Effect of phenolic antioxidants on the dispersion state and chemical stability of olive oil O/W emulsions

The effect of gallic acid, catechin and quercetin on physical and chemical stability of olive oil-in-water emulsions was investigated. These molecules, characterised by different polarity and antioxidant activity, showed different interface activity and efficiency in delaying lipid oxidation. Gallic acid contributed positively to stabilise the colloidal properties of the systems toward physical instability whilst showed a low activity towards secondary oxidation. Catechin showed an interfacial localisation which was reflected in the enhancement of primary oxidation and in the inhibition of secondary oxidation. Quercetin poorly partitioned in the aqueous phase and was proven not to slow down the bimolecular phase of auto-oxidation.Results confirmed that polarity is not the only parameter to determine efficiency of antioxidants in emulsions but other variables, such as its antioxidant activity in terms of capacity and rapidity in donating an hydrogen atom, can affect its protective role towards lipids auto-oxidation in emulsions.     

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

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

乳化体系中花生油氧化稳定性的研究

主要探讨花生油乳化体系中乳化剂类型、用量、pH值、EDTA、温度等对花生油氧化稳定性的影响,结果显示:乳化剂种类和pH对于乳状液体系的氧化稳定性有显著影响,阴离子乳化剂SDS稳定的乳化液,pH4.0的氧化速率最快;非离子乳化剂Tween20稳定的乳化液,pH的影响不是很显著;阳离子乳化剂CTAB稳定的乳化液,随着pH的升高,氧化速率变快。乳化液体系中微量金属离子对于体系也有相当大的影响,随着金属离子螯合剂EDTA浓度的增加,其乳化体系中花生油的氧化速率显著降低。乳化剂用量也会影响体系的氧化稳定性,随着乳化剂用量的增加,乳化乳化体系中花生油的氧化稳定性降低。     

Hemp-seed and olive oils: Their stability against oxidation and use in O/W emulsions

Hair treatment chemicals induce sudden and severe hair damage. In this study, we examined cuticles from untreated, permed, and bleached hair that were mechanically discriminated by shaking in water. Both perming and bleaching treatments are prone to easily delaminate cuticles. Confocal microscopy revealed that the cuticles of permed hair were delaminated with larger pieces than untreated ones. On the other hand, the cuticles of bleached hair tend to fragment into small peptides. At the minimum concentration of thioglycolate required to elute S100A3 protein from the endocuticle into the reductive permanent waving lotion, enlarged delaminated cuticle fragments were observed. Although S100A3 is retained in bleached hair, S100A3 is irreversibly oxidized upon bleaching treatment. It is likely that the oxidative cleavage of disulfide bonds between cuticle-constituting proteins, including S100A3, results in the fragile property of cuticles. Here we present a more comprehensive model of hair damage based on a diverse mechanism of cuticle delamination.     

各相体积比对W/O/W复合乳状液性质的影响

目的：研究用两步乳化法制备W／O／W型复合乳状液时，第一相体积比（内水相与油相的体积比）、第二相体积比（初乳与外水相的体积比）对W／O／W型复合乳状液性质的影响；方法：采用两步乳化法制备W／O／W型复合乳状液，固定制备工艺条件，改变第一相体积比和第二相体积比的数值制备初乳和复乳，用离心分层稳定性评价复乳的稳定性，初乳的离心稳定性、黏度和复乳的粒度分布被测定；结果：随着第一相体积分数增大，初乳黏度增大，初乳和复乳的离心稳定性都提高，但是内水相的体积分数达到65％时，初乳表现出凝胶的外观，所制备的复乳的稳定性反而降低，当内水相的体积分数增加到70％的时候，初乳转相形成O／W型乳状液，不能进一步制备复乳；随着第二相体积分数的增大，复乳黏度线性增大，复乳滴的体积平均粒径减小，复乳的离心稳定性提高。初乳中内水相与油相的适宜的体积比及复乳中初乳和外水相的适宜体积比皆为1：1左右。     

O/W乳状液对核桃油氧化稳定性影响的研究

以吐温80和95%乙醇混合物为乳化剂制备核桃油乳状液,研究乳液对核桃油氧化稳定性影响。乳化剂与核桃油质量比为1∶2时,D_(50)为0.95μm,乳化效果最好;相同条件,不添加或添加相同量茶多酚,乳液过氧化值都低于纯核桃油。试验结果说明,乳液对核桃油有很好的氧化保护作用。     

Microwave heating of different commercial categories of olive oil: Part I. Effect on chemical oxidative stability indices and phenolic compounds

The effect of microwave heating of extra virgin olive oil (EVOo), olive oil (Oo) and pomace olive oil (Po) in domestic appliances, was investigated in terms of chemical oxidative indices (peroxide, p-anisidine and Totox values), free acidity, water content, total phenol content and different classes of phenolic compounds.     

The influence of different stabilizers and salt addition on the stability of model emulsions containing olive or sesame oil

Stabilizers are widely used in low-fat emulsion production. However, food industry pays attention to ingredients, such as resistant starch (RS) that also present substantial benefits to human health. Low-fat model emulsions of either olive or sesame oil that also contained xanthan gum (XG), whey protein concentrate (WPC), and undigested (resistant) starch (RS) were produced and stored at 5 °C. Salt was added in selected samples. A multiple light scattering technique was applied for investigating destabilization phenomena. Microscopic observations and droplet size measurements took place. Rheological properties performing a heating–cooling cycle experiment (5–25–5 °C) were measured. Olive oil emulsions presented the greatest stability and the lowest droplet size. RS plays the role of solid particle stabilizer, mainly entrapped in the matrix of the continuous phase. By salt addition stability was significantly improved, whereas droplet size was decreased. Those samples had a more pronounced elastic character and significantly greater viscosity values than their counterparts without salt.     

橄榄油极性酚类物质对降血脂作用探究

极性酚类物质是橄榄油重要不皂化物之一。酚类物质不仅赋予橄榄油特殊风味、提高油脂氧化稳定性,并具有良好清除自由基和阻止低密度脂蛋白(LDL)氧化能力,从而能降血脂、有效预防心血管疾病发生。该文主要从体外实验、动物实验和人体餐后实验综述橄榄油酚类物质降血脂功效。     

大豆油乳状液体系氧化稳定性影响因素的研究

研究了乳状液体系中不饱和脂肪酸的氧化机制，重点探讨了乳化剂种类、用量、pH和EDTA对大豆油乳化体系（O／W）氧化稳定性的影响。结果显示：乳化剂种类和pH对于乳状液体系的氧化稳定性有显著影响，对于阴离子乳化剂SDS稳定的乳状液，pH4．0的氧化速率比pH7．0和9．0快得多；对于非离子乳化剂Tween20稳定的乳状液，pH的影响不显著；对于阳离子乳化剂CTAB稳定的乳状液，随着pH的升高，氧化速率变快；同时在pH4．0条件下，氧化速率SDS〉CTAB〉Tween20，而在pH7．0和9．0条件下，氧化速率CTAB〉SDS≌Tween20。乳状液体系中自带的微量金属离子对于体系也有相当大的影响，随着金属离子螯合剂EDTA浓度的增加，其乳状液氧化速率显著降低。乳化剂用量也会影响体系的氧化稳定性，随着乳化剂用量的增加，乳状液的氧化稳定性变差，这种稳定性的弱化是由于粒径变小、油滴表面积增大引起的。     

Droplet characterization and stability of soybean oil/palm kernel olein O/W emulsions with the presence of selected polysaccharides

Droplet characteristics, flow properties and stability of egg yolk-stabilized oil-in-water (O/W) emulsions as affected by the presence of xanthan gum (XG), carboxymethyl cellulose (CMC), guar gum (GG), locust bean gum (LBG) and gum Arabic (AG) were studied. The dispersed phase (40%) of the emulsions was based on soybean oil/palm kernel olein blend (70:30) that partially crystallized during extended storage at 5 °C. In freshly prepared emulsions, the presence of XG, CMC, GG and LBG had significantly decreased the droplet mean diameters. XG, LBG, GG and CMC emulsions exhibited a shear-thinning behavior but AG emulsion exhibited a Bingham plastic behavior and control (without gum) emulsion almost exhibited a Newtonian behavior. Both control and AG emulsions exhibited a severe phase separation after storage (30 days, 5 °C). The microstructure of stored XG emulsion showed the presence of partially coalesced droplets, explaining a large increase in its droplet mean diameters. Increases in droplet mean diameters and decreases in flow properties found for stored GG and LBG emulsions were attributed to droplet coalescence. Nevertheless, the occurrence of droplet coalescence in these emulsions was considered to be small as no free oil could be separated under centrifugation force. Increases in flow properties and excellent stability towards phase separation found for stored CMC emulsion suggested that CMC could retard partial coalescence. Thus, the results support the ability of CMC, GG and LBG in reducing partial coalescence either by providing a sufficiently thick continuous phase or by acting as a protective coating for oil droplets.     

Study of commodity properties of food emulsions Part 1. The effect of dispersion medium composition on kinetic stability of O/W emulsions containing proteins,acidic polysaccharides and calcium salts

The effect of concentrations of acidic polysaccharide and calcium ions on the kinetic stability, viscosity and dispersity of protein-containing O/W emulsions is studied. Variation of kinetic stability of the emulsions studied is independent of dispersion composition. In a wide range of calcium acetate concentrations a correlation is observed between kinetic stability and viscosity of emulsions at sodium alginate concentration in the dispersion medium ≤ 0.3%. The transition zone between liquid solution and gel is widened in the presence of sodium caseinate. Maximum kinetic stability is reached at calcium acetate: sodium alginate concentrations of 1.0-1.2 and ～ 6.0, corresponding to optimum conditions for formation of homogeneous crosslinked structures of calcium alginate and calcium caseinate.     

Influence of the malaxation time and olive ripening stage on oil quality and phenolic compounds of virgin olive oils

The main objective of this study was to evaluate the influence of the malaxation time (Mt) and ripening stage on oil quality and phenolic compounds of Hojiblanca and Picual virgin olive oils. In both varieties of oil, phenolic content and oxidative stability decreased as ripening progressed. The total level of tocopherols diminished by up to 40% as fruit ripened. The compositions of palmitic, stearic, lignoceric, oleic, linoleic and linolenic acids were significantly influenced by the ripening process. The present work shows that an increased Mt promoted the increase of free acidity (up to 13.3%) and tocopherols (up to 11.6%) and negatively affected the oxidative stability and the concentration of phenols. Further research is required to determine ripening stages and malaxation conditions for all olive oil varieties to achieve a satisfactory balance between the improvement of both oil yield and oil quality and composition.     

Effect of standard phenolic compounds and olive oil phenolic extracts on acrylamide formation in an emulsion system

In this work the effect of standard phenolic compounds such as trolox, phenolic acids (ferulic, gallic, protocatechuic and caffeic acid) and secoiridoids, extracted from virgin olive oil (VOO), on acrylamide formation in an emulsion system was investigated. The emulsion system was heated in an oil bath at different temperatures and for different periods of time. At 105 and 115 °C the generated amounts of acrylamide were negligible during the monitoring time. At 125 °C addition of standard phenolic compounds reduced acrylamide formation which was more pronounced at initial time of heating (20 min) reaching up to 70%. Protocatechuic and gallic acid were more effective than trolox, caffeic and ferulic acid in acrylamide reduction at the final time intervals of heating (30–60 min). On the contrary, addition of VOO extract in the emulsion system resulted in a remarkable increase of acrylamide level, which was ascribed to secoiridoids’ structure containing aldehydic groups.     

Characterization and fractionation of phenolic compounds extracted from olive oil mill wastewaters

Liquid–liquid extraction was used in order to recover phenolic compounds from olive mill wastewater (OMWW), a polluting by-product of olive oil production process, and the extraction parameters have been optimized. HPLC analysis showed that hydroxytyrosol is the most abundant biophenol in ethyl acetate extracts from an acidified OMWW. Many other biophenols (tyrosol, caffeic acid, vanillic acid, verbascoside, luteolin-7-glucoside, dialdehydic form of decarboxymethyl oleuropein aglycon, ligstroside, luteolin) were identified.     

Contribution of polyphenols to the oxidative stability of virgin olive oil

Stability, polyphenol, orthodiphenol, tocopherol, oleic/linoleic ratio, chlorophyll, carotenoid, peroxide and acidity values, K₂₃₂, K₂₇₀ and overall sensory score of virgin olive oils from Hojiblanca and Picual cultivars were determined during two consecutive seasons. Changes due to cultivar and season were evaluated, correlations between the changes were studied and their contribution to stability was investigated by multiple regression techniques. Removal of polyphenols from the original samples without altering other antioxidant components has permitted estimating, for the first time, the contribution of these compounds to virgin olive oil. Approximately 50% of the stability is contributed by polyphenols. © 2001 Society of Chemical Industry     

Rheological properties of O/W emulsions stabilized by soybean total globulins

O/W emulsions, stabilized by soybean globulins, are able to posses a shear strength limit as well as the capacity for thixotropic recovery. The pseudoplastic properties of the emulsions depend on the NaCI concentration. Shear strength limit and emulsion elasticity index have maximum at a salt concentration of 0.12 mol/1.     

Stability and rheology of concentrated O/W emulsions based on soybean oil/palm kernel olein blends

Droplet size distribution and rheological properties of egg yolk-stabilized emulsions were studied before and after storage (25 °C, 30 days). The dispersed phase (70%) of the emulsions was based on soybean oil (SBO) and 10–40% palm kernel olein (PKO) replacements of SBO. Replacement of PKO resulted in a significant increase in droplet mean diameters and a decrease in rheological properties of the emulsions. All emulsion exhibited a gel-like characteristic with storage modulus higher than loss modulus and tan δ greater than 0.3. Significant increase (p < 0.05) was found for droplet mean diameters and rheological properties of the emulsions after storage. Emulsion with fully SBO and the highest PKO replacement (40%) were found to be the most unstable, which was ascribed to a strong flocculation. With 10–30% PKO replacements, the emulsions displayed a better stability after storage, most probably promoted by significant content of short-medium chain fatty acids in PKO.     

Composition of total sterols (4-desmethyl-sterols) in extravirgin olive oils obtained with different extraction technologies and their influence on the oil oxidative stability

The composition and antioxidant activity of total sterols in extravirgin olive oils obtained with different extraction technologies from olives harvested at two ripening stages, were studied. The antioxidant activity was evaluated with an oxidative stability instrument (OSI), by using a model system (made of a mixture of treated/untreated commercial refined peanut oil) enriched with the total sterol fractions of the extravirgin olive oils. No correlation was found between the OSI time and the extraction technologies, the ripening stages or the actual amount of sterols added. No significant differences were observed in the percent composition of sterols of extravirgin olive oils produced with different technologies during the same harvesting period. The latter, however, had a significant effect on the percent of β-sitosterol and 5-avenasterol in extravirgin olive oils produced with the same technology.