Effect of porous structure and spreading pressure on the storage stability of red onion microcapsules produced by spray freezing into liquid cryogenic and spray drying

Red onion microcapsules were produced by spray freezing into liquid cryogenic (SFLC) and spray drying (SD) and their anthocyanin contents were evaluated kinetically at different water activities (a(w)) at 35 degrees C. The spreading pressure-area isotherms were determined at 35 degrees C. These isotherms provide important information about the different phases of adsorbed water present in SD and SFLC capsules, which can be related to minimal integral entropy and to chemical stability during storage. The porosity of the microcapsules was examined using low-temperature adsorption of nitrogen. The maximum anthocyanin stability occurred at a(w) from 0.108 to 0.318, and 0.108 to 0.515, for SD and SFLC, respectively. SD products were nonporous whereas SFLC were mesoporous. The tendency to contraction of the adsorbed water film was compared with the minimum integral entropy and was proposed as a new stability criterion to predict suitable storage conditions of dehydrated foods.