Preparation and characterisation of isoflavone aglycone-rich calcium-binding soy protein hydrolysates

Isoflavone aglycone-rich calcium-binding soy protein hydrolysates were prepared by subcritical water treatment and subsequent protease hydrolysis. Contaminated -glucosidase in the Protease M preparation could effectively convert glycosides into aglycones. Compared with Alcalase hydrolysates, Protease M hydrolysates exhibited higher molecular weight (>5000Da) and more hydrophobic characteristics because of its weaker proteolytic activity. The antioxidant activity of Protease M hydrolysates was obviously improved. Initial increased DPPH and ABTS radical scavenging rate of Protease M hydrolysates may be ascribed to the conversion of isoflavones (<30min) and a gradual release of antioxidant peptides. In the later hydrolysis, a gradual exposure of isoflavones involved in the interior of heat-induced protein aggregates was mainly responsible for further improved antioxidant activities. Higher calcium-binding capacity (up to 7.86%) with lower yield of peptide-calcium complex was observed for Protease M hydrolysates. These results could help researchers to develop a feasible protocol for producing nutrient-enhanced soy protein hydrolysates.