Molecular simulation of partially denatured β-lactoglobulin

From Elsevier via Jisc Publications RouterHistory: accepted 2023-04-22, issued 2023-04-29Article version: AMPublication status: AcceptedFunder: Heriot-Watt University; FundRef: https://doi.org/10.13039/100009767Funder: Engineering & Physical Sciences Research Council; Grant(s): EP/J501682/1Julien Lonchamp - ORCID: 0000-0001-7954-4745 https://orcid.org/0000-0001-7954-4745The unfolding of β-lactoglobulin (β-lac) upon heating was comprehensively studied through molecular dynamics computer simulations. A β-lac molecule in the aqueous solution was firstly heated at 500 K for unfolding and then annealed at 300 K to collect stable conformations. There were five meta-stable conformations observed based on the Free Energy Landscape (FEL). The β-lac molecule was found to exhibit an open and extended conformation on heating followed by limited refolding upon cooling. The cysteine residues –SH121 and S–S66-160 in the most open conformation were located at the opposite ends of the β-lac molecule. This would favour the intermolecular –SH/S–S interchange reactions that are known to occur in β-lac as part of the inter-molecular aggregation process. Furthermore, the unfolding of the β-lac increased the hydrogen bond forming capacity between water molecules and the protein and between water molecules themselves. The interactions and the properties of the water molecules in the protein hydration shell also indicated that the hydration shell was stabilized by protein unfolding. However, it was found that the unfolding of β-lac increased diffusion of hydration water molecules, including those in the first hydration shell that interact more strongly with the protein. This may partly explain why unfolded proteins are more likely to aggregate even though there were more hydration water molecules protecting them. Such results provided more detailed information on the structure-functionality relationship of β-lac based on both the protein molecule and its hydration shell. This provides insight into how we can control the processing of proteins for desirable functional properties such as thickening and gelation, which are modified through protein-water interactions.inpressinpres

Stable emulsions of droplets in a solid edible organogel matrix

Sitosterol–oryzanol organogels are unstable near water, but are shown to be stable in the presence of glycerol.</p

The major proteins of the seed of the fruit of the date palm (phoenix dactylifera l.): Characterisation and emulsifying properties

Proteins were extracted from the seeds of the fruit of the date palm. Proteomic analysis and SDS-PAGE electrophoresis of the extracted proteome suggested it is composed predominantly of the storage proteins glycinin and β-conglycinin, although over 300 proteins were detected, 91 of which were identified with confidence. In terms of protein type, the largest numbers of proteins were associated, not unexpectedly, with metabolism and energy functions, which reflected the requirements of the germinating and growing embryonic plant. The emulsifying properties of the extracted proteins were determined. Date seed protein exhibited a lower emulsifying activity than either whey protein concentrate or soy protein isolate at each of the pH values tested. However, the stability of the emulsions produced with all three proteins was very similar at the different pH values. This combination of large emulsion droplet size and high emulsion stability properties suggested that the date proteins may adsorb as large protein oligomers.https://doi.org/10.1016/j.foodchem.2015.11.046197pubpu

Electrostatic complexes of whey protein and pectin as foaming and emulsifying agents

Five types of electrostatic complex (macromolecular complexes, core-shell particles, and mixed homogeneous particles) were formed between whey protein (whey protein concentrate [WPC]) and pectin. By controlling the thermal treatment, composition, and order of mixing, it was possible to produce complexes that for the same biopolymer concentration gave differing functional properties. All protein-pectin complexes showed higher foaming ability and stability than native or heated WPC without pectin. Native WPC had higher emulsifying ability than protein-pectin complexes but exhibited the lowest emulsion stability. Ingredients based on such ideas might offer the food manufacturer greater control over food structure, stability, and organoleptic properties.sch_die20pub5156pubsup

Properties of partially denatured whey protein products: Viscoelastic properties

Partially denatured whey protein products (PDWPC's) can be classified based on the viscoelastic properties of their solutions. Strain sweeps show that PDWPC-A and -B and microparticulated WPC (MPWPC) with compact, spherical aggregated particles exhibit a strong strain overshoot. PDWPC-C and -D, on the other hand, which have open, elongated porous particles show a weak strain overshoot. The concentration dependence of the elastic modulus G' in the linear viscoelastic region has a biphasic power law dependence with concentration for all protein products studied, except for WPC where G' is independent of protein concentration. Frequency sweeps suggest that MPWC solutions form a strong physical gel at all concentrations above 14% (w/w). PDWPC-A and -B form weak gels over the same concentration range. PDWPC-C and -D also form weak gels at 14% protein (w/w) but strong physical gels at higher concentrations. The frequency dependence of G' and G'' for all aggregated proteins show a power law dependence indicating fractal type structures. For all solutions above a critical concentration, the fractal dimensions span the range 1.6-2.3, indicating a range of gel network structures from open and diffuse to compact and dense. Adherence to the empirical Cox-Merz rule was observed in PDWPC-A, -C and -D at concentrations of 14 and 16% (w/w) protein, suggesting liquid-like behaviour. At higher protein concentrations the deviations from the Cox-Merz rule suggest more pronounced elasticity in the structure. For PDWPC-B, the behaviour is complex, with deviation from the Cox-Merz rule at low frequencies/shear rates, but correspondence at higher frequencies/shear rates at all concentrations. This indicates a frequency-dependent change from liquid-like behaviour over long timescale deformations, to a solid-like behaviour at short timescale deformations. MPWPC solutions of all concentrations do not follow the Cox-Merz rule, suggesting solid-like behaviour. The PDWPCs exhibit a complex rheological behaviour which suggests they could be versatile thickening, texturizing and fat replacementsch_die80pub5157pu

Properties of partially denatured whey protein products 2: Solution flow properties

Partial denaturation of whey protein concentrates has been used to make protein powders with differing viscosity properties. PDWPC particles have been manufactured to have a range of aggregate sizes (3.3–17 μm) and structures (compact particle gel to open fibrillar gel). In solution the PDWPC samples show complex viscosity behaviour dependant on the size and morphology of the PDWPC aggregate particles. For the same protein content the compact particles have a lower viscosity than open, fibrillar particles. The viscosity also appears to depend on the surface structure of the particles, with particles of a similar size, but having a rougher surface giving higher viscosity than similar smooth particles. The viscosity of the WPC, MPWPC and PDWPC solutions are explained in terms of the postulated interactions between the protein aggregates in solution.Engineering & Physical Sciences Research Council grant No. EP/J501682/1.https://doi.org/10.1016/j.foodhyd.2015.12.01256pubpu

Properties of partially denatured whey protein products: Formation and characterisation of structure

Item previously deposited in Heriot-Watt University repository: https://researchportal.hw.ac.uk/en/publications/properties-of-partially-denatured-whey-protein-products-formationPartially denatured whey protein (PDWPC) products have been manufactured using a controlled heating process that allows control of the degree of denaturation of the whey proteins. This is assessed by following the change in free sulphydryl content of the protein as heating progresses. This allows the formation of soluble whey protein aggregates of diverse particle size and morphology. The PDWPC's have been made using different manufacturing conditions (temperature, pH, degree of denaturation) to give aggregated PDWPC powders with a degree of denaturation in the range 45–98% and particle size 3–17 μm. Particle size analysis, scanning electron microscopy and density analysis show that the particles have aggregated structures that range from compact, particulate gel-like to fibrillar phase-separated structures, with intermediate structures formed under some conditions. These structures are consistent with the known gel structures formed in whey protein concentrate gels. The structure of the PDWPC particles differs from that of microparticulated whey proteins. The possibility of using PDWPC's as ingredients tailored to the needs of food manufacturers is discussed.https://doi.org/10.1016/j.foodhyd.2015.06.00952pubpu