jf021180u [DOI] [PubMed] [Google Scholar]
- Pérez‐Boada, M. , Ruiz‐Dueñas, F. J. , Pogni, R. , Basosi, R. , Choinowski, T. , Martínez, M. J. , Piontek, K. , & Martínez, A. T. (2005). Versatile peroxidase oxidation of high redox potential aromatic compounds: Site‐directed mutagenesis, spectroscopic and crystallographic investigation of three long‐range electron transfer pathways. Journal of Molecular Biology, 354(2), 385–402. 10.1016/j.jmb.2005.09.047 [DOI] [PubMed] [Google Scholar]
- Triqui, R. , & Reineccius, G. A. (1995). Changes in flavor profiles with ripening of anchovy (Engraulis encrasicholus). Journal of Agricultural and Food Chemistry, 43(7), 1883–1889. 10.1021/jf00055a024 [DOI] [Google Scholar]
- Schnermann, P. , & Schieberle, P. (1997). Evaluation of Key Odorants in Milk Chocolate and Cocoa Mass by Aroma Extract Dilution Analyses. Journal of Agricultural and Food Chemistry, 45(3), 867–872. 10.1021/jf960670h [DOI] [Google Scholar]
- Tieman, D. , Taylor, M. , Schauer, N. , Fernie, A. R. , Hanson, A. D. , & Klee, H. J. (2006). Tomato aromatic amino acid decarboxylases participate in synthesis of the flavor volatiles 2‐phenylethanol and 2‐phenylacetaldehyde. Proceedings of the National Academy of Sciences of the United States of America, 103(21), 8287–8292. 10.1073/pnas.0602469103 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Van Gemert, L. J. (2011). Compilations flavour threshold values in water and other media. Oliemans, Punter & Partners. [Google Scholar]
- Wang, W. , Xia, W. , Gao, P. , & Xu, Y. (2017). Sarcoplasmic protein hydrolysis activity of Lactobacillus plantarum 120 Isolated from Suanyu: A traditional Chinese low salt fermented fish. Journal of Food Processing and Preservation, 41(2), e12821. 10.1111/jfpp.12821 [DOI] [Google Scholar]
- Wu, J. , Tian, T. , Liu, Y. , Shi, Y. , Tao, D. , Wu, R. , & Yue, X. (2018). The dynamic changes of chemical components and microbiota during the natural fermentation process in Da‐Jiang, a Chinese popular traditional fermented condiment. Food Research International, 112, 457–467. 10.1016/j.foodres.2018.06.021 [DOI] [PubMed] [Google Scholar]
- Zhang, L. , Che, Z. , Xu, W. , Yue, P. , Li, R. , Li, Y. , Pei, X. , & Zeng, P. (2020). Dynamics of physicochemical factors and microbial communities during ripening fermentation of Pixian Doubanjiang, a typical condiment in Chinese cuisine. Food Microbiology, 86, 103342. 10.1016/J.Fm.2019.103342 [DOI] [PubMed] [Google Scholar]
- Zhao, J. , Dai, X. , Liu, X. , Zhang, H. , Tang, J. , & Chen, W. (2011). Comparison of aroma compounds in naturally fermented and inoculated Chinese soybean pastes by GC‐MS and GC‐Olfactometry analysis. Food Control, 22(6), 1008–1013. 10.1016/j.foodcont.2010.11.023 [DOI] [Google Scholar]
- Zhao, Y. , Wang, P. , Zhan, P. , Tian, H. , Lu, C. , & Tian, P. (2020). Aroma characteristics of cloudy kiwifruit juices treated with high hydrostatic pressure and representative thermal processes. Food Research International, 109841, 10.1016/j.foodres.2020.109841 [DOI] [PubMed] [Google Scholar]
- Zhou, Z. , Liu, S. , Kong, X. , Ji, Z. , Han, X. , Wu, J. , & Mao, J. (2017). Elucidation of the aroma compositions of Zhenjiang aromatic vinegar using comprehensive two dimensional gas chromatography coupled to time‐of‐flight mass spectrometry and gas chromatography‐olfactometry. Journal of Chromatography A, 1487, 218–226. 10.1016/j.chroma.2017.01.014 [DOI] [PubMed] [Google Scholar]
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Data Availability Statement
The data that support the findings of this study are not shared.