Comparative Analysis of Alkaline and Enzymatic Whey Protein Isolate-Chlorogenic Acid Complexes: Structural Modifications, Antioxidant Enhancement, and Antimicrobial Activity

The interactions of whey protein isolate (WPI) with chlorogenic acid (CQA) using two techniques, alkaline (pH 9) and enzymatic (tyrosinase) were investigated. Complexes, formed between WPI and CQAby alkaline technique (AWPI-CQA) and enzymatic technique (EWPI-CQA), compared to control WPI (CWPI), were characterized in terms of their chemical, structural, emulsifying, antioxidant and antibacterial properties. The obtained data indicate that the interaction decreases the number of free amino and thiol groups and tryptophan content under both conditions. Decrease in AWPI-CQA complexes was higher than in EWPI-CQA complexes. Changes in protein structure were examined using internal fluorescence spectra, ultraviolet-visible spectra (UV-Vis) scan, and ultrahigh performance liquid chromatography with electrospray ionization and quadrupole time-of-flight mass spectrometry (UHPLC-ESI-Q-TOF-MS). WPI fluorescence spectra showed that CQA leads to quenching of protein fluorescence. ESI-MS data show that one or more CQA molecules are covalently bound to WPI under both conditions. In addition, AWPI-CQA showed high antioxidative capacity compared to EWPI-CQA and CWPI. On the other hand, EWPI-CQA exhibited notable antimicrobial activity against Staphylococcus aureus LMG 10147 and MU50 in comparison to AWPI-CQA and CWPI. The development of nutraceutical foods meets the modern consumer needs. Therefore, whey protein isolate-chlorogenic acid complexes can be used as functional components into many food products. Moreover, consumers may benefit from the health-enhancing effects of phenolic compounds.