† These authors contributed equally to this work. Abstract The concentration and distribution of isoflavones in 19 representative commercial douchi products and their acetylcholinesterase (AChE) inhibitory activity were investigated in this study. Isoflavone aglycones are the predominant isoflavone forms in Chinese commercial douchi samples. The total content of isoflavones in douchi extracts were observed from 24 to 1,471 μg/g (dry matter). Results indicated that Aspergillus-type douchi had

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... e isoflavone aglycones content than that of Mucor-type and Bacillus-type douchi. Nineteen samples also showed various extents of AChE inhibitory activity. The IC 50 value of AChE inhibitory activities of douchi extracts ranged from 0.040 to 2.319 mg/mL. Aspergillus-type douchi extracts exhibited significantly higher AChE inhibitory activity than that of Mucor-type and Bacillus-type douchi. Some brands of douchi which have low contents of isoflavone aglycones showed much lower inhibitory activity. However, high inhibitory activities did not mean high isoflavone content, maybe some other substances contributed to the inhibition which should be further studied.