Selected physical properties of convection dried apples after HHP treatment

- HHP pretreatment intensifies changes in colour parameters of convective dried apples.
- HHP pretreatment affects physical properties of dried apples and damages cell walls.
- Use of solution during the HHP pretreatment affects properties of dried apples.
- Destruction of apples tissue by HHP increases water availability during drying.

High hydrostatic pressure (HHP) pretreatment affected the physical properties of dried apples by modifying colour, density and porosity and by inducing shrinkage. Convective drying of apples cubes after HHP pretreatment resulted in a statistically significant changes in tissue colour compared to the raw apples tissue, with a tendency for darkening, where L varies in the range from 10.4 (raw dried apples) to 49.7% depending on the applied pressure and type of the solution. The use of the hypertonic solution during pretreatment at pressures of 0.1 and 300 MPa caused that the ΔE values were lower respectively by 10.5% and 16% than those for apples tissue pretreated in the isotonic solution. The shrinkage of apples tissue ranged from 70 to 89% and was determined by parameters of the HHP pretreatment. The dried products obtained after high pressure pretreatment of apples in the solutions were characterized by higher density and shrinkage. In turn, apples porosity was lower compared to the products obtained by convective drying with HHP pretreatment but without solution. Values of both total and closed porosity of the dried products were changing depending on the applied parameters of pretreatment and fitted within a very wide range from 1 to 66%.