Glucose, the Key Substrate in the Microbiological Changes Occurring in Meat and Certain Meat Products

The literature dealing with the role of glucose in the microbiological changes of meat and certain meat products is reviewed. Discussion is centered on two aspects. First, glucose plays a part in the selection of the dominant spoilage organisms, Pseudomonas fragi, Ps. lundensis, and Ps. fluorescens, on red meat stored aerobically under chill (2-7 degrees C) conditions. It is concluded that the pseudomonads flourish because they convert glucose to the less commonly used substrate, gluconate. The latter serves as an extracellular energy store. With its depletion, the pseudomonads utilize amino acids, thereby producing the characteristic off-odors of spoiled meat. Storage of meat in a modified atmosphere (viz., 20% CO2:80% O2) selects Gram-positive flora (lactobacilli and Brochothrix thermosphacta) which impart a "cheesy odor" through acid production from glucose and volatile fatty acids from amino acids. The first mentioned organisms produce the same off-odors in "acid" meat (pH 5.5) from which oxygen is excluded. So too does the less acid-tolerant Br. thermosphacta in less acid meat (pH greater than 5.8), especially if trace amounts of O2 are present. Such meat may be colonized by Shewanella putrefaciens also, with green discoloration resulting from the release of H2S from amino acids. The addition of glucose and NO2- to, and the exclusion of oxygen from, comminuted meat selects a flora dominated by Lactobacillus spp. and staphylococci such as Staphylococcus carnosus. Second, sulfite, the preservative of British-style sausages, has a sparing action on glucose. As a consequence of its curtailed breakdown there is only a meager acid drift with storage even though a fermentative flora of lactobacilli and Br. thermosphacta is selected. Yeasts also contribute to the microbial association in sausages; members of four of the six commonly occurring genera bind sulfite through acetaldehyde production. Glucose appears to be essential for acetaldehyde synthesis. The role of glucose in spoilage and the conditions which select particular groups of spoilage organisms are considered in the context of chemical probes and/or instrumental methods for routine assessment of the "freshness" of meat and meat products.