Optimisation of the Parameters for Bio-Processing of Cassava Peel to Increase Fermentable Sugars and Lysine Production
Loading...
Date
2017-07
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Ghana
Abstract
Bio-processing of cassava peel for Lysine production was done by characterising the cassava
peel for carbohydrate types. The process of enzymatic hydrolysis of the cassava peel was
optimised to produce fermentable sugars using response surface methodology. The
hydrolysed cassava peel was used as a source of carbon to optimise the conditions for lysine
production using mutant Corynebacterium glutamicum (AHP3) strain.
Cassava peel is a biomass generated as a result of processing cassava tuber by peeling
operations. It is a natural resource that shows heterogeneity in structure and chemical
composition. Physical and chemical composition analysis was done using standard methods.
It was found that nearly 83 % dry matter (DM) composition of the cassava peel was glucose
whiles xylose and arabinose have made up only small amount of 2.31 and 2.35 %
respectively. The cellulose and hemicellulose were 6.0 % DM and 2.23 % DM respectively
and the residual starch content was 47.16 %. The protein was 2.40 % and the cyanide level
was 9.3 mg/kg. The lignin and the ash contents were 1.92% and 6.30% respectively. The high level of residual starch and low amount of lignin make the cassava peel very susceptible to
enzymatic hydrolysis without laborious pretreatment regimes. Importantly, this study
provides a useful base line data for agro-economic evaluation of cassava peel as a feedstock
for an integrated biorefinery, because the valorisation of cassava peel is still overlooked and
not fully exploited. Additionally, deep understandings of the biomass chemical and physical
characteristics need to be known in order to assist in designing safe processing facilities.
Cassava peel is normally considered as waste because of its limited use. Composition
analysis revealed that it contained appreciable amount of starch which can be hydrolysed to
fermentable sugars. Response Surface Methodology using Central Composite Design (CCD)
was applied to optimise the enzymatic hydrolysis of cassava peel in order to produce glucose.
Two effective approaches were used in the study. The first one was to optimise the enzymatic
hydrolysis process using cellulase, β-glucosidase, amyloglucosidase and α-amylase. The
second approach was to optimise enzymatic hydrolysis using the mixture of these enzymes.
The effects of enzyme loading, hydrolysis time, substrate concentration, pH and temperature
on glucose recovery were investigated. The results were subjected to analysis of variance
(ANOVA) to produce polynomial regression model. Mean interaction plot and their effect on
glucose recovery were drawn to determine the optimal conditions for enzymatic process.
Targeted hydrolysis of specific carbohydrate types in cassava peels with single enzymes
showed optimised levels of glucose recovery of over 80% for starch hydrolysing enzymes
and about 5% for cellulose hydrolysing enzymes at 0.06 g/ml substrate water ratio at 24 hours of hydrolysis. Single step hydrolysis of cassava peel with mixed enzymes of starch and
cellulose hydrolysis enzymes at optimised conditions of celulase (30 FPU/g), β- glucosidase
(1.25 U/g), amyloglucosidase (30 U/g), α-amylase (30 U/g), pH 4 and 50 ᵒC at 24 hours
produced recovered glucose of about 100%.
The present study revealed that lysine biosynthesis from Corynebacterium glutamicum can be
significantly enhanced by optimising the fermentation process. Different ingredients have an
essential role in the metabolic pathway of the organism for lysine production. Carbon and
nitrogen sources from cassava peel hydrolysate have also been found to have influential role
in the amino acid production. Central Composite Design (CCD) was applied to optimise the amino acid fermentation
process in order to produce lysine. The effects of substrate concentration, microbial load and
time of fermentation on growth of C glutamicum, glucose utilisation and lysine production
were investigated. The results were subjected to analysis of variance (ANOVA) to produce
polynomial regression model. Mean interaction plot and their effect on microbial growth,
glucose consumption and lysine production were drawn to determine the optimal conditions
for amino acid fermentation process for lysine production. Glucose utilisation reduced at
higher hydrolysate concentration thereby affecting microbial growth. Lysine production was
optimum at low initial microbial load of 0.05 nm (OD) and cassava peel hydrolysate
concentration not more than 35% (v/v) at 48 hours fermentation.
Description
PhD.
Keywords
Bio-Processing, Cassava Peel, Fermentable Sugars, Lysine Production