The ecology of bacterial spoilage of fresh meat at chill temperatures.

At chill temperatures the spoilage flora of meat is composed of psychrotrophs originating largely from the hides of slaughtered animals. Under humid conditions, aerobic floras are usually dominated by pseudomonads while anaerobic floras are dominated by lactobacilli. In both cases growth occurs on low molecular weight soluble components of meat which are attacked in the order glucose, glucose-6-phosphate (Enterobacteriaceae only) and amino acids. Under aerobic conditions spoilage becomes detectable when the bacteria begin to degrade amino acids which remain abundant at the meat surface when growth ceases, probably because of limited availability of oxygen. Under anaerobic conditions growth ceases because the diffusion of fermentable substrates to the surface is not rapid enough to support further growth. Aerobically, there is no interaction between different bacterial species until the maximum cell density is approached; anaerobically, however, lactobacilli produce an antimicrobial agent which inhibits growth of competing species. The composition of spoilage floras can be affected by changes in water activity and the storage atmosphere.