DETECTION OF FURANOID FATTY-ACIDS IN SOYBEAN OIL - CAUSE FOR THE LIGHT-INDUCED OFF-FLAVOR

The following furanoid fatty acids were detected in soya-bean oil (SBO), wheat germ oil, rapeseed oil and corn oil: 10,13-epoxy-11-methyloctadeca-10,12-dienoic acid (I), 10,13-epoxy-11,12-dimethyloctadeca-10,12-dienoic acid (II), 12,15-epoxy-13,14-dimethyleicosa-12,14-dienoic acid (III). A model experiment indicated that II and III were quickly photooxidized with formation of the intense flavour compound 3-methyl-2,4-nonanedione (MND) as secondary product. MND causes the light-induced off-flavour of SBO. A method for the quantification of the three furanoid fatty acids in vegetable oils was developed. The amounts of II and III were relatively high (0.02-0.04%) in unprocessed and refined SBO and in one sample of wheat germ oil and quite low (0.0015-0.0035%) in corn oil and rapeseed oil. The furanoid fatty acids I, II and III were absent in olive and sunflower oils.