Abstract: In this study, ultra-high performance liquid chromatography-quadrupole-time-of-flight-mass spectrometry (UPLC-Q-TOF-MS) combined with principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) was used to analyze the changes of metabolites in high-salt liquid-state soy sauce during the fermentation process. The results showed that the number and the total peak area of metabolites on day 90 were 1.47 and 6.57 times as high as those on day 1, respectively. During the fermentation process, a total of 155 compounds were identified, 34 of which showed significant difference among fermentation times (variable importance in the projection, VIP > 1), including ten amino acid derivatives, nine fatty acids, five isoflavones, three esters, two organic acids and two alkaloids. The percentages of the peak areas of amino acid derivatives, isoflavones and alkaloids relative to the total peak areas of all differential metabolites increased from 0.44%, 6.82% and 0.02% to 20.11%, 14.88% and 10.81%, respectively. These compounds could be considered as key different metabolites during soy sauce fermentation. Our results may be meaningful for understanding the change of metabolites during soy sauce fermentation and for quality control.

Key words: high-salt liquid-state soy sauce; ultra-high performance liquid chromatography-quadrupole-time-of-flight-mass spectrometry; amino acid derivates; isoflavones; multivariate analysis