| With the development of Chinese economy and society,also the changes in the demand of the market,consumers’ requirements for pork have gradually changed from quantity to quality.As an important factor affecting the quality of pork,the content of intramuscular fat(IMF)is a classic index to measure the quality of pork.The traditional determination method is mainly using Soxhlet chemical extraction to determine the total fat content of fat in muscle tissue.In fact,total fat in muscle tissue includes fat between fibers and intrafiber fat.The latter mainly refers to fat in fat cells between muscle fibers and its main component is triglycerides.In contrast,muscle fibers contain higher levels of unsaturated fatty acids.Therefore,for muscles with the same intramuscular fat content,the difference in the ratio of fat between fibers and intrafiber fat will result in different meat quality.On the other hand,from a physiological point of view,the lipid content in muscle fibers is also an important factor affecting muscle physiological functions(such as insulin sensitivity).Therefore,the study of techniques and methods to distinguish between fat between fibers and intrafiber fat and its content is of great significance for the further detailed analysis of the role of the two parts of fat.This study intends to improve the Soxhlet extraction method,combining tissue digestion and Soxhlet extraction technology to measure intrafiber fat and fat between fibers At the same time,this study will explore the method of analysing fat content and proportion of intrafiber fat and fat between fibers through the electrical resistance measurement method,and then establish the data model between resistance and fat content.Select freshly slaughtered pig longissimus dorsi muscle samples(n=42),and each sample is about5g-7g.The weight of the added muscle to the volume of the injected trypsin ratio is 1:6,and then dispersed muscle fibers can be obtained after digestion for 29 h.Secondly,measure the intramuscular fat content in muscle fibers by the combination of Soxhlet extraction technology and trypsin digestion technology,and measure the total intramuscular fat content in another parallel muscle sample by traditional Soxhlet extraction technology.The results showed that the percentages of intrafiber fat and fat between fibers in the total intramuscular fat in the muscle samples were 51.86±14.52% and 48.12±14.52%,respectively,indicating that about half of the intramuscular fat measured by the traditional method comes from the muscle fibers.Marble Grain rating represents the fat content between muscle fibers,which cannot accurately reflect the level of intrafiber fat content.In order to quickly determine the muscle fat content,bioelectrical resistance measurement technology is used to explore the prediction of muscle fat content.By analyzing the factors that affect the measurement of muscle resistance,it can be known that the distance between electrodes,the depth of the inserted sample,and the temperature can all affect the resistance value.The resistance value of the muscle resistance measured horizontally(vertical to the muscle fiber direction)and longitudinally measured(along the muscle fiber direction)is different,and the resistance measured in the horizontal direction is higher than the resistance measured in the longitudinal direction.Compared with the horizontal measurement resistance(R2=0.4274),the vertical measurement resistance(R2=0.6525)has a better linear relationship with the fat content in the muscle fibers,while the horizontal(R2=0.5077)and longitudinal(R2=0.5468)measurement resistance and total muscle There was no significant difference in the linear relationship between internal fat.It is inferred that the longitudinal measured resistance is more susceptible to the influence of the fat content in the muscle fiber,and the prediction model for the fat content in the muscle fiber is: Y=0.655x+0.0002.Excessive fat deposition in muscle fibers may have an impact on muscle function and physiology.On the basis of establishing the fat content in muscle fibers,this study further analyzed the relationship between the fat content in muscle fibers and the blood glucose content,muscle lipid metabolism,and physiological functions.Related gene levels and other correlations(n=15),the results showed that total intramuscular fat and intramuscular fat and blood glucose levels were not significantly correlated(P>0.05).Quantitative gene expression analysis showed that there was no significant difference in the expression levels of GR,IGF1-R,LDLR-1,INSR,GHR and other receptor genes between the high and low intramuscular fat content groups(P>0.05).The expression levels of fat metabolism-related genes such as FAS,PPARγ,C/EBPβ,HSL,ACACA,FABP4,etc.were not significantly different between the groups with high and low intramuscular fat content(P>0.05),but in the high intramuscular fat content group,The expression level of C/EBPα gene has a rising trend(P=0.07).The expression levels of muscle secretion factors IL-15,TNF-α,MSTN and FGF-21 were not significantly different between the high and low intramuscular fat content groups(P>0.05).IL-6 and FNDC5 were among the high and low intramuscular fat content groups.The difference was significant(P<0.05),and the increase in fat content in muscle fibers significantly inhibited the expression of these two muscle secretory factors.In addition,the expression of IGF1 gene also showed a downward trend in the high intramuscular fat group(P=0.07).The results show that excessive fat deposition in muscle fibers will affect the endocrine function of the muscle.Compared with the traditional Soxhlet extraction method,this study establishes a method to rapidly analyze the fat content and ratio intrafiber fat and fat between fibers and build a data model between resistance and fat content,which can improve production efficiency and avoid the harm to individuals caused by sampling.This is of great significance to the live selection of high-quality meat individuals. |
