Effect of encapsulating materials on water sorption, glass transition and stability of juice from immature acerola

Immature acerola juice was dehydrated by spray drying, using as encapsulating material maltodextrin DE25, arabic gum, or a mixture of both in different proportions. A constant ratio of 1:1 was kept between juice solids and encapsulating material. The effect of encapsulation materials on water sorption, glass transition, and physical properties of encapsulated immature acerola juice was investigated. The monolayer moisture of the encapsulated juices, calculated according to the GAB theory, varied from 5.11 to 5.73g H2O/100g of solids (25 degrees C). The glass transition temperature (T-g) of maltodextrin and gum arabic varied from 60 (a(w) 0.33) to 38 degrees C (a(w) 0.54), and from 62 (a(w) 0.33) to 42.6 degrees C (a(w) 0.54), respectively. The addition of juice to the encapsulating materials decreased the T-g of the juice powder to 39.5-41.3 degrees C (a(w) 0.33) and 1.84-8.05 degrees C (a(w) 0.54), but no marked differences were found among the juice powders. The critical a(w) i.e., the point of onset of physical alterations in the encapsulated materials, was higher than the corresponding monolayer values. Stickiness was observed at temperatures close to T-g, and collapse occurred at temperatures of 20 degrees C or more above the T-g. Maltodextrin DE25 and gum arabic offered equivalent contributions to the stability of the system.