Glucose and oxygen limitation

In addition, it is often found that the residual concentration in the liquid phase of the limiting nutrient is very low, and thus negligible compared to the inlet concentration in the calculations. 

Application of calorimetry to oxygen-limited continuous cultures has been presented in detail in references [67,71,72]. In fact, reductive metabolism is almost athermic as compared to aerobic metabolism. In addition, it is possible to set the oxygen limitation to the desired value by changing the oxygen gas feed composition [67,73]. The level of oxygen limitation is quantified by the ratio PoiKi (called aerobicity and also denoted Q [74])  

The value of Pojio 1 during purely aerobic metabolism and 0 under anaerobic conditions. Values comprised between 0 and 1 correspond to oxido- 

The heat flow rate is calculated from the oxidative and reductive contributions  

Similarly, the other yields are expressed as a function of Aoj/g assuming a linear response of the metabolism between / 02/g = 0 and Aoj/g (glycerol formation is neglected), 

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Given the high dependency of cerebral energy production and neurotransmitter synthesis on glucose and oxygen, limitations in supply of these substrates results in metabolic encephalopathy. 

The major problem that has plagued these kinds of implantable biosensors is the gradual decrease in sensitivity and in some cases a complete loss of function within just hours of implantation. Biofouling, oxygen limitation, electrochemical interference and GOD inactivation have been considered as explanations of this behaviour. For instance, a tissue reaction to the sensor implantation may result in a limitation in the blood supply to the tissue surrounding the probe and thus in a lower availability of glucose and oxygen. 

Lin H Y, Mathiszik B, Xu B, Enfors S O, Neubauer P (2001). Determinantion of the maximum specific uptake capacities for glucose and oxygen in glucose-limited fed-batch cultivations of Escherichia coli. Biotechnol. Bioengin. 73 347-357. 

Figure 19 Variation of the yield of biomass on glucose as a function of /E o2/G,suppiy (ratio between oxygen transfer to glucose supply scaled by the glucose-limited yield) for the growth of K. marxianus. The culture is double limited by glucose and oxygen for / j/c.suppiy < 1- Redrawn from Reference [68] with permission of the author and publisher.

Lactose, the milk sugar, is a reducing disaccharide consisting of glucose and galactose moieties. The estimated annual worldwide availability of lactose as a byproduct from cheese manufacture is several million tons [1,2], but only about 400 000 t/a lactose is processed further from cheese whey [3], Non-processed whey is an environmental problem due to its high biochemical and chemical oxygen demand [2], The use of lactose as such is limited by two main factors relatively low solubility of lactose in most solvents and lactose intolerance in human body [1]. 

Figure 7. Noncompartmentalized glucose—oxygen biofuel cell. Reprinted with permission from refs 12 and 125. Copyright 2003 John Wiley and Sons Limited. Copyright 1999 Elsevier Science S.A.

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