| Summary: | The oxidative stability of phytosterols and tocopherols was investigated in this study by 1) heating phytosterol standards; 2) frying potato chips in canola oils and storing the fried products and 3) heating canola oils at frying temperatures to simulate frying. Pure B-sitosterol, campesterol and stigmasterol were heated at 75oC, 95oC, 120oC, 155oC and 180oC for 1 hour, 5 hours and 12 hours. The changes of phytosterols were determined by HPLC and the oxidation products formed during the heating were identified by GC-MS. B-Sitosterol and campesterol were stable at 75oC for 12 hours and began to oxidize at 95oC. Elevated temperatuers accelerated the oxidation rate of phytosterols. B-Sitosterol and campesterol produced large amounts of oxidation products when heated at 155oC and 180oC for 1 hour. Stigmasterol was the most stable phytosterol among all the evaluated phytosterols. The potato chips were fried in regular, low linolenic acid, high oleic acid and hydrogenated canola oils at 180+-5oC. The potato chips were collected on the first and fifth day of frying and stored at 60oC for 16 days without light. Major phytosterol changes in canola oils and in fried potato chips were determined by HPLC. During the potato chip frying, 50% to 60% of total sterols disappeared and several oxidation products were observed. Only a small amount of sterols disappeared during the storage of potato chips... Tocopherol changes in canola oils during frying and potato chip storage were determined by normal phase HPLC. At the end of the potato chip frying, the total tocopherol losses were at 47%, 47%, 58% and 92% in low linolenic, regular, high oleic and hydrogenated canola oils, respectively. Y-Tocopherol disappeared faster than a-tocopherol. During the heating at simulated frying temperature, similar changes of tocopherols were observed as during frying. Unsaturation was found to be the major factor affecting the disappearance of tocopherols during the storage of potato chips. Total tocopherol losses in the potato chips at the end of storage were at 10%, 50%, 85% and 96% for hydrogenated, low linolenic, high oleic and regular canola oils respectively. a-Tocopherol was found to decrease at a faster rate than Y-tocopherol during the storage of potato chips, which was different from frying.
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