A method for the large-scale isolation of β-casein

Bovine milk β-casein: Structure, properties, isolation, and targeted application of isolated products

β-Casein, an important protein found in bovine milk, has significant potential for application in the food, pharmaceutical, and other related industries. This review first introduces the composition, structure, and functional properties of β-casein. It then reviews the techniques for isolating β-casein. Chemical and enzymatic isolation methods result in inactivity of β-casein and other components in the milk, and it is difficult to control the production conditions, limiting the utilization range of products. Physical technology not only achieves high product purity and activity but also effectively preserves the biological activity of the components. The isolated β-casein needs to be utilized effectively and efficiently for various purity products in order to achieve optimal targeted application. Bovine β-casein, which has a purity higher than or close to that of breast β-casein, can be used in infant formulas. This is achieved by modifying its structure through dephosphorylation, resulting in a formula that closely mimics the composition of breast milk. Bovine β-casein, which is lower in purity than breast β-casein, can be maximized for the preparation of functional peptides and for use as natural carriers. The remaining byproducts can be utilized as food ingredients, emulsifiers, and carriers for encapsulating and delivering active substances. Thus, realizing the intensive processing and utilization of bovine β-casein isolation. This review can promote the industrial production process of β-casein, which is beneficial for the sustainable development of β-casein as a food and material. It also provides valuable insights for the development of other active substances in milk.

Caseins: Versatility of Their Micellar Organization in Relation to the Functional and Nutritional Properties of Milk

The milk of mammals is a complex fluid mixture of various proteins, minerals, lipids, and other micronutrients that play a critical role in providing nutrition and immunity to newborns. Casein proteins together with calcium phosphate form large colloidal particles, called casein micelles. Caseins and their micelles have received great scientific interest, but their versatility and role in the functional and nutritional properties of milk from different animal species are not fully understood. Caseins belong to a class of proteins that exhibit open and flexible conformations. Here, we discuss the key features that maintain the structures of the protein sequences in four selected animal species: cow, camel, human, and African elephant. The primary sequences of these proteins and their posttranslational modifications (phosphorylation and glycosylation) that determine their secondary structures have distinctively evolved in these different animal species, leading to differences in their structural, functional, and nutritional properties. The variability in the structures of milk caseins influence the properties of their dairy products, such as cheese and yogurt, as well as their digestibility and allergic properties. Such differences are beneficial to the development of different functionally improved casein molecules with variable biological and industrial utilities.

Maillard induced glycation of β-casein for enhanced stability of the self-assembly micelles against acidic and calcium environment

Bovine β-casein (β-CN) has attracted increasingly interest as biocompatible nanocarrier for hydrophobic flavonoid due to its self-assembly ability to form micelles. This paper reported Maillard induced glycation reaction of β-CN using dextran in order to improve stability of naringenin-loaded β-CN micelles under acidic and high calcium environments. Our results showed that solubility of β-CN-graft-dextran was remarkable increased at acidic pH and the conjugation with 20 kDa dextran had the highest level of graft degree. Glycation restrained β-CN from aggregating around pH 5.0 where was close to the isoelectric point, forming spherical micelles with irregular and rough surfaces, which were significantly larger than the micelles at pH 7.0. β-CN-graft-dextran also overcame destabilization of the micelles induced by excess calcium and had no impact on the chelating ability of calcium. These findings appeared to be promising for future applications of modified β-CN-graft-dextran based on Maillard reaction as fairly stable nanocarrier under extreme condition.

Structural Changes of β-Casein Induced by Temperature and pH Analysed by Nuclear Magnetic Resonance, Fourier-Transform Infrared Spectroscopy, and Chemometrics

This study investigated structural changes in β-casein as a function of temperature (4 and 20 °C) and pH (5.9 and 7.0). For this purpose, nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopy were used, in conjunction with chemometric analysis. Both temperature and pH had strongly affected the secondary structure of β-casein, with most affected regions involving random coils and α-helical structures. The α-helical structures showed great pH sensitivity by decreasing at 20 °C and diminishing completely at 4 °C when pH was increased from 5.9 to 7.0. The decrease in α-helix was likely related to the greater presence of random coils at pH 7.0, which was not observed at pH 5.9 at either temperature. The changes in secondary structure components were linked to decreased hydrophobic interactions at lower temperature and increasing pH. The most prominent change of the α-helix took place when the pH was adjusted to 7.0 and the temperature set at 4 °C, which confirms the disruption of the hydrogen bonds and weakening of hydrophobic interactions in the system. The findings can assist in establishing the structural behaviour of the β-casein under conditions that apply as important for solubility and production of β-casein.

Effect of pH and heat treatment on structure, surface characteristics and emulsifying properties of purified camel β-casein

Oil-in-water emulsions (20%/80%, w/w) were stabilised by two types of β-caseins (1 g/L, w/w) extracted by rennet coagulation from camel and cow's milk, respectively. Both extracts were treated under different ranges of pH (3.0, 6.0 and 9.0) and temperature (25, 65 and 95 °C for 15 min) before emulsification. The emulsifying properties of the proteins were studied by surface and interfacial measurements. Results show that the emulsifying activity (EAI) of camel β-casein is higher than the bovine protein. Yet, both proteins exhibited heat stability and nonsignificant effect of temperature was reported. Conversely, a significant effect of pH on camel β-casein was recorded: at pH 6.0, the lowest values of EAI were measured and explained by the formation of micellar protein structure. Under such conditions, camel β-casein is therefore a novel emulsifying protein with high potential to stabilise oil-in-water interfaces which provides numerous applications for the food chemistry field.

Study on β-Casein Depleted Casein Micelles: Micellar Stability, Enzymatic Cross-Linking, and Suitability as Nanocarriers

β-Casein is an amphiphilic protein and thus considered as multilaterally bound in casein micelles. Its polar molecule part, in particular the phosphoserine residues, can interact electrostatically with colloidal calcium phosphate (CCP) to form nanoclusters and its nonpolar molecule part enhances micellar stability by forming hydrophobic bonds to other caseins. Because cooling weakens hydrophobic interactions, a substantial portion of β-casein can be irreversibly removed from the casein micelle by repeated depletion steps, including cooling and subsequent ultracentrifugation. Although this effect of cooling on the micellar β-casein concentration has been well known for decades, the influence of depletion on the main characteristics of casein micelles has been less investigated yet. Therefore, we aimed to analyze the consequences of β-casein depletion on the stability as well as the functionality of casein micelles to evaluate the suitability of depleted compared to native casein micelles as nanocarriers. Up to 43.2% of the total β-casein was irreversibly sequestered from native casein micelles by repeated cooling and ultracentrifugation steps. Depletion showed no effect on size distribution as well as polydispersity and particle concentration of micelle suspensions as measured via dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA), respectively. Furthermore, the stability of the micelles against ethanol or the chelating agent ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) was not influenced by β-casein depletion. Notwithstanding, depleted micelles were less susceptible to enzymatic cross-linking by microbial transglutaminase (mTG), indicating narrowed water channels due to depletion. Additionally, loading experiments showed that depleted micelles could be loaded with linoleic acid (LA) as intensively as native micelles, whereupon LA displaces up to 81.3% of β-casein from native micelles. Our results confirm that depletion does not enhance the ability of the casein micelle to act as a nanocarrier for hydrophobic substances but could support the understanding of the casein micelle structure. Based on the observed unchanged stability against EGTA, the hindered enzymatical cross-linking, and the efficient displacing of β-casein by LA, we suggest that the major portion of micellar β-casein is hydrophobically incorporated into the micelle structure without impact on the formation of calcium phosphate nanoclusters. The main role of β-casein for the casein micelle structure, therefore, might be to facilitate the high hydration of the interior and thus the high permeability of casein micelles.

Flux and transmission of β-casein during cold microfiltration of skim milk subjected to different heat treatments

Raw skim milk was subjected to different heat treatments: thermization (65°C, 20 s), pasteurization (72°C, 15 s), and no heat treatment (milk was microfiltered using 1.4-µm membranes at 50°C for bacteria removal; 1.4 MF). The milk (thermized, pasteurized, and 1.4 MF) was cooled and stored at 2°C until processing (at least 24 h) with cold (∼6°C) microfiltration using a benchtop crossflow pilot unit (Pall Membralox XLAB 5, Pall Corp., Port Washington, NY) equipped with 0.1-µm nominal pore diameter ceramic Membralox membrane (ET1-070, α-alumina, Pall Corp.). The flux was monitored during the process, and β-casein transmission and removal were calculated. The study aimed to indicate the conditions that should be applied to maximize β-casein passage through the membrane during cold microfiltration (5.6 ± 0.4°C) of skim milk. The proper selection of heat treatment parameters (temperature, time) of the feed before the cold microfiltration process will increase β-casein removal. It is not clear whether the difference in β-casein transmission between 1.4 MF, thermized, and pasteurized milk results from the effect of heat treatment conditions on β-casein dissociation from the casein micelles or on passage of β-casein through the membrane. The values of the major parameters (permeation flux and tangential flow velocity, through the wall shear stress) responsible for a proper membrane separation process were considerably lower than the critical values. It seems that the viscosity of the retentate has a great effect on the performance of the microfiltration membranes for protein separation at refrigerated temperatures.

Concentration of Immunoglobulins in Microfiltration Permeates of Skim Milk: Impact of Transmembrane Pressure and Temperature on the IgG Transmission Using Different Ceramic Membrane Types and Pore Sizes

The use of bioactive bovine milk immunoglobulins (Ig) has been found to be an alternative treatment for certain human gastrointestinal diseases. Some methodologies have been developed with bovine colostrum. These are considered in laboratory scale and are bound to high cost and limited availability of the raw material. The main challenge remains in obtaining high amounts of active IgG from an available source as mature cow milk by the means of industrial processes. Microfiltration (MF) was chosen as a process variant, which enables a gentle and effective concentration of the Ig fractions (ca. 0.06% in raw milk) while reducing casein and lactose at the same time. Different microfiltration membranes (ceramic standard and gradient), pore sizes (0.14–0.8 µm), transmembrane pressures (0.5–2.5 bar), and temperatures (10, 50 °C) were investigated. The transmission of immunoglobulin G (IgG) and casein during the filtration of raw skim milk (<0.1% fat) was evaluated during batch filtration using a single channel pilot plant. The transmission levels of IgG (~160 kDa) were measured to be at the same level as the reference major whey protein β-Lg (~18 kDa) at all evaluated pore sizes and process parameters despite the large difference in molecular mass of both fractions. Ceramic gradient membranes with a pore sizes of 0.14 µm showed IgG-transmission rates between 45% to 65% while reducing the casein fraction below 1% in the permeates. Contrary to the expectations, a lower pore size of 0.14 µm yielded fluxes up to 35% higher than 0.2 µm MF membranes. It was found that low transmembrane pressures benefit the Ig transmission. Upscaling the presented results to a continuous MF membrane process offers new possibilities for the production of immunoglobulin enriched supplements with well-known processing equipment for large scale milk protein fractionation.

Mammals, Milk, Molecules, and Micelles

After a brief description of my family background and school days, my professional career as a dairy scientist is described under three headings: research, teaching, and writing. My research activities fall into four areas: biochemistry of cheese, fractionation and characterization of milk proteins, heat stability of milk, and dairy enzymology. Finally, I offer some advice to young scientists.

Adsorption of lysozyme, beta-casein and their layer-by-layer formation on hydrophilic surfaces: Effect of ionic strength

The adsorbed amount and layer structure of lysozyme, beta-casein and mixed layers of the two proteins were studied on hydrophilic silica and quartz surfaces using the following techniques: ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D) and total internal reflection fluorescence (TIRF). Particular emphasis was put on the effect of solution ionic strength on the layer formation. Both lysozyme and beta-casein showed a higher affinity for the silica surface when adsorbed from a solution of low ionic strength even though beta-casein and silica are negatively charged at the pH used. No beta-casein remained adsorbed after rinsing with a 150mM buffer solution. The adsorbed amount of lysozyme on silica exceeded a monolayer coverage irrespective of the solution conditions and displayed a rigid structure. beta-Casein forms more than a single layer on pre-adsorbed lysozyme; an inner flat layer and an outer layer with an extended structure, which largely desorbs on rinsing. The build-up through sequential adsorption of lysozyme and beta-casein is favoured at intermediate and high ionic strength. The total adsorbed amount increased slightly with each deposition cycle and the mixed lysozyme/beta-casein layers contain higher amounts of protein compared to those of pure lysozyme or beta-casein. Sequential adsorption gives rise to a proteinaceous layer consisting of both lysozyme and beta-casein. The protein layers are probably highly interpenetrated with no clear separation between them.