黄原胶对大豆分离蛋白乳状液聚集稳定性的影响

本研究以大豆分离蛋白(soy protein isolate,SPI)和黄原胶(xanthan gum,XG)为乳化剂及稳定剂制备了水包油乳状液。通过测定14 d储藏期内乳状液的流变学特性,并结合粒径和Zeta-电位,考察了XG浓度对SPI-XG水包油乳状液流变学特性及稳定性的影响。结果表明,XG的添加,明显增加了乳状液的黏度,改善了乳状液的黏弹性行为,促进了凝胶类乳液的形成。其中,XG浓度为0.10%时,在14 d储藏期内粒径变化程度较小,Zeta-电位绝对值较大,频率扫描和降温过程中储能模量(G′)和损耗模量(G″)相对稳定,赋予了乳状液良好的储藏稳定性;随着XG浓度的增加,形成的乳状液的粒径增大,G′和G″相对不稳定,流变学特性不佳。     

热处理乳清浓缩蛋白乳化体系储藏稳定性研究

主要研究了以预加热的乳清浓缩蛋白(90℃,5 min)为稳定剂的菜籽油水包油型乳状液在储藏期间物理稳定性的变化。测定乳状液在整个储藏期间(0~14 d)的ζ-电势、粒径、絮凝指数、分层指数、流变特性以及蛋白质界面分布指标。研究结果表明,经过预加热的乳清浓缩蛋白相对天然乳清浓缩蛋白能够显著降低乳状液在整个储藏期间的物理稳定性,具体表现为较低的ζ-电势(p0.05),以及较高的粒径、絮凝指数、分层指数和黏度(p0.05)。此外,加热导致的乳清浓缩蛋白变性和聚集,能够显著增加其在乳状液界面蛋白膜表面的分布(p0.05)。上述结果表明,预加热能够显著降低整个乳状液在储藏期间的物理稳定性,为乳清浓缩蛋白的预热处理在乳状液食品中的合理应用提供了理论依据。     

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.     

Droplet Size and Coalescence Stability of Whey Protein Stabilized Milkfat Peanut Oil Emulsions

Droplet diameter and the polydispersity of droplet size tended to decrease with increased proportion of peanut oil. Macromolecular additives affected droplet size. Xanthan gum or sodium carboxymethyl-cellulose (Na-CMC) produced smaller droplets than the controls, but the average diameter was independent of the composition of the dispersed phase. At 50°C the coalescence stability of these emulsions qualitatively correlated with the initial droplet diameter. Xanthan gum and Na-CMC, despite increasing continuous phase viscosity, gave lower stability than controls, primarily the result of flocculation of droplets due to depletion of the highly hydrophilic macromolecule from the intervening region between approaching droplets. At 25°C, stability increased as solid butter oil content of the dispersed phase increased.     

Effect of Propylene Glycol Alginate and Xanthan Gum on Stability of O/W Emulsions

The role of xanthan gum and propylene glycol alginate in stabilizing model oil-in-water salad dressing emulsions has been studied using rheological measurements, particle size analysis and surface tension. Increasing xanthan gum concentration within the gum ratio gave higher viscosity due to formation of aggregates with larger sizes. Propylene glycol alginate (PGA) was surface-active leading to reduction in surface tension of air/water surfaces. Reduction in viscosity was seen in the presence of PGA.     

Physicochemical Property and Oxidative Stability of Whey Protein Concentrate Multiple Nanoemulsion Containing Fish Oil

The objectives of this research were to produce whey protein concentrate (WPC) multiple nanoemulsion (MNE) and to study how whey protein concentration level and antioxidant type affected the physicochemical properties and oxidative stability of fish oil in MNE. The morphological and physicochemical characteristics of MNE were investigated by using transmission electron microscopy and particle size analyzer, respectively. The oxidative stability of fish oil in MNEs was assessed by measuring peroxide value (PV), p‐anisidine value, and volatile compounds. The spherical forms of emulsions with size ranging from 190 to 210 nm were observed indicating the successful production of MNE. Compared with free fish oil, fish oil in MNE exhibited lower PV, p‐anisidine value, and formation of maker of oxidation of fish oil indicating the oxidative stability of fish oil in MNE was enhanced. PV, p‐anisidine value, and makers of oxidation of fish oil were decreased with increased WPC concentration level. The combined use of Vitamin C and E in MNE resulted in a reduction in PV and p‐anisidine value, and development of maker of oxidation. In conclusion, WPC concentration level and antioxidant type are key factors affecting the droplet size of MNE and oxidative stability of fish oil.     

Formula Optimization of a Low-fat Food System Containing Whey Protein Isolate- Xanthan Gum Complexes as Fat Replacer

Whey protein isolate‐xanthan gum complexes (WPXC) have the potential to significantly reduce fat use in various products. However, their stability and functionality have not been extensively studied, particularly in neutral pH products. The objective of this study was to evaluate WPXC as a fat replacer in cake frostings and sandwich cookie fillings with reduced‐fat content (160 or 80 g/kg fat). Response surface methodology was used to analyze the effect of WPXC on the viscosity and textural response attributes of samples and to optimize the low‐fat formulations. It was found that WPXC had a positive effect (P > 0.001), providing acceptable viscosity and texture attributes to the low‐fat samples. A significant moisture‐WPXC interaction (P > 0.001) revealed that the optimum moisture‐WPXC ratio varied, depending on the targeted texture. This ratio was about 8:1 for cake frostings and about 5:1 for sandwich cookie fillings. Optimal formulations were found, and samples meeting the desirability specifications presented textural and melting profiles similar to those of the control products. However, for the production of sandwich cookie fillings, the use of other ingredients (for example humectants and emulsifiers) must be considered to maintain a low water activity (A_w) and prevent moisture migration to the cookie shell.     

黄原胶对蔗糖酯乳浊液流变特性及稳定性的影响

本文研究了黄原胶浓度对蔗糖酯溶液水力学直径DH、ζ-电势及乳浊液粒径、ζ-电势、显微结构、粘度、模量和乳析分层等指标的影响,在此基础上探讨了黄原胶对蔗糖酯乳浊液流变特性及稳定性的影响。结果表明:随着黄原胶浓度升高,蔗糖酯-黄原胶复合溶液的DH值逐渐增大,ζ-电势逐渐降低。乳浊液的粒径先增大后减小,ζ-电势没有显著的变化(p0.05),乳浊液的粘度和模量逐渐增大。低黄原胶浓度(0~0.01 wt%)条件下,乳浊液仅出现油析分层现象;黄原胶浓度为0.05 wt%时,由于排斥絮凝作用增强,导致乳浊液的水析及油析分层最严重;随着黄原胶浓度进一步升高,由于弱凝胶网络结构的形成,一定程度提高了乳浊液的稳定性;且黄原胶浓度高于0.15 wt%时,乳浊液仅出现水析分层现象。     

Disulfide Bond Formation Affects Stability of Whey Protein Isolate Emulsions

The viscosity and degree of flocculation of 20 wt% n-hexadecane oil-in-water emulsions stabilized by whey protein isolate (1 wt% WPI in 0.05M phosphate buffer, pH 7.0) increased as the emulsions aged. These effects were reduced when N-ethylmaleimide, a sulfhydryl blocking agent, was added to the emulsions immediately after homogenization, but were not completely eliminated. Gel electrophoresis (SDS-PAGE) showed an increase in the extent of intermolecular disulfide bond formation between proteins absorbed at the droplet interface with time. Floes were probably formed initially by noncovalent bonding or bridging flocculation, and then stabilized by disulfide bonds between proteins absorbed to different droplets.     

Thermal Aggregation of Whey Proteins in Model Solutions as Affected by Casein/Whey Protein Ratios

Model solutions (32.5 g protein/L) prepared from milk, ultrafiltration permeate, and whey protein isolate were adjusted at pH 6.7 to casein:whey protein (C:W) ratios of 80:20, 60:40, 40:60,20:80, and 0:100. Heating was performed in test tubes at 95 °C for 5 min. Observations of the heated suspensions revealed the occurrence of heterogeneous particulates from the existing casein micelles complexed with denatured whey proteins and from aggregates essentially consisting of denatured whey proteins. The proportion of whey protein aggregates increased as C:W was changed from 80:20 to 20:80. The results from this study confirmed that heat-induced aggregates were formed not only from casein micelles but also from heat-denatured whey proteins.     

Preparation and Characterization of Water/Oil/Water Emulsions Stabilized by Polyglycerol Polyricinoleate and Whey Protein Isolate

ABSTRACT: In this study we tried to prepare stable water-in-oil-in-water (W/O/W) emulsions using polyglycerol polyricinoleate (PGPR) as a hydrophobic emulsifier and whey protein isolate (WPI) as a hydrophilic emulsifier. At first, water-in-oil (W/O) emulsions was prepared, and then 40 wt% of this W/O emulsion was homogenized with 60 wt% aqueous solution of different WPI contents (2, 4, and 6 wt% WPI) using a high-pressure homogenizer (14 and 22 MPa) to produce W/O/W emulsions. The mean size of final W/O/W droplets ranged from 3.3 to 9.9 μm in diameter depending on the concentrations of PGPR and WPI. It was shown that most of the W/O/W droplets were small (<5 μm) in size but a small population of large oil droplets (d > 20 μm) was also occasionally observed. W/O/W emulsions prepared at the homogenization pressure of 22 MPa had a larger mean droplet size than that prepared at 14 MPa, and showed a microstructure consisting of mainly approximately 6 to 7-μm droplets. When a water-soluble dye PTSA as a model ingredient was loaded in the inner water phase, all W/O/W emulsions showed a high encapsulation efficiency of the dye (>90%) in the inner water phase. Even after 2 wk of storage, >90% of the encapsulated dye still remained in the inner water phase; however, severe droplet aggregation was observed at relatively high PGPR and WPI concentrations.     

乳清分离蛋白/阿拉伯胶复合物纳米颗粒制备及其pH稳定性

本实验对乳清分离蛋白(WPI)和阿拉伯胶(GA)分子内复合物进行热处理,旨在固化WPI/GA,使其形成稳定的纳米复合物颗粒并研究其pH稳定性。结果表明,当WPI/GA混合物浓度为1%,85℃加热15 min,可形成稳定分散的纳米复合物颗粒,并呈现出良好的pH稳定性。WPI/GA纳米复合物颗粒具有良好的乳化活性,1%浓度下的纳米复合物颗粒可制备含20%中链甘油三酯(MCT)的分散均一的水包油型乳液。结论:通过对WPI/GA分子内复合物进行热处理,使蛋白在聚集过程中与GA缠绕,形成稳定的WPI/GA纳米复合物颗粒,改善了WPI/GA分子内复合物的pH敏感性。并呈现出良好的乳化活性,为其作为纳米载体荷载功能因子方面的应用提供了很好的前景。     

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.     

乳清浓缩蛋白对松仁蛋白溶解度及其乳液稳定性的影响

为研究蛋白质-蛋白质相互作用对松仁蛋白(PKP)溶解度、结构和乳液性质的影响,以PKP和乳清浓缩蛋白(WPC)为研究对象,采用pH循环法制备PKP-WPC复合蛋白,利用SDS-PAGE、内源性荧光光谱、紫外-可见光谱、圆二色谱、荧光探针和ζ-电位等方法分析了复合蛋白结构特性和表面特性,再以PKP-WPC复合蛋白为原料,分别制备了油相体积分数为3%、10%和50%的乳液,并对制备的乳液性质进行了检测。结果表明:当WPC与PKP的质量比为1.0∶1.0,且体系pH值经历由7.0到12.0再回到7.0时的1次pH循环后,PKP的水溶性可从48.53%提高到92.43%。SDS-PAGE结果显示,PKP-WPC复合蛋白完整保留了PKP和WPC的亚基。内源性荧光光谱、紫外-可见光谱和圆二色谱结果表明,静电相互作用、疏水相互作用和氢键是驱动PKP和WPC相互作用的主要作用力,PKP与WPC相互作用使复合蛋白具有较高的结构韧性,抵抗酸诱导的构象折叠;WPC的加入改变了PKP的二级结构,α-螺旋、β-转角和无规卷曲结构的含量增加,而β-折叠结构相对含量降低。PKP-WPC复合蛋白具有较高的表面电荷(-34.74mV)来抵抗蛋白质的聚集。与由PKP制备的乳液相比,由PKP-WPC制备的乳液平均粒径和乳层析指数减小,ζ-电位绝对值增大,稳定性显著提高。乳液的性质因油相体积分数的不同而有较大的差异。油相体积分数为3%的复合乳液液滴小且分布均匀,稳定性好于油相体积分数为10%和50%的复合乳液。通过pH循环法,通过添加WPC,提高了PKP的溶解度,获得了稳定性较佳的PKP乳液,研究可为新型蛋白产品的研发提供理论基础,拓宽松仁蛋白在加工食品中的应用范围,推动PKP-WPC双蛋白乳液研究的发展。     

Stability of Emulsions Containing Highly Hydrolyzed Whey Protein and Starch During Retort Treatments

ABSTRACT: The influence of added unmodified amylopectin starch and modified amylopectin starch on the stability of oil-in-water emulsions (4 wt% corn oil), formed with a highly hydrolyzed commercial whey protein (WPH) product, during retort treatment (121°C for 16 min), was examined. The creaming, coalescence, and flocculation of the emulsions were studied by determining changes in the droplet size and the micro structure of the emulsions after retorting. At a low starch concentration (≤ 1.5%), the extent of coalescence was higher in the emulsions containing modified amylopectin starch than in those containing unmodified amylopectin starch. All emulsions containing moderate levels of unmodified or modified amylopectin starch showed flocculation of oil droplets by a depletion mechanism. The degree of flocculation, which was dependent on the molecular weight and the radius of gyration of the amylopectin molecules, was considered to correlate with the extent of coalescence of the oil droplets in these emulsions. At high levels of added starch (>1.5%), the degree of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase.     

Rheology and Oxidative Stability of Whey Protein Isolate-Stabilized Menhaden Oil-in-Water Emulsions as a Function of Heat Treatment

ABSTRACT:  Menhaden oil-in-water emulsions (20%, v/v) were stabilized by 2 wt% whey protein isolate (WPI) with 0.2 wt% xanthan gum (XG) in the presence of 10 mM CaCl₂ and 200 μM EDTA at pH 7. Droplet size, lipid oxidation, and rheological properties of the emulsions were investigated as a function of heating temperature and time. During heating, droplet size reached a maximum at 70 °C and then decreased at 90 °C, which can be attributed to both heating effect on increased hydrophobic attractions and the influence of CaCl₂ on decreased electrostatic repulsions. Combination of effects of EDTA and heat treatment contributed to oxidative stability of the heated emulsions. The rheological data indicate that the WPI/XG-stabilized emulsions undergo a state transition from being viscous like to an elastic like upon substantial thermal treatment. Heating below 70 °C or for less than 10 min at 70 °C favors droplet aggregation while heating at 90 °C or for 15 min or longer at 70 °C facilitates WPI adsorption and rearrangement. WPI adsorption leads to the formation of protein network around the droplet surface, which promotes oxidative stability of menhaden oil. Heating also aggravates thermodynamic incompatibility between XG and WPI, which contributes to droplet aggregation and the accumulation of more WPI around the droplet surfaces as well.     

Whey Protein Emulsion Film Performance as Affected by Lipid Type and Amount

Beeswax, candelilla wax, carnauba wax, and a high-melting fraction of anhydrous milkfat were homogenized with whey protein to produce edible emulsion films. Lipid type and amount were important in controlling the emulsion film water vapor permeability (WVP). The WVPs of the beeswax and milkfat emulsion films were significantly lower than that of films from lower moisture transmitters, carnauba and candelilla wax. Lipid WVP and degree of viscoelasticity determined the barrier properties of the films. A significant reduction in WVP of whey protein films could be achieved using large volume fractions of lipid depending on lipid type.     

Heat Gelation of Oil-in-Water Emulsions Stabilized by Whey Protein

The conditions under which a high volume fraction of oil can be trapped in whey protein gels were studied. Oil-in-water emulsions of whey protein and vegetable oil were subjected to heat treatment. Such emulsions, depending on their protein and oil content, on their pH and on the emulsification technique used, gelled or remained liquid. Homogenization was the major factor to achieve gelation and the firmness of heat-induced gels increased with increasing emulsion fineness and homogeneity. Emulsions with a high gelation capacity were characterized by a single droplet family of relatively narrow size distribution and a mean droplet diameter ranging from roughly 300–700 nanometers. The pH range suitable for gelation extended from 3.5–8.0.     

Heat-Induced Aggregation Properties of Whey Proteins as Affected by Storage Conditions of Whey Protein Isolate Powders

The control of storage as any other manufacturing steps of dairy powders is essential to preserve protein functional properties. This study aimed to determine the effects of different storage conditions on both protein denaturation and protein lactosylation in whey protein isolate (WPI) powder, and also on heat-induced aggregation. Two different storage temperature conditions (20 and 40 °C) were studied over 15 months. Our results showed that protein lactosylation progressively increased in WPI powders over 15 months at 20 °C, but heat-induced aggregation properties did not significantly differ from non-aged WPI. On the other hand, powders presented a high level of denaturation and aggregation at 40 °C from the first 2 weeks of storage, involving first protein lactosylation and then aggregation in the dry state. This was correlated with an increasing Browning Index from 15 days of storage. These changes occurred with a decrease in aggregate size after heat treatment at 5.8?≤?pH?≤?6.6 and modification of heat-induced aggregate shapes.