Jet-cooking process increases oxidation in starch-oil composites.

Starch-oil composites (SOCs) are stable suspensions of microscopic oil droplets (1 micron to 10 microns in diameter) in a starch dispersion or gel. The dispersions can be dried and reconstituted into an aqueous system without the need for emulsifiers. They will maintain their physical stability and properties.

SOCs have found use as fat replacers and stabilizers in beef patties, dairy products and baked goods. They have potential for delivering lipid soluble flavors, antioxidants or nutraceuticals into aqueous food systems.

However, the oil in SOCs is susceptible to oxidation. USDA-ARS scientists wanted to obtain a better understanding of how the type of starch used, as well as the ratio of oil to starch, would affect the oxidation rates in dried SOCs. They found that jet-cooking promotes the oxidation of SOCs, which could reduce their overall shelf life.

The scientists investigated the oxidative stability of SOCs made with either waxy or regular food-grade corn starch, and 10%, 20%, 30% and 40% oil-weight/weight of starch. The researchers analyzed the peroxide values (PVs) and hexanal in composites that were stored at 60 C for 8 days. Initial PVs and oxidation rates were much higher in oil that was extracted from composites compared to the oil before it was incorporated into the SOCs. This indicates that the jet-cooking process used by investigators promoted oxidation, we're told.

The type of starch used by the scientists did not affect the oxidation rates during storage. The rate of oxidation in food-grade SOCs was not affected by the percentage of oil, however, those SOCs made with 10% oil had significantly higher initial PVs compared to the SOCs that contained more oil. Waxy SOCs made with 10% oil also had significantly higher initial PVs, but the rate of oxidation was actually lower than that for SOCs made with 30% oil.

Steps should be taken in the jet-cooking drum-drying process to improve the oxidative stability of SOCs. One approach would be to use higher oil-to-starch ratios in the composites.

Further information. Jill Winkler, USDA-ARS National Center for Agricultural Utilization Research, Room 2201, 1815 N. University St., Peoria, IL, 61604; phone: 309-681-6390; fax: 309-681-6340; email: jill.winkler@ars.usda.gov.