Thermal oxidation of olive oil, sunflower oil and a mix of both oils during forty discontinuous domestic fryings of different foods

Changes in sunflower oil (SO), olive oil (OO) of 0.4 degrees acidity value and a mixture (1:1) of both oils (MO) were studied during forty domestic di scontinuous deep-fat frying of various foodstuffs, mostly frozen foods. The replenishment of the oil in the fryer with fresh oil was performed after e very ten uses to maintain the oil volume in the fryer. Alteration of oils w as evaluated by measuring polar content (PC) and compounds related to therm oxidative and hydrolytic changes. PC increased with different rates in the three oils, thus after twenty fryings, PC was 25.3 g/100 g oil for SO, 22.4 g/100 g oil for MO and 19.7 g/100 g oil for OO. At the fortieth frying, th e three oils surpassed the critical level for PC of 25 g/100 g oil, but SO and MO were abused oils with a PC value 30 g/100 g oil. Oxidized triacylgly cerols (OTG), triacylglycerol dimers (TD) and triacylglycerol polymers (TP) increased after forty fryings 6.1, 34.5 and 260 times, respectively, in SO ; 7.8, 50.9 and 115.8 times, respectively, in MO and 19.5, 70 and 149 times , respectively, in OO. The TP+TD/OTG ratio was used to assess the more pred ominant alteration through frying in the three oils. This ratio increased a fter forty fryings more in SO followed by MO, and then by OO, showing that oils rich in linoleic acid became more polymerized in frying than those ric h in oleic acid . According to PC and the thermoxidative changes, MO behave d as a mix of OO and SO. Data indicated that during the first twenty frying s, olive oil of 0.4 degrees acidity value and the oil mix performed more sa tisfactorily than sunflower oil in repeated fryings of frozen foods, howeve r, differences in frying oil behavior decreased during the last twenty fryi ngs.