Quantitative and qualitative analysis of high molecular compounds in vegetable oils formed under high temperatures in the absence of oxygen

• DOI: 10.1007/s00217-013-2015-9
• Publication Date: 2013-06-01T06:59:01Z
• Authors: Klara Cihelkova; Andreas Schieber; Daise Lopes-Lutz; Iveta Hradkova; Jan Kyselka; Vladimir Filip
• Keywords: Induction period; Peroxide; Sunflower oil

Conditions of deodorization/physical refining of sunflower oil were simulated by high temperature heating in laboratory at 240, 250, and 260 °C. Oxygen atmosphere was excluded by argon atmosphere. Influence of temperature, initial oxidation of incoming oil (peroxide value 2–30 mmol ½ O2/kg) on geometrical, positional isomerization, and polymerization was measured. The level of initial oxidation of the oil has a significant influence on rate of isomerization, polymerization, and duration of induction period of polymerization reactions. Induction period of polymerization is dependent linearly on temperature at constant hydroperoxide content and is extended with decreasing temperature and lower peroxide value of oil. Significant conjugation took place with geometrical isomerization and resulted in all-trans diene formation. All-trans dienes are incoming reactants for polymerization according to the Diels–Alder mechanism. Suggested “propagation” phase of polymerization took place later. Induction period was observed only in the case of polymerization reactions of triacylglycerols. This is the confirmation of the hypothesis that the cis/trans isomerization, positional isomerization, and polymerization are consecutive reactions in ascending order. Identification of molecular peaks and confirmation of fragments were possible by connecting HPSEC with APCI-MS. Dimers of triacylglycerols (TAG) dominated in studied system. Remaining compounds may have been formed from di-, monoacylglycerols, and other minor constituents of sunflower oil.