Abstract:

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.

Key words: protein oxidation, whey protein isolate (WPI), β-lactoglobulin (β-Lg), hydroxyl radical, chemical structure