Extracts from Fermented Black Soybean Milk Exhibit Antioxidant and Cytotoxic Activities

Kuan-Chen Cheng, Jiun-Tsai Lin and Wen-Hsiung Liu*

Institute of Microbiology and Biochemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, 106 Taipei, Taiwan, ROC

Article history:
Received July 27, 2009
Accepted November 27, 2010

Key words:
black soybean, Rhizopus oligosporous, antioxidant activity, cytotoxic activity, isoflavone

Summary:
In this study, ethanol extracts from 2-day fermented black soybean milk (FBE) by immobilized Rhizopus oligosporus NTU5 have been evaluated for both antioxidant and cytotoxic activities. The results reveal that a 2-day FBE had strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging effect (76 %). The extracts were further fractionated by silica gel column chromatography and an unknown compound, FBE5-A, was obtained, which exhibited strong antioxidant activity. IC₅₀ of the DPPH scavenging effect of FBE5-A was 7.5 μg/mL, which is stronger than a commonly used antioxidant, vitamin E (α-tocopherol; 17.4 μg/mL), and similar to vitamin C (ascorbic acid; 7.6 μg/mL). The cytotoxic test demonstrated that extracts of 2-day fermented broth exhibited selective cytotoxic activity towards human carcinoma cells, Hep 3B (IC₅₀=150.2 μg/mL), and did not affect normal human lung fibroblasts, MRC-5 (p<0.05). The results indicate the potential applications of fermented black soybean milk as functional food, pharmaceutical or cancer therapy formula.

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