Microwavevacuum and osmotic drying of cranberries

Modern food industry dictates strict conditions on energy use and application, preventing unnecessary energy dissipation. Energy demanding processes such as distillation and drying have to be optimised to the highest extent, while retaining or improving the final product quality. Pretreatments to drying can be used in order to optimize drying, and some of cranberry pretreatments such as chemical, mechanical and osmotic dehydration were optimized. Chemical pretreatment consisted of dipping cranberries into solution of ethyl oleate and sodium hydroxide at different temperatures, and process times. Mechanical pretreatment was cutting of berries into halves or quarters. Tested parameters for osmotic dehydration were the duration of process, osmotic agent type and its concentration.Once the appropriate pretreatment was selected, cranberries were subjected to hybrid drying under subatmospheric pressure and using microwaves as an energy source. Evaluated process parameters were microwave power level, microwave power mode, and the operating pressure of process. This drying method showed good potential, but in order to verify the results obtained, it was compared to microwave/convective drying. Slight advantages of the microwave/vacuum process over the microwave/convective process were apparent in almost all product quality parameters, as well as in process efficiency