1. Introduction
Freeze drying is widely used to obtain high quality dehydrated fruitsand vegetables (Ratti, 2001). The solid state of water, low temperatureand sublimation mode of moisture transport during freeze drying helpprotect the primary structure and shape of products and the resul-tant products often possess low bulk density, high porosity and betterrehydration characteristics (Cui et al., 2008; Huang et al., 2011). How-ever, freeze drying is slow and often low throughput process and alsorequires expensive equipment. Because of these reasons, its applica-tion is often restricted in producing high-value products (Wang et al.,2011). The low throughput and long residence time are due to veryslow mass and heat transfer rates as the freeze drying process has tobe maintained within triple point of water (Duan et al., 2007). Sincefreeze-drying is mass transfer controlled process, continuous heatingdoes not accelerate the rate of water removal (George and Datta, 2002).Therefore, in the conventional freeze drying systems, it is difficult tosignificantly increase the rate of drying without compromising prod-uct quality. Hence, it would be of practical importance if an alternative freeze drying method with shorter drying time, lower energy consump-tion and producing desirable product quality is developed.