Screening Of Microwave Combined Thawing Method And Its Mechanism For Improving Water-holding Of Pork

Freezing is the major means of storage for livestock,poultry and meat products to be involved in regional circulation and import and export trade.Thawing is an indispensable working procedure before the deep processing or cooking of frozen meat.Inappropriate thawing methods will influence the appearance and eating quality of meat and meat products,reduce the purchasing desire of consumers and cause economic losses.Therefore,the choice of proper thawing method is very important to maintain the quality of meat.Microwave thawing(MT)has attracted much attention owing to its high thawing rate.Nevertheless,MT has some disadvantages,such as localized overheating and poor penetration of samples,which limit its wide application in meat thawing.In recent years,combined thawing technology has gradually caught attention for being able to improve the quality of frozen meat with its complementary advantages.Some studies have also verified its feasibility,but fewer studies were made on combined thawing by microwave and other methods.Therefore,this article takes pork as the research object,chooses microwave to combine with ultrasonic wave,water with a temperature of 35?,traditional low temperature,air,and running water for thawing,and selects the best microwave combination thawing technology,and develops new high-efficiency and low-consumption pork thawing technology;The influence of the best microwave combination thawing technology on the oxidation and structure of pork myofibrillar were systematically studied;The effect of the best microwave combination thawing technology on the properties of protein gels was also studied,expecting to clarifies the relevance mechanism between myofibrillar protein oxidation and structure change with water-holding capacity of pork,and to explores effective measures to improve water-holding capacity,and to improve quality evaluation system,and to provide theoretical basis for the practical application of this technology.Major study contents are as following:1.Influence on the physicochemical quality and protein denaturation of pork by combining microwave with different thawing technologiesThis article takes water-holding capacity,freshness,color,tenderness,the degree of lipid oxidation,thermal stability of protein and rheological properties as the major quality evaluation indicators,explore the change degrees of pork quality after processed by thawing technologies such as microwave,microwave combined with ultrasonic,microwave combined with 35?water immersion,microwave combined with 4? low temperature,microwave combined with air convection,and microwave combined with running water,so as to select the best microwave combination thawing method(microwave combined with X).The result shows that microwave combined with air convection thawing(MAT)performs the best,which presents better water-holding capacity,color,tenderness,protein solubility and thermal stability compared with other thawing methods,relatively low degree of lipid oxidation,high G?value and same freshness with fresh meat.In addition,this thawing method is able to avoid the edge curing problem caused by uneven heating.In a word,microwave combined with air convection is the best microwave combination thawing method,which is highly efficient and easy to operate,and can better maintain the physicochemical quality of meat samples.2.The influence on myofibrillar protein oxidation and structure of pork subjected to microwave combined with air convection thawingAfter selecting MAT treatment,with comparison between single thawing methods(microwave thawing,MT;air thawing,AT)and fresh meat,the author further studies the influence on pork myofibrillar protein oxidation and conformation by MAT.Protein carbonyl content,total sulfhydryl content,dityrosine content,surface hydrophobicity and Ca²⁺-ATPase activity are introduced to evaluate protein oxidation degree of meat samples,intrinsic fluorescence,and UV second derivative spectra to analyze the myofibrillar protein conformation changes of meat samples,average particle size of protein and SDS-PAGE to reflect protein aggregation and degradation degree,and Low-field nuclear magnetic resonance(LF-NMR)to monitor water migration inside the meat samples.The result shows that:among different thawing methods,the carbonyl content,dityrosine content and surface hydrophobicity of samples applying MAT are the lowest,while its total sulfhydryl content,water-holding capacity and Ca²⁺-ATPase activity(P<0.05)are the highest,which boasts more stable tertiary structure,low protein aggregation and degradation degree and closer interaction between inside water and muscle proteins.In a word,MAT is able to relieve myofibrillar protein oxidation denaturation and enhance the water-holding capacity of the samples to some extent.3.Changes in gelling properties of myofibrillar proteins from porcine longissimus dorsi subjected to microwave combined with air convection thawingThis experiment takes fresh meat as the control group,and meat processed by MAT,MT,and AT as the experimental groups,aiming at further studying the influence on gel properties of myofibrillar protein of longissimus dorsi muscle of pork by MAT,expecting to improve quality evaluation system.The result shows that different thawing methods have different effects on the properties of pork MPS gel.The gel water-holding capacity,whiteness,turbidity,gel strength and texture properties of samples processed by MAT are obviously better than that of samples processed by single thawing methods(P<0.05)and are close to fresh meat sample(P>0.05).The result of rheological properties and scanning electron microscope shows that compared with other thawing methods,MAT processing forms a more flexible and even gel network structure with a higher G?value;LF-NMR analysis result also shows that among different thawing methods,water migration inside the gel of samples processed by MAT is the lowest.In a word,MAT is able to better improve the gel properties of pork protein,and enjoys broad prospects of application in meat industry.