Effect of Drying on Porous Characteristics of Orange Peel

The purpose of the study was to determine the effects of different temperatures (40, 50 and 60 °C) and air velocities (1 and 2 m/s) on shrinkage, porosity, pore size distribution, color and microstructure of orange peel. Empirical models were also proposed to predict shrinkage and porosity as a function of moisture. A strong negative correlation was determined between moisture and shrinkage. Air temperature had no significant impact on the final shrinkage and porosity values. During drying, porosity of the samples first increased until a critical value, at which point further decrease in moisture resulted in collapse of pores. The porosity of the orange peel was correlated with moisture by a third-order polynomial. Pore size distribution curve of raw sample showed two major peaks, a wider and a sharper peak at around 19.8 and 7.18 μm, respectively. After drying, the peaks became shorter and the curve shifted to the left, indicating that the amount of pores and their diameter decreased. The SEM analysis revealed that at extreme process conditions, the orange peel surface was cracked and the characteristic distribution of the waxy components was obstructed.