Abstract
Fat composition of beef, taken here to mean marbling, can be manipulated by time on feed, finishing diet, and breed type. These three factors also strongly influence the fatty acid composition of beef. Both the amount of marbling and the concentration of monounsaturated fatty acids (MUFA) increase with time on feed in grain-fed and pasture-fed cattle, but much more dramatically in grain-fed cattle. High-concentrate diets stimulate the activity of adipose tissue stearoyl-CoA desaturase (SCD), which is responsible for the conversion of saturated fatty acids (SFA) to their Δ9 desaturated counterparts. Also, grain feeding causes a depression in ruminal pH, which decreases those populations of ruminal microorganisms responsible for the isomerization and hydrogenation of polyunsaturated fatty acids (PUFA). The net result of elevated SCD activity in marbling adipose tissue and depressed ruminal isomerization/hydrogenation of dietary PUFA is a large increase in MUFA in beef over time. Conversely, pasture depresses both the accumulation of marbling and SCD activity, so that even though pasture feeding increases the relative concentration of PUFA in beef, it also increases SFA at the expense of MUFA. Wagyu and Hanwoo cattle accumulate large amounts of marbling and MUFA, and Wagyu cattle appear to be less sensitive to the effects of pastures in depressing overall rates of adipogenesis and the synthesis of MUFA in adipose tissues. There are small differences in fatty acid composition of beef from Bos indicus and Bos taurus cattle, but diet and time on feed are much more important determinants of beef fat content and fatty acid composition than breed type.
Highlights
In Japan, U.S beef previously was considered superior to Australian beef because i) Australian producers could not produce beef as highly marbled as beef from the U.S, even in long-fed cattle; and ii) Australian cattle previously had harder fat than U.S cattle
The Δ9 desaturase, which is encoded by the stearoyl-CoA desaturase (SCD) gene, converts trans-vaccenic acid (TVA) to its corresponding conjugated linoleic acid (CLA) isomer, cis-9,trans-11 CLA (Figure 1)
5% of the total fatty acids in beef are comprised of polyunsaturated fatty acids (PUFA), by far the most abundant of which is linoleic acid
Summary
ABSTRACT : Fat composition of beef, taken here to mean marbling, can be manipulated by time on feed, finishing diet, and breed type These three factors strongly influence the fatty acid composition of beef. The net result of elevated SCD activity in marbling adipose tissue and depressed ruminal isomerization/hydrogenation of dietary PUFA is a large increase in MUFA in beef over time. Pasture depresses both the accumulation of marbling and SCD activity, so that even though pasture feeding increases the relative concentration of PUFA in beef, it increases SFA at the expense of MUFA. There are small differences in fatty acid composition of beef from Bos indicus and Bos taurus cattle, but diet and time on feed are much more important determinants of beef fat content and fatty acid composition than breed type. (Key Words : Adipose Tissue, Bovine, Fatty Acids, Intramuscular, Stearoyl-CoA Desaturase)
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