Growth of spoilage bacteria in soy extended and nonextended ground beef with varying Ph levels

Author

Mark Andrew Harrison

Date of Award

12-1981

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Food Science and Technology

Major Professor

Curtis C. Melton

Committee Members

F.A. Draughon, H.O. Jaynes, J.O. Mundt

Abstract

Ground beef is commonly extended with textured soy protein (TSP). Addition of TSP may result in the formation of a more favorable environment for the growth of spoilage microorganisms. The influence of two factors which may contribute to this, possible changes in the microflora and the initial pH of meat-soy blends, were investigated in this study.

Ground beef and ground beef extended with 20% TSP were examined to determine the predominant bacterial flora present during storage at 4°C for 6 days. Bacterial numbers in the extended ground beef increased with time and at a faster rate than the nonextended product. Spoilage odors were also detected earlier in the ground beef containing TSP. From both extended and nonextended ground beef, Pseudomonas species were the predominant bacteria of fresh and stored samples. By the sixth day of storage at 4°C, the only psychrotrophs recovered were species of Pseudomonas. Considering these similarities, it appears that differences in the spoilage rate of extended and nonextended ground beef cannot be attributed to differences in the composition of their respective bacterial flora.

Bacterial isolates from the soy extended ground beef were used to test the effect of pH in trypticase soy broth (TSB), ground beef, and ground beef + 20% textured soy protein. First, growth was measured in TSB at pH levels from 5.4 to 6.2 using either hydrochloric, citric, lactic, or acetic acids. After incubation at 4°C for 7 days, acetic acid inhibited growth to the greatest extent with no growth at or below pH 5.8. Growth response was studied in meat blends at pH levels of 5.4, 5.7, 6.0, and 6.3. Mixtures were stored at 4°C with psychrotrophic plate counts performed at 48 hour intervals for seven days. In ground beef which had an initial pH of 5.4 and in ground beef + 20% TSP which had an initial pH of 5.4 and 5.7, bacterial growth was suppressed. Inhibition was thought to be due in part to the lower initial pH and to the acidulant (acetic acid) used in these blends.

Recommended Citation

Harrison, Mark Andrew, "Growth of spoilage bacteria in soy extended and nonextended ground beef with varying Ph levels. " PhD diss., University of Tennessee, 1981.
https://trace.tennessee.edu/utk_graddiss/7851