Calculations of bioprocess parameters
Production rates were calculated in terms of
mlproduct/Lreactor·day.
Yield (of lactic acid or ethanol) on a substrate is defined as the
amount of the metabolite obtained per unit of PPW used and given in Eq.
(1):
Y = (C – C0 ) · V / M · 100% (Equation 1)
where Y is the yield (ml/g), C is the actual concentration (ml/L),
C0 is the initial concentration (ml/L), V is the
bioreactor working volume (L), and M is the initial mass of PPW in the
bioreactor (g).
Sugar recovery was defined as the efficiency of the microorganism to
convert the starch available in the PPW to glucose. It is calculated as
the ratio between the mass of glucose in the hydrolysate to the total
mass of the starch in the PPW and expressed as a percentage (%).
A particularly useful parameter for characterizing ethanol and lactic
acid production is substrate conversion efficiency, which is a measure
of how much of the substrate has been utilized for ethanol and lactic
acid production rather than growth, cell maintenance, or alternative
biosynthesis. It was determined as the ratio of the mass of ethanol and
lactic acid that has actually been produced per mass of ethanol and
lactic acid expected through stoichiometric conversion of a substrate
according to the hypothetical reactions of lactic acid and ethanol
fermentations and expressed as a percentage (%).