Charge modifications to improve the emulsifying properties of whey protein isolate

Whey protein isolate was modified by ethylene diamine in order to shift its isoelectric point to an alkaline pH. The extent of the modification was studied using SDS-PAGE and MALDI-TOF mass spectrometry. The modified whey proteins were used as an emulsifier to stabilize oil-in-water emulsions at acidic and neutral pH ranges, and their emulsifying properties were compared with that of the unmodified whey proteins and with the previously studied ethylene diamine modified sodium caseinate. The emulsifying activity of the modified whey proteins was similar to that of the unmodified ones, but the stability of an emulsion at pH 5 was significantly improved after the modification. Charge and coverage of droplet surface and the displacement of the interfacial proteins by surfactant Tween 20 were further studied as a function of pH. As compared with the unmodified whey proteins, the modified ones were proven to cover the interface more efficiently with extensive surface charge at pH 5, although the interfacial layer was less resistant to the surfactant displacement.     

Comparative evaluation of the emulsifying properties of phosphatidylcholine after enzymatic acyl modification

The ability of enzymatically synthesized structured phosphatidylcholine (PC) containing caprylic acid to form and stabilize oil-in-water emulsions prepared with different triglycerides [medium chain triglycerides (MCT), soybean oil, and enzymatically synthesized structured lipids] was examined and compared with natural soybean PC and deoiled lecithin. Emulsions were prepared with varying oil and emulsifier concentrations. The particle size distribution, creaming stability, and viscosity were measured for the evaluation of the emulsifying properties. With an increase in the oil concentration, there was an increase in particle size, viscosity, and creaming layer. With an increase in the phospholipid (PL) concentration, there was usually a decrease in particle size and an increase in viscosity, where the emulsion stability was increased. General emulsions prepared with structured lipids resulted in smaller particle sizes as compared to MCT and soybean oil. Deoiled lecithin was able to increase the viscosity more significantly and give smaller particle sizes as compared to the other emulsifiers, thus producing more stable emulsions. However, in certain cases, structured PC was superior to deoiled lecithin and soybean PC. This observation was made for emulsions prepared with soybean oil or structured lipid at an oil/water ratio of 10:90. At an oil/water ratio of 30:70, the deoiled lecithin performed better as compared to the other PLs with all oil types. However, structured PC produced more stable emulsions as compared to natural soybean PC in MCT and soybean oil.     

Effect of transglutaminase-catalyzed polymerization of beta-casein on its emulsifying properties

beta-Casein was polymerized to various extents by the transglutaminase-catalyzed cross-linking reaction. Under the reaction conditions used, dimer, trimer, and tetramer of beta-casein were produced as predominant species at short reaction times (20-90 min) and large polymers at longer reaction times (3-24 h). Examination of the emulsifying properties of these cross-linked beta-casein polymers showed that although the emulsifying activity index decreased, the storage stability of the emulsions increased with increasing degree of polymerization. Experiments with mixtures of native and polymerized beta-casein also showed that increasing the fraction of polymerized beta-casein in the mixture increased the emulsion stability. This enhancement of emulsion stability might be due either to an enhancement in steric stabilization, attributable to the branched nature of the trasgutaminase-catalyzed polymers, or to stronger cohesive interactions between polymerized beta-casein molecules than between monomeric beta-casein molecules in the film.     

提高大豆蛋白冻融后乳化性改性工艺优化

为了制备出经冷冻-融化后仍能保持较高乳化性的大豆蛋白,试验以葡聚糖为糖基化供体,采用湿法糖基化技术改性大豆蛋白。根据单因素试验的结果,建立了Box-Behnken模型对加工工艺进行优化,所得的模型拟合度高,切实可行,可用于实际分析和预测。利用响应面分析法探讨了蛋白浓度、蛋白与糖质量比、反应时间3因素对改性产物冻融前后乳化活性和乳化稳定性的影响,优化的工艺条件为:大豆分离蛋白(soybean protein isolate,SPI)质量浓度40 mg/mL,SPI与葡聚糖的质量比为1∶3,反应时间4 h。在此条件下得到的改性产物冻融稳定性显著(P0.05)高于未改性蛋白,冻融前后的乳化活性(emulsifying activity index,EAI)分别是空白对照样的1.687和1.780倍,乳化稳定性(emulsion stability index,ESI)分别是空白对照样的1.367和1.274倍。傅里叶红外光谱证明葡聚糖通过共价键接到大豆蛋白分子中,研究结果为制备冷冻食品加工专用大豆蛋白的产业化生产提供参考。     

Fractionation, characterization, and study of the emulsifying properties of corn fiber gum

Corn fiber gum (CFG) has been fractionated by hydrophobic interaction chromatography on Amberlite XAD-1180 resin using ionic, acidic, basic, and hydrophobic solvents of different polarities. Characterization, including determination of total carbohydrate, acidic sugar, and protein content, has been done for each fraction together with measurements of molar mass, polydispersity, radius of gyration, Mark-Houwink exponent, and intrinsic viscosity using multiangle laser light scattering and online viscosity measurements. Emulsification properties of all fractions in an oil-in-water emulsion system with 20:1 oil to gum ratio were studied by measuring turbidity over 14 days. The results indicate that CFG consists of different components differing in their molecular weights and carbohydrate and protein contents. The main fraction eluted with NaCl, although low in protein content, has the highest average molecular weight and was determined to be a better emulsifier than the other fractions. The unfractionated CFG, which contains different molecular species, is the best emulsifier.     

等离子体对鹰嘴豆分离蛋白溶解性和乳化特性的影响

鹰嘴豆作为植物蛋白的优质来源,营养价值高,但功能性质较差无法满足现代食品工业需求。该研究利用介质阻挡放电（Dielectric Barrier Discharge,DBD）等离子体对鹰嘴豆分离蛋白（Chickpea Protein Isolates,CPI）进行改性处理,研究不同处理时间（0、1、2、3、4 min）对CPI溶解性、乳化特性、结构的影响及其之间的相关性。结果表明：经等离子体处理后,鹰嘴豆分离蛋白溶液的pH值降低,电导率增加。溶解性、乳化活性和乳化稳定性得到显著的改善（P < 0.05）。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析表明等离子体处理并未改变CPI的组成成分及种类,但7S和11S等主要亚基条带强度增加。等离子体处理后α-螺旋含量、自由巯基含量和表面疏水性显著增加（P < 0.05）,无规卷曲含量降低（P < 0.05）,表明蛋白的高级结构发生改变。扫描电镜显示随着处理时间的延长,样品的尺寸减小,表面结构变得更为松散。利用Pearson相关性分析和主成分分析表明,不同处理时间后,蛋白结构的变化与功能性质的改善呈现较强的相关性。等离子体处理4 min后,CPI的溶解性及乳化特性达到较优效果,研究结果可为开发利用鹰嘴豆分离蛋白和指导实际生产实践提供技术支持。     

空化射流对大豆分离蛋白结构及乳化特性的影响

为了探究空化射流处理对大豆分离蛋白结构及乳化特性的影响.该研究将不同浓度(2％和5％)的大豆分离蛋白溶液在不同时间(2、4、6、8、10 min)下进行空化射流处理,以未经处理大豆分离蛋白溶液作为对照,探究空化射流处理对大豆分离蛋白结构和乳化特性的影响.结果表明:适当时间的空化射流处理可以降低大豆分离蛋白的含硫氨基酸含...     

适宜物理-酶联合改性提高酸性条件下大豆分离蛋白乳化性

为提高酸性条件下大豆分离蛋白（soy protein isolates,SPI）的乳化性能,该文研究了物理-酶联合改性对SPI（pH值为4）的乳化性能影响,通过对比确定了物理-酶联合改性,即超声波-酶复合改性和挤压膨化-酶复合改性两种改性方法在酸性条件下的乳化性能效果最好;并通过对改性后 SPI（pH 值为4）进行溶解性、游离巯基、二硫键、粒径、扫描电镜（scanning electron microscope,SEM）和激光共焦扫描显微镜（confocal laser scanning microscopy,CLSM）分析,从蛋白结构变化上进一步揭示了乳化性能提高现象的原因。结果表明：超声波联合植酸酶-酸性蛋白酶改性的 SPI （Uphy-aci-SPI）的乳化活性（emulsifying activity index,EAI）为0.53 m2/g,比未改性SPI（0.18 m2/g）显著提高了196%（P<0.05）,乳化稳定性（emulsifying stability index,ESI）为17 min,比未改性SPI（13.5 min）显著提高了25.9%（P<0.05）;挤压膨化联合菠萝蛋白酶改性的SPI（Ebro-SPI）的EAI为0.46 m2/g,比未改性SPI显著增加了155%（P<0.05）,ESI为17 min,比未改性SPI显著增加了25.9%（P<0.05）。在pH值为4的条件下对物理-酶联合改性的SPI的性质分析发现,物理-酶联合改性的SPI与未改性SPI相比,物理-酶联合改性的SPI的溶解性显著增加（P<0.05）;物理-酶联合改性的SPI的乳状液平均粒径减小,CLSM观察乳状液中油与蛋白溶液稳定共融,改善了油滴之间的空间排斥力。物理-酶联合改性的SPI游离巯基的含量显著增加（P<0.05）,二硫键含量显著降低（P<0.05）。SEM观察物理-酶联合改性的SPI为结构松散、破碎均一的微观结构。由此可见,乳化性能的提高是通过深层改变蛋白的结构来实现的。该研究可为探索提高酸性条件下SPI的乳化性能的方法提供理论依据。     

基于共轭凸轮的强制推秧机构反求设计

针对传统推秧机构存在的推秧结束时间提前或滞后问题,提出了基于共轭凸轮的强制推秧新型机构。该新型推秧机构由共轭凸轮实现推秧杆的推出和缩回。根据椭圆齿轮行星系驱动机构及插秧农艺要求构造了推秧杆的运动学曲线,建立了该推秧机构反求模型,并基于Visual Basic 6.0编写了该推秧机构的反求设计及仿真软件,反求得到一组满足农艺要求的较优参数,包括机构参数和凸轮廓线。主副凸轮最大压力角都小于许用压力角,表明该新型机构能很好地满足推秧机构效率和受力要求。     

微射流均质预处理提高大豆分离蛋白酶解效率及酶解产物乳化性能

为了探讨微射流均质预处理对大豆分离蛋白酶解效率及酶解产物乳化性能的影响,该文研究比较了微射流均质预处理前后大豆分离蛋白酶解产物的理化性质(水解度、亚基组成、蛋白溶解性、表面疏水性和分子量分布)和乳化性能(通过测定分析样品乳状液的平均粒径和微观结构评估样品的乳化性能)的变化。研究表明:大豆分离蛋白经过微射流均质预处理后采用木瓜蛋白酶水解,其酶解产物(水解度为1.7%)与对照大豆分离蛋白和未经预处理的酶解产物相比,在较低浓度下(30 g/L)制备出粒径细小的稳定乳状液(体积平均粒径≈1.6μm)。微射流均质预处理提高了大豆分离蛋白中α-7S和A-11S亚基的酶解敏感性,使酶解产物在水解度1.3%~1.7%范围内蛋白溶解性显著增加(P0.05),同时保持较高的表面疏水性值,与未经预处理的酶解产物相比形成了更多具有界面活性的可溶性多肽(分子量主要分布在11.3 k Da左右),在乳化过程中可有效防止乳液滴间发生桥联絮凝。因此微射流均质预处理是一种辅助提高大豆蛋白酶解效率和酶解产物乳化性能行之有效的方法。研究结果可为大豆蛋白深加工蛋白乳化剂提供理论和方法参考。     

Study of the role of the carbohydrate and protein moieties of soy soluble polysaccharides in their emulsifying properties

The objective of this work was to investigate the role played by the protein fraction of soy soluble polysaccharide (SSPS) during its adsorption at oil/water interfaces. SSPS was separated in a high (HMF; 310 kDa) and low (LMF; 20 kDa) molecular weight fraction by gel filtration. SSPS/HMF consisted of 91.6% carbohydrate and 2.2% protein and showed better emulsifying properties than those of the whole SSPS, whereas SSPS/LMF seemed to affect negatively the adsorption behavior of SSPS. SDS-PAGE of the protein fraction obtained from SSPS/HMF showed a molecular mass of 50 kDa, was composed predominantly of proline (23.1%) and glutamic acid (15.2%), and still contained 8.8% of neutral sugar and 5.3% of uronic acid. Results indicated that not all of the protein material present in SSPS contributes to SSPS functionality but that only the material associated with HMF aids in the adsorption of SSPS onto oil/water interfaces.     

Effects of ultrasound pretreatment on the enzymatic hydrolysis of soy protein isolates and on the emulsifying properties of hydrolysates

Soy protein isolate (SPI) was modified by ultrasound pretreatment (200 W, 400 W, 600 W) and controlled papain hydrolysis, and the emulsifying properties of SPIH (SPI hydrolysates) and USPIH (ultrasound pretreated SPIH) were investigated. Analysis of mean droplet sizes and creaming indices of emulsions formed by SPIH and USPIH showed that some USPIH had markedly improved emulsifying capability and emulsion stabilization against creaming during quiescent storage. Compared with control SPI and SPIH-0.58% degree of hydrolysis (DH), USPIH-400W-1.25% (USPIH pretreated under 400W sonication and hydrolyzed to 1.25% DH) was capable of forming a stable fine emulsion (d43=1.79 μm) at a lower concentration (3.0% w/v). A variety of physicochemical and interfacial properties of USPIH-400W products have been investigated in relation to DH and emulsifying properties. SDS-PAGE showed that ultrasound pretreatment could significantly improve the accessibility of some subunits (α-7S and A-11S) in soy proteins to papain hydrolysis, resulting in changes in DH, protein solubility (PS), surface hydrophobicity (H0), and secondary structure for USPIH-400W. Compared with control SPI and SPIH-0.58%, USPIH-400W-1.25% had a higher protein adsorption fraction (Fads) and a lower saturation surface load (Γsat), which is mainly due to its higher PS and random coil content, and may explain its markedly improved emulsifying capability. This study demonstrated that combined ultrasound pretreatment and controlled enzymatic hydrolysis could be an effective method for the functionality modification of globular proteins.     

Effect of alkaline deamidation on the structure, surface hydrophobicity, and emulsifying properties of the Z19 alpha-zein

Different deamidation conditions for the Z19 alpha-zein were studied in order to find the best conditions for the development of the emulsifying properties. Alkaline deamidation was chosen, and the effects on the peptide bond cleavage, secondary structure, emulsifying properties, and surface hydrophobicity were studied. The Z19 alpha-zein was deamidated by using 0.5 N NaOH containing 70% ethanol at 70 degrees C for 12 h. A deamidation degree (DD) of 60.6 +/- 0.5%, and a degree of hydrolysis (DH) of 5 +/- 0.5% were achieved. Analysis by far-UV circular dichroism showed that the denaturation was mainly promoted by the high temperature used during the incubation. The adequate balance between the DD and the DH results in an effective emulsifying property improvement for the Z19 alpha-zein. Thus, after the deamidation treatment, the surface hydrophobicity decreased from 9.5 x 104 +/- 6.8 x 103 to 46 x 104 +/- 2.1 x 103, and the emulsion stability increased from 18 +/- 0.7% to 80 +/- 4.7% since the oil globules stabilized by the modified protein were smaller (57.7 +/- 5.73 nm) and more resistant to coalescence than those present in the native protein emulsions (1488 +/- 3.92 nm).     

Effect of denaturants on the emulsifying activity of proteins

The relationship between protein flexibility and emulsifying activity was investigated by disrupting disulfide bonds and/or noncovalent interactions of the protein. Oil-in-water emulsions using model proteins (apomyoglobin, beta-casein, alpha-casein, lysozyme, bovine serum albumin, kappa-casein, and beta-lactoglobulin) were made in the presence of chemical denaturants (dithiothreitol and/or urea). In most cases, the presence of denaturants enhanced emulsifying activity. The effect was protein-specific and depended on the relative importance of disulfide bonds and noncovalent interactions in stabilizing the native conformation of each protein. Implications for the design of novel protein emulsifiers are discussed.     

Isolation, characterization, and emulsifying properties of wattle seed (Acacia victoriae Bentham) extracts

Extracts from either ground whole wattle seeds or uncoated cotyledons were obtained using water, alkali, or ethanol. These extracts were then analyzed for their protein molecular weight and electrophoretic profiles using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and capillary electrophoresis, respectively. Water extracts and those from the cotyledons gave higher material yield and contained significantly more proteins than other extracts. Furthermore, the proteins ranged in molecular weight from 6 to 92 kDa, with the highest concentration between 27 and 61 kDa. Water extracts, even at very low protein concentrations (0.17-1.12%), formed stable emulsions, containing up to 50% canola oil, and these emulsions were affected by pH (4-9), ionic strength (0.25-1% NaCl), and retorting (115 degrees C for 30 min). The study showed that water-soluble wattle extracts have great potential as emulsifiers and stabilizers for the food industry, especially at low pH levels.     

挤压-酶解大豆蛋白结构与特性关系及其乳液乳化活性评价

以低温冷榨豆粕粉为原料,研究挤压-酶解处理对大豆蛋白酶解物蛋白结构及其乳液界面特性的影响,并探究酶解物乳液对蛋液稳定性的改善作用。结果表明,经挤压预处理的大豆蛋白酶解物柔性和表面疏水性随着酶解时间的延长呈现先增加后减少的变化趋势,在酶解30 min时分别达到最大值0.40和44.96;挤压大豆蛋白酶解物的二级结构由有序向无序状态转变,表现为β-转角和无规则卷曲的含量增加,β-折叠和α-螺旋的含量减少。挤压大豆蛋白酶解物乳液的储能模量G''和损耗模量G''及界面肽含量均随着酶解程度的增强呈现先增大后减小的趋势,乳化活性和乳化稳定性也在酶解30 min时分别达到最佳值28.45 m²/g和61.05 min。挤压大豆蛋白酶解物乳液与蛋液以3:3质量比混合时,采用多重光散射分析乳液的稳定性,其不稳定性系数（thermal instability index,TSI）较小,乳液体系呈现较好稳定性,表明挤压大豆蛋白酶解物乳液可以有效改善蛋液的稳定性。该研究为大豆蛋白酶解物在乳化食品领域中应用提供理论基础。     

反转式共轭凸轮蔬菜钵苗移栽机构的设计与仿真

国内外蔬菜移栽机核心工作部件均由不同功能的机构组合而成,以完成取苗、送苗和投苗等栽植动作。为简化机构提高移栽效率,该文提出一种以变性椭圆齿轮、正圆齿轮和共轭凸轮为传动机构的反转式蔬菜钵苗移栽机构,实现了用一套机构完成多个动作的要求。使蔬菜移栽机械达到自动、高效率(每行移栽效率可达到120株/min)的移栽水平。首先,在分析该移栽机构工作原理的基础上,建立该机构的运动学模型。然后基于Visual Basic6.0可视化编程软件,建立该机构的辅助分析与优化软件。最后,通过人机交互的优化方法,获得一组符合蔬菜钵苗移栽要求的结构参数,进行二维图纸绘制,三维模型建立,并导入ADAMS(automatic dynamic analysis of mechanical systems)软件中做虚拟仿真,与优化软件得到的结果进行对比分析验证理论的可行性,该研究可为蔬菜钵苗移栽机构的设计提供参考。     

Structural characterization of corn fiber gums from coarse and fine fiber and a study of their emulsifying properties

The stabilities of orange oil emulsions stabilized with various concentrations of two different types of corn fiber gum (CFG-1 and 2) isolated from coarse (pericarp) and fine (endosperm) fiber from corn wet milling have been studied. The emulsion stabilities in all these studies increased with increasing gum concentration up to a gum-to-oil ratio of 0.05, and after that it either levels off or changes very slightly. These results indicate that only 0.25% of CFG is required to make stable emulsion containing 5% orange oil under the experimental conditions used in this study. At this CFG concentration, CFG-2 from each fiber source was found to be a superior emulsifier relative to the corresponding CFG-1 from each source in a 10-day emulsion stability study at room temperature. The emulsion stability was also investigated by confocal laser scanning microscopy measurement, and it was found that CFG-1 and 2 from both coarse and fine fiber made stable emulsions with an average particle size of less than 1 mum for 10 days at room temperature. Sugar composition analysis of CFGs from both sources indicated that they were typical galactoglucuronoarabinoxylans containing mainly 55-59% xylose, 29-36% arabinose, and 4-6% galactose as neutral sugars and 3-5% glucuronic acid. Methylation analysis revealed a highly branched structure of all CFGs, in which only 16-25% of the 1--> 4-linked xylose residues were not substituted at O-2 and/or O-3. Arabinose is present both as a terminal residue and at branch points.     

Uptake and phloem transport of glucose-fipronil conjugate in Ricinus communis involve a carrier-mediated mechanism

Some compounds containing glucose are absorbed via the monosaccharide transporters of the plasma membrane. A glucose-fipronil conjugate, N-[3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazol-5-yl]-1-(β-d-glucopyranosyl)-1H-1,2,3-triazole-4-methanamine (GTF), has been synthesized in our previous work. GTF exhibits moderate phloem mobility in Ricinus communis. In the current paper, we demonstrate that the uptake of GTF by Ricinus seedling cotyledon discs is partly mediated by an active carrier system (K(m)1 = 0.17 mM; V(max)1 = 2.2 nmol cm(-2) h(-1)). Four compounds [d-glucose, sucrose, phloridzin, and carbonyl cyanide m-chlorophenylhydrazone (CCCP)] were examined for their effect on GTF uptake. Phloridzin as well as CCCP markedly inhibit GTF uptake, and d-glucose weakly competes with it. The phloem transport of GTF in Ricinus seedlings is found to involve an active carrier-mediated mechanism that effectively contributes to the GTF phloem loading. The results prove that adding a glucose core is a reasonable and feasible approach to confer phloem mobility to fipronil by utilizing plant monosaccharide transporters.     

菌根植物适应低磷胁迫的分子机制

丛枝菌根 (AM) 真菌能够和绝大多数陆生植物建立共生体系,对于植物适应低磷胁迫具有重要作用。已有很多研究从不同角度揭示了宿主植物和AM真菌协同适应低磷胁迫的生理机制,并已深入到分子和信号水平。本文归纳了近年来相关研究成果,从磷胁迫信号感知、有机酸分泌、磷酸酶与激素合成相关基因、磷酸盐转运蛋白基因、转录因子与小分子物质miRNA等若干方面讨论了菌根共生体系响应和适应磷胁迫的分子机理,重点介绍了1) 环境磷浓度作为营养信号诱发菌根植物的生理响应过程及其在共生体系建立中的关键作用;2) AM真菌调节植物激素平衡进而影响植物生长发育和根系构型的生理机制;3) 丛枝菌根涉及的植物、真菌以及菌根特异诱导植物产生的磷酸盐转运蛋白基因在磷酸盐摄取中的特殊作用及可能调控机制;4) 转录因子作为感知磷胁迫信号和调控转录表达水平的枢纽,在增强植物适应磷胁迫能力方面的重要贡献。这些因素既单独作用又相互关联,共同构成菌根植物适应磷胁迫的分子调控网络。未来需要着重加强菌根共生界面的磷转运机制、菌根植物适应低磷胁迫的转录因子调节,以及各调控因子相互作用研究,从而全面揭示菌根植物适应低磷胁迫的分子调控网络,为发展和应用菌根技术调控植物磷营养奠定理论基础。