胰蛋白酶制备乳蛋白水解物的研究

为降低牛乳蛋白中的致敏蛋白含量,制备婴儿配方乳,本研究利用蛋白酶水解牛乳蛋白,在筛选出最佳酶解用酶的基础上,以胰蛋白酶浓度、酶解时间、酶解温度为影响因子,在单因素实验结果的基础上．应用Centure—Composire Design中心组合方法进行三因素三水平的实验设计,以牛乳蛋白水解度为响应值,运用响应面法对水解条件进行进一步的优化。结果表明：酶解浓度、酶解时间对牛乳蛋白水解度影响显著;牛乳蛋白质水解的最佳工艺为：以胰蛋白酶为水解用酶,水解温度为55℃,酶添加量为0．8％,酶解时间为47min。牛乳在此条件下水解后,对其水解物进行SDS—PAGE分析及抗原性测定,表明αs-酪蛋白和β-乳球蛋白含量均有不同程度的减少,抗原性也有不同程度的下降。     

婴儿配方乳蛋白水解物酶解条件的研究

为降低牛乳蛋白中的致敏蛋白质量浓度,制备婴儿配方乳.利用风味蛋白酶水解牛乳蛋白,以风味蛋白酶质量分数、酶解时间、酶解温度为影响因子,在单因素试验结果的基础上,应用Centure-Composite Design中心组合方法进行三因素三水平的实验设计,以牛乳蛋白水解度为响应值,运用响应面法对水解务件进行进一步的优化.结果表明,酶解浓度、酶解时间对牛乳蛋白水解度影响显著;牛乳蛋白质水解的最佳工艺:水解温度为56.03℃,酶添加量为0.37％,酶解时间为39.02 min.通过对牛乳蛋白水解物进行SDS-PAGE分析,表明αs-酪蛋白和β-乳球蛋白均有不同程度的减少.经测定水解后的牛乳中β-乳球蛋白与鲜牛乳的抗原降低率有所增加.     

酶水解降低牛乳蛋白抗原性的研究

利用胰蛋白酶和风味蛋白酶对牛乳单酶一步或双酶两步酶解,研究两种酶解方法对牛乳中αs-酪蛋白、α-乳白蛋白、β-乳球蛋白抗原降低效果的影响。对酶解过程中3种蛋白抗原降低率进行测定及水解物的蛋白质分布进行分析,结果表明:双酶两步水解法与单酶一步水解法相比,可显著降低牛乳蛋白抗原性。水解液的SDS-PAGE分析显示双酶两步水解液中αs-酪蛋白、α-乳白蛋白、β-乳球蛋白残留量较单酶一步水解液中的这3种蛋白残留量少。水解液的高效液相色谱分析显示双酶两步水解液中有较多相对分子质量低于6 500的肽类,而单酶一步水解液中有较多相对分子质量大于12 300的蛋白。     

优先酶解乳清蛋白浓缩物中β-乳球蛋白工艺的研究

研究选用了几种商业蛋白酶对乳清蛋白浓缩物（WPC）进行酶解，通过比较各酶解产物中α-乳白蛋白（α-La）和β-乳球蛋白（β-Lg）存余率的高低，筛选出Protease A具有优先降解β-Lg的能力；通过单因素实验设计和正交实验设计优化了Protease A优先降解β-Lg的工艺。最佳工艺为温度40℃，pH值为7．3，E／S为800U／g蛋白，酶解时间为3h，此时水解物的水解率（DH）为8.40％，α-La和β-Lg的存余率分别为5．3％和1．4％，水解产物的溶解性得到了明显地改善（P〈0．05）。     

超声波协同马克思克鲁维酵母Z17胞内粗酶处理降低乳清蛋白的致敏性

以超声预处理过的乳清蛋白为酶解底物,采用OPA法、ELISA分析等手段,探究马克思克鲁维酵母Z17粗酶水解乳清蛋白、降低乳清蛋白致敏性【以α-乳白蛋白(α-LA)和β-乳球蛋白(β-LG)为抗原性表征】的最优超声预处理-酶解条件。结果表明:乳清蛋白水解度受初始pH值和酶解温度的影响显著,α-LA、β-LG抗原性受初始pH值的影响显著,超声间歇时间和超声功率的交互作用对α-LA、β-LG抗原性影响显著。采用响应面法获得马克思克鲁维酵母Z17转化乳清蛋白的最优酶解条件是:超声间歇时间16 s,超声功率400 W,初始pH 6.16,酶解温度18.48℃,预测α-LA抗原性、β-LG抗原性的降低率达到最大值,分别为65.56%和57.96%。     

酶解作用对牛乳乳清蛋白抗原性影响的研究

为了探明胰蛋白酶水解作用对乳清蛋白致敏性或者抗原性的影响,利用小鼠动物模型从体外和体内两个方面研究了水解作用对乳清蛋白致敏性的影响.结果表明,酶解物中β-乳球蛋白抗原性降低率为53.92％,α-乳白蛋白抗原性降低率为82.31％.酶解组小鼠过敏症状较未水解的乳清分离蛋白(WPI)组相比明显减轻.与WPI组相比,酶解物显著抑制特异性IgE的产生,IgE质量浓度下降了40.55％.血浆组胺实验表明,酶解物降低血浆中组胺的释放,组胺质量浓度比WPI组下降了28.72％.     

羊乳清蛋白部分和深度水解工艺、水解物致敏性及肽谱分析

利用羊乳清蛋白制备低致敏性配料是目前乳品工业的研究热点。乳清蛋白是乳中主要的蛋白质之一,也是引起婴幼儿过敏反应的主要成分,将蛋白质水解为小分子肽是降低其致敏性的有效方法。以山羊乳清蛋白为原料,研究了部分水解乳清蛋白和深度水解乳清蛋白的水解工艺和水解物特性(水解度、分子质量分布和β-乳球蛋白抗原性),并利用液相色谱串联质谱法(LC-MS/MS) 比较了部分水解和深度水解工艺中过敏表位酶切位点的差异。研究结果表明,中性蛋白酶和碱性蛋白酶对羊乳清蛋白水解效果较好,其中碱性蛋白酶的水解度最高,达21.26%。经电泳分析,单酶水解后的产物中仍存在大分子多肽链,深度水解工艺需要复合酶水解。在酶底比为4000U/g时,使用碱性蛋白酶在pH值为10.0、温度为55℃条件下水解羊乳清蛋白1.0h,部分水解产物的水解度为12.31%,分子质量在5kDa以下的多肽占95.18%,β-乳球蛋白抗原性下降率为9.40%。中性蛋白酶和碱性蛋白酶的质量比为1∶1,酶底比为6000U/g,在pH值为8.5、温度为50℃条件下,水解羊乳清蛋白3.0h,深度水解产物的水解度为35.58%,分子质量低于3kDa的多肽为97.26%,β-乳球蛋白抗原性下降率为40.97%。部分水解和深度水解均能破坏β-乳球蛋白的大部分过敏表位,但相较于部分水解,深度水解能更大程度地降低乳清蛋白的致敏性。研究旨在为低致敏性羊水解乳清蛋白的生产提供一定的理论参考。     

碱性蛋白酶限制性酶解乳清浓缩蛋白成胶特性的研究

研究了利用碱性蛋白酶限制性酶解乳清蛋白对其凝胶特性、成胶温度、凝胶粒径和蛋白组分水解情况的影响,结果表明,酶解可以提高乳清蛋白的凝胶特性,在酶解70min时达到最大值,此时乳清蛋白的水解度为7．22％,当酶解时间超过70min后随着水解时间的延长凝胶特性略有下降;各水解时间点乳清蛋白成胶温度均为80℃;酶解后乳清蛋白凝胶的粒径值下降了90％以上,且酶解30min后形成的凝胶粒径值都在50um以内;在碱性蛋白酶的限制性酶解作用下,仅部分β-乳球蛋白和很少部分牛血清白蛋白被酶解,而大部分α-乳白蛋白被酶解。     

复合酶降低牛乳蛋白致敏性的研究

利用胰蛋白酶、风味蛋白酶单独或分布水解牛乳,均使α-乳白蛋白、β-乳球蛋白、αs-酪蛋白的抗原性降低,结果表明,胰蛋白酶水解60 min后,αs-酪蛋白、α-乳白蛋白、β-乳球蛋白的抗原降低率分别为83％,91％,13％;风味蛋白酶水解60 min后,αs-酪蛋白、α-乳白蛋白、β-乳球蛋白的抗原降低率分别为93％,93％,55％;胰蛋白酶水解40 min,风味蛋白酶水解20min后,αs-酪蛋白、α-乳白蛋白、β-乳球蛋白的抗原降低率分别为96％,96％,71％.因此,胰蛋白酶和风味蛋白酶分步水解牛乳蛋白抗原降低最显著,苦味最低,双酶分步水解后,产生大量分子量在5 000 u以下的肽.胰蛋白酶和风味蛋白酶分步水解牛乳技术将为婴儿配方乳蛋白脱敏提供理论基础.     

复合酶制备牛乳低致敏性蛋白基料的研究

利用胰蛋白酶、风味蛋白酶单独或分步水解牛乳,研究了α-乳白蛋白、β-乳球蛋白、αs-酪蛋白的抗原性的变化.结果显示,胰蛋白酶水解60min后,αs-酪蛋白、α-乳白蛋白、β-乳球蛋白的抗原降低率分别为83％、91％、13％,风味蛋白酶水解60min后,αs-酪蛋白、α-乳白蛋白、β-乳球蛋白的抗原降低率分别为93％、93％、55％,胰蛋白酶水解40min,风味蛋白酶水解20min后,αs-酪蛋白、α-乳白蛋白、β-乳球蛋白的抗原降低率分别为96％、96％、71％.因此,胰蛋白酶和风味蛋白酶分步水解牛乳蛋白抗原降低最显著,苦味最低,双酶分步水解后,产生大量分子量在5000u以下的肽.胰蛋白酶和风味蛋白酶分步水解牛乳技术,将为婴儿配方乳蛋白脱敏提供理论基础.     

Co-precipitation of whey and pea protein – indication of interactions

The aim was to optimise the yield of co-precipitation of whey protein isolate (WPI) and pea protein isolate (PPI) and compare co-precipitates and protein blends with respect to solubility. The yield of co-precipitates was tested with different protein ratios of WPI and PPI in combination with different temperatures and acid precipitation (pH 4.6). The highest precipitation yield was obtained at protein ratios WPI < PPI, high temperature and alkaline protein solvation. The solubility was measured by an instability index and absorption spectroscopy of re-suspended precipitated proteins at pH 3, 7 and 11.5. Co-precipitates had significantly lower solubility than protein blends. Protein ratios WPI > PPI, low precipitation temperature and high pH showed the highest solubility. Differences in protein composition between co-precipitates and protein blends were observed with SDS-PAGE and matrix-assisted laser desorption ionisation time-of-flight, and indicated different protein–protein interaction in samples, which needs further investigations.     

大豆蛋白溶解性研究

该文概述大豆蛋白溶解特性及其与一般物质溶解差异,介绍提高大豆蛋白溶解性改性方法及研究现状,对比不同改性增溶方法优、缺点,并提出今后大豆蛋白改性研究方向。     

细菌中蛋白质样品制备方法研究进展

细菌在生长繁殖时,细菌蛋白的表达受到环境影响而存在较大差异,使得细菌蛋白表达具有复杂性.在食品生产加工过程中可能会受到致病菌污染,细菌产生的内毒素和外毒素均会对人体健康构成威胁,因此需要高灵敏度和高特异性的检测方法来定量分析和鉴定食品中的细菌毒素.蛋白组学方法可以揭示细菌蛋白组成及其潜在的生物学功能,感染过程中菌体蛋白...     

Physicochemical and Functional Properties of Soy Protein Substrates Modified by Low Levels of Protease Hydrolysis

ABSTRACT: Endo-protease treatments achieving low degrees of hydrolysis (DH 2% and 4%) were used to improve functional properties of hexane-extracted soy flour (HESF), extruded-expelled partially defatted soy flour (EESF), ethanol-washed soy protein concentrate (SPC), and soy protein isolate (SPI). These substrates had protein dispersibility indices ranging from 11% to 89%. Functional properties, including solubility profile (pH 3 to 7), emul-sification capacity and stability, foaming capacity and stability, and apparent viscosity were determined and related to surface hydrophobicity and peptide profiles of the hydrolysates. Protein solubilities of all substrates increased as DH increased. Emulsification capacity and hydrophobicity values of the enzyme-modified HESF and EESF decreased after hydrolysis, whereas these values increased for SPC and SPI. Emulsion stability was improved for all 4% DH hydrolysates. Hydrolyzed SPC had lower foaming capacity and stability. For substrates other than SPC, foaming properties were different depending on DH. Hydrolysis significantly decreased the apparent viscosities regardless of substrate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated differences in the molecular weight profiles of the hydrolysates. HESF and EESF, which had high proportions of native-state proteins, showed minor changes in the peptide profile due to hydrolysis compared with SPC and SPI.     

Effects of silage protein degradability and fermentation acids on metabolizable protein concentration: A meta-analysis of dairy cow production experiments

A meta-analysis was conducted using data from dairy cow production studies to evaluate silage metabolizable protein (MP) concentrations. The data consisted of 397 treatment means in 130 comparisons, in which the effects of silage factors (e.g., date of harvest, wilting, silage additives) were investigated. Within a comparison, a fixed amount of the same concentrate was fed. A prerequisite of data to be included in the analysis was that silage dry matter (DM), crude protein (CP), ammonia N, lactic acid (LA), and total acid (TA) concentrations and digestibility were determined. A smaller data set (n = 248) comprised studies in which silage water-soluble N concentration was also analyzed. The supply of MP was estimated as amino acids absorbed from the small intestine using a model with constant values for ruminal effective protein degradability (EPD) and intestinal digestibility of rumen undegraded protein. Microbial protein was calculated on the basis of digestible carbohydrates and rumen degradable protein (RDP). Alternative models were used to estimate microbial protein formation, assuming the energy values of RDP and TA to be equivalent to 1.00, 0.75, 0.50, 0.25, and 0 times that of digestible carbohydrates. Because EPD values are seldom determined in production trials, they were derived using empirical models that estimate them from other feed components. The goodness of fit of models was compared on the basis of root mean squared error (RMSE) of milk protein yield (MPY) predicted from MP supply (adjusted for random study effect) and Akaike's information criterion. Metabolizable protein supply calculated from basal assumptions predicted MPY precisely within a study (RMSE = 16.2 g/d). Variable contribution of RDP to the energy supply for microbial synthesis influenced the precision of MPY prediction very little, but RMSE for MPY increased markedly when the energy supply of rumen microbes was corrected for TA concentration. Using predicted rather than constant EPD values also increased RMSE of MPY prediction. These observations do not mean that the supply of MP from undegraded feed protein is constant. However, it suggests that our current methods overestimate the range in EPD values and that the techniques have so many inherent technical problems that they can mask the true differences between the feeds. Including new elements in feed protein evaluation models may not improve the precision of production response predictions unless the consequent effects on the supply of other nutrients are taken into account.     

大豆蛋白生产与应用现状

该文综述大豆蛋白制品—大豆蛋白粉、大豆分离蛋白、大豆浓缩蛋白、大豆组织蛋白生产现状、存在问题及大豆蛋白在面制品、肉制品、乳制品、饮料制品等中应用现状。     

The structures and functions of ice crystal-controlling proteins from bacteria

Many organisms have evolved into unique mechanisms which minimize freezing injury due to extracellular ice formation. Specifically, certain bacteria have produced a few proteins each with different functions. For example, the ice nucleation protein acts as a template for ice formation, which is responsible for imparting ice nucleating activity. The anti-nucleating protein inhibits the fluctuation of ice nucleus formation by a foreign particle in the water drop. Also, the antifreeze proteins depress the freezing temperature, modify or suppress ice crystal growth, inhibit ice recrystallization, and protect the cell membrane from cold-induced damage. In this article, a review on the current knowledge of the structure and the function of these three types of proteins, which are capable of interacting with ice itself or its nuclei from bacteria.     

Effect of amidation on the foaming and physico-chemical properties of bovine serum albumin

Amidation of bovine serum albumin (BSA) was achieved by a water-soluble carbo-diimide, ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-mediated reaction using ammonium chloride as the nucleophile. Partial and substantial amidation of 0.5% (w/v) BSA in 5.5 m ammonium chloride solution with 1 times 10-²mmol EDC over 120 min and 1 times 10^-1mmol EDC over 10 min respectively was achieved on a large scale using diafiltration for rapid termination of the reaction and purification. Residual ammonium chloride otherwise enhanced foaming properties. The amidated proteins were characterized by isoelectric focusing, electrophoresis and hydrophobicity and disulphide- and sulphydryl-group measurements. Compared with native BSA, partially amidated BSA (PA-BSA) produced enhanced foam expansion and foam stability values. This was attributed to minimal denaturation and to the presence of both acidic and basic components (pI range 5.25–7.50) within the single protein. In contrast, substantially amidated BSA (SA-BSA) (pI range 7–9.1) had similar foaming properties to those of the ultrafiltered BSA control which were slightly lower than those of native BSA. However SA-BSA interacted synergistically with native BSA producing enhanced foaming properties particularly at the 1:1 ratio through electrostatic interactions, conformational changes and increased hydrophobicity.     

大豆分离蛋白改性对其功能性质影响

大豆分离蛋白是大豆蛋白最为精制形式,广泛应用于食品工业,并在不同产品中表现出不同功能。该文综述近年来大豆分离蛋白物理、化学、酶法及基因工程改性对其功能性质影响,经不同方式改性可产生合适功能性质,从而拓宽大豆分离蛋白在食品工业中应用。     

芝麻蛋白研究概况

简述芝麻蛋白的结构及氨基酸组成、蛋白质性质和应用,并展望进一步研究芝麻蛋白的 前景。