Submitted to: Starch/Starke
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/14/2009
Publication Date: 10/22/2009
Citation: Fanta, G.F., Felker, F.C., Byars, J.A., Kenar, J.A., Shogren, R.L. 2009. Starch-Soybean Oil Composites with High Oil: Starch Ratios Prepared by Steam Jet Cooking. Starch/Starke. 61(2009):590-600. Interpretive Summary: Starch-oil composites prepared by steam jet cooking represent an important new platform technology through which biobased, environmentally friendly applications are being developed for delivering oil-based materials in a matrix of liquid, gel or solid starch dispersions. Oil droplet size and oil-holding capacity are two important characteristics of such composites, and certain applications would benefit from higher oil:starch ratios than were previously possible. This study was undertaken to determine how to increase the oil:starch ratio while maintaining a stable composite. Specific combinations of different types of starch and starch combined with a fatty acid allowed the production of composites with high oil loadings and smaller droplets stabilized by a network of micron-sized particles formed by interaction of starch and fatty acids. Manufacturers of food ingredients and industrial materials will benefit from this knowledge as new applications are developed, and consumers and farmers will benefit by expanded market opportunities and improved food products.
Technical Abstract: 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 x 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 carried out with normal dent, waxy, and high amylose cornstarches; and oleic acid was added during jet cooking to form helical inclusion complexes with amylose. With normal dent and waxy cornstarches, 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 cornstarch ranged from under 5 um to over 50 um. With high amylose starch, most of the oil droplets were encapsulated within networks of sub-micron spherulites that were formed from amylose-oleic acid inclusion complexes when the dispersions were cooled. SEM images of the interfacial starch shells formed from waxy cornstarch and normal dent cornstarch (in the presence and absence of oleic acid) showed only minor differences in morphology. X-ray diffraction showed that the starch shells formed from dent cornstarch in the presence of oleic acid were comprised largely of amylose-oleic acid complexes in the 61V conformation. Centrifugation at high versus low RCF produced only minor differences in the droplet size distributions. Droplet sizes increased with an increase in the oil:starch ratio, and decreased when oleic acid was added during jet cooking. The results obtained in this study will be used to design larger jet cooking experiments, in which continuous centrifugation will be used to isolate the buoyant, high-oil fractions in amounts sufficient to determine their properties and end-use applications.