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Effects of Pretreatment Method, Substrate Concentration and the Ratio of Koji to Cassava Flour Concentration on Ethanol Production from Cassava Tubers

Tubers from cassava variety 98/2101 were harvested at the age of 12 months and treated in 4 different ways: (a) peeled, sun dried and milled into flour (Flour); (b) peeled, fermented for 3 days by soaking in water, sun dried and milled into flour (fermented); (c) peeled and wet milled (Raw); and (d) the flour from (a) was gelatinized by suspending 10 g in 100 mL of distilled water, heating and stirring until it was gelatinized (Gelatinized). Gelatinization of cassava flour resulted in significantly (P<0.05) higher ethanol concentrations and yields but there were no significance differences in ethanol yields from other pre-treatment methods ((gelatinized cassava) > (fermented, wet milled, flour)). When nine different concentrations of nongelatinized or gelatinized cassava flour (10 ~ 100 g/L) were mixed inoculated with equivalent amounts of cassava koji, and 0.3 g (wet weight) of yeast cells, the ethanol concentrations increased with increase in the cassava flour concentration. However, the maximum ethanol yield (g-ethanol/g-cassava flour) for non-gelatinized cassava flour was obtained when 60 g/L was inoculated with 60 g cassava koji (total cassava flour concentration = 120 g/L). In the case of gelatinized cassava flour, the maximum ethanol yield was obtained with 80 g/L (total cassava flour concentration = 160 g/L). In this case, very high ethanol yield of 0.45 g-ethanol/gstarch was obtained. The results of the effects of the ratio of cassava koji to gelatinized cassava flour concentration on ethanol productivity and yield revealed that low cassava koji to cassava flour ratios resulted in incomplete utilization of cassava flour with resultant low final ethanol concentrations and yields. The optimum ratio of cassava koji to cassava flour for ethanol production was 20%w/v koji : 15%w/v gelatinized cassava flour.

1Ogbonna, C. N. and 2Okoli, E. C. Department of Biotechnology, Ebonyi State University, Abakaliki, Ebonyi State, Nigeria Department of Food Science and Technology, Ebonyi State University, Abakaliki, Ebonyi State, Nigeria

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