Prediction of kernel and bulk volume of wheat and canola during adsorption and desorption

Information on the shrinkage of grain both in bulk and as individual kernels is important in postharvest processing of these materials. The mass and volume of samples of wheat and canola seeds exposed either to humid or dry air were measured during adsorption or desorption cycles. When the grains were exposed to 90% r.h. at 40 degrees C, the bulk density of wheat decreased almost linearly from 790 to 686 kg/m(3) as the kernel moisture content increased from 8% to 22% w.b. The bulk density of canola descreased by 11 kg/m(3), from 672 to 661 kg/m(3) as the kernel moisture content increased from 5% to 19% w.b. The laws of mixtures were used to develop the following equations to predict grain kernel (upsilon(k)) and grain bulk volume (upsilon(b)) respectively as functions of moisture adsorption or desorption: upsilon(k)/upsilon(k0) = [1 - M(0)/1 + (gamma - 1)M(0)][1 + (gamma - 1)M/1 - M] and upsilon(b)/upsilon(b0) = [1 - (M(0) - M)][1 + (gamma + 1)M] (1 - epsilon(0))/[1 + (gamma - 1)M(0)] (1 - epsilon) where upsilon(k) and upsilon(k0) are the kernel volumes, upsilon(b) and upsilon(b0) are the bulk porosities at the kernel moisture contents of M and M(0) respectively; gamma is the dry kernel density and is assumed to be a constant for each grain. Compared with experimental data, the kernel volumes of both wheat and canola, adequately predicted by the first equation. The second equation gave an adequate prediction of the bulk volume of canola by assuming epsilon = epsilon(0), but not for wheat unless epsilon was expressed as a polynomial function of kernel moisture content. (C) 1996 Silsoe Research Institute