Quality of intramuscular fat in M-longissimus thoracis and M-semimembranosus in slaughter cows

Slaughter cows are an important source of meat. Fat quality, especially in old cows, can exhibit certain specificities that may influence both sensory and technological quality of meat. Observations of meat quality are most frequently made on dorsal and leg muscles which can provide relatively exact prediction of quality also in other major muscles. Percent contents of particular fatty acids and total cholesterol content were determined in intramuscular fat in m. longissimus thoracis and in m. semimembranosus in a trial on 10 cows of the Black-Pied Lowland breed with preslaughter live weight of 510-550 kg. Fat nonsaturation index (I-1) was calculated as the ratio of unsaturated to saturated fatty acid contents (Sigma MK(1,2,3)/Sigma MK(0)), while fat nutritive value index (I-2) was calculated as the ratio of essential fatty acids to saturated fatty acids (Sigma MK(2,3)/Sigma MK(0)). Petroleum ether was used for fat extraction from muscles. Extracted-fat Fatty acids were converted to methyl esters by alkaline transmethylation according to Bannon et al. (1992). Gas chromatographic analysis on a PACKARD instrument, 419 model, was applied to determine percent contents of fatty acids. Total cholesterol content was determined by a technique according to Hornakova et al. (1974). Tab. I shows percent contents of particular fatty acids with the chain C(10:)0-C-22:2, with the highest percentage of oleic (43.17% and/or 42.71%), palmitic (26.96% and/or 25.94%) and stearic acid (16.21% and/or 17.89%). Out of essential fatty acids, linoleic acid (4.04% and/or 4.06%) and linolenic acid (1.24% and/or 0.43%) were present. Significant differences between the muscles were observed in palmitoleic, linolenic and arachidic acids. But these differences did not influence significant values of both indexes of fat quality (Tab. II). The percentage of saturated fatty acids in lit. Iongissimus thoracis was 49.86%, and 47.45% in m. semimembranosus. There were not any significant differences between the muscles in total cholesterol content (73.88 and/or 72.77 mg/100 g). The content of total intramuscular fat in m. longissimus thoracis (3.90 g/100 g) was found to be higher than in m. semimembranosus (1.98 g/100 g). The results on the quality parameters of intramuscular fat in slaughter cows are close to the values determined in other trials on slaughter bulls (Palanska et al., 1993; Mojto et al., 1995).