Effect of caking and stickiness on the retention of spray-dried encapsulated orange peel oil

Flavour microcapsules containing amorphous carbohydrate as wall material can undergo changes such as crystallisation, clumping, sticking and caking during handling and storage. Such physical changes may lead to the release of entrapped flavours. The objective of this study was to investigate the effect of storage temperature and water activity on caking, stickiness and glass transition temperatures and to evaluate the relative degree of protection provided to orange peel oil entrapped in mesquite (Prosopis juliflora) gum by spray drying. The powders were stored at water activities (aw) ranging from 0.108 to 0.972 at 25 and 35 °C. The surface caking temperature (Tsc) and advance caking temperature (Tac) were determined by the modified ampoule and sealed glass tube methods respectively. The glass transition temperature was determined by differential scanning calorimetry. Changes in the amount of encapsulated oil were determined by Clevenger hydrodistillation. As expected, both Tsc and Tac decreased with increasing storage aw. Above aw 0.628 the powders caked and collapsed during storage at 35 °C. Below aw 0.628 the capsules were not damaged and high retention levels (above 90%) were obtained. Increasing aw in the range 0.743-0.972 caused progressive dissolution of the wall polymer, and the retention level dropped sharply. The volatiles are protected and retained by mesquite gum as long as the capsule structure remains intact.