Antioxidant Properties of Aqueous Extract of Roasted Hulled Barley in Bulk Oil or Oil‐in‐Water Emulsion Matrix

Antioxidant properties of the aqueous extracts of hulled barley (Hordeum vulgare L.) that had been roasted at 210 °C for 20 min were determined in bulk oil and oil‐in‐water (O/W) emulsions. Bulk oils were heated at 60, 100, and 180 °C, and O/W emulsions were oxidized under riboflavin photosensitization. The content of phenolic compounds was analyzed by high‐performance liquid chromatography, and in vitro antioxidant assays were also conducted. The major phenolics contained in the aqueous extract of roasted hulled barley (AERB) were p‐coumaric, ferulic, protocatechuic, chlorogenic, 4‐hydroxybenzoic, and vanillic acids. Depending on the concentration and oxidation temperature, AERB had antioxidant or prooxidant properties in bulk oil. At 60 °C, AERB at a concentration of 0.5% acted as a prooxidant, whereas at 1.0% it acted as an antioxidant. At 100 °C, AERB acted as an antioxidant irrespective of concentration. In 180 °C conditions, 0.5% AERB acted as a prooxidant, whereas other concentrations of AERB acted as antioxidants. In the case of riboflavin photosensitized O/W emulsions, AERB showed antioxidant properties irrespective of concentration. Antioxidant abilities of AERB are affected by the food matrix, including bulk oil and O/W emulsions, and concentrations of AERB, even though diverse phenolic compounds may display high antioxidant properties in in vitro assays.     

Inhibition of oxidation of omega-3 polyunsaturated fatty acids and fish oil by quercetin glycosides

The antioxidant properties of naturally occurring flavonols, quercetin glycosides, were examined and compared with common food antioxidants butylated hydroxytoluene (BHT) and α-tocopherol. Antioxidants were incorporated into selected polyunsaturated fatty acids (PUFA) or fish oil in aqueous emulsions and bulk oil systems. The effectiveness of quercetin was similar to or greater than quercetin glycosides in inhibiting lipid oxidation in the oil-in-water emulsion systems when oxidation was induced by heat, light, peroxyl radical or ferrous ion. In bulk fish oil, C-3 glycosylation enhanced the antioxidant activity of quercetin. The effectiveness of quercetin and its glycosides was greater than that of α-tocopherol in the emulsions. Quercetin and quercetin-3-O-glucoside exhibited a better antioxidant activity than BHT in bulk fish oil; however, the reverse was observed in the emulsions of omega-3 PUFA and fish oil systems in agreement with the polar paradox theory. Quercetin and its glycosides were more effective than α-tocopherol in emulsion systems.     

Grape skin extracts as a sustainable source of antioxidants in an oil-in-water emulsion: an alternate natural approach to synthetic antioxidants using principal component analysis

Grape (Kyoho) skin, used to retard lipid oxidation in edible oil foods, was investigated to reduce lipid oxidation in an oil-in-water (O/W) emulsion during 20 day of storage. The antioxidant efficacy of Kyoho skin extracts in O/W emulsions was determined by the measurement of secondary oxidation products. Moreover, principal component analysis (PCA) was conducted to determine similarities between emulsions treated with or without Kyoho skin extracts and standards. The data revealed that Kyoho skin extracts exhibited >93% inhibition and reported a similar p-anisidine (4.30–20.71) and TBARS (6.08–11.15 mg MDA L⁻¹) values over the standards during 20 day of storage. PCA (PCs 1 (51.83%) and 2 (18.85%)) demonstrated a similarity in the contribution of Kyoho skin extracts over the synthetic antioxidants in O/W emulsion. Overall, these findings highlighted the possibility of using Kyoho skin extracts as natural antioxidants to decrease oxidative rancidity in foods.     

Effects of chitosan and collagen containing α-tocopherol on the oxidative stability in bulk oil and oil-in-water emulsion

To provide efficient antioxidant capacities, proper carriers are needed to protect antioxidants against oxidative stress. Collagen mesh structure or chitosan gel was loaded with α-tocopherol and their effects were evaluated in bulk corn oil or oil-in-water (O/W) emulsion at 60 °C. Added collagen and chitosan enhanced oxidative stability in corn oil and O/W emulsions at 60 °C compared to corn oils without carriers or with addition of α-tocopherol (p < 0.05). Stability of α-tocopherol in corn oil loaded in collagen or chitosan was significantly enhanced compared to that in oils without carriers (p < 0.05). In O/W emulsions, α-tocopherol loaded collagen showed higher antioxidant properties than α-tocopherol loaded chitosan (p < 0.05). Collagen mesh structure and chitosan gel retarded the rates of lipid oxidation efficiently in both food matrices when α-tocopherol was not loaded. Collagen mesh structure and chitosan gel can be useful carriers for α-tocopherol in bulk oil or O/W emulsion.     

Evaluation of Antioxidant Activity of Rosemary Extracts,Carnosol and Carnosic Acid in Bulk Vegetable Oils and Fish Oil and Their Emulsions

The antioxidant effectiveness of two rosemary extracts, carnosol and carnosic acid, was significantly influenced by the type of system tested (bulk oils vs oil-in-water emulsions), by the oil substrates, the methods used to follow oxi-dation, and the concentrations of test compounds. The rosemary extracts and compounds effectively inhibited conjugated diene hydroperoxide formation in corn oil, soya bean oil, peanut oil and fish oil, when tested in bulk. Test compounds also inhibited hexanal formation in bulk vegetable oils, and propanal and pentenal formation in bulk fish oils. In contrast, these test compounds were either inactive or promoted oxidation in the corresponding vegetable oil-in-water emulsions. In fish oil emulsions, however, the rosemary compounds inhibited the formation of conjugated diene and pentenal but not that of propanal. Interfacial phenomena may explain why the hydrophilic rosemary antioxidants afford more protection in the bulk oil systems by being oriented in the air–oil interface, and less protection in the oil-in-water emulsion systems by partitioning into the water phase.     

Antioxidants in lipid foods and their impact on food quality

This paper reviews the antioxidant properties of tocopherols and ascorbic acid in edible oils, and the impact of interfacial phenomena on their activities in emulsions and the effects of edible oil processing. Tocopherols are the most important natural antioxidants found in vegetable oil-derived foods. These antioxidants can interrupt lipid autoxidation by interfering with either the chain propagation or the decomposition processes. α-Tocopherol at high concentrations inhibits hydroperoxide decomposition but promotes hydroperoxide formation. The effect of antioxidants in inhibiting hydroperoxide decomposition may thus be critical in preserving food quality by reducing rancidity due to aldehyde formation. Ascorbic acid can regenerate α-tocopherol, inactivate metal initiators and reduce hydroperoxides. The activity of natural antioxidants is greatly affected by complex interfacial phenomena in emulsions and multi-component foods. In an oil-in-water emulsion system, the lipophilic antioxidants α-tocopherol and ascorbyl palmitate are more effective than in bulk oil, while the opposite trend is found for the hydrophilic antioxidants Trolox and ascorbic acid. The methodology to evaluate natural antioxidants must be carefully interpreted depending on whether oxidation is carried out in bulk oils or in emulsions, and what method is used to measure lipid oxidation.     

Role of emulsifier layer,antioxidants and radical initiators in the oxidation of olive oil-in-water emulsions

Lipid oxidation in oil-in-water (O/W) emulsions is largely affected by the properties of the interfacial layer surrounding the oil droplets. In this work, the effect of the emulsifier layer structure, presence of both hydrophilic and lipophilic antioxidants and radical initiators on the development of lipid oxidation in olive oil-in-water emulsions was investigated. The olive oil-in-water emulsion is a suitable model of low fat food emulsions. The rationale of the work was to study the role of the interfacial layer when both the antioxidants and the radical initiators came from the two different emulsion compartments. Emulsions were prepared by using food grade emulsifiers of the Tween series (polyoxyethylene sorbitan esters) in the water phase and Span 80 (sorbitan monoleate) in the oil phase. The properties of the interfacial layer were changed by using Tween 20, Tween 60, Tween 80, which have different hydrophobic tails. These systems were oxidized by means of both hydrophilic (AAPH (2,2′-azobis,2-methyl-propanimidamide dihydrochloride), AIPH (2,2′-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride) and lipophilic (AMVN (2,2′-azobis(2,4-dimethylvaleronitrile)) radical initiators at 40 °C. A continuous fluorescent method based on the front face technique allowed us to follow directly the development of oxidation in the whole emulsion. The combination Tween 80/Span 80 produced an interfacial layer more resistant to radical attack. Moreover, a polar paradox was verified also for radical initiators, while the results suggest that the best way to protect emulsions is to use a combination of antioxidants in both phases, to promote a synergy and the regeneration of antioxidants mediated by the interfacial layer.     

Impact of antioxidants dispersions on the stability and oxidation of water-in-olive-oil emulsions

Water-in-olive-oil emulsion stability was studied as a function of the composition of the water dispersed phase. In particular, different polyphenolic extracts from natural sources were dispersed in the olive oil and their impact on emulsion kinetic stability and susceptibility to oxidation was evaluated. As natural sources, extra virgin olive oil, olive mill waste and green tea leaves were chosen. To test their impact on emulsion properties, the emulsions were prepared with fixed aqueous phase content. As emulsifiers, a fixed percentage of a mixture Span 80 (sorbitan monoleate)/Tween 80 (polysorbate 80) was used. The effect of the antioxidant dispersion on emulsion oxidation was studied by triggering the oxidation reaction in the oil phase with the lipophilic radical initiator AMVN (2,2-azobis(2,4-dimethylvaleronitrile). Then, the oxidation reaction was followed by using diphenyl-1-pyrenylphosphine, which becomes fluorescent when it is oxidized by hydroperoxides. The impact of antioxidant dispersions on emulsion kinetic stability was studied by UV–Vis turbidity measurements. The oxidation results were correlated to antioxidant extracts oxygen radical adsorption capacity (ORAC) and to emulsion kinetic stability. On the whole, antioxidants dispersions delayed the oxidation reaction to different extents in dependence on their ORAC values and their components amphiphilicity. Remarkably, among the antioxidants tested, the aqueous polyphenol extract from virgin olive oil was the most effective because it protected emulsions both from oxidation and from phase separation. Additionally, from this set of experiments, the primary role of the interfacial properties of olive oil polyphenols was highlighted.     

Oxidative Stability in Oil‐in‐Water Emulsions with Quercetin or Rutin Under Iron Catalysis or Riboflavin Photosensitization

The effects of quercetin and rutin on the oxidative stability of oil‐in‐water (O/W) emulsions were tested under riboflavin (RF) photosensitization in the presence or absence of FeCl₂. The degree of oxidation in O/W emulsions was determined by headspace oxygen content, conjugated dienes, and lipid hydroperoxides. Quercetin chelated more metal than did rutin in iron catalyzed O/W emulsions. Generally, 0.1 mM quercetin and rutin was oxidative while 0.5 and 1.0 mM quercetin and rutin was antioxidative in O/W emulsions under RF photosensitization. Depending on the analysis method, the antioxidants had different strengths. The antioxidative or oxidative properties of quercetin and rutin vary in O/W emulsions and depend the quercetin and rutin concentrations and oxidative forces like transition metals, RF photosensitization, or a combination thereof.     

Release rate profiles of magnesium from multiple W/O/W emulsions

Water-in-oil-in-water (W/O/W) emulsions were formulated based on rapeseed oil, olive oil, olein and miglyol. Polyglycerol polyricinoleate and sodium caseinate were used as lipophilic and hydrophilic emulsifiers, respectively. Magnesium was encapsulated in the inner aqueous droplets. Emulsion stability was assayed through particle sizing and magnesium release at two storage temperatures (4 and 25 °C) over 1 month. Irrespective of the oil nature, both the primary W/O and W/O/W emulsions were quite stable regarding the size parameters, with 10-μm fat globules and 1-μm internal water droplets. Magnesium leakage from W/O/W emulsions was influenced by the oil type used in the formulation: the higher leakage values were obtained for the oils characterized by the lower viscosity and the higher proportion of saturated fatty acids. Magnesium release was not due to droplet–globule coalescence but rather to diffusion and/or permeation mechanisms with a characteristic rate that varied over time. In addition, W/O/W emulsions were resistant to various thermal treatments that mimicked that used in pasteurization processes. Finally, when W/O/W emulsions were placed in the presence of pancreatic lipase, the emulsion triglycerides were hydrolysed by the enzyme. These results indicated a possible use of W/O/W emulsions loaded with magnesium ions in food applications.     

Chemical profiles of heated perilla meal extracts and their antioxidant activities

Chemical profiles of aqueous or ethanolic extracts of 140, 170 and 200 °C-heated perilla meal were identified by GC-MS, and antioxidant properties of the extracts were observed via in vitro assays and in bulk oil or oil-in-water (O/W) emulsion. A total of 22 and 27 chemicals were found in aqueous and ethanolic extracts from non-heated samples, respectively. As the heating temperature increased to 200 °C, the carbohydrate and derivative contents decreased significantly (P < 0.05), whereas rosmarinic acid concentration decreased in both extracts. Ethanolic extracts possessed higher antioxidant activities than aqueous extracts based on the results of radical scavenging and ferric-reducing antioxidant power assays and the Rancimat assay, but there were no significant differences among samples (P > 0.05). In the case of O/W emulsions, aqueous extracts inhibited lipid oxidation more efficiently than ethanolic extracts at 50 °C. In particular, heat treatment decreased the antioxidant activities of ethanolic extracts and not aqueous extracts in the O/W emulsion system. Aqueous extracts are recommended in moisture-rich emulsion-based foods while ethanolic extracts are more suitable in a lipid-rich environment for enhancing oxidative stability.     

Evaluation of Antioxidant or Prooxidant Properties of Selected Amino Acids Using In Vitro Assays and in Oil‐in‐Water Emulsions Under Riboflavin Sensitization

The antioxidant properties of selected amino acids were tested using in vitro assays and oil‐in‐water (O/W) emulsions under riboflavin (RF) photosensitization. Headspace oxygen content, lipid hydroperoxides, and conjugated dienes were determined for the degree of oxidation. Riboflavin photosensitization was adapted as the oxidation driving force. In vitro assays showed that cysteine had the highest antioxidant properties followed by tryptophan and tyrosine. However, in O/W emulsions under RF photosensitization, tyrosine inhibited lipid oxidation whereas tryptophan acted as a prooxidant. Tryptophan accelerated the rates of oxidation in O/W emulsion without RF. The antioxidant properties of amino acids differed depending on the antioxidant determination methods, oxidation driving forces, and food matrices.     

Antioxidant Activity of the Essential Oil and Oleoresin of Zingiber Officinale Roscoe as Affected by Chemical Environment

Three different biochemical test systems were chosen based on their solubility to study the antioxidant activity of ginger extracts. Reducing power and DPPH^. scavenging activity tests were considered to produce hydrophilic environments and the H₂O₂ test was considered as creating a lipophilic environment. The average yields were 10.23 ± 1.02% and 0.48 ± 0.19% for oleoresin and essential oil, respectively. The content of total phenols was 67.6 ± 1.08 mg GAE/g of dry extract. In terms of EC₅₀, in hydrophilic environment standards, it showed the highest effects compared to ginger extracts, with oleoresin presenting more activity than essential oil. In contrast, except for quercetin, essential oil showed the best scavenging activity in inhibiting H₂O₂ compared to all other antioxidants. The present work demonstrated that, when using reducing power, DPPH· free radical scavenging and H₂O₂ scavenging assays, the same ginger extracts exhibit different antioxidant activities, which were affected not only by the extract itself but also by the chemical environment (hydrophilic/lipophilic).     

Effects of Green Tea Extract and α‐Tocopherol on the Lipid Oxidation Rate of Omega‐3 Oils,Incorporated into Table Spreads,Prepared using Multiple Emulsion Technology

Abstract: This study examined the effectiveness of fat and water soluble antioxidants on the oxidative stability of omega (ω)‐3 rich table spreads, produced using novel multiple emulsion technology. Table spreads were produced by dispersing an oil‐in‐water (O/W) emulsion (500 g/kg 85 camelina/15 fish oil blend) in a hardstock/rapeseed oil blend, using sodium caseinate and polyglycerol polyricinoleate as emulsifiers. The O/W and oil‐in‐water‐in‐oil (O/W/O) emulsions contained either a water soluble antioxidant (green tea extract [GTE]), an oil soluble antioxidant (α‐Tocopherol), or both. Spreads containing α‐Tocopherol had the highest lipid hydroperoxide values, whereas spreads containing GTE had the lowest (P < 0.05), during storage at 5 °C, while p‐Anisidine values did not differ significantly. Particle size was generally unaffected by antioxidant type (P < 0.05). Double emulsion (O/W/O) structures were clearly seen in confocal images of the spreads. By the end of storage, none of the spreads had significantly different G′ values. Firmness (Newtons) of all spreads generally increased during storage (P < 0.05). Practical Application: Lipid oxidation is a major problem in omega‐3 rich oils, and can cause off‐odors and off‐flavors. Double emulsion technology was used to produce omega‐3 enriched spreads (O/W/O emulsions), wherein the omega‐3 oil was incorporated into the inner oil phase, to protect it from lipid oxidation. Antioxidants were added to further protect the spreads by reducing lipid oxidation. Spreads produced had good oxidative stability and possessed functional (omega‐3 addition) properties.     

Lipid oxidation in base algae oil and water-in-algae oil emulsion: Impact of natural antioxidants and emulsifiers

The impact of natural hydrophilic antioxidants, metal chelators, and hydrophilic antioxidant/metal chelator mixture on the oxidative stability of base algae oil and water-in-algae oil emulsion was investigated. The results showed that green tea extract and ascorbic acid had greatest protective effect against algae oil oxidation and generated four day lag phase, whereas rosmarinic acid, grape seed extract, grape seed extract polymer, deferoxamine (DFO), and ethylenediaminetetraacetic acid (EDTA) had no significant protective effect. Besides, there was no synergistic effect observed between natural antioxidants and ascorbic acid. The emulsifiers are critical to the physicochemical stability of water-in-algae oil emulsions. Polyglycerol polyricinoleate (PGPR) promoted the oxidation of emulsion. Conversely, the protective effect on algae oil oxidation was appreciated when defatted soybean lecithin (PC 75) or defatted lyso-lecithin (Lyso-PC) was added. The role of hydrophilic antioxidants in emulsion was similar to that in algae oil except EDTA which demonstrated strong antioxidative effect in emulsion. The results could provide information to build up stable food products containing polyunsaturated fatty acids (PUFA).     

What Makes Good Antioxidants in Lipid-Based Systems? The Next Theories Beyond the Polar Paradox

The polar paradox states that polar antioxidants are more active in bulk lipids than their nonpolar counterparts, whereas nonpolar antioxidants are more effective in oil-in-water emulsion than their polar homologs. However, recent results, showing that not all antioxidants behave in a manner proposed by this hypothesis in oil and emulsion, lead us to revisit the polar paradox and to put forward new concepts, hypotheses, and theories. In bulk oil, new evidences have been brought to demonstrate that the crucial site of oxidation is not the air-oil interface, as postulated by the polar paradox, but association colloids formed with traces of water and surface active molecules such as phospholipids. The role of these association colloids on lipid oxidation and its inhibition by antioxidant is also addressed as well as the complex influence of the hydrophobicity on the ability of antioxidants to protect lipids from oxidation. In oil-in water emulsion, we have covered the recently discovered non linear (or cut-off) influence of the hydrophobicity on antioxidant capacity. For the first time, different mechanisms of action are formulated in details to try to account for this nonlinear effect. As suggested by the great amount of biological studies showing a cut-off effect, this phenomenon could be widespread in dispersed lipid systems including emulsions and liposomes as well as in living systems such as cultured cells. Works on the cut-off effect paves the way for the determination of the critical chain length which corresponds to the threshold beyond which antioxidant capacity suddenly collapses. The systematic search for this new physico-chemical parameter will allow designing novel phenolipids and other amphiphilic antioxidants in a rational fashion. Finally, in both bulk oils and emulsions, we feel that it is now time for a paradigm shift from the polar paradox to the next theories.     

Designing emulsion droplets of foods and beverages to enhance delivery of lipophilic bioactive components – a review of recent advances

Lipophilic bioactive compounds such as lipids, vitamins and phytochemicals serve important antioxidant, functional, nutritional and structural roles in the human body. Colloidal systems such as emulsions are particularly suitable matrices for the protection and delivery of these compounds. This article summarises the principal lipophilic bioactives important for human health and challenges associated with their delivery. It discusses the compositional and physical characteristics of emulsions in relation to bioactive delivery, and chemical stability aspects to consider when engineering efficient emulsion delivery systems. The literature shows that aspects such as oil type, droplet size, interfacial composition and solubilisation capacity impact bioactive availability and that their effects are bioactive specific. Therefore, emulsions must be tailored to the bioactives delivered. Much of the present knowledge is based on in vitro studies, and more data from animal and human models are required to better understand the relationship between emulsion characteristics and bioavailability of lipophilic bioactives.     

A novel water-repellent o/w emulsion using a new water-soluble amphiphilic polymer

A novel O/W (oil-in-water) emulsion cosmetic that has strong water repellency and a >>water-splash feel« was prepared using the amphiphilic polymer hydrophilic-hydrophobic modified polysaccharide (INCI/Sodium Stearoxy PG-Hydroxyethylcellulose Sulfonate). This emulsion is composed of a hydrophobic–hydrophilic modified polysaccharide/water/oil system with a small amount of lipophilic non-ionic surfactant (hydrophilic–lipophilic balance<5) added to obtain finely emulsified oil particles. Hydrophilic–hydrophobic modified polysaccharide was used as a thickener and polymer surfactant, and it produced a stable O/W emulsion without the addition of a hydrophilic surfactant. Several types of oil droplets decrease in size upon addition of various kinds of lipophilic surfactant due to the lowering of tension at the water/oil interface. Rheological measurements revealed that the strong network structure of hydrophilic–hydrophobic modified polysaccharide retained oil droplets without occurrence of phase inversion. Such an emulsion is very different from those made using conventional hydrophilic surfactants, and it is water repellent. This system was characterized by the presence of hydrophilic–hydrophobic modified polysaccharide, and the state of the emulsion could be controlled by the ratio of hydrophobic/hydrophilic moieties introduced into the polysaccharide.     

Effects of flavonoids on physical and oxidative stability of soybean oil O/W emulsions

Flavonoids have attracted attention due to pharmacological and antioxidative activities. The effects of flavonoids on the physical and oxidative stabilities of lecithin emulsified soybean oil-in-water (O/W) emulsions were investigated at 25°C during 29 days of storage. Addition of 100 ppm hesperidin, hesperitin, rutin, or quercetin improved the physical stability of O/W emulsions but did not change particle size values, compared to a control with no flavonoids during storage. Quercetin showed the highest antioxidant activity for inhibition of lipid oxidation based on lowered lipid hydroperoxide formation and 2-thiobarbituric acid reactive substances values in emulsions, followed by rutin, hesperitin, and hesperidin. Hesperidin and hesperitin did not affect antioxidative activities in O/W emulsions under metal ion-catalyzed conditions. Addition of hesperidin, hesperitin, rutin, and quercetin to soybean oil O/W emulsions improved the physical and oxidative stability of emulsions lacking added metal ions.     

O/W emulsion and W/O/W multiple emulsion: physical characterization and skin pharmacokinetic comparison in the delivery process of caffeine

The aim of this study was to compare the characteristics of an O/W emulsion and a W/O/W emulsion, formulated with similar ingredients. The physical properties of these two types of vehicles were characterized first. Using three types of in vitro models, human skin biopsies, nitrate acetate cellulose membranes and human reconstituted epidermis, the delivery potential of each vehicle for one hydrophilic drug, caffeine, was compared. The assessment of physical parameters, such as particle size, conductivity and rheological behavior enabled the nature of the test emulsions to be clearly identified. Clear differences were observed in the ability of each type of emulsion to deliver caffeine. Whatever the nature of the membrane used for the pharmacokinetic study, the absorption of caffeine was roughly two-fold lower (2.6 for human skin) when the W/O/W multiple emulsion was used as the vehicle. The concomitant determination of physical and kinetic properties of these two test emulsions allowed the W/O/W multiple emulsion and a simple O/W emulsion to be clearly differentiated.