Effect of Vacuum Drying Temperature on Drying Kinetics, Effective Moisture Diffusivity and Quality of Peeled Litchi (Litchi chinensis Sonn.)

This study aimed at investigating the effect of vacuum drying temperature on drying kinetics, drying rates, effective moisture diffusivity and quality parameters of litchi fruits. Peeled litchi quarters were dried at 50-70 degrees C at an absolute pressure of 8kPa. Results show that the vacuum drying occurred in the falling rate period. Drying rates increased with drying temperature. The Page model provided the best fit to the drying kinetics. Effective moisture diffusivity ranged between 1.997 x 10(-9) and 5.012 x 10(-9)m(2)/s. The temperature dependence of the effective moisture diffusivity was well described by an Arrhenius-type equation. The activation energy for moisture diffusion was 41.81kJ/mol. Drying temperature did not significantly affect product sensory acceptance, density, shrinkage and rehydration. The products dried at 50 and 70 degrees C presented slightly superior texture and flavor, while the product dried at 60 degrees C presented significantly higher lightness and lower water activity. Practical ApplicationsThis work provides valuable information on the vacuum drying of litchi fruits, which are appreciated in many countries due to their pleasant sensory characteristics. Vacuum drying is not a costly drying method. At the same time, vacuum drying produces dried foods of relatively good quality. This study could be used as a reference by small and medium scale food processors interested in producing dried litchi of good quality with relatively low investment in equipment. The understanding of the influence of drying temperature on quality parameters is useful for deciding which temperature is more appropriate depending on the desired quality aspects, while the calculation of engineering parameters is important for designing the drying process.