Pulsed infrared radiation for drying raw materials of plant and animal origin

Abstract

The paper describes physical characteristics of drying animal- and plant-based raw materials with pulsed infrared emitters. Furthermore, it discusses how to select and use infrared emitters to produce high quality products with a long shelf-life. Using an experimental facility, we identified basic patterns of changes in the heat flux density. We also analysed the drying thermograms and assessed the influence of process factors on the removal of moisture from raw materials and the preservation of biologically active substances in dried and concentrated products. We determined specific kinetics of drying in different modes of power supply and selected the most efficient pulsed cera- mic emitters. These emitters had a high rate of heat transfer and an ability to accurately target molecular bonds, thus reducing the drying time and energy costs. Mathematical modelling enabled us to obtain specific values of process parameters for pulsed infrared drying of plant materials. The heating time constant was calculated for root and tuber vegetables, depending on their moisture content and size. The study showed that root and tuber vegetables should not be heated to more than 60°C when irradiated with a 500 W medium-wave emitter at a working distance of 250 mm during a full 10-minute cycle. The optimal modes of drying liquid products with milk and plant proteins included a heating power of 400 W, a radiant heating temperature of 60°C, and a layer thickness of 10 mm. The selected modes of pulsed infrared drying of sugar-containing root and tuber vegetables reduced the duration of moisture removal by 16–20% and cut energy costs by 16.6%. This unconventional method of infrared drying of whole milk, whey, whey drinks, and milk mixture preserves beneficial microflora and increases the nutritional value and shelf-life, with a pos- sible content of chemically bound water of polymolecular and monomolecular adsorption ranging from 10 to 15.58%.