1H NMR chemometrics and mechanistic insights on the thermal degradation of coconut oil

Abstract

The re-use and prolonged heating of cooking oils is a common practice in preparing deep-fried foods. However, this could be unsafe and pose a health threat to consumers. This work investigates the thermal degradation of edible coconut oil under prolonged heating using chemometrics analysis of proton nuclear magnetic resonance (¹H NMR) data. Coconut oil samples were heated continuously without food matrix at three different temperatures (150, 175, and 200°C) for 12 h and the ¹H NMR spectra were collected every hour. NMR data revealed the formation of aldehyde oxidation products. Partial least squares discriminant analysis (PLS-DA) discriminated the samples based on temperature and heating time. The Variable Importance Projection revealed the discriminating peaks highlighting the spectral feature due to hydroperoxides and aldehydes in the oil degradation. A probe into the ¹H NMR of the degradation products of saturated coconut oil confirmed the formation of a ketone as evidenced by a CH₂ triplet in the chemical shift region of protons alpha to a ketone. The results showed that the thermal degradation of coconut oil was influenced by temperature, time, moisture, and oxygen in the air which can contribute to the advancement in the control and assessment of coconut oil quality.