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The chemical properties and oxidative stability of perilla oils obtained from roasted perilla seeds as affected by extraction methods (supercritical carbon dioxide [SC-CO2], mechanical press, and solvent extraction) were studied. The SC-CO2 extraction at 420 bar and 50 °C and hexane extraction showed significantly higher oil yield than mechanical press extraction ( P < 0.05). The fatty acid compositions in the oils were virtually identical regardless of the extraction methods. The contents of tocopherol, sterol, policosanol, and phosphorus in the perilla oils greatly varied with the extraction methods. The SC-CO2-extracted perilla oils contained significantly higher contents of tocopherols, sterols, and policosanols than the mechanical press-extracted and hexane-extracted oils ( P < 0.05). The SC-CO2-extracted oil showed the greatly lower oxidative stability than press-extracted and hexane-extracted oils during the storage in the oven under dark at 60 °C. However, the photooxidative stabilities of the oils were not considerably different with extraction methods. [ABSTRACT FROM AUTHOR]

Singlet oxygen quenching by synthetic antioxidants (BHA, BHT, and TBHQ) was directly observed by spectroscopic monitoring of luminescence at 1268 nm. The luminescence data showed unambiguous evidence of singlet oxygen quenching by synthetic phenolic antioxidants with the highest activity for TBHQ, followed by BHA and BHT. The protective activities of these synthetic antioxidants on α-terpinene oxidation with chemically-induced singlet oxygen under dark further confirmed their singlet oxygen quenching abilities. Total singlet oxygen quenching rate constants ( kr + kq) of BHA, BHT, and TBHQ were determined in a system containing α-terpinene (as a singlet oxygen trap) and methylene blue (as a sensitizer) during light irradiation, and the values were 5.14 × 107, 3.41 × 106, and 1.99 × 108 M−1s−1, respectively. After the kr value of α-terpinene was first determined, the kr values of the synthetic antioxidants were calculated by measuring their relative reaction rates with singlet oxygen to that of α-terpinene under the identical conditions. The kr values of the BHA, BHT, and TBHQ were 3.90 × 105, 1.23 × 105, and 2.93 × 106, M−1s−1. The percent partition of chemical quenching over total singlet oxygen quenching ( kr × 100)/( kr + kq) for BHA, BHT, and TBHQ were 0.76%, 3.61%, and 1.47%, respectively. The results showed that the synthetic antioxidants quench singlet oxygen almost exclusively through the mechanism of physical quenching. This represents the first report on the singlet oxygen quenching mechanism of these synthetic antioxidants. Practical Application: The synthetic antioxidants, especially TBHQ, have been found to have a strong singlet oxygen quenching ability. This article also clearly showed that singlet oxygen quenching by synthetic antioxidants was mainly by the physical quenching mechanism. The results suggested that these synthetic antioxidants, especially TBHQ, could be used practically for the protection of the food components such as edible oils and vitamins against singlet oxygen induced oxidations without significant losses of antioxidant activity during storage under light. [ABSTRACT FROM AUTHOR]

The article discusses a study which examined the effects of fruit and vegetable juices on rubrene oxidation induced by a chemical source of oxygen in a microemulsion system. A description of the method for determining the radical scavenging activities of juices is given. Results of the study showed that excessive amount of hydrogen peroxide led to the destruction of juices' antioxidant component. It also found that the highest inhibitory activity on oxidation was shown by the pear juice.