Jinshun Ye,Xiaotong Li,Zhenzhao Weng,Yuting Li,Xiaozhen Liu,Xiangying Yu,Fengyuan Liu,Jingkun Yan,Lin Li
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.
Yuting Li,Xiaotong Li,Jinshun Ye,Zhenzhao Weng,Xiaozhen Liu,Fengyuan Liu,Jingkun Yan,Lin Li
The reactivity of amino acid residues in proteins towards quinones, along with the concentration of quinones, may play a crucial role in determining the specific sites of reaction between quinones and proteins. The reaction efficiencies of 20 different α-carbon amine group blocked amino acids with 4-methylbenzoquinone (4MBQ) were investigated at pH 7.0 by cyclic voltammetry. Among these, Nα-acetyl- l -lysine, Nα-Boc- l -histidine, Nα-acetyl- l -arginine, and Nα-acetyl- l -cysteine exhibited reactivity towards 4MBQ, with the reactivity sequence being: Nα-acetyl- l -cysteine > Nα-acetyl- l -lysine > Nα-acetyl- l -arginine > Nα-Boc- l -histidine. In addition, the reactivity of Nα-acetyl- l -cysteine towards 4MBQ was over 50-fold greater than that of Nα-acetyl- l -lysine, Nα-Boc- l -histidine and Nα-acetyl- l -arginine. Adducts formed from the reaction of 4MBQ with Nα-acetyl- l -lysine and Nα-acetyl- l -arginine were identified as quinone adducts. In contrast, those formed with Nα-acetyl- l -cysteine and Nα-Boc- l -histidine were identified as phenol adducts through UPLC-QTOF-MS/MS analysis. Irrespective of whether the molar ratio of 4MBQ to protein free thiol groups was 1:2 or 2:1, the residues of cysteine, lysine, arginine and histidine in β-lactoglobulin (β-Lg) invariably engaged in the reaction with 4MBQ. This work may provide valuable information for design polyphenol-protein covalent conjugates which can be further applied as functional additives in food industry by choosing protein with different proportion of lysine, histidine, arginine and cysteine residues.
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