Characteristics Of Intramuscular Connective Tissue In Yak And Its Effects On Tenderness And Digestibility Of Meat

Intramuscular connective tissue(IMCT)is an important part of muscle tissue,and its morphology and composition are affected by factors such as species,breed,sex,age,muscle location and function.IMCT changes during cooking,with complex effects on the texture of the meat.In this paper,Qinghai Tibetan yak was used as the experimental material to study the IMCT characteristics of different parts of yak and its changes during cooking and in vitro digestion.The purpose of this study was to provide a theoretical reference for further understanding the impact of IMCT on yak meat quality and promoting the development of the yak industry.First,four parts of yak meat(supraspinatus,psoas major,longissimus lumborum and semitendinosus)were selected to determine their basic components.IMCT was extracted by three chemical extraction methods,investigated changes in its chemical,thermal stability and mechanical properties.The results showed that the content of basic components differed slightly between muscles.Cutting force experiment showed that the tenderness differences of the four muscles in the raw state were basically consistent with the mechanical properties of IMCT,and had no correlation with the tenderness of cooked meat.The differences in collagen content among the four parts of muscles were consistent with the differences in collagen content in IMCT extracted by different chemical methods,and the difference in the onset temperature of degeneration of total IMCT,with relatively higher collagen content in semitendinosus and supraspinatus.The above results suggested that there may be molecular populations with different stability in collagen in IMCT.In addition,the infrared spectroscopy results showed that there were no significant differences in the secondary structure of the IMCT of the four muscles.Therefore,differences in chemical,thermal stability,and mechanical properties may account for differences in muscle toughness.Subsequently,the yak longissimus lumborum muscle was vacuum cooked at different temperatures(50,60,70,80 and 90 ℃)and time(2,4 and 6 h),to investigate the effect of heat treatment on the physical properties,texture and microstructure of yak meat,and to explore the thermal denaturation process of intramuscular collagen by using a highly sensitive method for detecting collagen damage(collagen hybridizing peptide staining,CHP staining).The results showed that meat tenderness was affected by the interaction of cooking time and temperature,as well as by changes in moisture and collagen composition.Compared with cooking time,the effect of temperature on cooking loss,moisture content and redness of yak meat was more obvious.Scanning electron microscopy showed that IMCT gradually degraded and muscle fibers became more compact with increasing temperature.CHP staining showed that the collagen in the perimysium was first denatured at 50 ℃,and more collagen was denatured and degraded with the increase of temperature.Finally,vacuum cooking,traditional cooking and high pressure cooking were used to treat yak meat and extracted IMCT to explore the effect of different cooking methods on the digestibility of yak meat and IMCT.The results showed that different cooking methods would affect the basic composition,color and texture of yak meat,and the effects of traditional cooking and high pressure cooking were similar.Cooking promoted the oxidation of meat,the carbonyl content of traditional cooking and high pressure cooking was significantly higher than that of raw and vacuum-treated meat.The electrophoresis results showed that compared with raw meat,the meat protein bands after vacuum cooking were slightly blurred,while traditional cooking and high pressure cooking reduced the content of myosin heavy chain,and the actin bands did not change much.IMCT still retained large molecular weight bands after high temperature cooking.In vitro digestion results showed that cooking methods affected the digestibility of yak meat and IMCT.During the gastric digestion stage,there were still relatively large molecular weight proteins in raw meat,while the protein bands after cooking were mainly concentrated below 48 kDa,and the fragments with molecular weight below 25 kDa after complete gastrointestinal digestion accounted for more than 95%.The molecular weight distribution of IMCT gastric digestion and whole process digestion was similar to that of yak meat.