1. Introduction
Baijiu, also known as Chinese liquor, is a transparent fermented alcoholic beverage dating back thousands of years [1]. Baijiu has a complicated manufacturing process that results in different types of aromas. Soy sauce aroma type Baijiu (SSAB) is a flagship variety that is relished by consumers. The SSAB are mainly characterized by sauce-like, alcoholic, roasted, nutty, floral and fruity aromas [2,3].
The mixture of volatile compounds in SSAB is quite complex. A total of 528 volatile compounds have been identified in SSAB by comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry [4]. Gas chromatography combined with an olfactory detector (GC-O), which involves the use of GC for separation and the olfaction of trained judges as a detector, is a useful tool for recognizing aroma-active compounds in Baijiu. A total of 186 aroma-active compounds were identified in SSAB by GC-O [5]. Odor activity values (OAVs, defined as the ratio of concentration to odor threshold) are usually determined after GC-O analysis [6]. The sensory effects of compounds with an OAV ≥1 will be further investigated by means of recombination and omission experiments [7]. Sub-threshold refers to concentrations below the olfactory threshold, and concentrations exceeding the olfactory threshold are supra-threshold. Volatile compounds with sub-threshold concentrations are usually known to have little or no impact on total sensory perception [8].
The aroma compounds of many foods are complex, and it is recognized that the aroma is not simply equal to the sum of its aroma compounds [9,10]. Perceptual interactions are indeed found for the aroma compounds. Some methods mainly determined the synergy between aroma compounds through the changes of odor threshold or aroma intensity before and after the combination of aroma compounds. For example, the presence of ethyl-3-hydroxybutanoate and 2-methylpropyl acetate in a wine model solution led to a significant decrease in the olfactory threshold of the fruity aroma [11]. Some studies have shown that certain compounds can play a role in the overall aroma at sub-threshold concentrations. Acetoin, acetic acid and γ-butyrolactone affect the fruity aroma intensity in wine at concentrations of approximately 2%, 12% and 40% of their odor thresholds, respectively [12]. At sub-threshold concentrations, ethylphenol has been shown to suppress the fruity aroma intensity in wine [13]. However, the impact of aroma compounds present at sub-threshold concentrations on odor perception has not previously been investigated in Baijiu.
Pyrazines are six-membered heterocyclic compounds with two nitrogen atoms at positions 1 and 4 [14]. Pyrazines are responsible for universally desirable and enjoyable aromas and have been identified in many foods and beverages, particularly as significant volatile components of various nuts, such as peanuts [15], almonds [16], hazelnuts [17] and pecans [18]. While the significance of a variety of pyrazines affecting roasted and nutty aromas has already been highlighted, existing studies have not explored potential perceptual interactions.
Pyrazines are one of the important classes of compounds in Baijiu and are found in highly variable concentrations, between ng·L−1 and mg·L−1 [19]. Aroma compounds with similar structures and/or aroma properties may create perceptual interactions in combination [20,21,22]. We were interested in whether the perceptual interaction between pyrazines occurred in Baijiu. Therefore, the aims of this study were (i) to quantify the pyrazines in SSAB by direct injection combined with UPLC–MS/MS, (ii) to estimate the relationships between the pyrazines and roasted aroma by chemosensory analysis, and (iii) to further investigate the possible perceptual interactions between pyrazines.
2. Materials and Methods 2.1. Chemical and Materials Pyrazine, 2-methylpyrazine (2M), 2,6-dimethylpyrazine (26DM), 2,3-dimethylpyrazine (23DM), 2-ethyl-3-methylpyrazine (2E3M), 2,3,5-trimethylpyrazine (235TM), 2,3-diethylpyrazine (23DE), 5-ethyl-2,3-dimethylpyrazine (5E23DM), 2,3,5,6-tetramethylpyrazine (2356TTM), 2-isobutyl-3-methylpyrazine (2I3M), 2,3-diethyl-5-methylpyrazine (23DE5M), 2-acetyl-3-methylpyrazine (2A3M), (3,5,6-trimethylpyrazin-2-yl)methanol (TM2YM) and 2-propylpyrazine were purchased from company Sigma-Aldrich (Shanghai, China). Meanwhile, 2-ethyl-6-methylpyrazine (2E6M), 2,6-diethylpyrazine (26DE) and 2-ethyl-3,5-dimethylpyrazine (2E35DM) were purchased from J&K Chemical Corp (Beijing, China). The above commercial standards (≥96% purity) were used. HPLC grade ethanol and LC–MS grade acetonitrile were purchased from Merck (Darmstadt, Germany). Ultra-pure water was obtained from a Milli-Q Gradient A10 system (Millipore, Billerica, MA, USA). 2.2. Baijiu Samples
A total of 11 commercial SSAB samples were selected for this study and labeled as GT, DYT, ZJ, XJ, QHZ, ZJ, WZJ, ZZY, WL, LJ and FM. The detailed information is given in Table S1. All Baijiu samples were compliant with the national soy sauce Baijiu standard (GB/T 267602011). After the Baijiu sample was passed through a nylon membrane (13 mm, 0.22 μm; ANPEL, Shanghai, China), internal standard (2-propylpyrazine, 5 mg·L−1 in ethanol) was added. All Baijiu samples were performed in triplicate.
2.3. Quantification of Pyrazines
Pyrazines were quantitated by UPLC–MS/MS according to the reference, with slight modifications [19]. UPLC was performed by an ACQUITY UPLC system (binary solvent manager; Waters, Milford, CT, USA) coupled to a triple quadrupole mass spectrometer (Xevo TQ-S; Waters, Milford, CT, USA). The solution (injection volume of 10 μL each time) was fractionated using a BEH C18 (100 × 2.1 mm, 1.7 μm; Waters, Milford, CT, USA) column. Electrospray ionization (ESI) generated the ions in a positive mode. The ion source parameters were operated with the previously described method [19]. Separately, mass spectrometer parameters for each pyrazine were optimized by direct infusion of individual standard solutions at concentrations of 200 μg·L−1 in acetonitrile. The precursor ion, quantification ion and confirmation ion, cone voltage and collision energy were established. Each pyrazine has two MRM (multiple reaction monitoring) transitions: the most intense transition for quantifications and the second most intense for confirmation purposes. The column temperature was maintained at 40 °C. Mobile phase A consisted of 0.1% formic acid in water and mobile phase B was 0.1% formic acid in acetonitrile. The eluting pump was programmed as follows (0.3 mL·min−1): 0–8 min, 3% B; 8–25 min, 3–12% B; 25–31 min, 12–20% B; 31–35 min, 20–70% B; 35–35.5 min, 70–3% B; 35.5–40 min, 3% B.
Three replicates were analyzed for each pyrazine to calculate the relative standard deviation (RSD). The limits of detection (LOD) and limits of quantification (LOQ) of pyrazines were estimated with pyrazine standard solutions when the signal-to-noise ratio reached 3 and 10, respectively. The recovery was calculated: (measured concentration after addition − measured concentration in no spiked Baijiu sample)/added concentration × 100%. 2.4. Sensory Analyses
2.4.1. Sensory Panels
All panelists came from Jiangnan University, China. Panel 1 featured 20 judges, 10 males and 10 females, with an average age of 25 years. Panel 2 composed of 12 judges, 6 men and 6 women, aged 27 on average. All staff had rich experience in sensory evaluation, including determination of odor thresholds and quantitative descriptive analysis [23,24]. For sensory training, 2,3,5-trimethylpyrazine (8 mg·L−1) in 53% v/v aqueous ethanol was used as the roasted aroma reference [24]. On the basis of the references, with slight modifications, the panelists scored the intensity of the roasted aroma on a 7-point scale (Table S2) [24,25]. Panel 2 spent ten sessions (1 h each) practicing on how to score the SSAB samples, using the references as anchor points. Panel 2’s performance was assessed by PanelCheck for agreement, discrimination and repeatability among assessors according to the Tucker-1, F- and MSE plots, respectively [26,27], and the results are shown in Figure S1.
2.4.2. Determination of Odor Thresholds and Calculation of OAVs
Some pyrazines’ odor thresholds were detected by a 3-AFC (3-alternative forced-choice) test at seven concentration steps. One glass of the pyrazine and two glasses of 53% ethanol–water solution (v/v) were prepared. Panel 1 was asked to select the differing one [7]. By dividing the concentration by the value of the pyrazine odor threshold, OAV was established.
2.4.3. SSAB Sample Evaluation
The SSAB samples were smelled by panel 2 with three or four samples per session and the samples were sent in triplicate. The samples were served (15 mL each) in regular Baijiu tasting glasses. Using a 7-point scale, the roasted aroma intensity was graded, varying from 0 (not perceived) to 7 (highest intensity) in contrast to the reference intensity (Table S2).
2.4.4. Discriminative Testing Methods
For various pyrazine addition experiments, 3-alternative forced-choice (3-AFC) studies were conducted by panel 1. In the first series of 3-AFC tests, each pyrazine applied to a SSAB sample (FM) was tested (Last table; tests 1 to 8). In the second step, multiple pyrazine addition experiments were conducted (Last table; tests 9 to 10). Each 3-AFC test provided three samples in random order, two of which were unaltered SSAB samples (FM), with the third being an SSAB sample (FM) with the corresponding pyrazines. Each panelist used direct smell to identify the different one among the three samples.
2.4.5. Determination of the Perceptual Interactions between Pyrazines
The odor threshold for a mixture of four stated supra-threshold pyrazines (2,6-dimethylpyrazine, 2-ethyl-6-methylpyrazine, 2,3,5-trimethylpyrazine and 2-ethyl-3,5-dimethylpyrazine) was established. Odor threshold was calculated in different matrices: dilute alcohol solution and dilute alcohol solution containing four sub-threshold pyrazine mixtures. Odor threshold was determined based on the 3-AFC test using panel 1. Each test included one positive sample, supplemented with volumes of the four supra-threshold pyrazines from 0.039 to 9.824 mL, increasing in each test by 2 times the volume (Table 1). The odor threshold was identified as the compound concentration at which the correct sample could be chosen by 50% of the panelists. Detailed procedures can be found in previous studies [13].
In addition, Feller’s additive model was used to analyze the interaction of the pyrazines after mixing [20,28]. The mixed solution of four sub-threshold pyrazines (2,3-dimethylpyrazine, 2,3-diethylpyrazine, 2,3-diethyl-5-methylpyrazine and 2-acetyl-3-methylpyrazine) was used as A. The mixed solution of four supra-threshold pyrazines (2,6-dimethylpyrazine, 2-ethyl-6-methylpyrazine, 2,3,5-trimethylpyrazine and 2-ethyl-3,5-dimethylpyrazine) using an ascending volume was used as B. For each trial, all panels received a set of three bottles (two blanks containing 53% ethanol/water solution and one supplemented with the pyrazines). The detection probability p was determined using 3-AFC. The detection probability of the mixture can be calculated as follows: p(AB) = p(A) + p(B) − p(A)p(B), where p(AB) indicates the probability of detecting the mixture, and p(A) and p(B) indicate the probability of detecting components A and B, respectively. If the actual detection performance is below the calculated p(AB), a synergistic effect of the two compounds has occurred; if the actual performance matches the calculated p(AB), no aroma interaction has occurred; and if the actual performance is above the calculated p(AB), some degree of suppression has occurred.
2.5. Statistical Analysis
Sensory analysis was submitted to variance analysis (ANOVA). The relationships between pyrazine concentrations and roasted aroma intensity were assessed by Spearman correlation coefficients (ρ) and significance thresholds (p) using SPSS Statistics 25 (IBM, Armonk, NY, USA). p < 0.05 and ρ > 0.5 were regarded as a positive relationship [24,29]. For the data processing of the Feller’s additive model, the Sigma Plot 12.0 software (Systat, San Jose, CA, USA) was used.
3. Results 3.1. Quantitation of Pyrazines by UPLC–MS/MS Approach
The most commonly used analytical methods for pyrazines utilize GC. However, since Baijiu is a liquid obtained by distillation, these pyrazines are more suitable for LC–MS analysis [19]. To the best of our knowledge, some pyrazines have not been reported for quantitative analysis by LC–MS; therefore, a vital step in reaching the optimum sensitivity for some pyrazines was to optimize the MS parameters. For example, for 2,3-diethyl-5-methylpyrazine, this was the first time that LC–MS was used for quantitative analysis. To acquire the precursor and quantifier ions with the highest fragment ion abundance, the cone voltage and collision energy were optimized. Two transitions were selected: the most intense transition (m/z 150.8–136.0) for quantification and the second most intense (m/z 150.8–122.5) for confirmation purposes (Figure S2). Then, under the same chromatographic conditions, qualitative and quantitative analyses of 2,3-diethyl-5-methylpyrazine were performed by comparing the peak in the SSAB sample with authentic standard (Figure S3). Using the same method, 16 pyrazines were studied.
In this study, a rapid direct injection method combined with UPLC–MS/MS for the determination of 16 pyrazines in Baijiu was developed. The MRM transitions, retention times, cone voltages and collision energies of the 16 pyrazines are summarized in Table 2. All pyrazine standards were used for identifying the retention times. The total ion chromatograms of pyrazines are presented in Figure S4. The obtained calibration curves were found to have good linearity, with a determination coefficient (R2) ≥ 0.99; the recoveries varied from 84.36% to 103.92%, and RSDs in triplicate of the samples were ≤6.36% (Table S3), indicating acceptable precision of the quantitative method.
3.2. Quantitation of Pyrazines and OAV Analysis
A total of 16 pyrazines were quantitated by UPLC–MS/MS. In all samples, the quantitative results (Table 3) showed that 2,3,5,6-tetramethylpyrazine (2356TTM, 475–1862 μg·L−1), 2,6-dimethylpyrazine (26DM, 460–1590 μg·L−1) and 2,3,5-trimethylpyrazine (235TM, 317–1755 μg·L−1) were the three most concentrated pyrazines. Lower concentrations were observed for 5-ethyl-2,3-dimethylpyrazine (5E35DM, 0.8–12.5 μg·L−1), 2-isobutyl-3-methylpyrazine (2I3M, 1.0–5.9 μg·L−1) and 2,3-diethyl-5-methylpyrazine (23DE5M, 1.1–15.5 μg·L−1). Using carbohydrates and amino acids/peptides as substrates, different model structures have been proposed to study the chemical synthesis of pyrazines in heat-treated foods [30]. In addition, pyrazines are biosynthesized by a few species of bacteria and fungi [31,32].
The OAVs were calculated to determine the contribution of pyrazines to the overall aroma of the SSAB (Table 3). The OAV estimation implied that four pyrazines contributed to the Baijiu’s overall aroma profile, since their concentrations surpassed odor thresholds. According to previous reports, and confirmed by this study, the important pyrazines for the aroma of Baijiu are 2-ethyl-3,5-dimethylpyrazine, 2-ethyl-6-methylpyrazine, 2,3,5-trimethylpyrazine and 2,6-dimethylpyrazine [3,33,34]. The highest OAV pyrazine in SSAB was 2-ethyl-3,5-dimethylpyrazine (2E35DM; OAVs: 11.2–69.5), followed by 2-ethyl-6-methylpyrazine (2E6M; OAVs: 6.4–17.3). This result is similar to previous research on roasted sesame-like flavor type Baijiu [33]. The OAVs of 2,6-dimethylpyrazine (OAVs: 0.6–2.0) and 2,3,5-trimethylpyrazine (OAVs: 0.4–2.4) were approximately 1. The OAV of 2,3-diethylpyrazine (23DE) ranged from 0.1 to 1.0 in in most SSAB samples. In addition, 2,3-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine and 2-acetyl-3-methylpyrazine (2A3M) had OAVs ranging from 0.1 to 1.0 in all SSAB samples.
3.3. Relationships between Pyrazine Concentrations and Roasted Aroma.
Aroma compounds have similar structures or aroma properties and may create a superimposing effect when combined [20,21,22]. Pyrazine is a class of nitrogen-containing heterocyclic compounds, most of which have roasted aroma characteristics [35,36]. Some studies have shown that certain compounds can play a role in the overall aroma at levels below their odor thresholds [11,13,36]. This means that OAVs <1.0 may not necessarily indicate that the aroma compounds will not be perceived in the Baijiu. Therefore, in the current study, we were interested in whether pyrazines at sub-threshold concentrations contribute to the roasted aroma of SSAB by sensory interactions.
To analyze whether sub-threshold concentrations of pyrazines may contribute to the roasted aroma in SSAB, the correlation between pyrazine concentrations and roasted aroma intensity was analyzed by combining chemical and sensory analyses. First, the roasted aroma intensities of all of the SSAB samples were sensorially evaluated. The PanelCheck software (Nofima Mat, Longyearbyen, Norway) was used to analyze panelists (Figure S1). The Tucker-1 plot highlights roasted aroma attribute used in the profiling. The panel showed very good agreement as they were well clustered at the outer ellipse. The low MSE value suggested that panelists had good discrimination capacity. At the significance level of 5%, all F values surpassed the horizontal axis, which meant that the panelists had a good repeatability capability [26,27]. The SSAB samples came from different regions and brands, and the roasted aroma intensities ranged from 0.93 to 6.26 (Figure 1A). Then, we explored the correlations between pyrazine concentrations (Table 3) and roasted aroma intensities (Figure 1A) based on Spearman’s rank correlations (ρ > 0.5, p < 0.05) [24,29]. The results showed that eight pyrazines significantly correlated with roasted aroma, indicating that these eight pyrazines may be important contributors to the roasted aroma differences among the SSAB samples (Figure 1B).
Among the eight correlated pyrazines, 2-ethyl-3,5-dimethylpyrazine had a higher Spearman’s rank correlation, suggesting that it has a greater contribution to the roasted aroma. This was consistent with the observation that 2-ethyl-3,5-dimethylpyrazine had the highest OAVs (11.2–69.5) in the SSAB samples (Table 3). In addition, it is worth noting that the OAVs of five pyrazines were sub-threshold concentrations in most SSAB samples. Among them, the OAV of 2-methylpyrazine was much less than 0.1, which was less likely to have an effect on overall aroma, so it was not considered from the perspective of sensory interaction. Moreover, 2,3-Dimethylpyrazine, 2,3-diethylpyrazine, 2,3-diethyl-5-methylpyrazine and 2-acetyl-3-methylpyrazine were within the OAV range of 0.1 to 1.0. We were interested in whether the four pyrazines could contribute to the roasted aroma of SSAB.
3.4. Organoleptic Impact of Pyrazines on SSAB Aroma Perception
Studies have shown that some sub-threshold aroma compounds may contribute to the overall aroma by an additive effect with supra-threshold aroma compounds [11,21]. To analyze whether sub-threshold pyrazines can affect the supra-threshold pyrazines, which in turn have an impact on the roasted aroma in SSAB, four sub-threshold pyrazines and four supra-threshold pyrazines were selected for additional tests. Based on the quantitative and roasted aroma intensity results (Table 3 and Figure 1A), the pyrazines present at higher concentrations in the GT sample were added in corresponding amounts to the FM sample (the lowest roasted aroma intensity), using different experimental schemes (Table 4). Thus, the solution prepared in Table 4 was compared to the FM sample by 3-AFC tests. Based on the responses to the tests, the outcomes were evaluated statistically [37].
The first set of triangulation tests (Table 4; tests 1 to 8) involved assessing the individual perception of each pyrazine. There were no significant differences among 2,3-dimethylpyrazine, 2-acetyl-3-methylpyrazine, 2,3-diethylpyrazine and 2,3-diethyl-5-methylpyrazine (Table 4; tests 1 to 4). These results correspond to those of the odor thresholds in Table 3. It is worth noting that the four pyrazines added surpassed the odor thresholds in ethanol–water solution, but they nonetheless resulted in no significant difference in perception (Table 4; tests 5 to 8). No previous studies have stated the odor thresholds of these pyrazines in the Baijiu matrix; the odor thresholds were obtained from ethanol solution. These results demonstrated that the four supra-threshold pyrazines alone had no direct odor effects on SSAB, which may be because Baijiu is extremely rich in aroma compounds and is far more complex than the ethanol–water solution. However, the addition of four supra-threshold pyrazines combined was significantly perceived (p = 0.01) (Table 4; tests 9). In addition, when four sub-threshold pyrazines were added, more sensory panelists perceived a change in roasted aroma, and the significance level was reduced from 0.01 to 0.001 (Table 4; tests 10). The sensory analysis also revealed that the roasted aroma intensity of FM was significantly increased (Figure S5). The results show that the sub-threshold pyrazines affect the overall sensory properties of SSAB. In combination, 2,3-dimethylpyrazine, 2,3-diethylpyrazine, 2,3-diethyl-5-methylpyrazine and 2-acetyl-3-methylpyrazine impacted the roasted aroma at concentrations of approximately 19%, 46%, 67% and 39% of their odor thresholds, respectively. This is the first time it has been reported that mixing sub-threshold pyrazines could contribute to the overall aroma in Baijiu.
3.5. Olfactory Properties of Pyrazines Present at Sub-Threshold Concentrations
According to the roasted aroma intensity of SSAB samples, the QHZ sample had an intermediate-intensity roasted aroma. Thus, the concentrations of eight pyrazines in QHZ were selected for the next study (Figure 2A). Comparing the odor thresholds of four supra-threshold pyrazines in different matrices between ethanol–water solution and four sub-threshold pyrazines ethanol–water solution, the odor threshold was 0.456 mL in ethanol–water solution and 0.143 mL in four sub-threshold pyrazines ethanol–water solution; the odor threshold was decreased by a factor of 3.2 (from 0.456 to 0.143 mL) (Figure 2B). The addition of four sub-threshold pyrazines had significant effects on the odor threshold of four supra-threshold pyrazines. These findings confirm that through perceptual interactions, pyrazines at sub-threshold concentrations function as roasted aroma enhancers.
The researchers separated the relationships between aroma compounds into four groups [38]. To verify whether the sensory contribution of these compounds was due to a simple addition phenomenon or excessive addition effect, the influence of the inclusion of four sub-threshold pyrazines on the odor of the four supra-threshold pyrazines was analyzed. The sensory test results showed that the probability of experimental detection of the roasted aroma in the blend was greater than the calculated value (Table S4). The estimated roasted aroma odor threshold was 0.143 mL, 2.0 times less than the calculated odor threshold (0.292 mL) (Figure 2C), revealing an excessive addition effect after the addition of sub-threshold pyrazines to the supra-threshold pyrazines.
4. Conclusions In this work, a total of 16 pyrazines were analyzed using UPLC–MS/MS in SSAB. Moreover, the sensory interactions of pyrazines were studied for the first time. The Spearman’s rank correlations indicated some sub-threshold pyrazines that were correlated with a roasted aroma, based on their concentrations, and roasted aroma intensity in SSAB samples. These findings showed the indirect effect of 2,3-dimethylpyrazine, 2,3-diethylpyrazine, 2,3-diethyl-5-methylpyrazine and 2-acetyl-3-methylpyrazine, present at sub-threshold concentrations, on roasted aroma expression. The results highlighted the contribution of sub-threshold pyrazines to the aroma of Baijiu, which play a role in perceptual interactions as roasted aroma enhancers. These findings provide new insight into the role of pyrazines in food aroma. This strategy can be used to recognize other significant aroma compounds in sub-threshold concentrations that can influence food aroma.
Enlarge this image.Figure 1. Roasted aroma intensities of the SSAB samples. The different letters indicate significant differences at α = 0.05 (A). Relationships between pyrazines and roasted aroma (B). Red line indicates a significant (p < 0.05) and strong (Spearman's ρ > 0.5) correlation. The thickness of each connection (edge) between two nodes is proportional to Spearman's correlation coefficient (ρ).
Enlarge this image.Figure 2. Four supra-threshold pyrazines and four sub-threshold pyrazines in most SSAB samples (number corresponds to Table 2) (A). Effect of four sub-threshold pyrazine addition on the detection probability of four supra-threshold pyrazines (B). Detection probability of four supra-threshold pyrazines determined experimentally and calculated according to Feller's additive model (C). OT, odor threshold.
| Reconstitution | Pyrazines Reconstitution Diluted in 15 mL of Matrix (mL) | Matrix |
|---|---|---|
| 26DM + 2E6M + 235TM + 2E35DM | 0.039/0.077/0.154/0.307/ 0.614/1.228/2.456/4.912/9.824 | 53% ethanol/water solution |
| 23DM + 23DE + 23DE5M + 2A3M in 53% ethanol/water solution |
26DM, 1110 μg·L−1; 2E6M, 250 μg·L−1; 235TM, 950 μg·L−1; 2E35DM, 150 μg·L−1; 23DM, 290 μg·L−1; 23DE, 100 μg·L−1; 23DE5M, 11 μg·L−1; 2A3M, 120 μg·L−1.
| No. | Compounds | Retention Time (min) ± Standard Deviation | Precursor Ion (m/z) | Quantification Ion (m/z) | Cone Voltage (V) | Collision Energy (eV) | Confirmation Ion (m/z) | Cone Voltage (V) | Collision Energy (eV) |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Pyrazine | 1.77 ± 0.03 | 80.7 | 54.1 | 35 | 14 | 41.2 | 37 | 16 |
| 2 | 2M | 3.35 ± 0.03 | 94.7 | 68.0 | 33 | 14 | 54.3 | 33 | 16 |
| 3 | 26DM | 6.45 ± 0.05 | 108.9 | 41.5 | 31 | 19 | 67.7 | 33 | 18 |
| 4 | TM2YM | 7.05 ± 0.04 | 152.7 | 53.2 | 7 | 22 | 94.1 | 9 | 22 |
| 5 | 23DM | 7.41 ± 0.06 | 108.9 | 41.5 | 31 | 19 | 67.7 | 33 | 18 |
| 6 | 2356TTM | 8.41 ± 0.04 | 137.0 | 55.3 | 31 | 21 | 42.1 | 31 | 24 |
| 7 | 235TM | 9.75 ± 0.03 | 123.0 | 82.2 | 33 | 17 | 42.0 | 33 | 20 |
| 8 | 2A3M | 14.00 ± 0.07 | 136.8 | 109.1 | 17 | 16 | 94.5 | 17 | 18 |
| 9 | 2E6M | 15.43 ± 0.06 | 123.0 | 108.2 | 27 | 19 | 81.5 | 29 | 19 |
| 10 | 2E3M | 16.29 ± 0.08 | 123.0 | 108.2 | 27 | 19 | 81.5 | 29 | 19 |
| 11 | 2E35DM | 18.76 ± 0.04 | 137.0 | 121.4 | 29 | 17 | 80.4 | 30 | 19 |
| 12 | 5E35DM | 19.49 ± 0.06 | 137.0 | 121.4 | 29 | 17 | 80.4 | 30 | 19 |
| 13 | 26DE | 25.48 ± 0.06 | 136.8 | 121.8 | 33 | 20 | 108.4 | 33 | 22 |
| 14 | 23DE | 26.26 ± 0.09 | 136.8 | 121.8 | 33 | 20 | 108.4 | 33 | 22 |
| 15 | 23DE5M | 29.43 ± 0.04 | 150.8 | 136.0 | 35 | 16 | 122.5 | 35 | 18 |
| 16 | 2I3M | 32.64 ± 0.03 | 151.0 | 108.0 | 29 | 26 | 135.8 | 28 | 23 |
| 17 | 2-Propylpyrazine (IS) | 20.73 ± 0.05 | 122.7 | 108.0 | 23 | 16 | 61.1 | 23 | 18 |
2M, 2-methylpyrazine; 26DM, 2,6-dimethylpyrazine; TM2YM, (3,5,6-trimethylpyrazin-2-yl)methanol; 23DM, 2,3-dimethylpyrazine; 2356TTM, 2,3,5,6-tetramethylpyrazine; 235TM, 2,3,5-trimethylpyrazine; 2A3M, 2-acetyl-3-methylpyrazine; 2E6M, 2-ethyl-6-methylpyrazine; 2E3M, 2-ethyl-3-methylpyrazine; 2E35DM, 2-ethyl-3,5-dimethylpyrazine; 5E35DM, 5-ethyl-2,3-dimethylpyrazine; 26DE, 2,6-diethylpyrazine; 23DE, 2,3-dimethylpyrazine; 23DE5M, 2,3-diethyl-5-methylpyrazine; 2I3M, 2-isobutyl-3-methylpyrazine.
| No. | Compounds | Threshold (μg·L−1) | GT d | WZJ | ZY | QHZ | DYT | XJ | LJ | ZJ | WL | FM | ZZY | Mean Value of All Samples |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Concentration (μg·L−1) | ||||||||||||||
| 1 | Pyrazine a | 300,000 b | 82.11 ± 4.08 | 192.41 ± 2.1 | 85.25 ± 3.66 | 176.21 ± 5.02 | 196.79 ± 1.45 | 193.92 ± 1.06 | 71.14 ± 0.67 | 117.55 ± 2.23 | 99.8 ± 4.11 | 73.08 ± 3.8 | 29.81 ± 4.5 | 119.82 |
| 2 | 2M a | 30,000 b | 135.21 ± 1.17 | 110.54 ± 3.64 | 148.2 ± 0.65 | 195.29 ± 0.59 | 159.41 ± 1.97 | 115.33 ± 2.2 | 62.15 ± 5.41 | 36.02 ± 3.41 | 71.56 ± 3.09 | 56.88 ± 2.16 | 51.06 ± 1.97 | 103.79 |
| 3 | 26DM | 791 [3] | 1257.48 ± 3.24 (1.6) | 992.28 ± 1.97 (1.3) | 1497.57 ± 3.96 (1.9) | 1116.28 ± 6.09 (1.4) | 1054.61 ± 0.88 (1.3) | 951.06 ± 1.28 (1.2) | 735.28 ± 0.69 (0.9) | 1589.16 ± 0.47 (2.0) | 878.3 ± 2.78 (1.1) | 459.48 ± 4.6 (0.6) | 618.19 ± 1.06 (0.8) | 1013.61 |
| 4 | TM2YM a | 267,946 c | 6.51 ± 1.76 | 74.7 ± 2.89 | 53.07 ± 3.37 | 54.1 ± 1.92 | 25.4 ± 6.17 | 39.28 ± 3.06 | 7.05 ± 2.71 | 17.33 ± 4.32 | 10.54 ± 3.66 | 18.14 ± 2.79 | 10.92 ± 1.78 | 28.82 |
| 5 | 23DM | 965 c | 312.01 ± 3.96 (0.3) | 175.8 ± 2.24 (0.2) | 682.51 ± 2.09 (0.7) | 290.8 ± 1.88 (0.3) | 195.26 ± 3.62 (0.2) | 315.7 ± 3.84 (0.3) | 112.66 ± 0.77 (0.1) | 295.3 ± 2.6 (0.3) | 237.4 ± 4.78 (0.2) | 125.89 ± 3.5 (0.1) | 167.2 ± 0.88 (0.2) | 264.59 |
| 6 | 2356TTM a | 80,100 [3] | 1861.98 ± 7.09 | 1634.52 ± 1.02 | 805.19 ± 0.56 | 1208.3 ± 1.70 | 895.22 ± 0.79 | 1183.12 ± 4.41 | 474.99 ± 4.27 | 1609.47 ± 2.28 | 601.51 ± 4.04 | 693.42 ± 2.19 | 886.07 ± 4.78 | 1077.62 |
| 7 | 235TM | 730 [3] | 1086.25 ± 0.71 (1.5) | 1328.06 ± 1.37 (1.8) | 866.33 ± 1.05 (1.2) | 950.19 ± 1.36 (1.3) | 760.57 ± 5.81 (1.0) | 906.55 ± 5.52 (1.2) | 440.1 ± 0.83 (0.6) | 1754.48 ± 1.27 (2.4) | 497.11 ± 3.74 (0.7) | 316.52 ± 1.53 (0.4) | 513.97 ± 4.24 (0.7) | 856.38 |
| 8 | 2A3M | 415 c | 236.75 ± 3.5 (0.6) | 156.34 ± 0.57 (0.4) | 79.26 ± 2.97 (0.2) | 125.41 ± 4.43 (0.3) | 196.22 ± 5.09 (0.5) | 261.07 ± 1.76 (0.6) | 78.15 ± 1.69 (0.2) | 56.12 ± 3.56 (0.1) | 65.4 ± 1.86 (0.2) | 72.3 ± 3.71 (0.2) | 49.49 ± 3.55 (0.1) | 125.13 |
| 9 | 2E6M | 40 [33] | 428.24 ± 2.04 (10.7) | 330.72 ± 1.45 (8.3) | 502.11 ± 0.54 (12.6) | 255.9 ± 4.15 (6.4) | 420.85 ± 6.20 (10.5) | 369.26 ± 0.63 (9.2) | 361.98 ± 6.02 (9.0) | 690.69 ± 0.57 (17.3) | 400.24 ± 7.64 (10.0) | 336.76 ± 2.3 (8.4) | 293.25 ± 5.29 (7.3) | 399.10 |
| 10 | 2E3M a | 297 c | 8.19 ± 0.74 | 19.33 ± 0.62 | 6.49 ± 2.51 | 23.1 ± 4.28 | 19.84 ± 4.2 | 7.11 ± 3.79 | 6.19 ± 2.09 | 46.19 ± 4.92 | 5.1 ± 0.79 | 6.71 ± 0.33 | 2.65 ± 2.81 | 13.72 |
| 11 | 2E35DM | 7.5 [33] | 389.85 ± 2.04 (52.0) | 294.45 ± 2.55 (39.3) | 240.44 ± 0.76 (32.1) | 153.61 ± 1.68 (20.5) | 486.49 ± 3.96 (64.9) | 251.42 ± 4.65 (33.5) | 100.23 ± 0.77 (13.4) | 521.57 ± 2.14 (69.5) | 112.3 ± 3.01 (15.0) | 83.75 ± 4.18 (11.2) | 95.1 ± 4.21 (12.7) | 248.11 |
| 12 | 5E23DM a | 530 b | 1.83 ± 4.22 | 6.42 ± 1.09 | 1.64 ± 0.41 | 2.04 ± 1.56 | 5.68 ± 2.8 | 12.52 ± 4.55 | 1.01 ± 3.09 | 1.64 ± 2.47 | 0.83 ± 0.85 | 1.75 ± 2.76 | 1.23 ± 3.09 | 3.33 |
| 13 | 26DE | 296 c | 25.33 ± 2.19 (<0.1) | 39.57 ± 3.44 (0.1) | 31.09 ± 1.09 (0.1) | 11.75 ± 0.77 (<0.1) | 43.21 ± 2.59 (0.1) | 52.41 ± 6.78 (0.2) | 75.21 ± 4.58 (0.3) | 17.08 ± 3.92 (<0.1) | 12 ± 2.06 (<0.1) | 17.63 ± 3.9 (<0.1) | 15.33 ± 2.77 (<0.1) | 30.96 |
| 14 | 23DE | 172 [3] | 159.15 ± 3.9 (0.9) | 240.14 ± 4.83 (1.4) | 125.61± 5.24 (0.7) | 107.55 ± 2.88 (0.6) | 167.61 ± 1.89 (1.0) | 110.9 ± 3.06 (0.6) | 64.8 ± 4.71 (0.4) | 97.14 ± 2.09 (0.6) | 62.4 ± 5.11 (0.4) | 78.6 ± 4.3 (0.5) | 28.08 ± 3.11 (0.2) | 112.91 |
| 15 | 23DE5M | 18 c | 13.76 ± 2.81 (0.8) | 10.54 ± 1.97 (0.6) | 15.47 ± 3.35 (0.9) | 11.86 ± 6.09 (0.7) | 4.5 ± 1.44 (0.3) | 6.69 ± 3.79 (0.4) | 4.39 ± 4.29 (0.2) | 2.71 ± 3.09 (0.2) | 4.16 ± 6.5 (0.2) | 1.7 ± 3.72 (0.1) | 1.09 ± 1.03 (0.1) | 6.99 |
| 16 | 2I3M a | 130 b | 2.31 ± 5.09 | 5.87 ± 2.78 | 4.25 ± 1.83 | 4.25 ± 1.09 | 1.33 ± 4.62 | 1.41 ± 3.7 | 3.82 ± 2.88 | 0.96 ± 6.47 | 1.14 ± 4.55 | 1.92 ± 3.29 | 3.18 ± 2.74 | 2.77 |
a The compounds with OAVs <0.1 were calculated in all SSAB samples in this study. b Odor thresholds were taken from www.thresholdcompilation.com (accessed on 6 November 2020). c Odor thresholds in 53% ethanol/water solution (v/v) detected in this study. d The SSAB samples were selected for this study. The detailed information is given in Table S1.
| Compounds | 23DM | 2A3M | 23DE | 23DE5M | 26DM | 235TM | 2E6M | 2E35DM | Difference Observed |
|---|---|---|---|---|---|---|---|---|---|
| Concn (μg·L−1) | 180 | 160 | 80 | 12 | 800 | 770 | 90 | 300 | |
| OAV | 0.19 | 0.39 | 0.46 | 0.67 | 1.00 | 1.10 | 2.25 | 40.00 | |
| test 1 | √ | × | × | × | × | × | × | × | ns |
| test 2 | × | √ | × | × | × | × | × | × | ns |
| test 3 | × | × | √ | × | × | × | × | × | ns |
| test 4 | × | × | × | √ | × | × | × | × | ns |
| test 5 | × | × | × | × | √ | × | × | × | ns |
| test 6 | × | × | × | × | × | √ | × | × | ns |
| test 7 | × | × | × | × | × | × | √ | × | ns |
| test 8 | × | × | × | × | × | × | × | √ | ns |
| test 9 | × | × | × | × | √ | √ | √ | √ | ** |
| test 10 | √ | √ | √ | √ | √ | √ | √ | √ | *** |
***, 0.1% significant level; **, 1% significant level; ns, p ≥ 0.05 (not significant); √, presence of listed compounds; and ×, absence of listed compound.
Supplementary Materials
The following are available online at https://www.mdpi.com/2304-8158/10/2/441/s1, Figure S1: Tucker-1 (A) plots visualizing the repeatability; MSE plot (B) visualizing the repeatability; F plots (C) visualizing the panels' ability to discriminate between the SSAB samples for roasted attribute, Figure S2: MS/MS method optimization (A and B) and mass spectra (C) for 2,3-diethyl-5-methylpyrazine; Figure S3: Comparison of the chromatograms of an authentic standard (A) of 2,3-diethyl-5-methylpyrazine and its peak in the sample (B), Figure S4: Total ion chromatograms all pyrazine under the optimal instrumental conditions, Figure S5: Roasted aroma intensities of the FM, Table S1: Information of soy sauce aroma type Baijiu samples in this study, Table S2: The complementary nominal scale for sensory analysis, Table S3: Linear range, R2, LOD, and LOQ of the established method for pyrazines, Table S4: Determination of the detection probability (p) of mixture of four supra-threshold pyrazines and four sub-threshold pyrazines: measured aroma threshold and calculated aroma threshold obtained by Feller's additive model.
Author Contributions
Conceptualization, Y.Y., S.C. and Y.X.; methodology, Y.Y., S.C. and Y.X.; formal analysis, Y.Y., S.C., Y.N. and Y.X.; investigation, Y.Y. and S.C.; resources, S.C., Y.N. and Y.X.; data curation, S.C., Y.N. and Y.X.; writing-original draft preparation, Y.Y. and S.C.; writing-review and editing, Y.Y., S.C., Y.N. and Y.X.; project administration, S.C. and Y.X.; funding acquisition, S.C., Y.N. and Y.X. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the National Natural Science Foundation of China (31530055, 21506074), China Postdoctoral Science Foundation (NO. 2018M631971), Open Foundation from the Key Light-Industry Laboratory of Solid-State Fermentation for Strong-Aroma Type Liquor (2017JJ018), National First-class Discipline Program of Light Industry Technology and Engineering (LITE2018-12), and the Jiangsu Province's "Collaborative Innovation Center for Advanced Industrial Fermentation" industry development program.
Data Availability Statement
The data presented in this study are available on request from the corresponding author.
Conflicts of Interest
The authors declare no conflict of interest.
1. Jin, G.Y.; Zhu, Y.; Xu, Y. Mystery behind Chinese liquor fermentation. Trends Food Sci. Technol. 2017, 63, 18-28.
2. Liu, H.; Sun, B. Effect of Fermentation Processing on the Flavor of Baijiu. J. Agric. Food. Chem. 2018, 66, 5425-5432.
3. Wang, X.X.; Fan, W.L.; Xu, Y. Comparison on aroma compounds in Chinese soy sauce and strong aroma type liquors by gas chromatography-olfactometry, chemical quantitative and odor activity values analysis. Eur. Food Res. Technol. 2014, 239, 813-825.
4. Zhu, S.; Lu, X.; Ji, K.; Guo, K.; Li, Y.; Wu, C.; Xu, G. Characterization of flavor compounds in Chinese liquor Moutai by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry. Anal. Chim. Acta 2007, 597, 340-348.
5. Fan, W.; Xu, Y.; Qian, M.C. Identification of Aroma Compounds in Chinese "Moutai" and "Langjiu" Liquors by Normal Phase Liquid Chromatography Fractionation Followed by Gas Chromatography/Olfactometry. Flavor Chem. Wine Other Alcohol. Beverages 2012, 1104, 303-338.
6. Chen, S.; Wang, C.; Qian, M.; Li, Z.; Xu, Y. Characterization of the Key Aroma Compounds in Aged Chinese Rice Wine by Comparative Aroma Extract Dilution Analysis, Quantitative Measurements, Aroma Recombination, and Omission Studies. J. Agric. Food. Chem. 2019, 67, 4876-4884.
7. Sha, S.; Chen, S.; Qian, M.; Wang, C.; Xu, Y. Characterization of the Typical Potent Odorants in Chinese Roasted Sesame-like Flavor Type Liquor by Headspace Solid Phase Microextraction-Aroma Extract Dilution Analysis, with Special Emphasis on Sulfur-Containing Odorants. J. Agric. Food. Chem. 2017, 65, 123-131.
8. Zhao, G.; Feng, Y.; Hadiatullah, H.; Zheng, F.; Yao, Y. Chemical Characteristics of Three Kinds of Japanese Soy Sauce Based on Electronic Senses and GC-MS Analyses. Frontiers in Microbiology 2021, 11, 579808.
9. Diez-Simon, C.; Eichelsheim, C.; Mumm, R.; Hall, R.D. Chemical and Sensory Characteristics of Soy Sauce: A Review. J. Agric. Food. Chem. 2020, 68, 11612-11630.
10. Zhao, G.; Liu, C.; Li, S.; Wang, X.; Yao, Y. Exploring the flavor formation mechanism under osmotic conditions during soy sauce fermentation in Aspergillus oryzae by proteomic analysis. Food Funct. 2020, 11, 640-648.
11. Lytra, G.; Tempere, S.; Le Floch, A.; de Revel, G.; Barbe, J.C. Study of Sensory Interactions among Red Wine Fruity Esters in a Model Solution. J. Agric. Food. Chem. 2013, 61, 8504-8513.
12. Lytra, G.; Tempere, S.; de Revel, G.; Barbe, J.C. Impact of perceptive interactions on red wine fruity aroma. J. Agric. Food. Chem. 2012, 60, 12260-12269.
13. Tempere, S.; Schaaper, M.H.; Cuzange, E.; de Lescar, R.; de Revel, G.; Sicard, G. The olfactory masking effect of ethylphenols: Characterization and elucidation of its origin. Food Quality and Preference 2016, 50, 135-144.
14. Masuo, S.; Tsuda, Y.; Namai, T.; Minakawa, H.; Shigemoto, R.; Takaya, N. Enzymatic Cascade in Pseudomonas that Produces Pyrazine from alpha-Amino Acids. ChemBioChem 2020, 21, 353-359.
15. Gama, A.P.; Adhikari, K. Sensory Characterization of Dominant Malawi Peanut Varieties After Roasting. J. Food Sci. 2019, 84, 1554-1562.
16. Manzano, P.; Diego, J.C.; Bernal, J.L.; Nozal, M.J.; Bernal, J. Comprehensive two-dimensional gas chromatography coupled with static headspace sampling to analyze volatile compounds: Application to almonds. J. Sep. Sci. 2014, 37, 675-683.
17. Nicolotti, L.; Cordero, C.; Bicchi, C.; Rubiolo, P.; Sgorbini, B.; Liberto, E. Volatile profiling of high quality hazelnuts (Corylus avellana L.): Chemical indices of roasting. Food Chem. 2013, 138, 1723-1733.
18. Gong, Y.; Kerrihard, A.L.; Pegg, R.B. Characterization of the Volatile Compounds in Raw and Roasted Georgia Pecans by HS-SPME-GC-MS. J. Food Sci. 2018, 83, 2753-2760.
19. Yan, Y.; Chen, S.; He, Y.; Nie, Y.; Xu, Y. Quantitation of pyrazines in Baijiu and during production process by a rapid and sensitive direct injection UPLC-MS/MS approach. LWT-Food Sci. Technol. 2020, 128, 109371.
20. Lytra, G.; Cameleyre, M.; Tempere, S.; Barbe, J.C. Distribution and Organoleptic Impact of Ethyl 3-Hydroxybutanoate Enantiomers in Wine. J. Agric. Food. Chem. 2015, 63, 10484-10491.
21. Zhao, T.; Ni, D.; Hu, G.; Wang, L.; Chen, S.; Xu, Y. 6-(2-Formyl-5-methyl-1 H-pyrrol-1-yl)hexanoic Acid as a Novel Retronasal Burnt Aroma Compound in Soy Sauce Aroma-Type Chinese Baijiu. J. Agric. Food. Chem. 2019, 67, 1666-1677.
22. Cometto-Muniz, J.E.; Cain, W.S.; Abraham, M.H. Odor detection of single chemicals and binary mixtures. Behav. Brain Res. 2005, 156, 115-123.
23. Yan, Y.; Chen, S.; Nie, Y.; Xu, Y. Characterization of volatile sulfur compounds in soy sauce aroma type Baijiu and changes during fermentation by GC × GC-TOFMS, organoleptic impact evaluation, and multivariate data analysis. Food Res. Int. 2020, 131, 109043.
24. He, Y.; Liu, Z.; Qian, M.; Yu, X.; Xu, Y.; Chen, S. Unraveling the chemosensory characteristics of strong-aroma type Baijiu from different regions using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry and descriptive sensory analysis. Food Chem. 2020, 331, 127335.
25. Etaio, I.; Elortondo, F.J.P.; Albisu, M.; Gaston, E.; Ojeda, M.; Schlich, P. Development of a quantitative sensory method for the description of young red wines from Rioja Alavesa. J. Sens. Stud. 2008, 23, 631-655.
26. Tomic, O.; Luciano, G.; Nilsen, A.; Hyldig, G.; Lorensen, K.; Naes, T. Analysing sensory panel performance in a proficiency test using the PanelCheck software. Eur. Food Res. Technol. 2010, 230, 497-511.
27. Krop, E.M.; Hetherington, M.M.; Holmes, M.; Miquel, S.; Sarkar, A. On relating rheology and oral tribology to sensory properties in hydrogels. Food Hydrocolloids 2019, 88, 101-113.
28. Miyazawa, T.; Gallagher, M.; Preti, G.; Wise, P.M. Synergistic mixture interactions in detection of perithreshold odors by humans. Chem. Senses 2008, 33, 363-369.
29. Wei, J.; Du, H.; Zhang, H.; Nie, Y.; Xu, Y. Mannitol and erythritol reduce the ethanol yield during Chinese Baijiu production. Int. J. Food Microbiol. 2021, 337, 108933.
30. Scalone, G.L.L.; Lamichhane, P.; Cucu, T.; De Kimpe, N.; De Meulenaer, B. Impact of different enzymatic hydrolysates of whey protein on the formation of pyrazines in Maillard model systems. Food Chem. 2019, 278, 533-544.
31. Rajini, K.S.; Aparna, P.; Sasikala, C.; Ramana, C.V. Microbial metabolism of pyrazines. Crit. Rev. Microbiol. 2011, 37, 99-112.
32. Zhu, B.F.; Xu, Y.; Fan, W.L. High-yield fermentative preparation of tetramethylpyrazine by Bacillus sp using an endogenous precursor approach. J. Ind. Microbiol. Biotechnol. 2010, 37, 179-186.
33. Zheng, Y.; Sun, B.; Zhao, M.; Zheng, F.; Huang, M.; Sun, J.; Sun, X.; Li, H. Characterization of the Key Odorants in Chinese Zhima Aroma-Type Baijiu by Gas Chromatography-Olfactometry, Quantitative Measurements, Aroma Recombination, and Omission Studies. J. Agric. Food. Chem. 2016, 64, 5367-5374.
34. Niu, Y.; Chen, X.; Xiao, Z.; Ma, N.; Zhu, J. Characterization of aroma-active compounds in three Chinese Moutai liquors by gas chromatography-olfactometry, gas chromatography-mass spectrometry and sensory evaluation. Nat. Prod. Res. 2016, 31, 938-944.
35. Liao, M.J.; Zhao, Y.Y.; Xu, Y.R.; Gong, C.T.; Jiao, S.S. Effects of hot air-assisted radio frequency roasting on nutritional quality and aroma composition of cashew nut kernels. LWT-Food Sci. Technol. 2019, 116, 108551.
36. Baker, G.L.; Cornell, J.A.; Gorbet, D.W.; O'Keefe, S.F.; Sims, C.A.; Talcott, S.T. Determination of pyrazine and flavor variations in peanut genotypes during roasting. J. Food Sci. 2003, 68, 394-400.
37. ISO-8586:2012. Sensory Analysis-General Guidelines for the Selection, Training and Monitoring of Selected Assessors and Expert Sensory Assessors; International Organization for Standardization (ISO): Geneva, Switzerland, 2012.
38. Guadagni, D.G.; Buttery, R.G.; Okano, S.; Burr, H.K. Additive effect of sub-threshold concentrations of some organic compounds associated with food aromas. Nature 1963, 200, 1288-1289.
Yan Yan
1,2,
Shuang Chen
1,
Yao Nie
1,* and
Yan Xu
1,*
1State Key Laboratory of Food Science & Technology, Key Laboratory of Industrial Biotechnology of Ministry of Education & School of Biotechnology, Jiangnan University, Wuxi 214100, China
2School of Liquor and Food Engineering, Guizhou University, Guiyang 550025, China
*Authors to whom correspondence should be addressed.
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