Effects Of Ohmic Cooking On Pork Meat Protein Degradations,Oxidations And Gellation Characteristics

This study was designed to track the changes of protein degradations, oxidations, colour, texture, nutritional qualities of pork longissimus dorsi at a certain endpoint temperature (EPTs) during ohmic cooking or thawing. Meanwhile, functional properties of heat-induced gels during ohmic cooking were also evaluated, The specific contents and results are as follows:The objective of this study was to investigate the effects of ohmic (OH) and waterbath (WB) cooking on colour attributes and sarcoplasmic protein changes of porcine longissimus dorsi muscle at the same endpoint temperatures (EPTs; range10℃-80℃). The results showed that lightness (L*) and browness (b*) values, deoxymyoglobin%(DeoMb) and metmyoglobin%(MetMb) of the OH-cooked meat were significantly lower (P<0.05) than those obtained by WB-cooking at the same EPTs (range60℃-80℃). SDS-PAGE analysis showed that the meat treated with WB-cooking had fainter protein bands, A higher sarcoplasmic protein solubility (5.97mg/g vs.14.89mg/g, P<0.05) and better waterholding capability were obtained in OH-cooked meat at EPTs above40℃. Strong correlations among lightness, browness, metmyoglobin%and soluble proteins were observed in meat following OH-cooking.The effects of ohmic (OH) and water bath (WB) cooking on changes of shear parameters, protein degradations, ultrastructure, lipid and protein oxidations, protein surface hydrophobicity, protein aggregation and in vitro digestion of pepsin, trpsin and a-chymotrypsin of porcine longissimus dorsi muscle at the same endpoint temperatures (EPTs; range,20℃-100℃) were investigated. The results showed that the cooking loss and warner-bratzler shear force (WBSF) of the OH-cooked meat were significantly lower (P<0.05) while protein solubility, pH and endothermic transition temperature were higher than those obtained by WB cooking at the same EPTs (range,20℃-80℃). Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that during OH cooking, the meat had slightly fainter protein bands than that of WB-cooked ones. Less obvious shrinkage of the sarcomere and loss in the structure of Z discs were detected especially in OH-cooked meat at EPTs (100℃). Strong correlations among pH, cooking loss, Warner-Bratzler shear force, sarcoplasmic protein solubility, Tmax2, and Tmax3were observed in meat following OH cooking.TBARS, carbonyl content, protein surface hydrophobicity of the OH-cooked meat were significantly lower (P<0.05) than those obtained by WB cooking at the same EPTs (range,40℃-100℃). No significant difference (P>0.05) in protein digestion in vitro between ohmically and waterbath-cooked meat. Results showed a direct negative relationship between pepsin in vitro and aggregation (P<0.01) in meat induced by ohmic cooking and proteolytic susceptibility to pepsin. However, no such correlations have been observed with trypsin and a-chymotrypsin in vitro (P>0.05). Changes in iipid and protein oxidation, non-heme iron (NHI) content, colour and texture parameters during refrigerated storage (7days/4℃) of ohmically (OH) and waterbath (WB)-cooked pork meat were studied. The results showed that a significant effect (P<0.05) of refrigerated storage duration and cooking method on colour, texture, Iipid oxidation and carbonyl content was detected OH-cooked and WB-cooked meat. The OH-cooked meat had better colour appearance, Iipid oxidative stability, slightly enhanced hardness and protein oxidation levels during7days of storage time, having lower values of TBARS, center lightness (L*), center/surface brownness (b*) and free thiol groups, whereas higher values of center/surface redness (a*), non-heme iron, protein carbonyl and hardness compared to those from WB-cooked meat.Gelation characteristics of pork batters, prepared in the absence and presence of0.5%transglutaminase (TG) were evaluated using either ohmic (OH) or water bath (WB) heating. The OH-cooked gels in the presence of0.5%transglutaminase exhibited higher breaking force, gel strength and a compact structure compared with other treated gel groups (P<0.05). The rapid heating method in the presence of0.5%transglutaminase could yield comparable or improved meat gels when compared to water bath heating.The frozen porcine longissimus dorsi muscle were thawed from-18℃to4℃during ohmic and conventional thawing treatments. The changes in the proximate, colour, total myoglobin and proportions of related pigments, soluble protein solubility and myofibrillar fragmentation index, differential scanning calorimetry for proteins, SDS-PAGE of sarcoplasmic and myofibrillar proteins, Iipid and protein oxidation as well as TEM of muscle ultrastructure of porcine longissimus dorsi muscle during ohmic thawing were compared with those during conventional thawing method. The results showed that The a*values in OH-thawed meat was significantly higher, whereas the MetMb%and MFI values were lower (P<0.05) than WB-thawed samples.