Effect of Fermentation Combined with Dry and Wet Process on the Basic Characteristics of Soybean Flour

Lactobacillus delbrueckii b8 fermentation combined with dry and wet processing methods was used to prepare soybean flour in this study, aiming to investigate the effects of fermentation on the main nutritional components, anti-nutritional factors, and the contents of total phenolics, total flavonoids, and isoflavones, antioxidant capacity, and volatile flavor compounds of soybean flour. The results showed that the protein and fat content in soybean flour was not reduced by fermentation, but the activity of urease and trypsin inhibitors was effectively inhibited, and phytic acid content was reduced. Furthermore, the total phenolic and total flavonoid contents in both wet and dry processed soybean flour were significantly increased by fermentation, with values of 2.48 mg GAE/g and 2.30 mg RE/g for wet-processed flour, and 1.82 mg GAE/g and 1.43 mg RE/g for dry-processed flour, respectively. The hydrolysis of isoflavone glycosides into more bioactive aglycones was also promoted by fermentation, with glycoside hydrolysis rates and aglycone contents in wet-processed and dry-processed soybean flour being 96.57% and 2163.39 mg/kg, and 94.01% and 3561.46 mg/kg, respectively. The scavenging rates of hydroxyl radicals and superoxide anions in soybean flour prepared by fermentation combined with dry processing and wet processing increased by 1.96 times and 11.75 times, and 2.14 times and 2.26 times, respectively. A total of 35 volatile compounds were identified using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS), revealing that the relative content of alcohols, esters, pyrazines, phenols, and organic acids was increased by fermentation, while the levels of compounds responsible for the beany odor in soybeans, such as pentanal, hexanal, and pentanol, were reduced. However, the content of 2-pentylfuran in soybean flour prepared by fermentation combined with the wet method increased from 6.90% to 10.91%, without a significant decrease. In conclusion, soybean isoflavones are effectively converted into more bioactive aglycones by Lactobacillus delbrueckii b8 fermentation, the nutritional value of soybean flour is enhanced, and its flavor characteristics are improved.