Comparison of Angiotensin I-Converting Enzyme Inhibitor Activities of Pre-Fermented Douchi (a Chinese Traditional Fermented Soybean Food) Started with Various Cultures

Abstract

Pre-fermented douchi, also called douchi qu, is a salt-free semi-product of a Chinese traditional fermented soybean food (douchi), which is classified into three types, that is, Aspergillus-type, Mucor-type and Bacteria-type. In this work, angiotensin I-converting enzyme (ACE) inhibitor activities of douchi qu started by different types of cultures were compared. It was found that douchi qu fermented with Aspergillus oryzae, Mucor wutungkiao, Bacillus subtilis natto and Bacillus subtilis B1 showed significantly different (p < 0.05) ACE inhibitor activities with decreasing IC50 values of 0.4991, 0.3535, 0.2294 and 0.0901 mg/mL, respectively. Twenty-five fractions were separated by gel filtration chromatography and the strongest ACE inhibitor activity was observed in a fraction with high contents of glycine, lysine and arginine from B. subtilis B1 fermented sample. Results indicated that the type of starter cultures affected significantly the production of ACE inhibitors in douchi qu, and that B. subtilis B1 could be potential candidate as an inoculant to prepare fermented soybeans with strong ACE inhibitor activity in functional food industry.