Deterioration of diacylglycerol- and triacylglycerol-rich oils during frying of potatoes

The stabilities of a commercial diacylglycerol-rich oil (DAG) and a salad oil (TAG) that had been prepared from a mixture of rapeseed and soybean oils were compared while frying potatoes at 180°C for 3 h. The representative chemical and physical characteristics of the oils were assessed before and after frying, together with the amount of volatile aldehydes in the exhaust of frying. Among the deterioration indications, the carbonyl value, polymer content, and residual polyunsaturated fatty acid content were similar and not significantly different between the TAG and DAG. On the other hand, the characteristics relating to free fatty acids, i.e. the acid value and emission of chemiluminescence at 100°C, were greater and the smoke and flash points were lower in the DAG than in the TAG. An irritating odor was generated from the DAG after 1 h of frying and got stronger as frying continued. These results suggested that DAG more easily forms free fatty acids under frying conditions than TAG.