1
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Holt C, Carver JA. Invited review: Modeling milk stability. J Dairy Sci 2024; 107:5259-5279. [PMID: 38522835 DOI: 10.3168/jds.2024-24779] [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: 02/12/2024] [Accepted: 02/15/2024] [Indexed: 03/26/2024]
Abstract
Novel insights into the stability of milk and milk products during storage and processing result from describing caseins near neutral pH as hydrophilic, intrinsically disordered, proteins. Casein solubility is strongly influenced by pH and multivalent ion binding. Solubility is high at a neutral pH or above, but decreases as the casein net charge approaches zero, allowing a condensed casein phase or gel to form, then increases at lower pH. Of particular importance for casein micelle stability near neutral pH is the proportion of free caseins in the micelle (i.e., caseins not bound directly to nanoclusters of calcium phosphate). Free caseins are more soluble and better able to act as molecular chaperones (to prevent casein and whey protein aggregation) than bound caseins. Some free caseins are highly phosphorylated and can also act as mineral chaperones to inhibit the growth of calcium phosphate phases and prevent mineralized deposits from forming on membranes or heat exchangers. Thus, casein micelle stability is reduced when free caseins bind to amyloid fibrils, destabilized whey proteins or calcium phosphate. The multivalent-binding model of the casein micelle quantitatively describes these and other factors affecting the stability of milk and milk protein products during manufacture and storage.
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Affiliation(s)
- C Holt
- School of Biomolecular Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
| | - J A Carver
- Research School of Chemistry, The Australian National University, Acton, ACT 2601, Australia
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2
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Yang Y, Xu Q, Wang X, Bai Z, Xu X, Ma J. Casein-based hydrogels: Advances and prospects. Food Chem 2024; 447:138956. [PMID: 38503069 DOI: 10.1016/j.foodchem.2024.138956] [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: 12/05/2023] [Revised: 02/29/2024] [Accepted: 03/04/2024] [Indexed: 03/21/2024]
Abstract
Casein-based hydrogels (Casein Gels) possess advantageous properties, including mechanical strength, stability, biocompatibility, and even adhesion, conductivity, sensing capabilities, as well as controlled-releasing behavior of drugs. These features are attributed to their gelation methods and functionalization with various polymers. Casein Gels is an important protein-based material in the food industry, in terms of dairy and functional foods, biological and medicine, in terms of carrier for bioactive and sensitive drugs, wound healing, and flexible sensors and wearable devices. Herein, this review aims to highlight the importance of the features mentioned above via a comprehensive investigation of Casein Gels through multiple directions and dimensional applications. Firstly, the composition, structure, and properties of casein, along with the gelation methods employed to create Casein Gels are elaborated, which serves as a foundation for further exploration. Then, the application progresses of Casein Gels in dairy products, functional foods, medicine, flexible sensors and wearable devices, are thoroughly discussed to provide insights into the diverse fields where Casein Gels have shown promise and utility. Lastly, the existing challenges and future research trends are highlighted from an interdisciplinary perspective. We present the latest research advances of Casein Gels and provide references for the development of multifunctional biomass-based hydrogels.
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Affiliation(s)
- Yuxi Yang
- College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi'an 710021, China
| | - Qunna Xu
- College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi'an 710021, China; Xi'an Key Laboratory of Green Chemicals and Functional Materials, National Demonstration Center for Experimental Light Chemistry Engineering Education, Xi'an 710021, China.
| | - Xinyi Wang
- College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi'an 710021, China; Institute of Biomass & Functional Materials, Shaanxi University of Science &Technology, Xi'an 710021, China
| | - Zhongxue Bai
- College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi'an 710021, China; Institute of Biomass & Functional Materials, Shaanxi University of Science &Technology, Xi'an 710021, China
| | - Xiaoyu Xu
- College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi'an 710021, China
| | - Jianzhong Ma
- College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi'an 710021, China; Xi'an Key Laboratory of Green Chemicals and Functional Materials, National Demonstration Center for Experimental Light Chemistry Engineering Education, Xi'an 710021, China.
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3
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Takagi H, Nakano T, Aoki T, Tanimoto M. A SAXS and USAXS study of the influence of pH on the casein micelle structure. Food Chem 2024; 443:138606. [PMID: 38301565 DOI: 10.1016/j.foodchem.2024.138606] [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: 09/27/2023] [Revised: 01/24/2024] [Accepted: 01/26/2024] [Indexed: 02/03/2024]
Abstract
Changes in milk pH significantly influence the behavior and physical properties of casein micelles; however, the effects of these changes on casein micelle structures are still unclear. The aim of this study was to elucidate the effect of changes in pH range from 5.9 to 7.1 on the structure of casein micelles in milk using small-angle X-ray scattering (SAXS) and ultra small-angle X-ray scattering (USAXS). The casein micelles formed one-dimensional aggregates. The micelle radius decreased with decreasing pH, whereas the size of the water domain increased. The distance between colloidal calcium phosphates (CCP) remained unchanged, whereas the CCP radius decreased with decreasing pH. Voluminosity, which was calculated from scattering intensities, increased at increased pH. In conclusion, the micelle structure changed significantly in response to changes in pH. Our findings help to understand the changes in the physical properties of milk at various pH levels in terms of the microscopic structure.
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Affiliation(s)
- Hideaki Takagi
- Institute of Materials Structure Science, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan.
| | - Tomoki Nakano
- Research Division, Minami Nippon Dairy Co-op Co., Ltd., 5282, Takagi, Miyakonojyo, Miyazaki 885-0003, Japan
| | - Takayoshi Aoki
- Professor Emeritus, Kagoshima University, Hoshigamine, Kagoshima 891-0102, Japan
| | - Morimasa Tanimoto
- Professor Emeritus, University of Yamanashi, 4-4-37, Takeda, Kofu, Yamanashi 400-8510, Japan; Department of Food Sciences, Tokyo Seiei College, 1-4-6, Nishishinkoiwa, Katsushika-Ku, Tokyo 124-8530, Japan
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4
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Raynes JK, Mata J, Wilde KL, Carver JA, Kelly SM, Holt C. Structure of biomimetic casein micelles: Critical tests of the hydrophobic colloid and multivalent-binding models using recombinant deuterated and phosphorylated β-casein. J Struct Biol X 2024; 9:100096. [PMID: 38318529 PMCID: PMC10840362 DOI: 10.1016/j.yjsbx.2024.100096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2023] [Revised: 01/08/2024] [Accepted: 01/17/2024] [Indexed: 02/07/2024] Open
Abstract
Milk contains high concentrations of amyloidogenic casein proteins and is supersaturated with respect to crystalline calcium phosphates such as apatite. Nevertheless, the mammary gland normally remains unmineralized and free of amyloid. Unlike κ-casein, β- and αS-caseins are highly effective mineral chaperones that prevent ectopic and pathological calcification of the mammary gland. Milk invariably contains a mixture of two to five different caseins that act on each other as molecular chaperones. Instead of forming amyloid fibrils, several thousand caseins and hundreds of nanoclusters of amorphous calcium phosphate combine to form fuzzy complexes called casein micelles. To understand the biological functions of the casein micelle its structure needs to be understood better than at present. The location in micelles of the highly amyloidogenic κ-casein is disputed. In traditional hydrophobic colloid models, it, alone, forms a stabilizing surface coat that also determines the average size of the micelles. In the recent multivalent-binding model, κ-casein is present throughout the micelle, in intimate contact with the other caseins. To discriminate between these models, a range of biomimetic micelles was prepared using a fixed concentration of the mineral chaperone β-casein and nanoclusters of calcium phosphate, with variable concentrations of κ-casein. A biomimetic micelle was also prepared using a highly deuterated and in vivo phosphorylated recombinant β-casein with calcium phosphate and unlabelled κ-casein. Neutron and X-ray scattering experiments revealed that κ-casein is distributed throughout the micelle, in quantitative agreement with the multivalent-binding model but contrary to the hydrophobic colloid models.
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Affiliation(s)
- Jared K. Raynes
- CSIRO Agriculture & Food, 671 Sneydes Road, Werribee, VIC 3031, Australia
- All G Foods, Waterloo, NSW 2006, Australia
| | - Jitendra Mata
- Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia
- School of Chemistry, University of New South Wales, Sydney 2052, Australia
| | - Karyn L. Wilde
- National Deuteration Facility, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia
| | - John A. Carver
- Research School of Chemistry, The Australian National University, Acton, ACT 2601, Australia
| | - Sharon M. Kelly
- School of Molecular Biosciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Carl Holt
- School of Molecular Biosciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
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5
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Wang T, Li Y, De Witte F, Rebry F, Li H, Vermeir P, Dewettinck K, Van der Meeren P. Influence of calcium concentration on the re-assembly of sodium caseinate into casein micelles and on their renneting behavior. Food Res Int 2024; 180:113991. [PMID: 38395543 DOI: 10.1016/j.foodres.2024.113991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2023] [Revised: 12/30/2023] [Accepted: 01/05/2024] [Indexed: 02/25/2024]
Abstract
Inducing the spontaneous aggregation from casein molecules (i.e. αs1, αs2, β, and κ-casein) into re-assembled casein micelles (RCMs) through the addition of salts as an alternative to native casein micelles, has garnered increasing attention in recent years. In this investigation, re-assembled casein micelles were generated by adding varying amounts of calcium, phosphate, and citrate ions to a sodium caseinate dispersion. The formed micelles were further characterized in terms of particle size, optical density, and partitioning of calcium ions and caseins. Besides, their small-angle X-ray scattering (SAXS) profiles and renneting properties were evaluated. The observations revealed that the particle size and optical density of RCMs increased with the continuous addition of salts, while the micellar yield improved and could exceed 85 %. Moreover, the quantity of individual casein molecules that contributed to the creation of micelles was in concordance with their level of phosphorylation (i.e. αs2-casein > αs1-casein > β-casein > κ-casein). Mineral analysis results and SAXS scattering profiles confirmed that the added calcium ions acted as cross-linkers and participated in the construction of calcium phosphate nanoclusters. The renneting ability of RCMs was primarily dependent upon the colloidal calcium content per gram of micellar casein.
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Affiliation(s)
- Teng Wang
- Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Gent, Belgium.
| | - Yadong Li
- Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Gent, Belgium
| | - Fien De Witte
- Food Structure and Function Research Group, Department of Food Technology, Safety and Health, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium
| | - Ferre Rebry
- Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Gent, Belgium
| | - Hao Li
- Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Gent, Belgium
| | - Pieter Vermeir
- Laboratory for Chemical Analysis (LCA), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium
| | - Koen Dewettinck
- Food Structure and Function Research Group, Department of Food Technology, Safety and Health, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium
| | - Paul Van der Meeren
- Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Gent, Belgium
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6
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M Ller TL, Nielsen SRB, Corredig M. Novel details on the dissociation of casein micelle suspensions as a function of pH and temperature. J Dairy Sci 2023; 106:8368-8374. [PMID: 37678779 DOI: 10.3168/jds.2023-23456] [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: 03/05/2023] [Accepted: 07/03/2023] [Indexed: 09/09/2023]
Abstract
Membrane filtration is a widespread process for fractionation and recombination of milk components. Although the dissociation of micellar caseins has been studied in detail in skim milk, it is important to better understand the dissociation dynamics occurring between the colloidal and noncolloidal fractions in systems of modified composition. This research aimed at understanding the dissociation of casein proteins in micellar fractions depleted of whey proteins. Casein micelle dispersions were tested at neutral pH and pH 6 (using glucono-δ-lactone as acidulant), after incubation at 4°C or 22°C, and compared with skim milk. The ionic composition of the serum phase was measured using inductively coupled plasma-mass spectrometry, and the protein distribution analyzed using reversed phase-HPLC coupled with mass spectrometry. When incubated at 22°C, there were no differences in casein micelle dissociation between skim milk and whey protein-depleted micelles (∼2.6% dissociated casein). No additional dissociation occurred by lowering the pH from 6.8 to 6 at 22°C, albeit there were more soluble ions at low pH (71% Ca and 65% P). At 4°C, there was an increased amount of β-casein found in the serum phase (23-33% of total β-casein). In addition, there was an uneven dissociation behavior of the various genetic β-casein variants, whereof A2 was more readily released with cooling. In skim milk, approximately 22%, 18%, and 14% of κ-, αS2, and αS1-caseins, respectively, were dissociated from the micellar phase upon cooling and acidification to pH 6.0. This was in contrast to whey protein-depleted casein suspensions, in which only 6%, 5%, and 3% of κ-, αS2, and αS1-caseins, respectively, had dissociated. The results suggested that the whey proteins in the serum phase play a role in the equilibrium between colloidal and soluble caseins in milk. This is of great relevance in processes such as cold membrane fractionation, where more attention should be given to the protein composition in the serum phase, especially when concentration is combined with fractionation of the serum proteins.
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Affiliation(s)
| | | | - Milena Corredig
- Department of Food Science, Aarhus University, 8200 Aarhus N, Denmark
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7
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Antuma LJ, Steiner I, Garamus VM, Boom RM, Keppler JK. Engineering artificial casein micelles for future food: Is casein phosphorylation necessary? Food Res Int 2023; 173:113315. [PMID: 37803629 DOI: 10.1016/j.foodres.2023.113315] [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: 05/18/2023] [Revised: 07/21/2023] [Accepted: 07/22/2023] [Indexed: 10/08/2023]
Abstract
Industrial-scale production of recombinant proteins for food products may become economically feasible but correct post-translational modification of proteins by microbial expression systems remains a challenge. For efficient production of hybrid products from bovine casein and recombinant casein, it is therefore of interest to evaluate the necessity of casein post-translational phosphorylation for the preparation of hybrid casein micelles and study their rennet-induced coagulation. Our results show that dephosphorylated casein was hardly incorporated into artificial casein micelles but was capable of stabilising calcium phosphate nanoclusters with an increased size through adsorption on their surface. Thereby, dephosphorylated casein formed larger colloidal particles with a decreased hydration. Furthermore, the presence of increasing amounts of dephosphorylated casein resulted in increasingly poor rennet coagulation behaviour, where dephosphorylated casein disrupted the formation of a coherent gel network by native casein. These results emphasise that post-translational phosphorylation of casein is crucial for their assembly into micelles and thereby for the production of dairy products for which the casein micelle structure is a prerequisite, such as many cheese varieties and yoghurt. Therefore, phosphorylation of future recombinant casein is essential to allow its use in the production of animal-free dairy products.
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Affiliation(s)
- Laurens J Antuma
- Laboratory of Food Process Engineering, Wageningen University & Research, Bornse Weilanden 9, 6708 WG, Wageningen, Netherlands.
| | - Isabell Steiner
- Laboratory of Food Process Engineering, Wageningen University & Research, Bornse Weilanden 9, 6708 WG, Wageningen, Netherlands.
| | - Vasil M Garamus
- Helmholtz Zentrum Hereon, Max-Planck Str. 1, D-21502 Geesthacht, Germany.
| | - Remko M Boom
- Laboratory of Food Process Engineering, Wageningen University & Research, Bornse Weilanden 9, 6708 WG, Wageningen, Netherlands.
| | - Julia K Keppler
- Laboratory of Food Process Engineering, Wageningen University & Research, Bornse Weilanden 9, 6708 WG, Wageningen, Netherlands.
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8
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Gebhardt R, Darvishsefat N. Regenerated Fibers from Rennet-Treated Casein Micelles during Acidification. Gels 2023; 9:538. [PMID: 37504417 PMCID: PMC10378896 DOI: 10.3390/gels9070538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Revised: 06/25/2023] [Accepted: 06/28/2023] [Indexed: 07/29/2023] Open
Abstract
Micellar casein fibers of defined size and internal structure can be produced by the extrusion of cold-renneted casein micelles into a warm, calcium-rich coagulation bath. Calcium phosphate contacts within the casein matrix are important for fiber stability and production but become less important under acidic pH conditions. We demonstrate this with swelling experiments in media with pH < 2, which we adjust with citric acid of different molarities. In contrast to the simple swelling of dried casein fibers in water, a two-phase process takes place in citric acid similar to swelling in 1 N HCl. However, instead of a second deswelling step, we observe in citric acid that the fiber swells further. The observation is explained by a pH-dependent transition from a rennet casein gel to an acidified rennet gel. This can be simulated with a kinetic model that couples two second-order rate equations via a time-varying ratio. The final swelling values decrease with increasing proton concentration via a scaling relation, which is also confirmed by swelling in other acids (HCl or acetic acid) in this pH range. We attribute this to a decrease in the molecular weights of the aggregated casein structures within the strands of the gel network.
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Affiliation(s)
- Ronald Gebhardt
- Chair of Soft Matter Process Engineering (AVT.SMP), RWTH Aachen University, 52062 Aachen, Germany
| | - Novin Darvishsefat
- Chair of Soft Matter Process Engineering (AVT.SMP), RWTH Aachen University, 52062 Aachen, Germany
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9
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Wang Y, Cui X, Li Y, Wang S, Yan G, Zhang L, Li Y. Effects of pH and Ionic Strength in Calcium on the Stability and Aeration Characteristics of Dairy Emulsion. Foods 2023; 12:foods12101976. [PMID: 37238793 DOI: 10.3390/foods12101976] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 05/05/2023] [Accepted: 05/08/2023] [Indexed: 05/28/2023] Open
Abstract
The effects of different pH levels and ionic strength in calcium on the stability and aeration characteristics of dairy emulsions were investigated in this study. The results revealed that the stability and aeration characteristics of the emulsion were enhanced as the pH value increased from 6.5 to 7.0 and were optimal within the pH of 6.8~7.0, while the concentration of free calcium ions (Ca2+) was 2.94~3.22 mM. With the pH subsequently fixed at 6.8 and 7.0, when the addition of CaCl2 was increased to 2.00 mM (free Ca2+ strength > 4.11 mM), stability and aeration characteristics reduced significantly, including the flocculation of fat globules, an increase in particle size, and a decrease in the zeta potential and viscosity of the O/W emulsion, all leading to an increase in interfacial protein mass and decreased overrun and foam firmness. Overall, the results indicated that pH changes and CaCl2 addition significantly influenced the stability and aeration characteristics of dairy emulsions, by influencing free Ca2+ strength, which is an important factor in determining the quality of dairy emulsions.
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Affiliation(s)
- Yunna Wang
- Beijing Engineering and Technology Research Centre of Food Additives, School of Food and Health, Beijing Technology and Business University, Beijing 100048, China
- Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Xin Cui
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Yang Li
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Shiran Wang
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Guosen Yan
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Liebing Zhang
- College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Yan Li
- Beijing Engineering and Technology Research Centre of Food Additives, School of Food and Health, Beijing Technology and Business University, Beijing 100048, China
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10
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Gebhardt R, Pütz T, Schulte J. Nearly Reversible Expansion and Shrinkage of Casein Microparticles Triggered by Extreme pH Changes. MICROMACHINES 2023; 14:678. [PMID: 36985085 PMCID: PMC10058559 DOI: 10.3390/mi14030678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Revised: 03/10/2023] [Accepted: 03/14/2023] [Indexed: 06/18/2023]
Abstract
Solvent flows in the fL/s range across the total surface of a casein microparticle cause its expansion and shrinkage. Microparticles prepared from the milk protein casein have a porous and flexible inner structure with water-filled channels and cavities. Solvent uptake occurs in two phases and results in disintegration if de-swelling is not triggered by acidification. So far, nothing is known about the reversibility of the swelling/de-swelling steps. We performed pH jump experiments between pH 11 and pH 1 on a single micro-particle and analyzed the swelling-induced size changes with system dynamics modeling. Both the swelling steps and the subsequent de-swelling process proceed reversibly and at an unchanged rate over a sequence of at least three pH exchange cycles. We observed that the duration of the first swelling step increased during the sequence, while the second step became shorter. Both of the time intervals are negatively correlated, while a statistical evaluation of only one swelling cycle for an ensemble of microparticles with different stabilities did not reveal any significant correlation between the two parameters. Our results indicate that the pH-induced swelling/shrinkage of casein microparticles is, to a large extent, reversible and only slightly influenced by the acid-induced decomposition of colloidal calcium phosphate.
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11
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The effect of acidification temperature and pH on intermolecular protein bonds and water mobility in heat and acid-induced milk gels. Int Dairy J 2023. [DOI: 10.1016/j.idairyj.2023.105611] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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12
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Discriminating between different proteins in the microstructure of acidified milk gels by super-resolution microscopy. Food Hydrocoll 2023. [DOI: 10.1016/j.foodhyd.2023.108468] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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13
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Spatial distribution of αs1-caseins and β-caseins in milk gels acidified with glucono-δ-lactone. Food Hydrocoll 2023. [DOI: 10.1016/j.foodhyd.2023.108506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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14
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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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15
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Assessment of structures in phosphocaseinate dispersions by A4F, NMR and SAXS: The impact of demineralization and heat treatment on viscosity. Food Hydrocoll 2022. [DOI: 10.1016/j.foodhyd.2022.108366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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16
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Khanna S, Gebhardt R. Influence of lactose on the rheological properties of reconstituted casein micelles concentrates. Int Dairy J 2022. [DOI: 10.1016/j.idairyj.2022.105449] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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17
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In situ SAXS study of non-fat milk model systems during heat treatment and acidification. Food Res Int 2022; 157:111292. [DOI: 10.1016/j.foodres.2022.111292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2022] [Revised: 04/20/2022] [Accepted: 04/21/2022] [Indexed: 11/20/2022]
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18
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Temperature dependence of the casein micelle structure in the range of 10–40 °C: an in-situ SAXS study. Food Chem 2022; 393:133389. [DOI: 10.1016/j.foodchem.2022.133389] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2022] [Revised: 05/12/2022] [Accepted: 06/01/2022] [Indexed: 11/22/2022]
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19
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20
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Molecular details of the formation of soluble aggregates during ultrafiltration or microfiltration combined with diafiltration of skim milk. Food Hydrocoll 2022. [DOI: 10.1016/j.foodhyd.2021.107244] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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21
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Quantitative multivalent binding model of the structure, size distribution and composition of the casein micelles of cow milk. Int Dairy J 2022. [DOI: 10.1016/j.idairyj.2021.105292] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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22
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The influence of sodium caseinate and β-casein concentrate on the physicochemical properties of casein micelles and the role of tea polyphenols in mediating these interactions. Lebensm Wiss Technol 2022. [DOI: 10.1016/j.lwt.2021.112775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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23
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Sadiq U, Gill H, Chandrapala J. Casein Micelles as an Emerging Delivery System for Bioactive Food Components. Foods 2021; 10:foods10081965. [PMID: 34441743 PMCID: PMC8392355 DOI: 10.3390/foods10081965] [Citation(s) in RCA: 37] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 08/18/2021] [Accepted: 08/20/2021] [Indexed: 12/18/2022] Open
Abstract
Bioactive food components have potential health benefits but are highly susceptible for degradation under adverse conditions such as light, pH, temperature and oxygen. Furthermore, they are known to have poor solubilities, low stabilities and low bioavailabilities in the gastrointestinal tract. Hence, technologies that can retain, protect and enable their targeted delivery are significant to the food industry. Amongst these, microencapsulation of bioactives has emerged as a promising technology. The present review evaluates the potential use of casein micelles (CMs) as a bioactive delivery system. The review discusses in depth how physicochemical and techno-functional properties of CMs can be modified by secondary processing parameters in making them a choice for the delivery of food bioactives in functional foods. CMs are an assembly of four types of caseins, (αs1, αs2, β and κ casein) with calcium phosphate. They possess hydrophobic and hydrophilic properties that make them ideal for encapsulation of food bioactives. In addition, CMs have a self-assembling nature to incorporate bioactives, remarkable surface activity to stabilise emulsions and the ability to bind hydrophobic components when heated. Moreover, CMs can act as natural hydrogels to encapsulate minerals, bind with polymers to form nano capsules and possess pH swelling behaviour for targeted and controlled release of bioactives in the GI tract. Although numerous novel advancements of employing CMs as an effective delivery have been reported in recent years, more comprehensive studies are required to increase the understanding of how variation in structural properties of CMs be utilised to deliver bioactives with different physical, chemical and structural properties.
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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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25
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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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26
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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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27
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黄 新, 李 莎, 高 嵩. [Progress in filters for denoising cryo-electron microscopy images]. BEIJING DA XUE XUE BAO. YI XUE BAN = JOURNAL OF PEKING UNIVERSITY. HEALTH SCIENCES 2021; 53:425-433. [PMID: 33879921 PMCID: PMC8072428 DOI: 10.19723/j.issn.1671-167x.2021.02.033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Indexed: 06/12/2023]
Abstract
Cryo-electron microscopy (cryo-EM) imaging has the unique potential to bridge the gap between cellular and molecular biology. Therefore, cryo-EM three-dimensional (3D) reconstruction has been rapidly developed in recent several years and applied widely in life science research to reveal the structures of large macromolecular assemblies and cellular complexes, which is critical to understanding their functions at all scales. Although the technical breakthrough in recent years, for example, the introduction of the direct detection device (DDD) camera and the development of cryo-EM software tools, made the three cryo-EM pioneers share the 2017 Nobel Prize, several bottleneck problems still exist that hamper the further increase of the resolution of single-particle reconstruction and hold back the application of in situ subnanometer structure determination by cryo-tomography. Radiation damage is still the key limiting factor in cryo-EM. In order to minimize the radiation damage and preserve as much resolution as possible, the imaging conditions of a low dose and weak contrast make cryo-EM images extremely noisy with very low signal-to-noise ratios (SNR), generally about 0.1. The high noise will obscure the fine details in cryo-EM images or reconstructed maps. Thus, a method to reduce the level of noise and improve the resolution has become an important issue. In this paper, we systematically reviewed and compared some robust filters in the cryo-EM field of two aspects, single-particle analysis (SPA) and cryo-electron tomography (cryo-ET), and especially studied their applications, such as, 3D reconstruction, visualization, structural analysis, and interpretation. Conventional approaches to noise reduction in cryo-EM imaging include the use of Gaussian, median, and bilateral filters, among other means. A Gaussian filter selects an appropriate filter kernel to conduct spatial convolution with a noisy image. Although noise with larger standard deviations in cryo-EM images can be suppressed and satisfactory performance is achieved in certain cases, this filter also blurs the images and over-smooths small-scale image features. This is especially detrimental when precise quantitative information needs to be extracted. Unlike a Gaussian filter, a median filter is based on the order statistics of the image and selects the median intensity in a window of the adjacent pixels to denoise the image. Although this filter is robust to outliers, it suffers from aliasing problems that possibly result in incorrect information for cryo-EM structure interpretation. A bilateral filter is a nonlinear filter that performs spatial weighted averaging and is more selective in the pixels allowing to contribute to the weighted sum, excluding the high frequency noise from the smoothing process. Thus, this filter can be used to smooth out noise while maintaining the edge details, which is similar to an anisotropic diffusion filter, and distinct from a Gaussian filter but its utility will be limited when the SNR of a cryo-EM image is very low. Generally, spatial filtering methods have the disadvantage of losing image resolution when reducing noise. A wavelet transform can exploit the wavelet's natural ability to separate a signal from noise at multiple image scales to allow for joint resolution in both the spatial and frequency domains, and thus has the potential to outperform existing methods. The modified wavelet shrinkage filter we developed can offer a remarkable improvement in image quality with a good compromise between detail preservation and noise smoothing. We expect that our review study on different filters can provide benefits to cryo-EM applications and the interpretation of biological structures.
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Affiliation(s)
- 新瑞 黄
- 北京大学基础医学院生物化学与生物物理学系,北京 100191Department of Biochemistry and Biophysics, Peking University School of Basic Medical Sciences, Beijing 100191, China
| | - 莎 李
- 北京大学医学部医学技术研究院,北京 100191Institute of Medical Technology, Peking University Health Science Center, Beijing 100191, China
| | - 嵩 高
- 北京大学医学部医学技术研究院,北京 100191Institute of Medical Technology, Peking University Health Science Center, Beijing 100191, China
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28
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Smith GN. An alternative analysis of contrast-variation neutron scattering data of casein micelles in semi-deuterated milk. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2021; 44:5. [PMID: 33590354 DOI: 10.1140/epje/s10189-021-00023-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Accepted: 01/20/2021] [Indexed: 06/12/2023]
Abstract
Contrast-variation small-angle neutron scattering (CV-SANS) is an excellent way to determine the structure of complex, hierarchical colloids, including self-assembled biological systems. In these experiments, the scattering length density of solvents is changed (by varying the ratio of water or [Formula: see text] and heavy water or [Formula: see text]) to highlight or mask scattering from different components in the system. This approach has been used with synthetic colloids, but it is also increasingly being used in the biological and food sciences. Perhaps the most studied food colloid is the "casein micelle," a self-assembled nanometer-scale colloid of the structure-forming casein protein in milk. CV-SANS data available in the literature are typically analyzed using approximations, which may be invalid for casein micelles, as they have been shown to be sticky spheres. To assess the applicability of this approximate approach, a comprehensive set of CV-SANS data from casein micelles in diluted milk was reanalyzed using a model-based approach, where the casein micelles were formally treated as interacting spheres. In general, the conclusions of the previous study are reproduced, but this new approach makes it more straightforward to distinguish the different components in milk and can be applied to any dairy sample with known form of interparticle interactions, which offers the possibility of studying semi-deuterated milk at its native concentration.
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Affiliation(s)
- Gregory N Smith
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark.
- ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK.
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29
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Lie-Piang A, Leeman M, Castro A, Börjesson E, Nilsson L. Investigating the effect of powder manufacturing and reconstitution on casein micelles using asymmetric flow field-flow fractionation (AF4) and transmission electron microscopy. Food Res Int 2021; 139:109939. [PMID: 33509493 DOI: 10.1016/j.foodres.2020.109939] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 11/12/2020] [Accepted: 11/27/2020] [Indexed: 11/25/2022]
Abstract
Milk powders are commonly used for a variety of food products in which among others the milk proteins add to the properties of the products. Processing of milk can, depending on the processing parameters, change the size and structure of the proteins. These changes can be difficult to measure due to the polydispersity of milk components, which makes it a challenge to obtain direct information about the individual proteins. In this paper, the results from an investigation of casein micelle size,size distribution, and structure in reconstituted skim milk and the comparison with raw and pasteurized skim milk are reported. The investigation used asymmetrical flow field-flow fractionation (AF4) in combination with online UV, multi-angle light scattering (MALS), and refractive index (RI) detection and the results were confirmed by transmission electron microscopy (TEM). The results show that there is a difference in casein micelle size distribution between the differently processed milk samples. The casein micelles of the reconstituted milk were found to have a z-average radius of gyration of 72 nm and the casein micelles in the raw and pasteurized skim milk were 58 and 62 nm respectively. The AF4 and TEM data suggest that the cause of the larger casein micelle size is a layer of aggregated whey proteins associated with the casein micelles surface. Moreover, the TEM investigation showed that a larger proportion of the casein micelles are aggregated in reconstituted milk compared to raw and fresh skim milk. Investigation of the effect of reconstitution time shows that the amount of aggregated casein micelles decreases during the first 20 min of reconstitution. The results show that the AF4-method can provide detailed insights into the reconstitution process and properties of different milk samples. Hence, it can be used as a reference or validation for more indirect methods to track the reconstitution of milk powders.
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Affiliation(s)
- Anouk Lie-Piang
- Tetra Pak Processing Equipment, Ruben Rausings gata, SE-221 86 Lund, Sweden
| | - Mats Leeman
- SOLVE Research and Consultancy AB, Medicon village, SE-223 81 Lund, Sweden
| | - Alejandra Castro
- SOLVE Research and Consultancy AB, Medicon village, SE-223 81 Lund, Sweden
| | - Erik Börjesson
- Tetra Pak Processing Equipment, Ruben Rausings gata, SE-221 86 Lund, Sweden
| | - Lars Nilsson
- Department of Food Technology, Engineering and Nutrition, Faculty of Engineering LTH, Lund University, 221 00 Lund, Sweden.
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30
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Zhang Y, Ren F, Wang P, Liang Q, Peng Y, Song L, Wen P. The influence of yak casein micelle size on rennet-induced coagulation properties. JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE 2021; 101:327-333. [PMID: 32629541 DOI: 10.1002/jsfa.10647] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 05/24/2020] [Accepted: 07/06/2020] [Indexed: 06/11/2023]
Abstract
BACKGROUND Yak milk formed stronger rennet-induced gels if the milk contained smalled casein micelles and a higher concentration of calcium. Also casein gels could formed after a shorter incubation time if the milk contained smalled casein micelles. The objective of this study was to estimate the importance of yak casein micelle size on rennet-induced coagulation properties. RESULTS Three fractions of different-sized, undamaged casein micelles (Ф112.17 ± 0.83 nm, Ф207.13 ± 0.59 nm and Ф269.37 ± 2.89 nm) were obtained by ultracentrifugation. The smallest casein micelles had the highest concentrations of calcium (803.21 ± 8.49 mM), phosphate (445.52 ± 10.66 mM), and κ-casein/total casein (19.45%). Rheological analyses determined the optimal gelation times of small, medium, and large casein micelles to be 9.5 ± 0.5, 10.8 ± 0.5, and 13.3 ± 0.2 min, respectively. Higher κ-casein concentration in the small casein micelles appeared to facilitate their shorter incubation time. Both the faster caseinomacropeptide (CMP) release rate and rennet-induced aggregation rate of small casein micelles contributed to a faster change in turbidity. Furthermore, small casein micelles had the highest elastic modulus (G', 73.21 ± 4.5 Pa) 60 min after the addition of rennet. This was consistent with micro-photographs, which showed that small casein micelles could form a more homogeneous gel, which had smaller pore sizes. Trial cheese manufacture verified that yak cheese containing small casein micelles, formed curd faster and the cheese had higher texture profile analysis (TPA) values for hardness, cohesiveness, and springiness. CONCLUSION This is important information for the optimization of yak cheese industrial production. © 2020 Society of Chemical Industry.
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Affiliation(s)
- Yan Zhang
- College of Food Science and Engineering, Gansu Agricultural University, Lanzhou, China
- College of Food Science & Nutritional Engineering, China Agricultural University, Beijing, China
| | - Fazheng Ren
- College of Food Science & Nutritional Engineering, China Agricultural University, Beijing, China
| | - Pengjie Wang
- College of Food Science & Nutritional Engineering, China Agricultural University, Beijing, China
| | - Qi Liang
- College of Food Science and Engineering, Gansu Agricultural University, Lanzhou, China
| | - Yun Peng
- Treasure of Plateau Yak Dairy Co., Ltd, Lhasa, China
| | - Li Song
- Gansu Hualing Biotechnology Research Center, Lanzhou, China
| | - Pengcheng Wen
- College of Food Science and Engineering, Gansu Agricultural University, Lanzhou, China
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31
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Effect of thawing procedures on the properties of frozen and subsequently thawed casein concentrate. Int Dairy J 2021. [DOI: 10.1016/j.idairyj.2020.104860] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Sruthi L, Srivastava V, Schmidt LE, Deshpande AP, Varughese S. Contributions from microstructural changes to the rheological behavior of casein dispersions during drying. SOFT MATTER 2020; 16:10954-10968. [PMID: 33146222 DOI: 10.1039/d0sm00992j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In several applications, a protein such as casein in dispersion form undergoes multiple processing steps including drying. In this work, the rheological and microstructural features of casein dispersions concentrated by evaporation of the solvent (drying dispersions) were studied in comparison with those of equal concentrations of the as-prepared dispersions without drying. The molecular assembly of casein is affected by drying along with the conformational composition changes in the secondary structures such as α-helix, β-sheets, turns and random structures of the protein. Modeling of the rheological data indicates that these changes also affect the packing of casein molecular assemblies and these molecular assemblies in alkaline dispersions can behave as soft deformable particles. During drying, casein dispersions show prominent shear thinning for concentrations higher than 20 wt% along with the prevalence of α-helices and β-sheets. In comparison, the as-prepared dispersions show different microstructural features, and therefore different rheological responses. A detailed analysis shows that alkalinity changes during drying is the crucial factor controlling the microstructural changes of the soft casein particles and hence the rheology.
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Affiliation(s)
- Lalitha Sruthi
- Department of Chemical Engineering, Indian Institute of Technology, Madras, India.
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33
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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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35
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Kensche A, Pötschke S, Hannig C, Dürasch A, Henle T, Hannig M. Efficacy of mouthrinses with bovine milk and milk protein isolates to accumulate casein in the in situ pellicle. Clin Oral Investig 2020; 24:3871-3880. [DOI: 10.1007/s00784-020-03253-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Accepted: 02/26/2020] [Indexed: 10/24/2022]
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36
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Singh R, Hemar Y, Gilbert EP, Wu Z, Yang Z. Effect of genipin cross-linking on the structural features of skim milk in the presence of ethylenediaminetetraacetic acid (EDTA). Colloids Surf A Physicochem Eng Asp 2020. [DOI: 10.1016/j.colsurfa.2020.125174] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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37
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Reitmaier M, Barbosa B, Sigler S, Heidebrecht HJ, Kulozik U. Impact of different aqueous phases on casein micelles: Kinetics of physicochemical changes under variation of water hardness and diafiltration conditions. Int Dairy J 2020. [DOI: 10.1016/j.idairyj.2020.104776] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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38
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Wu S, Li G, Xue Y, Ashokkumar M, Zhao H, Liu D, Zhou P, Sun Y, Hemar Y. Solubilisation of micellar casein powders by high-power ultrasound. ULTRASONICS SONOCHEMISTRY 2020; 67:105131. [PMID: 32339869 DOI: 10.1016/j.ultsonch.2020.105131] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Revised: 04/11/2020] [Accepted: 04/13/2020] [Indexed: 06/11/2023]
Abstract
High protein milk ingredients, such as micellar casein powder (MCP), exhibit poor solubility upon reconstitution in water, particularly after long-time storage. In this study, ultrasonication (20 kHz, power density of 0.75 W/ml) was used to improve the solubility of aged MCP powders. For all the MCP powders (concentration varying from 0.5 to 5%, and storage of MCP at 50 °C for up to 10 days) it was found that short time ultrasonication (2.5 min) reduced the size of the protein particles from >30 μm to ∼0.1 μm, as measured by light scattering. This resulted in an improvement of solubility (>95%) for all the MCP powders. Cryo-electron microscopy and small x-ray angle scattering showed that the MCP powders dissolved into particles with morphologies and internal structure similar to native casein micelles in bovine milk. SDS-PAGE and RP-HLPC showed that ultrasonication did not affect the molecular weight of the individual casein molecules. Compared to overhead stirring using a 4-blade stirrer, ultrasonication required less than 10 times the drawn electrical energy density to achieve a particle size 10 times smaller.
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Affiliation(s)
- Sinong Wu
- School of Food Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
| | - Guantian Li
- School of Chemical Sciences, The University of Auckland, New Zealand
| | - Yu Xue
- State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China
| | | | - Haibo Zhao
- School of Food Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
| | - Dasong Liu
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province 214122, China
| | - Peng Zhou
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province 214122, China
| | - Yang Sun
- School of Food Science and Technology, and School of Chemical Engineering, Hubei University of Arts and Science, Hubei, Xiangyang 441053, China
| | - Yacine Hemar
- School of Food Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China.
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39
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Interaction between casein and rice glutelin: Binding mechanisms and molecular assembly behaviours. Food Hydrocoll 2020. [DOI: 10.1016/j.foodhyd.2020.105967] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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40
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Zhao D, Sheng B, Li H, Wu Y, Xu D, Li C. Glycation from α-dicarbonyl compounds has different effects on the heat-induced aggregation of bovine serum albumin and β-casein. Food Chem 2020; 340:128108. [PMID: 33010643 DOI: 10.1016/j.foodchem.2020.128108] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 08/24/2020] [Accepted: 09/12/2020] [Indexed: 10/23/2022]
Abstract
α-Dicarbonyl compounds are generated in large amounts during heat treatment in food production. This work compared the influence of glycation by α-dicarbonyl on the hydrothermal aggregation of bovine serum albumin (BSA) and of β-casein (β-CN). Glycation by α-dicarbonyl compounds was found to be more efficient than glycation by glucose in reducing the free amino groups, surface hydrophobicity and isoelectric point of BSA, thus greatly inhibited the hydrothermal aggregation of BSA. In addition, glycation by α-dicarbonyl greatly transformed the rigid BSA aggregates into flexible structures, based on analysis by fluorescence spectrum, transmission electron microscope and small-angle X-ray scattering. In contrast, both the aggregation process and aggregates conformation of β-CN were found to be minimally affected by glycation, possibly due to the intrinsic disorder of β-CN. This work highlights the substantial influences of α-dicarbonyl on dietary proteins during heat treatment depending on the protein structural characteristics.
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Affiliation(s)
- Di Zhao
- Key Laboratory of Meat Processing, MOA, Key Laboratory of Meat Processing and Quality Control, MOE, Jiang Synergetic Innovation Center of Meat Production, Processing and Quality Control, Nanjing Agricultural University, Nanjing 210095, PR China.
| | - Bulei Sheng
- Department of Food Science, Aarhus University, Blichers Allé 20, Tjele 8830, Denmark
| | - Hao Li
- Key Laboratory of Meat Processing, MOA, Key Laboratory of Meat Processing and Quality Control, MOE, Jiang Synergetic Innovation Center of Meat Production, Processing and Quality Control, Nanjing Agricultural University, Nanjing 210095, PR China
| | - Yi Wu
- College of Food Science and Engineering, South China University of Technology, 381 Wushan Road, Tianhe District, Guangzhou 510640, PR China
| | - Dan Xu
- College of Food Science and Engineering, South China University of Technology, 381 Wushan Road, Tianhe District, Guangzhou 510640, PR China
| | - Chunbao Li
- Key Laboratory of Meat Processing, MOA, Key Laboratory of Meat Processing and Quality Control, MOE, Jiang Synergetic Innovation Center of Meat Production, Processing and Quality Control, Nanjing Agricultural University, Nanjing 210095, PR China
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41
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Influence of Microbial Transglutaminase on Physicochemical and Cross-Linking Characteristics of Individual Caseins. Molecules 2020; 25:molecules25173992. [PMID: 32887242 PMCID: PMC7504769 DOI: 10.3390/molecules25173992] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 08/30/2020] [Accepted: 08/31/2020] [Indexed: 11/16/2022] Open
Abstract
The effects of microbial transglutaminase (MTGase) cross-linking on the physicochemical characteristics of individual caseins were investigated. MTGase was used to modify three major individual caseins, namely, κ-casein (κ-CN), αS-casein (αS-CN) and β-casein (β-CN). The SDS-PAGE analysis revealed that MTGase-induced cross-linking occurred during the reaction and that some components with high molecular weights (>130 kDa) were formed from the individual proteins κ-CN, αS-CN and β-CN. Scanning electron microscopy (SEM) and particle size analysis respectively demonstrated that the κ-CN, αS-CN and β-CN particle diameters and protein microstructures were larger and polymerized after MTGase cross-linking. The polymerized κ-CN (~749.9 nm) was smaller than that of β-CN (~7909.3 nm) and αS-CN (~7909.3 nm). The enzyme kinetics results showed KM values of 3.04 × 10−6, 2.37 × 10−4 and 8.90 × 10−3 M for κ-CN, αS-CN and β-CN, respectively, and, furthermore, kcat values of 5.17 × 10−4, 1.92 × 10−3 and 4.76 × 10−2 1/s, for κ-CN, αS-CN and β-CN, respectively. Our results revealed that the cross-linking of β-CN catalyzed by MTGase was faster than that of αS-CN or κ-CN. Overall, the polymers that formed in the individual caseins in the presence of MTGase presented a higher molecular weight and larger particles.
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O'Grady J, Cronin U, Tierney J, Piterina AV, O'Meara E, Wilkinson MG. Gaps in the assortment of rapid assays for microorganisms of interest to the dairy industry. ADVANCES IN APPLIED MICROBIOLOGY 2020; 113:1-56. [PMID: 32948264 PMCID: PMC7426214 DOI: 10.1016/bs.aambs.2020.07.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
This review presents the results of a study into the offering of rapid microbial detection assays to the Irish dairy industry. At the outset, a consultation process was undertaken whereby key stakeholders were asked to compile a list of the key microorganisms of interest to the sector. The resultant list comprises 19 organisms/groups of organisms divided into five categories: single pathogenic species (Cronobacter sakazakii, Escherichia coli and Listeria monocytogenes); genera containing pathogenic species (Bacillus, Clostridium, Listeria, Salmonella; Staphylococcus); broad taxonomic groupings (Coliforms, Enterobacteriaceae, fecal Streptococci, sulfite reducing bacteria/sulfite reducing Clostridia [SRBs/SRCs], yeasts and molds); organisms displaying certain growth preferences or resistance as regards temperature (endospores, psychrotrophs, thermodurics, thermophiles); indicators of quality (total plate count, Pseudomonas spp.). A survey of the rapid assays commercially available for the 19 organisms/groups of organisms was conducted. A wide disparity between the number of rapid tests available was found. Four categories were used to summarize the availability of rapid assays per organism/group of organisms: high coverage (>15 assays available); medium coverage (5-15 assays available); low coverage (<5 assays available); no coverage (0 assays available). Generally, species or genera containing pathogens, whose presence is regulated-for, tend to have a good selection of commercially available rapid assays for their detection, whereas groups composed of heterogenous or even undefined genera of mainly spoilage organisms tend to be "low coverage" or "no coverage." Organisms/groups of organisms with "low coverage" by rapid assays include: Clostridium spp.; fecal Streptococci; and Pseudomonas spp. Those with "no coverage" by rapid assays include: endospores; psychrotrophs; SRB/SRCs; thermodurics; and thermophiles. An important question is: why have manufacturers of rapid microbiological assays failed to respond to the necessity for rapid methods for these organisms/groups of organisms? The review offers explanations, ranging from the technical difficulty involved in detecting as broad a group as the thermodurics, which covers the spores of multiple sporeforming genera as well at least six genera of mesophilic nonsporeformers, to the taxonomically controversial issue as to what constitutes a fecal Streptococcus or SRBs/SRCs. We review two problematic areas for assay developers: validation/certification and the nature of dairy food matrices. Development and implementation of rapid alternative test methods for the dairy industry is influenced by regulations relating to both the microbiological quality standards and the criteria alternative methods must meet to qualify as acceptable test methods. However, the gap between the certification of developer's test systems as valid alternative methods in only a handful of representative matrices, and the requirement of dairy industries to verify the performance of alternative test systems in an extensive and diverse range of dairy matrices needs to be bridged before alternative methods can be widely accepted and adopted in the dairy industry. This study concludes that many important dairy matrices have effectively been ignored by assay developers.
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Affiliation(s)
- John O'Grady
- Dairy Processing Technology Centre, University of Limerick, Limerick, Ireland
| | - Ultan Cronin
- Department of Biological Sciences, University of Limerick, Limerick, Ireland.
| | - Joseph Tierney
- Glanbia Ingredients Ireland, Ballyragget, Co. Kilkenny, Ireland
| | - Anna V Piterina
- Dairy Processing Technology Centre, University of Limerick, Limerick, Ireland
| | - Elaine O'Meara
- Department of Biological Sciences, University of Limerick, Limerick, Ireland
| | - Martin G Wilkinson
- Department of Biological Sciences, University of Limerick, Limerick, Ireland
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44
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Nasuda Y, Ohnuma M, Furusaka M, Hara K, Ishida T. Nanostructure Analysis of Dairy Products. J JPN SOC FOOD SCI 2020. [DOI: 10.3136/nskkk.67.186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
| | | | - Michihiro Furusaka
- Hokkaido University
- National Institute of Advanced Industrial Science and Technology
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45
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Hemar Y, Xu C, Wu S, Ashokkumar M. Size reduction of "reformed casein micelles" by high-power ultrasound and high hydrostatic pressure. ULTRASONICS SONOCHEMISTRY 2020; 63:104929. [PMID: 31945573 DOI: 10.1016/j.ultsonch.2019.104929] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 12/05/2019] [Accepted: 12/13/2019] [Indexed: 06/10/2023]
Abstract
We investigated the effect of ultrasound (US) and high hydrostatic pressure (HHP) on the size of reformed casein micelles (RMCs) obtained by titrating calcium and phosphorous solution into sodium caseinate solutions. Both US and HHP reduced the size of the RMCs. A decrease in size from ~200 nm to ~170 nm when US (20 kHz, 0.46 W/mL) was applied for 30 min; and down to ~85 nm when HHP was applied 500 MPa for 15 min. Electron microscopic analysis showed that the RMCs before and after US are similar to milk native casein micelles, and that HHP extensively disintegrated the RMCs. Small angle X-ray scattering and SDS-PAGE showed that the internal structure of the RMCs as well as the casein molecules are not affected by the US and HHP treatments.
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Affiliation(s)
- Yacine Hemar
- School of Food Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China; The Riddet Institute, Palmerston North, New Zealand.
| | - Cheng Xu
- School of Chemical Sciences. The University of Auckland, New Zealand
| | - Sinong Wu
- School of Food Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China
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Lazzaro F, Bouchoux A, Raynes J, Williams R, Ong L, Hanssen E, Lechevalier V, Pezennec S, Cho HJ, Logan A, Gras S, Gaucheron F. Tailoring the structure of casein micelles through a multifactorial approach to manipulate rennet coagulation properties. Food Hydrocoll 2020. [DOI: 10.1016/j.foodhyd.2019.105414] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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47
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Hettiarachchi CA, Swulius MT, Harte FM. Assessing constituent volumes and morphology of bovine casein micelles using cryo-electron tomography. J Dairy Sci 2020; 103:3971-3979. [PMID: 32171507 DOI: 10.3168/jds.2019-17016] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 01/21/2020] [Indexed: 11/19/2022]
Abstract
We investigated the applicability of cryo-electron tomography as a method to quantify changes in the major constituents of casein micelles (i.e., casein proteins, putative colloidal calcium phosphate nanoclusters, and serum-filled voids and channels) in response to their environment. Skim milk diluted 20-fold in milk serum was used for this study. Tomograms were generated for multiple casein micelles at 2 different pH values (6.7 and 6.0) and pixel intensity thresholds were identified for each constituent. The volume of each constituent was determined using these thresholds and expressed as a fraction of micelle volume. At the given dilution, a significant decrease in the volume fractions of casein proteins (∼37%) and putative colloidal calcium phosphate nanoclusters (∼67%) was observed with the reduction of pH from 6.7 to 6.0. Assessment of casein micelle fraction obtained by ultracentrifugation of corresponding skim milk samples produced comparable results. When using such an approach, the imaging conditions, denoising methods, and thresholding approaches used can all affect the precision of the measurements, but the overall trends in constituent volumes are able to be tracked. The primary advantage of using cryo-electron tomography is that analysis can be done at the level of individual micelles, within a 3-dimensional morphological context. This workflow paves the way for high-throughput exploration of milk micelles and how their environment shapes their composition and structure.
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Affiliation(s)
| | - Matthew T Swulius
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, Hershey 17033.
| | - Federico M Harte
- Department of Food Science, Pennsylvania State University, University Park 16802.
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The adhesion of homogenized fat globules to proteins is increased by milk heat treatment and acidic pH: Quantitative insights provided by AFM force spectroscopy. Food Res Int 2020; 129:108847. [DOI: 10.1016/j.foodres.2019.108847] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Revised: 11/13/2019] [Accepted: 11/18/2019] [Indexed: 02/07/2023]
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49
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Major Role of Voluminosity in the Compressibility and Sol-Gel Transition of Casein Micelle Dispersions Concentrated at 7 °C and 20 °C. Foods 2019; 8:foods8120652. [PMID: 31817715 PMCID: PMC6963684 DOI: 10.3390/foods8120652] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 11/28/2019] [Accepted: 12/03/2019] [Indexed: 11/16/2022] Open
Abstract
The objective of this work is to bring new information about the influence of temperatures (7 °C and 20 °C) on the equation of state and sol-gel transition behavior of casein micelle dispersions. Casein micelle dispersions have been concentrated and equilibrated at different osmotic pressures using equilibrium dialysis at 7 °C and 20 °C. The osmotic stress technique measured the osmotic pressures of the dispersions over a wide range of concentrations. Rheological properties of concentrated dispersions were then characterized, respectively at 7 °C and at 20 °C. The essential result is that casein micelle dispersions are less compressible at 7 °C than at 20 °C and that concentration of sol-gel transition is lower at 7 °C than at 20 °C, with compressibility defined as the inverse to the resistance to the compression, and that is proportional to the cost to remove water from structure. From our interpretations, these two features were fully consistent with a release of soluble β-casein and nanoclusters CaP and an increased casein micelle hydration and apparent voluminosity at 7 °C as compared with 20 °C.
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50
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Peyronel F, Marangoni AG, Pink DA. Using the USAXS technique to reveal the fat globule and casein micelle structures of bovine dairy products. Food Res Int 2019; 129:108846. [PMID: 32036933 DOI: 10.1016/j.foodres.2019.108846] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 11/15/2019] [Accepted: 11/18/2019] [Indexed: 11/26/2022]
Abstract
Cows' milk is a commodity used worldwide to make many dairy products. We have used the ultra small angle X-ray scattering (USAXS) technique to reveal the fat globule and casein micelle structures of some dairy products. USAXS covers the q-range 5 × 10-4 Å-1 < q < 10-1 Å-1, thereby allowing the study of micron-scale structures present in those dairy products. We measured the USAXS intensity, Iq, as a function of the scattering vector magnitude, q, for samples of skim milk, non-homogenized whole milk, homogenized whole milk, half and half and heavy cream, at two temperatures, 7 °C and 45 °C. The data collected from the scattering experiments were fitted using the Unified fit model run under the IRENA software from the Advanced Photon Source, Argonne National Laboratory (Illinois, USA). The fittings were carried out when the data were plotted as log[I(q)] vs log[q]. We observed a combination of linear regions (LRs) and knees. Two parameters of interest were obtained from the fittings, a radius of gyration, Rg, and a Porod exponent, P. Unified fit allowed us to fit up to four structural levels. One of the knees was centered at q ≈ 8 × 10-3 Å-1 for all samples measured at 7 °C, but vanished at 45 °C. Two LRs were identified as being either due to casein micelles (CMs) or to fat globules (FGs). The porod exponent obtained from these LRs allowed us to describe the surface morphology of CMs and FGs. Two of the Rg values gave a rough estimate of the FGs and CMs sizes. FGs were identified for samples of homogenized whole milk, half and half and heavy cream in the q-region 2 × 10-4 < q < 8 × 10-4 Å-1. We found that, in the absence of chymosin, or changes in pH, CaCl2 concentration or temperature changes, skim milk and non-homogenized whole milk displayed a Porod exponent that indicated a behavior characteristic of aggregation. Using computer simulations, we found that, seemingly, bovine CMs spontaneously formed approximately 1-dimensional aggregates possibly analogous to swollen randomly branched polymers.
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Affiliation(s)
| | | | - David A Pink
- Physics Department, St. Francis Xavier University, Antigonish, NS, Canada; Food Science Department, University of Guelph, Guelph, ON, Canada
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