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.     

Oxidative stability of oil-in-water emulsions with α-tocopherol,charged emulsifier,and different oxidative stress

α-Tocopherol is known to show different activity depending on the concentration and food matrix. Effects of α-tocopherol at the concentrations of 0, 0.1, 0.5, and 1.0 mM were determined in oil-in-water (O/W) emulsions containing anionic, neutral, and cationic emulsifiers under different types of oxidative stress including riboflavin photosensitization, photooxidation, and autoxidation. Headspace oxygen depletion, lipid hydroperoxides, and conjugated dienes were analyzed to determine the oxidative stability of O/W emulsions. α-Tocopherol served as an antioxidant in O/W emulsion with a cationic emulsifier irrespective of oxidative stress. α-Tocopherol acted as an antioxidant in O/W emulsion with a neutral emulsifier at riboflavin photosensitization while a prooxidant at photooxidation. However, in samples with an anionic emulsifier, α-tocopherol activity differed from the concentration and types of oxidative stress. Therefore, cationic transition metals or reactive oxygen species generated from RF photosensitization could play key roles of α-tocopherol in O/W emulsion.     

Effects of chlorophyll photosensitisation on the oxidative stability in oil-in-water emulsions

Effects of chlorophyll photosensitisation on the oxidative stability of oil-in-water (O/W) emulsions were determined by analysing headspace oxygen content, lipid hydroperoxides, and headspace volatiles. The roles of transition metals and singlet oxygen were tested by adding ethylenediaminetetraacetic acid (EDTA) and sodium azide, respectively. Emulsions with chlorophylls and visible light irradiation had significantly high lipid hydroperoxides and headspace volatiles and low headspace oxygen content (p < 0.05) after 32 h while samples without light irradiation did not show any significant changes (p > 0.05). Sodium azide did not show clear antioxidant capacities in O/W emulsion systems rather showed prooxidant properties at some concentration. Addition of EDTA, a metal chelator, accelerated the rates of lipid oxidation in a concentration dependent manner. EDTA may enhance the stability of chlorophylls in O/W emulsions and the resulting higher chlorophyll concentrations may generate more singlet oxygen thus accelerating the rates of lipid oxidation.     

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.     

Additions of caffeic acid,ascorbyl palmitate or γ-tocopherol to fish oil-enriched energy bars affect lipid oxidation differently

The objectives of the study were to investigate the effects of caffeic acid, ascorbyl palmitate and γ-tocopherol on protection of fish oil-enriched energy bars against lipid oxidation during storage for 10 weeks at room temperature. The lipophilic γ-tocopherol reduced lipid oxidation during storage when added at a concentration above 440 μg/g fish oil. However, the best antioxidative effect was observed when it was added at a concentration of 660 μg/g fish oil. In contrast, prooxidative effects were observed when using either γ-tocopherol at concentrations below 220 μg/g fish oil, or the hydrophilic caffeic acid, or the amphiphilic ascorbyl palmitate at concentrations of 75, 150 and 300 μg/g fish oil. Prooxidative effects were observed as an increase in the formation of lipid hydroperoxides and volatile secondary oxidation products, as well as the development of rancid off-flavours. The differences in the efficacies of the three antioxidants examined are expected to be related to their different localisations and mechanisms of action.     

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.     

The antioxidative activity of RRR-α-tocopherol vs RRR-δ-tocopherol in combination with ascorbyl palmitate in cooked,minced turkey

RRR-α-tocopherol and RRR-δ-tocopheroI (100 or 200 ppm) had similar and significantly better antioxidative effects compared to ascorbyl palmitate (200 ppm) in turkey meat balls during storage at 5 °C for up to 9 days, as determined by measurement of thiobarbituric acid reactive substances (TBARS) and by static head space detection of hexanal. The antioxidative effect of α-tocopherol at 100 ppm was, measured as a reduction of head space hexanal, significantly enhanced by ascorbyl palmitate (200 ppm), resulting in a further 50% reduction compared to δ-tocopherol. At the 200-ppm level, only the antioxidative activity of α-tocopherol was enhanced significantly by ascorbyl palmitate (200 ppm), in contrast to the effect on the antioxidative activity of δ-tocopherol (200 ppm). The antioxidative activity obtained by α-tocopherol at the 100-ppm level in combination with ascorbyl palmitate (200 ppm) was similar to the effect obtained by α-tocopherol at the 200-ppm level in combination with ascorbyl palmitate (200 ppm) measured as head space hexanal. Ascorbyl palmitate was in all storage experiments depleted in the product at a rate which appeared to be independent of the presence of tocopherols. Of the tocopherol homologues, α-tocopherol was most affected by the presence of ascorbyl palmitate, and the concentration of α-tocopherol was found to decrease during storage in the absence of ascorbyl palmitate, in contrast to when ascorbyl palmitate was present. A similar effect of ascorbyl palmitate was less evident for δ-tocopherol and for γ-tocopherol in a natural mixture of the tocopherol homologues added to turkey meat balls.     

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.     

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.     

Interactions between tocopherols,tocotrienols and carotenoids during autoxidation of mixed palm olein and fish oil

Electron spin resonance (ESR) and spin trapping detection of radical formation showed that the oxidative stability of palm olein/fish oil mixtures increased with the amount of palm olein. Mixtures with red palm olein were less stable than were mixtures with yellow palm olein. Addition of ascorbyl palmitate and citric acid gave further reduction of radical formation, whereas no effect was observed by adding lecithins. Storage of palm olein/fish oil mixtures (4:1) at 30 °C confirmed that red palm olein mixtures were less stable than were yellow palm olein mixtures. Ascorbyl palmitate together with citric acid improved the stability in both cases. The concentrations of α-tocopherol and α-tocotrienol decreased during storage, whereas β-, γ-, and δ-tocotrienols were unaffected. Ascorbyl palmitate reduced the losses of α-tocopherol and α-tocotrienol. The rate of loss of carotenoids was independent of the presence of fish oil and, except for an initial fast drop, also of the presence of ascorbyl palmitate.     

Effect of ascorbate and ascorbyl palmitate on lipid oxidation in semi-dry saugages manufactured from pork materials differing in stability towards oxidation

Semi-dry fermented sausages were manufactured from three batches of pork slightly differing in their polyenoic fatty acid levels and α-tocopherol contents. The sausage doughs were treated as follows: (1) control, (2) ascorbate, (3) ascorbyl palmitate and (4) a combination of ascorbate and ascorbyl palmitate. After brine fermentation, products ripened at 15°C were evaluated for rancidity by peroxide values and TBA numbers. During ripening important differences in stability towards oxidation were generally not observed. Both peroxide and TBA values gradually increased linearly with time. For the TBA values, gradients for the products derived from the three diet groups differed considerably. Only two of six batches containing increased levels of α-tocopherol and product antioxidants exhibited slightly improved stability towards oxidation, as judged by peroxide and TBA values. Sensory evaluations, performed only on the product series containing ascorbate, failed to reveal any positive effect in favour of the increased α-tocopherol content. Thus, for semi-dry sausages manufactured from pork materials with a slightly increased sensitivity towards oxidation, results indicated with there was little advantage to increasing the levels of α-tocopherol in the meat by dietary means or to changing the current commercial practice of adding ascorbate to the sausage doughs.     

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 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.     

Role of reverse micelles on lipid oxidation in bulk oils: impact of phospholipids on antioxidant activity of α-tocopherol and Trolox

Phospholipids self-assemble in bulk oils to form structures such as reverse micelles that can alter the microenvironment where chemical degradation reactions occur, such as lipid oxidation. In this study, we examined the influence of phospholipid reverse micelles on the activity of non-polar (α-tocopherol) and polar (Trolox) antioxidants in stripped soybean oil (SSO). Reverse micelles were formed by adding 1000 μM 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) to SSO. The addition of DOPC reverse micelles had a prooxidant effect, shortening the lag phase of SSO at 55 °C. DOPC improved the activity of low α-tocopherol or Trolox concentrations (10 μM) but decreased the activity of high concentrations (100 μM). Hydrophilic Trolox had better antioxidant activity than hydrophobic α-tocopherol. Fluorescence steady state and lifetime decay studies suggests that differences in the antioxidant activity of Trolox and α-tocopherol could be due to differences in their physical location in DOPC reverse micelles. These results will improve our understanding and control of lipid oxidation in bulk oils.     

α-Tocopherol Content and Oxidative Stability of Egg Yolk as Related to Dietary α-Tocopherol

Hens fed diets with 0.0, 7.5, 15.0, 30.0, 60.0 and 120.0 mg supplemental α-tocopherol/kg feed produced egg yolks with 25,30,35,45,50 and 75 μg/g yolk, respectively. The correlation coefficient between dietary α-tocopherol (mg/kg diet) and egg yolk α-tocopherol (μg/g egg yolk) after 28 days feeding was 0.99. The supplemented dietary α-tocopherol had an effect on the α-tocopherol in egg yolk (p<0.05). The oxidative stability of yolk was determined by measuring the oxygen and volatile compounds in the headspace of bottled yolk. α-Tocopherol had an effect on the stability of yolk as an antioxidant at 25, 45 and 50 μg/g yolk and a prooxidant at 75 μg/g or above (p<0.05). The addition of 60.0 mg α-tocopherol/kg diet resulted in the best egg yolk stability. The correlation coefficient between headspace oxygen disappearance and volatile compound formation in the headspace of bottled egg yolk was 0.84.     

The anti-inflammatory effect of lycopene complements the antioxidant action of ascorbic acid and α-tocopherol

Tomato foods contain bioactive compounds, such as lycopene, ascorbic acid and α-tocopherol, which are assumed to show synergistic effects. The aim of the study was to investigate this presumed synergy. The effect on lipid peroxidation and inflammation was assessed. Lipid peroxidation was effectively inhibited by combinations of the compounds compared to the single compounds. Synergy between the combination of ascorbic acid and α-tocopherol was confirmed. Lycopene on its own effectively reduced inflammation by inhibiting the release of TNF-α and stimulating IL-10 production. The combination of lycopene, ascorbic acid and α-tocopherol tended to display a synergistic interaction on IL-10 production. Our observations highlight that lycopene mitigates inflammation, whereas ascorbic acid and α-tocopherol efficiently protect against lipid peroxidation. Both activities are complementary since they diminish the process of inflammation differently on different levels. In relation to health, this is an added value of fruit and vegetables such as tomato products that contain complementary bio-active compounds.     

Effects of α-tocopherol, β-carotene and ascorbyl palmitate on oxidative stability of butter oil triacylglycerols

Butter oil triacylglycerols (BO-TAGs), free of antioxidants, including β-carotene, were obtained via sequential treatments with activated carbon (AC) adsorption and alumina column chromatography. α-Tocopherol, β-carotene and ascorbyl palmitate (AP) were added to BO-TAGs, individually, or in different combinations. An accelerated oven-oxidation test was carried out at 60 °C to determine the most effective dosages of the antioxidants. Among the antioxidants evaluated, α-tocopherol was found to be the most effective, at the concentration of 50 μg/g. To determine the possible synergism between the antioxidants, binary or ternary combinations of α-tocopherol, β-carotene and AP were added to BO-TAGs at concentrations of 50, 5, and 50 μg/g, respectively. Ternary combinations of these antioxidants were significantly better in retarding oxidation than were binary blends of α-tocopherol with β-carotene or AP. However, a prooxidant effect was observed, especially when β-carotene and AP were used individually or in binary combination.     

Effects of catechin and α-tocopherol addition on the autoxidative stability of diacylglycerol oil derived from an olive oil and perilla oil mixture

The effects of tea catechin and α-tocopherol addition (1 mM) on the oxidative stability of oleic and linolenic acid-rich diacylglycerol (DAG) oil derived from an extra virgin olive oil and perilla oil mixture (6:4, w/w) were evaluated. Oil was oxidized at 50°C for 10 days, after which oxidation was evaluated based on headspace oxygen consumption and peroxide values (POV). The polyphenol and tocopherol contents were also monitored. Addition of catechin did not affect the oxygen consumption or POV of DAG oil, whereas α-tocopherol acted as a prooxidant. Addition of antioxidants had no significant (p>0.05) effect on the fatty acid composition of the oil. Degradation of γ-tocopherol during oil oxidation was inhibited by addition of α-tocopherol, and addition of antioxidants inhibited polyphenol degradation. The autoxidative stability of DAG oil can be improved using polar rather than non-polar antioxidants.     

Effects and prooxidant mechanisms of oxidized alpha-tocopherol on the oxidative stability of soybean oil

ABSTRACT:  α-Tocopherol was oxidized in methanol containing methylene blue for 30 h under light. The effects of 0, 250, 500, 1000, and 1500 ppm of oxidized α-tocopherol on the oxidative stability of purified soybean oil in the dark at 55 °C were studied by measuring the peroxide values and headspace oxygen contents in sample bottles. As the concentrations of oxidized α-tocopherol increased, the peroxide values increased and the headspace oxygen contents decreased during the 6 d of storage. The oxidized α-tocopherol compounds acted as prooxidant on the peroxide values and headspace oxygen contents of purified soybean oil. Tukey's test showed that oxidized α-tocopherol had a significant effect on the peroxide value and headspace oxygen disappearance of oil at P < 0.05. The prooxidant mechanisms of oxidized α-tocopherol may be due to α-tocopherol peroxy radical, α-tocopherol oxy radical, hydroxy radical, and singlet oxygen formed from the α-tocopherol. The oxidized α-tocopherol containing polar and nonpolar groups in the same molecule may reduce the surface tension of oil to increase the transfer of headspace oxygen to oil and accelerate the oil oxidation.