Biochemical changes occurring during growth and storage of two yam species

Abstract

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 (18–31°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 8.0g/100g, 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 3.5–4.5g/100g while sugars and fibre values increased slightly in both cultivars.