Although polymers are the major oxidation products accumulating in oil during frying, mechanisms of polymerization have not been well understood. Polymers along with aldehydes in frying oil are known to be associated with adverse health effects. Understanding mechanisms of polymerization and structures of polymers is critical to understand their toxicity and to develop methods to prevent their formation. An earlier study reported that Diels–Alder reaction, a long-believed mechanism for the polymerization of oil, was not the major reaction to produce polymers. In this study, we found that ester bonds are one of the chemical bonds forming polymers during frying using NMR spectroscopy. Ester value increased as soybean oil oxidized and <sup>13</sup>C NMR spectrum showed new ester carbonyl carbon signals evidencing the formation of ester bonds. The NMR spectroscopy after the reaction of oxidized soybean oil with acetyl chloride was also employed to verify NMR signals corresponding to alcohol. By this method, proton signals at 3.61 and at 3.71 ppm, which were reported to be ether bonds forming polymers, were found to be those of alcohols produced in oil. Some uncertain assignments of proton signals of oxidized oil were clarified as signals of alcohols, several previously assigned signals as alcohols were confirmed, and a new proton NMR signal was assigned to be an alcohol. There are so many oxidation products that were not yet identified, and this study indicates that the NMR spectroscopy can be a great tool to identify oxidation products formed in oil.

NMR spectroscopy as a powerful tool for identification of polymers and other oxidation products in frying oil

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.