Nutrient optimisation

The carbohydrate (again often molasses, 15 - 25%) and added nutrients are pH-adjusted to below 4.0 and, for Otis process, have to be sterilised. It is necessary to add potassium hexacyanoferrate but greater care is required in this process compared to surface culture. The A. niger seems to be more sensitive to and more easily inhibited by hexacyanoferrate in submerged culture. It is essential however to lower the ferrous and manganese concentrations, probably below 200 and 5 pg l1 respectively, to optimise the performance of A. niger. 

A less known, but probably more important, protective mechanism is conditioned taste aversion (Cross-Mellor ef al. 2004), which induces a rapid, profound aversion to any taste associated with nausea or other indications of toxicosis. This study used an ingenious setup allowing continuous control of the induction of nausea to show that conditioned taste aversion is so precise that it allows rats to adjust their intake of toxin-containing food to obtain the optimal provision of nutrients while avoiding harm from the toxins. Such optimisation has been demonstrated in farm animals (Kyriazakis ef al. 1997) and is probably common for all animals. 

Khanna and Srivastava [19] reported optimising the nutrient feed concentration and the addition time for the production of PHB. A mathematical model was developed to describe the batch kinetics. This equation was then extrapolated for the fed-batch culture by including the dilution rate. At the end of the fed-batch fermentation, 32 g/1 biomass and 14 g/1 PHB was obtained with a productivity of 0.28 g/l/h. 

Paper 25. Optimisation of Food Nutrient Composition H. M. Sinclair... 

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