乳清蛋白乳液界面性质及其物理稳定性和氧化稳定性的研究

以乳清蛋白与玉米油为原料,采用高压均质技术制备水包油型(O/W)乳液。探究乳清蛋白浓度(0.45%~3.60%)、离子强度(250 mmol/L Na Cl)对乳清蛋白乳液界面特性及其物理稳定性和氧化稳定性的影响。结果表明:随着乳清蛋白浓度的增加,乳液的粒径、乳析指数、过氧化值(POV)和丙二醛生成物(TBARS)都呈现降低的趋势,而乳液的界面蛋白浓度、电位随着蛋白浓度的增加而增加。乳液中加入250 mmol/L Na Cl能够增加乳液的粒径、乳析指数、界面蛋白含量、电位值、POV和TBARS值。上述结果表明乳液界面蛋白浓度增多,乳液的物理稳定性和氧化稳定性得到增强,而乳液中加入Na Cl后能够减弱乳液的物理稳定性和氧化稳定性。     

大豆分离蛋白对大豆肽纳米颗粒Pickering乳液性能的影响

为提高大豆肽纳米颗粒(SPN)Pickering乳液稳定性,以大豆肽聚集体为原料,采用超声法制备SPN,对超声时间进行了优化;在SPN体系中引入大豆分离蛋白(SPI)构建复合乳化剂,研究不同乳化剂质量浓度下SPI对SPN界面活性和乳化稳定性的影响。结果表明：选取超声时间10 min制备SPN;随着乳化剂质量浓度的增大,乳液粒径逐渐减小,当乳化剂质量浓度较低(5 mg/mL)时,乳液出现桥联,乳化剂质量浓度过高(30 mg/mL)时则出现絮凝;界面蛋白吸附率随着乳化剂质量浓度的增加呈现先升高后降低的趋势。在相同乳化剂质量浓度下,添加SPI的SPN乳液(SPI-SPN乳液)的粒径分布峰左移,其粒径、界面蛋白吸附率显著小于SPN乳液的;在储存过程中,SPN乳液粒径逐渐增大,SPI-SPN乳液粒径没有显著变化;SPI-SPN乳液的乳析指数小于相同乳化剂质量浓度的SPN乳液,当乳化剂质量浓度为30 mg/mL时,储存15 d SPI-SPN乳液未出现分层现象。综上,SPI可以提高SPN的界面活性和SPN乳液储存过程中的絮凝稳定性和分层稳定性。     

不同配方制备紫檀芪纳米乳液及其稳定性

以葵花籽油、橄榄油和中链脂肪酸甘油三酯(MCT)为载体油相,以吐温80(Tween 80)和酪蛋白酸钠(SC)为乳化剂,采用高压均质法制备紫檀芪纳米乳液(pterostilbene nanoemulsions,PTSNE)。研究了油相种类和质量分数、乳化剂类型和质量分数以及添加助乳化剂(甘油)对PTSNE粒径大小的影响。同时考察了环境因素p H(3~9)、热处理(40~100℃,60 min)和离子强度(0~500 mmol/L Na Cl,0~500 mmol/L CaCl_2)对PTSNE稳定性的影响。结果表明:不同载体油相制备的PTSNE粒径大小为:葵花籽油≈橄榄油MCT,随着油相质量分数升高达到20%时,粒径变大,且储藏稳定性变差。不同乳化剂制备的PTSNE粒径大小为:Tween 80SC,且随着乳化剂质量分数升高,粒径均显著减小(p0.05)。在水相中添加甘油后,Tween 80和SC制备的PTSNE粒径均显著减小(p0.05)。Tween 80制备的PTSNE在p H(3~9)、热处理(40~90℃,60 min)和离子强度(0~500 mmol/L Na Cl,0~500 mmol/L CaCl_2)环境下均有良好的稳定性;在100℃保温60 min时,其粒径增大了约50 nm。SC制备的PTSNE具有较好的温度稳定性,但在其等电点(p H≈4.6)附近和高离子强度(≥50 mmol/L CaCl_2)环境下出现明显的液滴聚集现象。     

不同离子强度下罗非鱼肌球蛋白热变性聚集研究

以罗非鱼肉为原料,提取肌球蛋白,分析不同离子强度(1、50、150、300、600 mmol/L KCl)下热处理(40~80℃,1℃/min)对其浊度、溶解度、表面疏水性、α-螺旋含量及聚集体粒径的影响。结果显示,离子强度及热处理温度明显影响肌球蛋白的热变性聚集。在低离子强度(1~150 mmol/L KCl)下,肌球蛋白聚集成纤丝,溶解性差,热处理后分子聚集沉淀,溶解度和α-螺旋含量减小(p0.05),体系热稳定性差;在高离子强度(300~600 mmol/L KCl)下,肌球蛋白分子解离成单体,溶液澄清,当热处理温度高于50℃时,肌球蛋白溶解度下降,表面疏水性增加,α-螺旋含量显著减小(p0.05),但分子聚集不明显。总体分析,高盐离子的静电屏蔽作用导致肌球蛋白纤丝解离,由此也会对肌球蛋白分子结构有一定的保护作用,热稳定性相对较好。     

水相大豆分离蛋白对油包水乳液稳定性的影响

以富含多不饱和脂肪酸的核桃油为油相,于水相添加大豆分离蛋白(SPI),采用超高压微射流均质机制备油包水(W/O)乳液,乳液于45℃避光保存,每隔1 d测定乳液的平均粒径及粒径分布等物理特性,同时检测乳液初级及其次级氧化产物—脂质氢过氧化物与己醛,探究SPI对W/O乳液稳定性影响。结果表明,SPI应用于W/O乳液,乳液水滴粒径降低,乳液物理稳定性增大,SPI同时具有抗氧化活性。0.1%~0.4%SPI,蛋白质用量的增大对乳液物理稳定性无显著性影响;SPI用量增大(0.1%~0.2%)延长了脂质氢过氧化物与己醛形成延迟期,而用量进一步增大(0.4%)乳液脂质氧化稳定性影响不显著。乳液水相p H对SPI抗氧化活性有显著影响,水相p H 7.0,SPI抗氧化活性高于水相p H 3.0。研究同时表明,水相钙离子强度0~200mmol/L Ca Cl2,钙离子引入提高了乳液物理稳定性;乳液水相钙离子强度较低时(≤10 mmol/L Ca Cl2),离子强度的增大降低了SPI抗氧化活性,较高离子强度(100~200 mmol/L Ca Cl2)加速了乳液脂质氧化。     

魔芋葡甘露聚糖对酶解青花椒籽仁谷蛋白乳液稳定性的影响

为进一步了解多糖对于蛋白乳液稳定性的影响,该文以魔芋葡甘露聚糖为代表,研究对酶解青花椒籽仁谷蛋白乳液稳定性的影响。结果表明,0. 3%的魔芋葡甘露聚糖对青花椒籽仁谷蛋白乳液的稳定性具有较好的效果。添加了魔芋葡甘露聚糖的乳液具有良好的pH稳定性(5～7)、离子强度稳定性(0～400 mmol/L Na Cl,pH 3)以及热稳定性(30～90℃,0 mmol/L Na Cl,pH 3)。该文对多糖作为生物大分子天然稳定剂增强蛋白乳液稳定性的相关研究提供了参考,也为青花椒籽仁谷蛋白应用于食品工业中提供了理论基础。     

吐温20对界面大豆分离蛋白的取代及其对乳液稳定性的影响

研究了吐温20添加量、pH、离子强度和吐温20添加次序对大豆蛋白乳液界面蛋白取代率及界面吸附蛋白浓度(Γ)的影响,比较了均质前后添加吐温20乳液的粒径及储藏稳定性。结果表明,中性或碱性、低离子强度的条件有利于吐温20从油水界面取代大豆分离蛋白(SPI),酸性或高离子强度都不利于取代。均质后添加1%(w_(吐温20)/v_(乳液),下同)吐温20,界面蛋白取代率最高为48. 87%,新鲜乳液粒径显著变小;而均质前添加0. 4%吐温20,界面蛋白取代率最高为33. 93%,吐温20添加量对新鲜乳液粒径无显著影响。均质后添加吐温20几乎不影响乳液稳定性,而均质前添加吐温20则随着其添加量增加乳液失稳更快。通过激光扫描共聚焦显微镜观察发现,加入吐温后的乳液界面吸附蛋白层明显变薄。     

环境因素对叶黄素纳米乳液稳定性及其抗氧化活性的影响

以酪蛋白酸钠为乳化剂,高压均质构建叶黄素纳米乳液载运体系,并评价其对1,1-二苯基-2-三硝基苯肼自由基和2,2’-联氮-二(3-乙基-苯并噻唑-6-磺酸)阳离子自由基的清除能力和氧自由基吸收能力,及环境因素（pH值、热处理、离子强度和浓缩）对乳液体系中叶黄素稳定性和自由基清除活性的影响。结果表明：纳米乳液体系能够显著提高叶黄素的自由基清除活性（P＜0.05）;pH值为2.0或离子强度为50 mmol/L和100 mmol/L NaCl时,纳米乳液的叶黄素质量浓度和自由基清除活性有不同程度的减小,旋转蒸发浓缩后叶黄素质量浓度和自由基清除率均显著增加（P＜0.05）,而热处理（60、80 ℃和100 ℃）对叶黄素纳米乳液体系的影响则相对较小。     

牡丹籽油凝胶乳液的制备及稳定性评估

以辛烯基琥珀酸(octenyl succinic anhydride, OSA)淀粉为乳化剂,植物甾醇-卵磷脂-牡丹籽油凝胶为芯材,制备了4种水包油型牡丹籽油凝胶乳液,其分散相平均粒径在1～4μm, Zeta电位在-31 mV左右。以粒径、Zeta电位为指标,研究了pH值(3～9)、热处理(40～100℃)、盐离子种类(Na⁺、Ca²⁺、Al³⁺)及离子强度(100、200、300、400、500 mmol/L)对凝胶乳液稳定性的影响。结果表明,经酸处理后,油凝胶乳液的平均粒径和Zeta电位显著增大(电位绝对值减小),而弱碱条件对乳液粒径无显著影响,Zeta电位则逐渐减小(绝对值增加);在pH 3～9,4种凝胶乳液均表现出良好的稳定性。金属离子(Na⁺、Ca²⁺、Al³⁺)及其添加浓度的增加会导致凝胶乳液分散相粒径和Zeta电位增大,其中Al³⁺的影响最为显著,Ca²⁺次之,而Na⁺的影响较...     

不同乳化剂制备乳状液对大豆蛋白凝胶强度影响

通过静置分层实验和离心分层实验考察了不同乳化剂(卵磷脂、Tween20、大豆蛋白、卵清蛋白和酪蛋白)、p H(3、4、5、6、7、8)、氯化钠浓度(10、50、100、150、200 mmol/L)以及热处理(90℃、30 min)对机械乳化法和超声乳化法制备乳状液稳定性的影响;并考察p H 7及不同盐浓度(0 mmol/L和200 mmol/L)条件下不同乳状液对热诱导大豆蛋白凝胶15%(w/v),90℃加热30 min)凝胶强度的影响。结果表明,小分子乳化剂(卵磷脂和Tween20)制备的乳状液的稳定性优于大分子乳化剂(大豆蛋白、卵清蛋白以及酪蛋白)制备的乳状液;超声法制备的乳状液的稳定性高于机械法制备的乳状液;以超声乳化得到的卵清蛋白乳状液为溶剂制备的大豆蛋白凝胶强度最好;氯化钠的加入可以有效提高凝胶的强度。     

大豆分离蛋白-高酯柑橘果胶-没食子酸复合Pickering乳液制备及其稳定性分析

以大豆分离蛋白、高酯柑橘果胶、没食子酸为原料,制备一种蛋白质-多糖-多酚复合物,利用单因素试验、正交试验优化复合物制备条件,并通过流变特性、粒径及分布、Zeta电位、乳液稳定性等分析手段对Pickering乳液稳定性能进行表征。结果表明：在pH 4.5、温度35 ℃、没食子酸含量40 mg时复合乳液的吸光度达到最大值3.082,此时大豆分离蛋白-高酯柑橘果胶-没食子酸结合最紧密;当油相体积分数为0.7时,Pickering乳液弹性和黏性最好,形成的较好凝胶网络结构,此时的电位为（－54.08±2.74）mV,平均粒径为（220.36±7.13）nm;与25 ℃常温贮存相比,Pickering乳液在4 ℃冷藏析乳现象更弱,油滴粒径变化更小,更有利于维持乳液稳定性;随热处理温度升高,乳液析乳情况逐渐增强,油相体积分数为0.7和0.8时,液滴粒径受温度变化不明显;冷冻会破坏复合物形成的界面层,随着油相体积分数升高和冷冻时间的延长乳液析油现象明显导致稳定性大大降低;随着pH值升高,析油现象逐渐明显,当乳液体系pH值接近4时,乳滴粒径最小且分布相对均匀;高浓度的盐离子会破坏复合物结合的紧密程度,液滴发生聚集,乳液析乳情况明显,稳定性下降。     

Physical Properties of Whey Protein Stabilized Emulsions as Related to pH and NaCl

Corn oil-in-water emulsions (20 wt%, d₃₂～ 0.6 μm) stabilized by 2 wt% whey protein isolate were prepared with a range of pH (3–7) and salt concentrations (0–100 mM NaCl), and particle size, rheology and creaming were measured at 30°C. Appreciable droplet flocculation occurred near the isoelectric point of whey protein (pH 4–6), especially at higher NaCl concentrations. Droplet flocculation increased emulsion viscosity and decreased stability to creaming. Results are related to the influence of environmental conditions on electrostatic and other interactions between droplets.     

Disulfide-mediated Polymerization Reactions and Physical Properties of Heated WPI-stabilized Emulsions

Heating a 19 wt% corn oil-in-water emulsion stabilized by 1 wt% whey protein isolate from 30 to 70°C and then cooling to 25°C for at least 15 hr, brought about minimal changes in droplet aggregation, apparent viscosity and susceptibility to creaming. At 75°C, droplet aggregation occurred but this decreased on heating to 90°C. The apparent viscosity and susceptibility of droplets to creaming increased as the degree of droplet aggregation increased. Inclusion of the sulfhydryl blocking agent N-ethylmaleimide to inhibit thiol/disulfide interchange reactions did not affect droplet aggregation but resulted in higher apparent viscosity values and susceptibility to creaming at 85 and 90°C and not at lower temperatures. The results suggest that droplet aggregation results from noncovalent interactions between unfolded protein molecules adsorbed on different droplets and that the interactions are strengthened by disulfide bonds.     

Ability of flaxseed and soybean protein concentrates to stabilize oil-in-water emulsions

The ability of flaxseed protein concentrate (FPC) to stabilize soybean oil-in-water emulsion was compared with that of soybean protein concentrate (SPC). The stability of emulsions increased with increase in protein concentration. The FPC-stabilized emulsions had smaller droplet size and higher surface charge, but worse stability at the same protein concentration compared to SPC-stabilized emulsions. Oil-in-water emulsions stabilized by both proteins were diluted and compared at different pH values (3–7), ionic strength (0–200 mM NaCl) and thermal treatment regimes (25–95 °C for 20 min). Considerable emulsion droplet flocculation occurred around iso-electric point of both proteins: FPC (pH 4.2) and SPC (pH 4.5). FPC and SPC-stabilized emulsions remained relatively stable against droplet aggregation and creaming at NaCl concentration below 100 and 50 mM, respectively. The emulsions stabilized by both proteins were fairly stable within these thermal processing regimes. FPC appears to be less effective as an emulsifier compared to SPC due to its lower emulsion viscosity. Hence, FPC could be more effective in emulsions that are fairly viscous.     

Impact of a thermal treatment on the emulsifying properties of egg yolk. Part 2: Effect of the environmental conditions

The protein solubility and emulsifying properties of native and heat-treated egg yolk (EY) suspensions were investigated in various environmental conditions. Four distinct conditions were tested by combining two levels of pH, namely pH 4.0 and 6.5, and two levels of ionic strength, namely 0.15 and 0.52 M NaCl, in a model oil-in-water (O/W) emulsion containing 30% oil (v/v). Although the protein solubility was greatly reduced by the thermal denaturation in all tested environmental conditions, the average size of oil droplets obtained in emulsions made with heated EY was observed to be either similar or slightly smaller than that obtained with native EY, depending on the environmental conditions. Using heat-treated EY rather than native EY led to a significant increase of the interfacial protein concentration in all environmental conditions. This increased interfacial protein concentration was shown to have a major impact on the flocculation behaviour of the emulsions, as well as on their rheological properties and stability to creaming. Hypotheses regarding the mechanisms by which insoluble protein aggregates stabilise O/W emulsions at various pH and ionic strengths are discussed.     

Heat stability of oil-in-water emulsions formed with intact or hydrolysed whey proteins: influence of polysaccharides

The heat stability of emulsions (4 wt% corn oil) formed with whey protein isolate (WPI) or extensively hydrolysed whey protein (WPH) products and containing xanthan gum or guar gum was examined after a retort treatment at 121 °C for 16 min. At neutral pH and low ionic strength, emulsions stabilized with both 0.5 and 4 wt% WPI (intact whey protein) were stable against retorting. The amount of β-lactoglobulin (β-lg) at the droplet surface increased during retorting, especially in the emulsion containing 4 wt% protein, whereas the amount of adsorbed α-lactalbumin (α-la) decreased markedly. Addition of xanthan gum or guar gum caused depletion flocculation of the emulsion droplets, but this flocculation did not lead to their aggregation during heating. In contrast, the droplet size of emulsions formed with WPH increased during heat treatment, indicating that coalescence had occurred. The coalescence during heating was enhanced considerably with increasing concentration of polysaccharide in the emulsions, up to 0.12% and 0.2% for xanthan gum and guar gum, respectively; whey peptides in the WPH emulsions formed weaker and looser, mobile interfacial structures than those formed with intact whey proteins. Consequently, the lack of electrostatic and steric repulsion resulted in the coalescence of flocculated droplets during retort treatment. At higher levels of xanthan gum or guar gum addition, the extent of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase.     

Stabilization of soybean oil body emulsions using κ, ι, λ-carrageenan at different pH values

Oil bodies, with their unique structural proteins, oleosins, are known to be useful in foods and other emulsion systems. The influence of ??, ??, and ??-carrageenans on the stability of soybean oil body emulsions at different pH values (pH 3, 4, 5 and 7) was investigated by particle electrical charge, particle size distribution, creaming stability and confocal laser scanning microscopy measurements. In acidic environment (pH 3, 4 and 5), the droplet charge of soybean oil body emulsions stabilized with carrageenan decreased with increasing carrageenan concentration for all types of carrageenan investigated, suggesting their adsorption to the oil body droplet surfaces. Extensive droplet aggregation and creaming were observed in the emulsions stabilized with ??-carrageenan at pH 3 and 5, indicating that soybean oil body droplets were bridged by carrageenan. At pH 7, there was no significant change in the droplet charge of soybean oil body emulsions stabilized with three types of carrageenan, but the emulsions stabilized with ??-carrageenan were more stable to creaming due to depletion flocculation than the emulsions stabilized with ?? or ??-carrageenan after seven days storage. The probable reason was that ??-carrageenan, which had the most densely charged helical structure, was most effective at creating highly charged interfacial membranes, thus reducing the depletion flocculation to occur.     

Interaction between Emulsion Droplets and Escherichia coli Cells

ABSTRACT Oil‐in‐water emulsions (20% n‐hexadecane, v/v) were stabilized by dodecyltrimethylammonium bromide (DTAB), Tween 20, or sodium dodecyl sulfate (SDS). Particle size distribution and creaming stability were measured before and after adding Escherichia coli cells to emulsions. Both E. coli strains promoted droplet flocculation, coalescence, and creaming in DTAB emulsions, although JM109 cells (surface charge = ‐35 mV) caused faster creaming than E21 cells (surface charge = ‐5 mV). Addition of bacterial cells to SDS emulsions promoted some flocculation and coalescence, but creaming stability was unaffected. Droplet aggregation and accelerated creaming were not observed in emulsions prepared with Tween 20. Surface charges of bacterial cells and emulsion droplets played a key role in emulsion stability.     

Influence of chitosan and NaCl on physicochemical properties of low-acid tuna oil-in-water emulsions stabilized by non-ionic surfactant

An influence of low molecular weight (LMW) chitosan on physicochemical properties and stability of low-acid (pH 6) tuna oil-in-water emulsion stabilized by non-ionic surfactant (Tween 80) was studied. The mean droplet diameter, droplet charge (ζ-potential), creaming stability and microstructure of emulsions (5 wt% oil) were evaluated. The added chitosan was adsorbed on the surface of oil droplets stabilized by Tween 80 through electrostatic interactions. Such addition of chitosan at different concentrations (0–10 wt%) to emulsions showed slight effect on the mean droplet diameter. However, the degree of flocculation was a function of chitosan concentration assessed by emulsions' microstructure and creaming index. The impact of chitosan on the strength of the colloidal interaction between the emulsion droplets increased with increasing chitosan concentration. The mean diameter of droplet in emulsions increased with increasing NaCl because of the electrostatic screening effect. The addition of LMW chitosan could be performed to create tuna oil emulsions with low-acid to neutral character, as well as various physicochemical and stability properties suitable for health food products.     

蔗糖酯对酪蛋白乳浊液稳定性的影响

研究蔗糖酯用量对酪蛋白乳浊液的粒度分布、液相蛋白浓度、界面蔗糖酯浓度、脂肪部分聚结率及乳析率等指标的影响,探讨蔗糖酯对酪蛋白乳浊液稳定性影响的机理。实验表明:随着蔗糖酯用量增加,液相蛋白浓度与界面蔗糖酯浓度逐渐增加,脂肪部分聚结率呈下降趋势,乳浊液的粒径和乳析率逐渐减小,乳浊液稳定性逐渐提高。当蔗糖酯用量超过0.60%时,脂肪部分聚结率缓慢下降,而乳析率缓慢上升最后达到动态平衡。综合考虑,当蔗糖酯用量为0.60%时,乳浊液的稳定性最佳。