Thermodynamic sorption of red cabbage extract (Brassica oleracea L. var. capitata L. f. rubra) encapsulated by spray drying

Abstract

Red cabbage aqueous extract acidified with 2 % citric acid was spray-dried using gum Arabic as encapsulating agent. The concentration of anthocyanin in the powder was 253.45 ± 10.82 mg/100 g of dry basis and antioxidant activity of 4.6 ± 0.2 mmol trolox/kg of dry basis. The sorption isotherms were determined at 15, 25 and 35 °C, and the GAB model was the one that best adjusted to the experimental data. The differential enthalpy and entropy for moisture levels up to 2 g of water/g of dry basis decreased to a minimum value of −4.36 kJ/mol and −0.019 kJ/molK respectively, and then increased in magnitude with the rise in moisture content to levels close to the free moisture with a spontaneous process, governed by the entropy. The spreading pressure increased with the rise in water activity for all temperatures, while net integral enthalpy and entropy decreased with the rise in moisture content reaching levels close to 10 kJ/mol and 0.025 kJ/molK, respectively.