Isolation and evaluation of xylose-utilizing yeasts for ethanol production.

Seventeen xylose-utilizing yeasts were retrieved from different ecological niches and screened for production on xylose-contai ning medium. Seven of the isolates produced no alcohol at all on xylose. The ten isolates while on xylose produced 1—2%, on dextrose they produced 3—5% (vol/vol) ethanol. Six of the yeast isolates producing 5% (vol/vol) ethanol on dextrose with an ability to ferment xylose as well were screened for ethanol production on a medium containing a total of 10% both of dextrose and xylose (4 : 3 ratio). Isolate 11 produced the maximum of 4.5% (vol/vol) ethanol leaving behind only 0.5% residual sugars. It was further examined for ethanol production on media containing either dextrose or both dextrose and xylose (4 : 3) at 12 and 15% sugar levels. In dextrose production medium, a maximum of 5.5% (vol/vol) ethanol was achieved at an initial sugar concentration of 12% at 72 h. As against this a maximum of 4.7% (vol/vol) ethanol was produced on the medium containing both dextrose and xylose (4 : 3). Morphological and biochemical characteristics of isolate 11 were found to conform well to the genus Candida.