Purification of water soluble antioxidant compounds from Okara and its characterization

Major antioxidant substance in Okara (by-product of tofu manufacturing) was investigated. Each fraction of hexane soluble fraction (HSF), ethanol solu ble fraction (ESF) and water soluble fraction (WSF) were prepared from Okar a. In a linoleic acid system, antioxidant activity of'lVSF was stronger tha n that of HSF or ESF containing a large quantity of substances with antioxi dant activity originated from soybean, such as saponins, isoflavones and to copherols. The antioxidant fraction (WSF-S-A) was purified from WSF by dial ysis and DOWEX 50 W X-2 column chromatography. The contents of total peptid es containing amino acids in WSF-S-A was above 91 per cent. The peptides wi th molecular weight in the range of 800 to 1 400 showed strong antioxidant activity. Methionine and histidine with antioxidant activity were present i n antioxidant peptides as a part of constituent amino acid. The antioxidant activity of WSF-S-A was comparatively stable in the range of pH 5.0 to 7.0 and completely stable even after heating at 100 degrees C for 2 h in 10 pe r cent of saline solution.