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Effects of conventional and grass feeding systems on the nutrient composition of beef

J. M. Leheska^*, L. D. Thompson^*, J. C. Howe¹, E. Hentges, J. Boyce^*, J. C. Brooks^*, B. Shriver^*, L. Hoover^* and M. F. Miller^*

^* Texas Tech University, International Center for Food Industry Excellence and Department of Animal and Food Sciences, Lubbock, TX 79409 , ¹ USDA-ARS-BHNRC-Nutrient Data Laboratory, Beltsville, MD 20705 USDA Center for Nutrition Policy and Promotion, Alexandria, VA 22302-1594

mfmrraider{at}aol.com

Abstract

The objectives of this study were to determine the nutrient composition of grass-fed beef in the United States for inclusion in the USDA National Nutrient Database for Standard Reference (SR), and to compare the fatty acid composition of grass-fed and conventional-fed (control) beef. Ground beef (GB) and strip steaks (SS) were collected on 3 separate occasions from 15 grass-fed beef producers that represented 13 different states, whereas control beef samples were collected from 3 regions (Ohio, South Dakota, and Texas) of the U.S on 3 separate occassions. Concentration of minerals, choline, vitamin B₁₂, and thiamin were determined for grass-fed beef samples. Grass-fed GB samples had less Mg, P, and K (P < 0.05), and more Na, Zn, and vitamin B₁₂ (P < 0.05) than SS samples. Fat color, marbling and pH were assessed for grass-fed and control SS. Subjective evaluation of the SS indicated that grass-fed beef had fat that was more yellow in color than control. Percentage of total fat, total cholesterol, and fatty acids along with trans fatty acids and conjugated linoleic acid (CLA) were determined for grass-fed and control SS and GB. Grass-fed SS had less total fat than control SS (P = 0.001), but both grass-fed and control SS were considered lean, as their total fat content was 4.3% or less. For both GB and SS, grass-fed beef had a significantly lower (P = 0.001 and P = 0.023, respectively) content of monounsaturated fatty acids and a greater content of saturated fatty acids, omega-3 fatty acids, CLA, and trans vaccenic acid than did the control samples. Concentrations of polyunsaturated fatty acids, trans fatty acids, omega-6 fatty acids, and cholesterol did not differ between grass-fed and control ground beef. Trans vaccenic acid (18:1, 11t) made up the greatest concentration of the total trans fats in grass-fed beef, whereas CLA accounted for approximately 15% of the total trans fats. Although the fatty acid composition of grass-fed and conventional-fed beef was different, conclusions on the possible effects of these differences on human health can not be made without further investigation.

Key Words: beef • conjugated linoleic acid • conventional-fed • fatty acids • grass-fed • nutrient composition

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