3concentration from 1% to 2% did not lead to any significant increase
of reducing sugar (p > 0.05). The enzyme combination with the
highest release of reducing sugar was (g) Ternamyl 0.24
KNU + Viscozyme 24 FBGU + Celluclast 2% with a rate of
18.48 g L1 that corresponded to 0.92 g released sugar per g of
raw dry PPW. Using this combination, at the end of fermentation
the reducing sugars were 1.93 g L1. Therefore, the sugars consumed
were 16.55 g L1 (Table 2). In all treatments the non-fermented
sugar at the end of fermentation was very low. The
consumed sugar during fermentation was very high (up to 89%),
indicating the high ability of S. cerevisiae var. bayanus to bioconvert
reducing sugars.
Table 3 shows the ethanol production (g L1), product yield Y
p/s (g of product/g of sugar consumed) and percentage of the maximum
theoretical yield, with the use of various enzyme combinations.
In all enzyme treatments, S. cerevisae produced high
quantities of ethanol (6.0–7.6 g L1), with the exception of combination
(b) resulting in lower ethanol production (4.2 g L1). The
product yield Y p/s (g of product/g of sugar consumed) was about
0.46. In all cases the product yield corresponded up to 91% of the
max theoretical yield.
The results indicate that the critical parameters for ethanol production
from PPW were the enzyme combination, the dose and the
residence time of hydrolysis. After liquification and saccharification,
fermentation by S. cerevisae converted sugars to high yields