Sorption characteristics of rosehip, apple and tomato pulp formulations as determined by gravimetric and hygrometric methods

Water sorption behaviour of commercial furcellaran

Water sorption isotherms are important tool for designing the technological processes and predicting stability and shelf life of food. The aim of the work was to determine the water sorption isotherms of commercial furcellaran at different temperatures (20, 35 and 50 °C) using a gravimetric method under different levels of relative humidity (19–95%). The experimental data obtained have been interpreted in the terms of various isotherm models and it was found that the best results were obtained with the Peleg model (P < 2.1%; RSME <0.01; R² = 1.00). The obtained isotherms followed the type II pattern and, in all cases, the sorption capacity increased with increasing water activity and decreased with increasing temperature. The maximum net isosteric heat for adsorption and desorption was 938.9 and 988.6 J g ⁻¹, respectively, at an equilibrium moisture content of 0.05 g_w g_db⁻¹. The net isosteric heat of sorption decreased exponentially with increasing moisture content and approached zero at 0.26 g_w g_db⁻¹ for adsorption and 0.32 g_w g_db⁻¹ for desorption. The developed mathematical relationships can be used to optimize the drying processes and storage conditions of furcellaran.

•

Moisture sorption isotherms of furcellaran were determined.

•

The optimal isotherm model for furcellaran is the Peleg model.

•

An equation for the calculation of the net isosteric heat of the sorption of furcellaran was developed.

The Effect of Material Thickness, Load Density, External Airflow, and Relative Humidity on the Drying Efficiency and Quality of EHD-Dried Apples

Electrohydrodynamic drying is a novel non-thermal technique for dehydrating heat-sensitive foods. However, its industrial applications are limited due to the underexplored effects of material properties and environmental conditions on product quality. For this purpose, a multifactorial experiment was designed to study the effects of material thickness, load density, external airflow, and humidity on the EHD drying efficiency and quality of apple slices. The experiments show that the intensity of EHD drying increased with a decrease in humidity, slice thickness, and load density. The effective diffusivity of apple slices with EHD drying was about 5.17·10⁻¹² m²/s, slightly increasing with external airflow. The specific energy consumption of EHD drying was 10–12 times lower than hot air drying. The time of EHD drying at 20 °C was equivalent to hot air drying at 40 °C, but the impact of EHD drying on the product quality was significantly lower. EHD drying better preserved the color and phenolic content in dried apple slices, with less cellular damage. Hence, EHD drying can be employed in industry as a sustainable alternative to hot air drying.

Sorption Isotherms and Thermodynamic Properties of Pomegranate Peels

Convective drying is the most widely used technique to stabilize by-products in the food industry, permitting later processing. A thorough knowledge of the relationship between moisture content and water activity allows the optimization of not only drying operations, but the settings of storage conditions. Thus, the thermodynamic properties of pomegranate peels were determined during the desorption process. Experimental sorption isotherms at 20, 30, 40 and 50 °C showed type II Brunauer behavior. Eight different theoretical and empirical equations were fitted to the experimental results; the theoretical GAB model and the empirical Peleg model were the ones that achieved the best fit (R² of 0.9554 and 0.974, respectively). The Clausius–Clapeyron equation and the enthalpy–entropy compensation theory were used to determine the thermodynamic parameters. The isosteric heat determined from the sorption isotherms decreased regularly as the equilibrium moisture content rose (from 8423.9 J/mol at 0.11 kgH₂O/kg d.m. to 3837.7 J/mol at 0.2 kgH₂O/kg d.m.). A linear compensation was observed between enthalpy and entropy, which indicated an enthalpy-controlled sorption process.