Incorporation of dietary polyunsaturated fatty acids in pork tissues and its implications for the quality of the end products

Abstract

One hundred and ten fattening pigs of a Piétrain × Hybrid cross—barrows and gilts in equal numbers—were distributed over five feeding formulas, containing increasing amounts of polyunsaturated fatty acids (PUFA), in the form of rapeseed. The aim of the study was to evaluate the maximum admissible amount of PUFA in the pig diet before problems—in terms of backfat consistency and storage stability—occur and to investigate the incorporation of dietary PUFA in intramuscular fat as well. A tendency towards reduced feed (energy) intake was obvious from the 7% rapeseed inclusion level, apparently resulting in a somewhat thinner backfat layer. None of the backfat samples showed a visible yellow discolouration instead thin backfat layers appeared as pink. Backfat consistency was lower for gilts and decreased with increasing dietary PUFA levels. PUFAs in the feed and in backfat were very well correlated (0.8–0.9) as expected; correction for de novo fat synthesis (by means of backfat thickness) did not alter the correlations within one sex group. Thresholds for PUFA in feed—15 g PUFA/kg feed—and for PUFA in back-fat—iodine value of 70 or 15% PUFA—were all surpassed in this experiment: 18 g PUFA/ kg feed resulted in maximally 22% PUFA in the outer backfat layer. The backfat PUFA limit was reached at relatively low feed PUFA levels. This might be explained by thin and hence more unsaturated backfat layers in lean or underweight pigs. Oxidative stability of the backfat after storage for 1 year in the freezer was satisfactory. The total intramuscular fat (IMF) content showed no obvious relationship with diet, in contrast with sex: barrows had more IMF than gilts. IMF consisted in 80% apolar phase and 20% polar fraction. The apolar fraction showed similar feed and sex tendencies as backfat, although correlations between feed and apolar fraction PUFAs were higher for gilts than for barrows. The amount of phospholipid was invariable throughout all treatments. Only linoleic acid—the major fatty acid—showed some feed and sex influence. In view ofthf results obtained the threshold for feed and backfat PUFA can be as high as, respectively, 18 g PUFA/kg feed and 22% PUFA in backfat, without deterioration of fresh and frozen backfat. However, for meat processing, demands could be more severe.