Effect Of Restricted Grazing Time Systems On Volatile Compounds In Lamb Meat And Its Primary Mechanism

Fifty4-month-old healthy male Tan lambs (15.62±0.33kg) were divided into5groups (A, B, C, D and E,10/group) to investigate the effects of different restricted pasture grazing times and indoor supplementation on the volatile compound of meat and fat in growing lambs and the primary mechanism. The lambs grazed for different periods of time (12h/d,8h/d,4h/d,2h/d, and0h for A, B, C, D and E, respectively) on13-hec grassland for each group and received various amounts of supplementary feedings during the120-day trial (June to September). Besides, Lambs in group A were grazing without supplementary feeding throughout the experiment; lambs in group B were grazing with a150g-concentrate supplement per day in the former two months and300g-concentrate supplement per day in the later two months. While the concentrate supplement of group C was150g (the former two months) and300g (the latter two months). Meanwhile, these indexes in group D were300g and500g. Lambs in group E were the control. In this group, all lambs had the same opportunity to the concentrate supplement as group D, and they could eat caravans microphylla freely. Besides,200g (the former two months) and300g (the latter two months) alfalfa per day was added to the feed of group E. After4months, all the lambs were slaughtered. Each part of the body fat (subcutaneous fat, abdominal fat, tail fat, kidney fat and heart fat) and longissimus dorsi were collected and stored at-80℃to analyze the volatile compound by SPME and GC-MS, the key enzymes (FAS, LPL, HSL and NADPH generating enzymes) and the key genes (FAS, ACC, LPL, PPARγ and SCD) of different body adipose issues, and the fatty acid composition by GC. Besides, the relationships of PUFA and volatile compound were analyzed to find the initial of volatile compounds.The results of Experiment1(Effect of restricted grazing time systems on volatile compounds in meat and subcutaneous fat in Tan lamb) showed that:as the increase of grazing time per day and the decrease of concentrate supplemented, the volatile compound were increased in both subcutaneous fat and longissimus dorsi muscles, resulted in more abundant flavors in meat and fat. Higher aldehyde level was in the lamb meat. Experiment2(Effect of restricted grazing time systems on body fat deposition of Tan lamb) showed that:the fat deposition, the percentages of different part body fat out of total body fat and the different part body fat out of the empty weight of Tan lambs were all influenced by different restricted grazing time systems. Concentrate with higher ME improved the absolute values of body fats and the percentages out of empty weights, but not affected the percentages out of total body fat. The levels of IMF were related with body fat such as subcutaneous fat, abdominal fat and kidney fat. Experiment3(Effect of restricted grazing time systems on key enzymes in fat metabolism of Tan lamb) showed that:enzymes of FAS and NADPH generating enzymes were not influenced by restricted grazing time systems, while concentrate promoted the LPL enzyme. There were no obvious rules for HSL from the five treatments. The activity of NADPH generating enzymes in subcutaneous fat was higher than that in abdominal fat. Other enzymes were not affected by changes of adipose issues. Experiment4(Effect of restricted grazing time systems on the expression of key genes in fat metabolism of Tan lamb) showed that:to the genes controlling the synthesis of fat, concentrate improved their expression obviously. However, other key genes were not changed by different systems. The expression of FAS in subcutaneous fat was much higher than in other fat pot, while other genes were not changed by different body fat. Experiment5(Effect of restricted grazing time systems on fatty acids of body fat in Tan lamb and relationships between fatty acids and volatile compounds) showed that:grazing improved the healthy fatty acids in body fat, and decreased the harmful ones such as C12:0, C14:0and C16:0. Tail fat tended to have more n-3PUFA and CLA which are welcome to humans, but kidney fat and abdominal fat contained more SFA. The main volatile compounds were coming from the abundant C18:3n3in lamb fat due to the longer grazing time. More C18:3n3in fat of lambs under longer grazing time turned into volatile after a series of repercussion, that’s why lambs under grazing systems had fat with more abundant volatile compounds. Totally, grazing improved the species and values of volatile compounds in lamb fat and meat; concentrate made lambs have more fat with higher levels of key enzymes and gene expression in fat metabolism. Grazing made the fatty acid compositions in Tan lamb be healthy to humans; the main volatile compounds were coming from C18:3n3in the fat.