Drying kinetics and hygroscopic behavior of pirarucu (Arapaima gigas) fillet with different salt contents

- Drying and hygroscopic behavior of pirarucu were studied for the first time.
- Sorption isotherms of pirarucu with different salt content were obtained.
- The increase in salt content favored the moisture diffusion in the product.
- The increase in the salt content caused an increase in the product hygroscopicity.

The convective drying kinetics and hygroscopic behavior of pirarucu (Arapaima gigas) fillet with different NaCl contents (up to 40 g/100 g dry basis - d.b.) were studied. Pieces of fillet (5 × 3 × 1 cm3) were subjected to salting and drying in a fixed-bed with an airflow velocity of 1.5 m/s at 50 °C, and kinetic models were fitted to the drying data. Adsorption and desorption isotherms at 25 °C were built for the dry products and mathematical models were fitted to the sorption data. The effective diffusivity values showed that increased NaCl content in the product favored the drying process. Midilli, diffusion approximation and Page models were effective in predicting the drying kinetics of the products. In natura fillet showed type II isotherms while the addition of NaCl caused a change in behavior for type III isotherms. The adsorption indicated that a moisture level up to 15 g/100 g d.b. ensures the microbiological stability of all products. The Halsey model showed good fit to the sorption data of products with up to 20 g NaCl/100 g d.b., while the GAB model was efficient in predicting the isotherms for fresh fillet and for products with 30 and 40 g NaCl/100 g d.b.