Covalent interactions between Lonicera japonica extract and meat proteins: Adduct identification and process-dependent chlorogenic acid-cysteine formation in meat patties.

During meat processing, polyphenols are oxidized to quinones and react with nucleophilic groups in proteins, such as thiols and amines. Herein, adducts formed between polyphenols from Lonicera japonica Thunb. extract (LJE) and proteins in meat patties were characterized, and the effects of processing parameters on the formation of chlorogenic acid (CGA)-cysteine (Cys) adducts in patties added CGA were evaluated. Eight polyphenol-amino acid adducts were characterized in patties added LJE, among which the CGA-Cys adduct exhibited the highest relative intensity. Notably, a Cys-CGA-Cys diadduct was observed in patties containing 0.1% CGA. Quantitative analysis showed that CGA-Cys adduct formation was strongly affected by processing conditions. The CGA-Cys concentration increased with CGA dose and reached 133.82 nmol/g myofibrillar protein in patties containing 0.2% CGA. High‑oxygen modified atmosphere packaging, prolonged storage, and more intensive roasting conditions further promoted CGA-Cys adduct accumulation. The addition of CGA to patties reduced sulfhydryl content and induced protein polymerization through disulfide and non-disulfide covalent linkages. In addition, patties containing CGA showed reduced cooking loss and increased hardness and chewiness. These findings provide new insight into the chemical basis for applying plant polyphenols in processed meat products.