Characterization and Suitability of Dioscorea Alata (Water Yam) in the Production of Couscous

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Consumer utilization of Dioscorea alata could be enhanced by processing them into a more stable, acceptable and convenient food product. The aim of this study was to evaluate the suitability of Dioscorea alata for couscous production. Fifteen varieties of Dioscorea alata were used for this study. Yam couscous was prepared using both the blanched-grated-tuber and the flour methods. The yam tubers were first characterized for the chemical composition (moisture, ash and protein) and physicochemical properties (amylose content, starch granule size and pasting properties). A shelf life study was conducted over 24 week period within which the moisture content, pH, microbial load and sensorial qualities of the yam couscous were determined. The Dioscorea alata flours had relatively high gelatinization temperatures and low peak viscosities. The gelatinization temperature is positively correlated with the gelatinization time. The Dioscorea alata starches had granule sizes, ranging from 20 \im to 60 pm and very low amylose content. The blanched- grated-tuber (BGT) method was easier in terms of labour and time and gave better couscous than couscous made by the flour method in terms of sensory qualities. In decreasing order of goodness, couscous from TDa 99/00528, TDa 291 and TDa 98/001168, Matches, TDa 99/00199 and,TDa 99/00214 were judged as the most preferred. There was a general increase in bacteria count of yam couscous over storage period. However, no E. coli and Coliforms were present. The sensory quality of the yam couscous was acceptable over the storage period. It is possible to produce acceptable couscous from Dioscorea alata which will be safe for human consumption and keep for not less than 24 weeks in a cool dry place. 
A thesis submitted to the Department of Biochemistry and Biotechnology, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Master of Science