ULTRASTRUCTURAL STUDIES ON MICROENCAPSULATED OIL DROPLETS IN AQUEOUS GELS AND DRIED FILMS OF A NEW STARCH-OIL COMPOSITE

Combination of starch, water, and oil by a process utilizing an excess -steam jet cooker produces a new class of stable, oil-in-water dispers ions. Examination of aqueous gels by light microscopy (LM) and transmi ssion electron microscopy (TEM) and of dried thin films by scanning el ectron microscopy (SEM) shows that the oil is microencapsulated in the starch water matrix or in the dried starch matrix as droplets that ar e typically 1-10 mu m in diameter. The size and distribution of oil dr oplets in cornstarch-soybean oil composites are determined by a number of factors, such as oil:starch ratio, the number of times the formula tion is passed through the steam jet cooker during preparation, and th e steam pressure used during cooking. Oil droplet size can be reduced by addition of protein or starch-oil composites from a previous cook t o the formulation prior to cooking. Oil droplet distribution in these composites is observable not only in scanning electron micrographs of fracture surfaces, but also by light microscopy and by transmission el ectron microscopy of aqueous gels. Micrographs suggest the presence of a boundary layer surrounding the oil droplets which prevents them fro m coalescing.