Fermentation of Raw Cassava Starch Using Geotrichum candidum sp. Optimizing enzyme and starch concentrations for alcohol production

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% 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% viability). Brix value and alcohol percentage for these
six samples showed that 50% 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 % and 4 % starch
after 12 hrs incubation period when treated with 50%
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 % starch showed that a
high percentage of alcohol (2.5 %) could be obtained after 60 hrs
incubation. In conclusion, 50% saturated enzyme sample at room
temperature and 4% starch has yielded highest brix value and
resulted 2.5% of alcohol in 100 mL of fermentation medium.