Efficiency of Reaction between β-Lactoglobulin and o-Benzoquinones
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Abstract:
As an important raw material and component of nutritious and healthy food, interactions between whey proteins and o-benzoquinone, a result of polyphenol oxidation, are thought likely to affect the structure and function of the proteins. The reaction efficiency between whey proteins with o-benzoquinones is a useful scientific basis upon which the reaction behavior can be elucidated; thus, the reactions between β-lactoglobulin (β-LG), the main component of whey proteins, and different o-benzoquinones were investigated by cyclic voltammetry under different conditions. The reaction between β-LG (0.03 mmol/L) and non-flavonoid o-benzoquinones (0.60 mmol/L) was thus examined under conditions of pH 7.0 and a scan rate of 50 mV/s, resulting in the following efficiencies, in descending order: protocatechuic acid (54.72%) > caffeic acid (47.01%) > rosmarinic acid (41.86%) > chlorogenic acid (39.29%) > catechol (27.36%) > 4-methylcatechol (22.51%) > protocatechuic acid ethyl ester (19.24%), while reaction efficiencies of: luteolin (19.34%) > quercetin (14.68%) > rutin (12.50%) ≈ (+)-catechin (11.97%) > (-)-epicatechin (6.66%) were obtained for flavonoid o-benzoquinones (0.60 mmol/L), in descending order. These results prove that o-benzoquinone structure affects the efficiency of the reaction with β-LG, with the reactivity of o-benzoquinones and β-LG weakened by electron-donating groups and strengthened by the electron-withdrawing groups on the o-benzoquinone rings. The steric hindrance of the o-benzoquinone ring substituents also reduces the reactivity.
