地沟油特异性指标研究

精炼地沟油相比于食用植物油，经历了更长时间的高于200 ℃的高温历程，第三类地沟油或称煎炸老油也经历了长时间高温历程。本文应用ATR红外光谱法，研究了六种常用植物油中共轭脂肪酸甘油酯含量、反式脂肪酸甘油酯含量、不饱和度等三个指标值随加热温度及加热时间的变化情况，以期找出地沟油的特异性指标。研究结果表明: 从160 ℃开始，各植物油的共轭脂肪酸甘油酯含量及反式脂肪酸甘油酯含量随着加热温度升高及加热时间增长而增加，不饱和度则降低，当加热温度为200 ℃或以上、加热时间达到4 h或更长时，六种植物油的三个指标值有大幅变化。共轭脂肪酸甘油酯含量的变化幅度还与植物油中亚油酸含量有关，亚油酸含量越大其变化幅度越大;反式脂肪酸甘油酯含量变化幅度则还与植物油中油酸含量有关，油酸含量高者变化幅度大。此外，上述三个指标值与存储时间有关，随着六种植物油存放时间增长，共轭脂肪酸含量变大，不饱和度变小，而反式脂肪酸含量变化规律与高温长时间加热不同，其含量不是变大而是变小，保质期内三个指标值的变化幅度都小于经过高温长时间加热的变化幅度。因此，从三个指标值及其变化规律可以了解植物油是否经历了长时间高温历程，它们可以作为地沟油及精炼地沟油的特异性指标。

Research on Specific Indicators of Waste Oil

Because both refined “waste oil” and the third category “waste oil” known as frying old oil experience a longer history at temperature higher than 200 ℃ compared to the vegetable oil. In this study, the relative change rates of content of conjugated fatty acid glycerides, content of tans-fatty acid glycerides and unsaturation were investigated after being at high temperature for several hours by using FTIR-ATR in order to find out specific targets for “waste oil”. The results show that (1) Starting from 160 ℃, the contents of conjugated fatty acids glycerides and trans-fatty acid glycerids in the vegetable oils increase but unsaturation decreases with heating temperature and heating time increasing. (2) When heating temperature reaches 200 ℃ or more, the heating time up to four hours or longer, the three indicators(conjugated fatty glycerids，trans-fatty acid glycerids and unsaturation) of six kinds of vegetable oils have substantial changes. (3) The content of linoleic acid in the vegetable oil has some contributions to the change amplitude of contents of conjugated fatty acid glycerides, and the content of oleic acid in the vegetable oil has some contributions to the change amplitude of content of trans-fatty acid glycerides. (4) In addition, during the warranty period change amplitudes of three indicators are relative small compared with the case of after being at high temperature for several hours. Unsaturation decrease and content of conjugated fatty acid glycerides increase with storage-time increasing. However, unlike the case of after being at high temperature for several hours, the content of trans-fatty acid glycerids decreases with storage-time increasing. Experimental results show that three index value and its variation can be used as specific indicators for refined “waste oil” and “waste oil”.