Mass Transport Phenomena in Lipid Oxidation and Antioxidation

Abstract

In lipid dispersions, the ability of reactants to move from one lipid particle to another is an important, yet often ignored, determinant of lipid oxidation and its inhibition by antioxidants. This review describes three putative interparticle transfer mechanisms for oxidants and antioxidants: (a) diffusion, (b) collision-exchange-separation, and (c) micelle-assisted transfer. Mechanism a involves the diffusion of molecules from one particle to another through the intervening aqueous phase. Mechanism b involves the transfer of molecules from one particle to another when the particles collide with each other. Mechanism c involves the solubilization of molecules in micelles within the aqueous phase and then their transfer between particles. During lipid oxidation, the accumulation of surface-active lipid hydroperoxides (LOOHs) beyond their critical micelle concentration may shift their mass transport from the collision-exchange-separation pathway (slow transfer) to the micelle-assisted mechanism (fast transfer), which may account for the transition from the initiation to the propagation phase. Similarly, the cutoff effect governing antioxidant activity in lipid dispersions may be due to the fact that above a certain hydrophobicity, the transfer mechanism for antioxidants changes from diffusion to collision-exchange-separation. This hypothesis provides a simple model to rationalize the design and formulation of antioxidants and dispersed lipids.

Improvement in the Oxidative Stability of Flaxseed Oil Using an Edible Guar Gum‐Tannic Acid Nanofibrous Mat

“…Compared with macro particles of TA, encapsulating TA in a nanoscale delivery system is more effective for delaying both the primary and secondary oxidation reactions of FO throughout the tested storage time. The effectiveness of the antioxidant is highly dependent on the transmission rate of the antioxidant toward the minor surface‐active components of the lipid . In the present study, the electrospinning process facilitates dispersion of the active compound (i.e., TA) into a delivery system with decreased particle size and a three‐dimensional network structure, permitting relatively free interaction between the TA and FO due to the improved solubility and quick release into the oil as proved by the release test.…”

Toward a Spatiotemporal Model of Oxidation in Lipid Dispersions: A Hypothesis‐Driven Review

“…However, how LOOHs would diffuse between colloids separated by an aqueous phase wherein LOOHs are poorly soluble remains unclear. Given that the lag phase (if any) of lipid oxidation in dispersed systems corresponds to the production of LOOHs in only a few lipid colloids, our hypothesis is that when a critical concentration is attained, LOOHs which are surface‐active enough would form micelles alone or co‐micelles with surfactants present in the aqueous phase . Unlike individual LOOH molecules, micelles or co‐micelles of LOOHs can theoretically migrate over long distances because of their higher solubility in water.…”

“…Furthermore, considering the polydispersity/polymodality—and in some circumstances the fractal nature—of lipid dispersions, especially oil‐in‐water emulsions ( Figure 6e), it could also be possible that prooxidative compounds such as LOOHs are transported by microemulsion droplets. This mode of transport, called “collision‐exchange‐separation transfer,” can be slower than the micelle‐assisted one, but significantly faster than a mass transport mediated by macroemulsion droplets; the smaller the transporter, the faster the diffusivity. It has been recently found on Tween 80‐stabilized oil‐in‐water emulsion, that populations of small microemulsion droplets ( d : 12–22 nm) coexist with nanoemulsion ( d < 200 nm) and macroemulsion ( d > 200 nm) droplets, when the optical properties of the emulsion are those of a classical macroemulsion (opaque) .…”

Antioxidant Hydrophobicity and Emulsifier Type Influences the Partitioning of Antioxidants in the Interface Improving Oxidative Stability in O/W Emulsions Rich in n‐3 Fatty Acids

“…Such surfactant molecules in micelles organize so that their non‐polar tails are located in the interior (away from water) and their polar head groups are located at the exterior (in contact with water), thus amphiphilic or hydrophobic antioxidants can be solubilized within surfactant micelles due to the hydrophobic effect . In this frame, T65 and T80 are hydrophilic emulsifiers and their concentrations seem to be higher than the critical concentration, thus a fraction of them form micelles in the water phase, where they could act as reservoir to replace oxidized antioxidants according to several reports . However, in our study, this seems to be true for GA, PG, and AP, because of their hydrophobicity (relatively low) and their activity as antioxidant, but not for TC, the most hydrophobic one.…”

“…It has been reported to influence the inhibition of lipid oxidation by antioxidants. At this point, we have considered three recently cited hypotheses to explain the poor TC activity: a) the diffusion of molecules from one particle to another through the aqueous phase, b) the transference of molecules from one particle to another when the particles collide with each other, and c) the solubilization of molecules into micelles within the aqueous phase and then their transference among particles . In our system, neither the first nor the third transfer pathways were viable to transfer TC, due to the low affinity of such molecules with water, resulting in the absence of TC in the aqueous phase; and because all TC were present in the oil phase; which makes it clear that TC was not solubilized into emulsifier micelles to be transferred.…”