Mathematical modelling of diced konjac corms drying in a fluidised bed dryer

Abstract

Konjac glucomannan (KGM) can be obtained from tubers (called corms) of various species within the Amorphophallus genus. Among the most popular species for use in food industry is Buk Nuea Sai (Amorphophallus muelleri), a native species in Thailand. Drying process can be helpful in preserving KGM during long storage periods. However, the existing drying systems are often slow and lead to drying delays and subsequently quality reduction of the dried product. Given the economic importance of KGM, new, more efficient drying systems, have to be developed. The present study focuses on the drying kinetics of konjac dices in a fluidized bed, operating at a constant air velocity of 2.5 m/s and air temperatures of 50, 60, and 70?C. Six empirical mathematical models were selected to describe and compare the drying characteristics of konjac dices subjected to these conditions. The model coefficients were determined by non-linear regression analysis. Among the tested models used to describe the drying kinetics of konjac dices, the two-term model was found as the best one. The moisture loss from the dice was described by the Fick?s diffusion equation, and based on the obtained results the effective moisture diffusivity was estimated, getting a value in the range between 9.60526 ? 10?9 m2/s and 1.2006 ? 10?7 m2/s. The relationship between the temperature and the effective moisture diffusivity was described adequately by means of Arrhenius-type equation. An activation energy value between 8.65 kJ/mol and 61.28 kJ/mol was obtained. The findings allow the successful simulation of konjac dice drying in a fluidized bed between 50 and 70?C, 30-60 mm bed height and 6-15 mm dice thickness.