利用壳聚糖选择性去除乳清中β-乳球蛋白

采用壳聚糖对浓缩乳清蛋白溶液进行处理以除去牛乳中主要过敏原β-乳球蛋白(β-Lg).在室温条件下,应用响应面分析法对反应条件进行优化,以β-乳球蛋白的减少量来评价反应的程度,得到的最适条件:pH值为6.69,壳聚糖添加量为2.04 g/L;此条件下可去除94.89%的β-乳球蛋白,剩余78.68%的α-乳白蛋白(α-La和35.41%的牛血清白蛋白(BSA).此外,对β-乳球蛋白和壳聚糖的回收进行研究,采用正交试验设计考察pH、醋酸钠溶液浓度和添加比例β-乳球蛋白回收率的影响.结果表明,最佳工艺条件为pH值为9.0,醋酸钠溶液浓度0.2 mol/L,添加比例1:15,此条件下可回收87.23%的β-乳球蛋白,纯度为84.1%.     

β-葡聚糖提取分离工艺及其分子量测定研究

利用单因素和正交试验研究不同因素的不同水平对水提燕麦成分β-葡聚糖的工艺条件的影响。结果表明：β-葡聚糖的最佳提取工艺为提取温度80℃、液料比25:1(ml/g)、pH11、提取时间4h,影响因素由大到小依次为提取温度、pH值、液料比和提取时间,在此最佳工艺条件下得率达17.30mg/g左右。再将提取的粗β-葡聚糖进行纯化,纯度为75.30%,由此可用高效凝胶色谱测定其分子量,得到其平均分子量为9.697×105,平均分子半径为83.8nm,分子构型接近于球状。     

动态高压微射流协同糖基化对β-乳球蛋白乳化性和结构的影响

采用动态高压微射流（dynamic high pressure microfluidization,DHPM）协同糖基化处理β-乳球蛋白,研究改性β-乳球蛋白乳化性、乳化稳定性和结构的变化。研究发现DHPM协同糖基化处理过程中β-乳球蛋白结构变化与其乳化性能可能存在关联;DHPM协同糖基化处理能显著提高β-乳球蛋白的乳化性和乳化稳定性。0、40、120 MPa糖基化处理后β-乳球蛋白的乳化活性指数（emulsifying activity index,EAI）分别为136.3、168.1、177.9 m2/g。0 MPa协同糖基化处理后β-乳球蛋白的乳化稳定指数（emulsifying stability index,ESI）为52.3 min;随着压强逐渐增加至40 MPa和120 MPa,协同糖基化处理后ESI值分别升高为56.4 min和59.0 min。通过表征分析β-乳球蛋白结构变化发现：不同压力DHPM协同糖基化处理后,β-乳球蛋白分子质量升高;巯基含量升高;表面疏水性降低;二级结构变化以及氨基酸三维空间构象暴露程度发生变化。这些变化说明β-乳球蛋白与低聚半乳糖发生共价交联时改变了蛋白质结构,造成β-乳球蛋白表面亲水基团的增加,从而导致其乳化性能显著提高。     

β-葡萄糖苷酶的固定化及其用于制备大豆异黄酮的研究

采用25%脱乙酰壳聚糖滴入15%的NaOH与30%的CH3OH组合的成球凝结溶液制备中空球形脱乙酰壳聚糖。适量的β-葡糖糖苷酶用4%戊二醛与中空球形脱乙酰壳聚糖偶联,实现β-葡糖糖苷酶的固定化。中空球形壳聚糖固定化的β-葡萄糖苷酶适宜pH值为4.0、适宜温度为68℃、相对酶活力为87.9%。在50℃用60%乙醇提取大豆异黄酮糖苷,得率约为4.0mg/g。再用固定化β-葡糖糖苷酶水解异黄酮糖苷,70℃、1h后,再经超滤、固定化酵母细胞等处理,可制备纯度达94%的大豆异黄酮甙元。     

两种分离β-乳球蛋白方法的比较

以乳清粉为原料,比较研究了硫酸铵沉淀加凝胶层析法和高盐低pH加透析法两种技术路线分离纯化β-乳球蛋白的得率与纯度.实验结果表明,高盐低pH加透析法所得β-乳球蛋白浓度为11ms/mL、SDS-PAGE检测纯度达90%以上;硫酸铵沉淀加凝胶层析法所得β-乳球蛋白浓度为1mg/mL、纯度>90%.     

β-乳球蛋白IgE抗原决定簇的识别

以β- 乳球蛋白氨基酸序列为模板,错位合成β- 乳球蛋白多肽,以收集到的牛乳过敏患者血清为抗体,鉴定β- 乳球蛋白IgE 抗原决定簇,分析影响致敏性的关键氨基酸,探讨牛乳过敏机理。结果表明：β- 乳球蛋白IgE抗原决定簇有4 条,氨基酸序列分别为17～31、72～86、92～106、152～166,并且苏氨酸(AA20)、蛋氨酸(AA23)、天冬氨酸(AA27)是影响β- 乳球蛋白致敏性的关键氨基酸。说明特异性水解抗原决定簇或定点修饰氨基酸可以实现过敏原脱敏的目的。     

离子交换法去除乳清β-乳球蛋白的效果研究

采用离子交换树脂法处理乳清粉,结果显示通过阳离子交换树脂可以选择性吸附β-乳球蛋白,β-乳球蛋白质量分数由39.7%降至16.0%。     

不同沉淀方法分离甘薯β-淀粉酶的研究

研究盐析法、有机溶剂沉淀法分离甘薯β- 淀粉酶的工艺条件,分析盐析饱和度、有机溶剂体积比和溶液pH 值对回收率及提纯倍数的影响。结果表明：硫酸铵饱和度在70% 时,酶活性回收率达到78.1%,提纯1.56倍;乙醇体积比4:1 时,酶活性回收率达到76.8%,提纯2.61 倍;当溶液pH4.5～5.0、丙酮体积比3:1 时,酶活性回收率可达到90.66%,提纯了3.29 倍,此条件下β- 淀粉酶分离效果最佳。     

水牛乳中主要过敏原的分离纯化

牛乳和水牛乳存在免疫交叉反应,牛乳过敏患者可能对水牛乳过敏。因此,分离纯化出水牛乳中各种过敏原将为进一步的工作奠定物质基础。实验中以摩拉水牛乳为原料,通过等电点沉淀、凝胶柱层析法和阴离子交换法分离纯化水牛乳的酪蛋白、β-乳球蛋白α-乳白蛋白,得到了SDS-PAGE纯(纯度≥90%)的β-乳球蛋白α-乳白蛋白。离子交换层析分离β-乳球蛋白、α-乳白蛋白的得率分别为50.26%、52.86%;凝胶层析分离β-乳球蛋白、α-乳白蛋白的得率分别为49.39%、84.19%。实验结果表明,等电点沉淀、凝胶柱层析法和阴离子交换法适合于分离水牛乳中主要过敏原成分。     

羟基自由基氧化体系对乳清蛋白、β- 乳球蛋白化学结构的影响

本实验主要研究乳清蛋白(WPI)和β-乳球蛋白(β-Lg)经过FeCl3/抗坏血酸(AsA)/H2O2产生的羟基自由基氧化系统氧化后化学结构产生的变化。两种蛋白分别经过0.1mmol/L 或者1mmol/L FeCl3 氧化1、5 和12h 后,总巯基、游离氨都下降,而羰基、二聚酪氨酸和疏水性都呈增加的趋势。低Fe3+ 浓度氧化1h,WPI 巯基含量降低38.5%,β-Lg 降低11.6%;而游离氨分别降低20.68% 和0.64%。高Fe3+ 浓度氧化5h,WPI 羰基增加32.4%,β-Lg 增加8.4%;二聚酪氨酸分别增加132.4% 和28%;疏水值增加161.1% 和0.7%。高Fe3+ 浓度带来的氧化效果要比低Fe3+浓度明显(p ＜ 0.05)。这说明,氧化改变了蛋白的化学结构,氧化程度取决于浓度Fe3+ 的浓度,且β- 乳球蛋白比乳清蛋白有更好的稳定性。     

Effect of β-lactoglobulin A and B whey protein variants on cheese yield potential of a model milk system

Cheese yield mainly depends on the amount and proportion of milk constituents; however, genetic variants of the proteins present in milk may also have an important effect. The objective of this research was to study the effect of the variants A and B of β-lactoglobulin (LG) on cheese yield using a model system consisting of skim milk powder fortified with different levels of a mixture containing α-lactalbumin and β-LG genetic variants (A, B, or A-B) in a 1:2 ratio. Fortified milk samples were subjected to pasteurization at 65°C for 30 min. Miniature cheeses were made by acidifying (pH = 5.9) fortified milk and incubating with rennet for 1 h at 32°C. The clot formed was cut, centrifuged at 2,600 × g for 30 min at 20°C and drained for determining cheese yield. Cheese-yielding capacity was expressed as actual yield (grams of cheese curd per 100 g of milk) and dry weight yield (grams of dried cheese curd per 100 g of milk). Free-zone capillary electrophoresis was used for determining β-LG A or B recovery in the curd during rennet-induced coagulation. The presence of β-LG variant B resulted in a significantly higher actual and dried weight cheese yield than when A or A-B were present at levels ≤0.675% of whey protein (WP) addition. Results of free-zone capillary electrophoresis allowed us to infer that β-LG B associates with the casein micelles during renneting, as shown by an increase in the recovery of this variant in the curd when β-LG B was added up to a maximum at 0.45% (equivalent to 0.675% WP). In general, actual or dried weight cheese yield increased as WP addition was increased from 0.225 to 0.675%. However, when WP addition ranged from 0.675 to 0.90%, a drastic drop in cheese yield was observed. This behavior may be because an increase in the aggregation of casein micelles with a concomitant inclusion of whey protein in the gel occurs at low levels of WP addition, whereas once the association of WP with the casein micelles reach a saturation point at addition levels higher than 0.675%, rearrangements of the gel network result in larger whey expulsion and syneresis. This knowledge is expected to be useful to maximize cheese yield and optimize processing conditions during cheese and cheese analogs manufacturing.     

响应面法优化离子交换法固定化β-D-呋喃果糖苷酶

以大孔阴离子树脂D311 为载体,对日本曲霉来源的β-D- 呋喃果糖苷酶进行离子交换法固定化。研究温度、pH 值、时间、游离酶液酶活力对固定化效果的影响,并在此基础上运用响应面法对固定化条件进行优化。结果表明,最佳固定化条件为：室温、pH6.6、固定化时间4h、游离酶液酶活力为900U/mL,在此条件下,固定化β-D- 呋喃果糖苷酶生产的低聚果糖产量可达58.16%。     

Use of chitosan for selective removal of beta-lactoglobulin from whey

A method is described for selective removal of undenatured β-lactoglobulin from cheese whey based on interactions between whey proteins and chitosan. Whey was previously clarified at pH 4.5 with addition of chitosan (25 mg/100 mL), and selective removal of β-lactoglobulin was studied in the pH interval 4.6 to 6.5. Addition of chitosan caused selective precipitation of β-lactoglobulin that increased with pH. The content of β-lactoglobulin in whey decreased as the amount of chitosan added was increased. At pH 6.2, addition of 1.9 to 3.0 mg/mL of chitosan led to complete removal of β-lactoglobulin, whereas at least 80% of the rest of whey proteins remained in solution. The production of cheese whey without β-lactoglobulin could help to expand the applications of dairy by-products in food processing, and to isolate hypoallergenic whey protein concentrates.     

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%。     

乳清蛋白的热变性及其在酸奶生产中的应用

介绍了乳清蛋白与酪蛋白热缔合过程的模型、乳清蛋白热变性的动力学以及热变性作用对酸奶质构的影响。乳清蛋白的变性度与酸奶最终质量存在密切的关系。应用β-乳球蛋白（β-LG）的等变性度曲线可以选择酸奶生产中的最适热处理条件（温度／时间）。     

Roles of charge interactions on astringency of whey proteins at low pH

Whey proteins are a major ingredient in sports drink and functional beverages. At low pH, whey proteins are astringent, which may be undesirable in some applications. Understanding the astringency mechanism of whey proteins at low pH could lead to developing ways to minimize the astringency. This study compared the astringency of β-lactoglobulin (β-LG) at low pH with phosphate buffer controls having the same amount of phosphate and at similar pH. Results showed that β-LG samples were more astringent than phosphate buffers, indicating that astringency was not caused by acid alone and that proteins contribute to astringency. When comparing among various whey protein isolates (WPI) and lactoferrin at pH 3.5, 4.5, and 7.0, lactoferrin was astringent at pH 7.0 where no acid was added. In contrast, astringency of all WPI decreased at pH 7.0. This can be explained by lactoferrin remaining positively charged at pH 7.0 and able to interact with negatively charged saliva proteins, whereas the negatively charged WPI would not interact. Charge interactions were further supported by β-LG or lactoferrin and salivary proteins precipitating when mixed at conditions where β-LG, lactoferrin, or saliva themselves did not precipitate. It can be concluded that interactions between positively charged whey proteins and salivary proteins play a role in astringency of proteins at low pH.     

Rheological properties of acid gels prepared from heated milk fortified with whey protein mixtures containing the A,B and C variants of β-lactoglobulin

The effect of fortification of reconstituted skim milk with different levels of a whey protein mixture containing a 1:2 ratio of α-lactalbumin (α-la) and different genetic variants of β-lactoglobulin (β-LG) on the rheological properties of acid milk gels, formed by acidification with glucono-δ-lactone, was investigated. Milk samples were either unheated or heated at 80°C for 30 min before acidification. Acid gels prepared from unheated skim milk had very low G′ values, long gelation times and low gelation pH. Samples prepared from heated milk had markedly higher G′ values, a reduced gelation time and an increased gelation pH. The addition of increasing levels of whey protein mixtures containing β-LG B or β-LG C to the milk prior to heating and acidification caused an almost linear increase in the G′. In contrast, whey protein mixtures containing β-LG A caused a progressive increase in the G′ with added protein levels up to about 0.7% (w/w) but little further change at higher addition levels. A mixture of the A and B variants of β-LG gave an intermediate behaviour between those of the A and B variants. In all samples, the G′ value at 5°C was approximately twice that at 30°C so that the relative differences as a result of the β-LG genetic variants were similar for the two temperatures.