Changes in the physical properties,solubility, and heat stability of milk protein concentrates prepared from partially acidified milk

A limiting factor in using milk protein concentrates (MPC) as a high-quality protein source for different food applications is their poor reconstitutability. Solubilization of colloidal calcium phosphate (CCP) from casein micelles during membrane filtration (e.g., through acidification) may affect the structural organization of these protein particles and consequently the rehydration and functional properties of the resulting MPC powder. The main objective of this study was to investigate the effects of acidification of milk by glucono-δ-lactone (GDL) before ultrafiltration (UF) on the composition, physical properties, solubility, and thermal stability (after reconstitution) of MPC powders. The MPC samples were manufactured in duplicate, either by UF (65% protein, MPC65) or by UF followed by diafiltration (80% protein, MPC80), using pasteurized skim milk, at either the native milk pH (~pH 6.6) or at pH 6.0 after addition of GDL, followed by spray drying. Samples of different treatments were reconstituted at 5% (wt/wt) protein to compare their solubility and thermal stability. Powders were tested in duplicate for basic composition, calcium content, reconstitutability, particle size, particle density, and microstructure. Acidification of milk did not have any significant effect on the proximate composition, particle size, particle density, or surface morphology of the MPC powders; however, the total calcium content of MPC80 decreased significantly with acidification (from 1.84 ± 0.03 to 1.59 ± 0.03 g/100 g of powder). Calcium-depleted MPC80 powders were also more soluble than the control powders. Diafiltered dispersions were significantly less heat stable (at 120°C) than UF samples when dissolved at 5% solids. The present work contributes to a better understanding of the differences in MPC commonly observed during processing.     

Solubility of commercial milk protein concentrates and milk protein isolates

High-protein milk protein concentrate (MPC) and milk protein isolate (MPI) powders may have lower solubility than low-protein MPC powders, but information is limited on MPC solubility. Our objectives in this study were to (1) characterize the solubility of commercially available powder types with differing protein contents such as MPC40, MPC80, and MPI obtained from various manufacturers (sources), and (2) determine if such differences could be associated with differences in mineral, protein composition, and conformational changes of the powders. To examine possible predictors of solubility as measured by percent suspension stability (%SS), mineral analysis, Fourier transform infrared (FTIR) spectroscopy, and quantitative protein analysis by HPLC was performed. After accounting for overall differences between powder types, %SS was found to be strongly associated with the calcium, magnesium, phosphorus, and sodium content of the powders. The FTIR score plots were in agreement with %SS results. A principal component analysis of FTIR spectra clustered the highly soluble MPC40 separately from the rest of samples. Furthermore, 2 highly soluble MPI samples were clustered separately from the rest of the MPC80 and MPI samples. We found that the 900 to 1,200 cm⁻¹ region exhibited the highest discriminating power, with dominant bands at 1,173 and 968 cm⁻¹, associated with phosphate vibrations. The 2 highly soluble MPI powders were observed to have lower κ-casein and α-_S1-casein contents and slightly higher whey protein contents than the other powders. The differences in the solubility of MPC and MPI were associated with a difference in mineral composition, which may be attributed to differences in processing conditions. Additional studies on the role of minerals composition on MPC80 solubility are warranted. Such a study would provide a greater understanding of factors associated with differences in solubility and can provide insight on methods to improve solubility of high-protein milk protein concentrates.     

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.     

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.     

Comparison of composition, sensory, and volatile components of thirty-four percent whey protein and milk serum protein concentrates

The objectives of this study were to identify and compare the composition, flavor, and volatile components of serum protein concentrate (SPC) and whey protein concentrate (WPC) containing about 34% protein made from the same milk to each other and to commercial 34% WPC from 6 different factories. The SPC and WPC were manufactured in triplicate with each pair of serum and traditional whey protein manufactured from the same lot of milk. At each replication, SPC and WPC were spray dried (SD) and freeze dried (FD) to determine the effect of the heat used in spray drying on sensory properties. A trained sensory panel documented the sensory profiles of rehydrated SD or FD powders. Volatile components were extracted by solid-phase microextraction (SPME) and solvent extraction followed by solvent-assisted flavor evaporation (SAFE) with gas chromatography-mass spectrometry and gas chromatography-olfactometry. Whey protein concentrates had higher fat content, calcium, and glycomacropeptide content than SPC. Color differences (Hunter L, a, b) were not evident between SPC and WPC powders, but when rehydrated, SPC solutions were clear, whereas WPC solutions were cloudy. No consistent differences were documented in sensory profiles of SD and FD SPC and WPC. The SD WPC had low but distinct buttery (diacetyl) and cardboard flavors, whereas the SD SPC did not. Sensory profiles of both rehydrated SD products were bland and lower in overall aroma and cardboard flavor compared with the commercial WPC. Twenty-nine aroma impact compounds were identified in the SPC and WPC. Lipid and protein oxidation products were present in both products. The SPC and WPC manufactured in this study had lower total volatiles and lower concentrations of many lipid oxidation compounds when compared with commercial WPC. Our results suggest that when SPC and WPC are manufactured under controlled conditions in a similar manner from the same milk using the same ultrafiltration equipment, there are few sensory differences but distinct compositional and physical property differences that may influence functionality. Furthermore, flavor (sensory and instrumental) properties of both pilot-scale manufactured protein powders were different from commercial powders suggesting the role of other influencing factors (e.g., milk supply, processing equipment, sanitation).     

Effects of calcium chelating agents on the solubility of milk protein concentrate

The aim of this study was to determine the effects of calcium chelating agents on the dissolution and functionality of 10% (w/w) milk protein concentrate (MPC) powder. MPC powder dissolution rate and solubility significantly (P > 0.05) increased with addition of sodium phosphate, trisodium citrate (TSC) and sodium hexametaphosphate (SHMP), compared to MPC dispersions alone. Trisodium citrate and SHMP addition increased viscosity as a result of micelle swelling. However, dispersions containing SHMP showed a decrease in viscosity after prolonged time due to micelle dissociation. Overall, MPC powder dissolution was aided by the addition of calcium chelating agents.     

蛋白含量对牦牛乳清蛋白浓缩物功能特性的影响

通过不同截留分子质量的再生纤维素膜过滤纯化牦牛原乳清液和牦牛甜乳清液,分别制取牦牛原乳清蛋白浓缩物（native whey protein concentrate,NWPC）和牦牛甜乳清蛋白浓缩物（sweet whey protein concentrate,SWPC）,研究蛋白含量不同的乳清蛋白浓缩物（whey protein concentrate,WPC）主要成分（乳糖含量、pH值和总蛋白质含量）和功能特性（溶解性、持水性、持油性、起泡性、乳化性及热稳定性）的特征。结果表明：10 000 Da再生纤维素膜透析得到的牦牛WPC中总蛋白含量达到80%以上,不含乳糖,功能特性（溶解性、持水性、持油性、起泡性、乳化性及热稳定性）均显著高于经3 500 Da卷式膜、5 000 Da再生纤维素膜透析得牦牛WPC,WPC蛋白含量越高,其功能特性越好;不同蛋白含量的牦牛SWPC起泡能力、泡沫稳定性、乳化活性和乳化稳定性均显著（P＜0.05）高于牦牛NWPC。牦牛乳WPC最不稳定温度为85 ℃,高于荷斯坦牛乳WPC的80 ℃,热处理会适当改善牦牛WPC的起泡性能、乳化性能和热稳定性。通过膜牦牛处理获取的高蛋白含量的WPC,功能特性较好,应用广泛,对解决牦牛乳清资源的利用问题、保护环境、提高企业的经济效益起到关键性作用。     

Extrusion modifies some physicochemical properties of milk protein concentrate for improved performance in high‐protein nutrition bars

BACKGROUND

Extruded and ground milk protein concentrate powders, specifically those with 800 g kg^–1 protein (i.e. MPC80), imparted softness, cohesion and textural stability to high‐protein nutrition (HPN) bars. The present study evaluated some physicochemical properties of extruded and conventionally produced (i.e. spray‐dried) MPC80 to explain these improvements. Protein chemical changes and aggregations within MPC80‐formulated HPN bars during storage were characterized.

RESULTS

Extruded MPC80 powders had broader particle size distribution (P < 0.05) and smaller volume‐weighted mean diameter (P < 0.05) than the spray‐dried control. Loose, tapped and particle densities increased (P < 0.05) and correspondingly occluded and interstitial air volumes decreased (P < 0.05) after extruding and milling MPC80. Extrusion decreased water holding capacity (P < 0.05) and solubility (P < 0.05), yet improved the wettability (P < 0.05) of MPC80. MPC80 free sulfhydryl (P < 0.05) and free amine (P < 0.05) concentrations decreased after extrusion. Sulfhydryl and amine concentrations changed (P < 0.05) and disulfide‐linked and, more prominently, Maillard‐induced aggregates developed during HPN bar storage.

CONCLUSION

Extrusion and milling together changed the physicochemical properties of MPC80. Chemical changes and protein aggregations occurred in HPN bars prepared with either type of MPC80. Thus, the physicochemical properties of the formulating powder require consideration for desired HPN bar texture and stability. © 2017 Society of Chemical Industry     

Effect of succinylation on physicochemical and functional properties of milk protein concentrate

Milk protein concentrate (MPC) is a complete dairy protein ingredient (containing both caseins and whey proteins) available with protein concentrations ranging from 40 to 90%. However, MPC powders are poorly soluble which thus, restricts their potential use for food application. Succinylation involves chemical derivatisation of ϵ-amino group of lysine in proteins and enhances solubility of less soluble proteins. In the present investigation, highest degree of succinylation was achieved at the level of 4 mol of succinic anhydride/mole of lysine in MPC. Findings from intrinsic tryptophan intensities stated that succinylation of milk proteins showed structural modification and increase in hydrophobicity. Further, the effects of succinylation on the functional properties (solubility, water- and oil-binding capacities, viscosity, foaming capacity and stability, emulsion activity and stability) of MPC were evaluated. Succinylation of proteins significantly (P < 0.05) increased solubility as a result of altered charge on protein and reduced particle size of native MPC, which in turn improved other functional properties of native MPC. The microstructure of succinylated MPC at different degrees of succinylation by scanning electron microscopy revealed that the size and number of white patch like structures present on protein increased with degree of succinylation.     

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.     

Influence of protein content and storage temperature on the particle morphology and flowability characteristics of milk protein concentrate powders

Milk protein concentrate (MPC) powders are widely used as ingredients for food product formulations due to their nutritional profile and sensory attributes. Processing parameters, storage conditions, and composition influences the flow properties of MPC powders. This study investigated the bulk and shear flow properties of 70.3, 81.5, and 88.1% (wt/wt, protein content) MPC after storage for 12 wk at 25 and 40°C. Additionally, the morphological and functional changes of the MPC powders were investigated and correlated with flowability. After 12 wk of storage at 25°C, the basic flow energy values significantly increased from 510 to 930 mJ as the protein content increased from 70 to 90% (wt/wt). Flow rate index was significantly higher for samples with high protein content. Dynamic flow tests indicated that MPC powders with high protein content displayed higher permeability. Shear tests confirmed that the samples stored at 25°C were more flowable than samples stored at 40°C. Likewise, the higher-protein content samples showed poor shear flow behavior. The results indicated that MPC powders stored at 25°C had less cohesiveness and better flow characteristics than MPC powders stored at 40°C. Overall, the MPC powders had markedly different flow properties due to their difference in composition and morphology. This study delivers insights on the particle morphology and flow behavior of MPC powders.     

Stability of milk protein concentrate suspensions to in-container sterilisation heating conditions

Milk protein concentrate (MPC) powders, ranging from 35 (MPC35) to 87 (MPC90)% protein, were reconstituted to 8.5% protein and assessed for heat stability at 120 °C, Ca-ion activity, heat-induced dissociation of κ-casein, and heat-induced gelation of serum-phase proteins in ultracentrifugal supernatants of unheated MPC suspensions. Heat stability of MPC suspensions depended on the protein content of the powder from which the suspensions were prepared. MPC70 had excellent heat stability compared with MPC35; however, MPC80, MPC85 and MPC90 were highly unstable to heating. Ca-ion activity increased with increasing protein content of the MPCs, whereas the extent of heat-induced dissociation of κ-casein and gelation of serum-phase proteins decreased. Increased heat stability with increasing protein content from MPC35 to MPC70 was attributed to decreased κ-casein dissociation and reduced gelation of serum-phase proteins. Despite these stabilising factors, excessively high Ca-ion activity caused MPC80, MPC85 and MPC90 to have very poor heat stability at pH 6.3–6.8, 6.3–7.1 and 6.3–7.3, respectively.     

醇法大豆浓缩蛋白的加工、性能与应用

醇法大豆浓缩蛋白在大豆蛋白产品中占有重要地位,但它在国内的发展水平还很低.为了促进我国大豆浓缩蛋白的发展,对其加工、性能和应用进行了阐述.逆流浸出法是目前较常见的醇法大豆浓缩蛋白制备方法.醇法大豆浓缩蛋白的溶解度较低,但是它有较强的持水性、持油性以及较高的黏度,通过改性可以进一步改善其功能性质.传统的醇法大豆浓缩蛋白主要应用于肉制品加工,大量的醇法大豆浓缩蛋白被加工成组织蛋白.经过改性的醇法大豆浓缩蛋白可以应用于对乳化性及持油性要求较高的高脂肪食品中.     

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.     

Functionality of milk protein concentrate 80 with emulsifying salts and its applications in analogue cheeses

Milk protein concentrate 80 (MPC80) was prepared with different emulsifying salts (ES). The effects on particle size (D50), solubility, and surface hydrophobicity (H₀) of MPC80 were then observed after production. The molecular weight and secondary structure of MPC80 protein were also investigated through sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier Transform Infrared (FTIR) spectrometry. Particle size (D50) was reduced from 31.37 to 20.67 μm following the addition of sodium phosphate (SPS). The solubility of MPC80 fortified with sodium citrate salt (SCS), SPS, and sodium pyrophosphate (SPP) was improved by 80.32, 78.23, and 55.80%, respectively. The SDS-PAGE pattern showed no significant difference between the control and single-ES-fortified samples, but major protein bands (α_s-CN, β-CN, κ-CN, BSA, and β-LG) had a stronger intensity than binary-ES-fortified MPC80. The FTIR results showed that the β-sheet content of ES-fortified MPC80 was relatively higher than that in the control. Compared with analogue cheeses made by MPC80 with and without ES, SCS–SPP (92:8)-modified MPC80 presented a better fluid mass and homogeneous colour.     

Comparative studies on the functional properties of various protein concentrate preparations of peanut protein

The effect of different preparations on the functional properties of peanut protein concentrates was studied. Peanut protein concentrates were isolated from defatted peanut flour by isoelectric precipitation, alcohol precipitation, isoelectric precipitation combined with alcohol precipitation, alkali solution with isoelectric precipitation and their functional properties (protein solubility, water holding/oil binding capacity, emulsifying capacity and stability, foaming capacity and rheology) were evaluated. The results showed that the protein solubility, foaming capacity and stability of protein prepared by alkali solution with isoelectric precipitation were the best of all the peanut protein products. But the protein prepared by alcohol precipitation had better water holding/oil binding capacity, which was significantly different from other protein products. The emulsifying stability of protein concentrate prepared by different methods was significantly lower than that of defatted protein flour. The protein prepared by isoelectric precipitation and isoelectric precipitation combined with alcohol precipitation had better gel properties which indicated that they were a potential food ingredient.     

Rheological properties of rennet gels containing milk protein concentrates

Different milk protein concentrates (MPC), with protein concentrations of 56, 70, and 90%, were dispersed in water under different treatments (hydration, shear, heat, and overnight storage at 4°C), as well as in a combination of all the treatments in a factorial design. The particle size distribution of the dispersions was then measured to determine the optimal conditions for the dispersion. Heating at 60°C for 30 min with 5 min of shear was chosen as the best condition to dissolve MPC powders. The samples were also characterized for composition, presence of protein aggregates, and ratio of calcium to protein. The total calcium present in MPC increased with increasing concentration of protein; however, the total calcium-to-protein ratio was lower in MPC90 than in MPC56 and MPC70. The level of whey protein denaturation, the presence of κ-casein-whey protein aggregates in the supernatant after centrifugation, and the amount of caseins dissociated from the micelle increased as the protein concentration in the powder increased. The total amount of casein macropeptide released was lower in samples from powders with a higher protein concentration than for MPC56 or the skim milk control. The gelation behavior of reconstituted MPC was tested in systems dispersed in water (5% protein) as well as in systems dispersed in skim milk (6% protein). The gelation time of MPC dispersions was considerably lower and the gel modulus was higher than those of reconstituted skim milk with the same protein concentration. When MPC dispersions were dialyzed against skim milk, a significant decrease in the gelation time and modulus were shown, with a complete loss of gelling functionality in MPC90 dispersed in water. This demonstrated that the ionic equilibrium was key to the functionality of MPC.     

Physical and functional properties of whole milk powders prepared from concentrate partially acidified with CO2 at two temperatures

Effects of carbonation of whole milk concentrate on spray dried powder properties were investigated. Concentrate acidification by CO₂ addition (2000 ppm) was found to strongly modify the functional properties (solubility, dispersibility) and structural/physical properties (porosity, free fat) of the resulting powders. For concentrates treated at low temperature (where the majority of emulsified fat is in a solid state at 4 °C), colloidal calcium phosphate (CCP) release, casein dissociation and fat coalescence were observed. For warm CO₂ treated concentrates (30 °C) only CCP release was observed. The best functional properties (higher solubility and dispersibility) were found for powders produced from the warm treated concentrates, which were possibly due to the high porosity and better fat globule preservation.     

Rehydration process of milk protein concentrate powder monitored by static light scattering

Static light scattering (SLS) was applied to monitor the rehydration process of milk protein concentrate (MPC) powder. The size distribution and volume concentration of the suspended powder particles were measured to quantify the dissolution kinetics of MPC powder. The results obtained showed that the low solubility index reported for MPC85 (85% protein) powder at room temperature was the consequence of slow dissolution kinetics rather than the presence of a large amount of insoluble material in the rehydrated powder. The rehydration process of MPC85 powder occurs in two overlapping steps: the disruption of agglomerated particles into primary powder particles and, simultaneously, the release of material from the powder particles into the surrounding aqueous phase. The latter process appeared to be the rate-limiting step of dissolution of MPC85 and was accelerated by an increase of the solvent temperature.     

Functional properties of native and cheese whey protein concentrate powders

The objective of this study was to compare microfiltered native whey protein concentrate and traditional cheese whey protein concentrate powders and their functional properties. Solubility, viscosity, gelation, foaming properties, emulsification and water-holding capacity were studied. The effect of spray and freeze drying methods on functional properties was evaluated. Gel strength varied from 0.11 to 0.65 N. Foaming stability and overrun varied from 0 to 29.3 min and from 230 to 2200%, respectively. Foaming and gelation properties were clearly better with native whey protein powders. Differences between drying methods were not observed but higher heat load decreased solubility.