摘要或動機

家庭中為了節省油量的使用，常將所剩的油品另存於容器中，以待下次使用。近年來，已有不少文獻報告指出，這種「回鍋」的使用方式，往往使得油品品質變得相當低劣。近來市面上有不少的油品，標榜添加天然維生素E，使消費者趨之若鶩，作為一種吸引消費的手段；這激發了我們極高的興趣，因為在文獻中已知道維生素E在室溫下確實可抑制油品的氧化；但添加的油品經過回鍋後，其對油品的影響卻仍不得而知。我們利用鐵鍋油炸澱粉食物，並經由反覆的油炸與冷卻，模擬更真實的回鍋情形。並添加抗氧化劑，包括維生素E和酯化的維生素E，以及回鍋次數等不同的變因進行實驗，進行油品品質的化學變化的測量。經由實驗結果顯示，經數次的回鍋烹煮，油品品質因為一連串的化學反應變得十分低劣；另外，添加酯化的維生素E的油品在某些方面的確減少了某些不良生成物的形成(如游離脂肪酸、羰基化合物等)，但在某些方面如氧化程度的比較(共軛雙鍵的生成)卻與一般無添加的回鍋油無異。反倒是添加維生素E對於回鍋油品質的影響在實驗結果的每方面看來，不管是酸敗氧化或是裂解成羰基化合物都能夠有效地減少或產生抑制的作用；故添加維生素E對於回鍋油的品質的確有正面性的影響！Cooking oil is often reused in homes in order to economize on its use. In the past few years, many reports have pointed out that ”reusing” oil this way always changes the properties of oil and makes it spoiled. Also in the past few years, many oil products have appeared on market that highlight the fact that vitamin E has been added, in order to attract consumers. This attracted our interest, since we know that on the basis of several studies, vitamin E indeed has an antioxidizing effect at room temperature or below. However, it is not know what effect vitamin E has on re-cooked oil. Therefore, in this experiment we simulated the re-cooking process by frying steamed dumplings in an iron wok with soybean oil, and repeatedly cooling and re-using the oil. Variable factors were the added antioxidants(vitamin E and vitamin E acetate) and the number of re-cooking times. The chemical variation in the resulting oil was tested with regard to acid value, viscosity, carbonyl value, and the value of conjugated bonds. The results indicated that as the number of re-cooking times increased, the quality of the oil had undergone a series of chemical reactions and became spoiled. Also, the addition of vitamin E and vitamin E acetate indeed reduced the formation of certain unhealthful products such as free fatty acids, carbonyl groups, and so on. In certain respects, such as the quantity of oxidized components in the oil, there is no obvious difference between ordinary oil and oil with the vitamin E acetate additives. However, the addition of vitamin E to cooking oil, based on the results of this experiment, can effectively reduce or suppress processes causing rancidity and breakdown into carbonyl groups. Therefore, the addition of vitamin E or vitamin E acetate dose have a positive effect on re-cooked oil.