ENZYMATIC AND AUTOXIDATION OF LIPIDS IN LOW-FAT FOODS - MODEL OF LINOLEIC-ACID IN EMULSIFIED HEXADECANE

The oxidation of linoleic acid in emulsified hexadecane, which is inert to oxidation, was examined as a model for low fat foods. Static headspace gas chromatography was used to investigate the release of small amounts of volatile compounds in emulsion systems. At room temperature the initial rate of oxidation by lipoxygenase decreased in the presence of emulsion droplets. However, the total amounts of intermediate hydroperoxides formed after 4 h were similar, as well as the amounts of decomposition product hexanal formed after 22 h at 40 degrees C. There was no effect of droplet size of the emulsions tested. Increase of emulsion concentration from 0 to 2.4% gradually reduced the amount of hexanal released from the emulsions. The enzyme preparation used accelerated the formation of hexanal from methyl linoleate hydroperoxides prepared by autoxidation. However, hexanal was more readily formed from the linoleate hydroperoxide produced by the lipoxygenase preparation. Autoxidative decomposition of methyl linoleate at 40 degrees C produced about the same amounts of hexanal as the corresponding linoleate containing model systems at 60 degrees C. This study showed that lowering the fat contents of foods may increase the chances of flavour defects.