Masters Theses

Date of Award

8-1983

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

Sharon L. Melton

Committee Members

M. J. Riemann, C. C. Melton, W. R. Backus

Abstract

Sixty-eight Angus steers were separated into five treatment groups, each of which grazed a different type of pasture prior to grain feeding. Each pasture was composed of different mixtures of grasses. The grasses included fescue, clover, sudan grass, sorghum, bermuda grass, and orchard grass. Three steers from each treatment were slaughtered off grass (0-day feed group). The remainder were divided into feeding groups where at least two steers from each treatment were in each group, and all were adjusted to a corn diet for two weeks. After adjustment a group was slaughtered every 28 days up to 112 days on corn. Total lipid content, fatty acid composition, tocopherol content and sensory evaluation of flavor by Quantitative Descriptive Analysis were determined on the longissimus muscle from each steer carcass that was aged 10 days at 6°C. The muscle was stored in double-wrapped polyethylene coated freezer paper at -18°C until analyzed. Grasses from each pasture also were analyzed for moisture, total lipid and fatty acid composition. Across time on feed, milky-oily flavor and aroma decreased linearly in intensity; beef fat flavor and aroma increased linearly in intensity, and total lipid content increased curvilinearly. Beef from steers off grass had lower levels of monounsaturated and higher levels of saturated and polyunsaturated fatty acids than beef produced by grain. Fatty acids deposited in increasing lipid content across days on feed included 14:0, 14:1, 16:0, 16:1, 17:1, 18:1, 18:2ω6, and 20:1. Beef produced by grass had higher levels of ω3 fatty acids (18:3, 20:3, 20:5, 22:5, and 22:6) and lower levels of ω6 fatty acids (18:2, 20:3, and 20:4 than beef produced by corn. High levels of 18:3ω3 in all pastures was pro-bably the source of the ω3 acids, and the high levels of 18:2ω6 in corn, the source of the ω6 acids. Tocopherol (α and r) content in muscle decreased over time on feed, and the change in α-tocopherol content could be explained by the change in its dietary levels. Flavor of the beef was correlated with chemical characteristics of the beef. Fatty acids positively correlated with milky-oily flavor included 13:0, 15:0, 19:0, 19:1, 20:1, 20:3ω3, 20:3ω6, 20:5ω3, and the sum of the ω3 fatty acids. Fatty acids positively correlated with beef fat flavor included 12:0, 14:0, 14:1, and 16:1. Of all chemical characteristics, α-tocopherol had the highest positive correlation coefficient (0.58) with milky-oily flavor. Total lipid content and moisture content of the grasses in the different treatments were within reported literature levels. There were no significant differences among pastures in the fatty acid composition. All pastures had high levels of 18:2ω6 (23-38%) and 18:3ω3 (23-43%). Pasture type did not significantly affect the flavor of the beef or the lipid or tocopherol contents, but did affect a few fatty acids expressed in mg/100 g beef: 14:0 20:3ω3, 20:4ω6, 22:6ω3, and an unknown which was possibly a branched chain 18 carbon acid.

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