The influence of starch on the smoothness of high-protein and low-fat solution.

Protein adsorption in three dimensions

The influence of a hydrotropic agent in the properties of aqueous solutions containing poly(ethylene oxide)–poly(propylene oxide) surfactants

The risks of chronic diseases related to high fat intake lead to an increased demand for low-fat food products. However, reducing the fat content incorporates textural and sensory defect that significantly impacts consumer acceptability, especially for dairy products. Therefore, hydrocolloids are used as stabilisers and thickeners in food processing since they can be partial or total fat substitutes in foods that confer desirable characteristics normally provided by fats. This project firstly investigated physicochemical characteristics of pure hydrocolloids solutions (gelatin, k-carrageenan, low methoxyl (LM) pectin and curdlan) under conditions used in dairy products, then the influence of hydrocolloids addition on the stability, flow behaviour, microstructure and lubrication of milk protein solution within varying casein to whey protein ratios was studied. Further, the effect of hydrocolloids and casein to whey protein ratios on the physical property and oral perception of real dairy products (low-fat chocolate milk and yoghurt) was evaluated.The flow and tribological behaviors of hydrocolloids solution/suspension depended on the pH, addition of salts and dosage of hydrocolloids. Near its isoelectric point, gelatin solution had the lowest viscosity, gel strength, lubrication property and poor visual aspect of formed gel. k-Carrageenan solution had the highest viscosity and best lubrication property at neutral pH. The strength of formed gels from k-carrageenan solution was low in acid condition, and the formed gels had unchanged visual aspect. LM pectin solution showed the highest viscosity and best lubrication property at pH 4.0, and decreased with the raise of pH value. LM pectin solution only started to form a stable gel when the concentration reached 1.0% with moderate amount (g 0.025%) of CaCl2 existed. For curdlan suspension, the viscosity was stable at neutral or acidic condition, but increased under alkali condition, and the curdlan suspension showed the least lubrication property at pH 4.0. Adding salts improved the viscosity and tribology property of gelatin, k-carrageenan solution, while the viscosity of LM pectin solution and curdlan suspension decreased with the addition of KCl, and 2 or 3% CaCl2 addition decreased the lubrication property of curdlan suspension. To some extent, the addition of salts depressed gelation of curdlan suspension at pH 5.0, and the addition of CaCl2 (g 0.8%) increased formation of curdlan gel. However, for other hydrocolloids, salts addition increased the gel strength although lower gel strength was obtained when the addition of CaCl2 was beyond 0.8% for k-carrageenan formed gel.For milk protein solution with fixed protein content (3.4%), replacing casein with whey protein isolate improved the protein stability, increased the viscosity and lubrication property of protein solution, whilst the milky white colour of the solution reduced. Gelling was observed with independent addition of 0.05% of k-carrageenan and 0.25% of LM pectin to the protein solution with high casein to whey protein ratio (g 50/50). Addition of hydrocolloids caused significant increase in viscosity and improved the friction coefficient of protein solutions, and protein solution showed the best lubrication property with the addition of 0.25% curdlan. The solutions were more homogeneous when casein/whey protein ratio was 0/100, and adding hydrocolloids caused phase separation, especially for protein solutions with high casein fraction. While when the percentage of casein was fixed to 2.4%, the addition of whey protein isolate did not have any obvious influence on the appearances of protein solutions, although it increased the stability, viscosity and lubrication property of protein solution. Besides, it was further discovery that the protein solution containing curdlan showed the best lubrication property both at 15 and 37 dC.Finally, the influence of hydrocolloids and casein to whey protein ratios on the physical and sensory properties of chocolate milk and yoghurt were investigated. The dynamic sensory tool, Temporal Dominance of Sensations (TDS), was used to monitor the changes in textural perception as perceived during oral processing. Decreasing casein to whey protein isolate ratio (from 80/20 to 20/80) significantly decreased the sedimentation percentage (from 4% to 3%) and improved the lubrication property of chocolate milk, although the resulting chocolate milk samples were darker. Hydrocolloid addition improved the viscosity and lubrication property of chocolate milk, however a significant increase in the particle size and an obvious sedimentation (g 6%) happened with a high proportion of k-carrageenan, LM pectin and curdlan. The TDS data obtained showed that powderiness, thickness, and creaminess was significant dominant attribute (dominance rate of 30%) at the start of consumption for chocolate milk, while residual coating and astringency became dominant later during oral processing. For yoghurt, with the replacement of casein by whey protein or hydrocolloids addition, the texture and viscosity of yoghurt was significantly increased, although too much hydrocolloid caused increased syneresis. The TDS data obtained showed that graininess, thickness, and cohesiveness were the most perceptible attributes at the start of consumption for yoghurt, while the dominant attributes turned to creaminess and mouth coating in the later period of consumption (after 60% onwards).

The assembly behavior of aryl/alkyl imidazolium ionic liquid salts in aqueous solution has been investigated. These salts undergo self-assembly into one-dimensional stacks via hydrophobic and π-π interactions upon increasing concentration, which led to a substantial increase in the solution viscosity in water. Addition of the macrocyclic host molecules cucurbit[n]urils (CB[n]) were found to effectively alter the supramolecular assemblies, as evidenced from the dramatic increase (by CB[7]) and decrease (by CB[8]) in solution viscosity and aggregation size in water, on account of the different binding stoichiometries, 1:1 complexation with CB[7] and 2:1 complexation with CB[8]. Furthermore, the aggregate architectures were controllably modified by competitive guests for the CB[n] hosts. This complex supramolecular systems approach has tremendous implications in the fields of molecular sensor design, nonlinear viscosity modification, and controlled release of target molecules from a defined supramolecular scaffold in water.

Electrospinnability of hydrogen bonded supramolecular comb polymers based on Poly(4-vinylpyridine) and 3-pentadecylphenol

Critical Examination of the Colloidal Particle Model of Globular Proteins

Spectroscopic methods for assessing the molecular origins of macroscopic solution properties of highly concentrated liquid protein solutions

ABSTRACTConcentration-dependent reversible self-association (RSA) of monoclonal antibodies (mAbs) poses a challenge to their pharmaceutical development as viable candidates for subcutaneous delivery. While the role of the antigen-binding fragment (Fab) in initiating RSA is well-established, little evidence supports the involvement of the crystallizable fragment (Fc). In this report, a variety of biophysical tools, including hydrogen exchange mass spectrometry, are used to elucidate the protein interface of such non-covalent protein-protein interactions. Using dynamic and static light scattering combined with viscosity measurements, we find that an IgG1 mAb (mAb-J) undergoes RSA primarily through electrostatic interactions and forms a monomer-dimer-tetramer equilibrium. We provide the first direct experimental mapping of the interface formed between the Fab and Fc domains of an antibody at high protein concentrations. Charge distribution heterogeneity between the positively charged interface spanning complementarity-determining regions CDR3H and CDR2L in the Fab and a negatively charged region in CH3/Fc domain mediates the RSA of mAb-J. When arginine and NaCl are added, they disrupt RSA of mAb-J and decrease the solution viscosity. Fab-Fc domain interactions between mAb monomers may promote the formation of large transient antibody complexes that ultimately cause increases in solution viscosity. Our findings illustrate how limited specific arrangements of amino-acid residues can cause mAbs to undergo RSA at high protein concentrations and how conserved regions in the Fc portion of the antibody can also play an important role in initiating weak and transient protein-protein interactions.

The aim of this work was to compare the surface adsorption and lubrication properties of plant and dairy proteins. Whey protein isolate (WPI) and pea protein isolate (PPI) were chosen as model animal and plant proteins, respectively, and various protein concentrations (0.1–100 mg/mL) were studied with/without heat treatment (90 °C/60 min). Quartz crystal microbalance with dissipation monitoring (QCM-D) experiments were performed on hydrophilic (gold) and hydrophobic polydimethylsiloxane (PDMS) sensors, with or without a mucin coating, latter was used to mimic the oral surface. Soft tribology using PDMS tribopairs in addition to wettability measurements, physicochemical characterization (size, charge, solubility) and gel electrophoresis were performed. Soluble fractions of PPI adsorbed to significantly larger extent on PDMS surfaces, forming more viscous films as compared to WPI regardless of heat treatment. Introducing a mucin coating on a PDMS surface led to a decrease in binding of the subsequent dietary protein layers, with PPI still adsorbing to a larger extent than WPI. Such large hydrated mass of PPI resulted in superior lubrication performance at lower protein concentration (≤10 mg/mL) as compared to WPI. However, at 100 mg/mL, WPI was a better lubricant than PPI, with the former showing the onset of elastohydrodynamic lubrication. Enhanced lubricity upon heat treatment was attributed to the increase in apparent viscosity. Fundamental insights from this study reveal that pea protein at higher concentrations demonstrates inferior lubricity than whey protein and could result in unpleasant mouthfeel, and thus may inform future replacement strategies when designing sustainable food products.

The Fallacy of Misplaced Concreteness

Control of viscosity in biopharmaceutical protein formulations

Role of acetylation on metal induced precipitation of alginates

To assess the effect of sugar molecules on solution viscosity at high protein concentrations. A high throughput dynamic light scattering method was used to measure the viscosity of monoclonal antibody solutions. The effects of protein concentration, type of sugar molecule (trehalose, sucrose, sorbitol, glucose, fructose, xylose and galactose), temperature and ionic strength were evaluated. Differential scanning fluorimetry was used to reveal the effect of the same sugars on protein stability and to provide insight into the mechanism by which sugars increase viscosity. The addition of all seven types of sugar molecules studied result in a significant increase in viscosity of high concentration monoclonal antibody solutions. Similar effects of sugars were observed in the two mAbs examined; viscosity could be reduced by increasing the ionic strength or temperature. The effect by sugars was enhanced at higher protein concentrations. Disaccharides have a greater effect on the solution viscosity at high protein concentrations compared to monosaccharides. The effect may be explained by commonly accepted mechanisms of interactions between sugar and protein molecules in solution.

Effect of protein solution components in the adsorption of Herbaspirillum seropedicae GlnB protein on mica

1. The proof is completed that the influence of electrolytes on the viscosity of suspensions of powdered particles of gelatin in water is similar to the influence of electrolytes on the viscosity of solutions of gelatin in water. 2. It has been suggested that the high viscosity of proteins is due to the existence of a different type of viscosity from that existing in crystalloids. It is shown that such an assumption is unnecessary and that the high viscosity of solutions of isoelectric gelatin can be accounted for quantitatively on the assumption that the relative volume of the gelatin in solution is comparatively high. 3. Since isoelectric gelatin is not ionized, the large volume cannot be due to a hydration of gelatin ions. It is suggested that this high volume of gelatin solutions is caused by the existence in the gelatin solution of submicroscopic pieces of solid gelatin occluding water, the relative quantity of which is regulated by the Donnan equilibrium. This would also explain why the influence of electrolytes on the viscosity of gelatin solutions is similar to the influence of electrolytes on the viscosity of suspensions of particles of gelatin. 4. This idea is supported by experiments on solutions and suspensions of casein chloride in which it is shown that their viscosity is chiefly due to the swelling of solid particles of casein, occluding quantities of water regulated by the Donnan equilibrium; and that the breaking up of these solid particles into smaller particles, no longer capable of swelling, diminishes the viscosity. 5. This leads to the idea that proteins form true solutions in water which in certain cases, however, contain, side by side with isolated ions and molecules, submicroscopic solid particles capable of occluding water whereby the relative volume and the viscosity of the solution is considerably increased. This accounts not only for the high order of magnitude of the viscosity of such protein solutions but also for the fact that the viscosity is influenced by electrolytes in a similar way as is the swelling of protein particles. 6. We therefore reach the conclusion that there are two sources for the viscosity of protein solutions; one due to the isolated protein ions and molecules, and the other to the submicroscopic solid particles contained in the solution. The viscosity due to the isolated molecules and ions of proteins we will call the general viscosity since it is of a similar low order of magnitude as that of crystalloids in solution; while the high viscosity due to the submicroscopic solid protein particles capable of occluding water and of swelling we will call the special viscosity of protein solutions. Under ordinary conditions of hydrogen ion concentration and temperature (and in not too high a concentration of the protein in solution) the general viscosity due to isolated ions and molecules prevails in solutions of crystalline egg albumin and in solutions of metal caseinates (where the metal is monovalent) while under the same conditions the second type of viscosity prevails in solutions of gelatin and in solutions of acid-salts of casein; and also in solutions of crystalline egg albumin at a pH below 1.0 and at higher temperatures. The special viscosity is higher in solutions of gelatin than of casein salts for the probable reason that the amount of water occluded by the submicroscopic solid gel particles in a gelatin solution is, as a rule, considerably higher than that occluded by the corresponding particles of casein.