Study On Effects Of Ultra-High Pressure Combining With Heating On Myosin Gel Properties

The ultra-high pressure technology is considered as one of the most potential and promising technologies in the field of biological products and food filed in the21st century. Ultra-high pressure processing has important effects on meat and meat products such as the inhibition of microbial growth, changing the color of the meat, impacting on the organizational structure,flavor of meat and changing protein gel quality.Myosin which has highest content is the most important protein in meat. The quality of meat is determined by property of myosin gel in that it contributes to textural properties, shaping the product, retaining water, and holding other food components in the product. The material was rabbit psoas myosin. This research studied the effects of ultra-high pressure combining with heating on myosin gel properties and the mechanism of ultra-high pressure induced gels formation. The contents of this research included:(1) studying the effects of ultra-high pressure combining with heating on myosin gel properties with different processing conditions and adding functional foods gum;(2) studying changes of secondary structure of myosin by Fourier transform infrared spectroscopy (FT-IR) after ultra-high pressure pretreatment10min at20℃from100to600MPa then heating and studying the relationship of the protein structure and functional properties of myosin gel;(3) studying the preliminary mechanism of ultra-high pressure induced myosin gels formation with various pressure processing by determining changes of chemical force, native-page electrophoresis, scanning electron microscopy.The aim was to provide technical support and theoretical guidance for ultra-high pressure processing used in the meat industrial production.The detailed contents and results are shown as follows:1Effects of different processing conditions on the characteristics of ultra-high pressure-heating myosin gel propertiesThe effect of various pH, concentration of NaCl,keeping time of ultra-high pressure and ultra-high pressure temperature on textural properties (TPA), water holding capacity (WHC) and micro-structure of myosin gels was investigated. The results showed that at pH5.0and5.5there are not well formed network gel. At pH6.0-7.0, the gels have ordered filaments, porous and uniform pore size network structure. Hardness of gels increased with pH decrease. The hardness was highest in pH6.0. WHC of ultra-high pressure gel in the pH5-7, was first decreased then increased. The worst WHC myosin gels were at isoelectric points of pH5.5. Hardness and WHC of gels gradually increased when concentration of sodium chloride at0.1～0.5mol·L-1range. At sodium chloride concentration0.6mol·L-1, WHC and hardness were both decreased significantly. Low ionic strength (0.1-0.2mol·L-1), good gel was cannot form while at0.5mol·L-1, the gel hardness and WHC was highest. Keeping time of high pressure did not significantly affect gel textures and WHC. With the increase of ultra-high pressure processing temperature from20to60℃, hardness increased significantly.20℃gels had filament link while40℃gels had good network, uniform, orderly holes with smooth and delicate structure, accompanied maximum water holding capacity. The relationship of the7kinds of TPA variables and WHC were determined by principal component analysis.Significant correlations were found between TPA and WHC.2Effects of adding konjac glucomannan and sodium caseinate on ultra-high pressure-heating gels properties of myosinThis experiment with simulated the classic sausage formulations, was divided into four treatment groups:myosin;myosin:sodium caseinate (SC) mass ratio of15:4; myosin: sodium caseinate (SC):konjac glucomannan(KGM),15:4:2;myosin:sodium caseinate (SC):konjac glucomannan (KGM) is15:4:4.Two kinds of processing respectively:low pressure-heating gel(200MPa,5min+80℃,40min)and ultra-high pressure (500MPa,60℃,30min),in order to compare the differences of two gel properties.The results showed that SC and KGM can greatly improve TPA and WHC of the myosin gel.When the ratio of gel of myosin:sodium caseinate (SC):Konjac glucomannan(KGM) was15:4:2,the properties of gels was best. Results of scanning electron microscopy showed SC significantly improved the structure of gels, showing a small,porous,and orderly, uniform, smooth,and strong network structure. Adding KGM, gel structure was coarse with big pore size. Comparing with low pressure-heating and the ultra-high pressure gels, different gel properties was found:low pressure-heating of gel had good TPA properties and higher WHC.3Effects of various pressures on gel properties and the secondary structure of myosinTPA, WHC and secondary structure of the gel was determined after ultra-high pressure pretreatment10min at20℃,from100to600MPa then heated, the not ultra-high pressure treated sample as the control. Secondary structure, TPA and WHC of the gel were determined with the Fourier transform infrared spectroscopy methods. The relationship of the protein structure and functional properties of myosin gel was determined by correlation matrix. The results showed that the hardness of gel did not change significantly with various ultra-high pressure treatments. WHC decreased with the pressure increased. Compared with the control, the WHC of100and200MPa have no significant difference. Compared with the control, the WHC of above300MPa have a significant decrease.The structure of myosin was unfolded by ultra-high pressure. The order structure such β-sheet decreased while disordered structure such as β-turn increased.Significant correlations were found among in springiness, adhesiveness, WHC, the secondary structure of gels.4The preliminary mechanism of high pressure-induced myosin gelsMyosin (20mg·mL-1of0.6mol·L-1NaCl, pH6.5) was subjected to various pressures (0.1～400MPa) at20℃for10min to investigate pressure-induced gels mechanism by measurements of protein surface hydrophobicity, free sulfhydryl contents, molecular size by native polyacrylamide gel electrophoresis and ultra-structure using SEM. Surface hydrophobicity had no significant increase at100MPa but had significant increase upon200MPa. Free sulfhydryl groups had little increase below200MPa,but had significant increase at300and400MPa. Ultra-structure revealed that gels below200MPa were filament structure with many small cavities,while gels upon300MPa were globular aggregates with big cavities.Native-page electrophoresis showed that myosin heavy chain was involved in the process of gelation.Preliminary mechanism of myosin gels formation in ultra-high pressure treatment was that the secondary, tertiary, quaternary of myosin were changed by ultra-high pressure, and the sulfhydryl and hydrophobic groups were exposed. The contact between myosin and water were reduced, while the interaction of protein molecules with each other was increased. Then the protein molecules were aggregated to form a gel.