Simultaneous analysis of the oxidation of solvent-extracted and cold-pressed green coffee oil during accelerated storage using 1H NMR and 13C NMR spectroscopy

Green coffee oil (GCO) extracted from green coffee beans, is known for its antioxidant and anticancer properties, and has been increasingly utilised in cosmetic and other consumer products. However, lipid oxidation of GCO fatty acid components during storage may be harmful to human health, and there remains a need to understand the evolution of GCO chemical component oxidation. In this study, proton nuclear magnetic resonance (1H and 13C NMR) spectroscopy was used to investigate the oxidation status of solvent-extracted and cold-pressed GCO under accelerated storage conditions. Results show that the signal intensity of oxidation products gradually increased with increasing oxidation time, while unsaturated fatty acid signals gradually weakened. Five different types of GCO extracts were clustered according to their properties, except for minor overlapping in the two-dimensional plane of the principal component analysis. Partial least squares-least analysis results demonstrate that oxidation products (δ = 7.8-10.3 ppm), unsaturated fatty acids (δ = 5.28-5.42 ppm), and linoleic acid (δ = 2.70-2.85 ppm) in 1H NMR can be used as characteristic indicators of GCO oxidation levels. Furthermore, the kinetics curves of unsaturated fatty acids, linoleic, and linolenic acyl groups all fit an exponential equation with high coefficients of GCO for 36 days under accelerated storage conditions. Our results show that the current NMR system is a fast, easy-operated and convenient tool for the oxidation process monitoring and quality control of GCO.