Phenolics-protein interaction involved in silver carp myofibrilliar protein films with hydrolysable and condensed tannins

- Amino and sulfhydryl groups were decreased especially by tannic acid.
- Protein solubilities in the film were more greatly reduced by apple procyanidins.
- Non-disulfide covalent bonds were the main phenolics-protein interaction involved.
- Mechanical, water-resistant and thermal properties were improved by tannins.
- Apple procyanidins showed a greater reactivity and efficiency than tannic acid.

Silver carp myofibrillar protein films were prepared with tannins (tannic acid and apple procyanidins) at various concentrations (30 and 50 g/kg protein) under alkaline and heating condition. Phenolics-protein interaction as well as related properties of incorporated film was evaluated. Available amino and total sulfhydryl groups in film-forming solution (FFS) were decreased especially by tannic acid, whereas protein solubilities in the film were more sharply reduced by apple procyanidin. SDS-PAGE pattern suggested that non-sulfide covalent bonds were formed between tannins and protein molecules, and more protein polymerization was induced by apple procyanidin. On the other hand, the incorporation of tannic acid and apple procyanidin led to an increased tensile strength (TS) with accompanying decreases in elongation at break (EBA) and water vapor permeability (WVP). The film with apple procyanidin had higher TS and EBA as well as lower WVP than that with tannic acid. Tannins especially condense tannin could covalently crosslink with protein molecules to form protein-phenolics- protein polymers, and thus improve some physicochemical properties of the resulting protein films.