Residual ligneous material present in the B. napus clear hydrolysate(BNCH) may block yeast accessibility to the substrate, resulting in very little or no ethanol production.
Therefore, the suitability of BNCH for ethanol production was confirmed by coupling the fermentation and enzymatic saccharification processes.
BNCH was concentrated up to 5% (w/v) and supplemented with nutrients required for baker’s yeast (S. cerevisiae), growth: 5 g/L yeast extract, 10 g/L (NH4)2SO4, 4.5 g/L KH2PO4, and 1.0 g/L MgSO47H2O.
The pH of the growth medium was adjusted to 5.0 using 1 N HCl or 1 N NaOH, as required.
The ethanol production potential of BNCH was tested against a synthetic medium having glucose as the carbon source.
Both media were inoculated with a 2% (v/v) 48-h-old culture of S.cerevisiae (ATCC 32167) and incubated at 28 C under static conditions.
Samples from both media were collected at every 2 h and centrifuged (7500g; 15 min).
The supernatants were analyzed for glucose consumption and ethanol concentration using a flame ionization detector (FID) and the helium (He) gas mobile phase method.
Air and hydrogen were used in FID. Initial column temperature was maintained at 80 C and increased up to 190 C, with a hold time of 10 min.
Ethanol volumetric productivity (grams per liter per hour) was calculated as the ratio of ethanol concentration (grams per liter) at the end of the run to fermentation time (t,hours). The yield of ethanol in relation to consumed sugar (grams per gram) was defined as the ratio of ethanol concentration to sugar consumption (So Sf, where So is the initial sugar concentration
and Sf the final sugar concentration).
Sugar conversion (in percentage) was calculated as the ratio of sugar consumption in relation to the initial sugar concentration.
The efficiency of sugar conversion to ethanol (g, in percent) was estimated as the ratio of ethanol yield over the theoretical value of ethanol yield (0.51 g/g).