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<p>This study is the first to compare adduct formation between quercetin (Q) and selected amino acids, tert-butyloxycarbonyl-L-lysine (Boc-Lys) and L-Cysteine (L-Cys), and whey protein isolate (WP) under two distinct conditions: alkaline (pH 9) and enzymatic (Tyrosinase). The formed adducts were studied using flow injection - electrospray ionization - quadrupole time of flight - mass spectrometry (FI-ESI-QTOF-MS). The results showed that when Q was incubated with both amino acids at both conditions, covalent attachments of Q monomers and dimers were detected on specific amino acid side chains. L-Cys exhibited higher reactivity than Boc-Lys, forming seven distinct adducts under alkaline conditions compared to only three under enzymatic ones. Additionally, the study also delved into the interactions between whey protein isolates (WP) and Q under alkaline and enzymatic conditions. The conjugates formed were analyzed using ultra high performance liquid chromatography-electrospray ionization – quadrupole time of flight - mass spectrometry (UHPLC-ESI-QTOF-MS). The interaction of WP with Q led to changes in its physicochemical and functional properties depending on the interaction conditions. Alkaline conditions occupied more binding sites and a more significant loss of free amino/thiol groups and tryptophan fluorescence than enzymatic conditions. On the other hand, the antioxidant activity of enzymatically modified WP reached 441.64 µmol TE/g protein (TEAC assay), which is 2.4-fold and 9.8-fold higher than alkaline-modified and control WP, respectively. Overall, these findings enable the targeted design of WP-quercetin conjugates to enhance antioxidant capacity and functional food performance, which could have applications in developing enhanced food ingredients.</p>

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Covalent interactions of quercetin with amino acids and whey protein isolate: structural and functional impacts under alkaline and enzymatic conditions

  • 期刊论文

  • 发表日期：

    2025年10月13日

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  • Mostafa Ali,
  • Mahmoud Khalil,
  • Salwa G. Arafa,
  • Mohamed A. Salama,
  • Mahmoud Younis,
  • Reham M. Kamel,
  • Amira Rizk,
  • Samar Aly

摘要

This study is the first to compare adduct formation between quercetin (Q) and selected amino acids, tert-butyloxycarbonyl-L-lysine (Boc-Lys) and L-Cysteine (L-Cys), and whey protein isolate (WP) under two distinct conditions: alkaline (pH 9) and enzymatic (Tyrosinase). The formed adducts were studied using flow injection - electrospray ionization - quadrupole time of flight - mass spectrometry (FI-ESI-QTOF-MS). The results showed that when Q was incubated with both amino acids at both conditions, covalent attachments of Q monomers and dimers were detected on specific amino acid side chains. L-Cys exhibited higher reactivity than Boc-Lys, forming seven distinct adducts under alkaline conditions compared to only three under enzymatic ones. Additionally, the study also delved into the interactions between whey protein isolates (WP) and Q under alkaline and enzymatic conditions. The conjugates formed were analyzed using ultra high performance liquid chromatography-electrospray ionization – quadrupole time of flight - mass spectrometry (UHPLC-ESI-QTOF-MS). The interaction of WP with Q led to changes in its physicochemical and functional properties depending on the interaction conditions. Alkaline conditions occupied more binding sites and a more significant loss of free amino/thiol groups and tryptophan fluorescence than enzymatic conditions. On the other hand, the antioxidant activity of enzymatically modified WP reached 441.64 µmol TE/g protein (TEAC assay), which is 2.4-fold and 9.8-fold higher than alkaline-modified and control WP, respectively. Overall, these findings enable the targeted design of WP-quercetin conjugates to enhance antioxidant capacity and functional food performance, which could have applications in developing enhanced food ingredients.