Abstract
A strong bitter taste was reported previously in highly autoxidized soybean oil, especially in the free fatty acid fraction. In the present study, for the elucidation of bitter substances in autoxidized oils, autoxidized linoleic acid was fractionated by silicic acid column chromatography, and the fraction with maximum peroxide value was treated with cysteine-ferric trichloride, reduced with sodium borohydride, oxidized with chromic acid and esterified with diazomethane. The results indicated that the bitter substances of autoxidized linoleic acid possessed a particular structure between the carboxyl group and other functional groups. To verify this fact, four oxidized fatty acids [ricinoleic(l2-hydroxyoctadecenoic), 12-oxooctadecenoic, 9, 12-dioxooctadecenoic, and di-hydroxyoctadecenoic acids] were synthesized from castor oil, and their correlation to the bitter taste was investigated. The results showed that ricinoleic acid had a strong bitter taste, along with a strong stimulation, but this bitter taste was greatly reduced by methyl esterification. On the other hand, 12-hydroxy- and 9, 10-dihydroxystearic acids were tasteless. From these results we conclude that the presence of an unsaturated bond, a carboxyl, a hydroxyl and/or peroxyl groups is a requisite for the bitterness of ricinoleic and autoxidized fatty acids.
