1
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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2
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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3
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Liao M, Li W, Peng L, Li J, Ren J, Li K, Chen F, Hu X, Liao X, Ma L, Ji J. High hydrostatic pressure induced gastrointestinal digestion behaviors of quercetin-loaded casein delivery systems under different calcium concentration. Food Chem X 2024; 21:101177. [PMID: 38434693 PMCID: PMC10904925 DOI: 10.1016/j.fochx.2024.101177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Revised: 01/17/2024] [Accepted: 02/01/2024] [Indexed: 03/05/2024] Open
Abstract
Casein micelle has a structure of outer hydrophilicity and inner hydrophobicity, its typical digestion characteristic is gastric coagulation. Based on calcium content as the key factor to control this process, high hydrostatic pressure (HHP) was firstly used to modify the micelle structure by mediating the tight connection between casein molecules themselves and with colloidal calcium, then the quercetin-loaded delivery systems were prepared. And in order to investigate the effect of exogenous calcium, calcium chloride was added for digestion. The results indicated that HHP broke the limitation of casein micelles as delivery carriers for hydrophobic components and increased the EE from 51.18 ± 3.07 % to 76.17 ± 3.41 %. During gastric digestion, higher pressure and exogenous calcium synergistically increased the clotting ability and inhibited the release of quercetin. In the small intestine, curds decomposed more slowly under higher pressure and calcium concentration, so the degradation of quercetin was effectively inhibited.
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Affiliation(s)
| | | | - Lu Peng
- College of Food Science and Nutritional Engineering, National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture and Rural Affairs, Beijing 100083, China
| | - Jiahao Li
- College of Food Science and Nutritional Engineering, National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture and Rural Affairs, Beijing 100083, China
| | - Jinbo Ren
- College of Food Science and Nutritional Engineering, National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture and Rural Affairs, Beijing 100083, China
| | - Kaixin Li
- College of Food Science and Nutritional Engineering, National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture and Rural Affairs, Beijing 100083, China
| | - Fang Chen
- College of Food Science and Nutritional Engineering, National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture and Rural Affairs, Beijing 100083, China
| | - Xiaosong Hu
- College of Food Science and Nutritional Engineering, National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture and Rural Affairs, Beijing 100083, China
| | - Xiaojun Liao
- College of Food Science and Nutritional Engineering, National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture and Rural Affairs, Beijing 100083, China
| | - Lingjun Ma
- College of Food Science and Nutritional Engineering, National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture and Rural Affairs, Beijing 100083, China
| | - Junfu Ji
- College of Food Science and Nutritional Engineering, National Engineering Research Center for Fruit and Vegetable Processing, China Agricultural University, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture and Rural Affairs, Beijing 100083, China
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4
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Holt C, Carver JA. Invited review: Modeling milk stability. J Dairy Sci 2024:S0022-0302(24)00625-8. [PMID: 38522835 DOI: 10.3168/jds.2024-24779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [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 neutral pH or above but decreases as 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, UK..
| | - J A Carver
- Research School of Chemistry, The Australian National University, Acton, ACT 2601, Australia..
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5
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Zhang J, Liu D, Xie Y, Yuan J, Wang K, Tao X, Hemar Y, Regenstein JM, Liu X, Zhou P. Gastrointestinal digestibility of micellar casein dispersions: Effects of caprine vs bovine origin, and partial colloidal calcium depletion using in vitro digestion models for the adults and elderly. Food Chem 2023; 416:135865. [PMID: 36905711 DOI: 10.1016/j.foodchem.2023.135865] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 02/27/2023] [Accepted: 03/02/2023] [Indexed: 03/08/2023]
Abstract
In vitro coagulation and digestion of caprine and bovine micellar casein concentrate (MCC) with or without partial colloidal calcium depletion (deCa) were studied under simulated adult and elderly conditions. Gastric clots were smaller and looser for caprine than bovine MCC, and were further looser with deCa and under elderly condition for both caprine and bovine MCC. Casein hydrolysis and concomitant formation of large peptides was faster for caprine than bovine MCC, and with deCa and under adult condition for caprine and bovine MCC. Formation of free amino groups and small peptides were faster for caprine MCC, and with deCa and under adult condition. Upon intestinal digestion, proteolysis occurred rapidly, and was faster under adult condition, but showed less differences with increasing digestion between caprine and bovine MCC, and with and without deCa. These results suggested weakened coagulation and greater digestibility for caprine MCC and MCC with deCa under both conditions.
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Affiliation(s)
- Jie Zhang
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province 214122, China
| | - Dasong Liu
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province 214122, China.
| | - Yunqi Xie
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province 214122, China
| | - Jiajie Yuan
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province 214122, China
| | - Keyu Wang
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province 214122, China
| | - Xiumei Tao
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province 214122, China
| | - Yacine Hemar
- Institute of Advanced Studies, Shenzhen University, Shenzhen, Guangdong Province 518060, China
| | - Joe M Regenstein
- Department of Food Science, Cornell University, Ithaca, NY 14853-7201, USA
| | - Xiaoming 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
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6
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Oka D, Ono W, Tamaki S, Noguchi T, Takano K. Effects of the thermal denaturation degree of a whey protein isolate on the strength of acid milk gels and the dissociation of κ-casein. J DAIRY RES 2022; 89:1-5. [PMID: 35236515 DOI: 10.1017/s0022029922000103] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In this study, the effects of the degree of thermal denaturation of whey protein (WP) added to milk on the dissociation of κ-casein from casein micelles were investigated, since they are related to the strength of acid milk gel and its factors. Acid milk gels were prepared by heating thermally denatured WP isolate (WPI) and undenatured milk mixtures and treating them with glucono-δ-lactone as a coagulant. The strength of these gels was negatively correlated with the WPI denaturation degree and strongly positively correlated with the extent of κ-casein dissociation from casein micelles. This behavior was ascribed to the fact that α-lactalbumin (α-La) and β-lactoglobulin (β-Lg) contained in WPI denatured after heating and engaged in disulfide bond formation with each other. With an increase in the degree of denaturation and disulfide bond formation, the bonding between β-lactoglobulin and κ-casein was suppressed to decrease the amount of κ-casein-WPI complexes. When β-Lg forms SS bonds with α-La, the number of highly reactive, free SH groups decreases, which complicates the formation of SS bridges between β-Lg and κ-casein. Thus, the denaturation degree of WPI largely determined the degree of κ-casein dissociation from casein micelles and, consequently, the strength of acid milk gels. Adding WP to milk increases the strength of acid milk gel, and it can be controlled by changing the degree of thermal denaturation of the WP. Furthermore, it was clarified for the first time that the dissociation of κ-casein from casein micelles influences this effect. Further studies are needed to elucidate the structural features of κ-casein-dissociated micelles.
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Affiliation(s)
- Daiki Oka
- Department of Agricultural Chemistry, Tokyo University of Agriculture, Tokyo156-8502, Japan
| | - Wataru Ono
- Food Processing Technology Center, Faculty of Applied Bioscience, Tokyo University of Agriculture, Tokyo156-8502, Japan
| | - Shojiro Tamaki
- Milk Science Research Institute, Megmilk Snow Brand Co., Ltd., Saitama350-1165, Japan
| | - Tomohiro Noguchi
- Food Processing Technology Center, Faculty of Applied Bioscience, Tokyo University of Agriculture, Tokyo156-8502, Japan
| | - Katsumi Takano
- Department of Agricultural Chemistry, Tokyo University of Agriculture, Tokyo156-8502, Japan
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7
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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: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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8
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Han R, Shi R, Yu Z, Ho H, Du Q, Sun X, Wang J, Jiang H, Fan R, Yang Y. Distribution and variation in proteins of casein micellar fractions response to heat-treatment from five dairy species. Food Chem 2021; 365:130640. [PMID: 34329874 DOI: 10.1016/j.foodchem.2021.130640] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 06/02/2021] [Accepted: 07/17/2021] [Indexed: 02/04/2023]
Abstract
Casein micelles (CMs) contribute to the physicochemical properties and stability of milk. However, how the proteome of CMs changes following heat treatment has not been elucidated. Here, changes in the proteins of CMs in samples of Holstein, buffalo, yak, goat, and camel milk following heat treatment were investigated using a LC-MS/MS approach. According to the hierarchical clustering results, Holstein, yak, and buffalo milk samples had similar CMs protein components, followed by goat and camel milk samples. Changes in lipoprotein lipase and α-lactalbumin in CMs were dependent on the intensity of heat treatment and were similar among the studied species, whereas changes in κ-casein, lactoferrin, and apolipoprotein A-I differed among different types of milk. These results provide information on the distribution and variations of the proteomes of CMs following heat treatment, which will assist in the identification of proteins that are dissociated and attached to CMs from different dairy species during heat treatment.
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Affiliation(s)
- Rongwei Han
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Runjia Shi
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Zhongna Yu
- Haidu College.Qingdao Agricultural University, Laiyang 265200, Shandong, China.
| | - Harvey Ho
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand.
| | - Qijing Du
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Xueheng Sun
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Jun Wang
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Hongning Jiang
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Rongbo Fan
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Yongxin Yang
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
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9
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Holt C. A quantitative calcium phosphate nanocluster model of the casein micelle: the average size, size distribution and surface properties. Eur Biophys J 2021; 50:847-866. [PMID: 33866398 DOI: 10.1007/s00249-021-01533-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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10
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Lund P, Nielsen SB, Nielsen CF, Ray CA, Lund MN. Impact of UHT treatment and storage on liquid infant formula: Complex structural changes uncovered by centrifugal field-flow fractionation with multi-angle light scattering. Food Chem 2021; 348:129145. [PMID: 33524693 DOI: 10.1016/j.foodchem.2021.129145] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Revised: 12/20/2020] [Accepted: 01/17/2021] [Indexed: 01/27/2023]
Abstract
Protein modifications in liquid infant formula (IF) have been widely studied, but distinguishing between heat- and storage-induced structural changes remains challenging. A generic liquid IF was subjected to direct or indirect UHT treatment and stored at 40 °C up to 180 days. Colour and pH were monitored and structural changes were characterised by dynamic light scattering, SDS-PAGE and centrifugal field-flow fractionation (FFF) coupled with multi-angle light scattering (MALS) and UV detectors to evaluate whether heat-induced differences would level out during storage. Both direct- and indirect UHT treatment led to structural changes, where the higher heat load of the indirect UHT treatment caused more pronounced changes. Indications were that storage-induced changes in pH, browning and non-reducible cross-links were not dependent on UHT treatment. However, FFF-MALS-UV analysis allowed characterisation of complex aggregates, where structural changes continued to be most pronounced in indirect UHT treated samples, and different storage-induced aggregation behaviour was observed.
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Affiliation(s)
- Pernille Lund
- Department of Food Science, Faculty of Science, University of Copenhagen, Rolighedsvej 26, 1958 Frederiksberg C, Denmark
| | - Søren Bang Nielsen
- Arla Foods Ingredients Group P/S - Discover R&D, Department of Technology and Functionality, Sønderupvej 26, 6920 Videbæk, Denmark
| | - Christian Fiil Nielsen
- Arla Foods Ingredients Group P/S - Milk Powder Innovation, Sønderhøj 10, 8260 Viby J, Denmark
| | - Colin A Ray
- Arla Foods Ingredients Group P/S - Discover R&D, Department of Technology and Functionality, Sønderupvej 26, 6920 Videbæk, Denmark
| | - Marianne N Lund
- Department of Food Science, Faculty of Science, University of Copenhagen, Rolighedsvej 26, 1958 Frederiksberg C, Denmark; Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark.
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11
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Choi I, Zhong Q. Gluconic acid as a chelator to improve clarity of skim milk powder dispersions at pH 3.0. Food Chem 2020; 344:128639. [PMID: 33229152 DOI: 10.1016/j.foodchem.2020.128639] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 10/27/2020] [Accepted: 11/11/2020] [Indexed: 01/08/2023]
Abstract
Clear acidic protein beverages have a niche market. Acidification of skim milk powder (SMP) dispersions to pH 3.0 using citric acid (CA) lowers turbidity but the dispersion remains translucent. The present study aimed at comparing physicochemical properties of 5% w/v SMP dispersions acidified to pH 3.0 using chelating gluconic acid (GA) and CA and non-chelating hydrochloric acid. GA was the most effective in reducing the dispersion turbidity to 394 NTU at pH 3.0, which was further reduced to 248 NTU after heating at 90 °C for 2 min resulting in transparent dispersions. The better chelating ability of GA than CA was supported by the higher extent of dissolved CCP in serum phase. The aggregation of dissociated caseins was not observed for the GA treatment based on transmission electron microscopy. The findings from this study may be used to produce clear casein-based protein beverages.
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Affiliation(s)
- Inseob Choi
- Department of Food Science, The University of Tennessee, Knoxville 37996, USA
| | - Qixin Zhong
- Department of Food Science, The University of Tennessee, Knoxville 37996, USA.
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12
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Kieferle I, Hiller K, Kulozik U, Germann N. Rheological properties of fresh and reconstituted milk protein concentrates under standard and processing conditions. J Colloid Interface Sci 2018; 537:458-464. [PMID: 30469114 DOI: 10.1016/j.jcis.2018.11.048] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Revised: 11/12/2018] [Accepted: 11/12/2018] [Indexed: 10/27/2022]
Abstract
As the processability of fresh and reconstituted milk protein concentrates crucially depends on their rheological properties, a considerable amount of studies focuses on this topic. By means of a direct comparison, we are the first to clearly show that distinct rheological differences can exist between fresh and reconstituted milk protein concentrates under standard and processing conditions. We show that reconstituted milk protein concentrates made from commercial milk protein powders exhibit higher viscosities than fresh ones. Furthermore, we found that during intense shearing, the reconstituted milk protein concentrates undergo a loss of structure, which manifests itself in a significant viscosity decrease. The inverse effect can be observed for fresh milk protein concentrates. Besides these differences, the reconstituted milk protein concentrates exhibit gel-like properties above a certain protein content. We attribute these observations to protein-protein interactions in the milk protein powder, which are induced by manufacturing and/or storing conditions. Our results demonstrate that rheological properties of fresh and reconstituted milk protein concentrates are quantitatively not invariably interchangeable. Thus, the purpose of this article is to emphasize the necessity for researchers and engineers to take into account the rheological particularities of different milk protein concentrates prior to usage.
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Affiliation(s)
- I Kieferle
- Food and Bioprocess Engineering, School of Life Sciences Weihenstephan, Technical University of Munich, 85354 Freising, Germany.
| | - K Hiller
- Food and Bioprocess Engineering, School of Life Sciences Weihenstephan, Technical University of Munich, 85354 Freising, Germany
| | - U Kulozik
- Food and Bioprocess Engineering, School of Life Sciences Weihenstephan, Technical University of Munich, 85354 Freising, Germany
| | - N Germann
- Fluid Dynamics of Complex Biosystems, School of Life Sciences Weihenstephan, Technical University of Munich, 85354 Freising, Germany
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