Effect of hydrodrying conditions on shrinkage of pumpkin (Cucurbita maxima) pieces

Abstract

The method for properly drying fruits and vegetables should guarantee the quality of the finished product in
addition to being economically viable. For this reason, several technologies, including pre-treatments and
improvements to the drying technique itself, have been applied and developed. Using the methodology called “conductive hydro-drying” based on the Refractance Window (RW^TM) technique, rectangular pieces of pumpkin (1.2 x 1.1 x 5.9 cm³) were dehydrated using a thermostatic bath with water at 90±2 °C, for 3 hours. Hence, a 2²  factorial design were performed to analyse the effect of convection and conduction on the shrinkage of samples. The tested factors were the type of convection with two levels: natural convection (NC) and forced convection (FC); and the type of drying foil with two levels: Mylar^TM  (MY) and Mylar^TMwith aluminium foil (MY/AL). The volume change factor (V/V₀) from primary dimensions (width, height and length) of the samples was evaluated during drying. The smaller and the larger shrinkage, according to the volume change factor, were observed in natural convection treatments NC-MY/AL and NC-MY, respectively. An exponential relationship between drying rate and volume change factor was found. The ANOVA indicated that convection and convection-film interaction were statistically significan