Utilization of sisal bole juice - inulin as an Alternative chemical feedstock in citric acid Production

Abstract

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.