Establishment of a fingerprint database for fatty acids and its application in identification and discrimination of edible oils and hogwash oils

Objective To develop a capillary gas chromatographic (CGC) method for the determination of fatty acid contents and to establish a fingerprints database of fatty acids for the identification of hogwash oils and discrimination of edible oils.Methods We set the conditions for CGC measurement as following:using strongly polar stationary phase capillary column with temperature programming,pure nitrogen as carrier gas,with the injector temperature of 260 ℃,sample injection of 1 μL,and split/splitless mode for injection.Flame ionization detector (FID) was used in detection of fatty acid and peak area normalization method was adopted for quantification.The chromatograms were collected and summarized using Excel 2007.Then a standard fingerprints database for fatty acids of nine kinds of edible oils and hogwash oils was established based on detection results;the database was further utilized for the discrimination and identification of oil categories.The characteristic fingerprints of different type of oils or fats were compared with each other for their similarities and specificities.Results There was a good linear correlation between peak area of chromatogram and the mass concentration of three fatty acid methyl esters (C18:3,C20:5,and C22:6) with the concentration range of 0.05 mg/ml-20.0 mg/ml (r>0.999);the method detection limit was 1 ng;the average recoveries ranged from 95.3% to 98.5% at three different levels and the relative standard deviations (RSDs) were less than 5%.The contents of fatty acids in nine kinds of oils or fats (119 samples of animal fat,edible blend oil,and hogwash oil) were determined with the method;the fatty acids standard fingerprints in the database demonstrated significant differences in composite fatty acids,saturated fatty acids,and myristic acid (C14:0) of the nine kinds of oil and fat;the category of edible oils could be determined and the hogwash oil could be identified based on those differences.Conclusion The established method is easy for operation and is of good accuracy,selectivity and repeatability.The fatty acid fingerprint database could be utilized in the discrimination of edible oil category and the identification of hogwash oil.