[Effectiveness of modified atmospheres against psychrotrophic pathogenic microorganisms in proteinaceous food]

Modified atmosphere packaging (MAP) of proteinaceous raw foods (meat, poultry and fish) extends their shelf-lives. It is well established that modified atmospheres (MA) inhibit the psychotropic aerobic Gram-negative bacteria, the main spoilage microflora of proteinaceous raw foods stored under refrigeration. Several researchers have warned about the possible growth of food poisoning microorganisms on them. Considering the minimal growth temperatures of pathogens, this review only deals with Aeromonas hydrophila, Clostridium botulinum, Listeria monocytogenes and Yersinia enterocolitica. C. botulinum produces its toxin in many different atmospheres, but it is unable to grow at temperatures below 3.3 degrees C, and its production rate of the toxin at temperatures below 4.5 degrees C is very low, to the extent that fish can be spoiled before the toxin is detected. Therefore, the control of the storage temperature of MAP fish seems to be indispensable to assure the absence of botulinal toxin. With regard to the other pathogens, vacuum is the atmosphere that may support more readily its growth; the higher the CO2 concentration in the atmosphere, the lower the growth rate is. Some investigations have shown that the growth rates of the psychotropic pathogens in MAP are lower than those of the spoilage flora. It has been shown also that A. hydrophila and L. monocytogenes growth rates are lower under MA than under aerobic storage. In relation to Y. enterocolitica, more investigations should be carried out in order to clear up its behaviour, because the available data in the literature are still confusing and sometimes even contradictory. In conclusion, there are no evidences that support the concern about MAP of proteinaceous raw foods representing a greater hazard than its conventional storage under air.