Comparative Evaluation of Unpeeled Cassava (Manihot esculenta) and Tacca (Tacca involucrata) Tuber Flours as Substrates for Bioethanol Production

Abstract

The ever-increasing demand for alternatives to fossil fuel due to its negative impacts on the environment and high prices have resulted in the search for feedstock for bioethanol production. Cassava is one of the major staple foods that is processed into various preservative forms in Nigeria, while tacca is a plant growing in the wild and is eaten by a few people during scarcity of food. Unpeeled cassava and tacca tubers were processed into flour. The flour was hydrolyzed using Aspergillus niger and Saccharomyces cerevisiae, separately. The bioethanol potentials of tuber flours were evaluated using a single-step process. Hydrolysis of 10g of cassava tuber flour separately by Aspergillus niger and Saccharomyces cerevisiae produced (g/100mL) 0.720 and 0.765 of sugar, respectively, while hydrolysis of 10g of tacca tuber flour separately by Aspergillus niger and Saccharomyces cerevisiae produced (g/100mL) 0.392 and 0.367 of sugar respectively. Evaluation of the effect of time during hydrolysis of cassava tuber flour for 24h by Aspergillus niger and Saccharomyces cerevisiae separately produced (g/100mL) 1.44 and 0.737 of sugar, while hydrolysis of tacca tuber flour for 24h produced (g/100mL) 0.768 and 0.493 of sugar. Evaluation of the effect of varying pH values during hydrolysis of the tuber flours revealed that pH 5.6 produced the highest concentration of sugar (0.240g/100mL) and (0.803g/100mL) when Aspergillus niger and Saccharomyces cerevisiae were separately used to hydrolyze cassava tuber flour. When Aspergillus niger and Saccharomyces cerevisiae were separately used to hydrolyze tacca tuber flour at pH 5.6, 0.626g and 0.436g of sugar was produced. Fermentation of cassava tuber flour by mixed culture of Aspergillus niger and Saccharomyces cerevisiae for 48h produced 3.851%(w/v) bioethanol at 24h of fermentation, while fermentation of tacca tuber flour by mixed culture of Aspergillus niger and Saccharomyces cerevisiae produced 3.236% (w/v) bioethanol at 48h. Cassava tuber flour produced a higher concentration of bioethanol than tacca tuber flour. These results have shown that tacca tuber is a potential feedstock for bioethanol production, hence exploitation of nonfood materials such as tacca tuber for bioprocesses can reduce the over _dependence on cassava tuber.