2.4. Drying characteristics of taro slice

The moisture ratio (MR) of taro slice during drying experiments was calculated using Equation (1):

where M _t is moisture content at any drying time, M _o is initial, and M _e is equilibrium moisture content.

The values of M _e are relatively little compared to those of M _t or M _o, the error involved in the simplification is negligible (Goyal et al., ²⁰⁰⁸), and thus moisture ratio was calculated as Equation (2):

Doymaz (²⁰¹⁰) methods were used to determine the mass diffusion of drying taro slices and it is shown in the equation 3:

where

The solution of diffusion equation (Equation 4) for slab geometry is solved by Crank (¹⁹⁷⁵), and supposed uniform initial moisture distribution, negligible external resistance, constant diffusivity, and negligible shrinkage are as follows:

where D _eff is the effective moisture diffusivity (m²/s), n is a positive integer, t is the drying time (s), and L is the half‐thickness of samples (m).

For long drying times, a limiting of Equation (5) is obtained and expressed in a logarithmic form:

From Equation (5), a plot of ln MR versus drying time gave a straight line with a slope (K) of:

To select the best model which expresses the drying behavior of taro slices, five different thin‐layer models were evaluated. To fit the experimental data, the models were evaluated based on statistical parameters, including the root mean square error (RMSE), reduced chi‐square (χ ²), coefficient of determination (R ²), and relative mean present error (P). The statistical parameters can be described in the following equations:

where MR_pre is the predicted moisture ratio, MR_exp is the experimental moisture ratio, N is the number of observations, and z is the number of constants in the drying model (Sobukola et al., ²⁰⁰⁸).

The specific heat capacity and thermal conductivity were derived from proximate composition of the taro flour samples using the method of Barine and Victor (²⁰¹⁶) (Equations 11 and 12), respectively.

where X _w = mass fraction of water, X _a = mass fraction of ash, X _p = mass fraction of protein, X _f = mass fraction of fat, and X _c = mass fraction of carbohydrate.