Yield coefficients

The cell concentration in terms of the substrate concentration and the yield coefficient is ... 

Table II shows clearly the large differences between various theories for many-electron systems. The Kirkwood-Muller equation always yields somewhat too large coefficients for the atoms which are the only spherical systems but the London equation deviates by a greater amount on the low side. The Slater-Kirkwood equation gives a high value for He but yields coefficients smaller than the empirical ones for all other cases.

In any quantitative assessment of growth and/or product formation, it is essential to link formation of microbial biomass and products with the utilisation of substrate and nutrients. In the case of microbial biomass production, the total amount of cell mass yield formed is often proportional to the mass of substrate utilised. Mathematically this is coefficient expressed as the corresponding ratio, or yield coefficient ... 

Where yield coefficients are constant for a particular cell cultivation system, knowledge of how one variable changes can be used to determine changes in the other. Such stoichiometric relationships can be useful in monitoring fermentations. For example, some product concentrations, such as CO2 leaving an aerobic bioreactor, are often the most convenient to measure in practice and give information on substrate consumption rates, biomass formation rates and product formation rates. 

In practice, variations in yield factors are often observed for a given organism in a given medium. For example, yield coefficients often vary with growth rate. An explanation for these variations comes from a consideration of the fate of substrate in the cell, which can be divided into three parts ... 

Later in this chapter (section 3.2.1) we shall consider yield coefficients with respect to product formation. 

The product yield coefficient can then be calculated, taking into account the relative numbers of carbons in the substrate and product. The molar yield coefficient is then written as... 

Aim3 aerobic bioprocess was operated in a continuous mode with nitrogen as the growth limiting nutrient. The steady state biomass concentration (x), the biomass yield coefficient (Yx/S) and the product yield coefficient (Yp/t) were determined at a low and at a high dilution rate (D). 

In this section we will consider the energetics of exopolysaccharide production in some detail. We will see how chemostat (substrate limited) derived yield coefficients and slfbstrate elemental balances can be used to determine how the nature of the substrate influences... 

Anaerobic utilisation of carbohydrates is strongly inhibited by the end product ethanol, giving low yield coefficients compared to aerobic utilisation. 

Correct - Aerobic growth is more energy efficient (produces more ATP) than anaerobic growth, resulting in higher yield coefficients. 

Carbon substrate yield coefficient (g cells/g substrate)... 

Figure 4.10 Typical effects of yield coefficient on oxygen requirement when only biomass and CO2 are produced (methanol as substrate)...

Figure 4.11 Typical relationship between minimum oxygen-transfer rates and yield coefficients at various productivities (methanol as substrate).

Figure 4.13 Estimated relationships between heat production and productivity at various yield coefficients...

If the growth yield coefficient for ammonia was 10 g g 1, what concentration of biomass would you expect if ammonia was added to a concentration of 2-5 g l 1 ... 

Using these equations it is possible to calculate theoretical values for glucose yield coefficients (Yg). Yg values can be calculated for cell mass, phenylalanine and acetic add and is simply the amount of produd produced per unit amount of glucose consumed. So the theoretical yield of phenylalanine on glucose, for example using equation 8.1, is ... 

The maximum yield, as can be seen from Figure 85, is in the late exponential phase. Using the data given in Table 8.4 for the interval between 14 and 24 hours, we obtain a value of 0.27 g phenylalanine (g glucose) 1 for the maximum yield coefficient... 

Yx/S Yield coefficient of cell substrate, g cell g-1 substrate... 

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