Performance of vegetable oils during standardized domestic frying

The aim of this work was to investigate the behavior of vegetable oils (corn (CO), vitaminized corn (COVE), sunflower (SO) and peanut (PO) oils), under standardized domestic frying conditions using a deep-fryer and a frying-pan. In both frying experiments, prefried potato sticks were deep-fried at 160°C (potato:oil ratio, 1:3 (w/w)). Each frying cycle consisted of a first heating step of oil, followed by 2 repeated frying sessions with an re-equilibration time interval between them. The oxidative and hydrolytic stability of the vegetable oils were evaluated. After the second frying session, a slight reduction in the polyunsaturated fatty acid content (2.5-3.3%) was observed in both cooking modes. In general, the oxidative stability index (OSI) of all vegetable oils decreased during frying in both experimental conditions; in particular, CO and COVE displayed a similar behavior to PO, whereas SO showed the lowest OSI time (2.6 h after the second frying). Peroxide value (PV) of all oils rose faster and reached higher levels in the frying-pan with respect to the deep-fryer; after the second frying session, most oils had a PV lower than 17 meq O2/kg oil, except for SO (30 meq O2/kg oil). Regarding the hydrolytic stability, free acidity (< 0.2%) and total diacylglycerol content (1.3-2.7% mg/100 mg of fat) remained almost constant in all oils under both tested conditions. In addition, total polar compounds (TPC) of all oils did not exceed 22% in both cooking methods, thus being below the legal limit for TPC (< 25%). Finally, a sensory evaluation of fried potatoes was carried out by randomly chosen volunteers (n=10), who gave the lowest general assessment to products fried with PO regardless of the cooking mode. In general, CO, COVE and PO showed a similar oxidative and hydrolytic behavior under the household frying conditions here tested, but SO easily and faster degraded, thus being less suitable for domestic frying.