The effect of dietary antioxidants on iron-mediated lipid peroxidation in marine emulsions studied by measurement of dissolved oxygen consumption

Lipid oxidation in oil-in-water emulsions: Iron complexation by buffer ions and transfer on the interface as a possible mechanism

Lipid oxidation is the main hurdle for omega-3 fatty acid enrichment in food and beverages. Fat oxidation reduces the quality and safety of supplemented products. A tuna oil-in-water emulsion (20%v/v) was exposed to iron-induced oxidation. Emulsions with changing emulsifiers and buffers were analyzed under different storage conditions (argon purging, pH variation) using Conjugated Dienes and Thiobarbituric acid reactive substances assays. The results showed that free iron ions cannot interact with oxygen. However, buffers (Citrate and phosphate) chelate iron ions (Fe (II)). Depending on the pH value and the type of buffer-Fe (II) complex, its prooxidant activity and spatial distribution are influenced. The complex charge defines the interactions with the oil-water interface, i.e., positively charged interfaces repel positively charged complexes which keeps the prooxidant away. The mechanistic understanding of this work will help formulators and product developers to choose the right buffer and emulsifier combination for oxidation sensitive emulsions.

Exploring the possibility of predicting long-term oxidative stability in prototype skincare formulations using various lipid oxidation initiators

OBJECTIVE

The purpose of this study was to identify an effective lipid oxidation initiator which could predict, within 1 month, the long-term oxidative stability of a prototype skincare formulation. The main purpose was to find a potential initiator not to assess oxidation stability of the formulations.

METHODS

Four initiators (below) were examined in three steps: Reaction kinetics using a Clark electrode (Oxygraph); Effect of adding an initiator on the product's physical and oxidative stability in prototype skincare formulations by visual observation, peroxide value and headspace GC-MS determination of volatile oxidation products; and Ability to differentiate unstable vs. stable prototype creams by initiator addition. The four initiators explored were: FeCl₂ /H₂ O₂ , FeCl₃ /ascorbic acid, 2,2'-Azobis(2,4-dimethylvaleronitrile) (AMVN) and 2,2'-Azobis(2-methylpropionamidine) dihydrochloride (AAPH) RESULTS: In Oxygraph, the initiator systems FeCl₂ /H₂ O₂ and FeCl₃ /ascorbic acid were good accelerators of oxygen consumption. The addition of FeCl₂ /H₂ O₂ to prototype formulations did not affect the physical stability. However, the addition of FeCl₃ /ascorbic acid to prototype formulations resulted in phase separation and FeCl₃ /ascorbic acid was therefore deemed unusable. Moreover, the addition of AAPH or AMVN resulted in an increased and decreased viscosity respectively. In the oxidation stability study, peroxide value increased significantly when AMVN was added. However, the peroxide value remained low for the other initiators and the control (no initiator). The secondary volatile oxidation product, butanal, increased most with the FeCl₂ /H₂ O₂ addition. Three out of the four initiators did not have the ability to rank the stable and unstable formulations in accordance with the result obtained for volatile oxidation products after 42 days of storage at 20°C of formulations without initiator. Only, FeCl₂ /H₂ O₂ was able to rank the formulations in accordance with the oxidative stability observed for volatile oxidation products after 42 days of storage.

CONCLUSION

FeCl₂ /H₂ O₂ showed potential as an initiator to predict the oxidative stability of skincare formulations, but more studies are needed to confirm the result in a broader range of products over a longer time.

Interfacial Antioxidants: A Review of Natural and Synthetic Emulsifiers and Coemulsifiers That Can Inhibit Lipid Oxidation

There has been strong interest in developing effective strategies to inhibit lipid oxidation in emulsified food products due to the need to incorporate oxidatively labile bioactive lipids, such as ω-3 fatty acids, conjugated linoleic acids, or carotenoids. Emulsifiers or coemulsifiers can be utilized to inhibit lipid oxidation in emulsions. Both of these molecular types can adsorb to droplet surfaces and inhibit lipid oxidation, but emulsifiers can also stabilize droplets against aggregation whereas coemulsifiers cannot. There are a host of existing emulsifiers, covalent conjugates, or physical complexes that have the potential to inhibit lipid oxidation by a variety of mechanisms. Existing emulsifiers with antioxidant potential consist of surfactants, phospholipids, proteins, polysaccharides, and colloidal particles. Conjugates and complexes are typically formed by covalently or physically linking together a surface-active molecule with an antioxidant molecule. This article reviews the molecular and physicochemical basis for the surface and antioxidant activities of emulsifiers and coemulsifiers, highlights the important properties of interfacial layers that can be engineered to control lipid oxidation, and outlines different kinds of existing emulsifiers, conjugates, and complexes that can be used to inhibit oxidation.