Effect of temperature on water sorption properties of dried apples
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Authors: | Katarzyna Kędzierska1, Zbigniew Pałacha1 1Department of Food Engineering and Process Management, Faculty of Food Science, SGGW – Warsaw University of Life Sciences ul. Nowoursynowska 159C, 02-776 Warszawa |
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Abstract : | In the study presented in the paper water adsorption isotherms were determinated for dried apples at 5, 15, 25 and 35ºC over a range of water activity from 0.006 to 0.910. The water adsorption isotherms had a compatible course with II type of isotherms according to Brunauer’s classification. To describe dried apples water adsorption isotherms the following models were used: BET, GAB, Oswin, Lewicki and Peleg. The GAB and BET models (in the range of water activity 0,006-0,432) gave the best fit to the experimental sorption data for the material tested. The process temperature affected the course of adsorption isotherms. Hygroscopicity of the dried material increased with lowering of the temperature. An attempt was made to fit three models – the semi-empirical two-parameter Tsami et al. model and two empirical models: three- and four-parameter, to the experimental data of net isosteric heat of water adsorption in the function of water content. The biggest decline of net isosteric heat of water adsorption in dried apples was in the range of moisture content from 10 to 40 g water (100 g d.m.)-1. With increase in the amount of absorbed water over 40 g water (100 g d.m.)‑1, the net isosteric heat of water adsorption decreased slightly and approached the latent heat of vaporisation for pure water. |
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Keywords : | apples, adsorption isotherms, net isosteric heat of water adsorption | ||||||||
Language : | Polish |