Evaluation of the uniformity, quality and energy cost of four types of vegetables and fruits after pilot-scale pulse-spouted bed microwave (915 MHz) freeze-drying

Abstract

The homogeneity of dried products produced via pilot-scale pulse-spouted bed microwave (915 MHz) freeze-drying (pilot-scale PSBMFD) was investigated using sweet corn, potato, banana and hawthorn as experimental materials. The quality and energy cost of the dried products were also investigated. Regarding the moisture content, color difference and shrinkage ratio, pilot-scale PSBMFD achieved high drying uniformity (⩾90%, d.b.). Compared with the conventional freeze-drying (CFD) method used in industries, pilot-scale PSBMFD effectively increased the nutrient retention (d.b.) in dried samples. It increased the retention of flavonoids in sweet corn, potato cube, banana slice and hawthorn by approximately 11.68%, 15.82%, 5.76%, and 15.94% and the total phenolic content by 11.85%, 23.58%, 28.34%, and 24.17%, respectively. Further, pilot-scale PSBMFD resulted in a larger honeycomb porous structure, greater hardness and brittleness as well as shrinkage and lower apparent density than CFD. Regarding the energy cost, pilot-scale PSBMFD can save more energy than CFD (⩾39%, d.b.). This pilot-scale experimental study provides a theoretical basis and technical support for the commercial application of the PSBMFD technology.