脱钙程度对浓缩乳蛋白功能性质的影响

采用离子交换树脂对脱脂乳的超滤截留液进行脱钙预处理,制备了脱钙率为0%、11%、19%、27%和37%的浓缩乳蛋白(milk protein concentrate,MPC),并探讨了脱钙程度对MPC溶解液的起泡性、乳化性和胶凝性的影响。MPC溶解液的起泡性和起泡稳定性、以及乳化性和乳化稳定性都随着脱钙程度的增加而逐渐提高。通过对脱钙MPC凝胶流变学性质、质构特性、持水力和微观结构的变化测定,发现MPC的凝胶特性随脱钙程度的增加而逐渐降低,但在脱钙MPC的溶解液中回补钙至未脱钙MPC的含量时,其凝胶特性得到了显著的回复;其中11%脱钙率的MPC凝胶特性基本完全回复到了脱钙之前的水平。研究结果表明,离子交换脱钙技术可作为一种潜在的手段来调控和拓展MPC的功能性质。     

浓缩乳蛋白的离子交换脱钙及其对酪蛋白胶束的影响

研究了浓缩乳蛋白的离子脱钙技术,以及部分脱钙对截留液中酪蛋白存在形式及酪蛋白胶束水合率的影响。研究确定了离子交换树脂的平衡脱钙时间为2 h,并通过改变树脂添加量得到了0、5%.5%、10.5%、19.6%、29.6%、38.7%、49.9%、63.8%和83.6%系列脱钙程度的截留液。随着脱钙程度的增加,截留液超离心上清中游离酪蛋白的含量逐渐增加,而超离心沉淀的胶束酪蛋白减少,说明酪蛋白逐渐从酪蛋白胶束中游离出来。当脱钙程度为0~29.6%时,酪蛋白胶束的水合率从2.6 g/g(干基)增加到4.1 g/g(干基),而脱钙程度从29.6%进一步增加到83.6%时,酪蛋白胶束水合率则变小至3.3 g/g(干基)。浓缩乳蛋白的钙离子含量以及酪蛋白的存在状态决定了其在应用时的功能特性,研究对开发新型的浓缩乳蛋白配料具有重要的指导意义。     

浓缩乳蛋白的脱钙处理对高蛋白营养棒质构的影响

以一系列脱钙梯度的浓缩乳蛋白(milk protein concentrate,MPC)为原料制备高蛋白营养棒(highprotein nutrition bar,HPNB)模型体系,采用低场核磁和全质构分析等探究了MPC的脱钙处理对HPNB中小分子迁移和质构的影响。随脱钙率升高,HPNB中小分子迁移达到平衡所需时间变短,体系中蛋白颗粒更易与小分子相融合,得到的体系更均一稳定,当脱钙率 28. 3%时,体系中小分子分布差异较小,体系均为均一稳定相。脱钙使得体系硬度和内聚性均增大,不易发生碎裂,脱钙率为28. 3%时,体系硬度适中,内聚性显著提高,满足储藏要求,同时也可保留MPC中的大部分的钙成分;而脱钙率 28. 3%时,体系硬度过大,钙成分少,不易被消费者接受,这一研究结果有利于拓宽浓缩乳蛋白配料在高蛋白营养棒领域的应用。     

脂对浓缩乳蛋白溶解稳定性的影响

以浓缩乳蛋白(MPC)为研究对象,通过向MPC中加入不同熔点的乳脂模拟物来制备含脂浓缩乳蛋白模型体系,旨在研究脂对储藏过程中MPC溶解稳定性的影响。分别考察了模型含脂乳粉在45℃(相对湿度23%)和35℃(相对湿度11%)下分别储藏30 d和60 d后的溶解度变化,通过讨论储藏过程中脂质氧化、蛋白氧化、蛋白不溶物的形成等对MPC溶解度下降的分子机制进行了探索。研究结果表明,虽然不同熔点的脂在储藏初期时对MPC溶解度的下降具有一定的影响,但是脂质氧化和蛋白氧化都不是MPC在储藏过程中溶解度下降的关键因素,经由氢键、二硫键和疏水相互作用所形成的酪蛋白不溶物才是影响MPC溶解度的主要原因。     

超滤在生产浓缩乳蛋白类产品中的应用

超滤技术是一种先进的膜分离技术,其作为一种分离和浓缩的工具已经被广泛应用于乳品工业。本文对超滤技术进行了概述,综述了其在生产乳蛋白浓缩物及浓缩乳清蛋白产品中的研究及应用现状,同时对如何通过超滤过程中条件的选择以提高膜过滤性能进行了阐述,并且对该领域的未来发展趋势做了展望。     

浓缩牛乳蛋白水溶性下降机制

蛋白质是牛乳中重要的营养成分之一,因此浓缩牛乳蛋白(MPC)在食品工业中有着良好的应用前景。但当储藏一段时间后,MPC会表现出水溶性下降的现象,而水溶性是衡量蛋白质食品加工属性的重要指标,因此如何提高MPC的水溶性成为了研究的重点。文章就目前的研究现状,从机制的角度阐述了MPC水溶性下降的原因。     

乳蛋白肽饮料微生物脱苦研究

以乳蛋白肽饮料为原料,通过苦味值、短肽得率（TCA-SNI）、总蛋白酶活三个指标筛选得到苦味值小、总蛋白酶活力高、TCA-SNI值高的复合菌种。结果表明,脱苦效果方面,复合菌种>酿酒酵母>乳酸菌,复合菌种接种量为1%、发酵培养7h,总蛋白酶活最高,达到32U/mL,TCA-SNI达到峰值34.5%,溶液苦味值为0.5。      

木瓜蛋白酶水解大豆浓缩蛋白及糖基化修饰对水解产物溶解性的影响

为提高大豆浓缩蛋白(soy protein concentrate,SPC)在等电点处的溶解性,采用木瓜蛋白酶对大豆浓缩蛋白进行酶解,形成可溶性大豆蛋白,然后将其与葡聚糖进行糖基化反应,形成亲水的蛋白质-多糖复合物。结果表明:大豆浓缩蛋白酶解最佳条件为大豆蛋白与水质量配比5:100、酶添加量10000U/g、反应温度55～60℃;糖基化最佳条件为葡聚糖与蛋白配比1:1、反应时间3.5h;大豆浓缩蛋白在等电点附近(pH4)的氮溶指数由原来的9.53%提高到39.12%。本实验制备的等电点可溶大豆蛋白,可增加其在中等酸度食品中的应用。     

饮料中钙的溶解性研究

以纯柠檬酸溶液为体系研究了钙在其中的溶解性,研究结果表明在不超过国家规定的钙的添加量范围内,一般不同出现柠檬酸饮料钙盐沉淀问题,柠檬酸的最大许可深度为０．０８７ｍｇ／ｇ。     

浓缩工艺和MPC质量浓度对其乳化特性的影响

研究了蒸发浓缩乳蛋白浓缩物(EP-MPC)和纳滤浓缩乳蛋白浓缩物(NF-MPC)的乳化性能,并比较了MPC的质量浓度对两种乳蛋白浓缩物乳化能力和乳化稳定性的影响。结果表明,两种MPC均可以在质量浓度为60g/L时形成良好乳浊液,此时它们的乳化能力没有显著性差别。但无论是刚形成的乳浊液还是贮藏一段时间后,NF-MPC稳定的乳浊液的稳定性明显高于EP-MPC。同时EP-MPC对浓度的变化较为敏感,低于或高于最适浓度都会导致乳化液滴粒径大幅度增加,且乳化液更加不稳定。     

Correlations between the solubility and surface characteristics of milk protein concentrate powder particles

The solubility of high-protein milk protein concentrate (MPC) may decrease significantly during storage, particularly at relatively high temperatures and humidity. The objective of this study was to seek correlations between the solubility loss of MPC during storage and various surface characteristics determined on the basis of simultaneous nanoscale topographical imaging and nanomechanical mapping of MPC particle surfaces using atomic force microscopy. A control MPC and a calcium-depleted MPC were stored at 45°C and 66% relative humidity for up to 60 d. The solubility of the control MPC was 56% at the beginning of the storage and gradually decreased to 10% at the end of the 60-d storage. The calcium-depleted MPC exhibited more rapid decreases from almost 100% at the beginning of the storage to 18% after storage for 45 d, after which we observed no significant difference in solubility between the control and calcium-depleted MPC. Averaged or root mean squared roughness values calculated using topographical images were found to have no correlation with the solubility. Deformation, Derjaguin-Muller-Toropov modulus, and adhesion images revealed the presence of individual casein micelles and larger clusters of aggregated casein micelles at MPC particle surfaces, whereas we observed no correlation between the solubility and averaged values of these nanomechanical properties. Furthermore, Derjaguin-Muller-Toropov modulus and adhesion images showed that the peripheral edges of individual casein micelles and their clusters had significantly higher values of the corresponding nanomechanical properties than other regions in the images, indicating the occurrence of the fusion of casein micelles. The surface area coverage or the percent area of the fused regions in an image revealed significant negative linear correlations with the solubility for both the control and calcium-depleted MPC. The present results support the hypothesis that the fusion of casein micelles at MPC powder particle surfaces is a causative factor for the solubility loss of MPC during storage and in turn suggest that the solubility loss may be alleviated by inhibiting the formation of a crust or skin on powder particle surfaces.     

Effect of processing methods and protein content of the concentrate on the properties of milk protein concentrate with 80% protein

In recent years, a large increase in the production of milk protein concentrates (MPC) has occurred. However, compared with other types of milk powders, few studies exist on the effect of key processing parameters on powder properties. In particular, it is important to understand if key processing parameters contribute to the poor solubility observed during storage of high-protein MPC powders. Ultrafiltration (UF) and diafiltration (DF) are processing steps needed to reduce the lactose content of concentrates in the preparation of MPC with a protein content of 80% (MPC80). Evaporation is sometimes used to increase the TS content of concentrates before spray drying, and some indications exist that inclusion of this processing step may affect protein properties. In this study, MPC80 powders were manufactured by 2 types of concentration methods: membrane filtration with and without the inclusion of an evaporation step. Different concentration methods could affect the mineral content of MPC powders, as soluble salts can permeate the UF membrane, whereas no mineral loss occurs during evaporation, although a shift in calcium equilibrium toward insoluble forms may occur at high protein concentration levels. It is more desirable from an energy efficiency perspective to use higher total solids in concentrates before drying, but concerns exist about whether a higher protein content would negatively affect powder functionality. Thus, MPC80 powders were also manufactured from concentrates that had 3 different final protein concentrations (19, 21, and 23%; made from 1 UF retentate using batch recirculation evaporation, a similar concentration method). After manufacture, powders were stored for 6 mo at 30°C to help understand changes in MPC80 properties that might occur during shelf-life. Solubility and foaming properties were determined at various time points during high-temperature powder storage. Inclusion of an evaporation step, as a concentration method, resulted in MPC80 that had higher ash, total calcium, and bound calcium (of rehydrated powder) contents compared to concentration with only membrane filtration. Concentration method did not significantly affect the bulk (tapped) density, solubility, or foaming properties of the MPC powders. Powder produced from concentrate with 23% protein content exhibited a higher bulk density and powder particle size than powder produced from concentrate that had 19% protein. The solubility of MPC80 powder was not influenced by the protein content of the concentrate. The solubility of all powders significantly decreased during storage at 30°C. Higher protein concentrations in concentrates resulted in rehydrated powders that had higher viscosities (even when tested at a constant protein concentration). The protein content of the concentrate did not significantly affect foaming properties. Significant changes in the mineral content are used commercially to improve MPC80 solubility. However, although the concentration method did produce a small change in the total calcium content of experimental MPC80 samples, this modification was not sufficiently large enough (<7%) to influence powder solubility.     

Kinetics of enthalpy relaxation of milk protein concentrate powder upon ageing and its effect on solubility

Kinetics of enthalpy relaxation of milk protein concentrate (MPC) powder upon short-term (up to 67 h) storage at 25 °C and a_w 0.85, and long-term (up to 48 days) storage at 25 °C and a range of a_w values (0–0.85) were studied by differential scanning calorimetry (DSC). The short-term study showed a rapid recovery of enthalpy for the first 48 h, followed by a slower steady increase with time. The non-exponential β parameter was calculated using the Kohlrausch–Williams–Watts function and found to be 0.39. Long-term storage showed that enthalpy relaxation depends on both storage period and water activity. The enthalpy value was much less for lower moisture content (mc) (a_w ? 0.23, mc ? 5.5%) than for higher mc (a_w ? 0.45, mc ? 8%) samples for a particular storage period. The results suggest that the presence of more water molecules, in close proximity to the protein surface facilitates kinetic unfreezing and subsequent motion of molecular segments of protein molecules towards thermodynamic equilibrium. Although de-ageing of stored samples did not reverse storage-induced solubility losses, the timescale of enthalpy relaxation was similar to that of solubility loss. It is suggested that enthalpy relaxation within stored samples allows structural rearrangements that are responsible for subsequent solubility decreases.     

Effect of NaCl addition during diafiltration on the solubility, hydrophobicity, and disulfide bonds of 80% milk protein concentrate powder

We investigated the surface hydrophobicity index based on different fluorescence probes [1-anilinonaphthalene-8-sulfonic acid (ANS) and 6-propionyl-2-(N,N-dimethylamino)-naphthalene (PRODAN)], free sulfhydryl and disulfide bond contents, and particle size of 80% milk protein concentrate (MPC80) powders prepared by adding various amounts of NaCl (0, 50, 100, and 150 mM) during the diafiltration process. The solubility of MPC80 powder was not strictly related to surface hydrophobicity. The MPC80 powder obtained by addition of 150 mM NaCl during diafiltration had the highest solubility but also the highest ANS-based surface hydrophobicity, the lowest PRODAN-based surface hydrophobicity, and the least aggregate formation. Intermolecular disulfide bonds caused by sulfhydryl-disulfide interchange reactions and hydrophobic interactions may be responsible for the lower solubility of the control MPC80 powder. The enhanced solubility of MPC80 powder with addition of NaCl during diafiltration may result from the modified surface hydrophobicity, the reduced intermolecular disulfide bonds, and the associated decrease in mean particle size. Addition of NaCl during the diafiltration process can modify the strength of hydrophobic interactions and sulfhydryl-disulfide interchange reactions and thereby affect protein aggregation and the solubility of MPC powders.     

Effect of denatured whey protein concentrate and its fractions on rennet-induced milk gels

Denatured whey protein concentrate was fractionated by centrifugation to study the effect of its different components (sedimentable aggregates, non-sedimentable component, and diffusible component) on rennet-induced coagulation of milk and gel contraction capacity. Milk coagulation properties were characterized by optical density measurement and dynamic rheometry. The contraction kinetics of the gel during cooking was also characterized. The diffusible component of denatured whey protein concentrate showed no significant effect on coagulation or contraction parameters. Sedimentable aggregates negatively influenced the kinetics of rennet gel formation, as measured by rheology; these aggregates also reduced the contraction capacity of the gel. The non-sedimentable component negatively influenced milk coagulation properties, as measured with both optical and rheological methods, and decreased the contraction capacity of the gel. The results suggest that, beyond the effect of sedimentable whey protein aggregates, soluble proteinaceous complexes (non-sedimentable and non-diffusible) could interact with renneted casein micelles and limit gel formation and contraction.     

High-pressure structuring of milk protein concentrate: Effect of pH and calcium

In this study, we investigated the effect of pH and calcium on the structural properties of gels created by high-pressure processing (HPP, 600 MPa, 5°C, 3 min) of milk protein concentrate (MPC, 12.5% protein). The pH level of the MPC was varied between 6.6 and 5.1 by adding glucono-δ-lactone (GDL), and the calcium content was varied from 24 to 36 mg of Ca/g of protein by adding calcium chloride. The rheological properties and microstructure of the pressure-treated MPC were assessed. The pressurization treatments and analytical testing were conducted in triplicate. Data were analyzed statistically using one-way ANOVA with Tukey's honestly significant difference post hoc tests. A pressurization time of 3 min was sufficient to induce gel formation in MPC at pH 6.6, so it was used throughout the study. Adjusting either pH or calcium affected the structure of the HPP-created milk protein gels, likely by influencing electrostatic interactions and shifting the calcium–phosphate balance. Gels were formed after pressurization of MPC at pH above 5.3, and increasing the pH from 5.3 to 6.6 resulted in stronger gels with higher values of elastic moduli (G′). At neutral pH (6.6), adding calcium to MPC further increased G′. Scanning electron microscopy showed that reducing pH or adding calcium resulted in more porous, aggregated microstructures. These findings demonstrate the potential of HPP to create a variety of structures using MPC, facilitating a new pathway from dairy protein ingredients to novel, gel-based, high-protein foods, such as puddings or on-the-go protein bars.     

On quantifying the dissolution behaviour of milk protein concentrate

Milk protein concentrate (MPC) is a newly developed dairy powder with wide range of applications as ingredients in the food industry, such as cheese, yogurt, and beverage. MPC has relatively poor solubility as a result of their high protein content (40–90 wt%), with distinct dissolution behaviour in comparison to skim milk or whole milk powders. Here, a focused beam reflectance measurement (FBRM) was used to monitor the dissolution process of an MPC powder, with the data used to develop a kinetic dissolution model based on the Noyes–Whitney equation. The model was used to estimate the dissolution rate constant k and the final particle size in suspension d_∞, describing dynamic dissolution behaviours and final solubility respectively of a particular powder. In this work, the effects of dissolution temperature, storage duration and storage temperature on dissolution properties of an MPC powder were also investigated. A quantitative understanding of relationship between process and storage conditions with powder functionality could be achieved from k and d_∞ profiles. This approach can potentially be applied to predict the dissolution behaviour of specific dairy powders in a more robust manner than conventional solubility tests.     

Short communication: Effect of pH on the heat stability of reconstituted reduced calcium milk protein concentrate dispersions

This study aimed to investigate the heat stability of dispersions from reconstituted reduced-calcium milk protein concentrate (RCMPC) with 80% protein or more. The tested RCMPC powders were produced from skim milk subjected to CO₂ treatment before and during the process of ultrafiltration. The CO₂ injection was controlled to obtain 0 (control, no CO₂ injection), 20, 30, and 40% reduction in calcium levels in the RCMPC powders. The RCMPC powders were reconstituted to 10% (wt/wt) protein in deionized water. These dispersions were tested for heat stability in a rocking oil bath at 140°C at unadjusted, 6.5, 6.7, 6.9, and 7.1 pH. Calcium ion activity (CIA) and ionic strength measurements were carried out using a Ca ion-selective electrode and conductivity meter. Unadjusted pH of the dispersions varied from 6.8 in control to 5.96 in 40% RCMPC dispersions. The CIA of unadjusted dispersions ranged from 1.31 mM in control to 2.83 mM in 40% RCMPC. Heat stability, expressed as heat coagulation time (HCT) of unadjusted dispersions decreased as the level of Ca removal in powders increased (from 13.81 min in control to 0.46 min in 40% RCMPC) and was negatively correlated with the CIA of the dispersions. For control RCMPC dispersions, the minimum and maximum heat stability were observed at dispersion pH of 6.5 and 6.9, respectively, followed by a decrease at pH 7.1 (CIA was the lowest). Dispersions from 40% RCMPC and pH 7.1 had the maximum HCT of 30.94 min among all RCMPC dispersions at all pH values. From this study, it can be concluded that improved heat stability in high protein formulation beverages subjected to UHT processing could be achieved through calcium reduction in milk protein concentrates using CO₂ injection.     

不同预处理方式对豆浆品质特性的影响

选择大豆4种不同预处理方式,探讨其对豆浆品质特性的影响。对所制得豆浆的蛋白质含量、稳定性、色泽、感官品质、粒径分布进行对比分析,同时采用电镜扫描分析不同预处理方式下大豆微观形态的变化。结果表明:超声波预处理后豆浆蛋白质含量达到最大值为4.026 6%,大豆细胞结构更加紧密,但其稳定性、感官品质均差于冷冻处理制浆;微波预处理对大豆结构破坏程度最大,所制得的豆浆蛋白质损失严重,仅为3.241 4%,其感官品质、稳定性均差于冷冻处理制浆,且色泽偏暗;经过冷冻预处理的豆浆白度增加为75.12,蛋白质含量、稳定性较高,且感官评分最高,综合品质最好。     

Effect of manufacture and reconstitution of milk protein concentrate powder on the size and rennet gelation behaviour of casein micelles

Samples of raw skim milk, ultrafiltration/diafiltration retentate, concentrated retentate and milk protein concentrate powder (MPC80) from a single commercial production run were analysed using photon correlation spectroscopy. Measurements revealed insignificant differences in casein micelle size between the samples. In addition, there was no discernable difference between raw skim milk and MPC powder dissolved at 60 °C in the amount of casein remaining in supernatants from centrifugation at either 25,000 × g or 174,200 × g. Casein micelles did not appear to be altered during manufacture of MPC. The rennet gelation behaviour of reconstituted MPC was compared with raw skim milk. Reconstituted MPC did not coagulate unless supplemented with approximately 2 mm calcium chloride, which was attributed to the mineral removal during ultrafiltration/diafiltration. Addition of sufficient calcium could restore rennet coagulation kinetics and gel strength of reconstituted MPC to approximately that of raw skim milk.