Ethanol production at 45 °C by Kluyveromyces marxianus IMB3 during growth on molasses pre-treated with Amberlite® and non-living biomass

Abstract

The use of high concentrations of molasses as a fermentation feed-stock for ethanol production is normally precluded by the presence of inhibitory compounds. Use of the thermotolerant, ethanol-producing yeast strain Kluyveromyces marxianus IMB3 in fermentations containing high concentrations of molasses resulted in sub-optimal production of ethanol. The results suggested that this was caused by the presence of inhibitory materials rather than an intolerance to increased concentrations of ethanol. In the current study we describe the pretreatment of molasses preparations with either an Amberlite® monobed mixed ion-exchange resin or non-living microbial biomass from a local distillery. In the study molasses samples diluted to yield a final sugar concentration of 160 g/l were used as the substrate. Control fermentations using the untreated molasses dilutions yielded a maximum ethanol concentration of 40 g/l, representing 49% of the maximum theoretical yield. Fermentations using molasses samples pre-treated with Amberlite® or non-living biomass yielded maximum ethanol concentrations of 58 and 54 g/l, representing 71 and 66% of the maximum theoretical yield, respectively. The results suggest that pre-treatment brings about removal of toxic or inhibitory materials from the fermentation feed-stock and we believe that such pre-treatments, particularly using the less expensive non-living biomass preparations may find a role in processes concerned with the commercial production of ethanol from molasses using this microorganism.