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

Likang Qin^1,2 and Xiaolin Ding¹*

¹Key Laboratory of Food Science and Safety, Ministry of Education, Southern Yangtze University, Wuxi, 214036 Jiangsu Province, PR China
²Department of Food Quality and Safety, School of Life Science, Guizhou University, Guiyang, 550025 Guizhou Province, PR China

Article history:
Received November 28, 2005
Accepted March 1, 2006

Key words:
douchiba, peptides, free amino acids, tasty components

Summary:
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 8- and 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.

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