Physicochemical Properties of Yam Tuber (Dioscorea rotundata) According to Its Longitudinal Axis

Abstract

Yam is a tuber with a longitudinal growth gradient, resulting in heterogeneous slices after cooking. This poses the problem of delimiting the distal, medial and proximal parts. The aim of the present study is therefore to obtain information on the longitudinal distribution of physicochemical properties and the proportion that the distal, median and proximal parts of the yam tuber might represent. To this end, three 28 cm tubers of the "Assawa" variety were cut longitudinally. Some physicochemical properties of the slices and flour were determined. A general variation was observed from proximal to distal parts. Firmness of yam tissue decreased from 1.2 N ± 0.05 to 0.5 N ± 0.1. Apparent viscosity decreased from 235 mPa.s ± 3.4 to 212.4 mPa.s ± 1.1. The water content of yam tubers increased from 58.5% ± 0.9 to 89.1% ± 0.8. Protein content decreases from the proximal end to the apex of the yam tuber (4.88 ± 0.02 to 4.8 ± 0.01). The longitudinal distribution of physico-chemical properties enabled us to objectively delimit the length and proportion of the whole tuber that the distal, medial and proximal parts could represent. Thus, on a tuber of around 28 cm, the distal part could be estimated at 28.57% (8 cm), the medial part at 28.57% (8 cm) and the proximal part at 21.43% (6 cm). The medial-distal and proximal-medial parts occupy 7.14 to 14.29% or 2 and 4 cm of the tubercle, respectively. This delimitation makes it possible to obtain tuber portions with a homogeneous texture, which is useful for yam processing applications.