Concentration of apple juice with an intelligent freeze concentrator

Abstract

A 2.5-L multi-pass intelligent freeze concentration (FC) prototypical instrument with liquid food freezing point depression (FPD) data built into its controller was tested in this study for the concentration of apple juice. The instrument operates in suspension crystallization mode and integrates a traditional separated scraped surface heat exchanger (SSHE), crystallizer, and washing column into a compact three-in-one structure. Its concentration ratio in a single pass on apple juice was approximately 1.8 (e.g. from 10% to 18%). After three passes of FC, the apple juice concentration increased to 34.5 °Bx; the retention rate of vitamin C and aromatic substances, represented by ethyl butyrate, were both more than 90%, but little change in reducing sugars and color value occurred, and the partition coefficients of soluble solids in ice and the mother liquor were between 0.0081 and 0.067, obtaining a general yield of soluble solids of 97%. The controller correlates the juice concentration with its FPD to log the concentration change, and correlates the mechanical load current with the ice bed maturity to determine the end point of the freeze stage. This study contributes to our knowledge of FC of liquid food and future research and development efforts in this area.