Mathematical Modelling and the Effect of Blanching on the Drying Kinetics of White Yam (Dioscorea rotundata)

Many pretreatments methods are employed to reduce the total drying time which is more energy efficient and generate final superior products. Blanching is a long established thermal pretreatments used for processing of agricultural products since it can eradicate enzymes, which cause degeneration reactions, off-flavor and undesirable changes in color, texture and nutrients. The blanching pretreatment effect on the drying kinetics of white yam (Dioscorea rotundata) slabs was investigated. The yam tuber was cut to the required thickness (5cm×2cm×1cm) with a knife and scale rule. Blanching was done at 90oC for five minutes and the drying experiments were carried out in a microwave oven. The samples were weighed and recorded before and after drying. Three thin layer models were evaluated and the coefficient of determination (R2) and residual sum of squares (RSS) were used to study the model efficiency for both raw and blanched samples. A mathematical model to describe the drying kinetics of blanched yam slabs was developed and validated. The Newton, Midilli et al and Fick’s kinetic models selected for this study were fitted with the experimental data. The results of the experiment carried out, the effective moisture diffusivity coefficient D was obtained as 2.7x10-5m2s-1 with blanching effect of 0.001m for the blanched sample, whilst the value of diffusivity, D for the raw sample was 3.4x10-5m2s-1. Newton’s model gave the best fit among the three models and regressed well with the experimental data, with high value of R2 of 0.9969 and low RSS of 0.0138. These results depict that blanching as a pretreatment method can decrease the total drying time and improve the effective moisture diffusivity as well as the final product quality compared to the raw samples.