Moisture adsorption isotherms in yellow pitahaya (selenicereusmegalanthus)

Moisture adsorption isotherms for yellow pitahaya fruits were studied at 15, 25, and 35 °C using the gravimetric method for a0.111-0.901 water activity range. Experimental values were adjusted by using the GAB, BET, Henderson, Smith, Caurie, and Peleg models.The isosteric heat of adsorption (Qst) was determined using the Clausius-Clapeyron equation. The results showed that yellow pitahaya fruitsexhibit type III adsorption isotherms and that the equilibrium moisture content (EMC) is temperature-dependent. For the same water activityvalue, the EMC decreased when temperature increased. The GAB model presented the best fitto the experimental values. The Qst droppedfrom 57.154 to 45.79 kJ/mol when the EMC increased from 0.05 to 0.40 g water/g dry matter, respectively. These results are important forestablishing the best storage conditions for dehydrated pitahaya fruits as well as for shelf-life prediction and the design of packaging materials