Comparison and application of the extraction method for the determination of enzymatic profiles in matured soybean koji

In this study, two methods of extracting crude enzymes from soy sauce koji were compared to investigate the effect of replacing the buffer extraction with distilled water extraction by measuring the enzyme activity. Results showed the enzyme activities of the two extracts in each koji sample were not significant differences. The stability of the different enzymes in the extracts varied. Acid protease, β-glucosidase and cellulase activities showed the best stability during the storage. Neutral protease, glucoamylase and aminopeptidase were moderately stable and their activities needed to be determined within 3 d of extract preparation, while xylanase activity was the least stable, decreasing by 40% on the second day of storage. Therefore, the recommended procedure for the analysis of koji enzyme profiles was as follows, xylanase was determined immediately after distilled water extraction, and then all other enzyme activity analyses need to be completed within 3 d to ensure the validity of enzyme analysis. This method was applied to the enzymatic analysis of 7 kojis made by different strains of Aspergillus oryzae, and to explore the association between the enzyme profile and the taste characteristics of seven fermented soy sauce. The results showed proteases were correlated with sour and richness, while carbohydrate-degrading enzymes were relatively more relevant to umami taste.