FORMATION OF TASTE AND ODOR COMPOUNDS DURING PREPARATION OF DOUCHIBA, A CHINESE TRADITIONAL SOY-FERMENTED APPETIZER

Abstract

Douchiba (DCB), a Chinese traditional soy-fermented appetizer, is abundantly produced and widely consumed in Guizhou province of southwest China. In this study, an analysis of free amino acid (FAA) profiles, low-molecular weight peptide fractions (LMWPFs), hydrophobic bitter peptide fractions (HBPFs) and volatile compounds was conducted to understand the changes in taste and odor compounds of DCB during five consecutive manufacturing stages: steamed soybean (SS), 5-day incubated Koji (Koji), 6-month fermented Douchi, semifinished Douchiba (sm-DCB) and 6-month ripened finished Douchiba (DCB). The total free amino acids (TFAAs) increased significantly from SS to DCB by about 11 times and amounted to 20.1% of the crude protein. Arg, Glu, Phe, Leu and Lys were the most abundant FAA at the end of ripening, and were 64.6% of TFAA. The most abundant taste active FAA classes were the bitter FAA, representing eight- and threefold increases over sweet and MSG-like FAA, respectively. The final values of all bitter and monosodium glutamate-like (MSG-like) FAA at DCB stage were significantly higher than their respective thresholds. The of oligopeptides (500∼1000 Da) accounted for 13.8 and 2.5% of LMWPF and HBPF, respectively. However, the taste of DCB was predominated by saltiness, followed by moderate umami taste and slight bitterness, likely as a result of the and interaction among different taste components. A total of 122 volatile compounds were identified, including alcohols, acids, esters, aldehydes, ketones, phenols, sulfur-containing compounds, heterocyclic compounds, alkines, benzenes and spice aromatics. The subtle aroma of the finished DCB seemed to depend not only on particular key compounds but also on a critical balance or a weighted concentration ratio of 60 compounds. These volatile compounds, mainly derived from lipid oxidation, amino acid degradation, carbohydrate fermentation, Maillard reaction and Strecker degradation during the microbial metabolism, enzymatic catalysis and spontaneous reactions.