What is it about?

Our approach to interpretation shows the influence of changes in parameters of vacuum drying (temperature and pressure) on the sorption properties of dried strawberries. We applied constant and variable conditions of the process. Fruits were dried at 50 and 70°C under pressures of 4 and 16 kPa. Vacuum drying was also conducted during the first 4 h at 70°C and then the temperature was decreased to 50°C at a pressure of 4 kPa. The other combination included increasing the pressure after the first 4 h from 4 to 16 kPa at a drying temperature of 70°C. In addition to vacuum dried fruits we considered combined dried strawberries (by convective – vacuum drying 100 kPa/4 kPa or vacuum – convective drying 4 kPa/100 kPa). Measurements of the sorption properties were time consuming, but we could deduct from them stability of dried fruits.

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Why is it important?

Sorption isotherms were determined in the dried strawberries by following methods. For analysis we selected 4 models proposed by Oswin, Halsey, Lewicki and Peleg. We calculated parameters of fitting water vapour sorption for cited above models. It was shown that with increasing drying temperatures, there was a notable deterioration in the capacity for absorbing water vapour by the vacuum-dried fruit. On the other hand, the pressure at which vacuum drying proceeded did not significantly affect water vapour absorption. We looked for confirmation of our assumptions by presenting internal structures of strawberries (dried by vacuum or combined methods) on sets of photographs.


Changing the parameters of vacuum drying—that is, temperature in the range of 50–70°C and pressure in the range of 4–16 kPa—affected the shape and structure of the resultant dried strawberries. The combination of vacuum drying with convective drying also influenced the shape and structure of the dried fruit. We created a representative set laboratory research focused on the sorption properties of dried strawberries under constant and variable conditions for considered comparisons.

Dr hab. Dariusz Piotrowski
Instytut Ogrodnictwa - Państwowy Instytut Badawczy

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This page is a summary of: Sorption Properties of Vacuum-Dried Strawberries, Drying Technology, June 2012, Taylor & Francis, DOI: 10.1080/07373937.2012.668999.
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