Impacts of preliminary isolation and enzymatic treatment on antioxidant activities of glycosylated whey protein isolate with inulin

The effects of trichloroacetic acid (TCA), ethanol, ultrafiltration and enzymatic hydrolysis (pepsin and trypsin) on antioxidant activities of a glycosylated whey protein isolate (WPI)–inulin system were investigated. The antioxidant capacity of glycosylated WPI–inulin initially increased and then decreased after the TCA treatment. Correspondingly, the antioxidant activity of glycosylated WPI–inulin reached the highest level at a TCA concentration of 6% and an ethanol to sample ratio of 7:1. DPPH radical scavenging ability in fractions of glycosylated WPI–inulin > 50 kDa was enhanced about 24% after separation by ultrafiltration, compared with that of untreated glycosylated WPI–inulin. DPPH radical scavenging ability and ferrous reducing power of glycosylated WPI–inulin were about 32% and 15% higher than those of non-hydrolysis-treated glycosylated WPI–inulin after pepsin and trypsin hydrolysis. Chromatography revealed that more peptide molecules were produced by glycosylated WPI–inulin than by heated WPI. Therefore, TCA, ethanol, ultrafiltration, and enzymatic hydrolysis are effective ways to enhance the antioxidant activities of glycosylated WPI–inulin.