Masters Theses

Date of Award

3-1981

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

S. L. Melton

Committee Members

M. P. Penfield, M. J. Riemann

Abstract

Sixty steers (30 Hereford and 30 predominantly Angus) were grouped into 6 groups of 10 steers on the basis of breed, weight and frame size and were backgrounded on predominantly fescue pasture from April through July, 1979, after which one group of 10 steers was slaughtered. The other steers were adjusted to a whole shelled corn diet for 2 weeks. After the adjustment period, one group of 10 steers was slaughtered every 28 days up to 140 days on corn. Ground beef which was formulated to contain 20% fat was prepared from the semimembranosus muscle and outside brisket fat from the right side of each carcass after chilling 48 hours at 6°C. Ground beef from each steer was analyzed for fatty acid composition of total lipid, water soluble carbohydrates, lactic acid, volatile fatty acids, titratable acidity, total lipid content and moisture content. The flavor of the ground beef from each steer was evaluated by Quantitative Descriptive Analysis (QDA). Results were analyzed statistically as a function of time steers were fed corn, breed and frame size X breed. Significant time effects were separated by orthogonal polynomials, and equations for dependent variables as a function of time on corn were determined. During the 140 days steers were on grain, the following changes occurred in the ground beef: stearic acid decreased curvilinearly from 18.32 to 8.36%; oleic acid increased curvilinearly from 40.88 to 48.05%, linolenic acid decreased linearly from 2.16 to 0.86%. In addition, acetic acid increased linearly from 2.98 to 4.33 mg/100 g ground beef; water soluble carbohydrates increased linearly from 2.54 to 4.56 mg glucose equivalents/10 g ground beef; initial pH of the raw ground beef increased linearly from 5.42 to 5.63 while titratable acidity decreased linearly from 1.07 meg H⁺/10 g ground beef to 0.94. Lactic acid (X̳=76 mg/10 g ground beef), although accounting for 84.6 ± 6.3% of the titratable acidity, did not change significantly with time on corn. Descriptive terms chosen by the QDA panel for beef flavor were milky-oily, cooked beef fat, sour, metallic, liver, fishy and off-flavor. The milky-oily note decreased to a minimum intensity at approximately 114 days on corn and the cooked beef fat flavor note increased to maximum intensity at approximately the same time. Fishy and sour flavor notes also decreased as time steers were fed corn increased. Simple correlation coefficients were determined between flavor characteristics and chemical components of ground beef. Stearic acid had a positive correlation coefficient with milky-oily aroma and flavor (r=0.72 and r=0.62, respectively) (p < 0.001); while with the same terms, pentadecanoic acid and linolenic acid had correlation coefficients above 0.50 (p < 0.001). Monounsaturated fatty acids (C14:1, C16:1 and C18:1) and 15-methylhexadecanoic acid (αC17:0) were correlated positively with cooked beef fat flavor and aroma at or above the p < 0.05 level. Acetic acid was correlated negatively (p < 0.01) with sour flavor as well as with milky-oily flavor. Titratable acidity was correlated positively with sour flavor (p < 0.05) and initial pH was correlated negatively (p < 0.05) with sour aroma. Pasture grass samples obtained during the backgrounding period were analyzed for moisture content, total lipid content and fatty acid content of the total lipid. Moisture content decreased from 73.29 to 66.03% from the beginning to the middle of the period and then increased to 71.94% at the end of the period. Total lipid content of pasture grass protected from the grazing steers decreased from 2.47 to 1.91% while total lipid content of pasture grass grazed by the steers decreased from 2.21 to 1.75%. Linolenic acid was the predominant fatty acid in the pasture grass (X̳=40.19%) with C16:0, C18:0, C18:1 and C18:2 being the other major fatty acids. Linolenic acid decreased in percentage concentration from 51.52 to 33.37% in samples protected from the grazing steers and from 45.35 to 29.23% in grazed samples and the other major fatty acids increased in percentage concentration.

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