motion of water molecules (Lavoie et al., 1997; Pham et al., 1999). It has been demonstrated that water mobility may influence transport of nutrients to microbial cells and hence growth. Under conditions of limited moisture, mold spore germination and mycelial growth strongly correlate with water mobility (Pham et al., 1999). For the EFP, the type and composition of ingredients used will influence the interaction of solids with water, thereby affecting water mobility and a_w, and thus the survival and potential growth of pathogenic microorganisms. More importantly, should spores or vegetative cells of microorganisms able to withstand dry conditions survive the processing, they could germinate and grow during storage if moisture is not properly controlled in the product and other provisions, such as addition of preservatives, are not made to inhibit microbial growth. To minimize the risk of biological hazards, a multiple hurdle approach is highly recommended (Leistner, 1995). In this approach, also called the combined methods approach, several factors are used together to inhibit microbial growth, such as thermal processing, plus a_w, storage temperature, preservatives, and packaging. For the EFP, it can be expected that there will be little, if any, opportunity to control storage temperature and ambient humidity. On the other hand, the cost of production and materials (including packaging) that would be incurred in making an IMF-type EFP might be too high, and there would also be a price to pay in terms of product shelf life and safety. As pointed out earlier, dehydration and IMF technologies can only stop microorganisms from growing but do not necessarily inactivate them. Consequently, and although an EFP having IMF characteristics should not be ruled out as an option, the optimal approach to the microbiological stability of the EFP would be a product design having an a_w value lower than those in the IMF range (e.g., 0.4) and to add some preservatives.

Auto-oxidation of lipids occurs in foods largely via a self-propagating free radical mechanism. Since direct reaction of unsaturated linkages in lipids with oxygen is energetically difficult, production of the first few radicals needed to start the propagation reaction must occur through some catalytic mechanism (Nawar, 1996). It has been proposed that the initiation step may take place by decomposition to free radicals of preformed hydroperoxides via metal catalysis or heat, by exposure to light, by direct reaction of metals with oxidizable substrates, or by mechanisms where singlet oxygen is the active species involved (Nawar, 1996).

Upon formation of sufficient free radicals, a chain reaction is initiated by the abstraction of hydrogen atoms at positions alpha to double bonds followed by oxygen attack at these locations. The result is production of peroxy radicals,