Studies on Microwave-Vacuum Drying of Foods

Abstract

Microwave-vacuum drying is one of the most promising techniques for drying foods with proper quality at a relatively low cost. The short drying times make this process cost-effective thus allowing large scale dried food production. As shown in this chapter, microwave-vacuum dried foods include bananas, grapes, pomegranates, carrots, seeds, gels, honey and snacks. A couple of equations for calculating drying efficiency and modelling drying kinetics are presented. The values of effective moisture diffusivity for some other products are also presented. Most of the studies reported here investigate the effect of process conditions, especially vacuum pressure and microwave power level, on quality and engineering aspects of selected products. Some of them dealt with process optimization. The chapter presents studies from end the past century, when microwave-vacuum drying of foods started to be studied, until nowadays. The evolution of this technique can be confirmed by technical advances introduced over the years such as the use of product rotation, power intermittency, control of product temperature, osmotic pretreatment and improvements on the equipment design.