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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.

Niger seed oil has excellent quality and quantity (30-50%) and is rich in polyunsaturated fatty acids, mainly linoleic acid (about 70%). Thus, control of environmental temperature and relative humidity, and of seed moisture content is essential to maintain seed oil quality during storage. Thus, the objective of this study was to determine the desorption isotherms of niger seeds under different temperature and water activity conditions, to test the experimental data with different mathematical models, and discover which best represents the phenomenon, as well as calculate the isosteric heat value for the product. Hygroscopicity was determined by the static gravimetric method, at temperatures of 30, 35 and 40 ºC, and water activity between 0.07 and 0.79 (decimal). For the experimental data, mathematical models commonly used to test hygroscopicity in agricultural products were evaluated. From the results obtained, it was concluded that: water activity increases as moisture content rises; based on the statistical parameters, the models of Chung and Pfost, modified Henderson, Oswin, Sabbah, Sigma Copace, Halsey, Smith and Copace appropriatrely represented the desorption phenomenon of niger seeds; total isosteric desorption heat increased with reduction of moisture content, with values varying from 2539.62 to 3081.48 kJ kg-1, within the range of equilibrium moisture content of 2.4 to 12.2 (% dry basis).