| The high-altitude,low-pressure,cold-anoxic,free-grazing climatic environment have made yak meat safe,clean,high-quality,precious and rare,for the quality of green food.Compared with the mainland beef,yak meat has higher unsaturated fatty acids and protein,and has superior food quality and nutritional quality.Due to the difference between yak meat and other beef components,the existing experience and technology of beef storage and preservation are not applicable to the research on storage and preservation of yak meat.Therefore,it is necessary to further study its storage and preservation methods.Based on this,this topic uses Tibet yak meat as raw materials to explore the effects of cold(0?)and ice temperature(-2?)conditions,the combination of ice temperature combined with preservatives,ice temperature combined with preservatives and modified atmosphere packaging.In order to obtain the best preservation technology of yak meat,and use the UPLC-Q-TOF-MS technology to try to elucidate the preservation mechanism during the storage of yak meat from the level of lipidomics.Predict possible lipid function,analyze the interaction between lipids and the correlation between lipids and other nutrients during the process of decay in yak meat.The main research contents and conclusions are as follows:The effect of temperature on the sensory quality,physicochemical properties and flavor components of yak meat were studied.The results showed that the sensory ratings of yak meat were higher under ice temperature storage,and the pH value,TVB-N value,peroxide value,malondialdehyde increase rate,and moisture content loss rate were lower.The indicators show that the ice temperature is better than cold preservation.A total of 108 kinds of volatile components were detected during the storage of yak meat,of which 43 were hydrocarbons,followed by aldehydes,alcohols,esters,ketones,acids and others.With the prolongation of storage time,the relative contents of volatile components such as esters and alcohols related to fat oxidation increased gradually,and the trend of hydrocarbons was not very obvious.However,The characteristic flavor aldehydes of yak meat gradually decreased,especially the decrease rate of benzaldehyde and nonaldehyde,and the temperature at 0?decreased obviously faster than-2?.The time to maintain the first degree of meat freshness at storage temperatures of 0? and-2? was 18 days and 21 days respectively,indicating that the ice temperature preservation effect was good.The effects of preservatives such as lysozyme,chitosan,Nisin and tea polyphenols on the quality of yak meat were studied under ice temperature conditions.The results showed that the effect of these four preservatives on the preservation of yak meat was gradually weakened,and the interaction between the two was significant except for the insignificance between tea polyphenols and Nisin.The optimum concentration of composite preservatives obtained under ice-temperature storage conditions was:lysozyme 0.05%,chitosan 0.44%,tea polyphenols 0.22%,and Nisin 0.03%.After verification,it was found that compared with simple ice temperature storage,the combination of this preservative and ice temperature can extend the storage period of yak meat.The time of maintaining first-grade fresh meat was 21 days and 23 days respectively at-2? ice temperature and-2? ice temperature combined with compound preservatives storage conditions,thus indicating that the addition of preservatives improved the ice temperature preservation effect of yak meat.Under the conditions of ice temperature combined with preservatives,the effect of modified atmosphere packaging on the storage and preservation of yak meat was studied.The results showed that with the increase of storage time,the sensory rating of yak meat under nitrogen was the slowest.At the end of 32 days of storage,the yak meat under this package remained within the range of secondary freshness.The pH values of physiochemical indicators of yak meat under three kinds of packaging methods(nitrogen packaging,vacuum packaging,and ordinary air packaging)showed a trend of decreasing first and then increasing.The TVB-N value,malondialdehyde,and peroxide value all showed a rising trend.The water content decreased in 0-4 days,a slight increase in 4-8 days,and gradually decreased after 8 days,while the loss of moisture content and the change of physical and chemical characteristics under the nitrogen package were even smaller.A total of 102 flavor components were detected during storage of yak meat in atmosphere-modified packaging,and the main components were aldehydes,which accounted for 62.00%of the total flavor components.With the prolongation of storage time,the relative contents of esters,alcohols,etc.showed a gradual upward trend,while the aldehydes as a characteristic flavor material of yak meat,its relative content gradually decreased,among them,furfural and hexadecyl aldehyde decreased most rapidly.At the end of the 32 days of storage,furfural in the nitrogen group,vacuum group,and common air group decreased from the initial value(20.77%)to 17.50%,17.12%,and 16.96%,respectively.Aldehyde was reduced from initial values(10.73%)to 7.84%,7.69%,and 7.52%,respectively.It can be seen that the relative content of aldehydes in the nitrogen packaging group is the lowest,which indicates that the nitrogen packaging has better preservation effect.The time of maintaining first-grade fresh meat was 23 days and 28 days respectively at-2? ice temperature combined with compound preservatives and-2 ice temperature combined with compound preservative and nitrogen packaging.This shows that yak meat is packed with nitrogen,which further improves the ice temperature preservation effect of yak meat.In order to the best cold fresh yak meat preservation conditions were obtained.UPLC-Q-TOF-MS technology was used to study the changes of lipid groups in yak meat at 0 d,6 d,and 12 d at-2?‰ and 0? respectively.The metabolites were screened and identified by bioinformatics.The results showed that 98 and 136 differential metabolites were screened out at-2? and 0? storage for yak meat.,respectively.These differential metabolites were mainly fatty acids,sterol lipids,glycerides,glycerophospholipids,sphingolipids.Isoprenol esters and polyketides.In metabolomics,the lower the temperature,the lower the number of differentially expressed metabolites,which indirectly means that the lower temperature is conducive to preservation.Pathway enrichment analysis showed that the path of yak meat which was significantly enriched during storage was linoleic acid metabolism,anabolic biosynthesis of steroids.During the storage of yak meat at different temperatures,the rate of decrease of unsaturated fatty acids and aldehydes under linoleic acid and the rate of rise of alcohols associated with fat oxidation have all slowed,and these changes are more pronounced at low temperatures.In steroid metabolism,cholesterol is formed by a series of reactions of squalene,and cholesterol is indirectly produced by the action of 7?-hydroxylase.Bile acid emulsification accelerates the dissolution of lipids.Cholesterol can indirectly reduce the biosynthesis of steroid hormones and the degradation of steroids.The higher temperature will accelerate the rate of this series of reactions,thereby accelerating the reaction of cholesterol and molecular oxygen,and further accelerate the speed of deterioration of lipids. |
PDF Full Text Request