Purification of Water Soluble Antioxidant Compounds from Okara and its Characterization

Abstract

Major antioxidant substance in Okara (by-product of tofu manufacturing) was investigated. Each fraction of hexane soluble fraction (HSF), ethanol soluble fraction (ESF) and water soluble fraction (WSF) were prepared from Okara. In a linoleic acid system, antioxidant activity of WSF was stronger than that of HSF or ESF containing a large quantity of substances with antioxidant activity originated from soybean, such as saponins, isoflavones and tocopherols. The antioxidant fraction (WSF-S-A) was purified from WSF by dialysis and DOWEX 50 W X-2 column chromatography. The contents of total peptides containing amino acids in WSF-S-A was above 91 per cent. The peptides with molecular weight in the range of 800 to 1400 showed strong antioxidant activity. Methionine and histidine with antioxidant activity were present in 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°C for 2h in 10 per cent of saline solution.