Bioethanol production from white onion by yeast in repeated
In terms of sugar and nutrient content, it was
simple to use discarded onions as a source of
medium as they had been rejected mainly on
account of their shape or size [7]. Onions usually
contain sulphur-containing amino acids and alliin,
which are converted to allysine compounds
(propylallysine, methyl propylallysine) by cellular
alliinase during processing [9]. The allysine
compounds have a keen, stimulating smell and an
anti-microorganism function, which inhibits the
growth of yeast. In preliminary experiments, it was
found that raw onion juice was difficult to ferment
by yeast. However, the allysine compounds are
volatile and could be removed by autoclave
treatment before fermentation [9].
Ethanol production by nor mal S. cerevisiae and a
genetically modified strain of S. cerevisiae was
compared (Fig. 1). The modified strain had more
CO2 above the ethanol. The application of
modified yeast to improve ethanol production
from glucose is key in many biofuels production
programs [13].