The effect of minor components on canola oil oxidation: Oxidation kinetics explained by molecular interactions

Abstract

This study investigates the effect of various minor components (MCs) on the oxidation kinetics and molecular self-assembly in stripped canola oil during thermal and photo oxidation processes using experimental and simulation tools. The peroxide value (PV) and fatty acid content were measured to evaluate the formation of oxidation products and the consumption rate of unsaturated fatty acids. In the thermal oxidation experiment, adding MCs slightly increased the oxidation rate, while in the photo oxidation experiment, stearic acid (SA) and glycerol monostearate (GMS) significantly decreased it. GMS demonstrated a pronounced ability to self-assemble and form molecular organizations during photo oxidation, resulting in lower critical micelle concentration (CMC) values of lipid hydroperoxides (LOOHs) and reduced oxidation rates. These GMS self-assemblies seem to scatter light, thus decreasing absorbed energy during photo oxidation, leading to lower oxidation rates. SA exhibited the highest surface activity, effectively lowering the LOOH CMC and facilitating the formation of stable reverse micelles at lower concentrations. Interestingly, the addition of MCs did not influence the tendency of LOOHs to form hydrogen bonds with water, suggesting that the lower CMC resulted from the formation of mutual reverse micelles of MCs and LOOHs. Meso-phase formation was observed at very high PVs, indicating a high concentration of secondary oxidation products, which also possess surface activity. These findings underscore the importance of molecular interactions in oxidation stability, providing insights for improving edible oil preservation.

Keywords: Edible oil; MD simulations; Minor components; Oxidation; Reverse micelles; Self-assembly.

Graphical abstract

Fig. 1

The chemical structure of the studied molecules.

Fig. 2

The PV as a function of oxidation time as measured for the thermal (A) and photo (B) oxidation systems. The connective lines represent the spline fitting of the points to emphasize the PV changes over time. The initial PV values and the fitted linear regression lines for the thermal (C) and photo (D) oxidation systems. The lag period times as calculated for the thermal (E) and photo (F) oxidation systems using the intersections of the fitted linear lines in (C) and (D). The initial slopes fitted for the exponential period, indicating the initial oxidation rate for the thermal (G) and photo (H) oxidation systems.

Fig. 3

The ratio of the total USFA:PA as a function of oxidation time, as was measured for the thermal (A) and photo oxidation systems (B).

Fig. 4

Viscosity values as a function of oxidation time for the thermal oxidation (A) and photo oxidation (D) systems. Linear regression lines are included in the plots, representing the calculations used for determining the micelle formation times. These times were used to calculate the PV at the CMC and the meso-phase formation time for the thermal (B and C) and photo (E and F) oxidation systems, respectively.

Fig. 5

Typical RDFs computed between the different molecules for thermal and photo oxidation simulations. In the typical simulation box, the molecules were colored by their type: water molecules - blue, LOOHs - red, and MCs -green. For a clear presentation, only the simulation box of the system containing SA is presented.

Fig. 6

The maximum intensities of the RDF peak correspond to the hydrogen bonds formation between the water, different MCs, and different LOOHs, as was calculated for the thermal and photo oxidation simulations.