Some metabolic and biochemical characteristics of representative microbial isolates from vacuum-packaged beef

Consequences of packaging on bacterial growth. Meat is an ecological niche

Meat is a good support for bacterial growth and particularly for bacteria which are specific of meat and meat products. Little is known about the physiological and biochemical factors which could explain why some bacterial species are only isolated from meat. This review tentatively points out, from an ecological point of view, some of these factors in Gram negative and Gram positive micro-organisms influencing storage life.

Identification of psychrotrophic Micrococcaceae spp. isolated from fresh beef stored under carbon dioxide or vacuum

Seventy-four Gram-positive, catalase-positive coccal strains were isolated from fresh beef stored under carbon dioxide (< 500 ppm O2) or vacuum for up to 15 weeks at 0, 2 or 4 degrees C. Isolates were identified using biochemical tests listed in several published protocols and the API Staph-Ident System. No isolates were identified as Staphylococcus aureus. Twenty-nine isolates were identified as Staphylococcus saprophyticus (five distinct groups), 24 isolates were identified as Staphylococcus gallinarum and 21 isolates were identified as Micrococcus varians. The staphylococcal isolates were coagulase-negative, non-hemolytic and novobiocin resistant. They produced acid from several carbohydrates under aerobic conditions, hydrolysed gelatin but not collagen, showed lipolytic activity and grew in 15% NaCl. The Micrococcus varians isolates also were salt-tolerant, produced acid only from glucose, fructose and galactose (two strains), and were resistant to lysozyme (1600 micrograms/ml). Lactic acid was the major end product of aerobic glucose metabolism. All S. saprophyticus and M. varians isolates tested contained cell wall fatty acids with chain length > or = C20:0.

Factors affecting growth and lipase production by meat lactobacilli strains and Brochothrix thermosphacta

Lipolytic activity of lactobacilli strains and Brochothrix thermosphacta was cell-related; no significant activity was found in the supernatant fluids. Most lipase was produced during the logarithmic phase of growth and was greatly affected by growth conditions. The optimal temperatures for growth and lipase production were respectively 24 degrees C for B. thermosphacta and 30 degrees C for lactobacilli. For all strains, an initial pH of around 7.0 for the medium and low glucose concentration stimulated lipase production. Tributyrin inhibited both growth and lipase production at a concentration of 0.1% for B. thermosphacta or 1% for lactobacilli. Butyric acid (0.1%) and anaerobic culture inhibited lipase production by B. thermosphacta while these two factors had no effect on enzyme production by lactobacilli.

Glycerol utilization by Brochothrix thermosphacta

Growth of the meat spoilage organism, Brochothrix thermosphacta, was supported by either glucose or glycerol with acetoin production. Similar yields of bacteria were obtained at growth-limiting concentrations of either substrate. The rate of uptake of each substrate was similar but glycerol supported higher rates of respiration than glucose. These findings are discussed in relation to metabolism of glycerol and the use of glycerol for meat storage.