Simultaneous monitoring of the conventional qualitative indicators during frying of sunflower oil

Deterioration of sunflower oil during a 32 h frying was studied by monitoring the levels of polar compounds (total content, TPC; triglyceride polymers, TGP; triglyceride dimmers, TGD; oxidised triglyceride monomers, oxTGM; diglycerides, DG; and free fatty acids, FFA), carbonyl value (CV), oil/oxidative stability index (OSI), and conjugated diene value (CDV). The frying process increased the level of TPC in the oil from 2.8% to 28.9%. The TGP, TGD, oxTGM, DG, and FFA increased 186.5, 29.1, 6.1, 5.1, and 5.4 times, respectively. The CV, OSI, and CDV changed from 7.9 μmol/g, 2.7 h, and 10.6 mmol/l to 70.9 μmol/g, 1.2 h, and 61.6 mmol/l, respectively. The TPC or TGDP (TGD + TGP) contents were significantly correlated with the CV, OSI, or CDV. Finally, it was recommended that the sunflower oil should be discarded at 10% TGDP, 20% TPC, or 44 mmol/l CDV.