Comparisons of flavonoids and anti-oxidative activities in seed coat, embryonic axis and cotyledon of black soybeans

Flavonoids contents, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activities and the ferric-reducing antioxidant power (FRAP) were compared in three black soybean varieties CRWD, Tainan 3 and Tainan 5. Varietal differences in antioxidant contents existed among the tested varieties. Variety CRWD accumulated more total phenolics (7.49 mg g−1) and isoflavones (1.77 mg g−1) than varieties Tainan 3 (7.05 mg g−1 total phenolics and 1.58 mg g−1 isoflavones) and Tainan 5 (4.38 mg g−1 total phenolics and 0.63 mg g−1 isoflavones). CRWD also accumulated more proanthocyanidins in seed coat than Tainan 3 and Tainan 5. CRWD also demonstrated greater DPPH and FRAP activities than the other two cultivars. Stepwise regressions indicated that both DPPH and FRAP activities were correlated well with the total contents of phenolics and flavonoids, with total phenolics being the most important anti-oxidative factor. The present results indicate that CRWD has greater anti-oxidative responses than Tainan 3 or Tainan 5, and is useful in functional food and other applications.