iso 9-HODE and iso 13-HODE: Novel Markers of Thermal Processing in Vegetable Oils

Two novel oxylipins, iso 13-HODE (13-hydroxy-8E,10Z-octadecadienoic acid) and iso 9-HODE (9-hydroxy-11Z,13E-octadecadienoic acid), formed during thermal processing of vegetable oils, are identified. iso HODEs are formed during deodorization through heat-induced [1,5]-sigmatropic rearrangement of Z,E 13-HODE and E,Z 9-HODE. Industrial refining increases the concentration of iso 13-HODE in sunflower oil from 65 to 150 nmol/g and in rapeseed oil from 5 to 26 nmol/g upon deodorization, while iso 9-HODE increases in sunflower oil from 14 to 65 nmol/g and in rapeseed oil from 2 to 11 nmol/g. The ratios of iso 13-HODE to Z,E 13-HODE and of iso 9-HODE to E,Z 9-HODE are even more sensitive parameters, increasing from 10- to 100-fold during industrial deodorization. Complementary laboratory heating experiments have demonstrated that these ratios already increase at temperatures above 100 °C. Therefore, we suggest the novel oxylipins as new complementary authenticity markers for distinguishing heated from virgin oils, which warrant further investigation.