The influence of atmosphere composition on the metabolism of Brochothrix thermosphacta was studied by analyzing the consumption of glucose and the production of ethanol, acetic and lactic acids, acetaldehyde, and diacetyl-acetoin under atmospheres containing different combinations of carbon dioxide and oxygen. When glucose was metabolized under oxygen-free atmospheres, lactic acid was one of the main end products, while under atmospheres rich in oxygen mainly acetoin-diacetyl was produced. The proportions of the total consumed glucose used for the production of acetoin (aerobic metabolism) and lactic acid (anaerobic metabolism) were used to decide whether aerobic or anaerobic metabolism predominated at a given atmosphere composition. The boundary conditions between dominantly anaerobic and aerobic metabolisms were determined by logistic regression. The metabolism of glucose by B. thermosphacta was influenced not only by the oxygen content of the atmosphere but also by the carbon dioxide content. At high CO 2 percentages, glucose metabolism remained anaerobic under greater oxygen contents.Modified atmosphere packaging extends the shelf life of raw meat and fish by suppressing or slowing down the growth of gram-negative psychrotrophic bacteria, mainly pseudomonadlike organisms, which cause rapid spoilage of food stored in contact with air as a result of the presence of end products from aerobic metabolism. Different combinations of carbon dioxide, nitrogen, and oxygen have been used in modifiedatmosphere-packaged (MAP) meat and fish. The commercial approach to optimizing the bright red color of MAP fresh red meat consists in enriching the atmosphere in both carbon dioxide and oxygen, usually to ca. 20% CO 2 and ca. 80% O 2 (1,19,23). Color also plays an important role as a limiting factor in the shelf life of some species of scombroids, such as tuna and related species, stored under modified atmospheres. It has been reported elsewhere that 40% CO 2 and 60% O 2 are the most effective mixture to extend the shelf life of tuna, in which Shewanella putrefaciens was one of the dominant bacteria when stored in contact with air (18). This higher concentration of CO 2 recommended for MAP tuna (18) is due to the greater resistance of S. putrefaciens than of Pseudomonas spp. to CO 2 (20) and also to the relatively high pH of tuna, at which S. putrefaciens is able to grow (14).Brochothrix thermosphacta is one of the dominant microorganisms in CO 2 -and CO 2 -O 2 -enriched atmospheres. Therefore, this bacterium plays an important role in the spoilage of MAP meat (1, 6, 16, 28) and fish (8,17,18,24). The main factor limiting the shelf life of refrigerated MAP food is offensive odor development resulting from microbial metabolism (28). Gill and Newton (11) found that glucose was the substrate preferentially used by B. thermosphacta when growing in meat. No utilization of glucose-6-phosphate, lactic acid, and nucleotides was detected. Moreover, the range of amino acids that this bacterium could use was very restricted, and the re...
