Influence of xanthan gum on the formation and stability of sodium caseinate oil-in-water emulsions

Studies have been made of the changes in droplet sizes, surface coverage and creaming stability of emulsions formed with 30% (w/w) soya oil, and aqueous solution containing 1 or 3% (w/w) sodium caseinate and varying concentrations of xanthan gum. Addition of xanthan prior to homogenization had no significant effect on average emulsion droplet size and surface protein concentration in all emulsions studied. However, addition of low levels of xanthan (≤0.2 wt%) caused flocculation of droplets that resulted in a large decrease in creaming stability and visual phase separation. At higher xanthan concentrations, the creaming stability improved, apparently due to the formation of network of flocculated droplets. It was found that emulsions formed with 3% sodium caseinate in the absence of xanthan showed extensive flocculation that resulted in very low creaming stability. The presence of xanthan in these emulsions increased the creaming stability, although the emulsion droplets were still flocculated. It appears that creaming stability of emulsions made with mixtures of sodium caseinate and xanthan was more closely related to the structure and rheology of the emulsion itself rather than to the rheology of the aqueous phase.     

黄原胶对O/W乳状液稳定性的影响

报道了含有黄原胶的２０Ｏ／Ｗ乳状液贮藏在２７～３０℃的分层动力学的研究。实验运用超声波技术考察了从０．０００５～０．５ｗｔ％的一系列浓度的黄原胶对体系分层特性的影响。在非常低（＜０．００１ｗｔ％）的黄原胶浓度下，实验体系的稳定性变化不大。０．０１～０．０２ｗｔ％的黄原胶可引起样品底部富水层出现，但体系无明显分层。当黄原胶浓度增加到０．０２ｗｔ％以上，乳状液很快分层，且分层的状态取决于黄原胶添加量。只有当添加量超过０．２５ｗｔ％，黄原胶才能起到提高体系稳定性的作用。对非吸附性的黄原胶的这种影响，可以用“排除絮凝”和弱凝胶结构形成的机理进行解释。     

Physical and Oxidative Stabilities of O/W Emulsions Formed with Rice Dreg Protein Hydrolysate: Effect of Xanthan Gum Rheology

The shortening of shelf-life of food emulsions is frequently due to poor creaming and lipid oxidation stability. The lipid oxidation of O/W emulsions can be inhibited by rice dreg protein hydrolysate (RDPH); however, emulsions were stabilized by Tween-20. Polysaccharides can control the rheology and network structure of the aqueous continuous phase by increasing viscosity and yield stress, hence retarding phase separation and gravity-induced creaming, especially for xanthan gum. The objective of this research was to evaluate whether emulsions formed with 2 wt% RDPH and stabilized by xanthan gum (0–0.5 wt%) could produce 20 % (v/v) soybean oil-in-water emulsions that had good physical and oxidative stability. The degree of flocculation of droplets as a function of xanthan gum concentration was assessed by the microstructure, rheology, and the creaming index of emulsions. Addition of xanthan gum prior to homogenization had no significant effect on the mean droplet diameter in all emulsions studied. Increase in xanthan gum concentration led to the increase in creaming stability of emulsions, due to an increase in viscosity of the continuous phase and/or the formation of a droplet network with a yield stress, as well as the enhanced steric and electrostatic repulsion between the droplets. Lipid oxidation of the emulsions was significantly inhibited at xanthan gum concentrations of 0.12 wt% or above with RDPH, which could due to the fact that xanthan gum increases the viscosity of the aqueous phase and hindered the diffusion of oxidants to the oil droplet surface area, synergistic effect between RDPH and xanthan gum to suppress oil peroxidation, and metal ion chelation capability of xanthan gum. Thus, stable protein hydrolyzates-type emulsions could be obtained with increasing concentration of xanthan gum.     

黄原胶对酪蛋白酸钠乳状液稳定性的影响

研究了一定pH条件下,黄原胶浓度及剪切稀化效应对酪蛋白酸钠乳状液稳定性的影响。结果表明,在酸性条件下,黄原胶无法抑制酪蛋白的变性沉淀,乳液在制备之初,即产生严重絮凝。在中性和弱碱性条件下,黄原胶在一定浓度范围内,诱发了乳状液的排斥絮凝;体系的pH显著影响了乳状液的稳定性,pH6条件下,较低的黄原胶浓度(0.2wt%)便可赋予乳状液良好的稳定性。均质过程大大降低了黄原胶的粘度,导致乳状液的稳定性下降,与添加未经均质处理的黄原胶相比,添加量增大近一倍,才能获得稳定的乳状液。     

Stability of Whey Protein Concentrate/Sunflower Oil Emulsions as Affected by Sucrose and Xanthan Gum

The effect of the addition of sucrose and xanthan gum, protein concentration, and processing method on the stability and destabilization mechanism type of emulsions formulated with two commercial whey protein concentrate powders was described and quantified following system changes with a Turbiscan TMA 2000, a light scattering equipment and a confocal laser scanning microscope. Two different processing methods that gave particle sizes with different orders of magnitude were compared: homogenization by ULTRA-TURRAX (UT) and by ultrasound (US). The addition of sucrose to the aqueous phase of emulsions significantly diminished volume-weighted mean diameter (D _4,3) and improved stability. When the aqueous phase contained xanthan gum, the main destabilization mechanism for UT emulsions changed from creaming to flocculation. For US emulsions, although some aggregation was detected by confocal laser scanning microscopy, it was not great enough to modify the backscattering average (BS_av) in the middle zone of the tube (20–50 mm). At low protein concentrations, the profiles corresponded to destabilization of small aggregates. In those conditions, creaming was markedly enhanced as evident from creaming rate values. Independently of aqueous phase composition, US emulsions stabilized by protein concentrations higher than 5 wt% were stable, indicating that whey proteins were good emulsion stabilizers at pH close to 7. This study shows the relevance of protein type on stability and describes for the first time a behavior for whey proteins different from the one reported for caseins in literature.     

瓜尔豆胶对大豆分离蛋白乳浊液稳定性的影响

研究了不同pH值条件下瓜尔豆胶对大豆分离蛋白乳浊液乳析稳定性和絮凝稳定性的影响。研究结果表明 ,在瓜尔豆胶浓度低于 0 0 4%时 ,随着瓜尔豆胶浓度的增加 ,乳浊液的稳定性逐渐增加。当多糖浓度高于 0 0 4%时 ,液滴发生排斥絮凝 ,体系的稳定性急剧下降 ,更高浓度的瓜尔豆胶因与乳浊液液滴间的热力学不相容性而导致体系发生各向同性和各向异性相分离。     

阴离子多糖对大豆蛋白乳状液乳析稳定性的影响

研究了卡拉胶、黄原胶和羧甲基纤维素钠(CMC)3种阴离子多糖对大豆蛋白乳状液乳析稳定性的影响。结果表明:添加0.03%卡拉胶的乳状液乳析稳定性较好,而添加CMC或0.06%以上黄原胶的乳状液乳析稳定性则较差;随着阴离子多糖浓度的增加,添加CMC的乳状液顶部粒径d3,2增大,添加卡拉胶或黄原胶的大豆蛋白乳状液顶部粒径d3,2先减小后增大;添加阴离子多糖的乳状液的顶部粒径d3,2与乳析率呈较好的正相关性。     

Stability of oil: Water emulsions of amaranth proteins. Effect of hydrolysis and pH

In this contribution we have determined the effect of limited enzymatic hydrolysis on the emulsifying capacity of amaranth proteins. The action of enzyme (alcalase and trypsin) and the pH of the continuous phase of the oil/water emulsion (pH 2.0, 6.3 and 8.0) were the variables analyzed. The results obtained show that amaranth protein isolates, AI, contain proteins species capable of forming and stabilizing emulsions, mainly at acidic pH (2.0) and to a lesser extent at pH 8.0. While the emulsions obtained are sensitive to creaming and flocculation, they do not undergo destabilization by coalescence. The emulsions prepared from proteins subjected to low grade trypsin hydrolysis (TH2.2) are sensitive to creaming - flocculation, whereas alcalase-hydrolyzed proteins (AH1.7 and AH9.5) exhibited a significant destabilization by creaming, flocculation and coalescence, mainly at pH 6.3. The effect of the pH of the aqueous phase was determining on the emulsion stability beside the structural and physicochemical characteristics of protein species utilized as tensioactive. At acidic pH (pH 2.0) the unfolding and charge of polypeptides and the capacity of form a viscoelastic film at the interface were essential while at alkaline pH (pH 8.0) the balance among high and low molecular mass protein species and flexibility of the molecule fixed the emulsions properties.     

Effects of xanthan gum on physicochemical properties and stability of corn oil-in-water emulsions stabilized by polyoxyethylene (20) sorbitan monooleate

The influence of added xanthan gum on rheological and dispersion characteristics and stability of concentrated (50% w/w) corn oil-in-water emulsions, stabilized with 5% (percentage on oil amount) polyoxyethylene (20) sorbitan monooleate (Tween 80), have been investigated. Emulsion with no xanthan indicated coalescence and poor creaming stability. All emulsions, with and without xanthan, showed shear-thinning flow behavior. Addition of xanthan protected emulsions from coalescence during 15 days of storage. Increase in xanthan concentration led to decrease in droplet average radius and creaming index, and increase in elastic properties of emulsions. Decrease in the emulsions flow behavior indexes, which suggested the extent of non-Newtonian behavior of emulsions, was influenced by increase in xanthan concentration. Above 0.04% of xanthan concentration, G′ and G″ values indicated formation of weak gels. Gel structure existence arises from droplet network association, due to depletion flocculation. Standard deviation of emulsions droplet size mean diameter decreased while concentration of added xanthan increased.     

面筋蛋白粒子-黄原胶Pickering乳液的制备及其表征

制备黄原胶与面筋蛋白纳米粒协同稳的Pickering乳液,表征Pickering乳液的物理化学性能和微观结构。结果显示：通过黄原胶与面筋蛋白纳米粒协同作用,可制备出稳定性较好的Pickering乳液。低质量分数的黄原胶（0.2%）会促进乳析;当黄原胶质量分数不小于0.3%时,乳液于4 ℃贮存30 d仍无乳析现象;当黄原胶质量分数为1%时,贮存30 d乳液出现析油的现象。不同乳化顺序得到乳液的稳定性不同。乳液M-WG-XG（面筋蛋白纳米粒与玉米油乳化得粗乳液,然后加入黄原胶二次分散）的稳定性最好,同时乳液的平均粒径最小（21.4±0.314）μm。黄原胶的加入增大了乳液的净电荷,乳液的稳定性提高。共聚焦显微镜结果表明,乳液M-WG-XG液滴分布均匀,界面层呈现出多层结构。相比于其他方式制备的乳液,乳液M-WG-XG有更好的黏弹性和离子稳定性。     

Effect of Xanthan Gum Upon the Rheology and Stability of Oil-Water Emulsions

Soyabean oil-water emulsions were studied. In oil-water emulsions (up to 60% oil) xanthan is essential to prevent creaming. A yield stress arises primarily from the polysaccharide liquid crystalline structure. In concentrated systems where the oil droplets interact strongly there is a significant contribution to the yield stress arising from the need to modify individual droplet shapes when shear is applied to the system. Studies of droplet sizes suggest that the xanthan gum can also modify the equilibrium droplet size by lowering the oil-water interfacial tension.     

Flocculation of Whey Protein Stabilized Emulsions as Influenced by Dextran Sulfate and Electrolyte

The creaming stability and viscosity of oil-in-water emulsions stabilized by whey protein isolate were monitored as functions of dextran sulfate (DS) and electrolyte (NaCl) concentration. At a specific DS concentration (the critical flocculation concentration, CFC), the droplets became flocculated, which promoted creaming. Addition of electrolyte caused an increase in CFC. At NaCl concentrations <0.5 wt%, addition of electrolyte decreased emulsion viscosity, but at concentrations >0.5 wt% it caused an increase in viscosity due to increased flocculation. The results were due to the influence of electrostatic screening on the effective volume of DS molecules and colloidal interactions between droplets.     

κ-卡拉胶影响大豆分离蛋白乳浊液稳定性的研究

研究了卡拉胶对大豆分离蛋白乳浊液粒度分布、乳析率和离心沉淀率的影响,在此基础上分析了静置过程中乳浊液粒径与乳析率、离心沉淀率之间相关性,结果表明:乳浊液粒径随卡拉胶浓度由小到大依次为0.03%<空白样<0.06%<0.09%;而体系的表观粘度随卡拉胶浓度的增大而升高;静置过程中乳浊液顶部粒径d3,2与乳析率有较好的相关性;乳浊液底部d3,2与离心沉淀率有很好的相关性。进一步分析了其可能的作用机理:卡拉胶低浓度时,卡拉胶分子被吸附到液滴的蛋白质正电荷区域,增加了液滴间的静电排斥,从而增加了体系的絮凝稳定性;随着卡拉胶浓度增大,卡拉胶会引起体系排斥絮凝。     

Effect of Heating and Homogenization on the Stability of Coconut Milk Emulsions

: The effects of homogenization and heat treatment on the colloidal stability of coconut milk were studied. Fresh coconut milk (15% to 17% fat, 1.5% to 2% protein) was extracted and stored at 30 °C before homogenization at 40/4 MPa (stage I/stage II). Both homogenized and non‐homogenized samples were heated at 50 °C, 60 °C, 70 °C, 80 °C, and 90 °C for 1 h. Homogenization reduced the size of the primary emulsion droplets from 10.9 to 3.0 μm, but increased the degree of flocculation, presumably via a bridging mechanism. This flocculation was also responsible for increased viscosity of the homogenized samples. Heating increased the degree of flocculation in both non‐homogenized and homogenized samples. A slight amount of coalescence was also observed after heating above 80 °C. All samples creamed after 24 h of storage, but the heated samples formed a larger cream layer, presumably because the flocculated droplets packed together less efficiently. Optical microscopy was used to confirm the combination of flocculation and creaming responsible for changes in coconut milk quality. The information obtained from this study provides a better understanding of the emulsion science important in controlling coconut milk functionality.     

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.     

甲基纤维素对大豆分离蛋白乳浊液稳定性影响的研究

本文研究了甲基纤维素对大豆分离蛋白乳浊液稳定性的影响。研究结果表明，在低浓度时，甲基纤维素增加了体系的稳定性，对NaCl引起的液滴絮凝也有很好的抑制作用。而高浓度的甲基纤维素导致pH6．5和7．0的体系同时发生乳析和蛋白质沉积现象。其作用机理可能是，在低浓度时甲基纤维素吸附到液滴蛋白质层的外围形成次级保护层，增加了体系的稳定性，而高浓度时则可能置换出液滴的蛋白质吸附层。     

Characterisation of fish oil emulsions stabilised by sodium caseinate

Fish oil emulsions varying in sodium caseinate concentration (25% w/w oil and 0.1–1.0% w/w protein, giving oil-to-protein ratios of 250–25) were investigated in terms of their creaming stability, rheological properties, the mobility of oil droplets and the oil/protein interaction at the interface. The presence of excessive protein in an emulsion (i.e., at 1% w/w) caused the aggregation of oil droplets through depletion flocculation, resulting in low creaming stability and high low-shear viscosity. At a lower protein concentration (0.1% w/w), when protein was limited, the emulsion droplets were stabilised by bridging flocculation and showed good stability to creaming. Shear-thinning behaviour was observed for both flocculated emulsions. A reduction in the low-shear viscosity and a Newtonian flow was obtained for the emulsion containing an intermediate concentration of protein (0.25% w/w). At this concentration, there was relatively little excess unadsorbed protein in the continuous phase; thus the emulsion was most stable to creaming. NMR was used to characterise these emulsion systems without dilution. Shorter T₂ values (by low-field ¹H NMR), for the emulsions containing both high (1% w/w) and low (0.1% w/w) amounts of protein, indicated increased restricted mobility of oils, caused by depletion or bridging flocculation. The line broadening in oil signals in the high-field NMR spectra (¹H, ¹³C) indicated increased interaction between oil molecules and proteins at the interface with increasing protein concentration in emulsions. In addition, ³¹P NMR spectra, which reflect the mobility of the casein component only, showed increased line broadening, with reduction in protein content due to the relatively higher proportion of the protein being adsorbed to the interface of the oil droplets, compared to that in the continuous phase (i.e., as the oil-to-protein ratio was increased). The T₂ values of resonances of the individual groups on oil molecules, obtained using high-field ¹H NMR, reflected their different environments within the oil droplet.     

Stability of Cream Liqueurs Containing Low-Molecular-Weight Surfactants

The effect of adding low-molecular-weight surfactants, commercial glycerol monostearate (GMS) or sodium stearyl lactylate (SSL), on the stability of simulated cream liqueurs (dairy based oil-in-water emulsions containing alcohol) was investigated. The presence of 0.4–0.5 wt % GMS or SSL led to a substantial reduction in creaming at ambient temperature as well as a longer shelf-life at 45°C. A protein analysis of the aqueous phase after emulsion centrifugation showed that added GMS or SSL displaced a significant proportion of caseinate from the surface of the emulsion droplets. Improved stability with respect to creaming appeared to be associated with a change in bulk rheological properties of the emulsion, probably arising from complex formation between low-molecular-weight emulsifier and caseinate, both in bulk aqueous solution and at the surface of the fat droplets.     

搅打稀奶油品质及其影响因素的研究进展

搅打稀奶油是一类可搅打起泡的水包油乳液。作为重要的食品工业原料,搅打稀奶油可作为呈味物质赋予食品良好的感官特性,应用前景广阔。本文首先介绍搅打稀奶油贮藏期内常见的失稳作用,包括乳析、聚集、聚结、部分聚结及奥氏熟化,并阐述界面特性及脂肪球间的交互作如何影响搅打稀奶油的稳定性;其次介绍搅打稀奶油的搅打过程,阐述结晶特性、界面特性和液相蛋白特性如何影响搅打特性。本文可为搅打稀奶油产品的工业化生产提供一定的理论指导。     

Rheological properties and stability of model salad dressing emulsions prepared with a dry-heated soybean protein isolate–dextran mixture

The rheological characteristics of model salad dressing emulsions, incorporating a dry-heated soybean protein isolate (SPI)–dextran mixture as emulsifier, were investigated by applying dynamic rheometry tests in an attempt to probe the emulsion structure and to elucidate the mechanism of their stability against creaming. Both the viscoelastic properties and the creaming behaviour of the dressings were greatly influenced by the extent of protein–dextran conjugation and also by xanthan gum addition. The results are discussed in terms of emulsion droplet interactions which, depending on the extent of glyco-conjugation, may be dominated by depletion or ‘bridging’ flocculation effects and, thereby, influence the droplet network structure collapse during ageing.