FACTORS AFFECTING RETENTION IN SPRAY-DRYING MICROENCAPSULATION OF VOLATILE MATERIALS

Microencapsulation of volatile materials (aroma) was evaluated by using model systems in which gum arabic was the wall material and various esters were the core materials. The outer and inner structure of spray-dried microcapsules and the structural changes induced by exposure to various relative humidity (RH) levels were studied by SEM. The influence of capsule composition and drying conditions on the retention of the volatiles was evaluated. It was found that high retention levels, up to 90%, can be achieved. High solids concentration and high drying temperatures enhance retention, as long as there is no structural damage during preparation. Increase of the ester load in the feed emulsion adversely affects the retention. Aroma losses occur during the early stages of the drying process by stripping of volatile droplets. The losses are enhanced by internal mixing in the drying capsule. The retention of volatiles by spray-dried microcapsules was also studied as a function of storage at increasing relative humidity. At relative humidity below 64% the structure of the capsules was not damaged, and high retention levels of more than 85% were obtained. Increasing the relative humidity to 75-97% led to gradual dissolution of the capsule walls, and retention dropped sharply. The structure was completely destroyed at RH of 97 %, leading to total loss of the volatiles. © 1990, American Chemical Society. All rights reserved.