Combining MAP with other preservation techniques 291 outgrowth. Most food spoilage moulds species have an absolute requirement for oxygen and appear to be sensitive to high levels of CO2. Consequently foods with low aw values, such as bakery products, that are susceptible to spoilage by moulds can have their shelf-lives extended by MAP. Many yeasts are capable of growing in the complete absence of oxygen and most are comparatively resistant to CO2. Although MAP can inhibit the growth of bacterial and fungal spoilage microorganisms, its effect on the survival of enteric viruses, including hepatitis A viruses(HAV), has not been well investigated. Both mussels and lettuce that are packaged in MAP may be a vehicle in the transmission of hav(due to contact with contaminated water) and therefore can contribute to hepatitis A outbreaks(Cliver, 1997). Experiments by Bidawid et al.(2001)indicated that MAP does not influence HAV survival when present on the surface of produce with high CO2 levels. This may have been attributed to the inhibition of spoilage-causing enzymatic activities in the lettuce, which may have reduced exposure of viruses to potential toxic by-produo 14.2.2 Preventative techniques combined with MAP The main preservation techniques currently used act in one of three ways: (i) preventing the access of microorganisms to foods, (ii) inactivating them when they have gained access, or(iii) preventing or slowing down their growth when they have gained access and not been inactivated. During the past few years there has been increasing interest in modifying these approaches or in developing new ones, with the objective of reducing the severity of the more extreme techniques. Many such developments have involved new uses of existing techniques in new combinations to inhibit the growth of micro- organisms. Approaches where preservation techniques are used at lower intensity or at lower concentration, causes inactivation and bacterial growth inhibition to overlap. It is the safety level, the quality level or the outcome of inactivation or growth inhibition of target organisms that determines the final use of the chosen preservation method(s)(Table 14.2) 14.2.3 Hygienic conditions Hygienic production is not a preservation method, but ingredients or raw material used in MAP should always be of superior quality, i.e. low bacterial numbers and preferably without pathogenic bacteria. This is a prerequisite for fresh products with increased shelf-life, and preservation should never be used to compensate for inadequate hygiene or poor raw material quality. A strategy for the control of pathogens and, to a large extent, spoilage microorganisms is basically one of exclusion, which requires reducing or eliminating the initial microbial load or preventing or minimising further contamination. Since MA packaged products are hermetically sealed, recontamination is eliminated and the hygienic pre-packaging conditions are the most important steps. An appropriate design and construction of the pre-packaging premises is necessaryoutgrowth. Most food spoilage moulds species have an absolute requirement for oxygen and appear to be sensitive to high levels of CO2. Consequently foods with low aw values, such as bakery products, that are susceptible to spoilage by moulds can have their shelf-lives extended by MAP. Many yeasts are capable of growing in the complete absence of oxygen and most are comparatively resistant to CO2. Although MAP can inhibit the growth of bacterial and fungal spoilage microorganisms, its effect on the survival of enteric viruses, including hepatitis A viruses (HAV), has not been well investigated. Both mussels and lettuce that are packaged in MAP may be a vehicle in the transmission of HAV (due to contact with contaminated water) and therefore can contribute to hepatitis A outbreaks (Cliver, 1997). Experiments by Bidawid et al. (2001) indicated that MAP does not influence HAV survival when present on the surface of produce with high CO2 levels. This may have been attributed to the inhibition of spoilage-causing enzymatic activities in the lettuce, which may have reduced exposure of viruses to potential toxic by-products. 14.2.2 Preventative techniques combined with MAP The main preservation techniques currently used act in one of three ways: (i) preventing the access of microorganisms to foods, (ii) inactivating them when they have gained access, or (iii) preventing or slowing down their growth when they have gained access and not been inactivated. During the past few years there has been increasing interest in modifying these approaches or in developing new ones, with the objective of reducing the severity of the more extreme techniques. Many such developments have involved new uses of existing techniques in new combinations to inhibit the growth of micro￾organisms. Approaches where preservation techniques are used at lower intensity or at lower concentration, causes inactivation and bacterial growth inhibition to overlap. It is the safety level, the quality level or the outcome of inactivation or growth inhibition of target organisms that determines the final use of the chosen preservation method(s) (Table 14.2). 14.2.3 Hygienic conditions Hygienic production is not a preservation method, but ingredients or raw material used in MAP should always be of superior quality, i.e. low bacterial numbers and preferably without pathogenic bacteria. This is a prerequisite for fresh products with increased shelf-life, and preservation should never be used to compensate for inadequate hygiene or poor raw material quality. A strategy for the control of pathogens and, to a large extent, spoilage microorganisms is basically one of exclusion, which requires reducing or eliminating the initial microbial load or preventing or minimising further contamination. Since MA packaged products are hermetically sealed, recontamination is eliminated and the hygienic pre-packaging conditions are the most important steps. An appropriate design and construction of the pre-packaging premises is necessary Combining MAP with other preservation techniques 291