Starch‐Soybean Oil Composites With High Oil: Starch Ratios Prepared By Steam Jet Cooking

Aqueous mixtures of soybean oil and starch were jet cooked at oil: starch ratios ranging from 0.5:1 to 4:1 to yield dispersions of micron-sized oil droplets that were coated with a thin layer of starch at the oil-water interface. The jet cooked dispersions were then centrifuged at 2060 and 10,800×g, the buoyant, high-oil fractions that rose to the surface were isolated, and the size distributions of the oil droplets were determined. Experiments were conducted with normal dent, waxy, and high-amylose corn starches; and oleic acid was added during jet cooking to form helical inclusion complexes with amylose. With normal dent and waxy corn starches, nearly all of the oil was recovered in the buoyant layers, and only small amounts of oil were found in the aqueous mid layers and settled solids. Oil droplet diameters in the buoyant layers obtained with normal dent and waxy corn starch ranged from under 5 µm to over 50 µm. Centrifugation at high versus low relative centrifugal force produced only minor differences in the droplet size distributions. With high-amylose starch, microscopy showed that most of the oil droplets were entrapped within aggregates of sub-micron particles that were apparently formed from amylose-oleic acid inclusion complexes when the dispersions were cooled. Droplet sizes increased with an increase in the oil: starch ratio, and decreased when oleic acid was added during jet cooking.