C.O. Gill

The solubility of carbon dioxide in meat.

The solubility of CO(2) in muscle tissue of pH 5·5 at 0°C was approximately 960 ml at STP/kg of tissue. The solubility increased with increasing tissue pH by 360 ml/kg for each pH unit. The solubility decreased with increasing temperature by 19 ml/kg for each °C rise. Solubilities in beef, pork and lamb muscle tissue were comparable. The solubility of CO(2) in fat tissues initially increased as the temperature was raised above 0°C, but then declined at higher temperatures, with the temperature of peak solubility and the solubility curves being markedly different for fat tissue from the three species.

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.

Meat Spoilage and Evaluation of the Potential Storage Life of Fresh Meat

Microbiological processes by which meat develops qualities unacceptable to consumers vary with the composition of the meat and spoilage microflora. Composition of the spoilage microflora is affected by meat composition and storage conditions. Aerobic spoilage microfloras are usually dominated by pseudomonads. With this type of microflora, spoilage occurs when glucose in meat is no longer sufficient for the requirements of the spoilage microflora and the bacteria start to degrade amino acids. When meat is deficient in glucose, spoilage becomes evident while bacterial numbers are relatively small. Anaerobic microfloras are usually dominated by lactobacilli which produce spoilage by the slow accumulation of volatile organic acids. Meat of high utimate pH packaged anaerobically spoils rapidly because the high pH allows anaerobic growth of bacterial species of higher spoilage potential than the lactobacilli. Before overt spoilage develops, the spoilage status of meat can be accurately assessed from the bacterial numbers on meat only when there is assumption or knowledge of meat composition, storage conditions and the types of bacteria present. Methods for estimating spoilage which depend upon detection of products of amino acid degradation have little predictive value as such products will only be present after attack on amino acids has commenced and are irrelevant to spoilage under anaerobic conditions. Estimation of the concentrations of other spoilage products may be the only method applicable to assessment of incipient spoilage of meat stored anaerobically. It is, therefore, unlikely that any single test can give unequivocal information on meat quality under all circumstances, but rapid tests for meat quality could be of value for specific commercial purposes. provided such tests are appropriate to the circumstances and the inherent limitations of any test are recognized.

The microbiology of DFD fresh meats: A review

Muscle which is deficient in glycogen because of exercise or stress prior to slaughter produces dark, firm, dry (DFD) meat. Such meat is characterized by a high ultimate pH (>6·0) and deficiencies in glucose and glycolytic intermediates. These factors can result in bacterial spoilage becoming evident at an early stage of growth of the meat flora. Spoilage becomes apparent when bacteria attack amino acids. This does not occur under aerobic conditions until bacteria exhaust the glucose at the meat surface. However, since glucose is absent in DFD meat, amino acids are utilised without delay and spoilage becomes evident at lower cell densities than in normal meat. The absence of glucose also allows the anaerobic flora to produce spoilage odours at an early stage. Additionally, the high pH of DFD meat allows growth of potent spoilage organisms which are inhibited at the usual ultimate pH of meat. Early aerobic spoilage can be prevented by the addition of glucose, but prevention of early anaerobic spoilage requires the addition of a citrate buffer which reduces the surface pH, as well as providing a carbohydrate substrate which is utilised in preference to amino acids. Comparisons can be made between spoilage of DFD red meat and spoilage of white meats from poultry and fish, which normally have a high ultimate pH.

Controlled atmosphere packaging of chilled meat

Abstract The storage life of chilled meat can be extended by packaging product under a preservative gaseous environment to inhibit growth of spoilage bacteria. The maximum storage life is attained by packaging in a gas-impermeable pouch under an atmosphere of oxygen-free CO2, with the gas added in sufficient quantity to fully saturate the meat at the optimum storage temperature (−1.5°C) and atmospheric pressures. In such controlled atmosphere packaging (CAP), the storage life of meat is between 8 and 15 times that of the same product stored in air. The CAP environment assure retention of good raw meat colour, and development of good eating qualities in cooked product. CAP packaging is being used commercially for shipment of chilled lamb to distant markets. Continuing studies indicate that it could be applied equally effectively to prolonging the storage life of a wide range of other perishable food products.

Cold Storage Temperature Fluctuations and Predicting Microbial Growth

The hygienic consequences of the temperature regimes experienced by perishable product during storage, transport, and display can be assessed by a temperature function integration technique. The technique requires the collection of appropriate temperature histories from product units moving through a process and integration of the histories with respect to suitable models which describe the dependency on temperature of the growth of bacteria of concern. The distributions of the proliferation values obtained are characteristic of each process. However, when the duration of a process is highly variable for individual units passing through it the fundamental characteristics of the process may be difficult to discern from proliferation data. Then, a storage efficiency factor can be calculated from a proliferation value and the duration of each temperature history, and the distributions of those factors used to assess and compare processes. Procedures for the collection and analysis of product temperature history data from product cooling, storage, distribution, and display processes, and the use of such data for process assessment are discussed.