亚油酸氧化诱导大豆分离蛋白氧化对其结构的影响

利用脂肪氧合酶催化不同底物浓度亚油酸氧化大豆分离蛋白,通过测定氧化后大豆分离蛋白的羰基值、巯基、表面疏水性、内源荧光以及凝胶电泳等指标,对氧化修饰后大豆分离蛋白的结构进行分析,并通过分析氧化后大豆分离蛋白在不同溶剂中溶解性能表征其分子间相互作用力。结果表明,随体系中亚油酸浓度的增加,大豆分离蛋白羰基含量增加56.3%,总巯基和游离巯基含量降低,表面疏水性呈先增大后减小趋势,内源荧光强度降低,发生先红移后蓝移现象,大豆分离蛋白粒径先减小后增大,主要分布于5~40 nm之间,蛋白质氧化过程发生去折叠和重聚集,蛋白质交联中存在非二硫键共价键生成。     

高压脉冲电场作用下蛋清蛋白功能性质和结构的变化

研究高压脉冲电场(PEF)作用下蛋清蛋白功能性质与结构的变化。结果表明：25～35kV/cm PEF处理100～800μs可引起蛋清蛋白结构改变,蛋白质分子展开,疏水基团和巯基外露,蛋清蛋白的起泡和乳化功能提高,当PEF处理强度(电场强度和处理时间)增加时,蛋白质结构改变程度增加,蛋白质表面疏水基团和巯基增多,则会发生疏水作用和二硫键交联作用,SDS-PAGE电泳显示蛋清蛋白形成蛋白质聚集体,溶解度下降,蛋清蛋白起泡和乳化功能下降。     

大豆分离蛋白结构特性与表面疏水性的关系

对不同品种大豆分离蛋白溶解性、表面疏水性、巯基含量进行测定,同时采用拉曼光谱法对蛋白质二级结构及氨基酸侧链进行分析,探讨大豆分离蛋白结构特性与表面疏水性关系。结果表明:不同品种大豆分离蛋白表面疏水性由大到小顺序依次为:东农46(743.87)皖豆24(730.14)黑农46(717.54)五星4(625.22)中黄13(613.38)冀NF58(600.61),并与溶解性呈负相关,与巯基含量呈正相关。不同品种大豆分离蛋白具有不同的二级结构,当α-螺旋含量降低、无规卷曲含量升高时,蛋白分子结构变的松散,使包埋在分子内部的疏水性残基更多的暴露出来,导致表面疏水性增加。     

大豆分离蛋白水解研究

研究了大豆分离蛋白水解产物中巯基、疏水性以及蛋白亚基的变化.结果表明,水解不影响巯基含量,水解后巯基的热稳定性明显提高;水解对蛋白分子表面疏水性变化影响显著,水解后疏水性减小、溶解度增加;预热后再水解会产生更多低分子亚基.     

高压脉冲电场对大豆分离蛋白结构特征的影响

本文研究了高压脉冲电场对大豆分离蛋白结构特征的影响。结果表明：在其它脉冲条件一定时，脉冲处理时间在0-288us范围，大豆分离蛋白的分子量、粒径及二级结构改变较小或几乎没有改变。当脉冲处理时间大于432us时，由于蛋白质分子变性、亚基的解离以及通过非共价键相互作用重新聚集，大豆分离蛋白的分子量、粒径发生了变化，形成了大分子的聚集体，但二级结构变化较小。     

超高压处理对大豆拉丝蛋白特性的影响

本文研究了超高压处理对大豆拉丝蛋白特性的影响，以达到改善其再加工特性的目的。实验利用不同超高压处理条件（200～600 MPa,10～30 min）对大豆拉丝蛋白进行处理，采用傅里叶变换红外光谱、紫外吸收光谱和内源荧光光谱分析超高压对大豆拉丝蛋白结构的影响，并通过持水力、表面相对疏水性、游离巯基含量的变化研究超高压对大豆拉丝蛋白功能特性的影响。结果表明：随着压力和时间的增加，β-折叠、无规则卷曲相对含量上升，大豆拉丝蛋白的二级结构向着无序化方向进行；同时蛋白质三级结构伸展，内部疏水基团暴露量增多，但过大的压力和过长的时间则会使得疏水基团重新包埋。400 MPa、10 min时，大豆拉丝蛋白的持水力、游离巯基含量以及表面相对疏水性达到最大值，分别比对照组高32.87%、41.57%、15.66%。综上，适当条件的超高压处理有利于提高大豆拉丝蛋白再加工特性，这为超高压技术应用于大豆拉丝蛋白的生产提供参考。     

超声波对大豆分离蛋白结构及其形成谷氨酰胺转氨酶改性凝胶性质的影响

为探讨超声波对大豆分离蛋白（soybean protein isolate,SPI）结构及大豆分离蛋白形成谷氨酰胺转氨酶（transglutaminase,TG）改性凝胶的影响,研究了超声波处理前后大豆分离蛋白平均粒径、溶解性、表面疏水性、二级结构、微观结构及凝胶特性的变化规律。结果表明：超声波处理使大豆分离蛋白平均粒径减小,溶解性增加,表面疏水性增强,α-螺旋含量降低,无规卷曲含量升高,β-折叠和β-转角无显著变化;超声波处理可以促进大豆分离蛋白形成结构均匀、致密的TG改性凝胶,最佳处理时间为60 min,此时凝胶强度为146.57 g,提高幅度达62.12%,持水性为94.27%,提高幅度为3.66%。相关性分析表明,大豆分离蛋白的溶解性以及其形成TG改性凝胶的凝胶强度、持水性与平均粒径有显著的负相关性。     

pH偏移结合加热处理对大豆分离蛋白结构特性的影响

探讨了p H偏移结合加热处理对大豆分离蛋白结构特性的影响。将大豆分离蛋白经酸性条件(p H 1.5)结合加热(50和60℃)处理0,1,3,5 h,然后恢复到中性条件,测定处理前、后大豆分离蛋白的总巯基和活性巯基以及紫外二阶光谱、色氨酸内源荧光光谱和蛋白电泳的变化。研究结果表明,p H 1.5偏移结合加热处理条件,大豆分离蛋白的总巯基和活性巯基含量显著下降(P0.05),其随时间的变化不显著(P0.05)。紫外扫描和色氨酸荧光分析表明大豆分离蛋白的二级和三级结构发生改变,暴露出更多的疏水基团。SDS-PAGE电泳表明,大豆分离蛋白产生了非二硫键的共价聚集。p H偏移结合加热处理在一定程度上改变了大豆分离蛋白的结构特性。     

低温冷冻条件对大豆分离蛋白分散液表面疏水性及二硫键的影响

通过大豆分离蛋白（soybean protein isolate,SPI）冷冻前后结构的变化,研究了低温冷冻条件（SPI添加量、冷冻温度、冷冻时间）对SPI结构（巯基、二硫键及表面疏水性）的影响。实验发现在冷冻条件下随着SPI添加量的降低,游离巯基和二硫键逐渐减少、暴露巯基与表面疏水性先增加后减小;随着冷冻温度降低和冷冻时间延长,SPI的游离巯基、二硫键含量及表面疏水性逐渐减少。经过冷冻处理的SPI会有一定程度的变性,在不太低的冷冻温度下游离巯基含量明显大于未冷冻SPI,且在冷冻过程中SPI大部分的分子内二硫键转化为分子间二硫键。     

脉冲电场对牛奶酪蛋白功能性质的影响

研究了脉冲电场对酪蛋白功能性质的影响.结果表明:随着脉冲强度和脉冲处理时间的延长,酪蛋白的溶解度下降,乳化性、起泡性及疏水性增加.当脉冲强度或处理时间大于25kV/cm或144(288)μs时,部分功能性质反而下降.     

Properties of whey protein isolate–dextran conjugate prepared using pulsed electric field

Effect of pulsed electric field treatment on whey protein isolate-dextran conjugation in aqueous solution via Maillard reaction was investigated. Significant changes in browning intensity, free amino group content and SDS-PAGE profile showed that whey protein isolate-dextran conjugate was successfully formed using pulsed electric field treatment. Moreover, higher pulsed electric field intensity enhanced the extent of glycosylation. Meanwhile, the secondary structure of whey protein isolate had a considerable loss due to the covalent attachment of dextran. The functional properties, such as solubility, emulsifying activity and emulsion stability were also evaluated. Compared with initial whey protein isolate, the solubility and emulsifying properties were significantly improved. At the same time, glycosylation also inhibited heat-induced aggregation after treated at 80 °C for 20 min. All data showed that pulsed electric field treatment could be applied as a means to prepare WPI-dextran conjugate with better functional properties.     

Inactivation of soybean lipoxygenase in soymilk by pulsed electric fields

The inactivation of soybean lipoxygenase by pulsed electric fields (PEF) was studied. Effects of PEF parameters (treatment time, pulse strength, pulse frequency and pulse width) were evaluated. Soymilk was exposed to pulsed strengths from 20 to 42 kV/cm for up to 1036 μs treatment time in square wave pulse of bipolar mode. Moreover, pulse frequency (100–600 Hz) and pulse width (1–5 μs) was also tested at constant pulsed treatment time of 345 μs and strength of 30 kV/cm. Residual activity of soybean lipoxygenase decreased with the increase of treatment time, pulse strength, pulse frequency and pulse width. The maximum inactivation of soybean lipoxygenase by PEF achieved 88% at 42 kV/cm for 1036 μs with 400 Hz of pulse frequency and 2 μs of pulse width at 25 °C. Inactivation of soybean lipoxygenase by pulsed electric fields was modeled using several kinetic models. Weibull distribution function was most suitable model describing the inactivation of soybean LOX as a function of pulsed electric fields process parameters. Moreover, reduction of soybean LOX activity related to the electric field strength could be well described by the Fermi model.     

Effects of pulsed electric fields on physicochemical properties of soybean protein isolates

Effects of pulsed electric fields (PEF) treatment (0-547 μs and 0-40 kV/cm) on physicochemical properties of soybean protein isolates (SPI) were studied. Solubility, surface free sulfhydryls (SH_F) and hydrophobicity of SPI dispersions (20 mg/ml) increased with the increment of the PEF strength and treatment time at constant pulse width 2 μs, pulse frequency 500 pulse per second (pps) and sample flow rate (1 ml/s). When the PEF strength and treatment time were above 30 kV/cm and 288 μs, solubility, surface SH_F, and hydrophobicity of SPI decreased due to denaturation and aggregation of SPI by hydrophobic interactions and disulfide bonds. Size-exclusion chromatography and laser light scattering analyses demonstrated further that stronger PEF treatment-induced dissociation, denaturation and reaggregation of SPI. Circular dichroism analysis showed that PEF treatment did not produce significant secondary structure changes of SPI. These results suggested that controlled PEF could be applied to process liquid food including soybean protein ingredient and to modify their structure and function in order to get desired products.     

Inactivation of orange juice peroxidase by high‐intensity pulsed electric fields as influenced by process parameters

The inactivation of orange juice peroxidase (POD) under high‐intensity pulsed electric fields (HIPEF) was studied. The effects of HIPEF parameters (electric field strength, treatment time, pulse polarity, frequency and pulse width) were evaluated and compared with conventional heat pasteurization. Samples were exposed to electric field strengths from 5 to 35 kV cm^?1 for up to 1500 µs using square wave pulses in mono‐ and bipolar mode. Effect of pulse frequency (50–450 Hz), pulse width (1–10 µs) and electric energy on POD inactivation by HIPEF were also studied. Temperature was always below 40 °C. POD was totally inactivated by HIPEF and the treatment was more effective than thermal processing in inactivating orange juice POD. The extent of POD inactivation depended on HIPEF processing parameters. Orange juice POD inhibition was greater when the electric field strength, the treatment time, the pulse frequency and the pulse width increased. Monopolar pulses were more effective than bipolar pulses. Orange juice POD activity decreased with electric energy density input. The Weibull distribution function adequately described orange juice POD inactivation as a function of the majority of HIPEF parameters. Moreover, reduction of POD activity related to the electric field strength could be well described by the Fermi model. Copyright © 2005 Society of Chemical Industry     

超声波处理对低嘌呤脱脂豆粉巯基含量、疏水性及粒径分布的影响

为研究超声波处理对低嘌呤脱脂豆粉性质的影响,利用可见分光光度计、激光粒度分布仪、荧光分光光度计进行了检测分析。结果表明：超声波处理样品的游离巯基含量、体积平均粒径、粒径分布宽度及蛋白质表面疏水性均显著高于未经超声波处理的样品（P＜0.05）。超声波功率为405 W、超声波温度50 ℃、超声波时间30 min时,游离巯基含量达到最大值8.75 μmol/g;超声波功率为450 W、超声波温度40 ℃、超声波时间60 min时,相对表面疏水性达到3.86%。因此,超声波处理引起了低嘌呤脱脂豆粉蛋白质游离巯基含量、粒径分布和表面疏水性的变化。     

A pulsed electric field procedure for promoting Maillard reaction in an asparagine–glucose model system

Effects of pulsed electric field (PEF) on pH, intermediate products, asparagine and glucose content, browning value, reducing power as well as antioxidant activity of an asparagine–glucose solution were explored in this paper. Results showed that the solution’s UV–Vis absorbance at 294 nm and 420 nm was significantly increased from 0 to approximately 1.14 and 0.74, respectively, at PEF intensity of 40 kV cm^?1 for 7.35 ms treatment. The temperature of PEF treated samples were overall lower than 40 °C. It was also detected that the antioxidant activity of treated sample was correspondingly increased by 20.33%. Meanwhile, 14% reduction of asparagine content and 66% reduction of glucose content were observed. It was demonstrated from high performance liquid chromatography analysis that Maillard reaction in the model system had been enhanced by PEF treatment as no 5‐hydroxymethyl‐2‐furaldehyde was generated. This study indicates that pulsed electric field treatment, especially with higher intensities, is a means to significantly promote the Maillard reaction in an asparagine–glucose solution.     

响应面法优化灵芝孢子粉高压脉冲电场破壁工艺

本试验利用高压脉冲电场对灵芝孢子粉进行破壁试验以期提高其破壁率,以电场强度、脉冲个数和脉冲宽度为试验因子进行单因素试验,并在此基础上进行响应面试验。结果表明:三个试验因子对灵芝孢子粉破壁率的影响大小依次为电场强度、脉冲宽度和脉冲个数;灵芝孢子粉高压脉冲电场破壁最优工艺参数为电场强度25 kV/cm、脉冲宽度80 μs、脉冲个数40000个,破壁率可达到66.74%±0.03%;破壁孢子粉的多糖和总三萜溶出量分别达到了(0.99±0.11)g/100 g和(1.79±0.03)g/100 g。     

高压脉冲电场(PEF)对蛋清蛋白功能特性的影响

蛋清蛋白不仅具有重要的营养价值,而且还具有重要的功能特性如乳化性、起泡性等,作为一种重要的蛋白原料,本实验研究了高压脉冲电场对蛋清蛋白功能性质的影响。结果表明:蛋清蛋白的溶解度在脉冲电场强度大于35kV/cm时下降;蛋清蛋白的乳化性、起泡能力、泡沫稳定性及疏水性先随脉冲电场强度增加而增大,但当脉冲电场强度大于30kV/cm后,蛋清蛋白的乳化性、起泡能力、泡沫稳定性及疏水性下降;随着脉冲电场数的增加,蛋清蛋白的溶解度、乳化性、起泡能力、泡沫稳定性及疏水性变化不显著。     

High-intensity pulsed electric field variables affecting Staphylococcus aureus inoculated in milk

Staphylococcus aureus is an important milk-related pathogen that is inactivated by high-intensity pulsed electric fields (HIPEF). In this study, inactivation of Staph. aureus suspended in milk by HIPEF was studied using a response surface methodology, in which electric field intensity, pulse number, pulse width, pulse polarity, and the fat content of milk were the controlled variables. It was found that the fat content of milk did not significantly affect the microbial inactivation of Staph. aureus. A maximum value of 4.5 log reductions was obtained by applying 150 bipolar pulses of 8 μs each at 35 kV/cm. Bipolar pulses were more effective than those applied in the monopolar mode. An increase in electric field intensity, pulse number, or pulse width resulted in a drop in the survival fraction of Staph. aureus. Pulse widths close to 6.7 μs lead to greater microbial death with a minimum number of applied pulses. At a constant treatment time, a greater number of shorter pulses achieved better inactivation than those treatments performed at a lower number of longer pulses. The combined action of pulse number and electric field intensity followed a similar pattern, indicating that the same fraction of microbial death can be reached with different combinations of the variables. The behavior and relationship among the electrical variables suggest that the energy input of HIPEF processing might be optimized without decreasing the microbial death.