Antioxidant activities and changes in trans-resveratrol and indigestible oligosaccharides according to fermentation periods in Cheonggukjang

Abstract

Cheonggukjang was manufactured using three different kinds of soybeans, after which changes in the content of phytoalexins such as trans-resveratrol (3,5,4'-trihydroxy-trans-stilbene) were measured. Along with phytoalexins, changes in the content of functional oligosaccharides such as stachyose and raffinose were also measured, and the corresponding antioxidant activities were studied. The content of trans-resveratrol was found to be higher in fermented beans than in raw beans. Generally, the content was higher as the fermentation period increased. After 48 hours of fermentation, the contents of trans-resveratrol were 50.06±0.82, 39.04±0.49, and 34.00±0.54 μg/g (Nulchan, Daewon, and Taekwang), respectively, which is 4 times higher than the contents of raw beans. The contents of stachyose were 10.84±0.42~13.05±0.13 mg/g in raw beans, 11.37±0.03~12.05±0.52 mg/g immediately after boiling, and 0.16±0.01~0.33±0.02 mg/g after 12 hours of fermentation, which is a 97% decrease from those of raw beans. After 24 hours of fermentation, no amount of stachyose was detected. The contents of raffinose were the lowest in raw beans at 2.66±0.09~3.54±0.05 mg/g, but they increased 3~4 times between boiling and 24 hours of fermentation to 10.61±0.16~12.66±0.17 mg/g. However, raffinose content tended to decrease to 8.28±0.17~11.83±0.44 mg/g after 48 hours of fermentation. From FRAP, DPPH, and ABTS assays, antioxidant activities according to fermentation period of Cheonggukjang were rather low in boiled soybeans compare to raw soybeans. However, the activities were higher as the fermentation period increased. The antioxidant activity of trans-resveratrol showed an RC50 value of 4.71±0.36~8.46±0.05 μg/mL from the DPPH, ABTS, and FRAP assays. This could be partly due to the significant increase in trans-resveratrol according to fermentation periods. However, changes in functional oligosaccharides (stachyose and raffinose) during fermentation appear to not be related to the antioxidant effects of Cheonggukjang.