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。     

高压微射流压力对大豆蛋白-大豆多糖体系功能性质的影响

为提升大豆分离蛋白（soy protein isolate,SPI）的功能性质,该文引入大豆可溶性多糖（soybean soluble polysaccharides,SSPS）,构建大豆分离蛋白-大豆可溶性多糖体系（SPI-SSPS）,研究动态高压微射流（dynamic high-pressure microfluidization,DHPM）处理对SPI-SSPS功能特性的影响。分别采用0,60,100,140和180 MPa的 DHPM压力处理SPI-SSPS,探究不同压力对SPI-SSPS起泡特性、乳化特性、溶解性、粒度分布和表面疏水性的影响。结果表明,DHPM处理能提高SPI的溶解性和起泡特性,且SSPS的存在能显著提高DHPM对SPI功能性质的改善效果（P<0.05）。100和60 MPa的DHPM处理能使SPI-SSPS呈现较高的起泡能力和起泡稳定性,分别为未处理样品的1.2和2.4倍。140 MPa的DHPM处理使SPI-SSPS溶解性较强,为未处理样品的1.8倍。然而,DHPM处理会显著降低SPI-SSPS的乳化特性、粒径和表面疏水性（P<0.05）。随着处理压力的增加,SPI-SSPS的粒度和表面疏水性逐渐降低,在180MPa的DHPM处理下SPI-SSPS具有较小的粒径和较低的荧光强度。综上所述,DHPM结合SSPS改性技术可用于改善SPI的功能性质（如溶解性、起泡性）,促进SPI在食品工业的应用。该文的研究结果可为SPI的功能性质改性提供参考。     

葡聚糖分子量对玉米醇溶蛋白接枝物结构和乳化性的影

为了探究葡聚糖接枝作用对玉米醇溶蛋白结构和乳化性的影响,明确蛋白质结构与功能性的关系,本研究以玉米醇溶蛋白(Zein)和不同分子量(6、20、40和70 k Da)葡聚糖(dextran,DX)为原料,采用湿热法制备Zein-DX接枝物,并对接枝物的结构和乳化性进行研究。结果表明,低分子量(6 k Da)DX具有更高的反应活性,赖氨酸和精氨酸是参与Zein与DX接枝反应的主要氨基酸。傅里叶红外光谱(fourier transform infrared,FTIR)证明了DX以共价键与Zein形成了复合物。DX的共价接枝能够导致Zein荧光猝灭的发生,降低Zein的热稳定性,改善Zein的乳化活性(emulsifying activity index,EAI)和乳化稳定性(emulsifying stability index,ESI)。低分子量(6 k Da)DX与Zein形成的接枝物最大发射波长发生显著红移,三级结构变的松散,具有更低的热稳定性,且EAI最高达到(23.28±0.71)m2/g。然而,高分子量(70 k Da)DX与Zein形成的接枝物ESI高达(26.44±0.47)min,高于其他Zein-DX接枝物样品。乳状液粒径和流变性分析表明,随着DX分子量的增加,乳状液粒径降低,黏度增加,这与ESI的研究结果相符。研究结果可为改善玉米蛋白功能性和深入了解玉米蛋白改性机制提供理论依据。     

α和α'亚基缺失对大豆分离蛋白乳化特性的影响

为了探究β-伴大豆球蛋白(7S)中α和α′亚基缺失对大豆分离蛋白乳化特性的影响,该文以东农47(对照)和3种不同蛋白亚基缺失型(α缺失、α′缺失以及α、α′缺失)大豆为原料提取大豆分离蛋白(SoyProteinIsolate,SPI),通过十二烷基磺酸钠聚丙烯酰胺凝胶电泳(Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis,SDS-PAGE)技术分析其亚基组成,然后制备乳状液并测定乳化活性指数(Emulsifying Activity Index,EAI)、ζ-电位、粒径、微观结构、稳定动力学指数(Turbiscan Stability Index,TSI)及界面蛋白吸附量。结果表明:α′亚基缺失型SPI乳状液乳化活性指数最大,为87.59 m2/g;ζ-电位绝对值最大,为47.7 mV;粒径最小,为2.223μm;显微结构显示其分子最小且分布最均匀,稳定动力学指数最小;界面蛋白吸附量最大,为31.40%。4种不同SPI乳状液的稳定性结果由大到小为α′亚基缺失型、东农47、α亚基缺失型、α和α′亚基缺失型。研究结果可为高乳化性大豆蛋白系列产品的开发应用提供理论支撑和技术支持。     

挤压温度对大豆分离蛋白与原花青素复合物结构和功能特性的影响

为了探究不同挤压温度（40、60、80、100和120℃）对大豆分离蛋白（Soy Isolate Protein，SPI）与葡萄籽原花青素（Grape Seed Proanthocyanidin Extract，GSPE）复合物功能性质及结构特性的影响。该研究以溶解度、乳化性、乳化稳定性、ζ-电位、粒度为指标，利用荧光光谱、红外光谱分析该复合体系中大豆分离蛋白功能性质及结构的变化。结果表明：相较于挤压SPI，经过挤压处理的SPI-GSPE复合物的溶解度、乳化活性指数、乳化稳定性指数、ζ-电位绝对值及持水性均显著提高（P<0.05），其表面疏水性、持油性显著下降（P<0.05）。随着挤压温度的升高，SPI-GSPE复合物的溶解度、持油性及乳化活性均先增大后减小且在80℃达到最大值，而其表面疏水性先减小后增大且最小值在80℃，ζ-电位绝对值、乳化稳定性及持水性均随温度的升高而降低。粒径分析结果表明，挤压处理后SPI与GSPE形成了更加致密的复合物；荧光光谱及红外光谱结果表明，与GSPE的复合及挤压处理使SPI氨基酸残基所处微环境发生变化，蛋白结构发生变化。以上结果表明挤压温度为80℃时SPI-GSPE复合物功能性质提高幅度最大，为GSPE与SPI复合提高SPI的功能性质提供参考。     

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。     

蚕豆蛋白酶法改性增溶工艺优化及功能性研究

为了拓宽蚕豆蛋白在食品中的应用,解决传统工业方法制备的蚕豆蛋白溶解性差的问题,本文以传统的碱溶酸沉法提取的蚕豆蛋白为原料,采用限制性酶法对其进行增溶改性工艺优化,并对改性后的蚕豆蛋白的功能性质进行了研究。结果表明:风味蛋白酶是提高蚕豆蛋白溶解性的适宜用酶,酶解改性的最佳工艺条件为:料液比1∶14、酶加量(ES)0.1%、温度58℃、pH值7.5、酶解时间30 min,此条件下蚕豆蛋白的溶解性达到99.73%。改性后的蚕豆蛋白的溶解性、起泡性、乳化性及乳化稳定性在酸性和碱性条件下均显著提高,泡沫稳定性在碱性条件下显著提高,持水力在pH值为2~12的范围内显著下降。     

超声辅助制备抗冻融大豆分离蛋白工艺优化

为了提高大豆蛋白冻融稳定性,研究了超声波辅助下大豆分离蛋白(soybean protein isolate,SPI)与葡聚糖(dextran,D)发生美拉德反应改性蛋白的方法,以乳化稳定性(emulsion stability index,ESI)和乳析指数(creaming index,CI)为响应值,建立了优化工艺的Box-Behnken模型。验证试验表明,模型具有重现性和可靠性,在SPI质量浓度40 mg/m L、超声温度80℃、比功率5 W/m L条件下,与未改性SPI相比,改性后SPI乳化稳定性提高了43.80%,经1、2、3次冻融循环后乳析指数分别降低了57.76%、75.33%、96.20%。接枝物制备的乳液经冻融循环后粒径维持在50~55μm。红外光谱分析接枝物在1 010 cm-1处的C-N共价键振动增强,说明SPI和葡聚糖是以共价键的方式结合。扫描电镜结果表明,改性后蛋白颗粒更加疏松,分子间聚集程度降低。研究结果为冷冻食品专用大豆分离蛋白的产业化生产提供了理论和技术指导。     

高压均质-酶解改性提高酸性条件下花生蛋白的溶解性及其稳定性研究

花生蛋白在酸性条件下会絮凝沉淀,溶解性降低,限制了其在酸性饮料加工领域的应用。本研究通过利用高压均质-中性蛋白酶酶解复合改性提高花生蛋白在pH值4.0条件下的溶解度,并根据Turbiscan多重光散射稳定性分析仪的背散射光强值和体系不稳定指数(TSI)分析不同浓度改性蛋白添加量对酸性果汁稳定性的影响。响应面分析结果表明,高压均质-中性蛋白酶酶解复合改性的最优工艺为:均质压力79.74 MPa,料液比7.23%,加酶量517 U·g^-1,酶解时间48.20 min,此时,花生蛋白在pH值4.0条件下氮溶指数(NSI)从由4.04%提升至37.49%。将改性后蛋白加入pH值3.88的果汁中,改性后蛋白添加量为3%和4%的果汁稳定性指数(TSI)分别为1.95和2.23,显著优于蛋白质添加量为5%的样品(TSI为3.29)。研究表明高压均质-中性蛋白酶酶解改性可以显著提高花生蛋白在pH值4.0条件下的溶解度且改性后蛋白在酸性饮料中稳定性良好,为植物蛋白在酸性饮料中的应用提供了参考。     

含氢硅油改性稀土荧光竹塑复合材料的耐水性

为提高稀土荧光竹塑复合材料的耐水性能,拓宽其应用范围。利用含氢硅油改性竹粉和铝酸锶荧光粉表面,熔融共混,注塑成型的方法制备稀土荧光竹塑复合材料。通过接触角测量仪、荧光分光光度计、电子万能试验机、扫描电镜等仪器研究含氢硅油改性对复合材料接触角、吸水性能、发光性能和力学性能的影响。结果表明：未改性复合材料表面具有亲水性,改性复合材料表面具有疏水性。相比于未改性复合材料,改性复合材料的吸水率和吸水厚度膨胀率较低。经11 d水浸泡,改性复合材料的相对发光强度下降28.82%显著低于（P＜0.05）未改性复合材料的46.40%,改性复合材料的发光性能耐水性更好。随着浸水时间的延长,复合材料的弯曲强度、弯曲模量、拉伸强度均下降并趋于稳定,冲击强度先增大后减小,然后趋于稳定,与未改性复合材料相比,改性复合材料的弯曲强度、弯曲模量、拉伸强度的下降率较低（P＜0.05）,改性复合材料的力学性能遇水更稳定。扫描电镜显示,改性复合材料中荧光粉和竹粉在基体中分散较均匀、团聚减少、界面黏合强度改善。复合材料经含氢硅油改性后,游离羟基数量减小,羟基吸收峰向低波数移动,在1 387.75 cm-1处出现Si-CH3的特征吸收峰,表明含氢硅油与竹纤维和荧光粉表面羟基发生了化学反应,研究结果对提高稀土荧光竹塑复合材料的耐水性具有实际意义。     

Preparation and characterization of papain-modified sesame (Sesamum indicum L.) protein isolates

Defatted sesame meal ( approximately 40-50% protein content) is very important as a protein source for human consumption due to the presence of sulfur-containing amino acids, mainly methionine. Sesame protein isolate (SPI) is produced from dehulled, defatted sesame meal and used as a starting material to produce protein hydrolysate by papain. Protein solubility at different pH values, emulsifying properties in terms of emulsion activity index (EAI) and emulsion stability index (ESI), foaming properties in terms of foam capacity (FC) and foam stability (FS), and molecular weight distribution of the SPI hydrolysates were investigated. Within 10 min of hydrolysis, the maximum cleavage of peptide bonds occurred as observed from the degree of hydrolysis. Protein hydrolysates have better functional properties than the original SPI. Significant increase in protein solubility, EAI, and ESI were observed. The greatest increase in solubility was observed between pH 5.0 and 7.0. The molecular weight of the hydrolysates was also reduced significantly during hydrolysis. These improved functional properties of different protein hydrolysates would make them useful products, especially in the food, pharmaceutical, and related industries.     

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.     

Physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate

The amino acid composition and physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate (HPI) were evaluated and compared with those of soy protein isolate (SPI). Edestin, a kind of hexameric legumin, was the major protein component. HPI had similar or higher levels of essential amino acids (except lysine), in comparison to those amino acids of SPI. The essential amino acids in HPI (except lysine and sulfur-containing amino acids) are sufficient for the FAO/WHO suggested requirements for 2-5 year old children. The protein solubility (PS) of HPI was lower than that of SPI at pH less than 8.0 but similar at above pH 8.0. HPI contained much higher free sulfhydryl (SH) content than SPI. Differential scanning calorimetry analysis showed that HPI had only one endothermic peak with denaturation temperature (T(d)) of about 95.0 degrees C, attributed to the edestin component. The T(d) of the endotherm was nearly unaffected by 20-40 mM sodium dodecyl sulfate but significantly decreased by 20 mM dithiothreitol (P < 0.05). The emulsifying activity index, emulsion stability index, and water-holding capacity of HPI were much lower than those of SPI, and the fat adsorption capacity was similar. The data suggest that HPI can be used as a valuable source of nutrition for infants and children but has poor functional properties when compared with SPI. The poor functional properties of HPI have been largely attributed to the formation of covalent disulfide bonds between individual proteins and subsequent aggregation at neutral or acidic pH, due to its high free sulfhydryl content from sulfur-containing amino acids.     

Optimization of the enzymatic deamidation of soy protein by protein-glutaminase and its effect on the functional properties of the protein

The effects of enzymatic deamidation by protein-glutaminase (PG) on the functional properties of soy protein isolate (SPI) were studied. Conditions for the deamidation were evaluated by means of response surface methodology (RSM). Optimal conditions based on achieving a high degree of deamidation (DD) with a concurrently low degree of hydrolysis (DH) were 44 °C, enzyme:substrate ratio (E/S) of 40 U/g protein and pH 7.0. Under optimal conditions, both DD and DH increased over time. SDS-PAGE results indicated that lower molecular mass subunits were produced with increasing DD. Far-UV circular dichroism spectra revealed that the α-helix structure decreased with higher DD, while the β-sheet structure increased until 15 min of deamidation (32.9% DD), but then decreased at higher DD. The solubility of deamidated SPI was enhanced under both acidic and neutral conditions. SPI with higher DD showed better emulsifying properties and greater foaming capacity than SPI, while foaming stability was decreased. It is possible to modify and potentially improve the functional properties of SPI by enzymatic deamidation using PG.     

米糠谷蛋白与β-环状糊精热聚集对乳化性质和结构特性的影响

为提高米糠谷蛋白功能性质,本研究对米糠谷蛋白与β-环状糊精进行复合热处理（温度60、70、80、90、99℃,时间40、80、120、160、200 min）,分析复合聚集体的浊度、接枝度、乳化性质及结构特性等,探究米糠谷蛋白与β-环状糊精复合热聚集行为。结果表明,米糠谷蛋白与β-环状糊精在90℃条件下加热复合160 min时,复合聚集体乳化活性指数达到最大,与天然米糠谷蛋白相比提高了2.39倍;在80℃条件下加热复合200 min时,复合聚集体乳化稳定性指数最大,与天然米糠谷蛋白相比提高了2.39倍。复合物在80℃条件下受热后,米糠谷蛋白与β-环状糊精结合生成较大颗粒的聚集体;复合物中米糠谷蛋白肽链结构打开,游离巯基含量增加,二硫键断开,疏水基团暴露,β-折叠向α-螺旋和β-转角转化,以共价键的形式形成分子间氢键,使得复合聚集体分子更好地结合到油水的界面,复合聚集体乳化活性和稳定性显著提高（P<0.05）。本研究结果为后续米糠蛋白质功能性质的改善及米糠蛋白质的深加工提供了理论依据。     

Stabilization of oil-in-water emulsions by beta-lactoglobulin-polyethylene glycol conjugates

The disulfide bonds of beta-lactoglobulin (beta-lg) were modified by oxidative sulfitolysis to generate beta-lgSO(3). The native protein (beta-lg) and the modified protein (beta-lgSO(3)) were conjugated to activated polyethylene glycol (PEG) to generate beta-lgPEG and beta-lgSO(3)PEG, respectively. Oil-in-water (o/w) emulsions containing 1% beta-lg or beta-lg conjugates were prepared at pH 2.8, 5.0, and 7.0. Emulsion droplet diameters and zeta potentials were measured. For the same emulsifier, emulsion droplet diameters decreased when emulsion pH increased. Zeta potentials of emulsion droplets increased with pH for beta-lg and beta-lgSO(3). Zeta potentials of beta-lgPEG and beta-lgSO(3)PEG approached zero, suggesting that the protein molecule was covered by PEG chains. Accelerated and 7-day storage stabilities at 21 degrees C of the emulsions were monitored. The emulsifying activity index (EAI) of beta-lgPEG was not significantly different from the EAI of beta-lg. The EAI of beta-lg was enhanced following sulfitolysis of beta-lactoglobulin. The emulsifying activity increased more when the oxidatively modified protein was conjugated to polyethylene glycol. Emulsions made with beta-lgSO(3)PEG were more stable than emulsions made with beta-lg, beta-lgPEG, or beta-lgSO(3) under accelerated stability study and for 7 days at 21 degrees C. The stability of o/w emulsions stabilized with beta-lgSO(3)PEG increased because individual droplets were better protected, against protein bridging or coalescence, by the thick adsorbed protein-PEG layer.     

甘薯热变性蛋白限制性酶解产物的乳化特性研究

采用5种酶(Alcalase 2.4L, As1.398, Neutrase, Pepsin, Trypsin)对甘薯热变性蛋白(SPHP)进行限制性酶解。将各酶解产物离心后分别取上清和沉淀测定和观察其乳化液的乳化颗粒平均粒径(D_4,3)、乳化活性指数(EAI)、乳化稳定性指数(ESI)、乳化液的微观结构和表观黏度。结果显示:酶解产物上清和沉淀中蛋白的溶解度均有增加,但沉淀增加的幅度小于上清。SPHP的D_4,3是71.96μm,而酶解产物上清和沉淀乳化液的D_4,3均减小,且上清的D_4,3小于沉淀的。在5种酶解产物中,Pepsin酶解物上清的D_4,3最小,为14.94μm。SPHP酶解后上清的乳化颗粒大小较为均一,且沉淀的乳化颗粒酶解前后变化不大。SPHP的EAI为11.21m2/g,酶解产物上清和沉淀的EAI均有显著提高(P<0.05),其中Pepsin酶解物上清的EAI最高为70.32m2/g。此外,酶解产物上清和沉淀乳化液的ESI增大。与沉淀相比,5种酶解产物的上清具有较低的表观黏度,且酶解产物上清和沉淀的乳化液均呈剪切变稀的非牛顿流体特性。     

适宜含水率保持油茶籽贮藏品质

为了确定油茶籽贮藏适宜的含水率,研究了在4℃,不同含水率(7%、10%、13%、16%、20%)油茶籽贮藏期间的品质变化。结果表明,较低的含水率能较好保持油茶籽的贮藏特性及营养品质。其中,含水率为7%的油茶籽贮藏效果较好,但与10%处理效果差异不明显(P>0.05)。在整个贮藏期,含水率为7%时油茶籽可溶性蛋白下降了13.05 mg/g,油酸含量下降了2.38%,酸值、过氧化值等品质指标上升速率较慢,同时能较好保持β-谷甾醇和角鲨烯等生物活性成分;其次是10%的含水率处理。而含水率为20%的油茶籽贮藏期间可溶性蛋白下降较快,贮藏结束时为25.47 mg/g,油茶籽劣变严重,所提取的油样品质变差,营养物质含量较少,因此含水率20%的油茶籽不适宜长期贮藏。综合考虑油茶籽品质因素和处理成本,认为控制含水率在10%以下能较好保持油茶籽的贮藏品质。该研究可为科学合理地贮藏油茶籽提供参考。