Application of materials science approach to the structural properties of whey protein based composite gels influenced by change in pH

Despite the increasing appreciation that whey is a valuable resource of dairy industry, as opposed to a waste product of the cheese and casein industries, there have been drawbacks in its utilization as a functional ingredient in processed food products. Potential benefits include improvement in nutritional quality, imparting flavor and color due to the presence of lactose that takes part in Maillard reactions with the protein, as fat replacer in low-fat dairy products when co-gelled with polysaccharide, and as an ingredient in starch-based formulations (e.g. snacks and cereals). Therefore, the aim of this research is to apply the technique and concepts of the material science approach for the determination of the composition of individual phases in biphasic gels of whey protein in the presence of other polysaccharide such as agarose. The structural properties and morphology of mixed gels made of aqueous preparations of agarose and whey protein were modified by changing thermal treatment and pH. The conformationally dissimilar polymers phase separated and this process was followed by small-deformation dynamic oscillation in shear, differential scanning calorimetry and scanning electron microscopy. Experimental protocol encourages formation of a range of two-phase systems from continuous agarose matrices perforated by liquid-like whey protein inclusions to phase inverted preparations where a soft protein matrix suspends hard agarose-filler particles. These distinct morphologies have widely different mechanical moduli, which were followed by adapting a theoretical analysis (isostress-isostrain and Lewis-Nielsen blending laws) from the literature in synthetic block polymers and polyblends. Based on this framework of thought, reasonable predictions of the elastic moduli in the composite gels were made that led to patterns of solvent partition between the two polymeric networks. It was shown that proteins, in mixture with polysaccharide, exhibit favorable relative affinity (P-factor) for water molecules at a pH above their isoelectric point. This is an unexpected outcome that adds to the central finding of a single P value for the distribution of solvent between the continuous matrix and discontinuous inclusions of binary gels. It was thus proposed that phase continuity and solvent distribution in agarose/whey protein systems are under kinetic control that can be heavily governed by pH changes in the aqueous environment

Segregative phase separation in agarose/whey protein systems induced by sequence-dependent trapping and change in pH

The structural properties and morphology of mixed gels made of aqueous preparations of agarose and whey protein were modified by changing thermal treatment and pH. The conformationally dissimilar polymers phase separated and this process was followed by small-deformation dynamic oscillation in shear, differential scanning calorimetry and environmental scanning electron microscopy. Experimental protocol encourages formation of a range of two-phase systems from continuous agarose matrices perforated by liquid-like whey protein inclusions to phase inverted preparations where a soft protein matrix suspends hard agarose-filler particle

Modeling water partition in composite gels of BSA with gelatin following thermal treatment

A thorough experimental procedure of controlled cooling, isothermal at low temperature, heating, isothermal at high temperature and a second cooling run were carried out to record and rationalise the structural properties of BSA-gelatin mixtures over a wide range of temperature and polymer concentration. Research methodology included small-deformation dynamic oscillation in-shear, micro-differential scanning calorimetry, scanning electron microscopy and semi-theoretical modeling based on ideas of relating the elastic modulus of amorphous synthetic polymers to the topology of their binary blends. Cooling of solutions from ambient temperature produces gelatin continuous matrices supporting the BSA droplets, and modeling of the mechanical readings using an appropriate Lewis-Nielsen equation argues that the former is a highly hydrophilic molecule. Heating melts the gelatin network and leads to the formation of a continuous BSA structure, with dispersed inclusions of liquid gelatin, but produces a solvent partition factor in favour of the globular-protein gel. Subsequent cooling forms solid-like particles of gelatin within the interstices of the continuous BSA network. Modeling of steric exclusion phenomena in this filler composite using the isostrain blending law further supports the concept of increasing proportions of water being trapped within the continuous matrix of a biphasic gel

Calcium chloride effects on the glass transition of condensed systems of potato starch

The effect of calcium chloride on the structural properties of condensed potato starch undergoing a thermally induced glass transition has been studied using dynamic mechanical analysis and modulated differential scanning calorimetry. Extensive starch gelatinisation was obtained by hot pressing at 120 °C for 7 min producing materials that covered a range of moisture contents from 3.7% w/w (11% relative humidity) to 18.8% w/w (75% relative humidity). FTIR, ESEM and WAXD were also performed in order to elucidate the manner by which salt addition affects the molecular interactions and morphology of condensed starch. Experimental protocol ensured the development of amorphous matrices that exhibited thermally reversible glassy consistency. Both moisture content and addition of calcium chloride affected the mechanical strength and glass transition temperature of polymeric systems. Highly reactive calcium ions form a direct interaction with starch to alter considerably its structural properties via an anti-plasticizing effect, as compared to the polymer-water matrix

Shelf-life studies of flavour characteristics in model UHT liquid systems enriched with wholegrain oat

Development of malodourous compounds, hexanal and p-vinyl guaiacol (PVG), in UHT model liquid systems fortified with wholegrain oat were evaluated. Single and mixed systems using oat powder (3, 5, and 7% w/w), skim milk powder (SMP, 2.8% w/w) and sucrose (6.7% w/w) were subjected to UHT treatment and 29 days ambient storage. Both chromatographic analyses and panellists' perceived aroma intensity show a positive relationship between the content of hexanal and PVG, storage time and oat concentrations trialled. Ratio of the odour activity values (OAV) plotted against time shows that although PVG aroma initially is dominant, hexanal aroma, with a ratio of about 0.5, has twice the intensity of the PVG aroma for the remaining 29 days. Oat samples (with skim milk) were unacceptable when hexanal concentration was 35 times its threshold whilst the PVG level was still below its threshold in the same samples

Networks of polysaccharides with hydrophilic and hydrophobic characteristics in the presence of co-solute

The present investigation deals with the changing network morphology of agarose and high methoxy pectin when mixed with polydextrose as co-solute at concentrations varying up to high level of solids. Thermomechanical analysis and micro-imaging were performed using small deformation dynamic oscillation in shear, modulated differential scanning calorimetry and environment scanning electron microscopy. Fourier transform infrared spectroscopy and wide angle X-ray diffraction were practised to examine the nature of interactions between polymer and co-solute, and the extent of amorphicity of preparations. We observed a decline in the mechanical strength of aqueous agarose preparations upon addition of high levels of polydextrose, which should be attributed to reduced enthalpic content of the coil-to-helix transition of the polysaccharide network. Glass transition phenomena were observed at subzero temperatures in condensed preparations, hence further arguing for the formation of a lightly cross-linked agarose network with changing solvent quality. High levels of co-solute induce formation of weak pectin gels at elevated temperatures (even at 95 °C), which with lowering temperature exhibit increasing strength. This results in the formation of rubbery pectin gels at ambient temperature, which upon controlled cooling to subzero temperatures convert to a clear glass earlier than the agarose counterpart

Quantitative analysis of the phase volume of agarose-canola oil gels in comparison to blending law predictions using 3D imaging based on confocal laser scanning microscopy

Studying the phase behaviour of composite gels facilitates understanding of their structural and textural properties at low and intermediate levels of solids. In this work, the phase behaviour of a model system of agarose including various concentrations of canola oil was studied. This was pursued using a variety of techniques including SEM, FTIR, microDSC and dynamic oscillation in-shear. The structural studies recorded strong, continuous agarose networks supporting soft, discontinuous canola oil inclusions, with increasing levels of canola oil strengthening the composite system. A novel confocal laser scanning microscopy (CLSM) method for quantitative in situ examination of the oil phase volume was developed using three-dimensional (3D) imaging and image analysis software - FIJI and Imaris. Microscopic observations were assessed in relation to theoretical predictions from rheology-based blending-law analysis. Quantitative outcomes from the combined 3D imaging and image analysis are in close agreement with the volume predictions for the oil phase obtained from the isostrain blending law indicating the suitability of this approach in quantifying the phase behaviour of composite materials. The results of this work indicate that the developed microscopic method shows promise and could be used in the determination of phase volume in more complex and industrially relevant systems

Effect of whey protein agglomeration on spray dried microcapsules containing Saccharomyces boulardii

This work investigates the effect of whey protein agglomeration on the survivability of Saccharomyces boulardii within spray dried microcapsules. It attempts to go beyond phenomenological observations by establishing a relationship between physicochemical characteristics of the polymeric matrix and its effect on probiotic endurance upon spray drying. It is well known that this type of thermal shock has lethal consequences on the yeast cells. To avoid such undesirable outcome, we take advantage of the early agglomeration phenomenon observed for whey protein by adjusting the pH value of preparations close to isoelectric point (pH 4-5). During the subsequent process of spray drying, development of whey protein agglomerates induces formation of an early crust, and the protein in this molten globular state creates a cohesive network encapsulating the yeast cells. It appears that the early crust formation at a given sample pH and temperature regime during spray drying benefits the survivability of S. boulardii within microcapsules

Combined spectroscopic, molecular docking and quantum mechanics study of β-casein and p-coumaric acid interactions following thermal treatment

The molecular nature of interactions between ?-casein and p-coumaric acid was studied following exposure of their solutions to ultra-high temperature (UHT at 145 °C). Interactions were characterised by employing multi-spectroscopic methods, molecular docking and quantum mechanics calculations. FTIR demonstrates that the ligand lies in the vicinity of the protein, hence inverting the absorbance spectrum of the complex. This outcome changes the conformational characteristics of the protein leading to a flexible and open structure that accommodates the phenolic microconstituent. Results are supported by UVvis, CD and fluorescence quenching showing considerable shifts in spectra with complexation. Molecular docking indicates that there is at least a hydrogen bond between p-coumaric acid and the peptide backbone of isoleucine (Ile27). Quantum mechanics calculations further argue that changes in experimental observations are also due to a covalent interaction in the protein-phenolic adduct, which according to the best predicted binding pose involves the side chain of lysine 47

Molecular interactions of milk protein with phenolic components in oat-based liquid formulations following UHT treatment and prolonged storage

BACKGROUND: Nowadays there is a growing demand for nutritionally balanced breakfast beverages enriched with functional ingredients including wholegrain oat, which is rich in phenolic acids. Such beverages typically contain added food ingredients (e.g. milk protein, sugar and lipids) and undergo thermal processing that initiates many molecular processes. Therefore, this work aims to investigate the molecular interactions between milk protein and phenolic acids that govern bioactivity in model oat-based beverages. RESULTS: Findings showed the susceptibility of ferulic and p-coumaric acids, in model oat beverages, to ultra-high temperature (UHT) processing at 145 °C for 8 s. Among model beverages, those with added milk protein demonstrated a considerable loss of phenolic acids following UHT processing due to the interaction between these micronutrients and the protein. The nature of molecular interactions was mainly categorized as covalent with hydrogen bonds playing a supportive role. CONCLUSION: UHT processing of oat-based beverage formulations facilitates the formation of protein-phenolic acid complexes, which are largely covalent and static in nature. This finding underlines the ability of UHT treatment to induce chemical modifications of food ingredients