Adsorption of water by dried foods or low water activity foods is an undesirable process associated with their physical, chemical, and microbiological changes. Pine nut, as a low water activity food, is at high risk of microbial spoilage via water adsorption beside its lipid oxidation risk. Our aim was to study sorption isotherm of pine nut samples (with/without shell) by static gravimetric method at 25±1˚C using saturated solutions with water activities in the range 0.113 to 0.973. Results showed that both types of pine nut samples provided practically identical sorption isotherms of type III, which is also called Flory-Huggins sorption isotherm. The sorption data were analyzed using various conventional models: Guggenheim-Anderson-de Boer (GAB) model, Modified Halsey model, Iglesias-Chirife equation, Hailwood-Horrobin Model, and Peleg Model. The GAB model gave the best fit to the experimental sorption data for both tested samples in total over the range of investigated water activity with average coefficient of determination and average root mean square error of 0.984 and 0.008 respectively. The Peleg model gave also the closest fit to the sorption data, only with slightly lower coefficient of determination comparing to the GAB model. Modified Halsey model also fitted well experimental data of pine nut samples without shell, while for pine nut samples with shell it was the least desirable model among others.

Keywords: Equilibrium moisture content, gravimetric method, GAB model, pine nut, saturated salt solution, sorption isotherm, water activity.

The authors would like to thank for the financial contribution from the Scientific Grant Agency of the Ministry of Education of Slovak Republic VEGA no. 1/0363/19.

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