Effect of heat treatment and droplet size on the oxidative stability of whey protein emulsions

The present paper examines whether certain processing factors may influence the oxidative stability of whey protein oil-in-water emulsions, which are structurally close to innovative industrial products (e.g. “fresh-cheese” and “non-dairy cream” types).     

Effect of pH on the properties of soy protein–pectin complexes

The interactions of a commercial soy protein isolate (SPI) and a 2:1 SPI:high methoxy pectin (PEC) complex were evaluated over a range of pH values (3-7). The SPI formed very large (> 50 ??m) and largely insoluble aggregates (< 10%) close to its isoelectric point (IEP, pH 4 and 5) and smaller, more soluble (> 80%) particles at higher and lower pH values. The addition of PEC increased the solubility of SPI close to its IEP (pH 4 and 5) and prevented the formation of very large aggregates. However, PEC reduced the solubility of SPI at higher and lower pH values presumably via a depletion mechanism. The ??-potential of diluted SPI dispersions decreased from positive to negative with increasing pH, passing through zero at pH 4.6, the isoelectric point (IEP) of the protein. At pH < 6, the addition of PEC reduced the charge of the protein suggesting the formation of a complex while at pH 6 or 7 there was no evidence of complex formation. The increased SPI solubility in the IEP in the presence of PEC is probably due to the formation of charged complex which do not aggregate while the decreased solubility of protein in the presence at high and low PEC is probably due to the formation of insoluble complexes and a depletion interaction respectively. Thermal treatment (30 min, 90 °C) enhanced the solubility of the SPI:PEC complexes close to the IEP (pH 4 and 5), but reduces it at low pH (pH 3). The SPI:PEC complexes could be manufactured in the form of a beverage at pilot scale where their solubility was enhanced by homogenization.     

Physicochemical stability of egg protein‐stabilised oil‐in‐water emulsions supplemented with vegetable powders

The effect of vegetable powders on the physicochemical stability of egg protein‐stabilised oil‐in‐water emulsions was studied. Vegetable powders (beetroot, broccoli, carrot, celery, green pea, red pepper, spinach, swede, tomato and yellow pea) were added at 2.5% (w/v) to emulsions prepared with rapeseed oil. The physical stability of the emulsions was characterised using the emulsifying activity (EAI) and the emulsifying stability indices (ESI) in addition to bright field microscopy. The oxidative stability of the emulsions was monitored by means of an accelerated oxidation test (Rancimat method). The addition of most vegetable powders did not markedly affect the physical stability of the emulsions although an adverse effect of tomato was observed. The oxidative stability of the emulsions was significantly improved in most cases as indicated by the Rancimat method with broccoli exhibiting the highest increase in induction time (98.2%) compared with the control. Both polar and nonpolar antioxidants are likely to contribute to the overall chemical stability of this complex food system in a concentration‐dependent manner.     

热处理和碱处理对可食性大豆分离蛋白膜性能的影响

研究了热处理和碱处理对可食性大豆分离蛋白(SPI)膜性能的影响。对成膜液进行适当的加热和调节pH可以提高SPI膜的抗拉强度(TS)和伸长率(E),降低水蒸气透过系数(WVP)。调节成膜液的pH到9,在70℃加热20min,所得到的膜机械性能和阻湿性能最好。     

Formation of acid‐precipitated soy protein–dextran conjugates by Maillard reaction in liquid systems

The conjugation reaction between soybean acid‐precipitated protein (SAPP) and dextran in liquid systems via the initial stage of the Maillard reaction was studied. Functional SAPP–dextran conjugates were prepared in 80% ethanol‐reacting system at 50 °C for 6 h, along with 95% ethanol‐reacting system at 60 °C for 24 h. The covalent attachment of dextran to SAPP was confirmed by sodium dodecyl sulphate–polyacrylamide gel electrophoresis and gel filtration chromatography.Compared to the classical dry‐heating, the reaction time of glycosylation in the two ethanol systems was largely shortened. Emulsifying activity of SAPP–dextran conjugates obtained by dry‐heating incubation and in ethanol was similar at pH 7.0 and10.0, significantly higher than that of SAPP–dextran mixture or SAPP alone. In addition, SAPP–dextran conjugates obtained in 80% ethanol‐reacting system for 6 h were completely soluble after heating at 90 °C for 20 min. The impact of various processing conditions on the formation of SAPP–dextran conjugates was investigated. This study provides important guidance to create protein–polysaccharide conjugates at mild temperatures in liquid systems.     

高浓度大豆蛋白乳化体系的表征及探讨

以改性大豆浓缩蛋白(FSPC)、大豆分离蛋白(SPI)和商业大豆分离蛋白(CSPI)为主要原料,比较了在低速搅拌情况下,不同大豆蛋白制得的高浓度乳化体系在流变和微观结构上的性状和差异。各乳化体系都呈现出典型假塑性流体的性质,FSPC和CSPI高浓度乳化体系黏度远远高于SPI,弹性模量亦有显著差异,FSPC和CSPI体系表现出了更多的固体性质。电镜观察的结果证实,SPI、FSPC和CSPI高浓度乳化体系中发生了不同程度的絮凝或胶联。     

Effect of concentrated flaxseed protein on the stability and rheological properties of soybean oil-in-water emulsions

Flaxseed protein concentrate containing-mucilage (FPCCM) was used to stabilize soybean oil-in-water emulsions. The effects of FPCCM concentration (0.5, 1.0, 1.5% w/v) and oil-phase volume fraction (5, 10, 20% v/v) on emulsion stability and rheological properties of the soybean oil-in-water emulsions were investigated. Z-average diameter, zeta-potential, creaming index and rheological properties of emulsions were determined. The result showed that FPCCM concentration significantly affected zeta-potential, creaming rate and emulsion viscosity. The increasing of FPCCM concentration led to a more negative charged droplet and a lower creaming rate. Oil-phase volume fraction significantly affected Z-average diameter, rheological properties, creaming index and creaming rate. With the increase of oil-phase volume fraction, both Z-average diameter and emulsion viscosity increased, while creaming index and creaming rate decreased. The rheological curve suggested that the emulsions were shear-thinning non-Newtonian fluids.     

Formation of sunflower oil emulsions stabilized by whey proteins with high-pressure homogenization (up to 350 MPa): effect of pressure on emulsion characteristics

A new ultra-high-pressure homogenizer was used to make very fine oil in water emulsions. The effect of pressures up to 350 MPa on sunflower oil (20%) in water emulsions was studied. The emulsifier used was whey protein concentrate (1.5%). The properties of the emulsions were characterized by laser light scattering (droplet size distribution) and coaxial cylinders rheometry (rheological behaviour). The protein adsorption fraction was obtained by a spectrophotometric method using bicinchoninic acid reagent.
Significant modifications in the structure and the texture of the emulsions were observed as the pressure increased. No change was revealed by polyacrylamide gel electrophoresis of the whey protein within the pressure range studied. Microdifferential scanning calorimetry scans indicated that the changes of the structural and textural properties may be because of changes in the protein conformation.     

Physicochemical properties of soy protein prepared by enzyme‐assisted countercurrent extraction

Synchronous improvements of both nutritional properties and the flavour of protein by optimising preparation processes are highly challenging. The prehydrolysis of soy meals by cocktail enzyme (β‐glucosidase, phytase and acid protease) treatment and subsequent countercurrent extraction were designed based on similar hydrolysis conditions. The composition, flavour volatiles and physicochemical properties of soy proteins were investigated. Compared to alkaline extraction and acid precipitation, enzyme‐assisted countercurrent extraction significantly increased protein yield and carbohydrate content, accompanied by a decrease in protein purity. This protein exhibited larger molecular weight distribution, less flavour volatiles, higher thermal stability and surface hydrophobicity, as evidenced by higher denaturation temperature (T_d) and enthalpy change (ΔH) of protein. The conversion of isoflavone glycosides to aglycone and the partial degradation of phytic acid were observed for enzyme‐prepared soy proteins. These results suggest a feasible protocol for producing a nutrient‐improved soy protein with excellent flavour and thermal stability.     

Temperature and pH as factors influencing droplet size distribution and linear viscoelasticity of O/W emulsions stabilised by soy and gluten proteins

The influence of pH and two post-emulsification treatments (pH modification and thermal cycles) over linear dynamic viscoelasticity and droplet size distribution, DSD, of O/W emulsions (75% oil) stabilized either by soy protein isolate, SPI, or wheat gluten, WG were studied in the present work. Rheological properties and droplet size of fresh emulsions showed an important dependence on pH as a consequence of the role of electrostatic interactions, not being possible to obtain a stable emulsion for pH values close to the protein isoelectric point, pI, (4–5 for SPI and 6 for WG). In order to overcome this inconvenient, an alternative emulsification procedure, basically consisting in a modification of pH after emulsification (indirect emulsification), was successfully developed. Emulsions obtained after this post-emulsification treatment, showed higher elastic (G′) and loss (G″) moduli and also larger oil droplets than fresh emulsions prepared at the same pH. Moreover, the application of upward/downward temperature cycles from 20 to 70 °C to emulsions directly prepared at a pH yielded to significantly higher values of the rheological functions when compared to those found for fresh emulsions. Accordingly, both post-emulsification treatments lead to apparent enhancements in emulsion rheology and microstructure, which is indicative of a good potential to improve long-term emulsion stability.     

大豆蛋白预先热聚集对其凝胶性质的影响

在大豆蛋白聚集体与天然大豆蛋白混合的基础上,研究了聚集体对其葡萄糖酸内酯凝胶质构及流变性质的影响,结果表明:快速加热时pH下降迅速,且凝胶点的pH值比慢速加热要高;聚集体的添加可以增加凝胶硬度;快速加热可以降低持水率,慢速加热时结果相反;凝胶温度随聚集体添加量的增大而减小。     

蛋白浓度对热致大豆球蛋白颗粒Pickering乳液稳定剂的影响

该文利用大豆球蛋白(SG)为原料,通过在不同浓度下加热处理(100℃,30 min)得到一系列SG颗粒,利用动态光散射技术(DLS)、原子力显微镜(AFM)等手段研究了SG颗粒的性质(粒径、电位、微结构、表面疏水性)及其稳定乳液的性质。结果发现,加热处理可以显著地增加颗粒粒径(90~150 nm)及表面疏水性(提升了5~8倍),其程度受加热时蛋白浓度影响。加热处理不仅提高了SG颗粒的乳化性能,还提高了其抗乳液凝聚稳定性(储藏14 d内),表明了SG颗粒具有良好的作为Pickering乳液稳定剂的潜力。     

超声辐射对大豆分离蛋白膜性能的影响

研究了超声辐射在频率为20kHz,功率为800W条件下,不同处理时间对大豆分离蛋白膜性能的影响。结果表明,超声辐射对膜性能有明显的改善作用。经超声辐射处理2min可以显著提高膜的抗拉强度,相对于对照样提高了64.08%(P≤0.05);同时也明显降低了膜的水蒸汽透过系数,相对于对照样降低了25.70%(P≤0.05)。经超声处理后的膜机械强度和阻湿性能均得到了提高,同时具有均匀透明的外观。     

丙二醛氧化修饰对大豆蛋白热变性影响

以丙二醛代表脂质过氧化活性次生产物,采用圆二色谱、内源荧光光谱、粒径分析和差示扫描量热仪研究丙二醛氧化修饰对大豆蛋白热变性影响。结果发现,丙二醛氧化修饰使大豆蛋白热稳定性下降,相比大豆球蛋白,大豆β-伴球蛋白热稳定性下降更为显著。     

阴离子多糖对大豆蛋白性质的影响

通过在大豆蛋白中分别添加5%（w/w）的水溶性大豆多糖（SSPC）、果胶、羧甲基纤维素钠（CMC）,然后共同喷雾干燥。与对照相比较,添加这三种阴离子多糖后,大豆蛋白的氮溶指数略有下降,乳化活性有所下降,乳化稳定性显著提高,其中添加CMC后热性质也有提高。添加阴离子多糖后,大豆蛋白的zeta电位发生了明显变化,等电点下降超过了一个pH单位。粒径分析表明,三种阴离子多糖在pH4.5处对大豆分离蛋白的分散稳定效果依次为：SSPC〉果胶〉CMC。     

凝固剂及凝固条件对大豆蛋白胶凝性质的影响

以大豆蛋白的凝胶强度、持水性、凝固速率这3个胶凝特性为主要指标,测定了包括蛋白浓度、热处理温度和时间、凝固剂种类和添加量、pH值、离子强度在内的这些因素对上述胶凝性质的影响,并确定了最优凝固工艺条件:质量浓度60g/L的SPI溶液经95℃热处理15min后,分别以质量分数0.4%熟石膏(CaSO4·1/2H2O)和质量分数0.28%葡萄糖酸内酯(GDL)作为凝固剂,保温30min后,冷却至室温;最佳离子强度为0.01mol/L(NaCl)。     

超声处理对大豆蛋白膜性能和微观结构的影响

研究了超声处理对大豆分离蛋白膜性能和微观结构的影响。结果表明,大豆分离蛋白膜液经超声功率20W、10min的处理,可显著地增加膜的抗拉强度及阻湿性能;红外和扫描电镜结果显示,超声处理改变了膜的空间结构,使膜表面平滑、均匀。     

大豆分离蛋白的特性研究

研究水解后不同分子量范围的大豆分离蛋白功能性方面,分子量在1000～2000D时候乳化活性和乳化稳定性最大,分别为176.9mL/g和120min;持水性方面分子量小于1000D时候最大,为66.2%;黏度方面,分子量大于4000D时候最大,为1.8cp;持油率方面分子量范围在大于4000D范围内最大,为378.42%。     

高压均质对大豆分离蛋白功能性质的影响

为了了解高压均质技术对大豆分离蛋白（SPI）功能性质的影响,采用不同的均质压力、均质次数和料液比对大豆分离蛋白溶液进行了高压均质处理,并分析处理前后SPI功能性质的变化.结果表明：高压均质可在一定程度上提高SPI的溶解性、乳化活性及其稳定性和起泡性及泡沫稳定性.均质压力在0～70 MPa的范围内升高时,SPI的溶解性、乳化稳定性、起泡性和泡沫稳定性得到了相应的改善,而乳化活性在压力为40 MPa时达到最高;均质次数由1次向3次增加时,SPI的乳化稳定性、起泡性及泡沫稳定性得到了提高,而溶解性和乳化活性则降低;均质物料料液比在1∶16～1∶8 （g∶mL）的范围内逐步增大时,SPI的各项功能性质均有不同程度的提高,并在料液比为1∶8时达到了最高值.     

多糖类稳泡剂对大豆分离蛋白起泡性的影响

探讨了黄原胶等稳泡剂对大豆分离蛋白(SPI)起泡性的影响。黄原胶等稳泡剂可能是由于增加了连续相黏度,继而起到了稳泡作用;而由于热处理能够使蛋白质分子表面暴露的疏水性氨基酸残基增加,从而提高了起泡能力。通过响应面(RSM)分析实验,得出改善SPI起泡特性的最佳工艺条件:加热温度67℃,加热时间18 min,蛋白质浓度3.29(W/V),黄原胶添加量0.13(W/V),搅打时间4.56 min。将最终得到的SPI泡沫与蛋清白泡沫比较,发现二者具有类似的黏性和硬度,且在气泡大小和形状上也较为相近。