Journal
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
Volume 51, Issue 15, Pages 4240-4246Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jf034064f
Keywords
red yeast rice; red koji; polyphenols; Folin-Ciocalteu; vanillin-HCl assay; antioxidants; free radical scavenging activity; tyrosinase; tyrosinase inhibitor; DL-DOPA
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Red koji has been recognized as a cholesterol-lowering diet supplement because of it contains fungi metabolites, monacolins, which reduce cholesterol synthesis by inhibiting HMG-CoA reductase. In this study, water extracts of red koji were loaded onto a C-18 cartridge, and the acetonitrile eluate was collected as test fraction. Red koji water extracts and its C-18 cartridge acetonitrile eluent had total phenols concentrations of 5.57 and 1.89 mg/g of red koji and condensed tannins concentrations of 2.71 and 1.20 mg/g of red koji, respectively. Both exhibited an antioxidant activity and an inhibitory activity to mushroom tyrosinase. The higher antioxidant activity of the red koji acetonitrile eluent was due to the existence of a high percentage of condensed tannins. The results from the kinetic study for inhibition of mushroom tyrosinase by red koji extracts showed that the compounds in the extracts competitively inhibited the oxidation of tyrosine catalyzed by mushroom tyrosinase with an ID50 Of 5.57 mg/mL.
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