Effects Of Protein Oxidation On Protein Functional Properties And Quality Of Sausage In Chinese

Chinese-style sausage is one of Chinese traditional fermented meat products, which is popular with people for its unique flavor. Oxidation is a major factor that can affect the shelf life of Chinese sausage. However, the mechanism of effect of protein oxidation on functional properties of protein and quality of sausage product is unclear. The purpose of the study was that the Chinese-style sausage during processing and storage were treated with packaging, temperature, illumination and antioxidants, protein oxidation model was established, namely the control group (CK) prooxidation group (PO group) and antioxidation group (AO group), and then it studied the effect of protein oxidation on protein degradation, interactions between protein molecules, protein structure and product quality.Firstly, the changes of Aw, moisture content, pH and sodium chloride content of Chinese-style sausage were investigated during processing and storage.The results showed that the Aw and moisture content of three batches of sausages exhibited different degrees of decline. pH showed different variation trend at different stage of processing and storage. Sodium chloride content showed the different levels of rising trend.Secondly, the effect of protein oxidation on protein degradation of Chinese-style sausage was studied. The results indicated that protein carbonyl and free thiol groups of three batches of sausages both had significant difference (p<0.05). PO group was highly oxidized group, CK group was moderately oxidized group, AO group was mildly oxidized group. Along with protein oxidation, sarcoplasmic proteins and myofibril protein in Chinese-style sausage degraded in varying degrees. Molecular weight about150kDa and20kDa in sarcoplasmic protein degraded; Molecular weight about200kDa included myofibrillar protein degradated significantly, and Molecular weight about<25kDa included myofibrillar protein increased. The main free amino acids degraded by protein were Glu, Ala and Lys. The content of total free amino acid showed different levels of rising trend in three batches of sausages during processing and decreased during the later period of the storage.Next, the influence of protein oxidation on the protein surface hydrophobicity and protein secondary structure was analyzed. By the Pearson correlation analysis results, myofibrillar protein carbonyl and a-helix content of sarcoplasmic protein in sausage during processing were negatively correlated. Free thiol group of sarcoplasmic and myofibrillar protein had positive correlation with surface hydrophobicity, and had negative correlation with the α-helix content; Sarcoplasmic protein carbonyl and α-helix content were negatively correlated in sausage during storage, myofibrillar protein carbonyl and α-helix content of myofibrillar protein were positively correlated. Free thiol group of sarcoplasmic protein had negative correlation with α-helix content, free thiol group of myofibrillar protein had positive correlation with α-helix content. In the study of protein molecular interactions of sausage during processing and storage, protein molecules interaction of three batches of sausage appeared significant difference (p<0.05). Electrostatic force, hydrogen bond, hydrophobic interactions and disulfide bond in protein had been enhanced, and hydrogen bond, hydrophobic interactions and disulfide bond was stronger than electrostatic force. Hydrogen bonds, hydrophobic interactions and disulfide bonds were weakened during storage in the late, indicating the three forces were destroyed. The force of stabilizing the protein structure in Chinese-style sausage during processing and storage were mainly hydrogen bonding, hydrophobic interactions and disulfide bonds.Finally, the paper studied the effect of protein oxidation on sensory quality, including color, texture and flavor. Protein oxidation caused the decrease of L value, increase of a*value, and promoted elasticity, hardness and chewiness in Chinese-style sausage during processing. At the storage of sausage, sarcoplasmic proteins carbonyl and free thiol groups had positive correlation with a*value, hardness, cohesiveness, and had negative correlation with flexibility. Myofibrillar protein free thiol groups had negative correlation with hardness, chewiness, and had positive correlation with positive elasticity. Major volatile flavor compounds in sausages were aldehydes, alcohols and esters substances, which was differently contributed to the sausage flavors in different stages of processing and storage. Protein oxidation promoted the formation of ketones and esters in sausage during processing, and was not conducive to the accumulation of acid substances. Protein oxidation promoted the formation of aldehydes, ketones, esters substances in sausage during storage, and was not conducive to the formation of aromatic substances.