Effects of lipophilic and hydrophilic antioxidants in oil-in-water emulsions under chlorophyll photosensitization

Antioxidative or prooxidative properties of α-tocopherol, Trolox, ascorbic acid, and ascorbyl-palmitate at the concentration of 0.1 and 1.0 mM were determined in oil-in-water (O/W) emulsions under chlorophyll photosensitization. Headspace oxygen depletion, lipid hydroperoxides, and headspace volatile analyses were conducted to determine the oxidative stability of O/W emulsions. For 32 h visible light irradiation, depleted headspace oxygen content in O/W emulsions were in the order of samples containing Trolox, ascorbic acid, ascorbyl palmitate, α-tocopherol, without antioxidants under light, and samples in the dark, which implies that all the added compounds acted prooxidant. These prooxidative properties of added compounds can be observed in the results of lipid hydroperoxides and headspace volatiles. Samples containing ascorbic acid and ascorbyl palmitate retained higher chlorophyll content than those containing Trolox up to 16 h. Increases of concentration of Trolox, ascorbic acid, and ascorbyl palmitate from 0.1 to 1.0 mM increased the lipid oxidation products whereas α-tocopherol decreased the degree of lipid oxidation implying α-tocopherol may not share the same prooxidant mechanisms compared to other compounds in chlorophyll sensitized O/W emulsions.     

Effects of solubility characteristics of sensitiser and pH on the photooxidation of oil in tuna oil-added acidic O/W emulsions

The effects of sensitisers and pH on the oil oxidation of acidic O/W emulsions were studied under light by measuring hydroperoxide content and headspace oxygen consumption in the emulsions. The emulsions consisted of canola and tuna oil (2:1 w/w, 32%), diluted acetic acid (64%), egg yolk powder (4%), chlorophyll b or erythrosine (5 μM), and/or diazabicyclooctane (DABCO) or sodium azide (0.5 M). The emulsion pH values were 2.67, 3.68, and 6.27. Chlorophyll increased oil oxidation in the emulsion under light via singlet oxygen production while erythrosine did not. DABCO significantly decreased photooxidation of the oil containing chlorophyll, suggesting singlet oxygen involvement. However, sodium azide increased photooxidation of the oil containing chlorophyll possibly via azide radical production under acidic conditions. The oil photooxidation was higher in the emulsion containing chlorophyll at pH 6.27 than at pH 2.67 or 3.68, primarily by singlet oxygen and secondarily by free radicals produced from hydroperoxide decomposition.     

Antioxidant capacities of α-tocopherol,trolox, ascorbic acid,and ascorbyl palmitate in riboflavin photosensitized oil-in-water emulsions

Antioxidant capacities of α-tocopherol, trolox, ascorbic acid, and ascorbyl palmitate at 0.01, 0.1, and 1.0 mM in riboflavin photosensitized oil-in-water (O/W) emulsions were determined using headspace oxygen depletion, lipid hydroperoxide, and headspace volatile analyses. After 32 h visible light irradiation, headspace oxygen in O/W emulsions without adding antioxidants, with 1.0 mM α-tocopherol, trolox, ascorbic acid, and ascorbyl palmitate decreased to 18.50%, 18.85%, 16.01%, 17.92%, and 19.88%, respectively, whereas those samples in the dark were 20.74%. Trolox and ascorbic acid acted as prooxidants while their lipophilic counterparts, α-tocopherol and ascorbyl palmitate, respectively showed antioxidant properties. Similar antioxidative or prooxidative properties of the tested compounds can be observed in the results of lipid hydroperoxides and headspace volatiles. However, the prooxidant and antioxidant properties of the tested compounds were not clearly shown at 0.01 and 0.1 mM concentration. Both the type and concentration of antioxidants influenced the antioxidant capacities in riboflavin photosensitized O/W emulsions.     

Stability of Bisphenol A (BPA) in Oil-In Water Emulsions under Riboflavin Photosensitization

Effects of riboflavin photosensitization on the degradation of bisphenol A (BPA) were determined in oil-in-water (O/W) emulsions containing ethylenediaminetetraacetic acid (EDTA) or sodium azide, which are a metal chelator or a singlet oxygen quencher, respectively. Also, the distribution of BPA between the continuous and dispersed phases in O/W emulsions was analyzed by high-performance liquid chromatography (HPLC). The concentration of BPA in O/W emulsions significantly decreased by 38.6% after 2 h under visible light irradiation and in the presence of riboflavin (P < 0.05). Addition of EDTA and sodium azide protected the decomposition of BPA significantly in a concentration dependent manner (P < 0.05), which implies both transition metals and singlet oxygen accelerate the photodegradation of BPA in O/W emulsions. Approximately 21.7% of the BPA was distributed in the 2.5% (w/v) dispersed lipid particles and 78.3% was in the continuous aqueous phase of the emulsions. The amount of BPA in aqueous phase decreased faster than the amount of BPA in the lipid phase during riboflavin photosensitization (P < 0.05). Thus, the BPA in the aqueous phase was the major target of riboflavin photodegradation in O/W emulsions. Practical Application: Concentration of BPA, an endocrine disrupting chemical, was decreased significantly in oil-in-water emulsions under riboflavin and visible light irradiation. BPA in continuous aqueous phase was major target of riboflavin photosensitization. However, BPA was distributed more densely in lipid phase and more protected from riboflavin photosensitized O/W emulsions. This study can help to decrease the level of BPA in foods made of O/W emulsions containing riboflavin, which could be displayed under visible light irradiation.     

Influence of heat processing and calcium ions on the ability of EDTA to inhibit lipid oxidation in oil-in-water emulsions containing omega-3 fatty acids

The nutritional benefits of ω-3 fatty acids make them excellent candidates as functional food ingredients if problems with oxidative rancidity can be overcome. Oil-in-water emulsions were prepared with 2% salmon oil, stabilized by 0.2% Brij 35 at pH 7. To determine the effects of heating (50–90 °C), ethylenediaminetetraacetic acid (EDTA), and calcium on the oxidative and physical stability of salmon oil-in-water emulsions, particle size, thiobarbituric acid reactive substances (TBARS), and lipid hydroperoxides were measured. The heat-processed emulsions showed no significant difference, in particle size, TBARS or hydroperoxides during storage, from unheated emulsions. Above 2.5 μM, EDTA dramatically decreased lipid oxidation in all samples. Addition of calcium to emulsions containing 7.5 μM EDTA significantly increased both TBARS and hydroperoxide formation when calcium concentrations were 2-fold greater than EDTA concentrations. These results indicate that heat-processed salmon oil-in-water emulsions with high physical and oxidative stability could be produced in the presence of EDTA.     

Improvement of the lipid oxidative stability of soybean oil-inwater emulsion by addition of daraesoon (shoot of <Emphasis Type="Italic">Actinidia arguta</Emphasis>) and samnamul (shoot of <Emphasis Type="Italic">Aruncus dioicus</Emphasis>) extract

The effect of 75% ethanol extract of daraesoon and samnamul (200 mg/kg) on the lipid oxidation of soybean oil-in-water (4:6, w/w) emulsion containing iron (5 mg/kg) in dark conditions at 25°C was studied by determining headspace oxygen and hydroperoxide contents. Polyphenol, carotenoid, and chlorophyll contents were also evaluated using spectrophotometry. The headspace oxygen contents were higher and hydroperoxide contents were lower (p<0.05) in the emulsions with added daraesoon and samnamul extracts compared with the control emulsion without the extract. The antioxidant activity of the daraesoon and samnamul extracts in the lipid oxidation of the emulsions was comparable to that of dibutylhydroxytoluene at 200mg/kg. Polyphenols, carotenoids, and chlorophylls were degraded during oxidation of the emulsions, possibly due to a role of the antioxidants. The results suggest that contribution to the improved lipid oxidative stability of the emulsion with added samnamul and daraesoon would be due to polyphenols and pigments, respectively.     

Effects of riboflavin-photosensitization on the formation of volatiles in linoleic acid model systems with sodium azide or D2O

Effects of riboflavin-photosensitization on volatile formations were studied in linoleic acid model systems with sodium azide or D₂O. Linoleic acid with riboflavin solution were stored under light or in the dark and volatiles were analyzed by a combination of solid phase microextraction (SPME), gas chromatography (GC), and mass spectrometry (MS). Riboflavin-photosensitization produced 27.9% more total volatiles than samples stored in the dark for 16 h. Addition of sodium azide decreased the total volatiles by 28.4% compared to samples without sodium azide. Linoleic acid in D₂O had higher increases in total volatiles than samples in H₂O system. Decrease of total volatiles in samples with sodium azide and increase of total volatiles in D₂O sample indirectly showed the presence of singlet oxygen in riboflavin-photosensitization. Hexanal, 2-heptenal, 1-octen-3-ol, 2-octenal, and 2,4-decadienal were greatly influenced by the addition of sodium azide and in D₂O, which indicates that formation of these volatiles was related to singlet oxygen oxidation. Especially, 2-heptenal showed the highest peak area among volatiles under riboflavin-photosensitized linoleic acid for 16 h.     

Effects of caffeic acid and bovine serum albumin in reducing the rate of development of rancidity in oil-in-water and water-in-oil emulsions

The antioxidant properties of caffeic acid and bovine serum albumin in oil-in-water and water-in-oil emulsions were studied. Caffeic acid (5 mmol/kg emulsion) showed good antioxidant properties in both 30% sunflower oil-in-water (OW) and 20% water-in-sunflower oil emulsions (WO), pH 5.4, during storage at 50 °C. Although bovine serum albumin (BSA) (0.2%) had a slight antioxidant effect, the combination of caffeic acid and BSA showed a synergistic reduction in the rate of development of rancidity, with significant reductions in concentration of total volatiles, peroxide value (PV) and p-anisidine value (PA) for both emulsion types. The synergistic increase in stability of the OW and WO emulsions containing BSA and caffeic acid was 102.9% and 50.4% respectively based on total oxidation (TOTOX) values, which are calculated as 2PV + PA, with greater synergy calculated if based on formation of headspace volatiles. The OW emulsion was more susceptible to the development of headspace volatiles by oxidation than the WO emulsion, even though the degree of oxidation assessed by the TOTOX value was similar.     

Effects of α-tocopherol on the oxidative stability and incorporation of deuterium in volatiles from a linoleic acid-deuterium model system

The effects of α-tocopherol on the oxidative stability and incorporation of deuterium in volatiles were evaluated in linoleic acid-water model systems treated at 60°C by analyzing headspace oxygen depletion, formation of lipid hydroperoxides, and profiles of headspace volatiles. Deuterium oxide accelerated the rates of linoleic acid oxidation compared to samples in deuterium-free water. As the concentration of α-tocopherol increased from 0 to 1500 ppm, the consumption of headspace oxygen and the formation of volatiles decreased, whereas the contents of lipid hydroperoxides did not decrease in the linoleic acid-water system. The mass to charge ratios (m/z) of volatiles in linoleic aciddeuterium oxide were significantly higher than those with deuterium oxide-free water. Generally, the presence of α-tocopherol decreased the mass to charge ratios (m/z) of volatiles including pentanal, hexanal, t-2-heptenal, and 2-octenal, implying that α-tocopherol may be involved in the aldehyde formation from lipid oxidation.     

Contribution of minor compounds present in the peppermint (<Emphasis Type="Italic">Mentha piperita</Emphasis>) to the iron-catalyzed lipid oxidation of soybean oil-in-water emulsion

This study evaluated contribution of minor compounds naturally present in peppermint (Mentha piperita) to the iron-catalyzed lipid oxidation of oil-in-water emulsion. Emulsions consisted of tocopherol-stripped soybean oil and pH 4.0 citrate buffer (4:6, w/w) with iron. Minor compounds included α-tocopherol, rosmarinic acid, caffeic acid, β-carotene, and chlorophyll b at natural concentration in 400 ppm of the peppermint extract. The emulsions were oxidized in the dark, and headspace oxygen contents, hydroperoxide contents, and p-anisidine values were determined. Addition of phenolic compounds decreased headspace oxygen consumption and hydroperoxide and p-anisidine values of emulsions, however, β-carotene or chlorophyll b tended to increase them. The results suggest that tocopherols at low concentration were the most important to reduce lipid oxidation of emulsions via radical scavenging, followed by high contents of polyphenols via radical scavenging and iron-chelation. Carotenoids and chlorophylls should be precisely controlled even in the dark, possibly due to their oxidation products.     

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.     

Effects of emulsifier charges on the oxidative stability in oil-in-water emulsions under riboflavin photosensitization

The oxidative stability in oil-in-water (O/W) emulsions containing different emulsifier charges was tested under riboflavin photosensitization by analysis of headspace oxygen content and lipid hydroperoxides. Sodium dodecyl sulfate (SDS), Tween 20, and cetyltrimethylammonium bromide (CTAB) were selected as anionic, neutral, and cationic emulsifiers, respectively. The O/W emulsions containing CTAB had lower oxidative stability than those with SDS and Tween 20. The addition of ethylenediaminetetraacetic acid, a well-known metal chelator, increased the oxidative stability in O/W emulsions, irrespective of emulsifier charges. Oxidative stability in Tween 20-stabilized emulsions decreased in FeCl₃ and FeCl₂ concentration-dependent manner. However, oxidative stability in samples containing CTAB increased up to 0.5mM of FeCl₃ and FeCl₂ and then decreased, which implies that CTAB act differently during lipid oxidation compared to SDS and Tween 20.     

Effects of light and lipids on chlorophyll degradation

Stability of chlorophylls was studied in a system of paraffin oil with added oleic acid or triolein under 1,700 lx and in the dark. Chlorophyll contents were determined using HPLC. Sample oxidation was evaluated using the headspace oxygen content based on GC and the peroxide value. The chlorophyll content decreased with time and was higher and decreased faster under light than in the dark. Singlet oxygen was involved in chlorophyll degradation under light. Chlorophyll degradation was lower and slower in samples with added lipids than in samples without lipids. Protection of chlorophyll from photodegradation was greater using triolein than using oleic acid. Oxidation was slightly higher in samples with added lipids than in samples without lipids, however, there was no significant (p>0.05) difference between samples with added oleic acid or triolein. Decreased chlorophyll degradation under light by lipids is due to competition between lipids and chlorophyll for singlet oxygen.     

Oxidative stability of oil-in-water emulsions stabilised with protein or surfactant emulsifiers in various oxidation conditions

Many studies have investigated the effect of emulsifiers on the oxidative stability of oil-in-water (O/W) emulsions. A better oxidative stability of surfactant-stabilised O/W emulsions as compared to protein-stabilised emulsions has been recently shown in conditions when the major part of the emulsifier is adsorbed at the oil-water interface and oxidation is induced by iron−ethylenediaminetetraacetic acid (EDTA) complex. In this work, the contribution of the interfacial layer to the oxidation of emulsified lipids is investigated under various incubation conditions, involving different oxidation mechanisms. O/W emulsions were formulated at pH 6.7 with limited amounts of emulsifiers in the aqueous phase. Emulsions were incubated either at 33 °C without initiator at 25 °C in the presence of iron/ascorbate, metmyoglobin or 2,2′-azobis(2-amidinopropane)-dihydrochloride (AAPH). Oxygen uptake and volatile compound formation confirmed that protein-stabilised emulsions are less oxidatively stable than Tween 20-stabilised ones. This work also shows complex oxidative interrelationships between oxidation initiator and certain proteins, such as β-casein and bovine serum albumin.     

Antioxidant mechanisms of Trolox and ascorbic acid on the oxidation of riboflavin in milk under light

Antioxidant activities and the mechanism of water-soluble Trolox and ascorbic acid on the oxidation of riboflavin in milk were studied. Trolox or ascorbic acid at 0, 100, 250, 500, or 1000 ppm was added to milk with or without added 50 ppm riboflavin and stored under light at 27 °C. Headspace oxygen was analysed by GC and Trolox, ascorbic acid, and riboflavin were determined by HPLC. The headspace oxygen of milk with added 50 ppm riboflavin depleted faster than that of milk without added riboflavin (p < 0.05). Trolox and ascorbic acid decreased during storage under light and riboflavin was completely destroyed within 24 h. As the concentration of Trolox or ascorbic acid increased, the riboflavin loss decreased. Riboflavin, Trolox, and ascorbic acid competed to react with singlet oxygen which was formed in the presence of riboflavin under light. Trolox and ascorbic acid protected riboflavin in milk under light by reacting with singlet oxygen.     

Antioxidant and emulsifying properties of potato protein hydrolysate in soybean oil-in-water emulsions

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.     

Singlet Oxygen Quenching Effects of Phosphatidylcholine in Emulsion Containing Sunflower Oil

ABSTRACT:  Effects of phosphatidylcholine (PC) on the oxidation of oil by singlet oxygen in a W/O microemulsion and an emulsion food model containing tocopherol-stripped sunflower oil (TSSO) have been studied. The W/O microemulsion consisted of methylene chloride, butanol, and sodium dodecyl sulfate with PC (0, 250, 1000 ppm) and TSSO (0, 3.3, 16.5, 33 mg/mL). Production of singlet oxygen in the microemulsion was done chemically with hydrogen peroxide in the presence of sodium molybdate, and indirectly evaluated by rubrene oxidation at A₅₂₉. The emulsion food model consisted of TSSO, distilled water, and xanthan gum with addition of 250 ppm PC and 4 ppm chlorophyll b, and was placed at 25 °C under fluorescent lights (1700 lux) for 24 h. The oxidation of TSSO was determined by thin-layer chromatography and values of conjugated dienoic acid (CDA) and peroxides (POV). PC significantly decreased the oxidation of rubrene and TSSO in the W/O microemulsion, but its content was decreased to approximately one-half by a 20-min reaction, indicating its degradation. This clearly shows that PC acted as an antioxidant via chemical quenching of singlet oxygen in the W/O microemulsion. A possible synergism between PC and TSSO was observed in singlet oxygen quenching in the microemulsion. PC also significantly decreased the chlorophyll-photosensitized oxidation of TSSO in the emulsion food model, possibly by singlet oxygen quenching. This study clearly suggested that PC be used as an antioxidant to improve the lipid oxidative stability of an emulsion food containing chlorophyll under light.     

Impact of iron encapsulation within the interior aqueous phase of water-in-oil-in-water emulsions on lipid oxidation

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 7 days storage, suggesting that the emulsions were stable to lipid droplet flocculation and coalescence, and internal water diffusion/expulsion. The initial iron encapsulation (4 mg/100 g 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 7 days storage (≈10 μg/100 g 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 < iron in external aqueous phase < iron in internal aqueous phase. These differences were attributed to the impact of W/O droplets on the concentration and location of iron and lipid oxidation reaction products within the system.     

Effects of Chlorophyll and β-Carotene on the Oxidation Stability of Olive Oil

Virgin olive oil was purified by silicic acid column chromatography to remove non-triglyceride components. The effects of chlorophyll and β-carotene on the oxidation stability of purified olive oil were studied by a combination of measuring peroxide value and oxygen disappearance in the headspace of sample bottles by gas chromatography. Chlorophyll in the purified oil acted as a photosensitizer for singlet oxygen formation under light. β-carotene minimized lipid oxidation of purified oil under light storage by its light-filtering effect. Experiments clearly suggested that singlet oxygen was mainly responsible for the photooxidation of the oil containing chlorophyll.     

Activity of natural carotenoid preparations against the autoxidative deterioration of sunflower oil-in-water emulsions

The activity of natural carotenoid extracts against the autoxidative deterioration of sunflower oil-in-water emulsions was estimated in terms of primary (lipid hydroperoxides) and secondary (“off flavour” volatiles) oxidation products. At a concentration of 2 g l⁻¹, the tested carotenoids did not inhibit the production of hydroperoxides but they significantly retarded the formation of volatile aldehydes during the storage of simple tween-stabilised emulsions at 30 °C. In another series of experiments, several carotenoid extracts (paprika, annatto and marigold preparations) containing mainly polar carotenoids, added at an active concentration of 1 g l⁻¹, exerted a strong activity against hydroperoxides and TBARs during the accelerated oxidation (60 °C) of homogenised protein-based emulsions. On the contrary, carotene preparations rich in hydrophobic α- and β-carotenes and lycopene did not significantly differ from the control emulsion. Therefore, the carotenoid structure modulated their antioxidant effect, while concentration and emulsion structure may also affect carotenoid activity in protein dispersed systems.