Effect of the rearing system on the fatty acid composition and oxidative stability of the M. longissimus lumborum and M. semimembranosus in lambs

The effect of two rearing systems—on pasture and indoor rearing (intensive) on a high concentrate diet on lipid content, fatty acid composition of triacylglycerols and phospholipids, and lipid stability after 240 days of frozen storage was studied in the M. longissimus lumborum and M. semimembranosus muscles from lambs of a local Bulgarian sheep breed. Meats from the pasture and indoor reared animals had distinct differences in lipid content and fatty acid composition, which influenced the lipid stability. The phospholipid content in the M. longissimus lumborum was higher, and that of the triacylglycerols—lower (p < 0.05) in lambs raised on pasture compared to concentrate fed animals, while no differences in M. semimembranosus between the two rearing systems were recorded. The triacylglycerols of both muscles in extensive reared animals contained relatively more C18:3n−3 (p < 0.05), more saturated fatty acids and less proportions of C18:1 (p < 0.001) and C18:2 (p < 0.001), than the concentrate fed animals. Rearing conditions did not influence the sum of saturated and mono-unsaturated fatty acids in the muscle phospholipids. However, the phospholipids in both muscles of animals fed grass had twice as much as (p < 0.01) n−3 polyunsaturated fatty acids (PUFA) and less extent n−6 PUFA (p < 0.01), leading to a lower n−6 PUFA/n−3 PUFA ratio, compared to lambs reared intensively. M. longissimus lumborum from the outdoor animals showed significantly (p < 0.01) lower thiobarbituric acid-reactive substances (TBA-RS) levels than the same muscle in the concentrate fed lambs. No significant difference in the value of this parameter in the samples of M. semimembranosus was observed. This study suggests the meat of grass fed animals to have a higher appropriate lipid content and fatty acid profile with regard to human health, as well as a better oxidative stability of lipids during storage.