Potential of cashew gum exudates as substrate for bioethanol production using <i>Aspergillus niger</i>

Abstract

Crude cashew gum, a polysaccharide exudates was purified by way of dissolving the crude gum in hot water, centrifuging the solution to remove suspended particles, precipitating the resulting solution with concentrated ethanol, drying and finally grinding the precipitate to fine powder. Physicochemical analysis of the crude and purified gum showed that both solutions were acidic, with the pH ranging from 5.10 to 5.04 and 5.49 to 5.41 in a concentration range of 5 g/10ml to 20 g/ 10 ml respectively in the first week. Both sampled gum solutions showed initial drop in pH in the first day the solutions were made, but the pH stabilized for the remaining days. The pH of the gum solutions was stable throughout the second week, but there was slight drop as the concentration was increased. The purified gum was first adapted to Aspergillus niger and growth was observed only after 72 hours. The zone of clearance formed after Lugol’s iodine was applied is indicative of the fact that fermentation of the gum sample to ethanol took place. This result shows that fermentation of cashew gum to ethanol is possible and so the gum could be exploited to produce ethanol for various industrial and domestic uses thus reducing the dependence on grains currently used for the production of ethanol and thus availing humans and animals more grains for food and feed respectively. The practice of the use of cashew gum for ethanol production will increase the economic value of cashew gum globally.

Keywords: Adaptation, Aspergillus niger, Bioethanol, Cashew gum