The main objectives of reducing Aw in food are to prevent or reduce the growth of vegetative cells and germination and outgrowth of spores of microorganisms.
Prevention of toxin production by toxigenic molds and bacteria is also an important consideration. Microbial cells (not spores) also suffer reversible injury and death in foods with low Aw, although not in a predictable manner as in heat treatment. Finally,reduced Aw is also used to retain viability of starter-culture bacteria for use in food bioprocessing, which is discussed in Chapter 13. In this chapter, preservation of food by controlling microbial growth at low Aw is described