Higroscopic properties of castor seeds (Ricinus Comunis L.)

Sorption isotherms of castor seeds were evaluated at 30, 40, 50 and 60ºC using the static gravimetric method. Sigmoid trends were observed for isotherms obtained showing a clear effect of temperature. Experimental values were adjusted using the modified isotherms of Henderson, Halsey, Oswin and Guggenheim-Anderson-de Boer (GAB). Models were compared using four statistics parameters. The results showed that Modified Henderson model adjusted adequately the experimental values in the range of temperature evaluated. The experimental values of the safe storage moisture content for castor seeds varied between 6.1 to 8.4 % (d.b.) between 20 and 40ºC, showing lower values than those reported for other traditional oilseeds as sunflower or rapeseed. The sorption heats evaluated from the combination of Clapeyron equation and Modified Henderson equation varied between 3400 and 2373 kJ/kg for moisture contents between 1 and 28 % (d.b.). Through Othmer relationship the value of the ratio Lb/Lf varied between 1.01 and 1.34 (for 14.5 and 1% d.b. moisture content respectively). The values obtained showed an exponential relationship with moisture content, of the form Lb/Lf=1+0.44exp(-0.17M) with a determination coefficient R² of 0.97