The kinetic sub-model needs to describe how growth depends on the key environmental variables, since these variables typically cannot be simply controlled at their optimum values in an SSF bioreactor. The bioreactor model will be most useful if it can be used to explore how the operating variables affect the values of the key environmental variables, and how changes in the environmental variables in turn affect the overall performance of the bioreactor.
So which environmental variables are the "key environmental variables"? This question was raised in Sect. 13.2.1, where it was recommended that, at the very least, the effects of temperature and water activity on growth should be described. During a fermentation, these variables can change quite significantly. For example, the temperature might start at the optimum temperature for growth, but it can increase quite substantially during the mid parts of the fermentation, falling again time
dCXR Do dCXA
dt time time
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