Analysis Of Water Vapour Sorption Isotherms

Category: VI Ukrainian-Polish Symposium

ANALYSIS OF WATER VAPOUR SORPTION ISOTHERMS

ON STARCH PRODUCTS

L. Czepirski1, E. Komorowska – Czepirska1,

M. Soral – Śmietana2, M. Wronkowska2

1University of Mining and Metallurgy, Faculty of Fuels and Energy,

al. Mickiewicza 30, 30-059 Cracow, Poland

2Polish Academy of Sciences, Institute of Animal Reproduction and Food Research, Division of Food Science, ul. Tuwima 10, 10-747 Olsztyn, Poland

Knowledge of the isothermal equilibrium sorption properties of food products is very important for calculating of various processes like storage, drying and packaging, which depends mainly on the water activity of the product. In many cases, it is necessary to obtain an isotherm that can represent with reasonable accuracy the sorption data for the whole range of water activities.

In this work, moisture sorption on different samples of modified starch was examined at 298K by a volumetric method.

The adsorption isotherms of the samples under study exhibit some type II character according to IUPAC classification. The isotherm is the result of unrestricted monolayer – multilayer adsorption on heterogeneous substrate, the characteristic features influenced by the relative magnitude of the adsorbent – adsorbate and adsorbate – adsorbate interactions.

Several models, namely the BET, GAB (Guggenheim – Anderson – de Boer), Halsey, generalized Langmuir, BET modified by Kats and Kutarov, were evaluated to determine the best fit for the experimental data. Over the range of relative humidity examined (0.03–0.90), the last two models accurately predict equilibrium adsorption points.

The effect of the fractal surface on physical adsorption has been analysed, as well as, the hypothesis that water is adsorbed in two forms (primary and secondary adsorption sites) was also tested.

Although adsorption of water on starch should not be considered as a surface phenomenon, the approach proposed in this study validates the use multilayer adsorption concept in analysis of adsorption mechanism.



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