Effect of air temperature and relative humidity on the thin-layer drying of celery leaves (Apium graveolens var. secalinum)

Abstract

The thin-layer drying of celery leaves was studied under different conditions of air temperature (20-50℃) and relative humidity (10%-60%) in a through-flow laboratory dryer.  Both parameters influenced the drying time, although the effect of air temperature was more pronounced.  The effect of air relative humidity was practically negligible at 50℃.  The experimental data was fitted to six thin-layer drying models and their goodness of fit was tested, being the Two-term exponential model the one that showed the best fit in the majority of treatments.  The relationship between drying conditions and regression parameters of this model was analyzed to include it in the model.  Parameter a had a negligible effect on the drying curves and was set constant.  For parameter k a piecewise function was used in two parts, one for the temperatures between 20 and 40℃ and the other for 40 to 50℃, resulting in a good fit overall.  The color of the dried leaves did not appreciably change at temperatures between 20 and 40℃, except at very high levels of relative humidity, which should be avoided when air recirculation is used.  At 50℃ color was negatively affected.

Keywords: celery leaves, thin-layer drying, modeling, Apium graveolens, non-linear regression