基于改性果胶的纳米乳液包埋生物活性物质研究进展

果胶是从苹果渣、柑橘皮和甜菜粕等原料中提取的一种结构复杂的阴离子多糖,具有特殊的表面和界面特性,是构建纳米乳液的理想材料。然而,天然果胶的亲水性较强,疏水性不足,不易吸附到两相界面并发挥作用,限制了其在食品等领域的应用。对天然果胶进行甲酯化改性,或者将果胶与小分子表面活性剂(如吐温、司盘等)或大分子表面活性剂(如蛋白质等)联合使用,能够有效克服天然果胶在稳定纳米乳液时的缺陷,提高纳米乳液的稳定性和生物活性物质的包埋效果。本文综述基于改性果胶的纳米乳液制备方法、表征手段,以及不同形式的果胶基乳化剂的界面及乳化性质,旨在为果胶基纳米乳液体系的构建及其在生物活性物质包埋中的应用提供理论依据。     

果胶甲酯化反应及应用高甲氧基果胶制备纳米乳液

以商业橘皮果胶为原料,在无水甲醇环境中采用盐酸催化甲酯化反应制备高甲氧基果胶。通过对反应时间、反应温度、料液比以及盐酸添加量的调节,可以制备得到酯化度在90%以上的高甲氧基果胶。分子质量分布结果表明,随着反应温度升高、反应时间延长和盐酸浓度增加,产物的酯化度逐渐提高,但数均分子质量逐渐降低。在料液比1∶50,盐酸添加量0.1 mol/L,温度60℃下反应12 h,产物酯化度达到91.20%,但数均分子质量降低为15.00 kDa。基于极高酯化度果胶所具有的双亲性(甲氧基为疏水基团而羟基为亲水基团)和分子链短的特点,进一步研究了极高酯化度果胶的乳化性质。用高能量法(高速剪切)分别制备了油滴体积分数为10%、20%和30%的纳米乳液,并考察了7 d内乳状液的稳定性、粒径和Zeta-电位变化。结果显示采用极高酯化度果胶可制备得到粒径为3 500 nm的乳状液(油滴体积分数10%~30%),并具有较好的稳定性。     

果胶和热处理对蛋白质乳液凝胶结构特性和复合维生素稳定性的影响

利用大豆分离蛋白的乳化和凝胶特性制备蛋白质乳液凝胶,用以同时传递VE和D-异抗坏血酸钠,重点阐释果胶对凝胶结构特性和复合维生素稳定性的影响规律。结果表明,乳液的分散相油滴粒径随果胶质量分数的增加而增大,蛋白质-果胶复合溶液预加热处理温度越高乳液油滴粒径越大。乳液经葡萄糖酸-δ-内酯诱导形成凝胶,凝胶时间及凝胶强度（G’）受果胶质量分数影响。质构分析表明,果胶质量分数和预加热温度对凝胶硬度无显著影响,但凝胶弹性随果胶质量分数增加呈先增大后减小的趋势。当VE和D-异抗坏血酸钠被包埋于乳液凝胶后,其贮藏稳定性随果胶质量分数的增大而呈下降趋势,并且D-异抗坏血酸钠降解速率高于VE。本研究表明通过控制果胶质量分数可以调节乳液凝胶的结构特性,而不同的凝胶结构可以调控包埋于其中的功能因子的稳定性。     

蛋白质氧化影响乳液稳定性研究进展

乳液在食品工业中应用十分广泛,通常可以作为营养与风味物质的良好载体。作为乳液天然稳定剂的蛋白质在食品加工和贮藏过程中会不可避免地发生氧化,进而影响乳液稳定性。近年来,食品蛋白质氧化对乳液稳定性造成的影响已经受到了越来越多的关注。本文首先分析了蛋白质乳液的形成机制以及影响乳液稳定性的主要因素,随后重点探讨了蛋白质柔性对蛋白质乳液稳定性的影响,进而从蛋白质柔性的角度,阐述蛋白质氧化影响乳液稳定性的机理,可为蛋白质乳液的开发及其在食品体系中的应用提供一定的理论参考。     

酯化/球磨改性蜡质玉米淀粉及其皮克林乳液稳定与释放特性

针对酯化改性淀粉制备皮克林乳液稳定性较差的难题,以蜡质玉米淀粉为原料、辛烯基琥珀酸酐为酯化剂,对比研究酯化、酯化/球磨改性淀粉的理化性质以皮克林乳液的稳定性及释放性的差异。结果表明,酯化淀粉经球磨2～5 h改性淀粉制备的以大豆油为油相、以水为水相的O/W皮克林乳液具有长期稳定性,是由于酯化反应引入新基团赋予了两亲性、充分的球磨处理破坏淀粉的结晶结构从而改善了淀粉乳化性;酯化后再经球磨处理2 h的淀粉易消化,制备的皮克林乳液释放性好,所荷载的姜黄素生物可利用度高。     

多糖颗粒制备Pickering乳液稳定机制研究进展

多糖颗粒为潜在的Pickering乳液稳定剂,通过产生分子间静电相互作用和空间位阻,防止乳液液滴聚集。基于此,该文综述多糖颗粒的制备方法及多糖稳定Pickering乳液机制,并总结多糖相对分子质量、亲油性基团等特性对其乳化性的影响,为多糖颗粒稳定的Pickering乳液在食品中的应用开发提供参考。     

分子动力学结合拉曼光谱评价乳液界面蛋白结构变化

使用质量分数1.5%罗非鱼肌原纤维蛋白（myofibrillar protein,MP）和玉米油（0%、10%、68%、70%,V/V）制备乳液体系,并通过分子动力学（molecular dynamics,MD）结合拉曼光谱技术探究乳液界面蛋白结构的变化。MD模拟显示,蛋白吸附到不同油相体积分数的乳液界面上,肌球蛋白的空间构象改变,二级结构中均含有48%左右α-螺旋结构,且吸附到界面后结构相对稳定。肌球蛋白空间构象改变伴随溶剂可及表面积增大,疏水相互作用增强,使乳液呈稳定状态。拉曼光谱与MD模拟具有相似的二级结构变化。此外,拉曼光谱结果还显示,色氨酸和酪氨酸残基暴露于蛋白质表面,参与氢键形成和疏水相互作用,有利于乳液体系保持稳定。综上,MP主要通过改变界面蛋白质空间构象和侧链基团微环境,促进蛋白质之间的氢键和疏水相互作用,使MP在油-水界面形成紧密的界面膜,有利于提高乳液稳定性。     

蛋白质基Pickering乳液的研究进展

由于Pickering乳液的优良环保性、抗聚结稳定性以及在生物活性药物输送方面的潜在应用,其在化妆品、食品等领域受到广泛关注。相比较于传统乳液,Pickering乳液不含任何表面活性剂,具有安全稳定的特性。考虑到毒性和食品安全问题,无机粒子和合成粒子的应用受到很大限制。在稳定乳液方面,Pickering粒子在界面处的吸附几乎是不可逆的,因此,有必要寻找更合适的食品级Pickering粒子。该文综述了Pickering乳液的稳定机制,包括粒子润湿性、三相接触角、粒子形成的空间位阻,以及近年来蛋白质和蛋白质基的Pickering颗粒及其稳定Pickering乳液的生产、表征及稳定性等方面的最新进展,并讨论其发展方向,为进一步扩大蛋白质纳米粒子在食品领域中的应用奠定基础。     

花生蛋白-果胶复合乳液凝胶的流变学特性和微观结构

研究不同油相及其添加量对转谷氨酰胺酶诱导制备的花生蛋白-果胶复合乳液凝胶质地特性的影响规律,同时通过流变学和微观结构特性研究探索乳液凝胶的形成机理。结果表明：花生蛋白-果胶复合乳液凝胶的凝胶强度显著高于水凝胶。凝胶外观和储能模量（G’）结果表明油滴与蛋白-果胶组成的凝胶基质相互作用,从而影响乳液凝胶的质地和凝胶强度。油相添加量的增加可以使乳液凝胶的力学性能增强,网络结构更稳定。花生蛋白-果胶复合乳液凝胶的G’值和硬度随油相添加量的增加而增大,说明分散的油滴作为活性填料与凝胶基质相互作用。花生蛋白-果胶复合乳液凝胶的微观结构结果表明,油相添加量60%（V/V）时24度棕榈油为油相的乳液凝胶网络结构更致密。研究结果为花生蛋白-果胶复合乳液凝胶在食品领域的开发利用提供思路。     

食品功能因子传递系统——双层乳液研究进展

双层乳液是多层乳液的一种,一般通过层-层静电自组装技术形成两层界面层,其两个界面层可由蛋白质、多糖等生物聚合物或磷脂、吐温等小分子表面活性剂以静电吸附或共价结合的方式形成于乳液液滴的表面。作为一种传递体系,与传统的单层乳液相比,双层乳液在结构稳定性和抵抗环境压力（如酸碱度、温度和离子强度等）方面更具优势,能对所包埋的生物活性物质提供更好的保护,且具有一定的控释能力。双层乳液因其独特的优势在食品工业生产以及功能食品的开发等领域具有广阔的发展前景。本文结合近年来双层乳液的研究,从双层乳液的制备、界面层的材料、理化稳定性、作为一种传递体系的特点及其在食品领域的应用等方面进行综述。     

The Emulsifying and Emulsion‐Stabilizing Properties of Pectin: A Review

Pectin, a plant cell wall polysaccharide, is a natural multifunctional ingredientwhich imparts textural and rheological properties to a wide range of food systems. Up to the last decade, most pectin blank applications stemmed from its gel‐forming ability. Nowadays, pectin is gradually gaining acceptance as an effective emulsifier in numerous food applications. Accordingly, the emulsifying and emulsion‐stabilizing properties of this hydrocolloid are increasingly being assessed. These pectin functionalities are controlled by both the properties of the carbohydrate moieties and of the often attached protein groups. Generally, the protein moiety, feruloyl, and acetyl groups, play a major role in pectin emulsifying activities, while the emulsion‐stabilizing properties of the polymer are controlled by the homogalacturonan (HG) domain and the neutral sugar side chains of the rhamnogalacturonan‐I (RGI) structural element. However, the neutral sugar side chains might obstruct the accessibility of pectin hydrophobic species to the oil/water interface, thereby hampering emulsification. In addition, the contribution of HG to emulsion stabilization might be dependent on the polymer HG:RGI ratio. Hence, the influence of pectin structural features on the polymer emulsifying potentials is yet to be fully unraveled, as identified in this review. Furthermore, the emulsifying and emulsion‐stabilizing properties of pectin are influenced by the composition of emulsions.     

Modified pectins in whey protein emulsions

In the present work high methoxylic, low methoxylic and amidated pectins were tested for their actions in whey protein emulsions using a broad variation in the emulsion composition (content of protein, pectin, oil) and the solvent conditions (pH, ionic strength). Emulsifying activity index, long term stability and the particle size of the emulsions were determined, protein and galacturonan content of the serum were analysed after centrifugation. A strong relationship was found between emulsion stability and degree of esterification of the pectin, the influence of pectin amidation was relatively low. There were formed stable electrostatic complexes between the protein and the carboxylic groups of the pectin. They seemed to be much more important for emulsion stability than the hydrophobic or hydrogen bonds. The emulsion properties varied in dependence on the content of the single emulsion components and on the solution conditions. All pectins used stabilized the whey protein emulsions if their concentration was high enough. For any individual utilization it is necessary to choose the best suitable pectin.     

In vitro β‐Carotene Bioaccessibility and Lipid Digestion in Emulsions: Influence of Pectin Type and Degree of Methyl‐Esterification

Citrus pectin (CP) and sugar beet pectin (SBP) were demethoxylated and fully characterized in terms of pectin properties in order to investigate the influence of the pectin degree of methyl‐esterification (DM) and the pectin type on the in vitro β‐carotene bioaccessibility and lipid digestion in emulsions. For the CP based emulsions containing β‐carotene enriched oil, water and pectin, the β‐carotene bioaccessibility, and lipid digestion were higher in the emulsions with pectin with a higher DM (57%; “CP57 emulsion”) compared to the emulsions with pectin with a lower DM (30%; “CP30 emulsion”) showing that the DM plays an important role. In contrast, in SBP‐based emulsions, nor β‐carotene bioaccessibility nor lipid digestion were dependent on pectin DM. Probably here, other pectin properties are more important factors. It was observed that β‐carotene bioaccessibility and lipid digestion were lower in the CP30 emulsion in comparison with the CP57, SBP32, and SBP58 emulsions. However, the β‐carotene bioaccessibility of CP57 emulsion was similar to that of the SBP emulsions, whereas the lipid digestion was not. It seems that pectin type and pectin DM (in case of CP) are determining which components can be incorporated into micelles. Because carotenoids and lipids have different structures and polarities, their incorporation may be different. This knowledge can be used to engineer targeted (digestive) functionalities in food products. If both high β‐carotene bioaccessibility and high lipid digestion are targeted, SBP emulsions are the best options. The CP57 emulsion can be chosen if high β‐carotene bioaccessibility but lower lipid digestion is desired.     

Functional egg white–pectin conjugates prepared by controlled Maillard reaction

Changes in the functional properties of egg white (EW) protein/pectin mixtures and their chemical conjugation via the Maillard reaction were investigated. Pectin with high degrees of esterification was conjugated to EW protein at 60 °C and 79% relative humidity for 0, 6, 12, 24 and 48 h. The conjugates were compared with a physical mixture of the two components. There was a significant decrease in the available lysine (free amino groups) of the conjugated protein during incubation with the polysaccharides, negatively correlated to the emulsification properties. Oil–water emulsions prepared using the EW–pectin conjugates showed good stability, with oil droplet mean volume diameters of 0.29–1.2 μm. The conjugates showed higher emulsion viscosity and stability than the raw materials at ambient temperature. Addition of pectin (0.05–0.5% w/v) to EW at concentrations of 1% and 5% w/v had a significant effect on foam volume and stability.     

Extraction and characterization of pectin from pomelo peel and its impact on nutritional properties of carrot jam during storage

Pectin was extracted using 0.1 N HCl at 90 °C for 120 min at pH 1.5 and 2.0 from pomelo peel and characterized in this study. Influence of various concentrations of extracted pomelo peel pectin on physicochemical, bioactive compounds, color, and sensory attributes of carrot jam during storage was also studied. Pectin extracted at pH 2.0 had higher ash content, equivalent weight, and total anhydrouronic acid content than that extracted at pH 1.0. Extracted pomelo peel pectin was categorized as high‐methoxyl pectin based on the degree of esterification. The β‐carotene and total phenol content were increased in jam after 90 days of storage. Ascorbic acid content decreased with increasing storage period. Jam prepared using commercial pectin had higher ΔE values than jam prepared using pomelo peel pectin. Physico‐chemical properties were influenced by pectin concentrations and storage time. Overall acceptability was similar for all samples on the basis of sensory evaluation. The results showed that pomelo peel might be used as a rich source of pectin and pomelo peel pectin could be used as an alternative to commercial pectins for carrot jam preparation.

Practical applications

Pectin is one of the main ingredients for jam and jelly making. Citrus fruits are main sources of pectin. Usually pomelo peels are discarded as waste materials. However, it could be a good source of pectin. In this article, pectin was extracted from pomelo peel and its application was observed as carrot jam during storage. Therefore, it can be concluded that extraction of pectin from pomelo peel might be used as an alternative to commercial pectin for carrot jam preparation.     

Improvement of physicochemical stabilities of emulsions containing oil droplets coated by non-globular protein-beet pectin complex membranes

The potential of beet pectin for improving the physical and chemical stabilities of emulsions containing silk fibroin coated droplets was investigated. Five wt.% corn oil-in-water emulsions containing fibroin-coated droplets (0.5 wt.% fibroin) and anionic pectin (0.05 wt.%) were prepared at pH 7. The pH of these emulsions was then adjusted to pH 4, so that the anionic pectin molecules electrostatically deposited to the fibroin-coated droplets. The influence of pH (3 to 7) and sodium chloride concentrations (0 to 500 mM) on the properties of primary (0 wt.% pectin) and secondary (0.05 wt.% pectin) emulsions was studied. Pectin was deposited to the droplet surfaces at pH 3, 4, and 5, but not at pH 6 and 7. In addition, secondary emulsions were stable up to higher ionic strengths (< 500 mM) than primary emulsions (< 200 mM). The addition of beet pectin also prolonged the lag phase of lipid oxidation in the emulsions as determined by the formation of lipid hydroperoxides and headspace hexanal. The controlled electrostatic deposition method utilized in this study could be used to extend the range of application of silk fibroin in the industry.     

Multilayer emulsions as delivery systems for controlled release of volatile compounds using pH and salt triggers

Multilayer oil-in-water (M-O/W) emulsions were compared to primary oil-in-water (P-O/W) emulsions as carriers for volatile organic compounds (VOCs) under various environmental conditions (pH and salt). The M-O/W emulsion consisted of soy oil coated with β-lactoglobulin (βLG) and pectin layers. The release of VOCs with different physiochemical properties from aqueous solutions and emulsion systems was measured using static and dynamic headspace methods. The partition coefficients (K) calculated by the phase ratio variation (PRV) method, showed different volatile release profiles between the emulsion types. An increase in VOC release was found for the unstable P-O/W emulsion at pH 5, whereas M-O/W emulsions were stable at the same pH and retained the hydrophobic VOCs. Hydrophobic interactions and hydrogen bonds with the secondary dense layer of pectin may be responsible for the improved retention. Increasing pH and ionic strength acts as a VOC release trigger to detach the pectin from the interface. The release rates from initial dynamic curves support the results under equilibrium conditions. The results of this study demonstrate the capability of using M-O/W emulsions for controlled release of VOCs, as well as an alternative system to create stable emulsions with similar VOC release profiles.     

A novel improvement in whey protein isolate emulsion stability: Generation of an enzymatically cross-linked beet pectin layer using horseradish peroxidase

Extensive research has indicated that the electrostatic attraction between polysaccharides and proteins on the oil-water interface can improve the stability of emulsions. However, this electrostatic effect will be weakened or even eliminated as the solution pH or ionic strength of emulsions change, resulting in the shedding of the polysaccharide layer. We prepared primary oil-in-water emulsions at pH 7.0 using whey protein isolate (WPI) as an emulsifier and then beet pectin was added to form secondary emulsions. After the pH of emulsions was adjusted to 4.0 to promote electrostatic attraction between the beet pectin molecules and the protein-coated droplets, horseradish peroxidase was added to generate a cross-linked beet pectin coating. Results show that stable emulsions coated with WPI and cross-linked beet pectin interfaces could be formed. The sensitivity of the emulsions to the environmental stresses of pH changes, ions addition, thermal processing and freezing was also characterized in this work. Our results support the view that cross-linked beet pectin improves the stability of emulsions and is superior to simple deposition on the surface of lipid droplets. The interfacial engineering technology used in this study could be used to create food emulsions with improved stability to environmental stresses.     

Synergistic effects of polyglycerol ester of polyricinoleic acid and sodium caseinate on the stabilisation of water–oil–water emulsions

The inherent thermodynamic instability of water–oil–water (W/O/W) emulsions has restrictions for their application in food systems. The objective of this study was to develop a food grade W/O/W emulsions with high yield and stability using minimal concentrations of surfactants. Emulsions were prepared using soybean oil, polyglycerol ester of polyricinoleic acid (PGPR) alone or in combination with sodium caseinate (NaCN) as emulsifier(s) for primary water-in-oil (W/O) emulsions and NaCN as the sole emulsifier for secondary W/O/W emulsions. Increasing the concentration of PGPR (0.5–8%w/v) had no effect on the droplet sizes of the resulting W/O/W emulsions. However, significant increases in droplet sizes of W/O/W emulsions were observed when the concentration of NaCN in external phase was reduced from 0.5 to 0.03% (w/v) (p<0.05). Percentage yields of emulsions (using a water-soluble dye) improved when PGPR concentration in the inner phase was increased from 0.5 to 8% (w/v). A stable W/O/W emulsion with a yield >90% could be prepared with 4% (w/v) PGPR alone as primary hydrophobic emulsifier and 0.5% (w/v) NaCN as external hydrophilic emulsifier. The concentration of PGPR in the inner phase could be reduced to 2% (w/v) without affecting the yield and stability of the W/O/W emulsion by partially replacing PGPR with 0.5% (w/v) NaCN, which was added to the aqueous phase of the primary W/O emulsion. The results indicate that a possible synergistic effect may exist between PGPR and NaCN, thus allowing formulation of double emulsions with reduced surfactant concentration.     

Characteristics of Sodium Caseinate- and Soy Protein Isolate-Stabilized Emulsion-Gels Formed by Microbial Transglutaminase

ABSTRACT:  Protein-stabilized emulsion gels were prepared via microbial transglutaminase (mTGase) catalysis, and their physicochemical characteristics were examined. Emulsion oil droplet size and interfacial protein load were measured. The sodium caseinate and soy protein isolate emulsion gels exhibited different microstructures and physical properties. The emulsion gels improved the storage stability of aroma compounds. Rheological measurements of the emulsion gels revealed interesting strength, gelation kinetics, and thermal sensitivity properties. The mTGase-induced emulsion gels comprised a fine network which led to less release of aroma compounds upon storage than did emulsions. These results suggest that emulsion gels may be used to improve the texture of food emulsions and to control release of food aromas.