High-resolution ¹H NMR analysis of continuous and discontinuous thermo-oxidative susceptibility of culinary oils during frying at 180 ℃

Gilbert Ampem ^a, Adam Le Gresley ^a,*, Martin Grootveld ^b, Declan P. Naughton ^a

^a Department of Chemistry and Pharmaceutical Sciences, SEC Faculty, Kingston University, Kingston-upon-Thames, Surrey, KT1 2EE, UK

^b Leicester School of Pharmacy, HLS Faculty, De Montfort University, Leicester, LE1 9BH, UK

Lipid oxidations products (LOPs) are reactive mutagenic and carcinogenic species known to be generated in thermally stressed culinary oils. Mapping the evolution of LOPs in culinary oils exposed to standard frying practices – both continuous and discontinuous thermo-oxidation - at 180 ℃ is vital to our understanding of these processes, and to the development of scientific solutions for their effective suppression. Modifications in the chemical compositions of the thermo-oxidised oils were analysed using a high-resolution proton nuclear magnetic resonance (¹H NMR) technique. Research findings acquired showed that polyunsaturated fatty acid (PUFA)-rich culinary oils were the most susceptible to thermo-oxidation. Consistently, coconut oil, which has a very high saturated fatty acid (SFA) content, was highly resistant to the thermo-oxidative methods employed. Furthermore, continuous thermo-oxidation produced greater substantive changes in the oils evaluated than discontinuous episodes. Indeed, for 120 min thermo-oxidation durations, both continuous and discontinuous methods exerted a unique impact on the contents and levels of aldehydic LOPs formed in the oils. This report exposes daily used culinary oils to thermo-oxidation, and therefore, it permits assessments

of their peroxidative susceptibilities. It also serves as a reminder to the scientific community to investigate approaches for suppressing toxic LOPs generation in culinary oils exposed to these processes, most notably those involving their reuse.

Keywords: Continuous thermo-oxidation, Culinary oil, Discontinuous thermo-oxidation, Frying temperature, α,β-unsaturated aldehydes (α,β -UAs)

https://doi.org/10.38212/2224-6614.3439