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NomenclatureK, n: Page Model constants; r: Coefficient of Correlation; SE: Standard Error; P: Relative Percent Error (%); t: Time; X r: : Reduced moisture content; X 0 : Initial moisture content (kg water/kg db); X f : Final moisture content (kg water/kg db); R r : Reduced drying rate; N: Numbers of data points; n p : Numbers of parameters SubscriptsCal: Calculated; exp: Experimental; j: Samples number. Material and Methods MaterialFresh oranges (Citrus sinensis) and leaves of "Maltaise" variety were picked in Manzel Bouzalfa (Nabeul, Tunisia) in an advanced stage AbstractThe effect of microwave drying on drying characteristics of "Maltaise" peel and leaves was investigated. The effect of microwave power on color, total phenols and water and oil holding capacities was determined. By increasing microwave powers (100-850W), drying time decreased from 6960 to 420 s for peel and from 4800 to 210 s for leaves. Page model successfully described the drying kinetics. For microwave powers ranging from 100 to 850W, the values of r, SE and P are ranging respectively from 0.8636 to 0.9806, from 0.2292 to 0.4307 and from 15.0381 to 34.1190. The applied microwave powers affect significantly all color parameters of peel and leaves (P<0.001).Compared to the fresh state, functional properties of peel and leaves decreased after microwave drying except the water holding capacity of peel that increased. For both dried peel and leaves and at each applied microwave power, water holding capacity values were higher than oil holding capacity values. Microwave drying decreased total phenols of the dried leaves compared to the fresh ones. However, drying at 450W improved the extractible phenols amounts from peel (1.880 ± 0.050g caffeic acid/100g db).

The aims of this work were to determine the desorption isotherms of “Maltaise” orange peel and leaves and to investigate the effect of the infrared drying on the drying kinetics and on the physical and functional properties. The moisture desorption curves showed a sigmoïd shape (type II on the BET classification). GAB was found to be the best model for describing the desorption curves. The infrared drying rate increased, with temperature increasing at the same moisture ratio. High drying temperatures preserved initial color parameter values of “Maltaise” orange peels (from 21.893 ± 0.629 to 24.793 ± 0.525, from 37.973 ± 0.941 to 45.44 ± 0.390 and from 45.350 ± 1.077 to 50.439 ± 0.740 for a*, b* and C, respectively) and leaves (from -5.98 ± 1.651 to -5.276 ± 0.342, from 10.73 ± 1.547 to 16.42 ± 0.174 and from 12.283 ± 2.263 to 17.247 ± 0.384 for a*, b* and C, respectively) and maximal phenolic content. Nevertheless, water and oil holding capacities decreased significantly. Low temperatures gave the best functional properties.

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