DOI: 10.5176/2251-3701_2.2.78
Authors: S.N.T. DE SILVA, A.J.A. TILAKARATNA, M.M.W.K.B. MANCHANAYAKE and D.P.S.T.G.
ATTANAYAKA
Abstract:
Production of bioethanol is a global requirement to address the question of energy crisis. Attempts have been made to use agricultural starch based renewable resources to produce ethanol. Starchy materials should be converted into simpler sugars prior to fermentation and this is achieved by treating with enzymes. Fermentation medium containing 1.5 g, 3 g and 10 g of raw cassava were optimized for brix value by directly inoculating samples (DIS) with fungi G. candidum or treating the medium with different concentrations of crude enzyme (50 mL & 100 mL) and 50{6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} ammonium sulphate fractionated proteins (Enzyme Treated Samples -ETS). Highest brix values containing samples for 1.5 g, 3 g and 10 g of cassava under two different experimental conditions were ETS1, ETS2, ETS3, and DIS1, DIS2, DIS3 respectively. The samples were fermented with yeast stock cultures of maximum viable cells (7.065×106 cells cm-3 &86.4{6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} viability). Brix value and alcohol percentage for these six samples showed that 50{6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} Ammonium sulphate saturated enzyme samples is suitable to obtain higher brix value when compared to crude and direct inoculation method. Then the culture conditions were optimized for starch percentage, pH and viable cell numbers. The results showed that an effective increase in Brix value of 2.3 could be obtained with 3 {6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} and 4 {6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} starch after 12 hrs incubation period when treated with 50{6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} ammonium sulphate fractionated enzyme. Optimized fermentation conditions showed that the viable cell numbers of culture medium decreased during 36-48 hrs of incubation period. There was a sudden pH drop after 12 hrs and considerable changes were not observable in prolonged incubation. Optimization results for alcohol with 4 {6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} starch showed that a high percentage of alcohol (2.5 {6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465}) could be obtained after 60 hrs incubation. In conclusion, 50{6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} saturated enzyme sample at room temperature and 4{6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} starch has yielded highest brix value and resulted 2.5{6e6090cdd558c53a8bc18225ef4499fead9160abd3419ad4f137e902b483c465} of alcohol in 100 mL of fermentation medium.
Keywords: Alcohol, raw starch, α-amylase
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