Manipulation of the Fatty Acid Composition of Porcine Tissues with Respect to the Human Diet

[摘要] An attempt was made to manipulate the fatty acid composition of porcine tissues in accordance with contemporary human dietary guidelines and to investigate various factors affecting such manipulation. A review of the literature was undertaken with respect to; i) the alterations of the fatty acid composition of porcine tissues and ii) the effect of dietary n-3 polyunsaturated fatty acids on human health and disease. The first experiment attempted to define the minimum period of time required to alter the fatty acid composition of porcine tissues in line with human dietary recommendations. A diet containing 50 g/kg soybean oil plus 10 g/kg refined fish oil (Seven Seas Ltd., Hull, England) was fed to Large White x Landrace pigs for two, four and six weeks immediately before slaughter. Growth performance and carcass characteristics, including penetrometer firmness, were recorded. The total lipid contents of the outer and inner backfats, Semitendinosus, Longissimus dorsi and liver were determined by gravimetry. The content of cholesterol ester, triacylglycerol, free fatty acid and phospholipid of the tissues and their constituent fatty acid compositions were determined by thin-layer and gas-liquid chromatographies. Neither pig growth performance nor carcass characteristics were adversely affected by feeding the soybean oil/fish oil diet over differing pre-slaughter periods. Whilst the total lipid contents were generally not affected by treatment, the fatty acid composition of the lipid fractions of the tissues was significantly affected by diet. Marked increases in the levels of eicosapentaenoic acid and docosahexaenoic acid were observed in the presence of reductions in the levels of linoleic and oleic acids. The levels of linoleic acid in the outer and inner backfats were approximately 30 % of total fatty acids. Alterations in the ratios of total n-6 to n-3 fatty acids and polyunsaturated to saturated fatty acids were achieved in line with dietary recommendations; these ratios were approximately 6 and 1, respectively. Feeding the modified diet for six weeks gave the closest approximation to the dietary recommendations. The second experiment was an attempt to evaluate the effects of alterations in the levels of dietary copper and vitamin E on the fatty acid composition of tissues obtained after feeding the soybean oil/fish oil diet which had been fed in the first experiment. Copper (as copper (II) sulphate) at nominal levels of 20 or 100 mg/kg diet and vitamin E (as alpha-tocopheryl acetate) at 75 or 375 mg/kg diet were fed to Large White X Landrace entire males and females for six weeks pre-slaughter. The growth performance and carcass characteristics of the pigs were unaffected by diet. The fatty acid compositions of the muscle, backfats and liver were significantly affected by diet in accordance with the findings of the first experiment. Whereas tissue copper contents were not affected by diet, the contents of vitamin E in the tissues significantly increased as a result of dietary supplementation of alpha-tocopheryl acetate. The effect of vitamin E on fatty acid composition was more prominent than that of copper. Ratios of P;S and n- 6:n-3 were affected by both dietary copper and vitamin E. Olfactory sensory properties of samples of cooked outer backfat from two of the diets were determined by a trained taste panel. Whilst no marked effect of diet was observed, significant differences in fat flavour characteristics between two and six months of frozen storage were discerned. The third experiment attempted to evaluate the effects of alterations in dietary soybean oil (SO) and fish oil (FO) on the distribution of triacylglycerol (TAG) molecular species in pig outer backfat. In attempting this, a specific methodology involving silver ion high performance liquid chromatography was optimised. Pigs were fed diets containing (per kg diet): 50g tallow; 25g SO; 25g SO plus 10g FO; 50g SO; 50g SO plus 10g FO; and 75g SO. A total of 14 TAG fractions was identified. Neither growth performance, carcass characteristics, fat thickness (P2) nor backfat total lipid content was affected by diet. Significant differences in the fatty acid content and TAG molecular species content of the outer backfat were observed between the diets. In spite of a similarity in linoleic acid content (approximately 25% of total fatty acids), shoulder fat from pigs fed 25g SO plus 10g FO was significantly firmer than that from pigs fed 25g SO. The difference was probably related to the alterations in the content of TAG species containing the long chain n-3 polyunsaturated fatty acids.

[发布机构] University:University of Glasgow

[关键词] Animal sciences, Nutrition