اثر افزودن روغن‌هاي كلزا، سويا و ماهي به جيره خوراكي بر تركيب اسيدهاي چرب و كيفيت گوشت بره‌هاي پرواري

Effect of incorporation of canola, soybean and fish oils to the diet on fatty acid composition and quality of meat in fattening lambs

زمينه مطالعاتي: در سال­ هاي اخير استفاده از روغن­ ها در جيره دام به دليل داشتن برخي اسيدهاي چرب مفيد براي سلامتي انسان همچون اسيدلينولئيك و اسيدلينولنيك مورد توجه قرار گرفته است. هدف: بررسي تاثير افزودن روغن­ هاي كلزا، سويا و ماهي به جيره خوراكي بر كيفيت و تركيب اسيدهاي چرب گوشت بره ­هاي پرواري بود. روش كار: 35 راس بره نر با ميانگين وزن 2 ±27/8 كيلوگرم در يك دوره­ي 84 روزه مورد استفاده قرار گرفت. تيمارهاي آزمايشي شامل 1) شاهد (بدون افزودن روغن)، 2) 3 درصد روغن ماهي، 3) 3 درصد روغن كلزا، 4) 3 درصد روغن سويا، 5) 1/5 درصد روغن ماهي + 1/5 درصد روغن كلزا، 6)1/5 درصد روغن ماهي + 1/5 درصد روغن سويا و 7) 1/5 درصد روغن كلزا + 1/5 درصد روغن سويا بودند. نتايج: منابع مختلف روغن در سطح 3 درصد اثر معني‌داري بر رنگ،pH نهايي، شاخص­ افت حاصل از پخت و نيروي برش گوشت نداشتند. اسيدهاي چرب اولئيك، پالميتيك و استئاريك به ترتيب بشترين مقدار را در بين تمام اسيدهاي چرب گوشت داشتند. جيره­ هاي حاوي روغن سبب افزايش ميزان اسيدهاي چرب غيراشباع و كاهش اسيدهاي چرب اشباع در بره ­هاي تغذيه شده با روغن در مقايسه با تيمار شاهد شدند. بره­ هاي تغذيه شده با روغن ماهي بالاترين ميزان اسيدهاي چرب ايكوزاپنتانوئيك، دوكوزاپنتانوئيك و دوكوزاهگزانوئيك را داشتند. افزودن روغن به طور موثر نسبت اسيدهاي چرب امگا-6 به امگا-3 را در مقايسه با شاهد كاهش داد. نتيجه ­گيري نهايي: افزودن منابع مختلف روغن به جيره دام، مي‌تواند بدون اثرات منفي بر كيفيت گوشت، تركيب اسيدهاي چرب گوشت بره­ ها را تحت تاثير قرار ­دهد و به عنوان يك راهكار جهت افزايش اسيدهاي چرب غيراشباع گوشت، بخصوص اسيدهاي چرب امگا-3 و بهبود نسبت امگا-6 به امگا-3 استفاده شود.

Introduction: In recent years, there has been a growing interest in identifying strategies to enhance the concentration of healthy fatty acids in ruminant foods (meat and milk), such as conjugated linoleic acid (CLA) and n-3 polyunsaturated fatty acids (PUFAs). The composition of fatty acids in the meat has an important role in health consumers. Dietary supplementation oils rich in polyunsaturated fatty acids (PUFA) can be used to increase conjugated linoleic acid (CLA) and n−3 PUFA, and improve nutritional quality of ruminant meat. Fish oil is rich in omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), when added as a supplement to the diet of ruminants; they alter into vaccenic acid in the rumen, which can be used for synthesis of CLA in different tissues. Vegetable oils such as soybean and canola oils contain polyunsaturated fatty acids linoleic and linolenic acid and their potential benefits have been proved for human health. The composition of the diet fed to ruminants can influence the meat fatty acid composition. This study was carried out to investigate the effects of canola, soybean and fish oils on meat quality and fatty acid composition of longissimus muscle in fattening lambs. Material and methods: Thirty-five male lambs with an initial body weight of 27.8 ± 2 kg and 4-5 months old were used in a completely randomized design for an 84-day feeding experiment with a 14-day adaptation period. Experimental treatments included: 1- control diet based (without oil), 2- diet with 3 % fish oil, 3- diet with 3 % canola oil, 4- diet with 3 % soybean oil 5- diet with 1.5 % fish oil + 1.5 % canola oil, 6- diet with 1.5 % fish oil + 1.5 % soybean oil, 7- diet with 1.5 % canola oil + 1.5 % fish oil. Five lambs were then randomly allocated to each treatment. At the end of the experimental period, lambs were slaughtered after 16 h of starving. Sampling of longissimus muscle was performed between 12th and 13th ribs from the left halves of each carcass. Samples of muscle were dissected and ground to homogeneity for determination of fatty acid composition, for lipid extraction using a 2:1 solution of chloroform: methanol, according to the procedure described by Folch. PH values measured with pH meter at 24 h after slaughter. Meat colour was measured on muscle dissected from the after ageing for 48 h at 4 °C. Meat colour of samples was assessed using the L*, a* and b* system with a Hunter Lab colourimeter. The attributes of meat odour intensity, juiciness, flavour intensity, flavour quality and overall acceptability were assessed using an eight-point scale. Scores varied from 1 to 8, with 1 being the minimum score and 8 being the maximum score. Results and discussion: Different sources of lipid supplementation at 3% in the diet did not significant effect on meat colour and ultimate pH (p>0.05). There were no significant differences in cooking loss and shear force value among treatments (p>0.05). In this study, the most abundant fatty acid of meat was oleic (18:1 cis-9), followed by palmitic (16:0) and stearic (18:0), respectively. All experimental diets contain oils stimulated the accumulation of polyunsaturated fatty acids (PUFA) in the longissimus muscle of lambs compared with the control (P<0.05). The lambs fed with fish oil had the highest the 20:5n−3 (EPA) and C22:5 (DPA) or 22:6n−3 (DHA). The concentrations of saturated fatty acids significantly reduced with different oil supplementations. The oil supplementations effectively decreased n-6 to n-3 ratio in the longissimus muscle compared with the control diet. Inclusion of oil in diets increased the concentration of polyunsaturated fatty acids and decreased the proportion of saturated fatty acids in longissimus muscle. These results of current study show that oil sources with long chain contain polyunsaturated fatty acids can bypass rumen microbial degradation when added to diet of ruminant, and be absorbed in the small intestine and deposited in organs and muscles through the circulatory system. Conclusions: In conclusion, the incorporation of soybean, canola and fish oils up to 3% had beneficial effects on fatty acid composition of meat and can be used as a strategy to increase the meat content of polyunsaturated fatty acids, especially the level of long-chain n-3 fatty acids and improvement of n-6/n-3 ratio.