[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 °C 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 °C, 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 °C 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".