Effects Of Combined Ultra-high Pressure And Thermal Treatment On Oxidation,Structure And Properties Of Pork Proteins

Pork is rich in protein and occupies a very important position in Chinese family table, protein in addition to giving a unique flavor, taste and nutrition, but also plays an important role in the final nature of the product. High pressure processing is a kind of new technology and gets a rapid development in the last ten years. Application of high pressure in meat products are generally combined with heat treatment to kill microorganisms. In the process of ultra-high pressure combined with thermal treatment, the protein will be degraded and oxidized, it resulting in structural changes, thus affecting their functional properties and physicochemical properties. Knowing the changes of protein after ultra-high pressure treatment at different temperatures, not only can guide the production process, but also can design reasonable process parameters to produce high-quality products in the development of the new meat products. Therefore this research takes the white jade black pig as the study object, studying the effect of ultra-high pressure combined with thermal treatment on color, lipid oxidation, proteins structure, proteins oxidation degradation and properties in pork muscle, and to reveal the relationship among them. The specific research contents and results are as follows:1. Effects of combined ultra-high pressure and thermal treatment on color, Mb and lipid oxidation in pork muscle. longissimus pig muscles were used as material. Eleven parameters, including color parameters redness(a*), yellowness(b*), lightness(L*), total color difference( E), Mb, Met Mb, Mb O2, deoxy Mb, lipid oxidation(TBARS, POV, AV)were detected when the pressure was in the range of 100 to 600 MPa and the investigated temperatures were 25~55?. Each experiment was conducted for 15 minutes. Results showed that with the increasing pressure color values L*and E increased, a* values decreased and the meat becoming grey-white. The effects of ultra-high pressure and thermal treatment on Mb redox state had strong interrelationship, it cause complex changes needs further study. The results of RSM showed that pressure was the most significant factor for the Mb, while temperature was the most significant factor for the Met Mb, Mb O2, deoxy Mb, pressure, temperature and time had significant(p<0.01) interactive on the Mb, Met Mb, Mb O2, deoxy Mb. Simultaneously, TBARS, POV, AV increased significantly(p<0.01). By calculating with SPSS, optimal multinomial regression model between color parameters a*, b*, L* and Mb, deoxy Mb, Mb O2, Met Mb, lipid oxidation(TBARS, POV, AV) were obtained. The results of significance test and the comparision between predicted value and actual value showed that they were on a high level of significance(p<0.01). Therefore, in the ultra-high pressure combined with thermal treatment process, the color parameters can be used to quantitative describe Mb and lipid oxidation.2. The effects of combined ultra-high pressure and thermal treatment on oxidation, molecular interaction and structure of pork proteins This study was designed to investigate the effects of combined ultra-high pressure and thermal treatment on proteins oxidation, molecular interaction, surface hydrophobicity and structure in proteins. Porcine longissimus muscles were applied as material. The experiments were conducted under the pressure range of 100 to 600 MPa at 25~55 ?. Results showed that hydrogen bonds, hydrophobic interactions, and disulphide bonds are the primary molecular forces in maintaining the three-dimensional network structure of procine proteins after ultra-high pressure treatment at different temperatures. After the combined treatment of ultra-high pressure and thermal process, the amount of SH groups reduced significantly(p<0.01), whereas S-S groups, carbonyl content and surface hydrophobicity increased significantly(p<0.01). The microstructure of protein was destroyed and has different denaturation and degradation, degraded into a smaller fragment molecules eventually. The rearrangement of secondary structure was observed, which resulted in the reduction of helix, and increase of disordered structure. The tertiary structure of protein is affected, leading to protein unfolding, more sulfydryl groups as well as hydrophobic regions and amino acid residues which had ultraviolet absorbance had been found significantly.3. The effects of combined ultra-high pressure and thermal treatment on degradation and properties change of pork proteins Water holding capacity, solubility, particle size, turbidity and the activity of cathepsin are closely related in the process of ultra-high pressure and thermal treatment. 400 MPa is a critical points, before it, solubility, water holding capacity and the activity of cathepsin increased significantly(p<0.01), particle size and turbidity reduced significantly(p<0.01), whereas they has an opposite trend after 400 MPa. Under 55?, a lot of proteins denaturation, continue to increase the processing pressure, the impact is not significantly(p<0.05). TVB-N and p H increased significantly(p<0.01)after ultra-high pressure and thermal treatment. There was a significantly increase in free amino acid content at 45?, but decreased with the temperature increasing. The content of free amino acid increased at 200 MPa and then decreased with the pressure increasing. The results of RSM showed that temperature was the most significant factor for the cathepsin B and L, pressure and temperature had significant(p<0.01) interactive on the activity of cathepsin B and L. Use Design Expert 8.0, the optimal conditions were obtained by response surface methodology(RSM)based on single factor. The results were as follows: pressure was 495 MPa, temperature was 41?, time was 18 min. Under these conditions, the activity of cathepsin B and L reach the maximum, 19.40 and 19.80 U/g, respectively.4. Correlation analysis a significant relationship(p<0.01) exist among protein oxidation, pork color, lipid oxidation, molecular interaction of proteins, protein structure, functional properties and physicochemical properties of protein. Lipid oxidation play a mutual promoting role in the protein oxidation. The structure of protein was damaged by oxidation have caused aggregation and changes in surface hydrophobicity, at the same time, induce major proteins to degrade and promote the accumulation of free amino acids. The protein structure was changed by protein oxidation, and which have some effects on the functional properties and physicochemical properties.