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 (propyl allysine,
methyl propyl allysine) 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.