Oxidation of soybean oil during storage of starch-oil composites

The oxidative deterioration of dry starch-oil composites was investigated by chemical and sensory methods. The composites were stored at 37°C for 63 d, and changes in the hexanal content and odor attributes were monitored. Analysis of the extracted oil showed that the first run through the drum dryer presented higher hexanal concentrations than the subsequent runs. Starch-oil composites from the first run though the drum dryer showed higher metal concentrations and higher odor ratings during storage time than the subsequent runs. There was a significant correlation between odor attributes and hexanal concentration in the first run. Since both the oxidation and the metal content were higher in the first run and decreased in further runs, we concluded that oxidation might have been induced by the presence of metal in the drum dryer. It is likely that during drum drying, the metal drum and knife surfaces became coated with soy oil, reducing both abrasion and metal contact with the product. Since many applications of the starch-oil composite technology require drum drying, it will be necessary to take measures to minimize metal contamination of the product, perhaps by discarding the initial portion of product, which contains the most metal.