羟基自由基氧化体系对乳清蛋白、β- 乳球蛋白化学结构的影响

本实验主要研究乳清蛋白(WPI)和β-乳球蛋白(β-Lg)经过FeCl3/抗坏血酸(AsA)/H2O2产生的羟基自由基氧化系统氧化后化学结构产生的变化。两种蛋白分别经过0.1mmol/L 或者1mmol/L FeCl3 氧化1、5 和12h 后，总巯基、游离氨都下降，而羰基、二聚酪氨酸和疏水性都呈增加的趋势。低Fe3+ 浓度氧化1h，WPI 巯基含量降低38.5%，β-Lg 降低11.6%；而游离氨分别降低20.68% 和0.64%。高Fe3+ 浓度氧化5h，WPI 羰基增加32.4%，β-Lg 增加8.4%；二聚酪氨酸分别增加132.4% 和28%；疏水值增加161.1% 和0.7%。高Fe3+ 浓度带来的氧化效果要比低Fe3+浓度明显(p ＜ 0.05)。这说明，氧化改变了蛋白的化学结构，氧化程度取决于浓度Fe3+ 的浓度，且β- 乳球蛋白比乳清蛋白有更好的稳定性。

Effect of Hydroxyl Radical Oxidation System on Alterations of Chemical Structure of Whey Protein Isolate and β-lactoglobulin

The main objective of this study was to investigate the alterations on chemical structure of whey protein isolate (WPI) and β-lactoglobulin (β-Lg) subjected to the hydroxyl radical oxidation systems induced by 0.1 or 1 mmol/L ferric chloride-0.1 mmol/L ascorbic acid-1 mmol/L hydrogen peroxide system. The contents of total sulfhydryl groups and free amines in both proteins decreased when exposed to the above two hydroxyl radical oxidation systems for 1, 5, and 12 h, while the contents of carbonyl and bityrosine as well as the hydrophobicity increased. The contents of sulfhydryl groups in oxidized WPI and β-Lg decreased by 38.5% and 11.6%, repectively. after 1 h oxidation at low ferric chloride concentration, while the decreases in free amines were 20.68% and 0.64%, separately. Oxidation at high ferric chloride concentration for 5 h led to the elevations in carbony and bityrosinel contents and hydrophobicity in WPI by 32.4%, 132.4% and 16.1%, while for β-lactoglobulin, 8.4%, 28% and 0.7%, respectively. Oxidation induced by high ferric chloride concentration was more pronounced than that by low concentration. The results suggested that the oxidation alters the chemical structure of whey protein isolate and β-lactoglobulin and this effect is ferric chloride concentration-dependent (p < 0.05). β-Lactoglobulin demonstrates a better stability than whey protein isolate.