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F. C. FELKER, Biomaterials Processing Research Unit, USDA, ARS, NCAUR, 1815 N. University St., Peoria, IL 61604 and S. M. Erhan.

Stable aqueous starch-oil composites with a wide range of potential food applications are made with a new patented process (Fantesk™) consisting of co-cooking starch and oil with an excess steam jet cooker. Oil droplets typically range in size from 1 to 10 microns. Liquid composite can be drum dried and milled, yielding a dry powder which can be reconstituted in water. Previous research has demonstrated the formation of starch shells around the oil droplets which may contribute to the composite stability. It was necessary to know whether these oil droplets are completely prevented from coalescing by the starch shells, or whether some coalescence is still possible.

The purpose of this study was to investigate the effects of additional ingredients on droplet size, and determine the extent of coalescence of oil droplets with a double-labeling technique.

Waxy cornstarch was jet-cooked, soy oil incorporated by blending, then re-jet-cooked to form the initial starch-oil composite. To visualize coalescence, separate composites were prepared with soy oil saturated with Sudan red and with soy oil containing carbon black particles. Droplet size and coalescence were examined by light microscopy.

Small amounts of pectin or lecithin significantly decreased oil droplet size. Occurrence of doubly labeled droplets (showing both pink-stained oil and particulate inclusions) was similar in mixtures of liquid composites made either directly after cooking (while still hot) or after cooling overnight. Significantly fewer doubly labeled droplets were seen in mixtures of composites reconstituted in water at room temperature after drum drying.

These results suggest that droplet size in starch-oil composites can be further controlled by additions of pectin or lecithin. Separation of heterogeneous oil droplets can be maintained better by dry-mixing drum-dried powders and then reconstituting. These flexibilities enhance the range of applications of starch-oil composites in foods.