Growth models in defined systems

Many foodstuffs consist of gelled emulsions, due to deliberate addition of gums and thickeners to increase the mass thickness (e.g., sausages) or due to denaturation of proteins to form protein micelles (e.g., cheese). Food emulsions containing water in oil have an internal water phase that is dispersed as droplets within an oil (or lipid) phase. The microorganisms are mostly found in the droplets (Verrips and Zaalberg, 1980  

Charteris, 1995) and classical theories describing microbial growth usually rely on the microarchitecture of these droplets, which limits the availability of water, space, and growth nutrients (Wilson et al., 2002). 

A food surface is a simple form of microarchitecture that affects the growth of microorganisms. Foodstuffs may contain numbers of microarchitectures and the behavior of a microorganism will, therefore, be varied. Differences observed by manufacturers can be explained by organisms growing more slowly in structured systems than in broths (Wilson et al., 2002). 

Growth models that describe the dependence of primary model parameters on environmental factors (i.e., temperature, water activity, pH, and organic acids) are referred to as secondary growth models. A number of different secondary model types exist in predictive microbiology and are discussed in the following section (Wilson et al., 2002). 

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