Drying kinetics and effective diffusion of buckwheat grains

Abstract

Buckwheat has become important in the food sector as its flour does not contain gluten. Since buckwheat is a relatively new crop in the agricultural environment, there is little information available regarding its processing. Drying is one of the most important post-harvest stages of buckwheat. The aim of the present study was to describe the drying process of buckwheat grains. Buckwheat grains with a moisture content of 0.41 ± 0.01 (dry basis, d.b.) were harvested, followed by drying in an experimental dryer at the temperatures of 40, 50, 60, 70, and 80 °C, at an air speed of 0.8 m s-1. The drying rate was determined, and the mathematical models generally employed to describe the drying process of several agricultural products were fitted to the experimentally obtained data. Model selection was based on the Gauss-Newton non-linear regression method and was complemented by Akaike Information Criterion and Schwarz’s Bayesian Information Criterion. It was concluded that the drying rate increased with an increase in temperature and decreased with an increase in drying time. It is recommended to use the Midilli model to represent the drying kinetics of buckwheat grains at the temperatures of 40, 60, and 70 °C, while the Approximation of diffusion model is recommended for the temperatures of 50 and 80 °C. The magnitudes of effective diffusion coefficients ranged from 1.8990 × 10-11 m2 s-1 to 17.8831 × 10-11 m2 s-1. The activation energy required to initiate the drying process was determined to be 49.75 kJ mol-1.

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“…For higher temperatures, where the diffusion of water from the center to the periphery is greater, the effective diffusion coefficient has higher values (Silva et al, 2017). This behavior is in agreement with several studies on the drying kinetics of various agricultural products, such as seeds of V. unguiculata L. Walp (Camicia et al, 2015), grains of V. angularis (Resende et al, 2010), and grains of F. esculentum Moench (Siqueira et al, 2020). The activation energy for the drying process of cowpea seeds in a thin layer was 41.9894 kJ/mol for the temperature range of 40 to 60°C.…”

“…In general, the drying time is a direct result of the drying rate; that is, as the drying air temperature increased, the drying rate was higher, and the time taken to complete the process was shorter. This behavior has also been observed in several works on the drying of agricultural products due to the internal pressure generated inside the product (Siqueira et al, 2020).…”

“…The AIC and the BIC have been used as complementary in selecting models with a better fit, allowing reinforcing or dissipating eventual inaccuracies generated by the Gauss-Newton criterion. The AIC and BIC criteria were used in several works on drying kinetics of agricultural products favorably for grains of Fagopyrum esculentum Moench (Siqueira et al, 2020), leaves of Piper aduncum L. (Quequeto et al, 2019), and leaves of Cecropia pachystachya (Bastos et al, 2019). The values of the AIC and BIC of the mathematical models pre-selected by the Gauss-Newton method are shown in Table 2B.…”

“…To complement the selection of the models with the best fit, the AIC and the BIC (Equations 24 and 25) were used, submitting the pre-selected models by the Gauss-Newton criterion, commonly used with good accuracy for the selection of models with the best fit (Quequeto et al, 2019;Siqueira et al, 2020).…”

Drying kinetics of araticum (Annona crassiflora) epicarp

“…Recently, several researchers have updated, based on the AIC and BIC criteria to select with greater accuracy, the best mathematical model to represent the drying curves for different agricultural products (Gomes et al, 2018;Quequeto et al, 2019;Souza et al, 2019;Bastos et al, 2019;Pinheiro et al, 2020;Siqueira et al, 2020).…”