Influence of Time, Surface-to-Volume Ratio, and Heating Process (Continuous or Intermittent) on the Emission Rates of Selected Carbonyl Compounds during Thermal Oxidation of Palm and Soybean Oils

Abstract

The aim of this work was to compare the emission rates of selected carbonyl compounds (CC) produced by palm and soybean oils when heated at 180 °C in the presence of air, through different time intervals and at different surface-to-volume ratios (S/V), in continuous and intermittent processes. The CC were collected and derivatized onto silica C18 cartridges impregnated with an acid 2,4- dinitrophenylhidrazine solution, followed by extraction with acetonitrile and analysis by HPLC-UV and,in some cases, HPLC-MS with electrospray ionization. Among the CC quantified, namely, acetaldehyde, acrolein, propanal, butanal, hexanal, 2-heptenal, and 2-octenal, acrolein was the main emission in both oils and all S/V ratios, followed by hexanal and 2-heptenal. The soybean oil has presented greater emission rates of acrolein than palm oil. When different S/V ratios used during the heating process of the oil were compared, the emission rates, in general, were directly related to them, although saturated and nonsaturated CC have had different behaviors toward oxidation reactions. During intermittent heating, there was a trend of increasing emission rates of saturated aldehydes, whereas the opposite was observed with unsaturated aldehydes, probably due to the reactivity of the double bond present in these compounds.