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 k ernels 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 d ensity of wheat decreased almost linearly from 790 to 686 kg/m(3) as t he kernel moisture content increased from 8% to 22% w.b. The bulk dens ity 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 mix tures were used to develop the following equations to predict grain ke rnel (upsilon(k)) and grain bulk volume (upsilon(b)) respectively as f unctions 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 porositie s 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 an d canola, adequately predicted by the first equation. The second equat ion gave an adequate prediction of the bulk volume of canola by assumi ng epsilon = epsilon(0), but not for wheat unless epsilon was expresse d as a polynomial function of kernel moisture content. (C) 1996 Silsoe Research Institute