Thesis
Tanzanian Sisal industry is characterised by a severe biomass production for wastage
that is (2:98) product to waste ratio. Among the waste, 100% of plant residues in a
form of sisal boles, that are made of hydrolysable-fermentable sugars are slashed and
burned thus causing environmental emission concerns. The present study on
utilization of sisal bole juice-inulin as an alternative chemical feedstock in citric acid
production was divided into three parts. The first part involved the isolation and
characterisation o f the Aspergillus niger fungal strains generic to sisal boles for citric
acid production using sisal inulin hydrolysate-fructose. A high biodiversity of
microorganism with industrial potential were isolated and identified, including the
best performer A. niger (BYF KT) fungal strain which was used in citric acid
fermentation studies.
The second part involved the extraction and hydrolysis of inulin sugars from sisal
boles. HPLC analysis revealed that sisal boles had total sugar concentrations values
between (26.4±0.24 and 26.9±0.31 g/lOOml) with the corresponding fructose values
between (24.9±0.02 and 25.6±0.03 g/lOOml). Hydrolysis experiments were
performed by cooking at temperature range of 30-132°C and pH range of 2-5. The
effects of initial conditions (pH and temperature) were evaluated using 22 full
factorial design (FFD), with varying levels of pH and temperature. The factorial fit
and the analysis of variance (ANOVA), indicated that initial conditions for both pH
and temperature significantly affected hydrolysates-fructose yield, at confidence
interval (CI) of 95%. The optimum hydrolysates yields value of 97.2% (82.4%-
fructose) was obtained by cooking at temperature 110±5°C ~ (115°C) and pH 3.
The third set of experiments involved 101 pilot scale fermentation of sisal inulin-
hydrolyisates-fructose using A. niger (BYF KT) generic to sisal, at initial fructose
concentration range of 102-203 g/1, pH range 2-5 and nutrients additives values
coded between -1 and 1. The effects of initial hydrolysate-fructose concentration, pH
and nutrients additives were evaluated using a 23 full factorial design (FFD), with
varying levels of initial hydrolysates-fructose concentration, pH and nutrients
additives; The factorial fit and (ANOVA) for citric acid yield, indicated that initial
hydrolysate-fructose concentration and pH significantly effected citric acid yield, at
confidence interval (CI) of 95%, while nutrients additives was not significantly
affecting the yields. Results for pilot scale fermentation of 203g/l sisal juice
hydrolysate-fructose, in absence of nutrients additive and pH 5 produced highest
yields value of 46.66% (103.15±13.08 g/1). On the contrary, minimum citric acid
yield value of 9.51% (9.70±2.40 g/1) was obtained at low initial fructose
concentration of 102 g/1, pH 2 and with nutrient additions. The current findings
supported that sisal inulin has a great potential use as an alternative feedstock in
citric acid production, adding value to sisal industry and could be one way of dealing
with waste management.
SIDA SAREC