Effects of pre-freezing and sucrose impregnation methods on the quality of freeze-dried apple slices

Abstract

[Objective] This study aimed to investigate the effects of two pre-freezing methods (vacuum freezing and atmospheric pressure freezing) and two dipping methods (sucrose impregnation before pre-freezing and sucrose impregnation during freeze-drying) on the quality of freeze-dried apple slices. [Methods] The freeze-drying process was divided into six groups: vacuum pre-freezing without sucrose immersion (VFFD), atmospheric pre-freezing without sucrose immersion (CFFD), vacuum pre-freezing with sucrose immersion (BSVFFD), vacuum pre-freezing with sucrose immersion (MSVFFD), atmospheric pre-freezing with sucrose immersion (BSCFFD) and atmospheric pre-freezing with sucrose immersion (MSCFFD). The main quality indexes of freeze-dried apple slices in each group were analyzed. [Results] The color ΔL* of the MSVFFD group samples is relatively lower, while Δa* and ΔE are relatively higher, presenting a deep red color. Sucrose impregnation significantly increased the yield of freeze-dried samples, with the highest in the MSVFFD and MSCFFD groups, followed by the BSVFFD and BSCFFD groups, and the lowest in the two control groups of VFFD and CFFD (PPPP<0.05). [Conclusion] The methods of vacuum freezing and sucrose impregnation during freeze-drying are more helpful in improving the quality of freeze-dried apple slices, and the MSVFFD group endows freeze-dried products with better overall quality.

Keywords

• apple
• vacuum freeze-drying
• pre-freezing
• sucrose
• impregnation
• quality