Biochemical changes occuring during growth and storage of two yam species

The biochemical changes occurring during growth and storage of two yam cultivars (#Dioscorea rotundata$ cv. Oshei and #Dioscorea dumetorum$ cv. Jakiri) were studied. Tubers were harvested at monthly intervals from the fourth to the tenth month after 50 % emergence of the planted yam setts. For storage studies, Oshei and Jakiri tubers were harvested 9.5 and 9 months post-emergence, respectively. These were stored under prevailing tropical ambient conditions (18-310°C, 62-100 % RH) for 1, 2, 3 and 4 months. All samples were analysed for dry matter, crude protein, carbohydrate, essential amino acids and mineral contents. The maximum dry matter was reached in both cultivars 9 months post-emergence, being 40.4 and 26.4 %, respectively for Oshei and Jakiri tubers. This was judged to be the optimum time for harvesting. Starch reached maximum values of 86.7 and 78.3 g/100 g, respectively after 6 months. Ethanol-soluble sugars declined from 9.4 to 2.3 g/100 g in Oshei but remained constant at over 6.0 g/100 g in Jakiri tubers during growth. Crude protein values increased slightly to a maximum of 5.4 and 8.0 g/100 g, respectively for Oshei and Jakiri tubers. During storage, weight losses reached 31 % in Oshei tubers and 35 % in Jakiri after 110 days due to sprouting and dehydration. Starch decreased by approximately 3.5 - 4.5 g/100 g while sugars and fibre values increased slightly in both cultivars. (Résumé d'auteur