Moisture effective diffusivity in Kepok Kuning banana (Musa paradisiacal formatypica) during convective drying by considering its shrinkage phenomenon

Abstract

Determination of moisture effective diffusivity in Kepok Kuning banana (Musa paradisiacal formatypica) slab during drying was conducted as an effort to develop efficient production process of banana downstream product. Kepok Kuning Banana at ripeness state 2 and 4 was cut in slab with initial thickness ±5 mm and then dried separately in a hot air flow oven. The objective was to predict time required in oven for gaining dried banana slab with certain moisture content. Prediction was conducted by using Fick’s law equation. To solve the equation for Kepok Kuning Banana, moisture effective diffusivity of Kepok Kuning Banana as nature specific coefficient need to be determined. Shrinkage was measured by measuring thickness of banana slab after certain period of time in oven compared to initial thickness. Without considering shrinkage during drying, the effective diffusivity of Kepok Kuning banana at ripeness state 2 and 4 were 0.18x10−10 m2/s and 0.24x10−10 m2/s, respectively. Effective diffusivity of Kepok Kuning banana at ripeness state 2 is about two-third of the diffusivity of banana at ripeness state 4 which is significantly different. The effective diffusivity with considering shrinkage of Kepok Kuning banana at ripeness state 2 and 4 were 0.16x10−10 m2/s and 0.14x10−10 m2/s, respectively. Drying kinetics considering shrinkage gave better fitting of the Fick’s model to the experimental data with coefficient of determination (R2) for banana ripeness state 2 and 4 were 0.9508 and 0.9783, respectively. These coefficients closer to 1 compared to model without considering shrinkage which only 0.8894 and 0.8690 for banana ripeness state 2 and 4, respectively. Suzuki’s model could be used to explain shrinkage during hot-air drying process especially in range of low moisture content due to termination of shrinkage process as no more change in solid structure after some definite time in dryer. However, linear empirical model gave better correlation coefficient for both ripeness state in the overall range of moisture sample.