The microbiology of prepacked beef steaks stored at chill temperatures (-1 or 4°) was investigated. The changes in the composition of the microflora was determined by identification of isolates taken at intervals during storage. In the initial stages of the work the beef was subjectively assessed for acceptability by a panel of laboratory staff. Later, a colour measuring machine was also used. Preliminary experiments confirmed that if the initial level of contamination was low and/or the temperature was -1°, appreciable extensions in storage life were obtained. When steaks (packed in air with gas permeable film) were allowed to spoil, Pseudomonas was the dominant organism. No significant increase in storage life was found when a gas impermeable film was used, but under these conditions Microbacterium thermosphactum was the principal component of the flora. Novel methods of preservation arose from studying the influence of various gaseous environments on the microbiological and colour characteristics of beef. A gas mixture containing 80% 02 + 20% CO2 gave marked increases in storage life by maintaining the beef pigment in the oxygenated state whilst simultaneously depressing the growth of the Gram negative aerobic spoilage flora. Further extensions in shelf life were achieved by combining gas packing and storage at -1°. With gas packed beef stored at 4° and -1° the dominant microorganisms were M. thermosphactum and Leuconostoc respectively. The properties of a selection of the microbial groups isolated from beef i.e. Pseudomonas, M. thermosphactum, Acinetobacter, lactic acid bacteria, Micrococcus, Enterobacteriaceae and yeasts, were studied in detail. Based on these results the organisms were identified where possible to species level.
|Date of Award||1970|