Role of emulsifier layer,antioxidants and radical initiators in the oxidation of olive oil-in-water emulsions

Lipid oxidation in oil-in-water (O/W) emulsions is largely affected by the properties of the interfacial layer surrounding the oil droplets. In this work, the effect of the emulsifier layer structure, presence of both hydrophilic and lipophilic antioxidants and radical initiators on the development of lipid oxidation in olive oil-in-water emulsions was investigated. The olive oil-in-water emulsion is a suitable model of low fat food emulsions. The rationale of the work was to study the role of the interfacial layer when both the antioxidants and the radical initiators came from the two different emulsion compartments. Emulsions were prepared by using food grade emulsifiers of the Tween series (polyoxyethylene sorbitan esters) in the water phase and Span 80 (sorbitan monoleate) in the oil phase. The properties of the interfacial layer were changed by using Tween 20, Tween 60, Tween 80, which have different hydrophobic tails. These systems were oxidized by means of both hydrophilic (AAPH (2,2′-azobis,2-methyl-propanimidamide dihydrochloride), AIPH (2,2′-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride) and lipophilic (AMVN (2,2′-azobis(2,4-dimethylvaleronitrile)) radical initiators at 40 °C. A continuous fluorescent method based on the front face technique allowed us to follow directly the development of oxidation in the whole emulsion. The combination Tween 80/Span 80 produced an interfacial layer more resistant to radical attack. Moreover, a polar paradox was verified also for radical initiators, while the results suggest that the best way to protect emulsions is to use a combination of antioxidants in both phases, to promote a synergy and the regeneration of antioxidants mediated by the interfacial layer.     

二十二碳六烯酸微藻油乳状液稳定性的影响因素

以二十二碳六烯酸（docosahexenoic acid,DHA）微藻油微胶囊化过程中形成的乳状液为研究对象,通过测定乳状液稳定性、界面膜强度、界面张力、粒径和Zeta-电位,探究乳化剂、pH值和金属离子对乳状液稳定性的影响。结果表明,司盘80与吐温60复配的乳状液亲水亲油平衡（hydrophile-lipophile balance,HLB）值为11.19时,对乳状液稳定性的提升效果最明显。乳化剂的种类比HLB值更明显地影响乳状液稳定性,其作用机制与乳状液的界面膜强度紧密相关。吐温20与单甘酯复配乳化剂（体积比58∶42）添加量高于1.2%时,界面膜强度高,乳状液最稳定。此外,乳状液的pH值与金属离子均能明显影响乳状液稳定性。pH值越高,乳状液中静电斥力越强,从而促进稳定性提高。低浓度的金属离子能够提高乳状液稳定性;高浓度金属离子,尤其是高价金属离子,能明显降低乳状液稳定性。高浓度Fe3＋能够通过氧化DHA的方式破坏乳状液,甚至使乳状液形成不溶性的悬浊状态。结论：研究可为提高DHA微藻油乳状液稳定性和开发高质量微胶囊提供参考。     

共轭亚油酸多重乳状液的制备及稳定性研究

以多重乳状液相对体积为衡量标准,借助显微镜直接观察,探讨油水相质量比、亲油亲水乳化剂质量比、乳化剂的HLB值、乳化剂的含量等因素对共轭亚油酸多重乳状液体系稳定性的影响.结果表明,单一乳化剂体系中,以Tween80作亲水乳化剂制备的多重乳状液稳定性较好.当m(内水相):m(油相):m(外水相)=1:5:1.3,m(Span80):m(Tween80)=9,乳化剂的含量为9.7%时,多重乳液相对体积达到93%.复合乳化剂体系中,在第一相的HLB值为7.4,m(复合乳化剂):m(Tween80)=9,乳化剂质量分数为6.67%时,稳定性最好.     

Effects of bacteriostatic emulsifiers on stability of milk-based emulsions

For milk-based emulsion products such as canned coffee or tea, the addition of bacteriostatic emulsifiers is necessary to inhibiting the growth of heat-resistant sporeformers. Since bacteriostatic emulsifiers often cause the destabilization of emulsions, other type of emulsifiers, such as stability-enhancing ones, are necessary for the long-term stability of emulsions. Four milk-based emulsions were prepared from powdered milk combined with several types of emulsifiers. The long-term stability of emulsions, which was detected by the occurrence of a creaming layer after 3 months of storage, differed according to the composition of emulsifiers. To understand the reason for the differences in the stability of emulsions, particle size, distribution, ζ-potential, and the amount of proteins and phospholipids present in the cream layer (separated oil droplets) in the emulsions were measured. Only the amount of proteins adsorbed onto oil droplets was found to be closely related to the difference in emulsion stability, that is, the more proteins adsorbed, the higher the emulsion stability. SDS–PAGE analyses revealed that κ-casein and β-lactoglobulin play an important role in emulsion stability by adsorbing onto the oil droplet surface.     

Alginate‐Based Emulsion Template Containing High Oil Loading Stabilized by Nonionic Surfactants

Oil‐in‐water (O/W) emulsion‐gel systems containing high oil payloads are of increasing interest for food applications because of the reduction in encapsulation cost, consumption frequency or volume of food products. This study shows a facile approach to prepare stable alginate‐based O/W emulsions at high oil loading using a mixture of nonionic surfactants (Tween 80 and Span 20) as a template to form gelled‐emulsions. The synergistic effects of alginate and surfactants on the O/W emulsion properties were evaluated in terms of oil droplet size and emulsion stability. At 2% (w/v) of alginate and 1% (w/v) of surfactants, the size distribution of oil droplets was narrow and monomodal, even at an oil loading of 70% (v/v). The emulsions formed were stable against phase separation. The oil droplet size could be further reduced to below 1 μm using a high‐shear homogenizer. The emulsions formed could be easily molded and gelled into solids of different shapes via ionic gelation. The findings of this study create possible avenues for applications in food industries.     

三种乳化剂对橄榄油乳液稳定性的影响

乳化剂因亲水亲油平衡值的不同对油脂乳化效果表现出固有的差异,但这种差异会因加入辅助剂的影响而发生改变。以非离子型表面活性剂单甘酯、蔗糖酯和吐温20为乳化剂,以白果直链淀粉及阿拉伯胶(质量比1∶1)为辅助剂,对橄榄油进行乳化,考察了辅助剂加入前后在不同制备方法(先油后水和先水后油工艺)和乳化剂添加量下乳液的稳定性。结果表明:单独使用乳化剂时,经外观观察,在三种乳化剂添加量相同时,吐温20的橄榄油乳液稳定性较好,其次为蔗糖酯、单甘酯;加入辅助剂后,乳液的乳化状态较单一加入乳化剂的好,乳液黏度、粒径和浑浊度均随着乳化剂添加量的增大呈先减小后增加趋势,且在相同添加量下,由蔗糖酯制备的橄榄油乳液黏度较低,粒径和浑浊度较小,稳定性较好,吐温20及单甘酯次之;辅助剂加入前后,先油后水工艺制备的橄榄油乳液的稳定性总体优于先水后油工艺的。     

Impact of antioxidants dispersions on the stability and oxidation of water-in-olive-oil emulsions

Water-in-olive-oil emulsion stability was studied as a function of the composition of the water dispersed phase. In particular, different polyphenolic extracts from natural sources were dispersed in the olive oil and their impact on emulsion kinetic stability and susceptibility to oxidation was evaluated. As natural sources, extra virgin olive oil, olive mill waste and green tea leaves were chosen. To test their impact on emulsion properties, the emulsions were prepared with fixed aqueous phase content. As emulsifiers, a fixed percentage of a mixture Span 80 (sorbitan monoleate)/Tween 80 (polysorbate 80) was used. The effect of the antioxidant dispersion on emulsion oxidation was studied by triggering the oxidation reaction in the oil phase with the lipophilic radical initiator AMVN (2,2-azobis(2,4-dimethylvaleronitrile). Then, the oxidation reaction was followed by using diphenyl-1-pyrenylphosphine, which becomes fluorescent when it is oxidized by hydroperoxides. The impact of antioxidant dispersions on emulsion kinetic stability was studied by UV–Vis turbidity measurements. The oxidation results were correlated to antioxidant extracts oxygen radical adsorption capacity (ORAC) and to emulsion kinetic stability. On the whole, antioxidants dispersions delayed the oxidation reaction to different extents in dependence on their ORAC values and their components amphiphilicity. Remarkably, among the antioxidants tested, the aqueous polyphenol extract from virgin olive oil was the most effective because it protected emulsions both from oxidation and from phase separation. Additionally, from this set of experiments, the primary role of the interfacial properties of olive oil polyphenols was highlighted.     

Study of the Emulsifying Ability of Olive Oil Endogenous Compounds in Co-surfactant Free Olive Oil w/o Nanoemulsions with Food Grade Non-ionic Surfactants

In the present work, the preparation of olive oil w/o nanoemulsions was studied using non-ionic surfactants (Tween 20, Span 20) without the addition of a co-surfactant. Different olive oil endogenous compounds with an amphiphilic character (gallic acid, apigenin, quercetin, and trans-cinnamic acid) were dispersed into the aqueous phase, and their impact on the nanoemulsions stability and properties ability was determined. The stable nanoemulsions were presented in pseudo-ternary phase diagrams (oil–aqueous phase–surfactant) for each surfactant and endogenous compound. The nanoemulsions properties were evaluated in relationship to compositional components. The results of this study concluded that stable w/o olive oil nanoemulsions without use of a co-surfactant were obtained and moreover, the most efficient type of emulsifier and its ratio of addition in the system were determined. The incorporation of olive oil endogenous compounds resulted into more stable emulsions. In particular, gallic acid was proven to be the most efficient compound since it enhanced the emulsion properties prolonging simultaneously the emulsions’ stability.     

乳状液成分对O/W乳状液性质的影响

采用单因素实验设计,通过机械搅拌方法制备O/W乳状液。通过乳状液的离心稳定性、粘度和乳状液的显微结构,研究不同HLB值的复合乳化剂及含量、脱脂乳粉溶液的浓度以及油和水比例对乳状液性质的影响,最终确定较佳的乳状液成分。实验结果表明:当以Span-80和Tween-80为复合乳化剂,其HLB值为9.6、复合乳化剂含量为16%(w/w)、脱脂乳粉溶液浓度为25%(w/v)、油与水比为1∶1(w/w)时,可以获得状态较好的乳状液,此时乳状液的离心稳定性最高,可以达到97.5%。     

乳化剂对植脂淡炼乳乳化效果的研究

针对植脂淡炼乳中油脂含量较高，易出现油水分离、乳蛋白不稳定等现象而影响产品的质量和稳定性，研究了单甘酯、蔗糖酯、Tween60和Span60等乳化剂对植脂淡炼乳的乳化效果，为植脂淡炼乳的下一步开发利用奠定基础。     

单、双脂肪酸甘油酯(亚麻酸)乳液的制备及特性研究

针对单、双脂肪酸甘油酯（亚麻酸）极易氧化的特点,该研究以乳清浓缩蛋白（WPC）、大豆分离蛋白（SPI）、酪蛋白酸钠（SC）和吐温80（T80）为乳化剂制备乳液,考察乳化剂类型对乳液的理化性质、氧化稳定性和消化特性的影响。结果表明,乳液均具有较小的粒径（131.97~224.87 nm）,且在两周贮藏期内保持稳定。乳液包载能够提高单、双脂肪酸甘油酯（亚麻酸）的氧化稳定性,相比T80（过氧化值为377.40 mmol/kg）,蛋白质对油脂的氧化保护效果更好,其中SPI稳定的乳液过氧化值最低为197.73 mmol/kg。体外模拟消化试验表明,乳化剂类型对游离脂肪酸的释放影响较小,但蛋白稳定的乳液在胃消化阶段更容易发生液滴聚集;亚麻籽油的脂质水解程度最低为23.93%,而单、双脂肪酸甘油酯（亚麻酸）的初始消化速度更快,最终脂解程度更高（46.33%）。因此,蛋白质乳液能有效提高单、双脂肪酸甘油酯（亚麻酸）的氧化稳定性,且单、双脂肪酸甘油酯（亚麻酸）相比亚麻籽油具有更好的消化效率,有望替代亚麻籽油作为人体亚麻酸的食物来源。     

改善牛肉脂肪品质替代品的研究

以植物油为溶剂,水为溶质,添加卵磷酯、单硬脂酸甘油酯、山梨醇酐单油酸酯(Span80)、乳清蛋白等其他添加成分,研制肥牛脂肪替代品,采用了4因子二次通用旋转组合设计,得出最佳配比为单硬脂酸甘油酯0.434%,山梨糖醇酐脂肪酸酯0.110%,卵磷酯0.504%,乳清蛋白0.410%。用冲淡法检测乳状液类型为W/O型。乳状液稳定性的检测结果,测其体积比率为0.59%,达到了稳定体系的要求。     

乳化剂在甜橙乳化香精中的应用研究

本文通过对蔗糖酯(SE)、吐温(T)和司盘(S)系列的单体以及复配在甜橙乳化香精中的乳化效果研究，并应用正交实验确定了复合乳化剂的最佳配比以及相关的工艺参数。结果表明对甜橙乳化香精来说T-40，SE-15的乳化效果较好。适宜的工艺条件为：SE-15：2．00％，T-40：1．5％，S-60：0．7％，均质次数2次，均质条件一级压力150bar，二级压力50bar。     

Catastrophic inversion and rheological behavior in soy lecithin and Tween 80 based food emulsions

Emulsions inversion occurs in many industrial processes and may be influenced by the formulation conditions, composition and emulsification protocols. In this work, the influence of emulsifiers and stirring on catastrophic inversion (O/W to W/O) was evaluated. Emulsions were prepared with different stirring rates, using soy lecithin and Tween 80, at 2 and 5 wt%. The aqueous phase was distilled water with 1 wt% NaCl and the oil phase was soy oil. These emulsions were analyzed by conductivity, stability, microscopy and rheology assays. The most stable emulsions presented inversion with a smaller amount of the external phase. Rheological analysis showed that, with a higher concentration of emulsifier, it is better to use Tween 80 when lower viscosity is desired, while soy lecithin is more appropriate for higher viscosity products. The oscillatory tests showed that while the emulsions prepared using Tween 80 exhibited concentrated solution behavior, those prepared with soy lecithin exhibited strong gel behavior.     

水包油型食品乳液中天然小分子乳化剂的功能性质及与其他乳化剂相互作用关系的研究进展

水包油型乳液是食品、保健品、药品等的重要成分,单一或复合乳化剂对水包油型乳液的形成、稳定性和功能性质有重要影响。如今消费者对健康和环境保护的关注促使食品生产者更倾向使用天然成分取代合成成分。本文综述在食品工业中具有潜在应用价值小分子天然乳化剂的理化性质,讨论其对乳液稳定性的影响以及在食品工业中的应用情况,并总结在乳液中使用复合乳化剂,尤其是磷脂与其他乳化剂相互作用的性质和机理;最后概括复合乳化剂对乳液功能性质的影响,包括抗氧化活性、抗菌活性和胃肠道消化特性。以期为开发乳液产品、选择乳化剂及其组合提供理论参考。     

艾蒿油乳液稳定性的油相离心系数法表征

以N-十二烷基亚氨基二丙酸二钠(NCNA)和失水山梨醇单油酸酯(Span80)为乳化剂,采用界面复合物生成法制备艾蒿油乳液,通过油相离心系数对艾蒿油乳液的稳定性进行表征.讨论了搅拌速度、乳化温度、乳化时间、乳化剂质量分数、乳化剂配比等因素对乳液稳定性的影响.结果表明:搅拌速度为3 000 r/min、温度为60℃、乳化时间为15 min、乳化剂质量分数为5%、m(Span80)/m(NCNA)=8/2时油相离心系数为0,乳液最稳定.通过多媒体显微镜和透射电镜观察了乳液液滴的分布及大小形态,在最佳条件下制备的乳液液滴粒径集中分布在20～50 nm.     

甜橙乳化香精的生产工艺

通过对乳化香精中使用的主要添加剂增重剂、乳化剂和增稠剂在甜橙乳化香精中单独和复配使用的效果研究 ,发现对甜橙乳化香精来说乙酸异丁酸蔗糖酯 (SAIB)和松香甘油酯 (EG)的增重效果较好 ;聚山梨酸酯 40 (T 40 ) ,蔗糖脂肪酸酯 1 5 (SE 1 5 )的乳化效果较好 ;实验中选用的增稠剂在一定条件下可以增加乳状液的黏度 ,但是并没有提高乳状液的稳定性。并应用正交试验确定了添加剂最佳配比以及生产甜橙乳化香精的相关工艺参数。     

Physical characteristics of submicron emulsions upon partial displacement of whey protein by a small molecular weight surfactant and pectin addition

O/W emulsions (6 wt.% olive oil) were prepared at pH 3.3 using different WPI:Tween 20 weight ratios (1:0, 3:1, 1:1, 1:3, 0:1) at 1 wt.% total concentration. The emulsion droplet size was found to decrease with an increase in Tween 20. A minimum droplet size of d_3,2 300 nm was found for Tween systems alone, similar to that found (360 nm) for a 1:1 WPI:Tween 20 combination (p < 0.05). This specific composition showed a value for the interfacial tension close to that of Tween 20 alone. However, the emulsions presented low stability regardless of the WPI:Tween 20 ratio. To increase their stability, pectin was added, in various concentrations (0.2, 0.4 and 0.6 wt.%), using the Layer by Layer technique. In the presence of pectin, the ζ-potential of the oil droplets became negative; indicating that negatively charged pectin was absorbed onto the positively-charged droplet surface forming a secondary layer. The additional layer resulted in a wide range of emulsion stability. For all pectin concentrations, the 1:1 ratio of WPI:Tween 20 showed the highest stability. In most emulsions, extensive aggregation of oil droplets was observed, and their viscosity increased. Insufficient amounts of pectin to form the secondary layers led to bridging flocculation phenomena of oppositely charged pectin and proteins, leading to aggregation of the oil droplets. The higher the concentration of pectin, the greater the stability of the emulsion due to higher viscosity. All in all, the addition of a second layer consisting of pectin can be used to increase the stability of an emulsion containing emulsion droplets in the sub-micron range.     

Factors Influencing the Freeze‐Thaw Stability of Emulsion‐Based Foods

Many of the sauces used in frozen meals are oil‐in‐water emulsions that consist of fat droplets dispersed within an aqueous medium. This type of emulsion must remain physically and chemically stable throughout processing, freezing, storage, and defrosting conditions. Knowledge of the fundamental physicochemical mechanisms responsible for the stability of emulsion‐based sauces is needed to design and fabricate high‐quality sauces with the desired sensory attributes. This review provides an overview of the current understanding of the influence of freezing and thawing on the stability of oil‐in‐water emulsions. In particular, it focuses on the influence of product composition (such as emulsifiers, biopolymers, salts, and cryoprotectants), homogenization conditions, and freezing/thawing conditions on the stability of emulsions. The information contained in this review may be useful for optimizing the design of emulsion‐based sauces for utilization in commercial food products.     

The effect of emulsifier type and oil inclusion on stress-related gene expression of Salmonella typhimurium in oil-in-water emulsion

Salmonella has been associated with numerous outbreaks from contaminated food products, including emulsions. Emulsions are influenced by emulsifier type and oil presence, which can have varying degrees of stress or protection on bacteria. Although our previous research has shown that emulsifier solutions, rather than emulsions, provide a protective effect on Salmonella typhimurium after thermal treatment, the underlying mechanism remains unclear. This study selected S. typhimurium as the model microorganism and utilized the same emulsifiers (Tween 20, Tween 80, Triton X-100) to create emulsifier solutions and emulsions with the same oil fraction (60% (v/v)) to examine their effect on the expression of nine selected genes (rpoE, rpoH, otsB, proV, fadA, fabA, dnaK, ibpA, ompC) associated with stress response. Specifically, the study observed variations in gene expression under normal and thermal stress at 55°C. After 20-h incubation, Triton X-100 emulsion caused an upregulation of stress-related genes, rpoE, otsB, and fabA, suggesting stressful environment. After thermal treatment, S. typhimurium in Triton X-100 solution showed a longer 5-log reduction time with increased proV and decreased fabA and ompC expression, suggesting enhanced thermal protection compared to its emulsion. Conversely, Tween 80 solution increased fabA and ompC expression, indicating greater membrane fluidity and passive diffusion, potentially reducing thermal resistance. However, according to the upregulation of ibpA, this effect was likely mitigated by the overproduction of heat shock proteins. Notably, Triton X-100 environments exhibited the most significant gene expression changes after heat treatment, whereas Tween 80 without oil was the most inhospitable for bacterial survival. These findings inform bacterial responses under various conditions, aiding food safety strategies.