Masters Theses

Date of Award

12-1990

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

M.J. Riemann

Committee Members

Dwight Loveday, John Mount, Ann Draughon

Abstract

Twelve boneless beef strip loins were fabricated into top loin steaks for packaging. One half of the steaks were chilled in a liquid carbon dioxide spray while the other half were unchilled. Each steak was placed into a barrier bag and the package was injected with one of the following gas mixtures: 1) 80%O2:20%CO2, 2) 40%O2:15%CO2:45%N2 and 3) 10%O2:15%CO2:75%N2. Two other treatments used in the study consisted of a vacuum packaged steak and a steak wrapped with PVC film was used for a control. The steaks were placed into a cooler at 3.3°C for a period of 0, 3, 6, 10 and 13 days of display and subsequently evaluated for relative percentages of various gases in the intact packages; Hunter 'L', 'a', and 'b' color values; myoglobin percentages of myoglobin, oxymyoglobin and metmyoglobin percentages; pH; microbial condition and sensory evaluation.

Packages initially injected with modified gas atmospheres containing O2 increased in the amount of CO2 with increased display time. This increase in CO2 was due to either respiration of the meat tissue or to the conversion of O2 to CO2 by metabolism of certain bacteria on the meat surface.

The color of the meat was affected by the chilling time, packaging treatment and display time. The use of liquid CO2 decreased percentage of the desirable oxymyoglobin form of the myoglobin pigment. The Hunter color values were unaffected by the chilling treatment.

The packaging treatment had different affects on the color of the meat. The amount of time the steaks were displayed also affected color. The high oxygen packaged meat samples had increased levels of the oxymyoglobin while the meat samples packaged in a low oxygen level had high levels of myoglobin. As display time increased, the percentages of oxymyoglobin in the meat sample decreased and metmyoglobin levels increased. The decrease in oxymyoglobin was related to a decrease in the Hunter 'a' color value or redness.

The microbial condition of the meat was unaffected by chilling but was affected by packaging treatment and display time. The modified atmosphere packaged meat had an increase in the lag phase of growth attributed to increased CO2 levels. The vacuum packaged meat had the highest aerobic plate counts among the packaging treatments but did not show any indication of bacterial spoilage. The MAP meats exhibited off-odors after 10 days of display. An increase in pH among meat samples of each of the different packaging treatments was correlated with an increase in bacterial growth.

Consumer panelists indicated that the steaks in the high oxygen MAP had an acceptable color and would purchase these products based on the color after 2 hours of display. However, due to a darkening problem, the color was found to be unacceptable throughout the remainder of the study. Steaks in the low oxygen MAP did not have an acceptable color even after 2 hours of display. The vacuum packaged meat had an unacceptable color initially, but after the 10th day of display, the panelists indicated an acceptable color.

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