Correlation of antioxidant activity with polyphenolic content in soybeans

Abstract

Twenty soybean cultivars were analysed for their antioxidant activity and content of isoflavones, flavonoids and total polyphenolics. After extraction with methanol-water (8:2, v/v), isoflavones were determined by C18 reversed phase high-performance liquid chromatography coupled with photodiode array detector. Flavonoid and total polyphenolic content contents were established spectrophotometrically. Antioxidant activities of soybean extracts were measured using 2,2-diphenyl-1-pycril-hydrazil free radical method. Cultivars most abundant in polyphenolic compounds expressed the highest DPPH-radicals scavenging activities. Genotypes with low content of total polyphenolics, expressed approximately half of the activity of polyphenolic-rich genotypes. Correlation between total polyphenolic content and antioxidant activity was found to be statistically significant (p<0.01). At the same time, no correlation was found between content of isoflavones and antioxidant activity or content of flavonoids and antioxidant activity. The results suggested that total polyphenolic content could be considered a useful marker of antioxidant activity in soybeans and, beside isoflavone content, one of the criterions for identifying the cultivars with better health-promoting characteristics.