Tracing the change of the volatile compounds of soy sauce at different fermentation times by PTR-TOF-MS, E-nose and GC–MS

Proton-transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS), combined with electronic nose (E-nose), was first used to track the change of volatile organic compounds (VOCs) in soy sauce in this study. The results showed that 163 VOCs with different mass numbers were identified. Based on the differences in VOCs, the entire fermentation cycle was divided into four stages (0D and 15D; 30D-75D; 90D; 105D-120D). The key stage of aroma formation was on day 90, when the VOC content reached its peak. It was clear that the key feature differential component was nonanal and phenethyl acetate by partial least squares discriminant analysis model, which showed significant correlation with the fermentation time. Moreover, the Quadratic Discriminant Analysis and Linear Discriminant Analysis models can accurately predict the fermentation cycle of soy sauce. The results of study demonstrated the potential of PTR-TOF-MS for comprehensive online monitoring and distinguishing of VOCs change during soy sauce fermentation.