Effects of Curry Powder Addition and Frying Oil Reuse on the Oxidative Stability of Deep-Fried Oils Used in Croquette Preparation

摘要

Curry powder has a higher content of total phenols and 2,2'-diphenyl-l-picrylhydrazyl radical scavenging activity compared with wheat flour, and was examined for its antioxidant effect on oil oxidation during deep-frying. Instead of wheat flour (Control), curry powder was added to the inner (In-Curry) or outer (Out-Curry) cover for potato croquettes. The croquettes were consecutively deep-fried, using fresh oil on the 1st day, and reusing the oil on the 3rd and 10th days for frying the same amount ofcroquettes. The deep-fried oil samples were collected after each frying for analysis. With increasing number of frying frequency and oil reuse, there was a significant increase in the contents of hydroperoxides and malondialdehyde, p-anisidine value, and Lovibond redness, with no significant differences among the three groups. Lovibond yellowness was surprisingly higher in the Out-Curry oils, which was attributed to the migration of lipophilic antioxidant curcumin from the curry powder, and indicatingthat the released antioxidant was not effective in retarding oil oxidation during deep-frying. This demonstrates a 'polar paradox' theory which states that nonpolar antioxidants might not be effective in bulk lipids. In summary, our study results indicate that the antioxidant effect of food materials needs to be validated by employing not only in vitro assays, but also food cooking and processing systems.