Evolution of Proteolytic Tasty Components During Preparation of Douchiba, a Traditional Chinese Soy-Fermented Appetizer

Douchiba, a traditional Chinese soy-fermented appetizer, has been abundantly produced and widely consumed in Guizhou province of Southwest China. In this study, analysis of low-molecular mass peptide fractions, hydrophobic bitter peptide fractions, and free amino acid (FAA) profiles was conducted to understand the changes in tasty components of douchiba during five consecutive stages of its manufacture: steamed soybean (SS), 5-day incubated douchi qu (DQ), 6-month fermented douchi (DC), semi-finished douchiba (sm-DCB), and 6-month ripened douchiba as a finished product (DCB). Results indicated that the ratio of potentially taste-active oligopeptides (500–1000 Da) accounted for 13.98 and 2.54 % of low-molecular mass peptide fractions and hydrophobic bitter peptide fractions at DCB stage, respectively. The evolution patterns of total free amino acids (TFAA) increased significantly (p<0.05) from SS to DCB by about 11 times and amounted to 20.14 % of crude protein. At the end of the ripening period (6 months), Arg, Glu, Phe, Leu, and Lys were the most abundant FAA, adding up to 64.37 % of TFAA. The most abundant tasty FAA class was bitter FAA, about 8and 3-fold higher than the content of sweet and monosodium glutamate (MSG)-like FAA, respectively. The final values of all bitter and MSG-like FAA at DCB stage were significantly higher than their respective thresholds. However, the final characteristic taste of douchiba was predominated by saltiness, followed by moderate umami taste and slight bitterness, possibly as a result of the balance and interaction among different tasty components.