Identification And Formation Of Characteristic Aroma Compounds From Pixian Soybean Paste

Pixian soybean paste is product of Chinese geographical indication and essential seasoning in Sichuan food. This research focused on volatile flavor compounds of the grand one traditional Pixian soybean pastes. The volatiles and characteristic aroma compounds from the grand one traditional Pixian soybean pastes were identified by SPME-GC-MS and GC-O technologies. The changes of characteristic aroma compounds formed during the pastes fermentation process were discussed by Partial Least Squares(PLS) regression analysis and electronic nose(E-nose).The volatile flavor compounds from ten grand one traditional Pixian soybean pastes were extracted by SPME, isolated and identified by GC-MS. Eight grand one traditional Pixian soybean pastes were selected to establish a chromatographic fingerprint by cluster analysis.The reliability of chromatographic fingerprint was assessed according to similarity. The results indicated that the proposed fingerprint could effectively evaluate unqulified sample and qualified sample. In addition, three other fermented bean products as controls, these three samples could also be accurately distinguished with grand one traditional Pixian soybean pastes by principal component analysis(PCA). The results showed that the proposed fingerprint could effectively evaluate the deviation of grand one traditional Pixian soybean pastes and other fermented bean products.The volatile flavor compounds of one kind of grand one traditional Pixian soybean paste extracted by SPME were investigated by MS hyphenated to the GC-Olfactometry system with two olfactometric methods: detection frequency method and aroma extract dilution analysis. A total of 73 compounds were identified in this grand one traditional Pixian soybean paste. 29 volatile flavor components were detected and 27 identified by detection frequency method.And 19 volatile flavor components were detected by aroma extract dilution analysis. The results showed that the characteristic aroma compounds of grand one Pixian soybean paste were 3-methylbutyraldehyde, ethyl-2-methylbutyrate, ethyl isovalerate, 3-(methylthio)propionaldehyde, phenylacetaldehyde, tetramethylpyrazine, linalool, phenethyl alcohol,2-ethylphenol and 4-ethylguaiacol.The volatile flavor compounds in samples of grand one traditional Pixian soybean paste from different fermentation time(1, 2, 3, 4, 6, 9, 12 months) were analyzed by SPME-GC-MS in order to explore the formation rule of characteristic aroma compounds. The results showed that a total of 104 volatile compounds were identified by GC-MS in the headspace of at least one processing stage sample, which could be grouped into classes of esters, alcohols,aldehydes, heterocyclic compounds, ketones, acids, phenols, S-containing compounds, ethers,etc. As the fermatation continued, the kinds of flavor compounds increased gradually and theheterocyclic compounds were the major point of growth. The content of phenylacetaldehyde,linalool and phenethyl alcohol remained unchanged basically during fermatation. Meanwhile,3-methylbutyraldehyde, ethyl-2-methylbutyrate, ethyl isovalerate, 3-(methylthio)propionaldehyde, tetramethylpyrazine, 2-ethylphenol and 4-ethylguaiacol were increasing on pre-fermentation and then gradually reduced on post-fermentation. The E-nose and PLS analysis couldn’t distinguish the samples of primary fermentation well. So both the whole flavor and the kinds or content of volatile flavor compounds in the samples of changed during fermentation,its flavor was formed gradually.