Attributes of microbial associations of meat growing as xenic batch cultures in a meat juice at 4 °C

Strains of Gram-positive (Carnobacterium piscicola, Leuconostoc mesenteroides subsp. mesenteroides, Brochothrix thermosphacta) and Gram-negative (Pseudomonas fragi and Hafnia alvei) bacteria isolated from minced lamb packaged under a modified atmosphere were cultivated in a meat (lamb) juice at 4 °C. Carbohydrates were catabolised in the order glucose > glucose 6-phosphate during the development of the population. Under an atmosphere enriched with carbon dioxide the Gram-negative portion of the population was suppressed during the exponential phase but H. alvei became the dominant organism towards the end of a protracted stationary phase of growth. With the aerobic atmosphere P. fragi catabolised creatine and became the dominant species in the stationary phase. The inability of C. piscicola to catabolise glucose 6-phosphate was reflected in its population being smaller than those of the other Gram-positive organisms (C. piscicola < L. mesenteroides subsp. mesenteroides < B. thermosphacta). During the stationary phase of growth, indigenous l-lactic acid and the d-isomer produced by leuconostocs were oxidised to acetic acid by the Gram-positive flora under an atmosphere enriched with carbon dioxide. These oxidations, which occurred after depletion of glucose, were supported by the oxygen in the system. d-Lactic and acetic acid appeared to be possible parameters for the estimation of the microbiological quality of packaged meat.