Effect of Elevated Temperature on Development of Tocopherolquinones in Oils

Studies were conducted to determine the formation of tocopherolquinones (TOCQ) in heated sunflower (SUN) and soybean (SBO) oils with and without enrichment with added α-tocopherol (α-TOC). Samples of the heated oils were extracted with acidified hot methanol and analyzed for changes in TOC contents and TOCQ levels by high-performance liquid chromatography (HPLC). In the oils without added α-TOC, the α-TOC in SUN significantly decreased from 829 ppm at 0 h to 183 ppm at 5 h and to 0 ppm by 10 h. In contrast, α-TOCQ increased from 0 ppm at 0 h to 87 ppm at 5 h and 104 ppm at 10 h. The level of α-TOC in SBO decreased from 138 ppm at 0 h to 99 and 98 ppm after 5 and 10 h, respectively, with an increase in α-TOCQ from 0 ppm at 0 h to 29 ppm at 5 h and 53 ppm at 10 h. In the oils with added α-TOC, the α-TOC in the SUN decreased rapidly from 1128 ppm at 0 h to 225 ppm at 5 h and 28 ppm at 10 h; however, the α-TOC in the SBO was 1176 ppm at 0 h, 367 ppm by 5 h, and 242 ppm at 10 h. There was a corresponding increase of α-TOCQ in SUN with added α-TOC from 0 ppm at 0 h, 127 ppm at 5 h, and 164 ppm at 10 h, whereas the α-TOCQ in SBO with added α-TOC changed from 0 ppm initially to 159 ppm by 5 h and 187 ppm at 10 h. As expected, SUN with no added α-TOC formed significantly more α-TOCQ than the SBO. However, SBO with added α-TOC had significantly more α-TOCQ than the SUN with added α-TOC even though the α-TOC levels at 0 h were similar. These results indicate that TOCQs are formed easily from the decomposition of α-TOC and could be potential antioxidants even as α-TOC decomposes.

Keywords: α-Tocopherol; antioxidants; quinones; tocopherols; soybean oil; sunflower oil; tocopherols