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Zhang S, Sun Y, Xie Q, Jiang Y, Cheng J. Effect of different salts on the foaming properties of model protein systems for infant formula. J Dairy Sci 2024; 107:2668-2680. [PMID: 37863295 DOI: 10.3168/jds.2023-24080] [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: 08/11/2023] [Accepted: 09/29/2023] [Indexed: 10/22/2023]
Abstract
This multiscale study aimed to evaluate the effects of different salts (NaCl, KCl, MgCl2, and CaCl2) on the foaming capacity (FC) and foam stability (FS) of model protein systems (MPS) for infant formula via changes in surface and structural properties. Our results showed that the FC and FS of MPS were increased with the addition of NaCl, KCl, and MgCl2, whereas CaCl2 significantly decreased FC (79.5 ± 10.6%) and increased FS (93.2 ± 2.2%). The surface hydrophobicity was increased and the net charge and surface tension were reduced after the addition of salts. Structural analysis revealed the reduction of intensity of intrinsic fluorescence spectroscopy and UV absorption, and the conversion of α-helix into β-strand, which was attributed to protein agglomeration. Additionally, MgCl2 and CaCl2 exhibited larger size and lower net charge compared with NaCl and KCl, indicating a greater ability to bind to charged amino acids and form larger aggregates. Correlation analysis indicated that FC was positively related to adsorbed protein and β-turn and negatively correlated with particle size. In addition, FS showed a positive correlation with β-strand, apparent viscosity, and zeta potential. However, it exhibited a negative correlation with β-turn, α-helix, and sulfhydryl content. These results provide a theoretical reference for further understanding of the effect of salts on the foaming properties of MPS.
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Affiliation(s)
- Siyu Zhang
- College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China
| | - Yuxue Sun
- College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China
| | - Qinggang Xie
- College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China; Feihe Dairy Company, Heilongjiang 164899, China
| | - Yunqing Jiang
- College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
| | - Jianjun Cheng
- College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
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2
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Qiao X, Miller R, Schneck E, Sun K. Effect of surfactants on the interfacial viscoelasticity and stability of silk fibroin at different oil-water interfaces. JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE 2024; 104:2928-2936. [PMID: 38029349 DOI: 10.1002/jsfa.13185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2023] [Revised: 11/16/2023] [Accepted: 11/27/2023] [Indexed: 12/01/2023]
Abstract
BACKGROUND The biocompatible amphiphilic silk fibroin, extracted from domesticated silkworms, can adsorb at the oil-water interface and form elastic interfacial layers. In this study, three surfactants (cationic cetyltrimethylammonium bromide, the nonionic polyoxyethylene sorbitan monolaurate, and the anionic sodium dodecyl sulfate) were selected to investigate, through interfacial shear rheology, the influences of surfactants on the interfacial viscoelasticity and stability of silk fibroin at the interfaces between water and two different oils. RESULTS The presence of surfactant prolongs the equilibration time and enhances the interfacial elastic modulus and toughness of the interfacial silk fibroin layers, especially at the nonpolar dodecane-water interface. However, when the surfactant exceeds a critical concentration, the shear modulus and stability of interfacial silk fibroin layers begin to decrease due to the competitive adsorption of surfactant molecules and the weakening of the protein network. Owing to electrostatic interactions, the ionic surfactants cetyltrimethylammonium bromide and sodium dodecyl sulfate can form more hydrophobic complexes with silk fibroin, which results in higher shear moduli than for silk fibroin and silk fibroin-polyoxyethylene sorbitan monolaurate mixture. CONCLUSION Both the surfactant type and oil polarity play important roles in the adsorption, shear viscoelasticity, and stability of silk fibroin at the oil-water interface. Enhanced interactions between a silk fibroin-surfactant mixture and the oil phase delay the equilibration of the adsorption layers but strengthen the stability of interfacial layers. © 2023 Society of Chemical Industry.
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Affiliation(s)
- Xiuying Qiao
- State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Reinhard Miller
- Department of Physics, Technical University of Darmstadt, Darmstadt, Germany
| | - Emanuel Schneck
- Department of Physics, Technical University of Darmstadt, Darmstadt, Germany
| | - Kang Sun
- State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China
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3
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Paul B, Furst EM, Lenhoff AM, Wagner NJ, Teixeira SCM. Combined Effects of Pressure and Ionic Strength on Protein-Protein Interactions: An Empirical Approach. Biomacromolecules 2024; 25:338-348. [PMID: 38117685 DOI: 10.1021/acs.biomac.3c01001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2023]
Abstract
Proteins are exposed to hydrostatic pressure (HP) in a variety of ecosystems as well as in processing steps such as freeze-thaw, cell disruption, sterilization, and homogenization, yet pressure effects on protein-protein interactions (PPIs) remain underexplored. With the goal of contributing toward the expanded use of HP as a fundamental control parameter in protein research, processing, and engineering, small-angle X-ray scattering was used to examine the effects of HP and ionic strength on ovalbumin, a model protein. Based on an extensive data set, we develop an empirical method for scaling PPIs to a master curve by combining HP and osmotic effects. We define an effective pressure parameter that has been shown to successfully apply to other model protein data available in the literature, with deviations evident for proteins that do not follow the apparent Hofmeister series. The limitations of the empirical scaling are discussed in the context of the hypothesized underlying mechanisms.
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Affiliation(s)
- Brian Paul
- Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, United States
- NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States
| | - Eric M Furst
- Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, United States
| | - Abraham M Lenhoff
- Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, United States
| | - Norman J Wagner
- Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, United States
| | - Susana C M Teixeira
- Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, United States
- NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States
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4
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Adsorption, Surface Viscoelasticity, and Foaming Properties of Silk Fibroin at the Air/Water Interface. COLLOIDS AND INTERFACES 2022. [DOI: 10.3390/colloids6030040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Like other proteins, the natural silk fibroin (SF) extracted from domesticated silkworms can adsorb at the air/water interface and stabilize foam due to its amphiphilic character and surface activity. At the interface, the adsorbed SF molecules experience structural reorganization and form water-insoluble viscoelastic films, which protect foam bubbles from coalescence and rupture. The solution conditions, such as protein concentration, pH, and additives, have significant influences on the molecular adsorption, layer thickness, interfacial mechanical strength, and, thus, on the foaming properties of SF. The understanding of the relationship between the interfacial adsorption, surface viscoelasticity, and foaming properties of SF is very important for the design, preparation, and application of SF foams in different fields.
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5
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Zhan F, Youssef M, Shah BR, Li J, Li B. Overview of foam system: Natural material-based foam, stabilization, characterization, and applications. Food Hydrocoll 2022. [DOI: 10.1016/j.foodhyd.2021.107435] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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6
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Zhang T, Zhang M, Gong P, Jiang H, Liu J, Liu X. Ions-induced ovalbumin foaming properties enhancement: Structural, rheological, and molecular aggregation mechanism. Food Hydrocoll 2022. [DOI: 10.1016/j.foodhyd.2021.107221] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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7
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On the foaming properties of plant proteins: Current status and future opportunities. Trends Food Sci Technol 2021. [DOI: 10.1016/j.tifs.2021.10.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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8
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Carrera Sánchez C, Rodríguez Patino JM. Contribution of the engineering of tailored interfaces to the formulation of novel food colloids. Food Hydrocoll 2021. [DOI: 10.1016/j.foodhyd.2021.106838] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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9
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Effects of protein concentration, pH, and NaCl concentration on the physicochemical, interfacial, and emulsifying properties of β-conglycinin. Food Hydrocoll 2021. [DOI: 10.1016/j.foodhyd.2021.106784] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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10
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Interfacial properties of milk proteins: A review. Adv Colloid Interface Sci 2021; 295:102347. [PMID: 33541692 DOI: 10.1016/j.cis.2020.102347] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 12/14/2020] [Accepted: 12/14/2020] [Indexed: 12/22/2022]
Abstract
The interfacial properties of dairy proteins are of great interest to the food industry. Food manufacturing involves various environmental conditions and multiple processes that significantly alter the structure and colloidal stability of food materials. The effects of concentration, pH, heat treatment, addition of salts etc., have considerable influence on the surface activity of proteins and the mechanical properties of the interfacial protein films. Studies to date have established some understanding of the links between environmental and processing related parameters and their impacts on interfacial behavior. Improvement in knowledge may allow better design of interfacial protein structures for different food applications. This review examines the effects of environmental and processing conditions on the interfacial properties of dairy proteins with emphasis on interfacial tension dynamics, dilatational and surface shear rheological properties. The most commonly used surface analytical techniques along with relevant methods are also addressed.
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11
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Kubbutat P, Leitão L, Kulozik U. Stability of Foams in Vacuum Drying Processes. Effects of Interactions between Sugars, Proteins, and Surfactants on Foam Stability and Dried Foam Properties. Foods 2021; 10:foods10081876. [PMID: 34441652 PMCID: PMC8392398 DOI: 10.3390/foods10081876] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 08/05/2021] [Accepted: 08/11/2021] [Indexed: 01/16/2023] Open
Abstract
The hypothesis was that saccharides mediate interactions between surface-active components and that this will have an impact on foam decay during the drying process. Static light scattering was performed to determine changes in interactions between the foam stabilizer on a molecular level. Furthermore, pendant drop and oscillating drop measurements were performed to examine the surface tension and surface rheology. Foams were dried in conventional dryers as well as microwave-supported vacuum dryers. Final foam properties were determined. It was shown that the addition of sugars, often added as protective substances for sensitive organic molecules, resulted in lower repulsion between different types of surface-active components, namely polysorbate 80 and β-lactoglobulin (β-lg). Differences in impact of the types of sugars and between different types of surfactant, protein, and small molecules were observed influencing the foam decay behavior. The interfacial properties of polysorbate 80 and β-lg were influenced by the type of the used sugars. The surface elasticity of protein stabilized surfaces was higher compared to that of polysorbate stabilized systems. Protein stabilized systems remained more stable compared to polysorbate systems, which was also affected by the used saccharide. Overall, a correlation between molecular interactions and foam decay behavior was found.
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12
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Off-label use of plastic syringes with silicone oil for intravenous infusion bags of antibodies. Eur J Pharm Biopharm 2021; 166:205-215. [PMID: 34237379 DOI: 10.1016/j.ejpb.2021.07.001] [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: 04/06/2021] [Revised: 06/24/2021] [Accepted: 07/02/2021] [Indexed: 11/24/2022]
Abstract
The formation of particulates in post-manufacture biopharmaceuticals continues to be a major concern in medical treatment. This study was designed to evaluate the content of micro-sized particles using flow imaging of antibodies in intravenous infusion bags. Intravenous immunoglobulin (IVIG) and Avastin® were selected as model drugs and plastic syringes with and without silicone oil (SO) were used to transfer the drugs into the bags (0.9% saline or 5% dextrose). Antibodies exposed to SO had significantly increased levels of microparticles in both diluents, suggesting SO accelerates particle formation, especially at a higher antibody concentration. Even before the drop stress, their count exceeded the USP guideline. Dropping the bags in the presence of SO produced larger microparticles. Meanwhile, air bubbles were retained longer in saline suggesting more protein film formation on its air-water interface. Overall, both drugs were conformationally stable and produced less particles in dextrose than in saline.
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Kubbutat P, Kulozik U. Interactions of sugar alcohol, di-saccharides and polysaccharides with polysorbate 80 as surfactant in the stabilization of foams. Colloids Surf A Physicochem Eng Asp 2021. [DOI: 10.1016/j.colsurfa.2021.126349] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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14
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Doshi N, Giddings J, Luis L, Wu A, Ritchie K, Liu W, Chan W, Taing R, Chu J, Sreedhara A, Kannan A, Kei P, Shieh I, Graf T, Hu M. A Comprehensive Assessment of All-Oleate Polysorbate 80: Free Fatty Acid Particle Formation, Interfacial Protection and Oxidative Degradation. Pharm Res 2021; 38:531-548. [PMID: 33713012 DOI: 10.1007/s11095-021-03021-z] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 02/22/2021] [Indexed: 10/21/2022]
Abstract
PURPOSE Enzymatic polysorbate (PS) degradation and resulting free fatty acid (FFA) particles are detrimental to biopharmaceutical drug product (DP) stability. Different types and grades of polysorbate have varying propensity to form FFA particles. This work evaluates the homogenous all-oleate (AO) PS80 alongside heterogeneous PS20 and PS80 grades in terms its propensity to form FFA particles and other important attributes like interfacial protection and oxidation susceptibility. METHODS FFA particle formation rates were compared by degrading PS using non-immobilized hydrolases and fast degrading DP formulations. Interfacial protection of monoclonal antibodies (mAbs) was assessed by agitation studies in saline using non-degraded and degraded PS. Several antioxidants were assessed for their ability to mitigate AO PS80 oxidation and subsequent mAb oxidation by a 40°C placebo stability study and a 2, 2'-Azobis (2-amidinopropane) dihydrochloride stress model, respectively. RESULTS Visible and subvisible particles were significantly delayed in AO PS80 formulations compared with heterogeneous PS20 and PS80 formulations. Non-degraded AO PS80 was less protective of mAbs against the air-water interface compared with heterogeneous PS20. Interfacial protection by AO PS80 improved upon degradation owing to high surface activity of FFAs. Diethylenetriaminepentaacetic acid (DTPA) completely mitigated AO PS80 oxidation unlike L-methionine and N-Acetyl-DL-Tryptophan. However, DTPA did not mitigate radical mediated mAb oxidation. CONCLUSION AO PS80 is a promising alternative to reduce FFA particle formation compared with other PS types and grades. However, limitations observed here---such as lower protection against interfacial stresses and higher propensity for oxidation---need to be considered in assessing the risk/benefit ratio in using AO PS80.
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Affiliation(s)
- Nidhi Doshi
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA.
| | - Jamie Giddings
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Lin Luis
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Arthur Wu
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Kyle Ritchie
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Wenqiang Liu
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Wayman Chan
- Analytical Operations, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Rosalynn Taing
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Jeff Chu
- Analytical Operations, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Alavattam Sreedhara
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Aadithya Kannan
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Pervina Kei
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Ian Shieh
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
| | - Tobias Graf
- Pharma Technical Development Analytics, Roche Diagnostics GmbH, Nonnenwald 2, 82377, Penzberg, Germany
| | - Mark Hu
- Pharmaceutical Development, Genentech Inc., 1 DNA Way, South San Francisco, California, 94080, USA
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15
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Keppler JK, Heyse A, Scheidler E, Uttinger MJ, Fitzner L, Jandt U, Heyn TR, Lautenbach V, Loch JI, Lohr J, Kieserling H, Günther G, Kempf E, Grosch JH, Lewiński K, Jahn D, Lübbert C, Peukert W, Kulozik U, Drusch S, Krull R, Schwarz K, Biedendieck R. Towards recombinantly produced milk proteins: Physicochemical and emulsifying properties of engineered whey protein beta-lactoglobulin variants. Food Hydrocoll 2021. [DOI: 10.1016/j.foodhyd.2020.106132] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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16
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Influence of salt addition on the surface and foaming properties of silk fibroin. Colloids Surf A Physicochem Eng Asp 2021. [DOI: 10.1016/j.colsurfa.2020.125621] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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17
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Braun L, Kühnhammer M, von Klitzing R. Stability of aqueous foam films and foams containing polymers: Discrepancies between different length scales. Curr Opin Colloid Interface Sci 2020. [DOI: 10.1016/j.cocis.2020.08.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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18
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Kannan A, Shieh IC, Hristov P, Fuller GG. In-Use Interfacial Stability of Monoclonal Antibody Formulations Diluted in Saline i.v. Bags. J Pharm Sci 2020; 110:1687-1692. [PMID: 33141046 DOI: 10.1016/j.xphs.2020.10.036] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2020] [Revised: 09/29/2020] [Accepted: 10/12/2020] [Indexed: 11/16/2022]
Abstract
The use of monoclonal antibodies (mAbs) for the treatment of a variety of diseases is rapidly growing each year. Many mAbs are administered intravenously using i.v. bags containing 0.9% NaCl (normal saline). We studied the aggregation propensity of these antibody solutions in saline and compared it with a low ionic strength formulation buffer. The mAb studied in this work is prone to aggregate, and is known to form a viscoelastic network at the air-solution interface. We observed that this interfacial elasticity increased when formulated in saline. In the bulk, the mAbs exhibited a tendency to self-associate that was higher in saline. We also studied the aggregation of the mAbs in the presence of polysorbate-20, typically added to formulations to mitigate interfacial aggregation. We observed that with surfactants, the presence of salt in the buffer led to a greater mAb adsorption at the interface and resulted in the formation of more particulate aggregates. Our results show that the addition of salt to the buffer led to differences in the interfacial aggregation in mAb formulations, showing that stress studies used to screen for mAb aggregation intended for i.v. administration should be performed in conditions representative of their intended route of administration.
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Affiliation(s)
- Aadithya Kannan
- Stanford University, Stanford, CA, USA; Genentech, Inc., South San Francisco, CA, USA
| | - Ian C Shieh
- Genentech, Inc., South San Francisco, CA, USA
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19
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Dachmann E, Nobis V, Kulozik U, Dombrowski J. Surface and foaming properties of potato proteins: Impact of protein concentration, pH value and ionic strength. Food Hydrocoll 2020. [DOI: 10.1016/j.foodhyd.2020.105981] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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20
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β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 4. Impact on the Stability of Foam Films and Foams. MINERALS 2020. [DOI: 10.3390/min10070636] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The complexity and high sensitivity of proteins to environmental factors give rise to a multitude of variables, which affect the stabilization mechanisms in protein foams. Interfacial and foaming properties of proteins have been widely studied, but the reported unique effect of pH, which can be of great interest to applications, has been investigated to a lesser extent. In this paper, we focus on the impact of pH on the stability of black foam films and corresponding foams obtained from solutions of a model globular protein—the whey β-lactoglobulin (BLG). Foam stability was analyzed utilizing three characteristic parameters (deviation time, transition time and half-lifetime) for monitoring the foam decay, while foam film stability was measured in terms of the critical disjoining pressure of film rupture. We attempt to explain correlations between the macroscopic properties of a foam system and those of its major building blocks (foam films and interfaces), and thus, to identify structure-property relationships in foam. Good correlations were found between the stabilities of black foam films and foams, while relations to the properties of adsorption layers appeared to be intricate. That is because pH-dependent interfacial properties of proteins usually exhibit an extremum around the isoelectric point (pI), but the stability of BLG foam films increases with increasing pH (3–7), which is well reflected in the foam stability. We discuss the possible reasons behind these intriguingly different behaviors on the basis of pH-induced changes in the molecular properties of BLG, which seem to be determining the mechanism of film rupture at the critical disjoining pressure.
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Richert ME, Gochev GG, Braunschweig B. Specific Ion Effects of Trivalent Cations on the Structure and Charging State of β-Lactoglobulin Adsorption Layers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:11299-11307. [PMID: 31398284 DOI: 10.1021/acs.langmuir.9b01803] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The properties of proteins at interfaces are important to many processes as well as in soft matter materials such as aqueous foam. Particularly, the protein interfacial behavior is strongly linked to different factors like the solution pH or the presence of electrolytes. Here, the nature of the electrolyte ions can significantly modify the interfacial properties of proteins. Therefore, molecular level studies on interfacial structures and charging states are needed. In this work, we addressed the effects of Y3+ and Nd3+ cations on the adsorption of the whey protein β-lactoglobulin (BLG) at air-water interfaces as the function of electrolyte concentration. Both cations caused very similar but dramatic changes at the interface and in the bulk solution. Here, measurements of the electrophoretic mobility and with vibrational sum-frequency generation (SFG) spectroscopy were applied and consistently showed a reversal of the BLG net charge at remarkably low ion concentrations of 30 (bulk) and 40 (interface) μM of Y3+ or Nd3+ for a BLG concentration of 15 μM. SFG spectra of carboxylate stretching vibrations from Asp or Glu residues of interfacial BLG showed significant changes in the resonance frequency, which we associate to specific and efficient binding of Y3+ or Nd3+ ions to the proteins carboxylate groups. Characteristic reentrant condensation for BLG moieties with bound trivalent ions was found in a broad concentration range around the point of zero net charge. The highest colloidal stability of BLG was found for ion concentrations <20 μM and >50 μM. Investigations on macroscopic foams from BLG solutions revealed the existence of structure-property relations between the interfacial charging state and the foam stability. In fact, a minimum in foam stability at 20 μM ion concentration was found when the interfacial net charge was negligible. At this concentration, we propose that the persistent BLG molecules and weakly charged BLG aggregates drive foam stability, while outside the bulk reentrant zone the electrostatic disjoining pressure inside foam lamellae dominates foam stability. Our results provide new information on the charge reversal at the liquid-gas interface of protein/ion dispersions. Therefore, we see our findings as an important step in the clarification of reentrant condensation effects at interfaces and their relevance to foam stability.
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Affiliation(s)
- Manuela E Richert
- Institute of Physical Chemistry and Center for Soft Nanoscience , Westfälische Wilhelms-Universität Münster Corrensstraße 28/30 , 48149 Münster , Germany
| | - Georgi G Gochev
- Institute of Physical Chemistry and Center for Soft Nanoscience , Westfälische Wilhelms-Universität Münster Corrensstraße 28/30 , 48149 Münster , Germany
| | - Björn Braunschweig
- Institute of Physical Chemistry and Center for Soft Nanoscience , Westfälische Wilhelms-Universität Münster Corrensstraße 28/30 , 48149 Münster , Germany
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