桑叶蛋白抗氧化肽的酶法制备

为了提高桑叶蛋白MLP的抗氧化活性,用碱性蛋白酶Alcalase、复合蛋白酶Protamex、木瓜蛋白酶Papain、风味蛋白酶Flavourzyme、中性蛋白酶Neutrase及胰蛋白酶Trypsin等6种蛋白酶对MLP进行单酶酶解及双酶、三酶复合酶解,并对酶解前后的化学组成、分子量分布、多肽得率、氨基酸组成、自由基清除能力、还原能力等进行对比分析。结果表明,MLP主要由分子量大于6.5 ku的大分子肽及蛋白质组成,酶解物则主要由分子量为0.3~0.6 ku的小肽及0.6~6.5 ku的多肽组成;相较于过度酶解,适度酶解能更好的改善MLP的抗氧化活性;多肽得率与自由基清除能力显著正相关(r=0.916~0.985);6种蛋白酶中,碱性蛋白酶、中性蛋白酶及复合蛋白酶的酶解物抗氧化活性显著优于MLP及其他三种蛋白酶解物;中性蛋白酶单独酶解物的抗氧化活性显著优于双酶、三酶复合酶解物。对中性蛋白酶的单酶酶解条件进行优化,结果表明底物浓度为20 mg/mL,E/S为1%(W/W),用中性蛋白酶酶解2 h所得的酶解物(NH)的抗氧化活性最高,后期研究中可选用中性蛋白酶制备桑叶蛋白抗氧化肽。NH或许可以作为食品中较有潜力的抗氧化剂。

Enzymatic Preparation of Antioxidant Peptides of Mulberry (Morus atropurpurea Roxb.) Leaf Protein

In order to improve antioxidant activity of mulberry leaf protein (MLP), Alcalase, Protamex, Papain, Flavourzyme, Neutrase, and Trypsin were used to hydrolyze MLP. Effects of different enzymes on the chemical composition, molecular weight distribution, peptide yield, amino acid composition, radical scavenging activity and reducing power were investigated. Results showed that mulberry leaf protein was mainly composed of the fractions above 6.5 ku, while MLP hydrolysates were rich in the fractions of 0.3~0.6 ku and 0.6~6.5 ku. Limited hydrolysis of MLP could lead to higher antioxidant activity than extensive enzymatic hydrolysis. The radical scavenging activities of MLP hydrolysates were significantly correlated with the peptide yield (r=0.916~0.985). Hydrolysates prepared with neutrase, alcalase, and protamex showed significantly higher antioxidant activity than that of MLP and the other three hydrolysates. Meanwhile, the antioxidant activity of Neutrase hydrolysates was significantly better than the complex hydrolysates. Furthermore, the condition of an enzyme to substrate level of 1% (W/W), substrate concentration of 20 mg/mL and a hydrolysis time of 2 h was found to be the optimum conditions to obtain Neutrase hydrolysates (NH) with the highest antioxidant activity. In the further research, the antioxidant peptides of MLP will be prepared by Neutrase, and NH may be a promising antioxidant in food.