Formation/inhibition and toxicity of reactive carbonyl compounds from oxidized dietary oils: Antioxidant properties of phytochemicals measured by headspace solid-phase microextraction/gas chromatography

The formation of reactive carbonyl compounds from dietary oils upon oxidation was studied along with the toxicity of oxidized dietary oils. A malonaldehyde assay based on headspace solid-phase microextraction (HS-SPME) was developed and applied for the protective effects of phytochemicals on lipid peroxidation.; Dietary oils were oxidized under accelerated storage conditions (60°C) and cooking conditions by a conventional oven (200°C) and by a microwave oven (800W). Malonaldehyde, glyoxal, and methylglyoxal were quantified using a gas chromatograph with a nitrogen-phosphorus detector (GC-NPD). The method was validated using a cigarette smoke analysis. Fish oils produced higher amounts of those aldehydes than vegetable oils. Salmon oil produced the highest malonaldehyde (1070 ppm) of all oils when it was heated at 60°C for 7 days. When it was heated at 200°C for 1 hr using a conventional oven, malonaldehyde was formed at a concentration of 317 ppm. Salmon oil produced the highest glyoxal (12.8 ppm) of all oils when it was heated at 60°C for 3 days. When sardine oil was heated by a microwave oven for 8 min, it produced the highest malonaldehyde (688 nmol/g) and glyoxal (219 nmol/g) of all oils. The alpha-tocopherol content was inversely related to malonaldehyde levels in fish oils heated at 60°C for 3 days (p < 0.05).; Oxidized dietary oils (sardine oil, soybean oil, and lard) were orally administered to C3H/HeN mice for 12 months. The malignant tumor incidence in the liver increased in the mice fed with oxidized sardine oil compared to the controls (27.5% vs. 7.5%, p < 0.05). The amount of 8-OH-dG in the liver was higher in the mice treated with oxidized sardine oil (140%, p < 0.001) and oxidized lard (116%, p < 0.05). The oxidized sardine oil contained the highest levels of malonaldehyde (713 nmol/g) and glyoxal (33.3 nmol/g). The tumorigenesis caused by the oxidized oils appeared to be attributed in part to the dicarbonyl compounds including malonaldehyde and glyoxal.; The antioxidant effect of phytochemicals was investigated. Cod liver oil was oxidized with Fenton's reagent and inhibition of malonaldehyde formation was determined using HS-SPME and GC-NPD. Some phytochemicals, such as sesamol, eugenol, and vinylguaiacol, showed antioxidant activity comparable to BHT and alpha-tocopherol at a concentration of 10 mug/mL. Brewed coffee exhibited antioxidant property in a dose-dependent manner, however, chlorogenic acid showed pro-oxidant property at a concentration of 200 mug/mL.; The results suggest that thermally oxidized dietary oils contain considerable amount of reactive carbonyl compounds and possess carcinogenic effect in the liver of experimental animals. Natural antioxidants found in plants may prevent the formation of those carbonyl compounds; however, some may have pro-oxidative properties upon lipid peroxidation. HS-SPME is a useful technique to study oxidative stress and antioxidant status of biological metrics like blood and plasma.