Masters Theses

Date of Award

8-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

S.L. Melton

Committee Members

M.J. Riemann, W.R. Backus, P.M. Davidson

Abstract

The objective of this experiment was to determine the effect of different grass diets followed by a whole shelled corn diet on the chemical composition and flavor of beef. Ninety Angus, Hereford and Angus X Hereford steers weighing from 204 to 249 kg were obtained. During the spring and summer one-half of these steers were grazed on a temporary pasture of rye, rye grass and cover (Tl) and the other half on fescue, orchard grass and cover (T2). When the pasture died during the summer each lot of steers was removed from the pasture and divided into 5 groups of 9 steers. One group was killed directly off pasture (0-days on feed or DOF), and the other groups were adjusted to a whole shelled corn diet over a 14 day period and were fed the corn diet until slaughter. From each treatment (T), a group of steers was killed at 28, 56, 84, and 112 DOF. After slaughter, the longissimus muscle was removed from each steer and analyzed for contents of total lipids (TL), tocopherols, carotenoids (C), and total and individual phospholipids (PL), and for fatty acid (FA) composition of the TL. The cooked longissimus muscle was also evaluated for flavor by Quantitative Descriptive Analysis (QDA). The chemical components and the QDA flavor descriptors were evaluated as a function of DOF, T and their interaction. The effect of storage (-18 C) up to 4 months was also evaluated on the flavor. Identity of FA and fat soluble compounds were confirmed by gas chromatography- mass spectrometry (GCMS).

Levels of TL, sphingomyelin, and cephalin but not PL were significantly affected by DOF. In Tl, TL decreased from 4.9 to 3.7% at 0 to 28 DOF before increasing to 6.1% by 112 DOF. In T2, TL increased from 2.2 to 6.0% at 0 to 56 DOF before decreasing to 4.5% at 84 DOF followed by an increase to 5.3% at 112 DOF. PL content averaged .56% across DOF and T. Compared to grass-produced beef, corn-produced beef had lower levels of sphingomyelin (.03 versus .05%) and higher levels of cephalin (.22 versus .15%).

In all, some 82 peaks were found by GC analysis of FA. The relative percentages of 32 of these peaks were not affected by DOF or T and these were not identified. GGMS identification of the other 51 peaks revealed that 3 of these peaks were aldehydes: hexadecanal, octadecanal and 9-octadecenal. In general, as DOF increased in either T, the concentrations (mg FA/100 g beef) of the saturated and monounsaturated FA and PUFAw6 (18.2w6, 20:3w6, 20:4w6, 22:4w6 and 22:5w6 increased across DOF and the concentration of the PUFAw3 (18:3w3, 20:5w3, 22:4w3, 22:5w3 and 22:6w3) decreased.

Concentrations of tocopherols and carotenoids (C) in beef generally decreased across DOF. In Tl, the C content first increased from 0 to 28 DOF (354 to 642 pg/g TL) before decreasing to 236 by 112 DOF. In T2, the C content decreased from 755 to 362 Mg/g TL across DOF. In Tl, the level of alpha-tocopherol (A) increased from 3.0 to 4.7 pg/g beef at 0 to 28 DOF before decreasing to 1.8 at 112 DOF. In T2, the level of A decreased from 6.9 to 1.6 pg/g across DOF. No gamma-tocopherol (G) was found in beef from Q-DOF steers in either T, but beef from corn-fed steers contained an average of 0.2 μg/g. Levels of A in beef from 0- and 28-DOF steers were high enough to act as a prooxidant.

Grass-produced beef had higher intensities of a milky-oily aroma and flavor and lower intensities of a cooked beef fat aroma and flavor than corn-produced beef. Storage (-18 C) of the beef from 1 to 4 months significantly decreased the intensity of the beef fat aroma and flavor. Of all the chemical components, PUFAw3 FA and A had the highest positive correlation coefficients with the milky-oily aroma and flavor and 18:lw9 had the largest positive correlation coefficient with the beef fat aroma and flavor.

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