ABSTRACT
Drying alters the characteristics of vegetable products and leads to loss of juiciness and lignied tissue, both of which result in a harder or chewier product. Other typical quality-loss attributes include case hardening, wherein the outer layers of the product are overdried in the process of removing moisture from the less accessible inner core of the product along with product shrinkage, both of which are issues associated with convective air-drying. As a result, the present demand for highquality dehydrated vegetable products in the market requires dried vegetables to be maintained at a very high level to preserve the nutritional and organoleptical properties of the initial fresh product. Moreover, new technologies for drying of new products, higher capacities, better quality and quality control, reduced environmental impact, higher energy efciency and lower cost, and safer operation are needed. Freeze-drying (FD) produces the highest quality food product obtained by any drying method. Despite unmatched advantages, FD has always been considered as the most expensive operation for manufacturing a dehydrated product owing to high energy consumption and high operation and maintenance costs.
