Non-volatile organic acids and amino acids are important flavor compounds in Pixian broad-bean paste, which is a traditional Chinese seasoning product. In this study, non-volatile organic acids, formed in the broad-bean paste due to the metabolism of large molecular compounds, are qualitatively and quantitatively determined by high-performance liquid chromatography (HPLC). Amino acids, mainly produced by hydrolysis of soybean proteins, were determined by the amino acid automatic analyzer. Results indicated that seven common organic acids and eighteen common amino acids were found in six Pixian broad-bean paste samples. The content of citric acid was found to be the highest in each sample, between 4.1 mg/g to 6.3 mg/g, and malic acid were between 2.1 mg/g to 3.6 mg/g ranked as the second. Moreover, fumaric acid was first detected in fermented bean pastes albeit with a low content. For amino acids, savory with lower sour taste including glutamine (Gln), glutamic acid (Glu), aspartic acid (Asp) and asparagines (Asn) were the most abundant, noted to be 6.5 mg/g, 4.0 mg/g, 6.4 mg/g, 4.9 mg/g, 6.2 mg/g and 10.2 mg/g, and bitter taste amino acids followed. More importantly, as important flavor materials in Pixian broad-bean paste, these two groups of substances are expected to be used to evaluate and represent the flavor quality of Pixian broad-bean paste. Moreover, the results revealed that citric acid, glutamic acid, methionine and proline were the most important flavor compounds. These findings are agreat contribution for evaluating the quality and further assessment of Pixian broad-bean paste.

The odor-active compounds of Pixian Douban (PXDB) were identified by means of gas chromatography-olfactometry (GC-O) coupled with mass spectrometry (MS), and then the key odor components were figured out by odor activity values (OAVs) and aroma extract dilution analysis (AEDA) using three different methods. The 21 odor active areas were detected with flavor dilution (FD) factor ranging from 2 to 16, with 3-(methylthio) propionaldehyde, 2, 5-dimethyl pyrazine, 4-ethyl-2-methoxyphenol, and 2-ethylphenol yielding the highest FD factors. These odorants were then quantitated by application of external standard under selected ion monitoring (SIM) mode of MS, and their OAVs were calculated based on the odor thresholds. The highest OAV was obtained for 3-methylbutanal (malty, 614.89), followed by phenylacetaldehyde (honey-like, sweet, 94.34), four compounds obtained OAVs ≥10, and other eight compounds obtained OAVs between 1 and 10. All of them likely contributed to the aroma of PXDB. A reconstitution model containing 14 odorants (OAVs ≥1& FD>5) was able to mimic the aroma style of the original PXDB. In addition, the application of omission test was used to investigate the effects of the key odor compounds on the whole odor profile of PXDB, and 11 odorants detected were significantly different among the samples.

Pixian broad-bean paste (PBBP) is a famous fermented condiment in China, which may produce abundant flavor peptides during the fermentation process. Herein, the flavor peptides from fermented broad-bean (FB) were separated and identified via ethanol precipitation, macroporous resin, and ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS/MS) methods. The results showed that there were fifteen novel flavor peptides in FB. Among them, six peptides (i.e. ALDELGT, AELTPEP, SAALQAG, SFEAVEAAPT, EQDNDGNNIFSGFKR, QTFNTEEDTAK, and DAPASGN) were perceived umami with threshold values ranging from 0.76 to 1.84 mmol L⁻¹. And they had both salty-enhancing and umami-enhancing abilities. Meanwhile, novel peptides (i.e. GGLRIINPEGQQ, SIITPPERQ, GGLSIITPPERQA, GGLRIINPEG, SIITPPER, RIINPEGQQ, DALNVNRHIV, and LPKILLLQLV) were perceived bitter with threshold values ranging from 0.56 to 2.89 mmol L⁻¹. And the monosodium glutamate (MSG) solution had a certain masking effect on bitter peptides. GFSSEFLA showed a strong sweet taste. From peptide sequence analysis, it was found that Aspergillus oryzae and broad-bean were important taste-active sources of the flavor peptides in FB. Besides, the synthetic peptides showed a much better sensory taste than the mixtures of the corresponding amino acids. It indicated that peptides might play an important role in deciding the taste of FB. Significantly, it is the first time that the isolated flavor peptides were identified from FB.

Broad bean fermentation is of vital importance in PixianDouban (PXDB) production, as well as a key process for microorganisms to degrade protein, which lays the foundation for the formation of PXDB flavor. In this study, two fungi and bacteria were screened, and their morphology, molecular biology, growth, and enzyme production characteristics were analyzed, and then they were applied to the broad bean fermentation simulation system. The protein, peptide, amino acid, amino nitrogen, and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) in the system were evaluated. The results showed that the four microorganisms were Aspergillus oryzae, Aspergillus jensenii, Staphylococcus gallinarum, and Enterobacter hormaeche. Aspergillus oryzae had the highest protease activity at pH 7.0, while the other three strains had better enzyme activity stability under neutral acidic conditions. And the total protein (F1 and F2 were 18.32 g/100 g, 19.15 g/100 g, respectively), peptides (11.79 ± 0.04 mg/g and 12.06 ± 0.04 mg/g), and amino acids (55.12 ± 2.78 mg/g and 54.11 ± 1.97 mg/g) of the fungus experimental groups (F) were higher than the bacterial experimental groups (B). In addition, the enzyme system produced by fungi exhibited a stronger ability for albumin (20 kDa) and glutenin (<30 kDa) deterioration in neutral conditions, while the bacterial enzyme system was more efficient in degrading albumin (<30 kDa) and glutenin (20–30 kDa) in acidic conditions, as indicated by SDS‐PAGE. These findings showed that both bacteria and fungi played an important role in the degradation of protein in different fermentation stages of broad bean fermentation.Practical applications: There is a lack of comprehensive understanding of the protein composition and protein degradation mechanism of broad beans in the fermentation stage of PXDB. This research work explored the differences in the degradation of PXDB fermented protein by different microorganisms, and provided a theoretical basis for optimizing the production of PXDB and improving the quality of PXDB.