The covalent interactions between whey protein isolate (WPI) and rosmarinic acid (RosA) at two different conditions, alkaline (pH 9) and enzymatic (in the presence of tyrosinase, PPO), at room temperature with free atmospheric air were studied. The conjugates formed between WPI and RosA were characterized in terms of their physicochemical and functional properties. The changes in protein structure were analyzed by intrinsic fluorescence and binding of 8-anilino-1-naphthalenesulfonic acid. The findings show that the covalent interactions caused a decrease in free amino and thiol groups and tryptophan content at both conditions. The decrease at enzymatic conditions was lower than at alkaline conditions. In addition, modified WPI at alkaline conditions exhibited higher antioxidative capacity compared to the modification at enzymatic conditions. However, WPI modified at enzymatic condition showed mild antimicrobial activity against Staphylococcus aureus LMG 10147 and MU50 compared to WPI modified at alkaline conditions and unmodified WPI (control). The modified WPI can be used as multifunctional ingredient into various food products with an additional health promoting effect of the bound phenolic compounds.

中文翻译：

---

共价乳清蛋白-迷迭香酸相互作用：碱性和酶修饰对理化、抗氧化和抗菌特性的比较


研究了乳清分离蛋白 (WPI) 和迷迭香酸 (RosA) 在两种不同条件下的共价相互作用：碱性 (pH 9) 和酶促（存在酪氨酸酶、PPO）、室温和自由大气。 WPI 和 RosA 之间形成的缀合物的物理化学和功能特性进行了表征。通过内在荧光和 8-苯胺基-1-萘磺酸的结合分析蛋白质结构的变化。研究结果表明，在两种条件下，共价相互作用都会导致游离氨基和硫醇基团以及色氨酸含量的减少。酶促条件下的降低低于碱性条件下的降低。此外，与酶促条件下的修饰相比，碱性条件下修饰的WPI表现出更高的抗氧化能力。然而，与碱性条件下修饰的 WPI 和未修饰的 WPI（对照）相比，在酶促条件下修饰的 WPI 对金黄色葡萄球菌 LMG 10147 和 MU50 显示出轻微的抗菌活性。改性 WPI 可用作各种食品中的多功能成分，并且结合的酚类化合物具有额外的健康促进作用。