Effect Of Protein Oxidation On Heat-Induced Gel And Physicochemical Properties Of Chicken Breast Myofibrillar Proteins

The physicochemical and functional properties of protein play a critical role in the application of food. The thermal induced gel properties of myofibrillar protein (MPs) is a key factor in determining meat quality for its contribution in the texture, shaping, and retaining water and other compositions of products. The ability of gel adsorbing and maintaining food ingredients, such as water molecules and fatty, determines the taste and yield of meat products.The formation of heat-induced gel need to undergo degeneration, aggregation and cross-linking, and any factors impacting of these three processes may affect the heat-induced gel properties of myofibrillar protein. Muscle proteins are prone to oxidation during processing, and the changes of physicochemical properties such as protein conformation and intermolecular cross-linking induced by oxidation have an important effect on gel properties of myofibrillar protein which can finally affect the qualities of meat products. In this paper, myofibrillar proteins isolated from chicken breast muscle were treated with hydroxyl radical-generation systems (0、0.05、0.1、0.5、1and5mmol·L-1H2O2,10μmol·L-1FeCl3,0.1mmol·L-1ascorbic acid, incubation for24h) and the effect of oxidation on water holding capacity (WHC), microstructural properties and water relaxation of heat-induced gel of myofibrillar proteins were investigated. We also studied the changes of carbonyl content, solubility, surface hydrophobicity and other physicochemical indexs of myofibrillar proteins treated with different concentrations of H2O2. Finally, we discuss the relationship between the physicochemical properties and heat-induced gel of myofibrillar protein so as to provide theoretical guidance for the processing and production of meat products such as sausages and pressed cooked ham. 1Study on heat-induced gel properties of myofibrillar proteins and water relaxation of gel at different oxidation degreeThe effect of different concentrations of H2O2(0～5mmol·L"1) treatment on microstructure, hardness, elasticity, WHC and water relaxation of myofibrillar protein gel was investigated. The results showed the hardness and WHC of gel presented increase first and decrease afterwords while there was no significant change(P>0.05) in the elasticity of gel with increasing of the H2O2concentration. The hardness of gel reached the maximum value and increased by20%compared with the control group when the H2O2concentration up to0.1mmol·L-1. Also, the WHC of gel reached the maximum value and increased by23%compared with the control group when the H2O2concentration up to0.5mmol·L-1. However, the WHC decreased when H2O2concentrations continued to increase up to5mmol·L-1,(P<0.05) and significantly lower than those of the controls. Scanning electron microscopy showed that the gel had an orderly microstructure when H2O2concentration increased from0to0.5mmol·L-1, but the pore diameter of gel network became larger along with broken when H2O2concentration increased from0.5to5mmol·L-1. The NMR data was fitted to four components, which were merged into three states of water, i.e. bound, mobile and free water. T23relaxation time decreased from364.26ms to316.82ms and its peak area fraction decreased from84.79%to78.38%as H2O2concentrations increased. These results indicate that mild oxidation enhances WHC of MPs gel, in terms of improved gel microstructure and the relaxation properties of water molecules.2Study on physicochemical properties of myofibrillar proteins at different oxidation degreeIn order to further analyze the effects of oxidation on thermal induced gel properties of myofibrillar protein, we studied the changes of carbonyl content, sulfhydryl content, solubility, surface hydrophobicity, particle diameter and other physicochemical indexs of myofibrillar proteins treated with different concentrations of H2O2. The results showed that carbonyl content and particle diameter of myofibrillar proteins increased, while sulfhydryl content decreased with increasing of the H2O2concentration. This indicated the aggregation and carbonyl and disulfide cross-linking increased with the enhancement of the degree of oxidation. The solubility and surface hydrophobicity of myofibrillar proteins were reduced with no difference(P>0.05) when H2O2concentration increased from0to0.1mmol·L-1, these results indicated that at lower degree of oxidation, protein conformation has little variation, protein molecules aggregated to form dissoluble oligomers through intermolecular cross-linking, which contributed to gel network stability. When H2O2concentration continued to increase up to5mmol·L-1, the surface hydrophobicity index increased significantly and protein solubility decreased by28.8%compared with control group (P<0.05), these results indicated that as oxidation enhanced to a certain degree, more hydrophobic amino acids exposed,which result in soluble aggregates formation and decreased solubility because of intermolecular cross-linking through hydrophobic interactions. The solubility decline revealed that the number of protein molecules involved in the gel formation was reduced, which was not conducive to the formation of gels. In addition, turbidity results showed that oxidation could promote thermal aggregation of myofibrillar protein during gel formation. The correlation analysis results showed that the hardness of protein gels had high significant positive correlation with the protein solubility, and significant correlations were also found between the carbonyl content, sulfhydryl content, surface hydrophobicity, turbidity, particle diameter and solubility. Thses results indicated that the effect of oxidation on protein solubility mainly through changing the degree of denaturation, crosslinking and aggregation, and further affect gel properties of myofibrillar protein.