Effects Of Addition With Vegetable Oil And Vitamin E On Meat Quality Of Huzhou Sheep And Approach To The Mechanism

This study consisted of three experiments. The chemical composition, fatty acid profiles and flavor compounds of Huzhou sheep meat were studied in Experiment 1. In second one, a feeding trial was conducted to manipulate the carcass characteristics, serum metabolites, and fatty acid composition of longissimus muscle by supplemental vegetable oil and vitamin E (VE). Acetyl CoA Carboxylase (ACC) and stearoyl-CoA desaturase (SCD) gene segments were cloned and their mRNA levels in intramuscular, subcutaneous fat and liver were analysed in Experiment 3 in approach to the mechanism involved in manipulation of the fatty acid profiles of the sheep meat.Experiment 1:Forty Huzhou sheep (ten each, at age of 5 months,10 months and 18 months and 4 years old) were used as experiment animals for analysis of chaemical composition, fatty acid profiles and flavor compounds. The longissimus muscle and triceps brachii were used for chemical composition analysis. The moisture content was 68.9-74.2%, ether extract was 4.1-6.2%, crude protein was 20.3-24.0%, and crude ash was 1.1-1.4% in meat of Huzhou sheep respectively. The meat protein included all 8 essential amino acids and the grades of each essential amino acid were >1 compared with the Protein Mode of FAO. The major fatty acids intramuscular fat and subcutaneous fat were oleic (C18:1), palmitic (C16:0) and stearic (C18:0), with oleic being the most. These three FAs occupied 74.2-79.7% of the total FA. Short, medium and long chain FAs were presented at 0.2-0.5%, about 4% and 95%in both fat tissues. The percentage of saturated fatty acid (SFA), monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) were 44.1-45.1%,45.7-46.9%and 8.2-10.1%in intramuscular fat, respectively. The subcutaneous fat contained more SFA and less MUFA, PUFA than intramuscular fat. The ratio of PUFA to SFA (P/S) was 0.13-0.23, and n-6/n-3 was 0.64-1.46 in Huzhou sheep. The FA profiles were effecte by slaughter age,10 months lamb having the optimal meat FA composition. There were 70 volatile flavor compounds detected by solid phase micro-extraction (SPME) and gas chromatograph-mass spectrometry (GC-SM) in intramuscular fat of Huzhou sheep, which including 14 acids,7 ketones,9 aldehydes,5 alcohols,10 esters, 13 hydrocarbons, and 12 other compounds (furan, pyrazines, pyridines, indole, and other N, S, O-containing compounds). The major volatiles were esters (24.1-28.3%), hydrocarbons (20.5-21.2%) and acids (19.0-20.0%). Among the volatile compounds presented in intramuscular fat,3-Methylbutyraldehyde, thiophenes, branch-chain fatty acid,3-Methylindole,2,3-Octanedion, may related to flavor compounds of Huzhou sheep.Experiment 2:This study was conducted to determine the effects of'supplemental vegetable oil and vitamin E (VE) on carcass characteristics, serum metabolites, liver antioxidated enzymes, and fatty acid composition of longissimus muscle in Huzhou lambs. A total of 40 male Huzhou lambs (average initial live weight of 12.75 kg) at age of 45 d, were allocated to five dietary treatments:basal (Control),3% soybean oil (SBO),3%SBO plus 500 mg/kg VE (SOE),3% corn oil (CNO), and 3% CNO plus 500 mg/kg VE (COE). All diets with roughage to concentrate ratio at 60:40 (DM base) were formulated to be isoengenetics and isonitrogenous. Feed intake was controlled to be similar among the five groups to minimize the meat differences resultant from growth rate. The experiment lasted for 12 weeks, the first 2 weeks of which was for adaptation and the following 10 weeks for experimental. At the end of the experiment, blood samples of all animals were taken via jugular vein puncture and serums were separated from the blood samples for analysis. All animals were slaughtered and carcass were weighed and dissected. Samples of longissimus muscle and liver were taken immediately after slaughting, stored in liquid nitrogen until frozen, and kept at-70℃until analyzed for FA profiles and enzyme activities. No differences were observed in animal growth performances, carcass qualities among five treatments (P>0.05). The contents of serum total protein, albumin, triglyceride, and low density lipoprotein-cholesterol were shown no difference among the five groups (P>0.05). The concentrations of cholesterol, high density lipoprotein-cholesterol, urea nitrogen, and non-esterified fatty acid increased, while glucose decreased significantly (P＜0.05) in oil added groups, compared to the control. Addition of VE had no further effects on these serum metabolites. The oil added diets increased PUFA, MUFA contents and decreased the SFA (P<0.05) of longissimus muscle in Huzhou lambs. The concentrations of C8:0, C14:0 and C15:0 were lower in oil added animal than those in the control (P＜0.05). The oil addition induced a significant increase in concentrations of trans-11 C18:1, cis-9 trans-11 conjugated linoleic acid (CLA) and total CLA (P＜0.05), but the contents of C18:2 and C18:3 were not different (P>0.05) in muscle lipids compared to the control. The ratio of n-6 to n-3 was not effected by oil added to diet (p>0.05). The oil added diets increased superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) activities and decreased maleic dialdehyde (MDA) contents in both serum and liver. VE plus diets decreased both antioxidant enzyme activities and MDA compared to oil added diets. The enzyme activities were not significant different between VE pluse animals and controls, except that liver SOD was lower and serum GSH-Px was higher in VE added animals.Experiment 3:The longissimus muscle, subcutaneous fat, and liver tissuses were taken from the animals in Experiment 2 and used for gene clone and mRNA expressin. The SCD mRNA levels were reduced significantly (P＜0.05) in liver, subcutaneous fat and intramuscular fat by feeding sheep with vegetabe oil added diet. The ACC mRNA levels were also reduced markedly in liver and subcutaneous fat in oil addition anmals, while the level in intramuscular fat was only slightly reduced. VE addition diets had no more effects on these two enzymes mRNA expressions.In summary, the meat of Huzhou sheep was enriched in protein and essential amino acids. The fatty acid profiles and the ratio of PUFA to SFA were in consistant with other sheep meat. Dietary addition of oil and VE elevated the antioxidation capacity and resulted in increased of PUFA, MUFA and decreased SFA. The de novo synthesis of fatty acids was decreased by adding vegetable oil and VE through the reduced expression of ACC gene.