Renewable Plant Waste As Substrates for Enzyme Production, Saccharification and Direct Bioethanol Production by Indigenous Yeast Strain Pichia Exigua

Abstract

Renewable plant wastes constitute environmental nuisance. Their conversion by enzymes into bioethanol can be beneficial. We investigated the use of renewable plant waste as substrate for enzyme production and hydrolysis of the plant waste for ethanol production using an indigenous yeast strain. Five yeast strains; MCC-1, MCC-2, MCC-3, MCC-4 and MCC-5 were evaluated for production of sugars, α-amylase, glucoamylase and bioethanol using soluble starch. Phylogenetic analysis using partial sequence of the ITS gene classified MCC-4 as Pichia exigua. Proximate composition of plant wastes – cassava, wild yam, mango seed, udara seed and breadfruit were determined. Results showed total carbohydrate of (83.9%) for cassava flour. The ability of yeast to utilize these substrates and the effect of culture conditions (inoculum, pH, nitrogen source and substrate concentration) were also determined. Cassava pulp flour was the best substrate producing reducing sugar (1.471 ± 0.056mg/mL), α-amylase (0.573 ± 0.019U/mL), glucoamylase (1.605 ± 0.119U/mL), and ethanol (4.440 ± 0.014g/L). Culture conditions revealed optimum for inoculum concentration as (1mL), pH (4), nitrogen source (soya bean, 3g/L) and substrate concentration of (8%). Pichia exigua (MCC-4) a natural yeast strain isolated from the soil has the potential for both enzyme and ethanol production in a single step process.