Influence of plant proteins blend or polydextrose on freeze-dried açaí (Euterpe oleracea) sorption isotherms and thermal properties

Abstract

The influence of polydextrose or plant proteins blend, as a drying aid in freeze-dried açaí pulp, was evaluated regarding stability by vapor sorption isotherms at 20 °C in a water activity range of 0.1–0.95, obtained by vapor sorption analyzer and by saturated salt solutions, and the enthalpic properties were obtained by differential scanning calorimetry.The experimental isotherms data presented a good fit to the Peleg and Guggenheim-Anderson-de Boer (GAB) equations, açaí powder with polydextrose presented a Brunauer-Emmett-Teller (BET) type III, while the açaí powder without and with a plant proteins blend, type II. The freeze-dried açaí powders showed two endothermic peaks between −15 °C and 10 °C, probably related to linoleic and oleic fatty acids fusion. Fusion enthalpies of these peaks were lower when a carrier agent was used, which could be explained by a lower lipids content (25.0 J/g and 3.5 J/g for powder without the carrier and 12.0 J/g and 1.5 J/g for powder with plant proteins blend). The glass transition temperatures were between 49 °C and 58 °C, depending on the water activity, for powder without carriers and from 45 °C to 54 °C for the one with proteins.