Food-Drying Applications for Plant Products: A Comparative Analysis

Abstract

Consumable plant products are seasonal and perishable items, generally only available in a fresh state for a few months each year. Therefore, the produce requires processing and/or storage at low temperatures. Drying is one of the oldest methods of preserving plant products. Through this process, water is removed from the food matrix, resulting in a product that is microbiologically stable, with an extended shelf life and a reduced volume and mass, and thus its storage and packaging are facilitated. Drying is normally accompanied by the evaporation of water from the biological material and the transfer of moisture to the surrounding environment. The evaporation of the inner water through heat transfer is the oldest form of food drying and is still the dominant method, although it comes with certain drawbacks. However, there are many other methods for plant material drying, such as solar drying, conductive drying, convective drying, vacuum drying, freeze-drying, microwave drying, IR drying, drying in a fluidized bed, etc. Many authors have combined drying methods, accompanied by raw material pretreatment. However, every drying method causes certain undesirable physical, chemical, and biochemical transformations, such as material deformation (i.e., changes in the structure of the biological material) and degradation and reduction of bioactive substances (such as antioxidants, vitamins, and aromas) that have a positive effect on human health. On the other hand, when developing food-drying technologies, we have to consider their drying efficiency and lower their energy consumption. The drying process now needs to be accelerated, but this must not occur at the expense of the product quality. Nowadays, consumers demand high-quality and additive-free products with an extended shelf life; these might be considered healthier options and even functional foods. Therefore, processors of food products of plant origin are constantly searching for drying methods, which will be either optimized traditional techniques, completely novel approaches, or synergistic combinations of several known methods.