EFFECT OF SUCCESSIVE ADSORPTION-DESORPTION CYCLES AND DRYING TEMPERATURE ON HYGROSCOPIC EQUILIBRIUM OF CANOLA

Moisture sorption isotherms of both ambient-air dried (25-degrees-C) a nd heated-air dried (50-degrees-C) canola Brassica napus L. 'Westar' w ere measured up to the fifth adsorption-desorption cycle at the equili bration temperatures of 3.5, 25, and 40-degrees-C. Successive adsorpti on-desorption cycles and a raised drying temperature affected the hygr oscopic equilibrium of canola in such a way that the isotherms were sh ifted downward, especially at relative humidities below 60%. Compared with those on higher-numbered cycles, the isotherms of ambient-air dri ed canola appeared irregular on the first and second adsorption-desorp tion cycles at relative humidities around 30%. The EMC data of canola exposed to successive adsorption-desorption cycles were fitted to the Halsey equation. The Halsey equation was statistically shown to descri be marginally well the successively cyclic isotherms of canola. Consta nt B in the Halsey equation was found to vary little, while constant C changed considerably with increased numbers of adsorption-desorption cycles.