Effects of docosahexaenoic acid positional distribution on the oxidative stability of model triacylglycerol in water emulsion.

ABSTRACT The effect of the positional distribution of docosahexaenoic acid (DHA) within triacylglycerol (TAG) molecules on the oxidative stability of oil-in-water emulsions was investigated by using a synthetic TAG regio-isomer pair SDS (1,3-dioctadecanoyl-2-[4,7,10,13,16,19-docosahexaenoyl] glycerol) and SSD (1,2–dioctadecanoyl-3-[4,7,10,13,16,19-docosahexaenoyl] glycerol), where S and D represent stearic acid and DHA, respectively. Oil-in-water emulsions (10%, w/w) of each isomer were subjected to accelerated autoxidation by continuous exposure to air at 50C in the absence of light. Oxidation during the exposure (storage) was monitored by measuring a series of volatile compounds characteristic of DHA oxidation. SSD emulsion oxidized faster than SDS emulsion, showing that DHA is more stable to oxidation when located at the sn-2 position of the TAG compared with the sn-1(3) position. This regio-isomeric effect is similar to that previously reported for bulk oil oxidation. PRACTICAL APPLICATIONS Many of the food products that have been selected for fortification with omega-3 oils such as milk, yoghurt, salad dressings and juices are oil-in-water emulsions. This study, for the first time, demonstrated that the regio-isomeric effects on oxidative stability of docosahexaenoic acid observed for bulk oil also apply to oil-in-water emulsion. Thus, potential exists for enhancing the oxidative stability of omega-3-fortified emulsion foods through modification of triacylglycerol structure.