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Models predicting lipid oxidation in oil-in-water (O/W) emulsions are a requirement for developing effective antioxidant solutions. Existing models do, however, not include explicit equations that account for composition and structural features of O/W emulsions. To bridge this gap, a mechanistic kinetic model for lipid oxidation in emulsions is presented, describing the emulsion as a one-dimensional three phase (headspace, water, and oil) system. Variation in oil droplet sizes, overall surface area of oil/water interface, oxidation of emulsifiers, and the presence of catalytic transition metals were accounted for. For adequate predictions, the overall surface area of oil/water interface needs to be determined from the droplet size distribution obtained by dynamic and static light scattering (DLS, SLS). The kinetic model predicted well the formation of oxidation products in both mono- and polydisperse emulsions, with and without presence of catalytic transition metals. • Mechanistic kinetic model describes lipid oxidation in oil-in-water (O/W) emulsions. • Compositional and structural features of O/W emulsions are included in the model. • Droplets with sizes <300 nm need to be accounted for in the model. • Kinetic rates of lipid oxidation vary with the droplet size. • Model provides good predictions for mono-and polydisperse emulsions. [ABSTRACT FROM AUTHOR]

Salts reduction/substitution have gained a lot interest from food industry since the US Food and Drug Administration (FDA) has issued a draft guidance for salt reduction. However how changes of salts in food formulation could influence lipid oxidation is still not fully understood. Using oil-in-water emulsions stabilized by a natural emulsifier – lecithin at pH 7.0 as a model system, this study evaluated how salts affect the physical parameters of the emulsion, the chelating activity of lecithin and thus the lipid oxidation of these emulsions. Results showed that salts increased the particle size, the negative charge of the oil droplets, and the amount of iron chelated by lecithin. Lipid oxidation lag phases were shortened by addition of salts, by 1 day and 2 days for lipid hydroperoxides and thiobarbituric acid reactive substances measurements respectively. These results provide some new insights on the mechanisms of how salts could affect the lipid oxidation of food emulsions. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the relative reaction rate of protein and lipid oxidation in different biphasic model systems (linoleic acid; liposome; emulsion) containing myofibrillar protein (MFP at 1, 8 and 20 mg/mL) under hydroxyl radical stress. Protein oxidation markers exhibited significant changes in 2 h: reduced tryptophan fluorescence intensity, carbonyl formation, and extensive polymerization of myosin. In contrast, no detectable changes ( P  > .05) in lipid peroxide occurred within 2 h except for samples with 1 mg/mL MFP which showed an early TBARS formation. Of the three biphasic systems, the oxidative stability of lipids followed the order of emulsion > linoleic acid > liposome, indicating the steric role of proteins. In general, MFP was more susceptible to radicals than lipids, and a higher protein:lipid ratio was associated with a slower TBARS production and more rapid protein oxidation, suggesting a sacrificing role of MFP to protect lipids. [ABSTRACT FROM AUTHOR]

• We investigated potential lipid oxidation product transfer between oil droplets. • Triglyceride-bound hydroperoxides are not prone to such a transfer. • Smaller, more hydrophilic molecules (e.g. 4-hydroperoxy-2-nonenal) can be transferred. • These molecules can also promote lipid oxidation when added to emulsions. Lipid oxidation is a major factor limiting the shelf life of food and other emulsion products. In this work, we explore which lipid oxidation products may transfer between oil droplets in model food emulsions stabilized by excess amounts of surfactant, and whether this affects the overall reaction. No significant differences in concentrations of triglyceride-bound hydroperoxides were found before and after mixing 'clean' oil droplets with pre-oxidized ones. Shorter and more hydrophilic lipid oxidation products, such as 4-hydroperoxy-2-nonenal and 2,4-decadienal, were found to equilibrate between oil droplets within 30 min. Adding exogenous 4-hydroperoxy-2-nonenal to an emulsion led to overall higher lipid oxidation values, although this effect was not systematic nor instantaneous. Therefore, it may be questioned whether transfer and subsequent initiation are always relevant for oxidizing emulsion systems. In future research, this question should be addressed for complex emulsions that are closer to real-life food products. [ABSTRACT FROM AUTHOR]

The initiation of lipid autoxidation within single oil droplets in Tween-20-stabilized oil-in-water emulsion was achieved by highly focused two-photon (2P) irradiation at excitation wavelength ( λ ex ) 700 nm. The radical formation was enhanced by inclusion of the photo-cleavable radical initiator di- tert -butyl peroxide (DTBP) into the droplets, and demonstrated with confocal microscopy using radical-sensitive probe BODIPY 665/676 . The radical chain reactions progressed up to 60 μm; however, there were no indications of oxidation in neighboring droplets demonstrating that radicals and oxidized probe molecules were not able to migrate between oil droplets. In addition, the spatial propagation of lipid autoxidation increased with the degree of oil unsaturation. [ABSTRACT FROM AUTHOR]

Lipid oxidation in oil-in-water (O/W) emulsions is an important factor determining the shelf life of food products. Salts are often present in many types of emulsion based food products. However, there is limited information on influence of salts on lipid oxidation in O/W emulsions. Thus, the purpose of this study was to examine the effects of sodium and potassium chloride on lipid oxidation in O/W emulsions. Tween 20 stabilized corn O/W emulsions at pH 7.0 were prepared with different concentrations of sodium chloride with or without the metal chelators. NaCl did not cause any changes in emulsion droplet size. NaCl dose-dependently promoted lipid oxidation as measured by the lipid oxidation product, hexanal. Both deferoxamine (DFO) and ethylenediaminetetraacetic acid (EDTA) reduced lipid oxidation in emulsions with NaCl, with EDTA being more effective. Potassium chloride showed similar impact on lipid oxidation as sodium chloride. These results suggest that salts are able to promote lipid oxidation in emulsions and this effect can be controlled by metal chelators. [ABSTRACT FROM AUTHOR]

In food systems, lipid oxidation can cause oxidation of other molecules. This research for the first time investigated oxidative degradation of β-glucan induced by lipid oxidation using an oil-in-water emulsion system which simulated a multi-phased aqueous food system containing oil and β-glucan. Lipid oxidation was monitored using peroxide value and hexanal production while β-glucan degradation was evaluated by viscosity and molecular weight measurements. The study showed that while lipid oxidation proceeded, β-glucan degradation occurred. Emulsions containing β-glucan, oil and ferrous ion showed significant viscosity and molecular weight decrease after 1 week of oxidation at room temperature. Elevated temperature (40 °C) enhanced the oxidation reactions causing higher viscosity drop. In addition, the presence of β-glucan appeared to retard the hexanal production in lipid oxidation. The study revealed that lipid oxidation may induce the degradation of β-glucan in aqueous food systems where β-glucan and lipids co-exist. [ABSTRACT FROM AUTHOR]

Highlights: [•] Influence of authentic human gastric juice on oxidation of marine lipids is evaluated. [•] Marine lipids in emulsion and liposomes oxidised during a modelled digestion period. [•] No difference was found between oxidation in an authentic gastric juice and a hydrochloric acid solution. [•] Gastric juice inhibited pro-oxidative activity of dietary iron ions, but not met-hemoglobin. [•] Beverages may both positively and negatively affect post-prandial oxidation of marine lipids. [Copyright &y& Elsevier]

Highlights: [•] Structured lipid-based infant formula emulsion was developed. [•] Response surface methodology was successfully applied to optimise the formulation. [•] Increased lecithin concentration led to a decrease in lipid oxidation. [•] Monoacylglycerol content affected particle size and emulsion viscosity. [Copyright &y& Elsevier]

• A lipid and protein co-oxidation model containing fish oil and WPI was established. • Resveratrol significantly suppressed lipid oxidation and protein carbonylation. • Formation of MDA-bound proteins in WPI was restrained by resveratrol. • Decrease in protein digestibility under oxidation was mitigated by resveratrol. • Phenol-protein interactions also contribute to physicochemical changes in WPI. In this study, the impact of resveratrol (RES) on co-oxidation of lipid and protein in a fish oil-fortified whey protein isolate (WPI) emulsion was investigated. Oil-in-water (O/W) emulsions containing 1% fish oil, 6 mg/mL of WPI and RES (0.08 ~ 2 mM) were oxidatively stressed using a Fenton system at 25 °C for 24 h. The incorporation of RES significantly suppressed lipid oxidation (TBARS) and protein carbonylation. Oxidation-induced decrease on protein sulfhydryl content and surface hydrophobicity were partially attenuated by RES, but protein tryptophan fluorescence was further decreased with the increased concentration of RES. Visualization of protein patterns and MDA-bound protein suggested that RES is capable of inhibiting protein modification induced by secondary products of lipid oxidation. Significant decrease in protein digestibility under oxidizing condition was also mitigated by RES. Our study contributes to the exploration of complicated interactions between oxidized lipids and proteins when phenolic compounds are present. [ABSTRACT FROM AUTHOR]

Abstract: Effect of tannic acid (0.02% and 0.04%) and ethanolic kiam wood extract (EKWE) (0.04% and 0.08%) on lipid oxidation and textural properties of fish emulsion sausages during 20days of refrigerated storage was investigated. Control samples (C) had the highest peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS) value up to day 16 and 8 of storage, respectively. With the addition of tannic acid and EKWE, PV and TBARS values in the sausages were retarded effectively, compared to the control (P <0.05), especially when the tannic acid and EKWE at higher level were used. At the same level, EKWE showed the lower ability in retarding the lipid oxidation, in comparison with tannic acid. Tannic acid at both levels (0.02% and 0.04%) was also effective in retarding the formation of fishy odour in the samples throughout the storage, compared to the control and EKWE treated samples (P <0.05). Both tannic acid and EKWE had no detrimental effect on the sensory attributes of sausages. However, EKWE treated sample had lower L ∗ and higher a ∗ and ΔE ∗ values, compared to the control samples (P <0.05). After 20days of storage, the sample added with 0.04% tannic acid had higher hardness, gumminess and chewiness, compared with others (P <0.05). Samples added with 0.04% tannic acid also displayed more compact structure with no visible voids. Furthermore, oil droplets with smaller size were dispersed more uniformly, compared to others. Thus, tannic acid (0.02% and 0.04%) and EKWE (0.08%) were effective in retarding lipid oxidation and fishy odour development as well as could maintain the textural properties of fish emulsion sausages during the refrigerated storage of 20days. [Copyright &y& Elsevier]

Abstract: Free fatty acids are strong prooxidants in both bulk and emulsified oils. Addition of oleic acid to an oil-in-water emulsions increased lipid hydroperoxide and hexanal formation at free fatty acid concentrations as low as 0.1% of the lipid. The prooxidant effect of free fatty acids was dependent on fatty acid type with lipid oxidation rates being in the order of linolenic

Abstract: Bulk oils and oil-in-water emulsions were subjected to high hydrostatic pressure (HHP) (200, 650MPa) treatment so as to estimate the effect of applied pressures on lipid oxidation. HHP-treated and non-treated samples were left to autoxidise under accelerated conditions (2weeks, 70°C) and their oxidative status was periodically estimated by measurement of conjugated dienes and peroxide value. Total changes of thiobarbituric acid-reactive substances were recorded as additional oxidative markers for emulsions. Results showed an increase in oxidation as pressure was increased especially at 650MPa. Lipid oxidation rates that were more pronounced for HHP-treated samples can be correlated to measured dissolved oxygen that was also higher. HHP did not seem to have an effect on emulsion droplet size. The addition of Majorana syriaca (200ppm) ethyl acetate extract led to protection against lipid oxidation under HHP and atmospheric conditions, 20.9–38.7% and 28.9–43.2%, respectively. It was observed that the antioxidant effect of M. syriaca extract under HHP was weaker. [ABSTRACT FROM AUTHOR]

Abstract: The efficacy of a previously developed antioxidative potato protein hydrolysate (PPH) for the stabilisation of oil droplets and inhibition of lipid oxidation in soybean oil-in-water (O/W) emulsions was investigated. Emulsions (10% lipid, pH 7.0) with PPH-coated oil droplets were less stable than those produced with Tween 20 (P <0.05). However, the presence of PPH, whether added before or after homogenisation with Tween 20, retarded emulsion oxidation, showing reduced formation of peroxides up to 53.4% and malonaldehyde-equivalent substances up to 70.8% after 7-d storage at 37°C (P <0.05), when compared with PPH-free emulsions. In the emulsions stabilised by PPH+Tween 20, 8–15% of PPH was distributed at the interface. Adjustment of the pH from 3 to 7 markedly increased ζ-potential of such emulsions (P <0.05). Inhibition of lipid oxidation by PPH in soybean O/W emulsions can be attributed to both chemical and physical (shielding) actions. [Copyright &y& Elsevier]

Abstract: Antioxidative activities of different phenolic compounds (catechin, caffeic acid, ferulic acid and tannic acid) at various levels were determined by different assays. Among all the phenolic compounds tested, tannic acid exhibited the highest 2,2-diphenyl-1-picryl hydrazyl (DPPH) and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activities and ferric reducing antioxidant power (FRAP). Nevertheless, catechin showed the highest metal chelating activity (P <0.05), whereas caffeic acid had the highest lipoxygenase (LOX) inhibitory activity (P <0.05). The impact of different phenolic compounds at a level of 100mg/l on lipid oxidation of menhaden oil-in-water emulsion and mackerel mince was investigated. Tannic acid showed the highest efficacy in retardation of lipid oxidation for both model systems as evidenced by the lower peroxide value (PV), conjugated diene (CD) and thiobarbituric acid-reactive substances (TBARS) values. This was also related with the lower non-heme iron content in tannic acid treated samples. Tannic acid was therefore considered as the most potential natural antioxidant for controlling oxidation of fish oil-in-water emulsion and fish mince, whereas ferulic acid seemed to possess the lowest preventive effect on lipid oxidation. [Copyright &y& Elsevier]

Abstract: In oil-in-water emulsions, the physical location of antioxidants has been postulated to be one of the most important factors impacting activity. The purpose of this research was to examine how the esterification of various hydrocarbon chains (C4, C8, or C12) onto chlorogenic acid (CGA) influenced physical properties and antioxidant activity in menhaden oil-in-water emulsions. Both surface activity and partitioning of CGA and its hydrocarbon esters into the lipid phase of oil-in-water emulsions increased with increasing size of the hydrocarbon chain. When CGA and its esters were added to a menhaden oil-in-water emulsion at concentration that resulted in equal free radical scavenging activity, CGA, butyl CGA and octyl CGA had similar antioxidant activity while dodecyl CGA was ineffective. These results suggest that phenolic antioxidants conjugated with hydrocarbon chains are more highly associated with lipid emulsions droplets, but these changes in physical properties did not increase antioxidant activity. [Copyright &y& Elsevier]

Abstract: Iron (Fe3+) was encapsulated within the internal aqueous phase of water-in-oil-in-water (W/O/W) emulsions, and then the impact of this iron on the oxidative stability of fish oil droplets was examined. There was no significant change in lipid droplet diameter in the W/O/W emulsions during 7days storage, suggesting that the emulsions were stable to lipid droplet flocculation and coalescence, and internal water diffusion/expulsion. The initial iron encapsulation (4mg/100g emulsion) within the internal aqueous phase of the water-in-oil (W/O) emulsions was high (>99.75%), although, a small amount leaked out over 7days storage (≈10μg/100g emulsion). When W/O/W emulsions were mixed with fish oil droplets the thiobarbituric acid-reactive substances (TBARS) formed decreased (compared to fish oil droplets alone) by an amount that depended on iron concentration and location, i.e., no added iron

Abstract: Grape phenolic compounds were obtained from grape (Vitis vinifera) pomace by pressing and posterior maceration. Phenolics resulting of the crude grape extract were fractionated by preparative chromatography. The ability of fractions, containing flavanol monomers, oligomers (procyanidins) and glycosylated flavonols, for inhibiting oxidation of fish lipids was determined. The tests were conducted in fish oils, fish oil-in-water emulsions and in fatty fish species such as mackerel during frozen storage. Partitioning coefficients of grape phenolics showed high solubility in the aqueous media and low in oily media. The results suggest that an optimal combination of procyanidin, degree of polymerization and percentage galloylation may be related to the highest antioxidant efficacy of grape polyphenols in the different systems tested. Monomers were more effective in oily systems. Flavanol oligomers were the most potent inhibitors of oxidation in emulsions and in frozen fish muscle. [Copyright &y& Elsevier]