Metabolomic and proteomic profiling reveals the formation mechanism of volatile flavor in egg whites during fermentation by Streptococcus thermophilus

In this study, the flavor of egg whites was significantly improved by lactic acid fermentation, and the metabolic networks of metabolites, volatile compounds, and enzymes were established using gas chromatography–mass spectrometry, metabolomic, and proteomic. Results indicate that among ten types of common lactic acid bacteria , Streptococcus thermophilus endowed egg white with the most pleasant flavor through increasing aldehydes, ketones, alcohols, esters, terpenoids, and aromatic compounds. Amino acid catabolism was the predominant pathway for generating most aldehydes, alcohols, acids, and esters. The changes in the organic acids and derivatives (mainly amino acids, peptides, and analogues) concentration during fermentation are attributed to the hydrolysis of egg white proteins by proteinases and peptidases, and the regulation of enzymes involved in amino acid biosynthesis and other reactions. This study provides a valuable reference for future investigations focusing on regulating the flavor release of egg whites. • Among 10 bacteria, S. thermophilus fermentation offered the best aroma for egg white. • Fermented egg white had more aldehydes, ketones, alcohols, terpenoids, and aromatics. • During fermentation, amino acid catabolism generated most of the volatile compounds. • The activity of multiple amino acid biosynthesis increased during 6 h-fermentation. • The glycolysis pathway was inhibited during 6 h of fermentation.