Thesis summary: Development and study of low-pressure superheated steam drying system for a heat-sensitive material

At present, there is limited experience with superheated steam drying (SSD), especially for a process operated at reduced pressure. One of the objectives of the thesis was thus to study low-pressure superheated steam drying (LPSSD), especially from the dried product quality point of view. Using carrot cubes as a model heat-sensitive material, experimental investigations were conducted to examine the drying kinetics and various quality parameters of the dried product undergoing low-pressure superheated steam, vacuum, and hot air drying. Effects of operating parameters, i.e., pressure and temperature, on the drying characteristics as well as physical quality attributes, i.e., volume, shrinkage, apparent density, color, and rehydration behavior, of the dried product undergoing two drying processes were also evaluated and compared. Although low-pressure steam drying required a longer dwell time to achieve the same final moisture content as vacuum drying, some of the quality attributes were superior to those obtained in vacuum drying. The effects of LPSSD and other drying methods on the chemical quality attribute of a model material, i.e., β-carotene in carrot, were also evaluated. LPSSD and vacuum drying led to less degradation of b-carotene in carrot than in the case of hot air drying. The empirical models, which can describe the experimental data of b-carotene degradation in carrot undergoing different drying techniques, were also proposed. β-Carotene degradation in carrot depended more on the carrot temperature than its moisture content in all cases.