Antioxidant Activity of Potato Peel Extracts in a Fish-Rapeseed Oil Mixture and in Oil-in-Water Emulsions

The objectives of the present work were (a) to extract the phenolic fraction from the peels of two Danish varieties of potatoes, viz. Sava and Bintje, and examine their antioxidant capacity in in-vitro systems (b) to evaluate the effect of these extracts on the storage stability of a fish-rapeseed oil mixture and oil-in-water emulsions. Multiple antioxidant activity of the potato peel extracts was evident from in-vitro systems as they showed strong reducing power, radical scavenging ability, ferrous ion chelating activity and prevented oxidation in a liposome model system. The Sava variety, which showed strong antioxidant activity in in-vitro systems, was tested in oil and oil-in-water emulsions. Ethanolic extracts of Sava (≥1,600 mg/kg) prevented lipid oxidation in emulsions and in oil. Water extracts showed no antioxidant activity in oil whereas it showed pro-oxidant activity in emulsions. Thus, the results of the present study show the possibility of utilizing waste potato peel as a promising source of natural antioxidants for retarding lipid oxidation.     

Antioxidant and Emulsifying Activities of Corn Gluten Meal Hydrolysates in Oil-in-Water Emulsions

Corn gluten meal (CGM) is a protein-rich coproduct generated during corn wet milling. In this study, CGM was hydrolyzed using Neutrase protease for 1 and 3 hours, respectively, to obtain antioxidative corn gluten meal protein hydrolysates (CGMPH), which could be a potential antioxidant in various products to retard lipid oxidation. Our objective was to evaluate the emulsion properties and oxidation stability of oil-in-water emulsions containing different types (1-hour and 3-hour hydrolysates) and amounts of CGMPH. The results showed that the emulsions with CGMPH had significantly improved oxidative stability than the control based on both peroxide value and thiobarbituric acid reactive substance (TBARS) analysis. The emulsion with higher concentration of CGMPH (e.g., 5 mg mL⁻¹) showed more effective inhibition on lipid oxidation. The emulsion turbidity of 1-hour CGMPH at 2.5 mg mL⁻¹ had a lower value than that of other emulsions, and overall, the turbidity for 3-hour CGMPH had a slightly higher value than that with 1-hour CGMPH. Addition of CGMPM did not affect emulsion morphology and droplet sizes. Zeta potential analysis showed that emulsions with 1-hour hydrolysate had more negative charges with better emulsion stability than that with 3-hour hydrolysate at the same pH. In conclusion, the CGMPH were able to inhibit lipid oxidation in reducing the formation of hydroperoxides and TBARS, and could be a potential functional antioxidant for food emulsion applications.     

Prooxidant Activity of Polar Lipid Oxidation Products in Bulk Oil and Oil-in-Water Emulsion

Lipid oxidation products can arise when oils are subjected to high temperature and exposed to oxygen. Many of these oxidation products have higher polarity than the original triacylglycerols due to the incorporation of oxygen. These polar oxidation products could have a negative impact on oxidative stability by acting as prooxidants. In this study, the influence of polar lipid oxidation products on the oxidative stability of bulk oils and oil-in-water emulsions was investigated. Polar compounds were isolated from used frying oil by silica gel column chromatography. They were added to bulk stripped corn oil (with/without reverse micelles formed by dioleoylphosphatidylcholine, DOPC) and oil-in-water (O/W) emulsion to evaluate their prooxidative activity. Polar compounds increased lipid oxidation in bulk oil with and without DOPC. The presence of DOPC reverse micelles decreased the prooxidant activity of the polar oxidation products. On the other hand, there was no significant effect of the polar compounds on oxidation of O/W emulsions. To gain a better understanding of the polar compounds responsible for the prooxidant effect, linoleic acid and linoleic hydroperoxide were added into bulk oil at the same concentration as those in the polar fraction of the frying oil. However, they did not show the same prooxidative activity compared to oil with the polar fraction.     

How to Efficiently Remove tert-butylhydroquinone from Commercial Soybean Oils to Obtain Stripped Oils: Eliminating tert-butylhydroquinone's Influence on Oxidative Stabilities of Model Oil-in-Water Emulsions

The present study proposes an efficient method to effectively strip tert-butylhydroquinone (TBHQ) from commercial soybean oils. Ethanol, a typically common and relatively safe organic solvent, can successfully strip TBHQ by employing a liquid-liquid extraction strategy. The results show that the volume ratio of ethanol to oil is a key factor for stripping efficiency (SE), and 4:1 (v/v) is considered the optimal parameter. When compared with traditional stripping methods via adsorbing materials (such as activated charcoal or alumina powder), the proposed ethanol extraction method can more effectively strip TBHQ from commercial oils with lower adsorption loss and higher SE. Moreover, the model O/W emulsion systems prepared using ethanol stripped oils showed the highest degree of lipid oxidation. The method can completely strip TBHQ from commercial soybean oils, thereby eliminating its influence on oxidative stabilities of model oil-in-water emulsions. Practical Applications : The ethanol stripping method can be applied as a pretreatment method to completely strip TBHQ from commercial soybean oils, and subsequently eliminate the influence of TBHQ on lipid oxidation in model O/W emulsion systems during storage.     

Comparison of Antioxidant Capacities of Rosmarinate Alkyl Esters in Riboflavin Photosensitized Oil-in-Water Emulsions

Effects of the alkyl chain length of rosmarinate alkyl esters on the oxidative stability in photosensitized oil-in-water (O/W) emulsions were determined by lipid hydroperoxides and headspace volatile analyses. Antioxidant capacities of 20 μM rosmarinate esters with alkyl chain length of 0, 4, 8, 12, 18, and 20 were tested in O/W emulsion containing stripped soybean oil, Tween 20 as an emulsifier, and riboflavin as a photosensitizer. Synergistic or antagonistic effects of 20 μM α-tocopherol in the presence of rosmarinate alkyl esters were also determined. Samples containing rosmarinate with 4 and 8 alkyl esters showed lower lipid hydroperoxides and headspace volatiles than those without rosmarinate and those with 0, 12, 18, and 20 alkyl esters, which indicates that phenolic free radical scavengers showed antioxidant capacities non-linearly in riboflavin photosensitized O/W emulsions. Antagonistic rather than synergistic effects were observed in all rosmarinate alkyl esters with α-tocopherol in current conditions although rosmarinates with 4, 8, and 12 alkyl esters showed better antioxidant capacities than those with other alkyl chain length. The results of this study clearly showed that rosmarinates need the proper length of non-polar groups to show optimum antioxidant capacities in O/W emulsions with Tween 20 as an emulsifier under riboflavin photosensitization.     

Flow Behavior of Oleic Acid Liposomes in Sucrose Ester Glycolipid Oil-in-Water Emulsions

Liposomes have been used widely as carriers for active ingredients in cosmetics because of their ability to encapsulate both hydrophilic and hydrophobic compounds. In this work, fatty acid liposomes were prepared and introduced into olive oil-in-water emulsions stabilized by C₁₄–C₁₈ sucrose ester mixtures at pH 8.5. Light microscopy images of the emulsions showed evidence of the coexistence of oleic acid liposomes with the emulsions. As the alkyl chain length of the sucrose ester increased, the average droplet size decreased, while the zeta potential became more negative. Further decrease in droplet size was observed when borate buffer was added to the aqueous phase. The free fatty acids in the sucrose esters and olive oil are neutralized in borate buffer; consequently, fatty acid salts were produced and served as co-surfactants. The synergistic stabilization of emulsions by the mixture of sucrose esters and fatty acid salt resulted in higher stability, smaller droplet size, and lower polydispersity. The drastic increase in negative zeta potential was possibly due to the presence of free fatty acid salts in the emulsion systems. The flow curves at steady rate displayed five distinctive regions. The polydispersity of droplets enhanced the shear thickening effect at low shear rates and shear-banding effect at middle shear rates. Formation of fatty acid salts as co-surfactants caused the viscosities of the emulsions to increase by an order of magnitude. The presence of oleic acid liposome significantly reduced the viscosities of the emulsion by half an order of magnitude; this decreased viscosity helped enhance better spreadability.     

Effects of Acidity, Temperature and Emulsifier Concentration on the Distribution of Caffeic Acid in Stripped Corn and Olive Oil-in-Water Emulsions

We evaluated the effects of oil type, oil to water ratio, emulsifier concentration, acidity, and temperature on the distribution of caffeic acid, CA, in emulsions composed of stripped olive and corn oils, acidic water, and Tween 20. CA mainly distributes between the water and interfacial regions because it is sparingly soluble in oils, as demonstrated by auxiliary partitioning experiments in the absence of an emulsifier. The distributions of CA were determined in the intact emulsions from values of the partition constant between the water-interfacial region, P _W ^I , determined under different experimental conditions. At any given pH, CA is mostly located in the interfacial region of the emulsion,  %CA_I > 50 % at the lowest emulsifier volume fraction, Φ_I = 0.005, and its percentage increasing upon increasing Φ_I with  %CA_I > 90 % at Φ_I = 0.04. At any given Φ_I,  %CA_I decreases substantially with increasing pH because of the ionization of the CA. Our results indicate that the main parameters affecting the distribution of CA are Φ_I and the acidity, while the nature of the oil, the oil to water ratio and temperature have only minor effects. Results should aid the understanding of how environmental conditions affect the distribution of phenolic acids in emulsions.     

Antioxidant Properties of Three Aromatic Herbs (Rosemary, Thyme and Lavender) in Oil-in-Water Emulsions

Lipid oxidation is the major form of deterioration in foods because it decreases food quality and nutritional value, and may have negative health implications. Selected aromatic plant extracts from leaves, flowers and stems of rosemary, thyme and lavender were investigated for their antioxidant activity. The total polyphenol content was determined by the Folin–Ciocalteu assay and the antioxidant capacity was determined by the Trolox equivalent antioxidant capacity, 1,1-diphenyl-2-picrylhydrazyl, oxygen radical absorbance capacity and ferric-reducing antioxidant power assays. For all four antioxidant assays, the extracts from thyme flowers, lavender leaves and thyme leaves had the highest antioxidant activity, followed by rosemary stems, rosemary leaves, and lavender stems, and the lavender flowers and thyme stems had the lowest antioxidant activity. The antioxidant activity was correlated with the polyphenol content, although minor deviations were observed. In oil-in-water emulsion, extracts from rosemary leaves and thyme leaves were most effective at retarding oxidation followed by the rosemary stems and thyme flowers. Extracts from thyme flowers and lavender leaves were less effective in the emulsion than predicted by the homogeneous antioxidant assays. This study demonstrated the potential use of plants extract as substitutes for synthetic antioxidants.     

Effect of Processing Conditions on the Crystallization Behavior and Destabilization Kinetics of Oil-in-Water Emulsions

The objective of this research was to systematically study the effect of processing conditions on the crystallization behavior and destabilization mechanisms of oil-in-water emulsions. The effect of crystallization temperature (T _c) and homogenization conditions on both thermal behavior and destabilization mechanisms were analyzed. Results show that the crystallization of lipids present in the emulsions was inhibited when compared with bulk lipids as evidenced by a lower onset and peak temperature (T _on and T_p, respectively) in differential scanning calorimetry crystallization exotherms. The smaller the droplet size in the emulsion, the more significant the inhibition (lower T _on and T _p). Lower values of T _on and T _p were not necessarily indicators of emulsion stability. Homogenization conditions not only affected the T _on and T _p of crystallization but also the crystallization profile of the samples. Lipids present in emulsions with small droplets were crystallized and melted in a less fractionated manner when compared to lipids in bigger droplets or even to the bulk lipids. The amount of lipid crystallized as evidenced by enthalpy values, did not have a direct relationship with the emulsions stability. Although enthalpy values increased as T _c decreased, the destabilization kinetics did not follow the same tendency as evidenced by back scattering measurements.     

草桥稠油O/W乳状液的稳定性与流变性研究

采用OP-10作乳化剂,制备了油水体积比为7:3的草桥稠油O/W乳液.通过显微镜观察和流变实验研究了乳化条件对乳液流变性的影响.随着乳化剂浓度的提高(0.5%～5%),乳滴直径减小而乳液黏度先减小,再增大.当乳化剂浓度≤4%时,乳液为简单的牛顿流体;增大乳化剂浓度到5%将导致乳液转变为非牛顿流体.随着乳化温度的提高(40～70℃),乳液黏度和液滴直径均减小而乳液始终为牛顿流体.随着乳化强度的提高,乳滴直径减小而乳液黏度增大,乳液逐渐从简单的牛顿流体转变为非牛顿流体.此外,通过稳定性评价实验,考察了乳化条件和水相盐浓度对乳液动、静态稳定性的影响.乳液静态稳定性随乳化剂浓度、乳化温度的提高明显提高,随盐浓度的提高而变差;随着乳化强度的提高,在低乳化剂浓度下(1%)制备的乳液的静态稳定性变差,而在高乳化剂浓度下(3%)制备的乳液的静态稳定性提高.乳液动态稳定性随乳化剂浓度的提高得到改善,随水相盐浓度和价态的提高而变差.     

Reconstitution of Food Powders Granulated with Oil-in-Water Emulsions

Vegetable soups are complex mixtures containing vegetables in different percentages, thickeners, salt, fat, and emulsifying/wetting agents. When prepared as dehydrated powders in convenience foods, they need to be rehydrated before consumption and this can lead to formation of undesired lumps when carried out in hot water. Elimination of lumps and simplification of the preparation procedure were reached by granulating three different vegetable mixtures, each with a predominant vegetable (spinach, beetroot, and carrot), using an alternative liquid binder besides water. The use of an oil-in-water emulsion affected positively some technological properties of the dry products like granule strength and flowability, and the rehydrated soups in terms of complete dispersion in hot water. Also, the interplay between starches and soluble sugars, naturally present in vegetables, was found to impact the complete rehydration of the soups.     

Improving the Oxidative Stability of Krill Oil-in-Water Emulsions

A positively charged protein (fish gelatin) or a negatively charged protein species (heat-treated milk protein–carbohydrate mixture) was added to a primary krill oil (KO) emulsion stabilized by the phospholipids inherent in KO, with the aim of improving the oxidative stability of KO-in-water emulsions at pH 8.0 (10 % KO). The positively charged fish gelatin deposited on the primary interface of the oil droplets in the primary KO-in-water emulsion improved the oxidative stability of the KO-in-water emulsion as evidenced by the higher eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) remaining and lower propanal produced after accelerated oxidation (40 °C, 25 days). The addition of the negatively charged heat-treated milk protein–carbohydrate mixture containing Maillard reaction products (MRP) to the bulk phase of the emulsion also enhanced the oxidative stability of the KO-in-water emulsion. The addition of MRP to the aqueous phase of phospholipids stabilized emulsion droplets offered more protection to EPA and DHA of the KO emulsions compared to the formation of an additional layer at the interface of the KO emulsion droplet. This suggests that interventions based on addition of antioxidant species to the formulation were more effective for arresting oxidation than increasing the thickness of the droplet interface. The addition of proteins into KO containing emulsion formulations is a promising strategy for protecting omega-3 marine phospholipids against oxidation.     

Kinetics of Isothermal Crystallization of Hydrogenated Castor Oil-in-Water Emulsions

Kinetics of isothermal crystallization of hydrogenated castor oil in water emulsions exhibiting multiple crystal morphologies have been studied experimentally by DSC and polarized light microscopy. The induction time of nucleation increases with the increase of the isothermal temperature under which crystallization occurred. Crystal growth has been observed by microscopy showing that both crystal morphologies, fibers and rosettes, grow linearly at the initial stage of crystallization and then slow down to reach a plateau value. The Avrami model, which has been widely used in kinetics studies of triacylglycerol systems, was employed to fit experimental results at different isothermal temperatures. It was found that experimental trends could be captured by introducing the volume fraction of each type of morphology into three-dimensional and one-dimensional full Avrami models.     

Antioxidant Activity of Sesamol in Soybean Oil Under Frying Conditions

Antioxidant activity of sesamol was investigated in soybean oil using a miniaturized frying experiment with potato cubes fried at 180 °C. Oxidation of soybean oil was determined by gel permeation chromatography for polymerized triacylglycerols and by ¹H-NMR spectroscopy for reactions at reactive sites of soybean oil molecules including olefinic, bisallylic and allylic protons during frying. Sesamol showed lower antioxidant activity than 0.02 % (w/w) tert-butylhydroquinone (TBHQ) at the same molar concentration. Higher concentrations of sesamol provided better antioxidant effects indicating that no prooxidant activity occurred. Sesamol in this frying test showed better results than 0.02 % TBHQ when the concentration was as high as 0.66 % by weight. An HPLC experiment showed that the concentration of sesamol decreased sharply during frying. Thermogravimetric analysis indicated that sesamol is highly volatile and easily oxidizes when exposed to air. To overcome this problem, two multiple addition methods were evaluated in which sesamol was added portion by portion every hour. The multiple additions of divided portions of 0.66 % (w/w) sesamol maintained the concentration of sesamol at the minimum of 0.04–0.06 % throughout the frying process and showed improved antioxidant activity compared to one single addition of 0.66 % sesamol at the beginning of frying. One of the multiple addition methods showed 28, 18, 59, and 27 % less polymerized triacylglycerols and losses of olefinic, bisallylic and allylic protons, respectively, than 0.02 % TBHQ after 8-h frying. This study shows that sesamol can be used as an alternative for synthetic antioxidants for frying oil.     

Comparison of Biopolymer Emulsifier Performance in Formation and Stabilization of Orange Oil-in-Water Emulsions

The effectiveness of various biopolymer emulsifiers at forming and stabilizing model beverage emulsions was examined: β-lactoglobulin (BLG); gum arabic (GA); conventional modified starch (MS-old); new modified starch (MS-new). Orange oil-in-water emulsions (5% oil) were prepared using high pressure homogenization. For BLG, MS-new, MS-old and GA, the minimum droplet diameters produced were 171, 254, 222 and 497 nm, while the minimum mass ratio of emulsifier-to-oil required to produce small droplets were 0.5:5, 1:5, 3:5 and 5:5, respectively. The influence of pH (3–8), ionic strength (0–500 mM NaCl, 0–50 mM CaCl₂) and thermal treatment (30–90 °C) on the stability of the emulsions was examined. Extensive droplet aggregation occurred in BLG-stabilized emulsions around their isoelectric point (pH ≈ 5), at high salt concentrations (≥300 mM NaCl, ≥10 mM CaCl₂, pH 7) and at high temperatures (>70 °C, 200 mM NaCl, pH 7) due to changes in electrostatic and hydrophobic interactions. There was little effect of pH, ionic strength and temperature on emulsions stabilized by GA or MS due to strong steric (rather than electrostatic) stabilization. The new type of modified starch used in this study was capable of forming stable emulsions with small droplet sizes at low concentrations.     

Antioxidant Activity Evaluation of Tocored through Chemical Assays,Evaluation in Stripped Corn Oil,and CAA Assay

γ‐Tocopherol‐5,6‐quinone (tocored) is a crucial oxidized product of γ‐tocopherol (γ‐T) found in edible oil. Previously published studies on antioxidant activity (AOA) of tocored are not consistent. This study aims to monitor its AOA comprehensively through chemical assays (1,1‐diphenyl‐2‐picrylhydrazyl [DPPH] and ferric reducing antioxidant power [FRAP]), antioxidant evaluation in a food model system (stripped corn oil), and cellular antioxidant activity (CAA) assay, which would reasonably widen the knowledge of the AOA of γ‐T and tocored. In both DPPH and FRAP assays, tocored shows less AOA than γ‐T. Results of chemical properties in the Schaal oven test show that tocored possesses better AOA than γ‐T. Correlation coefficients of γ‐T and tocored between peroxide and K₂₃₄ or p‐AnV are 0.8784–0.9875 and 0.8716–0.9879, respectively. The CAA assay also shows that tocored possesses better cellar AOA than γ‐T, with an EC₅₀ at 21.55 µg mL^?1. Drawing conclusions from the results from chemical assays, evaluation in stripped corn oil, and CAA assay, tocored is verified as a potent antioxidant in edible vegetable oils compared to γ‐T. Practical Applications: The present work widens the knowledge of antioxidant activity of tocored and gamma‐tocopherol, and contributes to the understanding of existing antioxidant activity when gamma tocopherol is depleted when edible oils are in storage and processing processes.     

氢化大豆磷脂的制备

研究了大豆磷脂的催化加氢, 讨论了其优惠工艺条件、获得了碘价为２０ ～３０ 、磷含量为３２ ％ 、氮含量为０６２ ％ 的淡黄色无难闻气味的氢化大豆磷脂产品, 收率为８０ ％ 。     

Hydroperoxide as a Prooxidant in the Oxidative Stability of Soybean Oil

Fifteen milliliters of soybean oil having peroxide value (PV) of 0, 2, 4, 6, 8, or 10 meq/kg oil in a 35 mL serum bottle was sealed air-tight with a Teflon rubber septum and aluminum cap and was stored in a forced-air oven at 50 °C. The oxidative stability of soybean oil was evaluated daily for six days by measuring the headspace oxygen content and volatile compounds in the headspace of a sample bottle by gas chromatography. As the initial PV of the oil increased from 0 to 2, 4, 6, 8 and 10, the headspace oxygen decreased and the volatile compounds increased at p < 0.05. Hydroperoxide accelerated the oxidation of soybean oil. The correlation coefficient (R ²) between the headspace oxygen and the volatile compounds was 0.95. The increase of tertiary butyl hydroquinone (TBHQ) from 0 to 50 ppm for the oil of PV 4 or 8 had a significant effect on the oxidative stability at p < 0.05. The increase from 50 to 100 ppm for the oil of PV 4 or 8 did not significantly increase the stability at p > 0.05. The oxidative stability of PV 8 meq/kg and 50 ppm TBHQ was better than the control with PV 0 and 0 ppm TBHQ at p < 0.05. TBHQ was an effective antioxidant to improve the oxidative stability of soybean oil.     

油水乳化液在疏水复合涂层网膜上破乳分离的实验研究

油水分离对于采油、炼油以及含油废水的处理有着重要的意义。采用喷涂-高温塑化的方法,在400目不锈钢网上复合PPS(聚苯硫醚)-PTFE(聚四氟乙烯)涂层,构造微米级细长纤维结构,形成了一种复合涂层网膜。该网膜具有良好的疏水性和亲油性,最大孔径<10μm,对乳化液具有破乳分离的功能。考察了渗透通量以及水包油型乳化液破乳分离效果的影响因素。实验结果表明这种膜对水包油型乳化液具有良好的分离效果,在0.4 mm膜厚下,压力小于70 kPa时,水中的含油量小于10 mg·L-1。渗透通量随压力的升高而增加,膜厚对其也有一定影响,但操作压力太高、膜的面层厚度太薄均不利于分离,料液初始浓度对破乳分离的影响则不太大。     

The Influence of Secondary Emulsifiers on Lipid Oxidation within Sodium Caseinate-Stabilized Oil-in-Water Emulsions

The effect of protein displacement at the interface by a secondary emulsifier on the oxidative stability of sodium caseinate-stabilized tuna oil-in-water emulsion systems was determined. Emulsions were prepared with a selection of anionic and non-ionic emulsifiers and stored at both 25 and 50 °C with no added prooxidant, and at 4 °C in the presence of ferrous sulfate. The progress of oxidation during storage was monitored through solid phase microextraction headspace analysis. Metal ion catalyzed oxidation was enhanced for the emulsions stabilized with an anionic emulsifier in comparison to emulsion systems stabilized with non-ionic emulsifiers and sodium caseinate alone. The increased oxidation observed for the emulsion with the anionic surfactant is due to electrostatic interactions between divalent metal ions and the negatively charged surfactant at the oil-water interface. The sodium caseinate interfacial layer had little prooxidant effect at the droplet surface, most likely due to the ability of free protein molecules in solution to sequester metal ions, which may have provided some protection against oxidative deterioration.