Chemical composition and quality changes occurring in Dioscorea dumetorum pax tubers after harvest

Studies were conducted on the chemical composition, as well as the biochemical and textural changes, occurring during storage of two cultivars of Dioscorea dumetorum yam tubers, The tubers were harvested and stored under tropical ambient (28 degreesC) and cold room conditions (4 degreesC) for 24, 48 and 72 h. The samples were evaluated for moisture, starch, sugars, fibres and textural properties. Chemical analysis showed no significant differences between the means obtained for moisture, ash, protein, fibre, fat, carbohydrate, calcium, phosphorus, iron, vitamin A and vitamin C contents of the cultivars (white and yellow) studied. During storage, moisture contents decreased by approximately 6 10% after 72 h of harvest due to dehydration. Starch levels declined from 70.5-66.5 g/100 g, while sugars and fibre contents increased slightly in the samples. Textural properties (peak force and curve areas) also increased considerably during storage. Peak force (hardness) increased from 1143.0 to 5711.5 g in the white cultivars whilst the yellow cultivars increased from 2130.5 to 4194.1 g. Curve areas (adhesiveness) also increased from 12.2254 to 29.5646 g in the white cultivars and from 17.1316 to 24.3108 g in the yellow cultivars. There were very high correlation co-efficients (r=-0.9503-0.9913, P less than or equal to0.05) between peak force (hardness) and all the biochemical constituents of the white cultivars, and (r=-0.9876-0.9380, P less than or equal to0.05) for the yellow cultivars investigated. However, the rate of hardening varies with cultivars and temperature of storage. (C) 2001 Elsevier Science Ltd. All rights reserved.