Cell wall polysaccharides and mono-/disaccharides as chemical determinants for the texture and hygroscopicity of freeze-dried fruit and vegetable cubes.

In order to select the critical factors on the texture and hygroscopic characteristics of freeze-dried fruit and vegetable cubes, the correlation analysis was performed on the major chemical compositions of 12 fresh materials, and the microstructure, texture, hygroscopicity of corresponding freeze-dried samples. The dry proportion of starch-rich materials, such as taro, was mainly composed of polysaccharides (0.76-0.89 g/g db), while the dry proportion of starch-poor materials such as apple was mainly composed of mono-/disaccharides (0.70-0.95/g db). Data from the microscopy showed that cell wall polysaccharides constituted the scaffold of freeze-dried cubes and natural starch granules attached to the scaffold as fillers. Both of them inhibited structural collapse. Mono-/disaccharides were accountable for the hardness and crispiness of freeze-dried cubes, however, excessive mono-/disaccharides could reduce the size of the pores and cause severe shrinkage. Polysaccharides reduced the hygroscopicity of freeze-dried cubes, on the contrary, mono-/disaccharides promoted hygroscopicity, especially fructose.