油炸對薯餅3-單氯丙二醇、3-單氯丙二醇酯與縮水甘油酯的影響

Abstract

食品在熱加工處理中，會生成熱誘導污染物 (heat-induced contaminants)，其中包含3-單氯丙二醇酯 (3-monochloropropane-1,2-diol esters, 3-MPCD esters)與縮水甘油酯 (glycidyl esters, GEs)。經腸道水解後會成為具有毒性的3-單氯丙二醇 (3-MCPD)及縮水甘油 (glycidol)。世界衛生組織癌症研究署 (International agency for research on cancer, IARC)分別將3-單氯丙二醇及縮水甘油類歸於Group 2B及2A物質。3-MCPD esters的成因主要為雙酸甘油酯在高溫環境下脫去脂肪酸基，或在酸性環境中脫水時與氯離子反應；而GEs則是在高溫下造成單、雙酸甘油酯進行分子內重排而生成。有氯離子存在時，會使GEs部分轉變成3-MCPD esters。精製植物油中常發現3-MCPD esters及GEs存在，特別在棕櫚油中含量最高。由於棕櫚油品質穩定，常作為油炸用油。以油炸作為加熱方式時能夠賦予食品特殊的風味，因此油炸食品相當受歡迎。在油炸過程中，水分的散失使油脂進入到孔隙中，也將油炸過程中所生成的物質帶入，這些熱誘導物質會增加人類發生疾病的風險，因此這些物質的變化是需要被關注的。本研究係利用不同油炸溫度處理含有氯化鈉之薯餅，探討3-MCPD, 3-MCPD esters及GEs於油和薯餅中含量的變化。在高溫長時間的情況下，油炸油及薯餅中3-MCPD esters與GEs隨著時間增加皆有下降的趨勢，且未測得3-MCPD，顯示在開放式油炸系統中傾向於分解作用發生，下降的幅度隨著時間增加逐漸趨緩。進一步測定油脂含量，得知油炸過後的薯餅油脂含量受油炸溫度與時間影響，使薯餅中3-MCDP esters及GEs的含量隨吸油量改變。由於氯離子為3-MCPD esters的生成因子，本研究以薯餅中的氯化鈉作為反應物，觀察氯離子的利用情形。酸價在油脂劣變中扮演著重要角色，薯餅的水分在高溫中蒸發，水解作用使游離脂肪酸、單酸甘油酯及雙酸甘油脂的含量增加。酸價的增加代表3-MCPD esters的反應物增加，使棕櫚油中3-MCPD esters在200℃ 時降解幅度較緩。實驗結果可以得知薯餅及棕櫚油在油炸過程中熱誘導物質含量的變化，得知薯餅最適的油炸溫度為180℃。

During thermal processing of food, few heat-induced contaminants are generated such as 3-monochloropropane-1,2-diol esters (3-MCPD esters) and glycidyl esters (GEs). After intestinal hydrolysis, these esters get hydrolyzed to their free forms, 3-MCPD and glycidol, which are toxic. The International Agency for Research on Cancer (IARC) classifies 3-MCPD and glycidol into Group 2B and 2A substances, respectively. The cause of generation of 3-MCPD esters is mainly the removal of fatty acid groups by diglycerides in high temperatures and dehydration in acidic environment in the presence of chloride ions. GEs are generated at high temperatures from mono- and diglycerides by rearrangement through charge migration and these are partially converted to 3-MCPD esters in presence of chloride ions. High-content of 3-MCPD esters and GEs are often found in refined vegetable oils, especially in palm oil. Deep frying is one of the popular methods for the preparation of foodstuff. During deep-frying of food, the loss of moisture causes oil to enter the food along with these heat-induced contaminants which increase the risk of disease in humans. In this study, the 3-MCPD esters and GEs contents in hash browns was investigated at different frying temperatures. In case of exposure to high temperature for a long time, the 3-MCPD esters and GEs contents of hash browns and palm oil have been found to decrease and no 3-MCPD was detected. This indicates that the 3-MCPD gets decomposed slowly with prolonged frying time in an open frying system. Further, it is known that the fat content of the hash brown after frying is affected by the frying temperature and time, hence, its 3-MCDP esters and GEs content increases with the oil absorption. Moreover, as hash brown contains sodium chloride, it supplies the chloride ions as reactants to frying-oil system and proceeds the reaction. The moisture of hash brown evaporates at high temperatures. The hydrolysis increases the content of free fatty acids, monoglycerides and diglycerides and the increase in acidity results in deterioration of oil. Theoretically, the increase in acid value increases the reactivity of 3-MCPD esters, but in the present study, it was found to result in a slower degradation of 3-MCPD esters in palm oil at 200°C. To sum up, this study aims to evaluate the generation and deterioration of heat-induced contaminants in hash brown during frying process. The optimum frying temperature of hash brown was found to be 180℃.