Biochemical changes occurring 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. Jakri) were studied. Tubers were harvested at monthly intervals from the fourth to the tenth month after 50% emergence of the planted yam sets. For storage studies, Oshei and Jakri tubers were harvested 9.5 and 9 months post-emergence, respectively. These were stored under prevailing tropical ambient conditions (18-31 degrees 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 Jakri tubers. This was judged to be the optimum time for harvesting. Starch reached maximum values of 86.7 and 78.3 g/100g, respectively after 6 months. Ethanol-soluble sugars declined from 9.4 to 2.3 g/100g in Oshei but remained constant at over 6.0 g/100g in Jakri tubers during growth. Crude protein values increased slightly to a maximum of 5.4 and 8.0 g/100g, respectively for Oshei and Jakri tubers. During storage, weight losses reached 31% in Oshei tubers and 35% in Jakri after 110 days due to sprouting and dehydration. Starch decreased by approximately 3.5-4.5 g/100g while sugars and fibre values increased slightly in both cultivars.