A model to reduce tyrosine crystallization in Chinese fermented soybean curd by adjusting NaCl, ethanol and temperature during fermentation

Abstract

Abstract Objectives White spots, mainly consisting of tyrosine, refer to small white particles that exist on the surface of mature Chinese fermented soybean curd or in the fermentation broth and have affected the appearance of Chinese fermented soybean curd. Materials and Methods The study determined the composition of the white spots throughout mass spectrometry and high-performance liquid chromatography and investigated the relationship between tyrosine content, amino acid nitrogen content, depth of the proteolysis index and protease activity to interpret the mechanism of white spot formation during fermentation. Results In this study, the results confirm that tyrosine accounts for 78.22% of the white spots. Excessive tyrosine content can promote the formation of white spots during fermentation. Free tyrosine content, amino acid nitrogen content, depth of the proteolysis index and protease activity during the fermentation process increased during fermentation. Correlation analysis results show that free tyrosine content was positively correlated with amino acid nitrogen content, depth of the proteolysis index and protease activity, which showed that the production of tyrosine is related to the degree of proteolysis. Solubility studies show that high concentrations of NaCl and ethanol affect the production of tyrosine and reduce its solubility, while the increase in temperature increases the solubility of tyrosine. Taking NaCl, ethanol and temperature as influencing factors, a mathematical model of tyrosine solubility was established. Conclusion This study lays the groundwork for understanding the mechanism of white spot formation during Chinese fermented soybean curd fermentation and provides solutions for controlling white spot formation.