Study of the drying behaviour and color kinetics of convective drying of yam (Dioscorea hispida) slices

Abstract

Drying is a crucial step in processing for enhancing the storability of yam (Dioscorea hispida) slices. In this present work, the drying of yam slices was carried out in a lab-scale auto weighing forced convective hot air drier at a temperature span of 50–70 0C after 30 min of boiling. The study focused on drying behavior, fitting mathematical models to drying and color kinetics, examining the texture and rehydration ratio of dries yam slices. To exhibit the mass and color change characteristics, experimental data were fitted to seven drying kinetics and two color kinetics models. Model fitness was compared and selected based on chi-square (X2), goodness of fit (R2), residual sum of squares (RSS), and root mean square error (RMSE). Moisture diffusivity ranged from 4.5133 × 10−10- 7.522 × 10−10 m2/s and increased with temperature. The activation energy of 23.53 kJ/mol was obtained. Midilli-kucuk model confirmed the superior fitting to experimental data followed by two-term model. Color kinetics was determined using L, a, b values, total color change (∆E), chroma, hue and browning index. L value reduced with drying time, while b and a value increased. Zero order kinetics fitted a and ∆E values adequately while first order kinetics described the changes in L and b values. It can be concluded that the Midilli-kucuk model can be used for predicting drying process behavor, system design of convective hot air drying of Dioscorea hispida for industrial scale up.