小麦蛋白组分调节改善乳液的稳定性及消化特性

本研究通过调节麦醇溶蛋白和麦谷蛋白的比例,构建结构稳定且能够延缓脂肪释放的小麦蛋白基食品乳液体系。结果表明,在小麦蛋白组分当中,麦醇溶蛋白具有良好的界面性质,能形成稳定的界面层,麦谷蛋白的界面活性虽然较差,但其能够在界面上形成强有力的网络支撑,保护乳液不受外界环境的干扰。相比于单独小麦蛋白稳定的乳液,经组分调节后的复合蛋白具有较低的界面张力,可形成致密的纤维状蛋白界面层及较小的乳液液滴。当麦醇溶蛋白和麦谷蛋白的比例为1:2时,乳液在4℃贮藏1个月或经90℃加热30min后粒度基本保持在28.33μm左右,其贮藏稳定性和热稳定性也显著提高。此外,小麦蛋白组分间通过界面协同作用形成的复合界面层在胃肠消化过程中难以被胆盐和胰脂肪酶所取代。因此,通过小麦蛋白组分调节可改善乳液稳定性并一定程度上抑制脂肪在乳液中的消化速率。     

自由基接枝改性对乳清分离蛋白乳化稳定性的影响

为研究蛋白的共价接枝改性对其乳化稳定性的影响,本文以乳清分离蛋白（whey protein isolate,WPI）和表没食子儿茶素没食子酸酯（epigallocatechingallate,EGCG）为原料,通过自由基接枝法制备WPI-EGCG复合物。利用扫描电镜（SEM）对其微观结构进行观测,通过测定界面蛋白吸附量、界面流变学特性来探究共价接枝对界面特性的影响;进而以WPI-EGCG接枝物为乳化剂构建番茄红素纳米乳液,并对其物理化学稳定性及储藏稳定性进行研究。结果表明,EGCG的自由基接枝改变了WPI的结构,使之具有更高的黏度和界面稳定性,使以接枝物为乳化剂的番茄红素纳米乳液体系具有更高的物化稳定性。WPI-EGCGE接枝物稳定的番茄红素纳米乳液在37 ℃下储藏30 d后粒径和ζ-电位绝对值分别增加了268.3 nm和17.6 mV,乳液中番茄红素的保留率仍有66.23%,呈现出更佳的番茄红素保护效果。本研究为功能活性物质纳米乳液载运体系的构建提供了参考。     

罗非鱼蛋白-乳清蛋白复合乳液负载β-胡萝卜素的研究

为了提高β-胡萝卜素的稳定性和生物利用率,充分利用双蛋白的营养和功能特性优势,以罗非鱼分离蛋白（tilapia protein isolate,TPI）和乳清分离蛋白（whey protein isolate,WPI）混合液作为乳化剂,通过高压均质结合热处理制备负载β-胡萝卜素的TPI-WPI复合乳液,探讨两种蛋白的质量比（2∶1、1∶1、1∶2）对乳液稳定性、抗氧化活性及体外消化特性的影响。结果表明,与单一的TPI和WPI乳液比较,TPI-WPI复合蛋白乳液的稳定性及β-胡萝卜素的生物利用率提高。当TPI与WPI质量比为1∶2时,复合蛋白乳液初始粒径为259.18 nm,zeta电位绝对值为28.23 mV,乳液的稳定性好,4℃贮藏21 d不分层;当TPI与WPI质量比为2∶1时,复合蛋白乳液贮藏21 d后β-胡萝卜素保留率达到62.36%,DPPH自由基和ABTS+自由基清除率分别为54.83%和40.11%,经体外消化后,β-胡萝卜素的生物利用率达24.76%,乳液游离脂肪酸释放率高。因此,WPI的添加可以提高复合蛋白乳液的稳定性,而TPI的添加可以提高乳液负载β-胡萝卜素的稳定性和生物利用率。研究结果可为混合蛋白构建稳定的乳液体系及活性成分的递送提供参考。     

利用示踪粒子及膨胀流变学研究β-乳球蛋白聚集体的界面行为

在热加工过程中,蛋白易形成聚集体,不同聚集形态蛋白质的界面结构、流变学特性对乳液体系的稳定性及油脂消化特性具有显著影响。为探究β-乳球蛋白聚集体的界面行为,本研究通过调节pH值和加热时间制备了β-乳球蛋白(β-lactoglobulin,β-lg)的不同聚集体,包括β-lg、纳米颗粒聚集体(β-lg NP)和纤维状聚集体(β-lg F),并对这3种形态蛋白质的形貌进行了表征;利用示踪粒子微流变学及膨胀流变学对不同质量分数的β-lg、β-lg NP、β-lg F在油-水(癸烷-水)界面的吸附过程及胆盐取代行为进行研究,并通过体外消化模型实验研究了3种形态蛋白质乳液的消化特性。结果表明,质量分数越高,蛋白向界面扩散越快,形成界面黏弹性越强;蛋白质聚集体比β-lg向界面吸附更快,且形成界面膜弹性更高;在胆盐取代界面蛋白过程中,发现β-lg NP抵抗胆盐取代能力最强,β-lg最弱,与乳液的体外消化模型实验结果一致。     

苹果果胶对不同来源油体乳液稳定性和脂肪酸利用率的影响

为探究果胶（0～5 g/L）对大豆或花生油体复合乳液稳定性和脂肪酸利用率的影响,借助动态光散射、凝胶电泳、激光共聚焦显微镜和气相色谱等评价复合乳液储存稳定性,并在此基础上,研究体外模拟消化对复合乳液界面蛋白结构、乳液结构和脂肪酸利用率的影响。得出结果：当果胶含量<3 g/L时,乳液的储存稳定性高度依赖于果胶含量;当果胶含量>1.5 g/L时,果胶通过降低乳液聚集程度和增加液滴间静电排斥的方式,显著改善乳液稳定性;当果胶含量介于3～5 g/L时,果胶对乳液的稳定作用达到平衡。在体外模拟消化试验中,胃蛋白酶水解界面蛋白形成低于15 ku的小肽,而果胶可抑制胃蛋白酶水解界面蛋白。负电肽的形成和胆盐的添加以及游离脂肪酸的释放使得乳液ζ-电位显著降低。与大豆油体相比,果胶通过延缓界面蛋白水解和控制大豆复合乳液粒度大小,使得大豆复合乳液脂肪酸利用率降低3.3%。相反,与花生油体相比,因花生复合乳液具有更大的胰蛋白酶水解面积,故花生复合乳液脂肪酸利用率增加33.8%。     

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。     

界面结构对叶黄素纳米结构脂质载体生物可及性及稳定性的影响

为探究界面结构对叶黄素纳米结构脂质载体(Lutein-NLCs)稳定性及生物可及性的影响,通过乳清分离蛋白和小分子表面活性剂吐温80复配,构建复合界面、双界面以及单界面的Lutein-NLCs,对3种界面结构的Lutein-NLCs的基本性质、界面吸附特性、生物可及性以及稳定性进行研究,结果表明:3界面结构Lutein-NLCs粒径为127.60~180.86 nm,包封率最高达97.78%,其叶黄素生物可给率显著高于普通纳米乳液和游离叶黄素(P < 0.05),其中,单界面Lutein-NLCs的叶黄素生物可给率显著高于复合界面和双界面(P <0.05)。3种界面结构Lutein-NLCs中叶黄素释放速率显著低于普通纳米乳液,且与单界面Lutein-NLCs相比,复合界面和双界面Lutein-NLCs的缓释效果更为显著。在贮藏过程中,Lutein-NLCs提高了叶黄素的保留率,其中复合界面Lutein-NLCs的保留率最高,是叶黄素对照组的12.06倍。     

氧化对大豆蛋白结构、乳液稳定性及消化特性的影响

以大豆分离蛋白为原料,以脂质过氧化产物丙二醛（malondialdehyde,MDA）为氧化引发剂,逐级研究氧化对大豆蛋白结构、乳液稳定性及乳液消化特性的影响。结果发现：随着MDA浓度的升高,蛋白羰基及席夫碱含量明显升高而巯基含量显著降低。同时,MDA可促进蛋白聚集并诱导β-伴大豆球蛋白（7S）组分形成二硫键和非二硫键诱导的共价交联。进一步制备O/W型乳液,发现不同浓度MDA处理蛋白对乳液的形成影响较小,但可以显著改变界面蛋白组成。其中经中高浓度（2.5～10 mmol/L）MDA氧化后,更多7S组分以聚集状态参与界面组成。体外模拟胃肠道消化实验进一步表明,乳液消化主要在肠道进行,氧化诱导的蛋白交联/聚集可延缓或降低胆盐在界面的替代,进而减缓乳液消化并降低脂质释放率。     

基于内源性磷脂-乳清分离蛋白交互作用的磷虾油乳液稳定性研究

构建具有较高物理稳定性的乳液体系对最大限度提高磷虾油生物利用率和拓宽其在健康食品中的应用尤为重要。基于此,本文研究了内源性磷脂-乳清分离蛋白（WPI）交互作用对磷虾油乳液理化特性、微观结构和物理稳定性的影响规律和作用机理。结果表明,当载油量为25%时,磷虾油乳液平均粒径和Zeta电位值分别为35.03 nm和?27.3 mV,乳液趋于不稳定。添加0.5% （w/v）WPI使磷虾油乳液的平均粒径和Zeta电位绝对值分别增加84.0%、31.4%（P<0.05）,低剪切速率下表观粘度值增加7倍（P<0.05）,稳定性指数（TSI）值降低70.3%（P<0.05）,乳液趋于稳定。进一步结果显示,内源性磷脂能够与WPI交互作用改善其界面活性,并使WPI中α-螺旋结构含量降低1.60%（P<0.05）,内源性荧光强度和表面疏水特性明显增强。环境胁迫稳定性结果表明,模拟巴氏杀菌热处理能够增加磷虾油乳液物理稳定性,且向弱碱性pH迁移过程中（pH6~9）表现出较强的物理稳定性。因此,内源性磷脂-WPI交互作用对构建高物理稳定性磷虾油乳液和拓宽其在健康食品体系中的应用提供了可能。     

乳清分离蛋白-南极磷虾油乳液理化稳定性和流变特性

比较分析不同质量分数（0%、1.5%、3%、6%）乳清分离蛋白（whey protein isolate,WPI）对水包油型南极磷虾油（Antarctic krill oil,AKO）(30%,m/m)乳液理化特性、物理稳定性、流变学特性和微观结构的影响。结果表明,不添加WPI的AKO乳液平均粒径和Zeta电位值分别为516.67 nm和-14.03 mV;随着WPI质量分数从0%增加到6%,乳液平均粒径显著降低了42.28%(P<0.05),而Zeta电位绝对值显著增加了18.05%(P<0.05),乳液物理稳定性明显提高。剪切流变学测试显示,随着WPI质量分数的增加,乳液表观黏度逐渐增大。微流变学测试显示,乳液体系中WPI引入使脂滴运动速率减慢、弹性行为增加,而流动性降低。微观结构观察发现,WPI添加能够使乳液网络结构趋于完整且均一,进而束缚更多脂滴以维持乳液体系稳定;WPI质量分数达到6%时,过多的蛋白会使乳液发生絮凝,进而削弱乳液体系稳定性。因此,适量WPI添加能够减小乳液粒径、增加脂滴电斥力、提高乳液黏弹性、增强蛋白网络结构束缚等,从而有效改善AKO乳液的稳定性。...     

Impact of surfactants on the lipase digestibility of gum arabic-stabilized O/W emulsions

The bioavailability of lipids from an emulsion can be controlled and regulated by the property of the stabilizing interfacial layer. Here we evaluate how low-molecular weight surfactants including hexadecyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Tween 80 (T80) influence the interfacial behavior of lipase and bile extract on the surface of lipid droplets stabilized with gum arabic (GA). The lipolysis behavior was influenced by surfactant type and concentration. The results showed that anionic SDS could completely displace GA from droplet surface. Cationic CTAB might either adsorb onto existing GA layers or displace GA, whereas non-ionic T80 could co-adsorb with GA on the interface. When the concentration of surfactants was much higher than the critical micelle concentration (CMC), all the surfactants would form a dense adsorption layer on the droplet interface to prevent lipase from the direct contact with lipids. A considerable amount of surfactant in the aqueous phase may also compete with the bile salt and lipase, thus leading to suppressed digestion of lipids. Ionic surfactants would denature the lipase resulting in reduced enzyme activity, and T80 micelles may interact with the lipase, hindering their adsorption onto the droplet interface as well. These results were confirmed both by the digestion model and interfacial techniques. The results provided guidance for the development of emulsion-based delivery systems for functional lipid foods.     

Stability of citral in protein- and gum arabic-stabilized oil-in-water emulsions

Citral is a major flavor component of citrus oils that can undergo chemical degradation leading to loss of aroma and formation of off-flavors. Engineering the interface of emulsion droplets with emulsifiers that inhibit chemical reactions could provide a novel technique to stabilize citral. The objective of this study was to determine if citral was more stable in emulsions stabilized with whey protein isolate (WPI) than gum arabic (GA). Degradation of citral was equal to or less in GA- than WPI-stabilized emulsion at pH 3.0 and 7.0. However, formation of the citral oxidation product, p-cymene was greater in the GA- than WPI-stabilized emulsion at pH 3.0 and 7.0. Emulsions stabilized by WPI had a better creaming stability than those stabilized by GA because the protein emulsifier was able to produce smaller lipid droplets during homogenization. These data suggest that WPI was able to inhibit the oxidative deterioration of citral in oil-in-water emulsions. The ability of WPI to decrease oxidative reactions could be due to the formation of a cationic emulsion droplet interface at pH 3.0 which can repel prooxidative metals and/or the ability of amino acids in WPI to scavenge free radical and chelate prooxidative metals.     

Oil-in-Water Emulsions Stabilized by Sodium Caseinate or Whey Protein Isolate as influenced by Glycerol Monostearate

Competitive adsorption between glycerol monostearate (GMS) and whey protein isolate (WPI) or sodium caseinate was studied in oil-in-water emulsions (20 wt % soya oil, deionized water, pH 7). Addition of GMS resulted in partial displacement of WPI or sodium caseinate from the emulsion interface. SDS-PAGE showed that GMS altered the adsorbed layer composition in sodium caseinate stabilized emulsions containing < 1.0 wt % protein. Predominance of β-casein at the interface in the absence of surfactant was reduced in the presence of GMS. The distribution of α-lactalbumin and β-lactoglobulin between the aqueous bulk phase and the fat surface in emulsions stabilized with WPI was independent of the concentration of added protein or surfactant.     

Chemical and physical stability of protein and gum arabic-stabilized oil-in-water emulsions containing limonene

ABSTRACT:  An important flavor component of citrus oils is limonene. Since limonene is lipid soluble, it is often added to foods as an oil-in-water emulsion. However, limonene-containing oil-in-water emulsions are susceptible to both physical instability and oxidative degradation, leading to loss of aroma and formation of off-flavors. Proteins have been found to produce both oxidatively and physically stable emulsions containing triacylglycerols. The objective of this research was to determine if whey protein isolate (WPI) could protect limonene in oil-in-water emulsion droplets more effectively than gum arabic (GA). Limonene degradation and formation of the limonene oxidation products, limonene oxide and carvone, were less in the WPI- than GA-stabilized emulsions at both pHs 3.0 and 7.0. These data suggest that WPI was able to inhibit the oxidative deterioration of limonene in oil-in-water emulsions. The ability of WPI to decrease oxidative reactions could be due to the formation of a cationic emulsion droplet interface at pH 3.0, which can repel prooxidative metals, and/or the ability of amino acids in WPI to scavenge free radical and chelate prooxidative metals.     

Influence of gastric digestive reaction on subsequent in vitro intestinal digestion of sodium caseinate-stabilized emulsions

In this study, in vitro intestinal lipid digestion and the physicochemical and microstructural changes of sodium caseinate-stabilized emulsions were examined after the emulsions had been digested in a model simulated gastric fluid containing pepsin for different times. The average size, size distribution, microstructure, proteolysis of interfacial proteins and lipolysis of the emulsion droplets were monitored as a function of digestion time. The emulsion droplets underwent extensive droplet flocculation, with some coalescence together with proteolysis of interfacial proteins, in simulated gastric fluid, resulting in changes in the droplet size and the microstructure of the emulsions. In general, digestion in simulated gastric fluid containing pepsin accelerated coalescence of the emulsion droplets during subsequent digestion in simulated intestinal fluid containing pancreatic lipase. However, the changes in the size, the microstructure and the proteolysis of the interfacial proteins of the emulsions under gastric conditions did not influence the rate and the extent of lipid digestion in the subsequent intestinal environment.     

Interfacial design of protein-stabilized emulsions for optimal delivery of nutrients

Proteins are often used as ingredients in food emulsions, as their amphiphilic structures provide electrostatic and steric stabilization. Significant attention has recently been directed at understanding how the composition and structure of oil-water interfaces change during digestion and how these can be manipulated to enhance the delivery of nutrients contained within the oil droplets. These efforts have necessitated the development of more sophisticated in vitro digestion models of greater physiological relevance and increased efforts in research to identify the role of the various digestive parameters on interfacial dynamics. The changes occurring at the oil-water interface will affect the adsorption of gastro-intestinal lipases and, ultimately, affect lipid digestion. The composition of a protein-stabilized oil droplet changes continuously during digestion, because of proteolysis and the formation of peptides with different affinities for the interface. In addition, natural bio-surfactants such as phospholipids and bile salts, other surface- active molecules present in foods, and the products of lipolysis (i.e. mono and diglycerides, lysophospholipids), all compete for access to the interface, and contribute to the dynamic changes occurring on the surface of the oil droplets. A better understanding of how to tailor the composition of oil droplet surfaces in food emulsions will aid in optimizing lipid digestion and, as a result, delivery of lipophilic nutrients. This review focuses on the physico-chemical changes occurring in protein-stabilized oil-in-water emulsions during gastric and small intestine digestion, and on how interfacial engineering could lead to differences in fatty acid release and the potential bioavailability of lipophilic molecules.     

In vitro study of intestinal lipolysis using pH-stat and gas chromatography

Developing healthy products requires in-depth knowledge of digestion. This study focuses on lipid digestion in relation to emulsion properties typically followed by pH-stat. Although this is a fast and easy method to follow the overall digestion, it provides no details on lipid digestion products. Thus, the aims of the present study were to use gas chromatography (GC) to determine all products present during lipolysis, i.e. monoglycerides (MG), diglycerides (DG) and triglycerides (TG), and to compare this method with the pH-stat method for free fatty acids (FFA). Fine, medium and coarse emulsions stabilized with two different emulsifiers (whey protein isolate (WPI) or gum arabic) were digested under in vitro intestinal conditions. Although the amount of FFA increased for both methods for WPI stabilized emulsions, the amount of FFA was 2-3 times higher when determined by GC compared with pH-stat. GC analysis showed decreasing amounts of MG and DG with increasing droplet size for both emulsions. Molar ratios of FFA/DG and MG/DG were twofold higher for WPI than for gum arabic stabilized emulsions. This indicates that the total production of lipolytic products (i.e. FFA + MG + DG) depends on the droplet size and the emulsifier but their proportions only depend on the emulsifier. Although pH-stat provides a fast measure of FFA release, it is influenced by the emulsifier type at the oil-water interface and therefore care should be taken when interpreting pH-stat results. We suggest combining this method with GC for accurate FFA determination and further evaluation of all lipolytic products.     

Digestibility and β-carotene release from lipid nanodispersions depend on dispersed phase crystallinity and interfacial properties

The influence of interfacial structure and lipid physical state on colloidal stability and digestibility of solid lipid nanoparticle dispersions (SLN) and canola oil-in-water emulsions (COE) stabilized with the non-ionic surfactants Poloxamer 188 (P188) and Tween 20 (T20) were examined and the release of encapsulated β-carotene (BC) under simulated gastrointestinal conditions determined. While the SLN and COE were all stable during exposure to gastric conditions (mean diameter ～115 nm), more destabilization was observed for the COE than SLN during the duodenal phase. ζ-Potential measurements indicated rapid adsorption of bile salts (BS) and phospholipids (PL) to both solid and liquid interfaces, with greater surfactant displacement observed for the COE. Compared to the SLN, significantly more lipolysis and BC transfer to the aqueous phase was observed for both the COE-P188 and COE-T20 (p < 0.05). The properties of the colloidal structures present in the aqueous phase, which are important in terms of the uptake of lipolytic products and lipophilic bioactives, depended on non-ionic surfactant type, the extent of lipid digestion, as well as the presence of BS and PL.     

Interactions between Whey Protein Isolate and Soy Protein Fractions at Oil–Water Interfaces: Effects of Heat and Concentration of Protein in the Aqueous Phase

ABSTRACT:  The 2 main storage proteins of soy—glycinin (11S) and β-conglycinin (7S)—exhibit unique behaviors during processing, such as gelling, emulsifying, or foaming. The objective of this work was to observe the interactions between soy protein isolates enriched in 7S or 11S and whey protein isolate (WPI) in oil–water emulsion systems. Soy oil emulsion droplets were stabilized by either soy proteins (7S or 11S rich fractions) or whey proteins, and then whey proteins or soy proteins were added to the aqueous phase. Although the emulsifying behavior of these proteins has been studied separately, the effect of the presence of mixed protein systems at interfaces on the bulk properties of the emulsions has yet to be characterized. The particle size distribution and viscosity of the emulsions were measured before and after heating at 80 and 90 °C for 10 min. In addition, SDS-PAGE electrophoresis was carried out to determine if protein adsorption or exchanges at the interface occurred after heating. When WPI was added to soy protein emulsions, gelling occurred with heat treatment at WPI concentrations >2.5%. In addition, whey proteins were found adsorbed at the oil–water interface together with 7S or 11S proteins. When 7S or 11S fractions were added to WPI-stabilized emulsions, no gelation occurred at concentrations up to 2.5% soy protein. In this case also, 7S or 11S formed complexes at the interface with whey proteins during heating.     

Investigating the effect of surfactants on lipase interfacial behaviour in the presence of bile salts

It is known that non-ionic surfactants and phospholipids provide large protection in emulsions against lipase-induced destabilization as compared to proteins, even in the presence of bile salts. In relation to this, the aim of this study is to probe the ability of two surfactants of industrial interest, poloxamer Pluronic F68 (non-ionic) and Epikuron 145V (phospholipid), to modify the adsorption of lipases at an oil–water interface under the physiological conditions existing in the duodenum. We have designed an experimental procedure by means of a pendant drop film balance equipped with a subphase exchange technique, which allows sequential adsorption of the compounds. This allows the investigation of the interfacial behaviour of lipase in the presence and absence of surfactant. According to this experimental approach, the lipase is added directly into the subphase only after the surfactant has been adsorbed onto the oil–water interface. We have used interfacial dilatational and shear rheology techniques to characterise the interfacial layers. The results suggest that Pluronic F68 reduces the interfacial activity of lipase more efficiently than Epikuron 145V. Furthermore, it seems that Pluronic F68 affects the accessibility of the lipase to the oil–water interface, even in the presence of the bile salts. These results may have applications in the development of novel strategies to rationally control lipid digestion in the diet.