罗非鱼-豆粕共沉淀蛋白的提取工艺及蛋白组成分析

以罗非鱼肉和脱脂豆粕为原料,采用p H调节法制备罗非鱼-大豆共沉淀蛋白（Co-p）,探讨溶解p H、不同质量比混合的原料、溶解时间对可溶性蛋白得率的影响及沉淀p H对蛋白沉淀得率的影响。结果表明,p H调节法回收罗非鱼-豆粕共沉淀蛋白的最佳酸溶p H2.0、3.0,碱溶p H11.0、12.0,原料比1∶1,溶解时间30 min;SDS-PAGE分析显示,可溶性共沉淀蛋白条带深/浅（极端p H2.0蛋白降解）,表明可溶性蛋白含量高/低,从分子量分布范围可知,共沉淀蛋白主要由肌球蛋白重链、7 S抗原蛋白的三个亚基、肌动蛋白、肌球蛋白轻链、11 S抗原蛋白的两个亚基和小分子水溶性蛋白组成,表示可溶性共沉淀蛋白组成齐全;酸/碱可溶性共沉淀蛋白最佳沉淀p H为4.5,在此条件下,溶解、沉淀过程的蛋白得率分别为88.05%⁹4.70%。经冷冻干燥得到共沉淀蛋白粉即Co-p（1∶1）,其蛋白含量高于85%,脂肪含量在0.84%左右,灰分含量低于4.17%;可用p H调节法回收罗非鱼-豆粕共沉淀蛋白。      

罗非鱼-豆粕共沉淀蛋白的提取及溶解性、氨基酸组成分析

以罗非鱼和脱脂豆粕为原料,将两者按不同质量比(1∶0、1∶1、1∶2、2∶1和0∶1,以干基计)混合,采用pH调节法提取罗非鱼-豆粕共沉淀蛋白,冷冻干燥制备罗非鱼分离蛋白(FPI)、共沉淀蛋白(Co PP-1∶1、Co PP-1∶2、Co PP-2∶1)和大豆分离蛋白(SPI)等18种蛋白粉,分析了其基本成分、溶解性、白度及氨基酸组成。结果表明,共沉淀蛋白粉的粗蛋白含量均高于80%,脂肪含量低于1.07%,高于或者接近FPI和SPI中粗蛋白和脂肪;共沉淀蛋白在pH 4.0~6.0范围内溶解性较差,而pH值低于4.0或高于6.0时,溶解度提高,且在极端酸碱pH范围内溶解度达到最大;比较而言,Co PP-1∶1和Co PP-1∶2在pH 7.0~8.0时溶解度高于Co PP-2∶1和FPI,但低于SPI的水溶性,蛋白粉的白度较好,表明Co PP-1∶1和Co PP-1∶2更接近SPI的蛋白组成,SPI主要由水溶性球蛋白组成,在水中的溶解性较高;共沉淀蛋白的必需氨基酸种类齐全,占总氨基酸的比例约42%左右,属于优质蛋白质。因此,pH调节法可用于提取蛋白含量高和营养价值高的共沉淀蛋白。     

罗非鱼酶解多肽的乳化性及乳化稳定性研究

考察罗非鱼蛋白酶解蛋白酶种类及其水解度(DH)对罗非鱼蛋白酶解多肽的乳化性及乳化稳定性的影响,并探讨多肽的疏水性与其乳化性及乳化稳定性之间的关系。研究发现,蛋白酶种类及罗非鱼蛋白水解度对酶解多肽乳化性及乳化稳定性有不同的影响,中性蛋白酶和复合风味蛋白酶酶解罗非鱼可以得到乳化性和乳化稳定性均较好的多肽。低水解度的多肽乳化性及乳化稳定性高,DH=5%时,经中性蛋白酶酶解的多肽乳化性及乳化稳定性分别为62.05%和28.90%,经复合风味蛋白酶酶解的多肽乳化性及乳化稳定性分别为67.46%和44.89%。不同DH酶解多肽疏水性与乳化性及乳化稳定性趋势大致相同。     

罗非鱼水解多肽的乳化性及乳化稳定性

采用复合风味蛋白酶和中性蛋白酶水解罗非鱼蛋白,考察水解多肽的质量分数、p H、Na Cl浓度对多肽乳化活性指数(Emulsifying activity index,EAI)和乳化稳定性指数(Emulsifying stability index,ESI)的影响,并对不同p H条件下水解多肽的溶解度、疏水性与EAI和ESI的关系进行探讨。结果表明,罗非鱼水解多肽的EAI和ESI随多肽质量分数的增加而降低,高于等电点的p H时,EAI和ESI随p H的增大而增大,高浓度的Na Cl会降低多肽的EAI和ESI。多肽在不同p H环境下的疏水性与多肽的溶解度成负相关,溶解度与EAI及ESI成正相关。     

大豆分离蛋白乳化性的研究

采用蛋白质乳化容量电导法,对不同浓度、ＰＨ和酶水解条件下大豆分离蛋白乳化容量和乳化稳定性进行测定,结果表明：大豆蛋白的乳化性在低密度时随浓度上升而增加,浓度达到６％以后趋于稳定;等电点时（ＰＨ４．５）,乳化性最差,偏离等电点后尤其在偏碱性条件下,乳化性明显增加,酶水解后,乳化性变化产大,水解度１７％时,乳化性最佳。     

介质对蛋清蛋白乳化性及乳化稳定性的影响

探讨了蛋白浓度、pH、温度、氯化钠、蔗糖、可溶性淀粉对蛋清蛋白乳化性及乳化稳定性的影响。结果表明:添加蔗糖及可溶性淀粉、提高蛋白浓度都能提高蛋白的乳化性及乳化稳定性,提高氯化钠浓度、温度和pH,蛋白的乳化性及乳化稳定性都是先增后减。这些变化规律为开发和利用蛋清蛋白提供一定理论依据。     

提高大豆分离蛋白乳化性及乳化稳定性的研究

为了拓宽大豆分离蛋白在食品中的应用，提高其乳化性及乳化稳定性。研究了大豆分离蛋白物理、化学和生物改性，并对改性前后大豆分离蛋白的乳化性及乳化稳定性进行了比较。同时也探讨了pH对大豆分离蛋白及其改性物形成乳状液的影响，并利用成膜蛋白质分子所受的相互作用解释了蛋白质的乳化稳定性受外界条件和内部因素所发生的变化。研究发现适度改性可以提高大豆分离蛋白乳化性及乳化稳定性；碱性有利于大豆分离蛋白及其改性物乳化性的提高；而且用吸光值比(K)可较好地表示乳化稳定性．     

干法糖基化改性提高大豆分离蛋白的乳化性

在干热条件下,大豆分离蛋白与葡聚糖两种大分子通过Maillard反应进行共价键合,以共价物的乳化活性为指标,确定影响糖基化蛋白乳化活性的因素依次为:反应温度＞反应时间＞pH＞底物配比,最佳工艺条件为:反应温度70℃,反应时间24 h,糖-蛋白(2:1),pH 8.0.以共价物的乳化稳定性为指标,确定了影响糖基化蛋白乳化稳定性的因素依次为:底物配比＞反应时间＞反应温度＞pH.最佳工艺条件为:糖-蛋白(3:1),反应时间24 h,反应温度70℃,pH8.0.通过聚丙烯酰胺凝胶电泳验证了大豆分离蛋白与葡聚糖发生了接枝反应.     

不同处理方式对鹰嘴豆分离蛋白乳化性质的影响

研究发现微波、超声波、超高压、不同的pH、不同的油含量和不同的离子浓度等都能够影响鹰嘴豆分离蛋白的乳化性质:当微波处理时间为60s,其乳化活性和乳化稳定性都达到最大值;当超声波处理时间为4min时,其乳化活性和乳化稳定性达到最大值;当压力为400MPa时,其乳化活性和乳化稳定性达到最大值;当pH在5.0时,鹰嘴豆蛋白的乳化活力最小,乳化稳定性最高;当NaCl浓度在0.2mol/L时,乳化活性最小,乳化稳定性最高;当加油量在10～30mL范围内,乳化活性逐渐增加,乳化稳定性逐渐降低。      

大米蛋白-酪蛋白共架体构建及其自乳化行为研究

构建可溶性大米蛋白/酪蛋白共架体并探究其自乳化行为。大米蛋白与酪蛋白以质量比1:1在碱性条件下(pH=12)混合,并用0.1 mol/L HCl中和得到共架体蛋白(pH=7)。溶解度及疏水性表征实验表明,大米蛋白与酪蛋白之间通过疏水作用结合,且大米蛋白的溶解度从1.67%提高至91.0%。此外,等温滴定量热法表明共架体蛋白与丁香酚进行自发放热反应。共架体蛋白与不同比例丁香酚进行自乳化,形成平均粒径200 nm,Zeta-电位-30 mV的纳米乳,乳液中蛋白质利用率最高达79.75%,丁香酚装载量为28.54μg/mL,蛋白质与丁香酚的最大结合量为336.78μL/g。贮藏28 d乳液粒径均匀分布且Zeta-电位值不变,表明该乳液具有良好贮藏稳定性。乳液控释研究表明,乳液具有良好控释作用且符合一级释放动力学模型。     

Emulsifying properties of undenatured potato protein concentrate

The emulsifying properties of an undenatured potato protein concentrate (PPC) have been studied in a model system. Emulsification capacity, emulsion activity and stability and emulsion viscosity were studied under a wide variety of conditions.
PPC proved to be superior in all cases to commercial soy isolate except for emulsion viscosity with the same amount of oil added. The emulsification capacity of PPC could be even further improved (50%) by removal of low molecular components by dialysis. The present results indicate that PPC might be considered as a replacement for soy isolate in food formulations.     

Emulsifying properties of soy protein isolates obtained by microfiltration

Soy protein isolate (SPI) fractions were produced using two different pore size microfiltration membranes. Microfiltration was carried out on SPI produced by isoelectric precipitation of a crude protein extract. Five fractions were obtained: two retentates and two permeates from the two membranes plus an intermediate fraction obtained as the retentate on the small‐pore‐size membrane using the permeate from the larger‐pore‐size membrane. Emulsions stabilised by the retentate fractions exhibited higher values (P < 0.01) of emulsion stability index (ESI) and emulsifying activity index (EAI) than those stabilised with fractions made from the permeates. The intermediate fraction gave intermediate ESI values, while the EAI values were not significantly different from those for SPI and one of the retentates. SDS‐PAGE profiles indicated that the fractions exhibiting high functionality in terms of ESI and EAI were also richer in 7S globulin soy protein subunits. © 2002 Society of Chemical Industry     

红松种子水溶性蛋白乳化性及起泡性研究

以红松种子为原料,制备红松种子水溶性蛋白,研究了pH、蛋白质量浓度、NaCl浓度对红松种子水溶性蛋白起泡性和泡沫稳定性以及乳化性和乳化稳定性的影响.结果表明:蛋白的起泡性和乳化性随蛋白质量浓度的增加而增大;pH的变化对起泡性和乳化性的影响也较大,等电点处红松种子水溶性蛋白的起泡性和乳化性最差,pH 11时起泡性和乳化性均较好;NaCl浓度对泡沫稳定性影响不大,对乳化稳定性影响较大.     

Emulsifying properties of an ultrafiltered protein from minced fish wash water

Centrifugation and ultrafiltration were used to concentrate soluble proteins in the water used to wash minced muscle of sardine caught at two different times of year. The proteins thus extracted were largely of less than 67 kDa molecular weight. Part of the resulting concentrate was frozen-stored and part freeze-dried. Irrespective of the season of capture, samples exhibited high emulsifying capacity and emulsion stability, values being higher in freeze-dried samples. Both properties were virtually unaffected by solutions, with NaCl concentrations ranging from 0 to 3%.     

Emulsifying properties of soy protein isolate fractions obtained by isoelectric precipitation

Soy protein isolate (SPI) fractions were produced by isoelectric precipitation based on results of isoelectric focusing carried out on the crude soy extract. The fractions were produced from crude protein extract (pH 9.0) sequentially and non‐sequentially at isoelectric points (pIs) of 5.6, 5.1 and 4.5. Emulsions stabilised by soy proteins with pIs between 5.6 and 5.1 had the highest (P < 0.01) emulsion stability index (ESI), while those stabilised with proteins having pIs between 5.1 and 4.5 resulted in the lowest ESI for sequentially precipitated fractions. Non‐sequential fractionation at pI 5.1 produced fractions with higher emulsifying activity index (EAI) than sequential fractionation. SDS‐PAGE profiles indicated that the fractions exhibiting high functionality in terms of ESI and EAI were also richer in 7S globulin protein subunits. © 2001 Society of Chemical Industry     

Emulsifying and foaming properties of protein isolates prepared from heated milks

Surface activities at the air-water interface and the emulsifying and foaming properties of sodium caseinate, conventional casein-whey protein co-precipitate prepared from milk heated at 90°C × 15 min at pH 6.6 and milk protein isolates prepared from milks heated at 90°C × 15 min at pH 7.5 or at 60°C × 3 min at pH 10.0 were determined. The surface activities of the four proteins at the air-water interface were similar, while the emulsifying capacity and emulsion stabilizing ability of casein was less than that of the milk protein isolates or the conventional co-precipitate. Fat surface areas formed on emulsification with the four proteins were similar and increased with increasing power input. Total protein adsorbed at the interface and protein load (mg protein/m₂ fat) for the emulsions stabilized by sodium caseinate and the milk protein isolate prepared from the milk heated at 90°C × 15 min at pH 7.5 were similar and lower than those for emulsions stabilized by the other two proteins. Foam overruns followed the order: sodium caseinate > milk protein isolate prepared from milk heatedat90°C × 15min, pH 7.5 > milk protein isolate prepared from milk heated at 60°C × 3 min, pH 10.0 > conventional co-precipitate, while foam stabilities followed the reverse order.     

Emulsifying properties of sweet potato protein: Effect of protein concentration and oil volume fraction

The effect of protein concentrations (0.1, 0.25, 0.5, 1.0, 1.5 and 2.0% w/v) and oil volume fractions (5, 15, 25, 35 and 45% v/v) on properties of stabilized emulsions of sweet potato proteins (SPPs) were investigated by use of the emulsifying activity index (EAI), emulsifying stability index (ESI), droplet size, rheological properties, interfacial properties and optical microscopy measurements at neutral pH. The protein concentration or oil volume fraction significantly affected droplet size, interfacial protein concentration, emulsion apparent viscosity, EAI and ESI. Increasing of protein concentration greatly decreased droplet size, EAI and apparent viscosity of SPP emulsions; however, there was a pronounced increase in ESI and interfacial protein concentration (P < 0.05). In contrast, increasing of oil volume fraction greatly increased droplet size, EAI and emulsion apparent viscosity of SPP emulsions, but decreased ESI and interfacial protein concentration significantly (P < 0.05). The rheological curve suggested that SPP emulsions were shear-thinning non-Newtonian fluids. Optical microscopy clearly demonstrated that droplet aggregates were formed at a lower protein concentration of <0.5% (w/v) due to low interfacial protein concentration, while at higher oil volume fractions of >25% (v/v) there was obvious coalescence. In addition, the main components of adsorbed SPP at the oil–water interface were Sporamin A, Sporamin B and some high-molecular-weight aggregates formed by disulfide linkage.     

Emulsifying properties of chickpea protein isolates: Influence of pH and NaCl

Structure and emulsifying properties of chickpea protein isolates (CPI) as a function of protein concentration, oil volume, pH and ionic strength were studied. The optimum protein concentration 2 g l⁻¹ used to determine the emulsifying properties was obtained. Emulsifying activity index (EAI) increased from 244 to 376 m² g⁻¹ with pH from 3.0 to 11.0 except the protein isoelectric point (pI 5.0), where the EAI was 20 m² g⁻¹ and emulsion droplet size was the largest. At lower ionic strengths (0.0–0.1 M NaCl, pH 7.0), EAI decreased from 253 to 72.4 m² g⁻¹; however, it increased from 72.4 to 231.4 m² g⁻¹ at higher ionic strengths (0.1–1.0 M NaCl). A positive relation between EAI and surface hydrophobicity (S₀) of CPI at various ionic strengths was obtained, while EAI was independent of S₀ under different pH values. α-Helix was the major configuration of CPI at the pI or lower ionic strength.     

Emulsifying properties of pea protein/guar gum conjugates and mayonnaise application

Modified plant protein may be used as a healthy and more functional emulsifier in food products. The objective of this study was to evaluate the emulsifying properties of functionally enhanced pea protein (i.e. pea protein conjugated with guar gum, G-PPI) and its potential application to mayonnaise, compared with unmodified pea protein. Emulsions containing G-PPI were prepared at different pH, salt concentrations, protein concentrations and oil/water ratios. Mayonnaise samples were prepared using the pea proteins or egg yolk powder. Various characteristics of the emulsions, including droplet size, apparent viscosity, viscoelasticity and microstructure, were analysed. The emulsions with G-PPI had significantly increased stability of up to 89.4% and apparent viscosity of up to 48.62 mPa.s. The G-PPI emulsion had a smaller average droplet size of 934.4 nm at pH 7 compared with the PPI emulsion (stability 62.7%, apparent viscosity 22.8 mPa.s and droplet size 1664.8 nm). The pH, NaCl concentration, protein concentration and oil/water ratio greatly affected the emulsifying properties. The G-PPI mayonnaise at higher protein concentrations (6 or 8%) exhibited excellent emulsifying and rheological properties. The modified pea protein through the green modification process with natural polysaccharides could be used as a safe and functional emulsifier in different emulsified foods.