Isolation and characterization of local fungi for alcohol production from sugars in cane molasses and inulin in sisal stems.

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University of Dar es Salaam
A total of 57 morphologically different yeast strains were isolated from Tanzanian environments. From these, 5 isolates could grow and ferment molasses at 40°C and only 3 at 45°C. One of the three isolates coded Thereto 1 fermented molasses to 7.4 + 0.25 and 5.2 + 0.14% (w/v) ethanol at 43°C and 45°C, respectively. Further studies on Thereto 1 revealed an optimum growth temperature of 38°C and specific growth rates of 0.86h-1 and 0.64h-1 in supplemented glucose and molasses, respectively. Preculture of Thereto 1 at (40°C) rather than the optimum 38°C significantly enhanced ethanol production at 43°C (P < 0.001). Ethanol yields from Thereto 1 at 43°C were improved by 30% through 20 fold increase in inoculum concentration. When production of process by-products by the isolate Thereto 1 was compared to a typical industrial yeast, there was no significant difference in either acetic acid formation (P = 0.405) or methanol (P = 0.092). From these results, it was concluded that Thereto 1 has an industrial potential in high temperature molasses fermentation worth further studies. The potential of selected local nutrients as molasses supplements in high temperature alcoholic fermentation was investigated. The best results were from food grade soy bean flour. Soy flour (l%) significantly enhanced ethanol yield by the thermotolerant yeast Thereto 1 at elevated temperatures (P = 0.021), achieving a 20-22% increase in ethanol production from molasses at 43°C. Soy flour supplementation significantly enhanced yeast growth rates (P = 0.0176) at elevated temperatures. No significant difference was observed when soy supplementation was compared to analytical grade yeast extract/peptone in the promotion of yeast growth (P = 0.808) or ethanol production (P = 0.649) at supra-optimal temperatures. The effect of soy-supplementation on acetic acid formation showed no significant increase (P = 0.124) during molasses fermentation at elevated temperatures. These findings indicate a large potential for the utilization of soy flour as a cheap industrial yeast supplement in Tanzania. In an endeavour to enzymatically depolymerize inulin from waste sisal stems into fructose, a strain of Penicillium was isolated and the inulinase potential of its supernatant was studied. The inulinase secretion into the supernatant was highest when the mold isolate was cultured at 28-30°C and pH 5.5. Out of a number of industrial grade nutrients studied for supplementation of the sisal stem medium, ammonium sulphate produced the highest secretion of inulinase with 17 U/ml although with analytical grade nutrients up to 23 ± 0.4 U/ml could be detected from the mold supernatant. Studies on the inulinase activity of the supernatant revealed an optimum temperature of 50°C and pH 5:5. The Penicillium supernatant (20 U/ml) applied as 15% (v/v) was able to hydrolyse 69.7 ± 0.41% inulin of sisal stem medium into fructose in 30 hours at 45°C. It was concluded from these results that an enormous potential exists for sisal inulin hydrolysis using such an enzymatic process. With a view to alcoholic fermentation of waste sisal stems, an attempt was made to isolate naturally occurring sisal yeasts. Among the isolates, one coded Skly 1 was capable of growth on inulin of the sisal but able to ferment only the sisal hydrolysates or fructose but not inulin. This behaviour was interpreted as a kind of "Kluyver effect" and the yeast upon further studies revealed an optimum fermentation pH of 2.8 and a growth optimum of pH 5.5. However, the maximum amount of ethanol produced by the isolate from sisal stem hydrolysates was 23% (w/v). From these low ethanol amounts, it was concluded that the strain is presently unsuitable for alcohol production but the Kluyver phenomenon and the pH modulation of metabolism were found interesting and worth further studies.
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Hosea, K. M. M. (1996). Isolation and characterization of local fungi for alcohol production from sugars in cane molasses and inulin in sisal stems. Master dissertation, University of Dar es Salaam. Available at (