乳清中酪蛋白糖巨肽的分离纯化

以酶凝干酪乳清为原料,通过沉淀、透析、超滤和离子交换层析等操作,分离提取酪蛋白糖巨肽,通过单因素分析和正交实验,优化出最佳提取工艺条件,同时采用SDS-聚丙烯酰胺凝胶电泳进行分析.结果表明:硫酸铵沉淀乳清中杂蛋白终饱和度为20%;超滤法纯化最佳工艺条件为温庹45℃,压力0.2 MPa,时间30 min;D201GF离子交换层析处理后制得的酪蛋白糖巨肽的纯度为83.97%;SDS-聚丙烯酰胺凝胶电泳结果显示,酪蛋白糖巨肽的相对分子量在15 ku左右.     

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.     

Viscoelastic properties of caseinmacropeptide isolated from cow,ewe and goat cheese whey

Caseinmacropeptide (CMP) is a C‐terminal glycopeptide released from κ‐casein by the action of chymosin during cheese‐making. It is recognised as a bioactive peptide and is thought to be an ingredient with a potential use in functional foods. CMP occurs in sweet cheese whey and whey protein concentrate (WPC). Its composition is variable and depends on the particular whey source and the fractionation technology employed in the isolation. There were no significant (P < 0.05) differences in the relative apparent viscosities between species of CMPs (cow, ewe and goat). Analyses at different pH (2, 4, 7, 10), ionic strength (0, 0.2, 0.4 and 0.7 as NaCl molarity) and protein concentration (50, 100 and 200 g kg^?1) at temperatures from 10 to 90 °C carried out found pH 7 and high protein concentration (200 g kg^?1) conditions to be the best for CMP solutions to keep low and constant relative viscosity values with increasing temperature up to 75 °C. The viscoelastic properties–storage modulus, loss modulus and phase angle–of the different CMPs and WPC solutions were determined. Heat‐induced rheological changes in CMP solutions occurred at moderate temperatures (40–50 °C) with no appreciable differences in viscosity. Gelation took place significantly (P < 0.05) earlier in goat CMP (41 °C), followed by cow CMP (44 °C), ewe CMP (47 °C) and WPC (56 °C). Heating at 90 °C showed that WPC required significantly (P < 0.05) longer times to form gels (>5 min) than the CMPs (<5 min). WPC gels had higher (>20°) phase angle than CMP (<20°), which could be associated with untidy structures, limiting elastic properties of the gel. Copyright © 2006 Society of Chemical Industry     

Survey of salty and sweet whey composition from various cheese plants in Wisconsin

Salty whey is currently underutilized in the dairy industry because of its high salt content and increased processing and disposal costs. Salty whey accounts for 2 to 5% of the total whey generated during Cheddar and other dry-salted cheese manufacture. Because relatively little information is available on salty whey, this study was conducted to determine the range of compositional components in salty whey from commercial cheese plants. Gross compositional differences in percent protein, salt, solids, and fat between sweet whey and salty whey from various dry-salted cheeses from 8 commercial plants were determined. Differences between individual whey protein compositions were determined using sodium dodecyl sulfate-PAGE. Average total solids, fat, and salt content were significantly greater in the salty whey compared with the corresponding sweet whey. True protein was reduced in salty whey although great variability existed among samples. Individual whey proteins identified included lactoferrin (Lf), BSA, immunoglobulin G, β-lactoglobulin, and α-lactalbumin. Salty whey showed an increase in Lf content and a decrease in α-lactalbumin and β-lactoglobulin content when compared with sweet whey. Salty whey may be a source of Lf, potentially increasing its value to whey processors. However, the compositional assessments showed that commercial salty whey is a highly variable waste stream.     

Whey Protein Isolate and Glyco-macropeptide Recovery from Whey Using Ion Exchange Chromatography

ABSTRACT: Cation exchange was used to recover whey protein isolate (WPI) from sweet whey, and the effluent was fed to an anion exchanger to recover glycomacropeptide (GMP). Nearly all of the major whey proteins (α-lactalbu-min, β-lactoglobulin, immunoglobulin G, and serum albumin) and about half of the total Kjeldahl nitrogen (TKN) were recovered by the cation exchanger. No GMP was recovered by the cation exchanger. The anion exchanger recovered nearly all of the GMP from the effluent of the cation exchanger, accounting for about half of the remaining TKN. This process is the first to simultaneously manufacture WPI and GMP from a single stream of whey, increasing the value obtained from whey.     

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.     

Incorporated glucosamine adversely affects the emulsifying properties of whey protein isolate polymerized by transglutaminase

Glucosamine (GlcN) and microbial transglutaminase (Tgase) are used separately or together to improve the emulsifying properties of whey protein isolate (WPI). However, little is known about how the emulsifying properties change when GlcN residues are incorporated into WPI cross-linked by Tgase. We used Tgase as a biocatalyst to cross-link WPI in the presence of GlcN in a liquid system for 12 h at a moderate temperature (25°C). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analyses indicated that protein polymerization and GlcN conjugation occurred simultaneously, phenomena also supported by the loss of free amines (9.4–20.5%). Addition of 5 U Tgase/g protein improved the emulsifying properties of moderately cross-linked WPI polymers. The Tgase-treated WPI polymers had a larger particle size (～2.6-fold) than native WPI, which may have reduced coalescence and flocculation in an oil-in-water emulsion system. However, the incorporation of GlcN residues into WPI, predominantly via enzymatic glycation, partly inhibited the cross-links between the WPI molecules catalyzed by Tgase, reducing the size of the WPI polymers 0.81- to 0.86-fold). Consequently, WPI+GlcN conjugates provided less stability to the emulsion. Moreover, high NaCl concentration (0.2 M) decreased the emulsifying properties of the WPI+GlcN conjugates by neutralizing negative electric charges in the glycoconjugates. However, the improved emulsifying properties of WPI cross-linked by Tgase may be useful in food processing at higher NaCl concentrations due to the formation of the thicker steric barrier at the oil-water interface.     

Production of low antigenic cheese whey protein hydrolysates using mixed proteolytic enzymes

This study examined the effect of different proteolytic enzymes on the production of cheese whey protein (CWP) hydrolysates with low antigenicity. Four enzyme combinations (1:1) trypsin + papain W‐40 (TP), trypsin + neutrase 1.5 (TN), papain W‐40 + protease S (PP) and papain W‐40 + neutrase 1.5 (PN) were added at the rate of 1% of the CWP and it was incubated for 15, 30, 60, 90, 120 and 180 min at 50 °C. CWP hydrolysis and its non‐protein nitrogen concentrations were higher with TP and TN compared with PP and PN at all incubation times. The SDS‐PAGE revealed complete removal of α‐lactalbumin (α‐LA) and β‐lactoglobulin (β‐LG) from hydrolysates produced by trypsin‐containing enzyme mixtures. Reverse‐phase HPLC analysis ascertained the CWP hydrolysis and SDS‐PAGE results. The lowest antigenicity in CWP hydrolysates was observed with the use of trypsin‐containing enzyme mixtures compared with other enzyme combinations. Present results suggested that TP and TN combinations were the most effective for CWP hydrolysis for the removal of β‐LG from CWP. Further research is warranted to identify the peptides in CWP hydrolysates produced with these enzyme combinations that may help enhance the utilisation of whey protein in human food. Copyright © 2007 Society of Chemical Industry     

Low‐fat Cheddar cheese made using microparticulated whey proteins: Effect on yield and cheese quality

Influence of different levels (0, 0.15, 0.35 or 0.50%) of microparticulated whey protein (MWP) on yield and quality of low‐fat (~7.3 g/100 g) Cheddar cheese was investigated. MWP improved cheese yield due to the water‐binding ability of denatured whey protein. MWP addition decreased meltability but improved the textural properties beneficial for shredding and slicing, by decreasing sensory firmness. The results emphasise the role of MWP as an inert filler within cheese matrix, in improving cheese yield and creating a softer texture without compromising the sensory or overall quality of cheese, even with moisture increases in 0.35 or 0.50% MWP cheeses.     

Technical note: Direct enzyme immunoassay of progesterone in bovine milk whey

A simple extraction-free or direct quantitative ELISA for progesterone in bovine milk whey was developed. Whey samples are easy to collect, transport, and store. This method also allows for monitoring progesterone levels in cattle, which is important in reproductive management. The assay was designed to cover the concentration range 0.05 to 2 ng/mL, and the sensitivity of the method was 1.5 pg/mL. The intra- and interassay coefficients of variation were 8 and 12%, respectively. A high correlation (r = 0.90) between ELISA and radioimmunoassay measurements of progesterone in the same milk whey samples was obtained. The method can be easily applied in practice because samples can be stored at room temperature (22 to 26°C) for 4 d. Moreover, because analysis requires milk coagulation, that process can be initiated during transport by standard mail services to the laboratory. Upon arrival at the laboratory, whey can be kept refrigerated for 1 wk before analysis. This tool is useful for monitoring luteal activity of dairy cows.     

Minimizing variations in functionality of whey protein concentrates from different sources

Enhancement in processing technology has improved the nutritional and functional properties of whey protein concentrates by increasing the content and quality of the protein, leading to their increased use in different food products. The extent of heat treatment affects the quality of the whey protein concentrate, and wide variation in product quality exists due to the various means of manufacture and from the whey product history from farm to factory. The study was carried out with 6 commercial whey protein concentrates with 80% protein (WPC80) to determine variations in physical properties, particle size and density, and functional properties--solubility, gel strength, foam volume, and stability. Significant differences were observed among all the products for every property compared. Particulate size was the most important determinant of functional characteristics. Larger particulate WPC80 had significantly higher fat content and were less soluble with poor foam stability; but narrowing the particle size distribution through sieving, minimized variations. We determined that sieving all products within the particle size distribution range of 100 to 150 microns minimized variation in physical composition, making functionality uniform. WPC80 from different manufacturers can be made to perform uniformly within a narrow functionality range by reducing the particle size distribution through sieving.     

Impact of whey protein isolates and concentrates on the formation of protein nanoparticles‐stabilised Pickering emulsions

Whey protein nanoparticles (NPs) were prepared by heat‐induced method. The influences of whey protein isolates (WPIs) and concentrates (WPCs) on the formation of NPs were first investigated. Then Pickering emulsions were produced by protein NPs and their properties were evaluated. After heat treatment, WPC NPs showed larger particle size, higher stability against NaCl, lower negative charge and contact angle between air and water. Dispersions of WPC NPs appeared as higher turbidity and viscosity than those of WPI NPs. The interfacial tension of WPC NPs (~7.9 mN/m at 3 wt% NPs) was greatly lower than that of WPI NPs (~12.1 mN/m at 3 wt% NPs). WPC NPs‐stabilised emulsions had smaller particle size and were more homogeneous than WPI NPs‐stabilised emulsions. WPC NPs‐stabilised emulsions had higher stability against NaCl, pH and coalescence during storage.     

Slower proteolysis in Cheddar cheese made from high-protein cheese milk is due to an elevated whey protein content

A growing number of companies within the cheese-making industry are now using high-protein (e.g., 4–5%) milks to increase cheese yield. Previous studies have suggested that cheeses made from high-protein (both casein and whey protein; WP) milks may ripen more slowly; one suggested explanation is inhibition of residual rennet activity due to elevated WP levels. We explored the use of microfiltration (MF) to concentrate milk for cheese-making, as that would allow us to concentrate the casein while varying the WP content. Our objective was to determine if reducing the level of WP in concentrated cheese milk had any impact on cheese characteristics, including ripening, texture, and nutritional profile. Three types of 5% casein standardized and pasteurized cheese milks were prepared that had various casein:true protein (CN:TP) ratios: (a) control with CN:TP 83:100, (b) 35% WP reduced, 89:100 CN:TP, and (c) 70% WP reduced, 95:100 CN:TP. Standardized milks were preacidified to pH 6.2 with dilute lactic acid during cheese-making. Composition, proteolysis, textural, rheological, and sensory properties of cheeses were monitored over a 9-mo ripening period. The lactose, total solids, total protein, and WP contents in the 5% casein concentrated milks were reduced with increasing levels of WP removal. All milks had similar casein and total calcium levels. Cheeses had similar compositions, but, as expected, lower WP levels were observed in the cheeses where WP depletion by MF was performed on the cheese milks. Cheese yield and nitrogen recoveries were highest in cheese made with the 95:100 CN:TP milk. These enhanced recoveries were due to the higher fraction of nitrogen being casein-based solids. Microfiltration depletion of WP did not affect pH, sensory attributes, or insoluble calcium content of cheese. Proteolysis (the amount of pH 4.6 soluble nitrogen) was lower in control cheeses compared with WP-reduced cheeses. During ripening, the hardness values and the temperature of the crossover point, an indicator of the melting point of the cheese, were higher in the control cheese. It was thus likely that the higher residual WP content in the control cheese inhibited proteolysis during ripening, and the lower breakdown rate resulted in its higher hardness and melting point. There were no major differences in the concentrations of key nutrients with this WP depletion method. Cheese milk concentration by MF provides the benefit of more typical ripening rates.     

Rheological properties of commercial whey protein samples from the MADGELAS survey

Summary Thermally induced gelation of commercial whey protein samples from the Molecular Basis of the Aggregation, Denaturation, Gelation and Surface Activity of Whey Proteins ( MADGELAS ) survey has been studied in order to develop a current status report on their rheological properties. Solutions of 10% protein (w/v) were prepared in distilled water, 200 mm NaCl or 10 mm CaCl₂ at neutral pH. Small-scale deformation of the samples was measured by dynamic oscillatory rheometry using a Bohlin CS Rheometer. Large-scale deformation at penetration mode was measured using a Texture Analyser (Stable Micro Systems, Surrey, UK). For solutions containing salts, there was a general trend for gel point to decrease and G' values to increase, the effect being more marked in the presence of NaCl. Similarly, force values at failure also tended to increase in the presence of salts. Results obtained with samples of similar protein composition dissolved in water were highly scattered, these differences being reduced in the presence of added salts.     

Bioactive whey peptide particles: An emerging class of nutraceutical carriers

Whey-based diets have been linked with prolonged life expectancy and improved physical performance. These observations based on numerous clinical and simulated studies are attributed to diverse biological activities of whey peptides. Recently, bioactive whey peptides were exploited for enveloping nutraceuticals and drugs in view of fabricating capsules that the carrier matrix is also bioactive.

Some of the most considered bioactivities of whey peptides including antihypertension, antioxidant, anti-obesity, anti-diabetes, and hypocholesterolemic properties with corresponding underlying mechanisms are briefly discussed. Then, we overview the supramolecular and gelation-prompted encapsulation of nutraceuticals with whey proteins, followed by summarizing recent developments in utilization of synthetic peptides for gene and drug delivery. Finally, particulation of bioactive whey peptides are communicated.

Whey peptides may exert both biologically beneficial and technologically appreciated activities. Two procedures including desolvation and internal gelation have been so far employed for bioactive peptides particulation. Crosslinking is a prerequisite to confer acid-induced cold-set gelation to bioactive peptides. It also increases peptides Fe³⁺-reducing power. Surface activity of a population of peptides in whey protein hydrolysate may result in co-adsorption of the peptides together with small molecule surfactants onto oil–water interface, leading to modulated interfacial architecture and particle morphology.     

应用二次回归正交旋转组合设计优化转谷氨酰胺酶作用的乳清蛋白交联条件

考察了pH、催化时间、催化温度及加酶量对转谷氨酰胺酶作用WPI形成交联产物的粘度影响,并对影响因素进行优化,找出最佳组合。该研究共分两个实验进行,实验1考察pH、时间、温度及加酶量单个因素对转谷氨酰胺酶交联作用的影响;实验2是基于单因素实验结果,采用四因素(pH、催化时间、催化温度、加酶量)五水平回归正交旋转设计,对WPI经转谷氨酰胺酶交联后产生最大粘度的最佳条件进行优化,以便确定实验多元回归方程和获得较大WPI黏度的最佳条件。实验结果表明:交联时间4h、交联温度50℃、pH8.0和加酶量20u/g时,具有最佳粘度值,转谷氨酰胺酶作用效果最佳。