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.     

Albumin causes a synergistic increase in the antioxidant activity of green tea catechins in oil-in-water emulsions

Model oil-in-water emulsions containing epicatechin (EC) and epigallocatechin gallate (EGCG) showed a synergistic increase in stability in emulsions containing added albumin. EGCG showed a stronger synergy (35%) with ovalbumin than did EC. Oxidation of the oil was monitored by determining peroxide values and hexanal contents. The effect of bovine serum albumin (BSA) on model oil-in-water emulsions containing each of the green tea catechins [epicatechin gallate (ECG), EGCG, EC and epigallocatechin (EGC)] was studied during storage at 30 °C. The green tea catechins showed moderate antioxidant activity in the emulsions with the order of activity being ECG ≈ EGCG > EC > EGC. Although BSA had very little antioxidant activity in the absence of phenolic antioxidants, the combination of BSA with each of the catechins showed strong antioxidant activity. BSA, in combination with EC, EGCG or EGC, showing the strongest antioxidant activity with good stability after 45 days storage. Model experiments with the catechins stored with BSA in aqueous solutions confirmed that protein–catechin adducts with antioxidant activity were formed between the catechins and protein. The antioxidant activity of the separated protein–catechin adducts increased strongly with storage time and was stronger for EGCG and ECG than for EC or EGC.     

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.     

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.     

Free-radical scavenging and antioxidative activities of some polysaccharides in emulsions

The antioxidant activity in linoleate emulsion systems, radical scavenging activity and inhibition of autoxidation in sunflower oil-in-water emulsions were studied in the presence of polysaccharide produced by Rhizobium meliloti (RPS), xanthan, curdlan, and carboxymethylcellulose (CMC) and compared to tertiary butylhydroxyquinone (TBHQ). The antioxidant activity in the linoleate emulsion was improved with increasing pH from 3 to 9 and concentration of polysaccharide from 20 to 60 mg/100 g emulsion, while it decreased with increase in storage temperature between 30 and 90 °C. The antioxidant activity of xanthan, curdlan, and RPS at concentration of 40 mg/100 g emulsion was equal to that of TBHQ at 20 mg/100 g emulsion. RPS showed the highest thermal stability and the lowest linoleic oxidation values compared to TBHQ, xanthan, and curdlan at 90 °C. The antioxidant activity of xanthan, curdlan, and RPS in linoleate emulsions at pH 3 and 5 was in the first order with significant (P<0.05) values compared to emulsion, prepared using TBHQ.Curdlan and RPS were effective in radical scavenging being 60-90% at pH values ranging between 3 and 7. They showed an ability to inhibit lipid oxidation in sunflower oil emulsions during holding time for 50 h at 60 °C. In general, the polysaccharides RPS and curdlan can be used as food additives having many functions as stabilizers, radical scavengers, and antioxidants in emulsified foods such as mayonnaise, salad dressings, and cake products.     

Oxidative properties of lactoferrins of different iron-saturation in an emulsion consisting of metmyoglobin and cod liver oil

Lactoferrins (LFs) at iron-saturation 8 (native) and 100%, respectively, were present in an oil-in-water (O/W) emulsion composed of 5% (w/v) cod liver oil (CLO) and metmyoglobin (metMb) in 50 mM phosphate buffer at pH 6.0. Initially both LFs acted as antioxidants and reduced initial peroxide formation, but after 48 h holo LF revealed the most peroxides but the least trienes. Native LF (0.8 mg/ml) gave the highest (p < 0.05) amounts of lipid derived volatiles after 48 h incubation at 4 °C. Both LFs gave similar increases in adducts to metMb with time. The most extensive aggregation induced by radicals or peroxides was found for native LF. The results pointed at reactions at the O/W interphase as highly influential for lipid and protein oxidation kinetics. Added ascorbic acid (1 mM), however, behaved as an antioxidant in the pro-oxidative oil-in-water emulsion system and prevented lipid degradation and protein adductation as well as protein aggregation.     

Impact of thermal processing on the antioxidant mechanisms of continuous phase β-lactoglobulin in oil-in-water emulsions

The influence of native and thermally (50–95 °C) denatured β-lactoglobulin (β-Lg) on the oxidative stability of surfactant-stabilized menhaden oil-in-water emulsions (pH 7.0) was evaluated. β-Lg (500 μg/g oil) heated at 95 °C for 30 min provided the best protection against lipid oxidation, inhibiting the formation of lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS) by 87% and 88%, respectively, following 7 days of storage. The possible mechanisms of antioxidant activity of native and heated β-Lg were evaluated by measuring peroxyl radical scavenging and iron chelating capacities of the protein treatments, as well as reactive sulfhydryl concentrations and tryptophan fluorescence (a marker of protein conformation changes). The aforementioned in vitro assays only partially corroborated the results from the oxidizing emulsion system since β-Lg heated at 95 °C exhibited the lowest iron chelation capacity and free sulfhydryl concentration, yet displayed the highest peroxyl radical scavenging capacity and inhibition of lipid oxidation in oil-in-water emulsions of all treatments tested. The results of this study demonstrate the feasibility of proteins as a natural class of antioxidants in food emulsions, and further elucidate the possible mechanisms by which proteins inhibit lipid oxidation.     

Inhibition of lipid oxidation by encapsulation of emulsion droplets within hydrogel microspheres

The purpose of this study was to assess whether the oxidation of polyunsaturated lipids could be inhibited by encapsulating them within protein-rich hydrogel microspheres (size range 1-100 μm). Filled hydrogel microspheres were fabricated as follows: (i) high methoxy pectin, sodium caseinate, and casein-coated lipid droplets were mixed at pH 7, (ii) the mixture was acidified (pH 5), (iii) casein was cross-linked using transglutaminase, (iv) the pH was adjusted to pH 7. Samples were stored in the dark at 55 °C and were monitored for lipid hydroperoxide formation and headspace propanal. Oxidation of fish oil (1% vol/vol) in the microspheres was compared with that in oil-in-water emulsions stabilised by either sodium caseinate or Tween 20. Emulsions stabilised by Tween 20 oxidised faster than either microspheres or emulsions stabilised by casein, while microspheres and the casein stabilised emulsion showed similar oxidation rates. Results highlight the natural antioxidant properties of food proteins.     

Antioxidant activity of hydroxytyrosol in frankfurters enriched with n-3 polyunsaturated fatty acids

The capacity of hydroxytyrosol (HXT) to inhibit lipid oxidation in cooked pork meat batter, oil-in-water emulsions and potential functional frankfurters formulated with a healthier oil combination (as animal fat replacer) was studied during chilling storage, and its effect compared with those produced by synthetic antioxidants (BHA/BHT). Although efficiency varied, HXT was an effective antioxidant during chilling storage in the three food matrices studied. In general the order of inhibition capacity of HXT against lipid oxidation (thiobarbituric acid-reactive substances-TBARS) was cooked meat batter > oil-in-water emulsion > frankfurters, whereas in the case of BHA/BHT (with lower inhibitory activity than HXT) it was cooked meat batter > oil-in-water emulsion, and there was no antioxidative effect in frankfurters. Whereas significant correlations were established between lipid oxidation (TBARS) and antioxidative capacity measured by photochemiluminescence (PCL) in frankfurters supplemented with HXT and BHA/BHT, no significant correlations were found between ferric reducing/antioxidant power assay (FRAP) and TBARS and PCL.     

Effect of pH on the antimicrobial activity and oxidative stability of oil-in-water emulsions containing caffeic acid

ABSTRACT:  Antioxidant properties in food are dependent on various parameters. These include the pH value and interactions with food components, including proteins or metal ions. Food components affect antioxidant stability and also influence the properties of microorganisms and their viability. This paper describes an investigation of the effect of pH on the antioxidant and antibacterial properties of caffeic acid in different media. The pH values studied, using an oil-in-water emulsion as model system, were 3, 5 (with and without phosphate buffer), and 9. Effects of mixtures of caffeic acid, bovine serum albumin (BSA), and Fe (III) on oxidative deterioration in the emulsion samples were studied. The results show that the antioxidant activity of caffeic acid was increased by the presence of BSA. This effect was pH dependent and was affected by the presence of iron ions. Antibacterial properties were also pH dependent. The minimum concentration of caffeic acid required to inhibit some microorganisms in the pH range of 5 to 7 was determined. A concentration of 0.4% (w/w) caffeic acid was enough to inhibit the growth of some of the studied microorganisms in the pH range of 5 to 7. However, near-neutral pH concentrations higher than 0.4% were needed to inhibit some microorganisms, including Listeria monocytogenes , E. coli, and Staphylococcus aureus , in the medium.     

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 effect of Majorana syriaca extract in bulk corn oil and o/w emulsion after applying high hydrostatic pressure

Bulk oils and oil-in-water emulsions were subjected to high hydrostatic pressure (HHP) (200, 650 MPa) 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 (2 weeks, 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 650 MPa. 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 (200 ppm) 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.     

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.     

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.     

Interfacial and emulsifying properties of lentil protein isolate

The dynamic interfacial tension (DIFT) at oil–water interface, diffusion coefficients, surface hydrophobicity, zeta potential and emulsifying properties, including emulsion activity index (EAI), emulsion stability index (ESI) and droplet size of lentil protein isolate (LPI), were measured at different pH and LPI concentration, in order to elucidate its emulsifying behaviour. Sodium caseinate (NaCas), whey protein isolate (WPI), bovine serum albumin (BSA) and lysozyme (Lys) were used as benchmark proteins and their emulsifying property was compared with that of LPI. The speed of diffusion-controlled migration of these proteins to the oil/water interface, was in the following order: NaCas > LPI > WPI > BSA > Lys, while their surface hydrophobicity was in the following order: BSA > LPI > NaCas > WPI > Lys. The EAI of emulsions stabilised by the above proteins ranged from 90.3 to 123.3 m²/g and it was 93.3 ± 0.2 m²/g in LPI-stabilised emulsion. However, the stability of LPI-stabilised emulsions was slightly lower compared to that of WPI and NaCas-stabilised emulsions at the same protein concentration at pH 7.0. The ESI of LPI emulsions improved substantially with decrease in droplet size when protein concentration was increased (20–30 mg/ml). Reduction of disulphide bonds enhanced both the EAI and ESI compared to untreated samples. Heat treatment of LPI dispersions resulted in poor emulsion stability due to molecular aggregation. The stability of LPI-stabilised emulsions was found to decrease in the presence of NaCl. This study showed that LPI can be as effective emulsifiers of oil-in-water emulsions as are WPI and NaCas at ?20 mg/ml concentrations both at low and neutral pH. The emulsifying property of LPI can be improved by reducing the intra and inter-disulphide bond by using appropriate reducing agents.     

Antioxidant and antimicrobial activities of tea infusions

Tea polyphenols, especially the catechins, are potent antimicrobial and antioxidant agents, with positive effects on human health. White tea is one of the less studied teas but the flavour is more accepted than that of green tea in Europe. The concentrations of various catechins in 13 different kinds of infusion were determined by capillary electrophoresis. The total polyphenol content (Folin–Ciocalteu method), the trolox equivalent antioxidant capacity (TEAC value determined with the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation) and the inhibitory effects of infusions on the growth of some microorganisms were determined. Five different infusions (black, white, green and red teas and rooibos infusion) were added to a model food system, comprising a sunflower oil-in-water emulsion containing 0% or 0.2% bovine serum albumin (BSA), and the oxidative stability was studied during storage at 37 °C. Oxidation of the oil was monitored by determination of the peroxide value.     

Comparison of the activities of hydrophilic anthocyanins and lipophilic tocols in black rice bran against lipid oxidation

The antioxidant capabilities of anthocyanin and tocol extracts from black rice bran were evaluated using an emulsion system containing either cholesterol (1.0 mg/ml) or fish oil (10 mg/ml). The cholesterol oxidation product, 7-ketocholesterol, increased to 180.1 μg/ml in the control emulsion after 168 h of oxidation, while it was only 15.4 and 39.0 μg/ml in the emulsions containing 1 μg/ml of the anthocyanin and tocol extracts, respectively; but below 1.2 μg/ml in the emulsion having 5 μg/ml of anthocyanins or tocols. In the fish oil emulsion, over 80% of C20:5 and C22:6 were oxidised after a 48 h incubation at 37 °C, while they were retained above 38% and 65% in the emulsions containing 10 μg/ml of anthocyanins and tocols, respectively, and above 85% in the emulsion containing 20 μg/ml of anthocyanins or tocols. Compared with the tocols extract, the capability of the anthocyanin extract was relatively greater in stabilising cholesterol but lower in inhibiting fatty acids oxidation.     

Improvement of physicochemical stabilities of emulsions containing oil droplets coated by non-globular protein-beet pectin complex membranes

The potential of beet pectin for improving the physical and chemical stabilities of emulsions containing silk fibroin coated droplets was investigated. Five wt.% corn oil-in-water emulsions containing fibroin-coated droplets (0.5 wt.% fibroin) and anionic pectin (0.05 wt.%) were prepared at pH 7. The pH of these emulsions was then adjusted to pH 4, so that the anionic pectin molecules electrostatically deposited to the fibroin-coated droplets. The influence of pH (3 to 7) and sodium chloride concentrations (0 to 500 mM) on the properties of primary (0 wt.% pectin) and secondary (0.05 wt.% pectin) emulsions was studied. Pectin was deposited to the droplet surfaces at pH 3, 4, and 5, but not at pH 6 and 7. In addition, secondary emulsions were stable up to higher ionic strengths (< 500 mM) than primary emulsions (< 200 mM). The addition of beet pectin also prolonged the lag phase of lipid oxidation in the emulsions as determined by the formation of lipid hydroperoxides and headspace hexanal. The controlled electrostatic deposition method utilized in this study could be used to extend the range of application of silk fibroin in the industry.     

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.     

Comparative studies of four different phenolic compounds on in vitro antioxidative activity and the preventive effect on lipid oxidation of fish oil emulsion and fish mince

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 100 mg/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.