Effect of 4-methylbenzoquinone concentration on its covalent conjugates with β-lactoglobulin: Structural and functional properties

This study examined the effect of quinone concentration on covalent interaction between β-lactoglobulin (β-Lg) and 4-methylbenzoquinone (4MBQ). β-Lg-4MBQ-0.2, β-Lg-4MBQ-0.4, and β-Lg-4MBQ-0.8 were prepared at 1:2, 1:1, and 2:1 M ratio of 4MBQ to β-Lg thiols, respectively. β-Lg-4MBQ-0.8 had the highest polyphenol content (19.04 ± 0.17 mg/g) and the lowest free sulfhydryl (17.12 ± 0.18 μmol/g) and amino group (181.28 ± 5.37 μmol/g) contents. Compared to β-Lg, β-Lg-4MBQ conjugates showed reduced α-helix (0.82–1.26 %) and increased β-sheet (1.17–1.50 %) content. β-Lg-4MBQ-0.8 and β-Lg-4MBQ-0.4 exhibited higher surface hydrophobicity and emulsifying properties than β-Lg-4MBQ-0.2 and β-Lg. Antioxidant activity (DPPH and ABTS scavenging) followed: β-Lg-4MBQ-0.8 (46.75 ± 0.17 % and 50.97 ± 0.51 %) > β-Lg-4MBQ-0.4 (39.50 ± 0.27 % and 46.63 ± 0.59 %) > β-Lg-4MBQ-0.2 (33.35 ± 0.71 % and 43.00 ± 0.39 %) > β-Lg (31.50 ± 0.56 % and 36.25 ± 0.90 %). β-Carotene emulsions stabilized by β-Lg-4MBQ-0.4 exhibited the highest stability. These findings provide insights into developing antioxidant emulsifiers.