Date of this Version
Thesis (M.S.)—University of Nebraska—Lincoln, 1960. Department of Dairy Husbandry.
The purpose of this study was to determine how pimaricin and mycostatin improved the keeping quality of cottage cheese. The specific objectives were as follows: (1) to develop a method for the determination of pimaricin and mycostatin in cottage cheese, (2) to determine the stability of the antibiotics in the cheese, (3) to determine the effect of the antibiotics upon the sugar utilization of Saccharomyces cerevisiae, and (4) to determine the effect of these antibiotics upon lipolytic microorganisms.
Warburg technique trials were made to determine the residual concentrations of the antibiotics in cheese, washed with antibiotic solution, and to determine the stability of the antibiotics during storage at 40°, 50°, or 60°F. In general, the cheeses with the higher concentration of antibiotics and held at the lower storage temperature had the maximum stability.
It was observed that mycostatin was less stable and lost its potency more rapidly at the higher storage temperature than pimaricin. The antibiotics retarded the fungal growth and spoilage of cottage cheese. The cheese stored at lower temperature and containing higher concentration of antibiotics had the best keeping quality.
A comparison of endogenous oxygen consumption, and the aerobic utilization of lactose, glucose, and galactose by Saccharomyces cerevisiae, in the presence and absence of the antibiotics showed that both of these processes are inhibited by the antibiotics. The results showed that the antibiotics blocked the metabolism of the three sugars approximately at the same extent indicating that the three sugars are metabolized by somewhat similar processes by Saccharomyces cerevisiae. Also, it appears that the inhibition of the growth Saccharomyces cerevisiae, by the antibiotics, may be directly related to the inhibition of the sugar utilization.
The antibiotics exhibited extremely mild inhibitory effects upon the cell production of the culture.
The microbial lipase was shown to be inhibited by the antibiotics. In general, it was found that pimaricin and mycostatin increased the shelf-life of cottage cheese. The antibiotics seem to be more effective in retarding the spoilage of cheese when added through cream dressing than when added through wash water. In the latter case, the antibiotics are probably retained in cheese by their being adsorbed upon the cheese proteins. The keeping quality of the cheese was maximum at lower temperatures (40°F.) presumably because the antibiotics were more stable at that temperature.
Advisor: Khem M. Shahani