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.

The antioxidant effectiveness of two rosemary extracts, carnosol and carnosic acid, was significantly influenced by the type of system tested (bulk oils vs oil‐in‐water emulsions), by the oil substrates, the methods used to follow oxi‐dation, and the concentrations of test compounds. The rosemary extracts and compounds effectively inhibited conjugated diene hydroperoxide formation in corn oil, soya bean oil, peanut oil and fish oil, when tested in bulk. Test compounds also inhibited hexanal formation in bulk vegetable oils, and propanal and pentenal formation in bulk fish oils. In contrast, these test compounds were either inactive or promoted oxidation in the corresponding vegetable oil‐in‐water emulsions. In fish oil emulsions, however, the rosemary compounds inhibited the formation of conjugated diene and pentenal but not that of propanal. Interfacial phenomena may explain why the hydrophilic rosemary antioxidants afford more protection in the bulk oil systems by being oriented in the air–oil interface, and less protection in the oil‐in‐water emulsion systems by partitioning into the water phase.

Increasing heat treatment given to canola seed prior to pressing resulted in press oils with progressively increasing contents of non-triglyceride components. Phosphorus and chlorophyll contents ranged from 13 ppm and 7 ppm, respectively, in cold press oil to 64 ppm and 68 ppm, respectively, in oil from heated seeds. Refining reduced the amount of these components to 19 ppm and 60 ppm, respectively, in degummed oil and to 4 ppm and 11 ppm, respectively, in bleached oil. Oil with the lowest amount of non-triglyceride material was obtained by cold pressing and/or bleaching.The major sterols were ~-sitosterol (55%), campesterol (35%) and brassicasterol (10%}, and the major tocopherols were ), (60%), a (30%) and 6 (10%). The content of sterols and tocopherols ranged from 620 to 773 rag/100 g and from 47 to 64 mg/100 g, respectively, in the press oils. The total content of sterols was reduced by 15% and a further 1% on degumming and bleaching, respectively. The total tocopherol content was reduced by 20% and 60% on degumming and on subsequent bleaching. Refining had no effect on the sterol isomer ratio, but there was a significant relative loss of a-tocopherol on bleaching.