Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2006
Publication Date: 3/1/2006
Citation: Rennick, K.A., Warner, K.A. 2006. Effect of elevated temperatures on development of tocopherolquinones in oils. Journal of Agricultural and Food Chemistry. 54:2188-2192. Interpretive Summary: Degradation of oils used for frying decreases nutritional quality and produces off flavors and poor quality fried food. The current trend away from hydrogenated frying oils in the U.S. has increased the need for additional protection of the oil from degradation during frying. Although chemical additives such as BHA, BHT and TBHQ can be added to frying oils, there is increasing interest in naturally occurring compounds to help inhibit oil degradation. Some compounds such as tocopherols that are naturally present in vegetable oils can help protect the oil from deterioration. We found that even though some of these tocopherols disappear when oil is heated to frying temperature, other potential compounds are formed that can help protect the oil. Consumers will benefit from increased protection of frying oils and fried foods from degradation while still enjoying the desirable flavors of fried foods.
Technical Abstract: Quinones including tertiary butylhydroquinone (TBHQ), rosmariquinone and tocopherolquinones (TOCQ) are of interest because of their antioxidant properties. However, few studies have reported the isolation and quantification of TOCQ in heated vegetable oils. Studies were conducted to determine the formation of TOCQ in heated sunflower (SUN) and soybean (SBO) oils with and without added alpha tocopherol (alpha-TOC). In the first study, SUN and SBO oils without added alpha-TOC were heated to 180oC and sampled periodically. In the second study, SUN with added alpha-TOC (1128 ppm alpha-TOC total) and SBO with added alpha-TOC (1176 ppm alpha-TOC total) oils were heated. Samples of the heated oils were extracted with acidified hot methanol and analyzed for changes in tocopherol contents and TOCQ levels by high-performance liquid chromatography (HPLC). In the study without added alpha-TOC, the alpha-TOC in SUN significantly decreased from 829 ppm at 0 h to 183 ppm at 5 h, then 0 ppm by 10 h; whereas alpha-TOCQ increased from 0 ppm at 0 h to 80 ppm at 5 h and to 100 ppm at 10 h. The level of alpha-TOC in SBO decreased from 138 ppm at 0 h to 100 ppm after 10 h with an increase in alpha-TOCQ from 0 ppm at 0 h to 25 ppm at 5 h and 53 ppm at 10 h. In the study with added alpha-TOC, the alpha-TOC in the SUN decreased rapidly from 1128 ppm at 0 h to 210 ppm at 5 h and only 28 ppm at 10 h, but the alpha-TOC in the SBO was 1176 ppm at 0 h, decreasing to 350 ppm by 5 h then to 225 ppm at 10 h. There was a corresponding increase of alpha-TOCQ in SUN with added alpha-TOC from 0 ppm at 0 h, to 125 ppm at 5 h and 164 ppm at 10 h; while the alpha-TOCQ in SBO with added alpha-TOC changed from 0 ppm initially to 165 ppm by 5 h and 180 ppm at 10 h. As expected, SUN formed significantly more alpha-TOCQ than the SBO, but the SBO with added alpha-TOC had significantly more alpha-TOCQ than the SUN with added alpha-TOC even though the alpha-TOC levels at 0 h were similar. These results indicate that frying oils and fried foods may still have some antioxidant protection from tocopherolquinones even after tocopherols have disappeared from the oil.