Two-step Enzymatic Modification Method to Enhance the Zn2+-chelating Activity and Antioxidant Activity of Zein

Abstract

Zein is a major by-product of corn processing and has a wide range of applications in many fields due to its unique solubility and specific amino acid composition. The aim of this study is to hydrolyze zein stepwise using alcalase and proteinase K while considering the enzymatic hydrolysis sequence and assessing the zein-chelating ability, solubility, foaming, and emulsification properties of the zein hydrolysate. The antioxidant activity of Zn²⁺ chelating peptide was determined. Zinc-chelating ability was used as the evaluation index, and proteinase K was further hydrolyzed on the basis of alcalase hydrolysis. The optimal hydrolysis conditions were reaction time of 2 h, substrate concentration of 10 mg mL⁻¹, enzyme addition amount of 2.8 U mg⁻¹, reaction temperature of 60 °C, and hydrolysate chelation ability of 12.16 mg g⁻¹, thereby corresponding to a degree of hydrolysis (DH) of 35.30%. On the basis of the hydrolysis by proteinase K, alcalase was further hydrolyzed, and the optimal hydrolysis conditions were reaction time of 3 h, substrate concentration of 10 mg mL⁻¹, enzyme addition amount of 8.0×10⁵ U mg⁻¹, reaction temperature of 50 °C, and hydrolysate chelation ability of 13.72 mg g⁻¹, thereby corresponding to a DH of 29.32%. Zein Zn²⁺-chelating peptide is significant for 1,1-diphenyl-2-picrylhydrazyl free radicals, hydroxyl radicals, and ABTS·⁺. The clearance effect is positively correlated with the mass concentration of the polypeptide. Zein Zn²⁺-chelating peptide has good Zn²⁺ chelating ability and antioxidant activity. Hence, it has broad research prospects for new dietary supplements.