Effects of freezing on microorganisms

Technical information Food refrigeration and freezing Effects Of Freezing On Micro-Organisms Associated With Meat, Poultry And Fish

Influence Of Freezing On Micro-Organisms Associated With Meat, Poultry And Fish

The speed of freezing, as known to affect the microbiological status of meat, poultry and fish, and although it is generally the case that the total number of microorganisms to decrease slightly during freezing, a storage of frozen and thawing, the growth of some microorganisms can occur at temperatures below 0C, with frequent reports of growth of -5C and rarely up to -10C (Larkin and Stokes, 1968). Frozen poultry meat shows the rapid growth of putrefactive microorganisms when stored at a temperature of -5C (Abu Ruwaida et al., 1996) and between -5 and 7C, where the main organisms of concern psychrophilic yeast and fungi that cause moustache-like growth (e.g. Thamnidium spp.), black spots (e.g. Cladosporium spp.) and white patches (e.g. Sporotrichum spp.). Generally speaking, the temperature below 10C are considered to be effectively inhibits the growth of microorganisms associated with food. Thus, the rate of cooling is not only relates to murder or 'cidal effect on microorganisms, but it's also important to prevent growth in sub-zero temperatures, and it is important to prevent damage to the meat, poultry and fish.

Template for survival in various taxonomic groups during freezing and storage of frozen fish, a similar trend is observed in poultry meat with Gram-negative bacteria, surviving on less than gram-positive and disputes, showing no significant change in the number.

However, despite the freezing inhibits the metabolism of microorganisms in the process of frozen storage, enzymatic activity still continues. This is important in frozen fish, where histi dine-decarboxylase activity results in histamine production, increased levels which exceed the damage limitation (approx. 5 ppm) or even the safety limits (ca. 50 ppm), especially if the temperature of the abuse occurs in the supply chain.

In cidal influence of freezing on the different types of organisms vary significantly. Spores of bacteria and fungi mostly remain in force by freezing although there is some evidence that the spores of C. botulinum, which are more susceptible to the effects of ionising radiation as a result of frozen storage within 30 days -75C (Lim et al., 2003). Disputes are inert and is extremely resistant to different stresses and have a minor injury, provided by freezing and repeated freezing and thawing. Vegetative bacterial cells vary in their response to freezing. Some organisms (e.g. E. coli, B. subtilis, Vibrio cholerae and some lactic acid bacteria) responds to a low temperature, voltage for the production of cold shock protein (CSP or cold-induced proteins, CIPs) and the gradual change in cold conditions, has been shown to improve survival of E. coli (Bollman et al., 2001), L. monocytogenes (Bayles et al., 2000) and Salmonella (Jeffreys et al., 1998), frozen.

There is quite a large amount of information on the survival of L. monocytogenes subjected to freezing under different conditions, showing variable and a synthesis of the responses Archer (2004). Photo-bacterium phosphoreum related to marriage modified atmosphere Packed cod and salmon, and the formation of histamine, are very sensitive to freezing and one freeze-thaw cycle has been shown to significantly increase shelf-life of these and similar products. However, significant histidine decarboxylase activity halophilic histamine-forming bacteria can continue after freezing although the number of cells is reduced by more than six log10 cycles (Fuji et al., 1994). There is some evidence that frozen fish storage for more than 3-6 weeks leads to a significant reduction in the level of V. cholerae, but there are also a few studies reporting recovery Vibrio, including V. cholerae and other potentially pathogenic species of frozen seafood, such as frozen raw shrimp and fish. Epidemiological data from major outbreaks of cholera associated with ice, also points to the survival of numbers high enough to cause infection...

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