Samples of 300 g of soybean seed, variety Forrest, conditioned to 14, 16 and 18% moisture content (m.c.; w.b.), were dried for 4 hr in a small batch fluidized-bed rig with a test section of 120 mm diameter and air flow rate set at 0.03 kg/s. Air inlet temperatures of 40, 50, 55, 60, 65, 70 and 80°C were used to determine the effects on quality. Conditioned and unconditioned samples, together with samples dried in the bed for 4 hr at room temperature, served separately as controls. Samples of 25 g of the conditioned seed, sealed in test tubes, were heated for 4 hr in an air oven at 40, 45, 50, 55 and 60°C to study the effect of heating at a constant m.c.
Seed germination and seedling vigour clearly indicated the onset of heat damage and showed that no single criterion was more sensitive than any other. Safe drying air temperatures of 65, 60 and 55°C were obtained for initial moisture contents of 14, 16 and 18% respectively. Heating soybeans up to 60°C at a fixed m.c. increased the susceptibility to heat damage. Oil vield, free fatty acid content and fatty acid composition were not affected by any of the heat treatments. The peroxide value, however, showed some increase at temperatures above 50°C. Fluidizing at room temperature did not affect germination.
The colour of crude oil, after heat bleaching, for 50–80°C heat treatments was paler than the controls, while 40°C gave a very dark colour. Degumming of oils followed by refining removed all detectable phospholipids from all samples and produced oils paler in colour, when heat bleached, except for 80°C at 16 and 18% m.c. which produced oils slightly but noticeably darker.
Soybeans were found to dry slowly compared to sunflower seed and rapeseed, and the logarithmic drying model was fitted to the various drying curves. Computer program DRIER was modified to be applicable to soybeans and some runs were carried out for a farm batch radial-flow drier. Results indicated the advantage of using a high inlet air temperature provided that seed quality is not affected.
