Microwave, convective, and intermittent microwave-convective drying of pulsed vacuum osmodehydrated pumpkin slices

Abstract

The drying of pumpkin slices (Cucurbita moschata Duch.) by microwave, convective, and intermittent microwave–convective techniques was studied. The samples were pretreated by blanching followed by pulsed vacuum osmotic dehydration. The microwave output power was 780 W. Air temperatures were 30 °C and 60 °C and air velocities were 2.22 and 4.44 m s−1. The final moisture content was set at 0.08 kg [H2O] kg−1 [dry matter]. The drying kinetics were obtained and fitted with the Fick's model and the Page's empirical correlation. Color, water activity, shrinkage, and rehydration were evaluated. Shorter drying times, higher diffusivity and better color quality were obtained by employing microwave. Convective experiments carried out to higher water activity and lower shrinkage. For describing the drying behavior, the better adjustment was reached by the Page's empirical correlation. Practical applications The pumpkin (Cucurbita moschata Duch.) is well known as an important source of carotenoids, vitamins and minerals. After the harvest, techniques are required to assist the preservation of fruits, once they present high moisture contents. Microwave drying is an alternative method to preserve temperature-sensitive compounds and to economize energy and time. Microwave energy combined with other drying methods can improve the drying efficiency as well as the quality of food products which is far better than that achievable by the application of each method alone. This study investigates the efficacy of convective, microwave and intermittent microwave–convective drying techniques for osmodehydrated pumpkin slices. The mathematical models provide information about the processes. It was also evaluated the changes on physical characteristics of the product after drying.