Identification and analysis of the flavor characteristics of unfermented stinky tofu brine during fermentation using SPME-GC-MS, e-nose, and sensory evaluation

The volatile flavor components of stinky tofu are an important measure of quality and play a vital role in its flavor. Researching the flavor characteristics of stinky tofu will improve product quality, production processes, and safety controls. Solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS), electronic nose (e-nose), and sensory evaluation were used to identify and analyze the flavor characteristics of stinky tofu brine during fermentation. Analysis showed that the variation in the volatile compound content of brines was similar to that observed in the microbial growth curve, and fermentation process of brine has a decomposition-inhibition effect on some unpleasant and characteristic odor. Fifty-five types of volatile compounds were identified and quantified in brines during fermentation; acids, alkenes, alcohols, ketones, alkanes, amines, esters, naphthalene, sulfur compound, phenol, aldehyde, ether, and pyridine were the important components and six primary components were analyzed by principle component analysis (PCA). 5-(1,5-dimethy-4-hexenyl)-2-methyl-1,3-cyclohexadiene (0.9785%), with a characteristic and prominent odor of ginger, had the highest average content during fermentation. E-nose detection results showed that during fermentation, the flavor component types of unfermented stinky tofu brine were similar to the variation of volatile components observed via GC-MS. The 12 brines were divided into four categories. Sensory evaluation results showed that the overall differences between the 12 brines were generally small. Fried stinky tofu from March and May obtained the highest sensory evaluation scores. The correlation of GC-MS, e-nose, and sensory evaluation was analyzed by multiple regression analysis to obtain the main characteristic volatile compounds in unfermented stinky tofu brine.