Lipid and cholesterol composition of the longissimus muscle from Angus, Brahman, and Romosinuano
Dinh, Thu T. N.
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Lipid and cholesterol composition of red meat has been extensively studied for years, especially on genetic variation. However, Romosinuano cattle were recently adopted into America and its lipid composition remains unclear. An investigation is needed to compare this breed to other well-known breeds of cattle in the U.S. Study in chapter II was to compare the fatty acid (FA) composition of the longissimus muscle (LM) from three divergent breeds of cattle: Angus (AN, n = 5), Brahman (BR, n = 4), and Romosinuano (RM, n = 9) regarding intramuscular (i.m.) fat content. Cattle were blocked by breed and fed the same identical commercial finishing diets in a commercial feedlot prior to harvest. LM samples were collected from each carcass between 10th and 13th ribs, trimmed of external fat, frozen in liquid nitrogen, homogenized, and utilized for fat extraction using the modified Folch procedure. Extracted fat was analyzed using GLC with an HP-88 capillary column. FA composition was determined using both normalized percentage (%) to the total fatty acids in samples and gravimetric calculation (mg/g of fresh muscle tissue), in relation to degree of saturation, which was expressed by saturation index (ratio of saturated fatty acids to unsaturated fatty acids, SI). Crude fat determination showed that LM from AN purebred cattle had the highest amount of i.m. fat (7%, P < 0.001). Intramuscular fat of LM from AN contained higher percentage of total SFA (P = 0.003) whereas that from RM had higher percentage of total PUFA (P = 0.002). The percentage of total MUFA was the same among three breeds (P = 0.9). Unlike the normalized percentage, the gravimetric calculation, which was a measure of actual FA concentration in LM, revealed a significantly higher concentration of SFA (26.39 mg/g) and MUFA (26.70 mg/g) in LM from AN cattle as compared to BR and RM cattle (P < 0.001). Additionally, BR purebreds had the lowest PUFA concentration (1.63 mg/g, P = 0.009) in the LM although this difference in percentage of total fatty acids was not found to be statistically significant as compared to AN and RM (P = 0.088, P = 0.015, respectively). Regardless of breeds, the MUFA proportion was always highest (48.2%, P < 0.001) while PUFA was least contributory to FA composition (1.33 mg/g to 2.69 mg/g and 2.91% to 10.98%, P < 0.001). Beef LM fatty acid composition was also characterized by palmitic and oleic acids being the most abundant fatty acids (P < 0.001). These results suggested a genetic variation in FA synthesis and deposition among breeds that influenced both marbling content and its composition. In chapter II, the fatty acid (FA) composition of the longissimus muscle (LM) from crossbred cattle of Angus, Brahman, and Romosinuano were analyzed, again, in relation to intramuscular (i.m.) fat content to investigate the effects on crossbreeding on lipid composition. Using the same methods, which were used for purebred cattle, results from this study showed that no difference in i.m. fat content was found among crossbred cattle, which resulted in their very similar fatty acid compositions. However, small but significant higher percentage of palmitic acid was found in ANxBR cattle (P < 0.001), which suggested a genetic variation of fatty acid synthesis. As compared to our previous study on purebred cattle, the results from this study indicated significant effect of crossbreeding, by which Angus cattle was most influenced. This study also confirmed the importance of muscle fatness, which is also genetically caused, in determining fatty acid composition. In chapter IV, cholesterol composition became the subject, in which the study was focused on development of a highly accurate and repeatable method for cholesterol quantification in meat samples and its application to evaluate the differences in cholesterol content of longissimus muscles (LM) from Angus (AN, n=5), Brahman (BR, n=4), and Romosinuano (RM, n=9) purebreds. Validation of this method was performed using SRM1546 sample, a meat homogenate from the National Institute of Standard and Technology (NIST), and three different LM test samples. The results indicated that the modified method was highly efficient and accurate with more than 95% cholesterol recovered. The method was also found to be repeatable with an average coefficient of variation of 3.12%. This modification reduced 90% of chemicals used and eliminated time-consuming steps that hindered high throughput application of the traditional method. Application of this method for cholesterol quantification of LM samples revealed differences among the three breeds evaluated. The Angus LM samples with higher fat content (50% higher than Brahman and Romosinuano) which was associated with significantly higher cholesterol concentration (70.25%, P=0.007). Interestingly, the cholesterol concentration was found to relate to fatness of muscle (r=0.90, P