Question

How to calculate the product yield(g) per gram of substrate in a batch culture experiment?

Answer 1

I'm having some difficulties in calculating specific consumption rates from the data I generate from my cultivations with the yeast Pichia stipitis.

Let's consider the specific substrate consumption ratewith these data:

TIME of inoculation (0 h)

9.66g of substrate present in the medium

inoculum corresponds to around 0.25 gDW

TIME 13.25 h

0.94 g of substrate left in the medium

biomass concentration is 5.3 gDW

First of all I would like to know if the formula I'm using is correct:

qs = g of substrate consumed / (time * g DryWeight)

Here's how I do it:

qs = (9.66 g - 0.94 g) / (13.25 h * 5.3gDW) = 8.72  / 70.2 = 0.124 g g-1 h-1

Now, what I would also like is to express the result on a C-mmole base. To do that I convert the grams of substrate in mmoles and then I multiply by 6 (substrate is mannitol, C6H14O6, MW 182.2 g/mol). So:

8.72 g of mannitol = 47.85 mmol * 6 = 287.2 C-mmol,

qs = 287.2 / (13.25 h * 5.3gDW) = 4.08 C-mmol g-1 h-1

I'm not so sure these is all correct since these numbers seem to be on a totally different order of magnitude from the data I find in literature.