Abstract: In this study, the effect of modifying the pectin content of freeze-dried reconstituted apple cubes by adding either pectin or pectinase on its hardness, crispness, microstructure, and hygroscopic properties was addressed. The results showed that apple cubes with 0.5%–4% of pectin exhibited a typical honeycomb-like porous structure, whose hardness and brittleness increased by 2.01–5.41 folds and 1.17–1.27 folds, whose breaking rate during oscillation decreased by 38.97%–55.78% compared with the control sample. In contrast, the microstructure of apple cubes treated with pectinase was disordered with big pores, the hardness decreased by 34.03%, the brittleness increased by 1.13 times, and the breaking rate during oscillation was increased by 1.24 times relative to the control sample. In addition, the addition of pectin reduced the hygroscopicity of the cubes, and caused desorption hysteresis in 70%–90% relative humidity. The cubes treated with pectinase showed a greater mass change and consequently increased moisture absorption when reaching adsorption equilibrium. In summary, manipulation of the pectin content in apple puree can be used as an effective approach to modify the texture and hygroscopic characteristics of reconstituted apple cubes, which can provide a theoretical reference for further research to improve the texture quality of freeze-dried plant-based foods.

Key words: freeze drying; reconstituted apple cubes; pectin; texture; hygroscopicity