Changes in pork and shark (Rhizopriondon terraenovae) protein emulsions due to exogenous and endogenous proteolytic activity

The dose-dependent effects of polyphenols and malondialdehyde on the emulsifying and gel properties of myofibrillar protein-mulberry polyphenol complex

The effects of mulberry polyphenols and malondialdehyde (MDA) on the emulsifying and gel properties of myofibrillar protein (MP) were studied. Emulsibility and gel properties of MP were compared in range of mulberry polyphenol/MDA concentrations by particle size, Zeta potential, antioxidant capacity, gel strength, water-holding capacity (WHC), rheological properties and microstructure. Mulberry polyphenols enhanced the inoxidizability of MP emulsion but decreased its emulsifying property. MDA at intermediate concentrations (5-20 mM) improved the elasticity, strength, and WHC of polyphenols-modified MP emulsion gel, while at high concentration (40 mM) it destroyed the emulsion gel, resulting in "oil leakage". Polyphenol is not conducive to the gelation but weaken the oxidative damage of MDA to protein. The gel structure of MP emulsion collapsed after high dose of polyphenols or MDA treated. Thus, to maintain uniform textural and antioxidant activity of meat product, both polyphenols addition and oxidation intensity should be controlled simultaneously.

Effect of yerba mate extract on the performance of starch films obtained by extrusion and compression molding as active and smart packaging

Native or hydrolyzed starch and yerba mate extract (10 wt.% or 20 wt.%) films prepared by extrusion and compression molding were investigated. Native starch material (TPNS) exhibited lower water vapor permeability and higher Young's Modulus (E) compared to hydrolyzed starch matrix (TPHS) but decreases in strain at break (ε_b) and toughness (T). The incorporation of 10 wt.% of extract in TPNS led to greater E and ε_b and it resulted the most hydrophobic material. Conversely, TPHS with 20 wt.% of additive resulted the film with the highest ε_b and T, indicating a plasticizing effect of the extract in this concentration and system. All materials disintegrated after 10 weeks of burial, contributing to waste reduction. Biofilms containing yerba mate extract showed antioxidant activity and color changes in different pH, indicating their promising role as active and smart packaging for food, in accordance with the new trends for biodegradable and functional packaging.

Effect of hydroxyl radicals on biochemical and functional characteristics of myofibrillar protein from large yellow croaker (Pseudosciaena crocea)

The oxidative modification effect of hydroxyl radicals generated by an H₂ O₂ oxidative solution on the biochemical and functional characteristics of myofibrillar protein (MP) from large yellow croaker (Pseudosciaena crocea) was investigated. The results showed that MP of large yellow croakers was vulnerable to hydroxyl radicals. Incubation of MP with increased concentration of H₂ O₂ led to the gradual formation of carbonyl derivatives, disulphide bonds and dityrosine, and loss of available lysine, sulphydryl, and free ammonia. Surface hydrophobicity increased, while tryptophan residues decreased, indicating a conformational transition of MP. SDS-PAGE demonstrated that both disulphide and nondisulphide bonds were involved in MP aggregation. The MP functionalities were also affected by hydroxyl radicals, including reduced solubility, gelling, and emulsifying properties. Mild oxidation (0.1 mM H₂ O₂ ) slightly improved MP gel strength and water-holding capacity, while excessive oxidation caused a reduction in gel properties. The results suggested that the MP oxidation should be controlled. PRACTICAL APPLICATIONS: Protein oxidation mediated by hydroxyl radicals is one of the most crucial reasons affecting the quality of large yellow croaker during processing and storage. Additionally, it is well known that the quality of protein in fish systems directly determines the quality stability and nutritional value of the fish products. Hence, the study explored how the hydroxyl radicals influenced the physicochemical and functional properties of fish MP. The changes in amino acid residues (carbonyl, available lysine, sulphydryl, free ammonia, tryptophan residues, etc.) of MP and its gelling and emulsifying properties after oxidation not only benefit the awareness of quality deterioration and quality control of large yellow croaker, but also provide a basis for the understanding of protein oxidation on the nutritional value of aquatic products and human health.