Masters Theses

Date of Award

6-1987

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

Sharon L. Melton

Committee Members

M. James Riemann, John R. Mount, William R. Backus

Abstract

A total of 48 yearling Angus, Hereford, and Charolais breeds were divided into two groups of 24 steers, and during the 1985 spring and summer, each group grazed a different pasture (PType): fescue- orchardgrass-clover or ryegrass. When each pasture no longer could sustain grazing in the summer, each group of steers was divided into 3 sub-groups of 8 steers each. One sub-group from each PType was killed directly off-pasture and represented the 0 days on feed (DOF) group. The other sub-groups were accustomed to a whole-shell com diet over a two-week period and were fed the com diet up to 112-DOF in a drylot at the University of Tennessee Plateau Experiment Station, Crossville, TN. At 0-, 56-, and 112-DOF, the sub-groups from each PType was transported to and slaughtered at Lay's Packing Co. Knoxville, TN. Before slaughter, fat thickness at the 12th-13th rib and steer weight were recorded along with hot carcass weight at the plant for each animal. After the carcass of each steer was chilled at 6°C for a 48-hr period, a hindquarter from each was transported to The University of Tennessee Meats Laboratory. Ground beef containing approximately 20% fat was formulated from the biceps femoris muscle and external fat from the round of each carcass. Ground beef from each steer was analyzed for total lipid content. From each steer, cooked ground beef patties held at an internal temperature of 55 °C, were evaluated for aroma and flavor by Quantitative Descriptive Analysis (QDA). The headspace volatiles of cooked ground beef from 6 steers in each sub-group were also analyzed. Volatile compounds from cooked ground beef held at 55 °C were trapped on a Tenax GC trap, and then analyzed on a 30-m, 0.25 mm i.d. fuzed silica SPB-35 capillary column by gas chromotography and mass spectrometry. The relative percentage of abundance (RPA) of each volatile, intensity of each QDA flavor descriptor, total lipid content and animal measurements were statistically analyzed as a function of PType, DOF and their interaction. Factor analysis was also applied separately to the volatiles and the QDA descriptors to reduce these analyses to the lowest number of factors. The chemical volatiles were also correlated with QDA flavor analysis and the ground beef samples classified into sources by statistical procedures. Levels of the undesirable milky-oily aroma and flavor were significantly reduced and the desirable beef fat aroma and flavor intensities increased by feeding a com diet to beef cattle after they had grazed on pasture. Although the QDA panel used 6 different descriptors to evaluate beef flavor, factor analysis reduced all 6 to a single factor which was called "Beefy". Differences found in the flavor descriptor intensities allowed the panel to correctly classify approximately 94% of the samples into their sources of PType and DOF groups. Forty volatile compounds, of which 29 were positively identified, were found in the headspace of the ground beef samples. Changes in the RPA of 22 volatile compounds of ground beef were found with increasing DOF. Levels of 11 volatiles (toluene, ethyl-benzene, propyl-benzene, l-ethyl-2-methyl-benzene, pentanal, nonane, 4-methyl-3-penten-2-one, 3-penten-2-one, and 3 unknown compounds) were found to be important in describing DOF affects for ground beef. Six of these compounds (toluene, pentanal, l-ethyl-2-methyl-benzene, 4-methyl-3-penten-2-one, and 2 unknowns) were able to correctly classify approximately 94% of the feeding groups into the correct days on feed classification, RPA of 16 volatile compounds were correlated with the intensities of QDA descriptors (P <.05). Toluene was the only compound found to be positively correlated with milky-oily flavor in ground beef. Seven compounds were positively correlated with beef fat flavor with octane having the highest correlation coefficient (r=0.62). Five compounds (pentanal, ethyl-benzene, toluene, l-ethyl-2-methyl-benzene, and an unknown) were found to account for 51% of the variation for beef fat flavor thus indicating that any of these compounds may be suitable as indicators for "Beefy" flavor.

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