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Chen R, Song Y, Wang Z, Ji H, Du Z, Ma Q, Yang Y, Liu X, Li N, Sun Y. Developments in small-angle X-ray scattering (SAXS) for characterizing the structure of surfactant-macromolecule interactions and their complex. Int J Biol Macromol 2023; 251:126288. [PMID: 37582436 DOI: 10.1016/j.ijbiomac.2023.126288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 08/08/2023] [Accepted: 08/09/2023] [Indexed: 08/17/2023]
Abstract
The surfactant-macromolecule interactions (SMI) are one of the most critical topics for scientific research and industrial application. Small-angle X-ray scattering (SAXS) is a powerful tool for comprehensively studying the structural and conformational features of macromolecules at a size ranging from Angstroms to hundreds of nanometers with a time-resolve in milliseconds scale. The SAXS integrative techniques have emerged for comprehensively analyzing the SMI and the structure of their complex in solution. Here, the various types of emerging interactions of surfactant with macromolecules, such as protein, lipid, nuclear acid, polysaccharide and virus, etc. have been systematically reviewed. Additionally, the principle of SAXS and theoretical models of SAXS for describing the structure of SMI as well as their complex has been summarized. Moreover, the recent developments in the applications of SAXS for charactering the structure of SMI have been also highlighted. Prospectively, the capacity to complement artificial intelligence (AI) in the structure prediction of biological macromolecules and the high-throughput bioinformatics sequencing data make SAXS integrative structural techniques expected to be the primary methodology for illuminating the self-assembling dynamics and nanoscale structure of SMI. As advances in the field continue, we look forward to proliferating uses of SAXS based upon its abilities to robustly produce mechanistic insights for biology and medicine.
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Affiliation(s)
- Ruixin Chen
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, Yunnan, China
| | - Yang Song
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, Yunnan, China
| | - Zhichun Wang
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, Yunnan, China
| | - Hang Ji
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, Yunnan, China
| | - Zhongyao Du
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, Yunnan, China
| | - Qingwen Ma
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, Yunnan, China
| | - Ying Yang
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, Yunnan, China
| | - Xingxun Liu
- College of Food Science and Engineering, Nanjing University of Finance and Economics, Nanjing, Jiangsu, China
| | - Na Li
- National Facility for Protein Science in Shanghai, Shanghai Advanced Research Institute, CAS, Shanghai, China.
| | - Yang Sun
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, Yunnan, China.
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2
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Pedersen JS, Møller TL, Raak N, Corredig M. A model on an absolute scale for the small-angle X-ray scattering from bovine casein micelles. SOFT MATTER 2022; 18:8613-8625. [PMID: 36331028 DOI: 10.1039/d2sm00724j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Casein micelles extracted from milk are 100-400 nm-sized particles, made up of proteins and calcium phosphates, with the latter as colloidal calcium phosphate particles (CCPs) in a size range of 2-4 nm embedded in a protein network. The hierarchical structures give rise to a variation of scattering intensity over many orders of magnitude, which can be measured by small-angle X-ray scattering and static light scattering. Expressions for the scattering intensity of a general simple model for composite particles with polydispersities of overall size and subparticles are derived, and some approximations are checked by generating scattering data for systems generated by Monte Carlo simulations. Based on the simpler models, a new model has been developed for casein micelles, where the scattering is expressed on an absolute scale and where the concentrations of, respectively, protein and CCPs are used as constraints, providing a consistent model. The CCPs are modelled as oblate ellipsoids and the protein as star structures. Correlations between the substructures of CCPs and protein structures are taken into account in terms of partial structure factors. The overall structure as well as some heterogeneities at intermediate length scale are modelled as polydisperse spheres. The model fits the data very well on all length scales and demonstrates that both the scattering from CCPs and protein is important. Thus, the model provides a detailed description of the casein structure, which is consistent with the information available in the literature.
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Affiliation(s)
- Jan Skov Pedersen
- Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.
| | - Thea Lykkegaard Møller
- Department of Food Science, CiFOOD Center for Innovative Food Research, Aarhus University, Agro Food Park 48, 8200 Aarhus N, Denmark
| | - Norbert Raak
- Department of Food Science, CiFOOD Center for Innovative Food Research, Aarhus University, Agro Food Park 48, 8200 Aarhus N, Denmark
| | - Milena Corredig
- Department of Food Science, CiFOOD Center for Innovative Food Research, Aarhus University, Agro Food Park 48, 8200 Aarhus N, Denmark
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Christiansen MV, Smith GN, Brok ES, Schmiele M, Ahrné L. The relationship between ultra-small-angle X-ray scattering and viscosity measurements of casein micelles in skim milk concentrates. Food Res Int 2021; 147:110451. [PMID: 34399453 DOI: 10.1016/j.foodres.2021.110451] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 04/26/2021] [Accepted: 05/21/2021] [Indexed: 11/16/2022]
Abstract
Skim milk concentrates have important applications in the dairy industry, often as intermediate ingredients. Concentration of skim milk by reverse osmosis membrane filtration induces water removal, which reduces the free volume between the colloidal components, in particular the casein micelles. Thermal treatment before or after concentration impacts the morphology of casein micelles. These changes affect the flow behavior and viscosity, but the consequences for supermicellar structure have not been elucidated. In the present study, skim milk concentrates with different total solid contents from 8.7% (control) up to 22.8% (w/w), prepared by reverse osmosis membrane filtration of non-heated and pasteurized skim milk, were heat treated at 75 °C for 18 s, and compared with non-heated concentrates. The structure of the concentrates was studied using Ultra Small Angle X-ray Scattering (USAXS), and the viscosity of concentrates was measured. The USAXS intensity I(q) was fitted at small and intermediate q-regions (0.0005 < q < 0.003 Å-1 and 0.0035 < q < 0.03 Å-1, respectively) with a power law. The value of the power law exponent was used to assess the heat- and concentration-induced aggregation of the milk solids and correlate it with the apparent viscosity. The results showed that increased viscosity of skim milk concentrates, due to water removal and heat-load, can be explained by increased aggregation of the casein micelles into elongated aggregates and increased smoothening of the casein micelle surface.
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Affiliation(s)
- Morten V Christiansen
- Department of Food Science, University of Copenhagen, Rolighedsvej 26, 1958 Frederiksberg C, Denmark
| | - Gregory N Smith
- ISIS Neutron Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom
| | - Erik S Brok
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 København Ø, Denmark
| | - Martin Schmiele
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 København Ø, Denmark
| | - Lilia Ahrné
- Department of Food Science, University of Copenhagen, Rolighedsvej 26, 1958 Frederiksberg C, Denmark.
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Yang S, Tyler AII, Ahrné L, Kirkensgaard JJK. Skimmed milk structural dynamics during high hydrostatic pressure processing from in situ SAXS. Food Res Int 2021; 147:110527. [PMID: 34399505 DOI: 10.1016/j.foodres.2021.110527] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2021] [Revised: 05/27/2021] [Accepted: 06/11/2021] [Indexed: 10/21/2022]
Abstract
Understanding the changes in milk at a nanostructural level during high-pressure (HP) treatment can provide new insights to improve the safety and functionality of dairy products. In this study, modifications of milk nanostructure during HP were studied in situ by small-angle X-ray scattering (SAXS). Skimmed milk was pressurized to 200 or 400 MPa at 25, 40 or 60 °C and held for 5 or 10 min, and the effect of single- and double-HP treatment was also investigated. In most cases, the SAXS patterns of skimmed milk are well fitted with a three-population model: a low-q micellar feature reflecting the overall micelle size (~0.002 Å-1), a small casein cluster contribution at intermediate-q (around 0.01 Å-1) and a high-q (0.08-0.1 Å-1) population of milk protein inhomogeneities. However, at 60 °C a scattering feature of colloidal calcium phosphate (CCP) which is normally only seen with neutron scattering, was observed at 0.035 Å-1. By varying the pressure, temperature, holding and depressurization times, as well as performing cycled pressure treatment, we followed the dynamic structural changes in the skimmed milk protein structure at different length scales, which depending on the processing conditions, were irreversible or reversible within the timescales investigated. Pressure and temperature of the HP process have major effects, not only on size of casein micelles, but also on "protein inhomogeneities" within their internal structure. Under HP, increasing processing time at 200 MPa induced re-association of the micelles, however, the changes in the internal structure were more pressure-dependent than time dependent.
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Affiliation(s)
- Shuailing Yang
- Department of Food Science, University of Copenhagen, DK-1958 Frederiksberg C, Denmark
| | - Arwen I I Tyler
- School of Food Science and Nutrition, University of Leeds, LS2 9JT Leeds, United Kingdom
| | - Lilia Ahrné
- Department of Food Science, University of Copenhagen, DK-1958 Frederiksberg C, Denmark.
| | - Jacob J K Kirkensgaard
- Department of Food Science, University of Copenhagen, DK-1958 Frederiksberg C, Denmark; Niels Bohr Institute, University of Copenhagen, DK-2100 København Ø, Denmark.
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Holt C. A quantitative calcium phosphate nanocluster model of the casein micelle: the average size, size distribution and surface properties. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2021; 50:847-866. [PMID: 33866398 DOI: 10.1007/s00249-021-01533-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 01/22/2021] [Accepted: 03/28/2021] [Indexed: 10/21/2022]
Abstract
Caseins (αS1, αS2, β and κ) are the main protein fraction of bovine milk. Together with nanoclusters of amorphous calcium phosphate (CaP) and divalent cations, they combine to form a polydisperse distribution of particles called casein micelles. A casein micelle model is proposed which is consistent with the way in which intrinsically disordered proteins interact through predominantly polar, short, linear, motifs. Using the model, an expression is derived for the size distribution of casein micelles formed when caseins bind to the CaP nanoclusters and the complexes further associate with each other and the remaining mixture of free caseins. The result is a refined coat-core model in which the core is formed mainly by the nanocluster complexes and the coat is formed exclusively by the free caseins. Example calculations of the size distribution and surface composition of an average bovine milk are compared with experiment. The average size, size distribution and surface composition of the micelles is shown to depend on the affinity of the nanocluster complexes for each other in competition with their affinity for free caseins, and on the concentrations of free caseins, calcium ions and other salts in the continuous phase.
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Affiliation(s)
- Carl Holt
- Institute of Molecular, Cell and Systems Biology, University of Glasgow, Glasgow, G12 8QQ, UK.
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Smith GN, Brok E, Christiansen MV, Ahrné L. Casein micelles in milk as sticky spheres. SOFT MATTER 2020; 16:9955-9963. [PMID: 33034319 DOI: 10.1039/d0sm01327g] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Milk is a ubiquitous foodstuff and food ingredient, and milk caseins are key to the structural properties of milk during processing and storage. Caseins self-assemble into nanometer-sized colloids, referred to as "micelles", and particles of this size are ideally suited to study by small-angle scattering (SAS). Previous SAS measurements have almost exclusively focussed on the internal structure of the micelles. While important for milk's properties, this attention to the interior of the micelles provides limited information about the structure-forming properties of milk and milk ingredients. The ultra-small-angle X-ray scattering (USAXS) measurements and analysis in this study extend to the micrometer scale, which makes it possible to characterize the interaction between the micelles. Until now, SAS studies have generally excluded a consideration of the interparticle interactions between casein micelles. This is inconsistent with these new data, and it is not possible to model the data without some interparticle attraction. If the micelles are treated as sticky spheres, excellent agreement between experimental data and model fits can be obtained over the length scales studied, from micrometers to ångströms. The stickiness of casein micelles will impact ultra-small-angle scattering and small-angle scattering measurements of casein micelles, but it particularly limits the application of simple approximations, which generally assume that particles are dilute and noninteracting. In summary, this analysis provides an approach to modelling scattering data over many orders of magnitude, which will provide better understanding of interactions between caseins and during food processing.
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Affiliation(s)
- Gregory N Smith
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark
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Sun Y, Zhang J, Wang H, Wang T, Cheng H, Yu B, Oliveira CL. Sulfate dodecyl sodium-induced stability of a model intrinsically disordered protein, bovine casein. Food Hydrocoll 2018. [DOI: 10.1016/j.foodhyd.2018.03.043] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Ingham B, Smialowska A, Kirby NM, Wang C, Carr AJ. A structural comparison of casein micelles in cow, goat and sheep milk using X-ray scattering. SOFT MATTER 2018; 14:3336-3343. [PMID: 29658047 DOI: 10.1039/c8sm00458g] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The casein micelle is a flexible construct, with its key structural components being casein proteins and colloidal calcium phosphate nanoclusters. According to literature, milk from different species exhibits differences in composition and physicochemical properties. X-ray scattering techniques were used to investigate and compare the nanoscale structure of casein micelles present in cow, goat and sheep milk. Although there were differences in the size and density of larger scale protein structures, at an atomic level the protein structures were similar. There were also strong similarities in the structure of the calcium-containing nanoclusters, namely that they had similar sizes and separations within the casein micelle for all three species.
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Affiliation(s)
- B Ingham
- Callaghan Innovation, P.O. Box 31310, Lower Hutt 5040, New Zealand.
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Ingham B, Smialowska A, Erlangga GD, Matia-Merino L, Kirby NM, Wang C, Haverkamp RG, Carr AJ. Revisiting the interpretation of casein micelle SAXS data. SOFT MATTER 2016; 12:6937-53. [PMID: 27491477 DOI: 10.1039/c6sm01091a] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
An in-depth, critical review of model-dependent fitting of small-angle X-ray scattering (SAXS) data of bovine skim milk has led us to develop a new mathematical model for interpreting these data. Calcium-edge resonant soft X-ray scattering data provides unequivocal evidence as to the shape and location of the scattering due to colloidal calcium phosphate, which is manifested as a correlation peak centred at q = 0.035 Å(-1). In SAXS data this feature is seldom seen, although most literature studies attribute another feature centred at q = 0.08-0.1 Å(-1) to CCP. This work shows that the major SAXS features are due to protein arrangements: the casein micelle itself; internal regions approximately 20 nm in size, separated by water channels; and protein structures which are inhomogeneous on a 1-3 nm length scale. The assignment of these features is consistent with their behaviour under various conditions, including hydration time after reconstitution, addition of EDTA (a Ca-chelating agent), addition of urea, and reduction of pH.
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Affiliation(s)
- B Ingham
- Callaghan Innovation, P.O. Box 31310, Lower Hutt 5040, New Zealand.
| | - A Smialowska
- School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - G D Erlangga
- School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - L Matia-Merino
- School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - N M Kirby
- Australian Synchrotron, 800 Blackburn Road, Clayton, VIC 3168, Australia
| | - C Wang
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - R G Haverkamp
- School of Engineering and Advanced Technology, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - A J Carr
- School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
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Sørensen H, Mortensen K, Sørland GH, Larsen FH, Paulsson M, Ipsen R. Dynamic ultra-high pressure homogenisation of whey protein-depleted milk concentrate. Int Dairy J 2015. [DOI: 10.1016/j.idairyj.2014.09.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Ingham B, Erlangga GD, Smialowska A, Kirby NM, Wang C, Matia-Merino L, Haverkamp RG, Carr AJ. Solving the mystery of the internal structure of casein micelles. SOFT MATTER 2015; 11:2723-5. [PMID: 25711160 DOI: 10.1039/c5sm00153f] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The interpretation of milk X-ray and neutron scattering data in relation to the internal structure of the casein micelle is an ongoing debate. We performed resonant X-ray scattering measurements on liquid milk and conclusively identified key scattering features, namely those corresponding to the size of and the distance between colloidal calcium phosphate particles. An X-ray scattering feature commonly assigned to the particle size is instead due to protein inhomogeneities.
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Affiliation(s)
- B Ingham
- Callaghan Innovation, P. O. Box 31-310, Lower Hutt 5040, New Zealand.
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12
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Dynamic ultra-high pressure homogenisation of milk casein concentrates: Influence of casein content. INNOV FOOD SCI EMERG 2014. [DOI: 10.1016/j.ifset.2014.09.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Zamora A, Guamis B. Opportunities for Ultra-High-Pressure Homogenisation (UHPH) for the Food Industry. FOOD ENGINEERING REVIEWS 2014. [DOI: 10.1007/s12393-014-9097-4] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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De Kruif CG. The structure of casein micelles: a review of small-angle scattering data. J Appl Crystallogr 2014. [DOI: 10.1107/s1600576714014563] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Casein micelles are association colloids found in mammalian milk. Small-angle scattering data on casein micelles have been collected and are reviewed, including contrast variation. The scattering spectra are quite consistent at medium and high scattering wavevectors [Q= 4πnsin(θ/2)/λ, wherenis the refractive index, λ is the wavelength and θ is the scattering angle]. Differences are noted, especially at lowQ, which may be attributed to sample preparation, particularly the presence of residual fat globules. Scattering spectra are calculated using a generalized scattering function and a composite particle model, and it is possible to give a self-consistent calculation of the spectra using one set of parameters for all contrasts in both small-angle X-ray scattering and small-angle neutron scattering. The data and calculations show that a casein micelle is a homogeneous particle. The polydispersity in size is about 35% and therefore experimental data on particle size depend very much on the method used. A `reference set' of numbers is proposed for casein micelles from pooled cows' milk, which may be given as follows: β = 0.35,R10= 60 nm,Rg= 110 nm,Rhydr= 96 nm (at 90° scattering). Often, use is made of dynamic light scattering (DLS), which gives anRhydr= 〈R6〉/〈R5〉 of 80–100 nm at 90° scattering. Values will be considerably higher at low(er) angles, and lower at backscattering angles, which are currently used in many DLS setups. Larger values are probably due to clusters of casein micelles or residual fat. The structure of a casein micelle can best be described as a protein matrix in which calcium phosphate clusters (2 nm radius) are dispersed. The protein matrix has density variations on a similar length scale. The casein micelle–submicelle model and models with large voids and channels are highly improbable.
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