超声辅助处理对乳清分离蛋白糖基化产物的理化特性影响

采用超声辅助技术对乳清分离蛋白(WPI)进行糖基化改性,并与水浴加热法进行比较,探究两种处理方式对糖基化反应产物理化性质的影响。结果表明,与水浴法相比,超声辅助法可以更快地促进糖基化反应的进行,且对糖基化产物的理化性质有较大改善;当超声温度为70℃,功率为300 W,超声时间为40min时,乳清分离蛋白和葡萄糖的接枝度达到48. 10%,且乳清分离蛋白—葡萄糖接枝物的乳化性、在等电点处溶解性均增大。乳化系数由23.67 m~2/g增大到40.84 m~2/g;等电点附近的溶解度由19.09%增大到47.95%。且以接枝物为基质的乳液的粒径更小,储藏稳定性更好。     

High hydrostatic pressure modification of whey protein concentrate for use in low-fat whipping cream improves foaming properties

Whey is the inevitable by-product of cheese production. Whey can be incorporated into a variety of foods, but little has been done to investigate its suitability in whipping cream. The objective of this work was to evaluate the foaming properties of selected low-fat whipping cream formulations containing whey protein concentrate (WPC) that did or did not undergo high hydrostatic pressure (HHP) treatment. Fresh whey was concentrated by ultrafiltration, pasteurized, and standardized to 8.23% total solids and treated with HHP at 300 MPa for 15 min. Viscosity, overrun, and foam stability were determined to assess foaming properties. Sensory evaluation was conducted with 57 panelists using a duo-trio difference test. The optimal whipping time for the selected formulations was 3 min. Whipping cream containing untreated WPC and HHP-treated WPC resulted in greater overrun and foam stability than the control whipping cream without WPC. Panelists distinguished a difference between whipping cream containing untreated WPC and whipping cream containing HHP-treated WPC. High hydrostatic pressure-treated WPC can improve the foaming properties of low-fat whipping cream, which may justify expansion of the use of whey in whipping cream and application of HHP technology in the dairy industry.     

以乳清蛋白为基质的脂肪替代品对冰淇淋品质的影响

以乳清蛋白WPC-80为基质制备脂肪替代品,替代中脂冰淇淋中25%的脂肪。随着脂肪替代率的增加,冰淇淋浆料黏度和膨胀率增大,抗融化率和硬度下降,制得的低脂冰淇淋的各项感官指标均与中脂冰淇淋相当。当替代全部脂肪时,所制得的无脂冰淇淋也有较好的感官接受性。     

Production of a high gel strength whey protein concentrate from cheese whey

In order to develop a process for the production of a whey protein concentrate (WPC) with high gel strength and water-holding capacity from cheese whey, we analyzed 10 commercially available WPC with different functional properties. Protein composition and modification were analyzed using electrophoresis, HPLC, and mass spectrometry. The analyses of the WPC revealed that the factors closely associated with gel strength and water-holding capacity were solubility and composition of the protein and the ionic environment. To maintain whey protein solubility, it is necessary to minimize heat exposure of the whey during pretreatment and processing. The presence of the caseinomacropeptide (CMP) in the WPC was found to be detrimental to gel strength and water-holding capacity. All of the commercial WPC that produced high-strength gels exhibited ionic compositions that were consistent with acidic processing to remove divalent cations with subsequent neutralization with sodium hydroxide. We have shown that ultrafiltration/diafiltration of cheese whey, adjusted to pH 2.5, through a membrane with a nominal molecular weight cut-off of 30,000 at 15 degrees C substantially reduced the level of CMP, lactose, and minerals in the whey with retention of the whey proteins. The resulting WPC formed from this process was suitable for the inclusion of sodium polyphosphate to produce superior functional properties in terms of gelation and water-holding capacity.     

热处理温度及蛋白浓度对乳清分离蛋白-黄油乳液体系的影响

稳定的乳清分离蛋白（WPI）-黄油乳液体系在乳制品加工及乳制品营养传递系统中有良好的应用前景。对不同质量分数（2%、4%、6%、8%）的WPI分别进行不同的热处理（未加热、80 ℃和90 ℃）,加入黄油并进行超声波处理,制备成乳液,对乳液体系粒径、絮凝指数（FI）、乳化活性（EA）、乳化稳定性（ES）、物理稳定性、储藏期粒径变化和脂肪上浮情况进行分析。结果表明：随着热处理温度的升高,乳液的平均粒径增大,未加热乳液平均粒径均小于1 μm,经加热处理后,不同蛋白质量分数乳液的粒径均有不同程度的增大;经过热处理,乳液的EA和ES均有所改善;随着蛋白质量分数的增大,乳液的物理稳定性提高,其中WPI质量分数为6%和8%时,90 ℃热处理样品的稳定性指数（TSI）均小于0.6,稳定性最好,同一蛋白质量分数下,热处理温度越高,蛋白对乳液的稳定作用越强;乳液储藏期脂肪上浮情况与热处理温度和蛋白质量分数显著相关,较高的蛋白质量分数及热处理温度能够改善乳液体系中脂肪上浮情况。研究表明,通过控制蛋白质量分数和WPI热处理温度可以有效提高WPI-黄油乳液体系的乳化特性及稳定性。     

Effect of protein content, casein–whey protein ratio and pH value on the foaming properties of skimmed milk

The average bubble diameter (ABD) and density of skimmed milk foam decreased with increasing protein content, up to 4%, while drainage was widely comparable. Samples with casein–whey protein ratios (C/W) of 94/6 and 7/93 showed smaller ABD than samples from mixtures with C/W ratios between 60/40 and 20/80. Foams prepared from samples with C/W of 20/80 exhibited the lowest drainage values after 10 min. Increasing pH from 6.4 to 7.0 led to increased overrun and ABD, while drainage was widely comparable, with a minimum value at pH 6.7. The protein composition of skimmed milk and foams prepared from this milk in relation to protein content, C/W ratio and pH value differed only slightly.     

Utilizing whey protein isolate and polysaccharide complexes to stabilize aerated dairy gels

Heated soluble complexes of whey protein isolate (WPI) with polysaccharides may be used to modify the properties of aerated dairy gels, which could be formulated into novel-textured high-protein desserts. The objective of this study was to determine the effect of polysaccharide charge density and concentration within a WPI-polysaccharide complex on the physical properties of aerated gels. Three polysaccharides having different degrees of charge density were chosen: low-methoxyl pectin, high-methoxyl type D pectin, and guar gum. Heated complexes were prepared by heating the mixed dispersions (8% protein, 0 to 1% polysaccharide) at pH 7. To form aerated gels, 2% glucono-δ-lactone was added to the dispersions of skim milk powder and heated complex and foam was generated by whipping with a handheld frother. The foam set into a gel as the glucono-δ-lactone acidified to a final pH of 4.5. The aerated gels were evaluated for overrun, drainage, gel strength, and viscoelastic properties. Without heated complexes, stable aerated gels could not be formed. Overrun of aerated gel decreased (up to 73%) as polysaccharide concentration increased from 0.105 to 0.315% due to increased viscosity, which limited air incorporation. A negative relationship was found between percent drainage and dispersion viscosity. However, plotting of drainage against dispersion viscosity separated by polysaccharide type revealed that drainage decreased most in samples with high-charge-density, low-methoxyl pectin followed by those with low-charge-density, high-methoxyl type D pectin. Aerated gels with guar gum (no charge) did not show improvement to stability. Rheological results showed no significant difference in gelation time among samples; therefore, stronger interactions between WPI and high-charge-density polysaccharide were likely responsible for increased stability. Stable dairy aerated gels can be created from WPI-polysaccharide complexes. High-charge-density polysaccharides, at concentrations that provide adequate viscosity, are needed to achieve stability while also maintaining dispersion overrun capabilities.     

浓缩乳清蛋白替代全蛋液对海绵蛋糕品质的影响

研究了以浓缩乳清蛋白替代全蛋液对海绵蛋糕品质的影响,分析了不同替代比例下海绵蛋糕的面糊比重、蛋糕比容、蛋糕硬度、弹性和咀嚼性的变化情况,并对蛋糕进行了感官评定。研究表明,在替代比例不超过50%时,得到面糊比重、蛋糕比容、充氮气密封包装保存60d后蛋糕的质构性能均接近采用全蛋液制作的蛋糕,感官评定结果表明,当替代比例为50%时蛋糕的品质最佳。由此可见,浓缩乳清蛋白部分替代全蛋液来制作海绵蛋糕是可行的。     

微波加热对牛乳清蛋白氧化的影响

本研究旨在探究普通加热和微波加热对牛乳清分离蛋白（WPI）氧化影响的差别。分别比较普通方式加热15、30、60和90min以及微波加热60、120、240和360s后WPI的羰基含量、巯基含量、二聚酪氨酸水平、表面疏水性、荧光光谱和SDS-PAGE电泳的变化。结果表明,与普通加热相比,较长时间（>120s）的微波加热会使WPI的羰基含量、二聚酪氨酸含量明显的增加,巯基含量明显下降,表面疏水性与荧光光谱结果显示长时间微波加热可能对WPI结构有明显修饰作用并改变其空间构象,SDS-PAGE结果显示长时间微波加热有明显的交联现象产生。      

热处理对Ca-乳清浓缩蛋白纳米纤维起泡性的影响

通过向乳清浓缩蛋白纳米纤维中添加一定量的氯化钙后热处理不同时间（0、1、2、3、4、5 h）,研究不同热处理时间对Ca-WPC纳米纤维聚合物起泡性的影响。结果表明Ca-WPC纳米纤维聚合物的起泡能力在热处理3 h时达最大值96.00%±0.02%,是对照组Ca-WPC常规聚合物热处理3 h时的2.13倍;Ca-WPC常规聚合物在不同热处理时间后其泡沫稳定性均为零,而Ca-WPC纳米纤维聚合物随着热处理时间延长其泡沫稳定性先增加后减小,热处理3 h时达到最大值为62.38%±1.51%,即热处理一定时间可以显著提高Ca-WPC纳米纤维聚合物的起泡性。      

High hydrostatic pressure modification of whey protein concentrate for improved functional properties

Whey protein concentrate (WPC) has many applications in the food industry. Previous research demonstrated that treatment of whey proteins with high hydrostatic pressure (HHP) can enhance solubility and foaming properties of whey proteins. The objective of this study was to use HHP to improve functional properties of fresh WPC, compared with functional properties of reconstituted commercial whey protein concentrate 35 (WPC 35) powder. Fluid whey was ultrafiltered to concentrate proteins and reconstituted to equivalent total solids (8.23%) as reconstituted commercial WPC 35 powder. Solutions of WPC were treated with 300 and 400 MPa (0- and 15-min holding time) and 600 MPa (0-min holding time) pressure. After HHP, the solubility of the WPC was determined at both pH 4.6 and 7.0 using UDY and BioRad protein assay methods. Overrun and foam stability were determined after protein dispersions were whipped for 15 min. The protein solubility was greater at pH 7.0 than at pH 4.6, but there were no significant differences at different HHP treatment conditions. The maintenance of protein solubility after HHP indicates that HHP-treated WPC might be appropriate for applications to food systems. Untreated WPC exhibited the smallest overrun percentage, whereas the largest percentage for overrun and foam stability was obtained for WPC treated at 300 MPa for 15 min. Additionally, HHP-WPC treated at 300 MPa for 15 min acquired larger overrun than commercial WPC 35. The HHP treatment of 300 MPa for 0 min did not improve foam stability of WPC. However, WPC treated at 300 or 400 MPa for 15 min and 600 MPa for 0 min exhibited significantly greater foam stability than commercial WPC 35. The HHP treatment was beneficial to enhance overrun and foam stability of WPC, showing promise for ice cream and whipping cream applications.     

Relationship between functional properties and aggregation changes of whey protein induced by high pressure microfluidization

Aggregation changes of whey protein induced by high-pressure microfluidization (HPM) treatment have been investigated in relation with their functional properties. Whey protein was treated with HPM under pressure from 40 to 160 MPa. Functional properties (solubility, foaming, and emulsifying properties) of whey protein concentrate (WPC) ultrafiltered from fluid whey were evaluated. The results showed significant modifications in the solubility (30% to 59%) and foaming properties (20% to 65%) of WPC with increasing pressure. However, emulsifying property of WPC treated at different pressures was significantly worse than untreated sample. To better understand the mechanism of the modification by HPM, the HPM-induced aggregation changes were examined using particle size distribution, scanning electron microscopy, and hydrophobicity. It was indicated that HPM induced 2 kinds of aggregation changes on WPC: deaggregation and reaggregation of WPC, which resulted in the changes of functional properties of WPC modified by HPM.     

乳清浓缩蛋白对搅拌型酸奶品质特性影响的研究

研究了以全脂奶粉和乳清浓缩蛋白（WPC-3503）为原料，按照全脂奶粉：乳清浓缩蛋白为100：0，90：10，80：20，70：30的质量配比生产乳固形物含量为12％的酸奶，对含有不同乳清蛋白比例的酸奶在贮藏过程中理化特性、乳酸菌总数的变化以及感官特性进行了比较分析。结果表明，WPC-3503代替10％-20％全脂奶粉生产酸奶时，在贮藏过程中可减缓pH值及酸度的变化速度，提高酸奶的黏度和保水率，改善感官特性，但对乳酸菌总数无明显的影响。     

Astringency of bovine milk whey protein

Whey protein solutions at pH 3.5 elicited an astringent taste sensation. The astringency of whey protein isolate (WPI), the process whey protein (PWP) that was prepared by heating WPI at pH 7.0, and the process whey protein prepared at pH 3.5 (aPWP) were adjusted to pH 3.5 and evaluated by 2 sensory analyses (the threshold method and the scalar scoring method) and an instrumental analysis (taste sensor method). The taste-stimulating effects of bovine and porcine gelatin were also evaluated. The threshold value of astringency of WPI, PWP, and aPWP was 1.5, 1.0, and 0.7 mg/mL, respectively, whereas the gelatins did not give definite astringency. It was confirmed by the scalar scoring method that the astringency of these proteins increased with the increase in protein concentration, and these proteins elicited strong astringency at 10 mg/mL under acidic conditions. On the other hand, the astringency was not elicited at pH 3.5 by 2 types of gelatin. A taste sensor gave specific values for whey proteins at pH 3.5, which corresponded well to those obtained by the sensory analysis. Elicitation of astringency induced by whey protein under acidic conditions would be caused by aggregation and precipitation of protein molecules in the mouth.     

乳清蛋白-甘油二酯纳米乳液制备及其质量评价的研究

采用高压均质法制备乳清蛋白-甘油二酯纳米乳液,以粒径和包埋率为综合指标,在单因素实验的基础上,采用响应面分析法优化纳米乳液的制备条件,并对纳米乳液的表面性质、表征、温度、氧化及贮藏稳定性进行研究。结果表明,乳清蛋白-甘油二酯纳米乳液的最佳工艺条件为:壁材浓度15.83%,壁芯比3.35∶1,乳化剂添加量4.02%,此时,纳米乳液的包埋率最高,为75.5%。纳米乳液带负电,分布均匀,平均粒径在142 nm左右,有明显的壳核结构,包被效果较好。纳米乳液在80℃以下具有较好的稳定性,且能有效延缓甘油二酯的氧化,最佳贮藏温度为4℃。     

超微粉碎与超声波组合辅助胃蛋白酶水解乳清蛋白效果研究

本文将超微粉碎技术和超声波技术组合应用于胃蛋白酶水解乳清蛋白效果的研究。目的在于探讨两种技术的联合作用下,胃蛋白酶水解乳清蛋白的效果和规律。在单因素实验的基础上,选取了超微粉碎目数、超声波处理功率、超声波处理时间为影响因子,以水解后可溶性蛋白含量为响应面值,应用响应面设计方法建立数学模型,进行响应面分析。结果表明,获得最佳水解效果的实验因素组合为:超微粉碎目数2000目,超声波处理功率250 W,超声波处理时间50 min。各实验因素对可溶性蛋白含量影响由大到小依次为:超声波处理功率>超声波处理时间>超微粉碎目数。经过最佳实验因素组合处理获得的可溶性蛋白含量为6.03 mg/m L,为未采用组合处理样品可溶性蛋白含量的1.39倍。      

高酰基结冷胶对乳清分离蛋白热诱导凝胶特性的影响

蛋白质-多糖凝胶具有良好的稳定性和机械强度,在稳定和传递生物活性物质、营养强化剂方面的应用前景广阔。该研究以乳清分离蛋白、高酰基结冷胶为原料制备热诱导混合凝胶,分析高酰基结冷胶对乳清分离蛋白-高酰基结冷胶混合凝胶的凝胶强度、保水性及显微结构等,揭示乳清蛋白-高酰基结冷胶凝胶形成机理。结果表明,高酰基结冷胶促使蛋白质巯基暴露从而使凝胶形成稳定结构,提高混合凝胶的凝胶强度和保水性,且随着高酰基结冷胶含量增加而显著增大,其质量浓度为4 g/L时,复合凝胶的凝胶强度最大,为26.97 g;保水性最好,为97.41%;透光率最低,为1.87%。温度扫描结果表明,增加高酰基结冷胶可以提高乳清分离蛋白的相转变温度,傅里叶红外光谱显示,乳清分离蛋白与高酰基结冷胶存在分子间作用力,扫描电子显微镜表明高酰基结冷胶诱导混合凝胶形成结构紧密的三维网络结构。该研究为拓展乳清分离蛋白和结冷胶的新型凝胶食品,提高传统食品的质量,改善食品的加工工艺提供基础理论数据。     

Efficiency of removal of whey protein from sweet whey using polymeric microfiltration membranes

Our objective was to measure whey protein removal percentage from separated sweet whey using spiral-wound (SW) polymeric microfiltration (MF) membranes using a 3-stage, 3× process at 50°C and to compare the performance of polymeric membranes with ceramic membranes. Pasteurized, separated Cheddar cheese whey (1,080 kg) was microfiltered using a polymeric 0.3-μm polyvinylidene (PVDF) fluoride SW membrane and a 3×, 3-stage MF process. Cheese making and whey processing were replicated 3 times. There was no detectable level of lactoferrin and no intact α- or β-casein detected in the MF permeate from the 0.3-μm SW PVDF membranes used in this study. We found BSA and IgG in both the retentate and permeate. The β-lactoglobulin (β-LG) and α-lactalbumin (α-LA) partitioned between retentate and permeate, but β-LG passage through the membrane was retarded more than α-LA because the ratio of β-LG to α-LA was higher in the MF retentate than either in the sweet whey feed or the MF permeate. About 69% of the crude protein present in the pasteurized separated sweet whey was removed using a 3×, 3-stage, 0.3-μm SW PVDF MF process at 50°C compared with 0.1-μm ceramic graded permeability MF that removed about 85% of crude protein from sweet whey. The polymeric SW membranes used in this study achieve approximately 20% lower yield of whey protein isolate (WPI) and a 50% higher yield of whey protein phospholipid concentrate (WPPC) under the same MF processing conditions as ceramic MF membranes used in the comparison study. Total gross revenue from the sale of WPI plus WPPC produced with polymeric versus ceramic membranes is influenced by both the absolute market price for each product and the ratio of market price of these 2 products. The combination of the market price of WPPC versus WPI and the influence of difference in yield of WPPC and WPI produced with polymeric versus ceramic membranes yielded a price ratio of WPPC versus WPI of 0.556 as the cross over point that determined which membrane type achieves higher total gross revenue return from production of these 2 products from separated sweet whey. A complete economic engineering study comparison of the WPI and WPPC manufacturing costs for polymeric versus ceramic MF membranes is needed to determine the effect of membrane material selection on long-term processing costs, which will affect net revenue and profit when the same quantity of sweet whey is processed under various market price conditions.