Enhancement of antioxidant and antimicrobial properties of Whey protein isolate and chlorogenic acid complexes through enzymatic and alkaline techniques

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 CQA by 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. Compared to CWPI, both complexation methods significantly reduced free amino groups (CWPI: 588.00 nmol/mg; AWPI-CQA: 409.85 nmol/mg; EWPI-CQA: 412.50 nmol/mg), sulfhydryl groups (CWPI: 68.01 nmol/mg; AWPI-CQA: 18.43 nmol/mg; EWPI-CQA: 48.91 nmol/mg), and tryptophan content (CWPI: 61.21 nmol/mg; AWPI-CQA: 30.12 nmol/mg; EWPI-CQA: 37.64 nmol/mg). 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 10,147 and MU50 in comparison to AWPI-CQA and CWPI. The development of nutraceutical foods meets the modern consumer needs. Therefore, WPI-CQA complexes can be used as functional components in many food products. Moreover, consumers may benefit from the health-enhancing effects of phenolic compounds.