Modification of myoglobin structure and in vitro digestion by phenolic compounds with different structures

Abstract

The interactions between phenolic compounds and proteins are crucial for the quality and nutritional value of muscle-based foods. However, the influence of phenolic structure on the conformational and digestive properties of myoglobin remains inadequately elucidated. This study systematically investigated the effects of three structurally distinct phenolic compounds—epigallocatechin gallate (EGCG), ferulic acid (FA), and caffeic acid (CA)—on the structural integrity, oxidative stability, and in vitro digestive behavior of a tuna myoglobin model system. Myoglobin was incubated with each phenolic at varying concentrations (0.1, 0.5, and 1.0 μmol/mL), and the resulting modifications were evaluated by a combination of spectroscopic, physicochemical, and microstructural analyses. Our results revealed that EGCG, a galloyl-containing flavonoid, exhibited the most pronounced activity, significantly enhancing the antioxidant capacity of myoglobin, as evidenced by the lowest metmyoglobin formation and carbonyl content. Conversely, all phenolics induced concentration-dependent alterations in myoglobin secondary and tertiary structures, characterized by a reduction in α-helix content and intrinsic fluorescence quenching, with EGCG again causing the most substantial conformational perturbations. Furthermore, these structural modifications directly influenced the in vitro digestibility of myoglobin; EGCG treatment markedly decreased the overall digestibility, likely attributable to the formation of protein–polyphenol complexes that mask enzymatic cleavage sites. Notably, the simple hydroxycinnamic acids (FA and CA) exhibited more moderate effects, suggesting a structure-dependent activity primarily governed by the number of hydroxyl groups and the presence of a galloyl moiety. This study provides compelling evidence that phenolic structure is a critical determinant in modulating myoglobin's physico-chemical properties and digestive fate, offering fundamental insights for optimizing the application of polyphenols in processed meat products to balance their antioxidant benefits with potential impacts on protein bioavailability.