Effect Of Puerarin On Meat Quality And Fat Deposition In Heat-stressed Beef Cattle And Its Mechanism

High temperature and high humidity in summer in southern China may induce heat stress reaction,reduce fattening performance of beef cattle and make meat quality worse after slaughter.The deposition of intramuscular fat（IMF）is closely related to body fat metabolism,and its content is the key to affect beef quality.Puerarin is the main active component of radix puerariae,which can effectively alleviate stress response and regulate fat metabolism.However,its effect on beef quality and its mechanism are still unclear.The aim of this study was to investigate the effect of Puerarin on meat quality and fat deposition in heat-stressed beef cattle and its mechanism.Twenty four healthy Jinjiang bulls with 15 month old and were randomly divided into three groups as following:0（control）,400mg/kg and 800mg/kg puerarin groups.The experiment was carried out under high temperature and humidity environment in summer（from July to September）,the test period was 10 days pre-test period and 60 days pre-test period.Experiment 1:The slaughter performance,antioxidant activity and meat quality of beef cattle were determined.The results showed that:compared with the control group,all treatments enhanced the activity of superoxide dismutase（SOD）;and total antioxidant capacity（T-AOC）of 0.08%group was increased,the content of reactive oxygen species（ROS）of 0.08%group was declined（P<0.05）.The contents of crude fat and crude protein of the 0.08%group were increased（P<0.05）;the shear force of beef in the 0.04%group was decreased（P<0.05）,the contents of tetradecenoic acid（C14:1）and heptadecaenoic acid（C17:1）in muscle were increased（P<0.05）.Experiment 2:The changes of blood biochemical indexes and enzyme activities related to fat metabolism in longissimus dorsi muscle,liver and subcutaneous fat were analyzed.The results show that:compared with the control group,on the 30^thday,the contents of urea,total cholesterol（TC）,high density lipoprotein cholesterol（HDL-C）,low density lipoprotein cholesterol（LDL-C）and growth hormone（GH）in the 0.04%group were increased,while the level of cortisol（COR）was decreased（P<0.05）;the levels of triglyceride（TG）,TC and HDL-C in the 0.08%group were increased（P<0.05）.On the60^thday,the levels of serum leptin（LEP）in all treatments were decreased（P<0.05）.In addition,compared with the control group,the activity of fatty acid synthase（FAS）in longissimus dorsi and liver of 0.04%group were increased,and the activity of hormone sensitive lipase（HSL）in subcutaneous fat was decreased（P<0.05）.In the 0.08%group,the activities of lipolipase（LPL）and FAS in liver were increased,and the activities of FAS in subcutaneous fat was increased,and the activity of HSL in longissimus dorsi was decreased（P<0.05）.Experiment 3:According to the previous results,0.04%Puerarin level was selected,and high-throughput m RNA sequencing technology was used to study the regulation mechanism of Puerarin on postmortem muscle quality of beef cattle.The results showed that:compared with the control group,in Puerarin group,341 genes were up-regulated and492 genes were down regulated.KEGG function significance enrichment analysis showed that peroxisome proliferator-activated receptor（PPAR）signaling pathway,adenylate activated protein kinase（AMPK）signaling pathway and forkhead transcription factor（Fox O）signaling pathway were significantly enriched in the differential expression genes.Also Puerarin up regulated the expression levels of c GMP dependent protein kinase 2（PRKG2）,mitogen activated protein kinase 10（MAPK10）and calcium/calmodulin dependent protein kin1（CAMMK1）in AMPK pathway;it was also found that Puerarin up regulated the expression levels of fatty acid transporter（FATP）,fatty acid binding protein（FABP）,and FAS in PPAR pathway,and down regulated the expression levels of HSL,adiponectin（ADPN）,LEP and acyl Co A oxidase 3（ACOX3）in PPAR pathway.These results indicated that Puerarin can improve the antioxidant function,regulate lipid metabolism,promote intramuscular fat deposition,and improve the tenderness and flavor of postmortem beef.Its mechanism may be related to activation of AMPK signaling pathway and PPAR signaling pathway,up regulation of fat synthesis gene expression and down regulation of fatty acid oxidation gene expression.