English

Abstract

The present work aimed to assess the effect of the initial moisture content of grains (at harvest), velocity of the harvester cylinder and air temperature on the diffusion coefficient, as well as to achieve the activation energy of the drying process of two popcorn cultivars. Grains of popcorn from the cultivars Zelia and CMS 43 were mechanically and manually harvested and thrashed. The rotations of the threshing cylinder were fixed at 500, 600 and 700 rpm, with initial moisture contents of 0.235 and 0.175 db. They were dried with drying air temperatures of 40, 50 and 60oC, until reaching the final moisture content of 0.137 db. The diffusion coefficient increased with increased air temperature, presenting average values from 6.345 × 10-11 to 3.075 × 10-13 m2s-1 for the temperature range studied, depending on the initial moisture content, cultivar and level of mechanical damage. The cultivar CMS 43 (C2) is more resistant to the mechanical damage caused by the threshing cylinder, and the structural changes caused by it increased the diffusion coefficient. The relation between diffusion coefficient and temperature can be described by the Arrhenius expression, which presents activation energy for liquid diffusion in the grains of popcorn from 1.50 to 45.92 kJ mol-1. Key words: Mechanical damage, initial moisture content, diffusion coefficient.