No abstract

This study was aimed at evaluating the antioxidant activity of a commercial rosemary extract and the active constituents carnosol, carnosic acid, and rosmarinic acid, in inhibiting the formation and decomposition of hydroperoxides in tocopherol-stripped corn oil and in the corresponding corn oilin-water emulsions. In bulk corn oil, the rosemary extract, carnosic acid, rosmarinic acid, and R-tocopherol were significantly more active than carnosol. In contrast, in corn oil-in-water emulsion, the rosemary compounds were less active than in bulk oil, and the rosemary extract, carnosic acid, carnosol, and R-tocopherol were more active than rosmarinic acid. Similar results were obtained in corn oil-in-water phosphate buffer emulsion at pH 5, but R-tocopherol was less active. Carnosol and carnosic acid were much more active antioxidants in corn oil-in-water emulsions buffered at pH 4 and 5 than at pH 7. The decreased antioxidant activity of the polar hydrophilic rosemary compounds in the emulsion system may be explained by their interfacial partitioning into the water, thus becoming less protective than in the bulk oil system. The effect of pH may be related to the stability of the rosemary antioxidants.

No abstract

This study was aimed at evaluating the antioxidant effectiveness of R-tocopherol and its watersoluble analogue, Trolox, in different lipid systems. The oxidative stability of lipids in bulk and emulsion systems at 37 °C decreased in the order corn oil triglycerides > methyl linoleate > linoleic acid. In both bulk and emulsified linoleic acid, Trolox was a better inhibitor of hydroperoxide formation and decomposition than R-tocopherol. However, in bulk methyl linoleate and corn oil triglycerides, although Trolox was a better inhibitor of hydroperoxide formation, in emulsions, R-tocopherol was a better inhibitor of both the formation and decomposition of hydroperoxides. In emulsified methyl linoleate and corn oil, the partition coefficients of Trolox between lipids and water at high concentrations were not affected by Tween 20, and the antioxidant activity of Trolox decreased because it partitioned into the water phase and Tween 20 micelles. In contrast, in linoleic acid emulsified with Tween 20, the formation of mixed micelles of linoleic acid and Tween 20 increased the percentage of Trolox in the water phase and Trolox was more effective as an antioxidant than R-tocopherol because it diffused in the water phase and into mixed micelles. The physical states of lipid systems affect the distribution of antioxidants and thus significantly influence their antioxidant behavior. Because linoleic acid has unique physical properties in aqueous micelles, it may not be a valid substrate for evaluating food antioxidants.