Changes in the carbohydrate constituents of yam tuber (dioscorea rotundata, poir) during growth

The amounts of sugars, starch, hemicellulose and cellulose in yam tubers were estimated at different stages of maturity and in yam tuber (“EgbodO”) sections. Maltose, sucrose, glucose and fructose were the free sugars identified in the ethanolic extracts of the yam samples. Sucrose formed the bulk of the total sugars. The “bottom” portion of the “Egbodo” yam tuber was richer in total sugars (4.9%) than either the “middle” (1.8%) or the “head” (2.4%) regions. Starch accounted, respectively, for 60, 77 and 78% of total carbohydrates in the “bottom”, “middle” and “head” regions of the “egbodo” yam tuber. A peak value of 84% starch was obtained 6 months after planting the yam setts. Its decrease to 64% at 8 months has been partly attributed to reduced photosynthetic activity through yellowing and subsequent loss of leaves. The sum of cellulose and hemicellulose, regarded as non‐available carbohydrates was less than 7% of the total carbohydrates. The linear fraction, amylose, formed about 17.8% of the starch prepared from whole yam tubers of varying maturities, and from yam tuber sections, the remaining being amylopectin. The observed amylose and amylopectin values did not vary significantly over the period of observation. These amylose and amylopectin fractions had iodine affinities of 17 and 0.1%, respectively.