Structural studies of biopolymers/co-solute interactions in high-solid preparations

High-solid biomaterials increasingly include a number of non-starchy polysaccharides, i.e dietary fibre to deliver a range of properties such as structure, storage stability, processability, etc. The first type of high-solid biomaterials analysed this Thesis consists of agarose and co-solute (polydextrose), with the investigation dealing with changes in network morphology of agarose when mixed with polydextrose from low to high-solid preparations. There was a central observation of decline in the mechanical strength of aqueous agarose preparation upon addition of high levels of polydextrose, which was accompanied by a reduced enthalpic content of the coil-to-helix transition in 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.<br><br>The second system consists of high methoxy pectin and co-solute in the form of polydextrose or glucose syrup, with a view to examining the potential of replacing sugar with polydextrose in commercial formulations. Structural properties of pectin preparations were recorded in relation to the molecular weight and concentration of added co-solute in an acidic environment (pH ~ 3.0). High levels of co-solute induce formation of weak pectin gels at elevated temperatures (even at 95°C), which upon subsequent cooling exhibit increasing strength and convert to a clear glass at subzero temperatures. Glucose syrup is an efficient plasticiser leading to a reduction in the glass transition temperature of the pectin network, whereas polydextrose assists in the formation of stronger pectin gels in the rubbery state and accelerated vitrification properties.<br><br>The investigation on the third system, gelatin and polydextrose as the co-solute, focused on the understanding of structural behaviour in the presence of the non-sugar co-solute and in comparison with polysaccharides. A progression in the mechanical strength and thermal stability of the gelatin network was observed with the addition of polydextrose to the system, which was distinct from that of polysaccharide/co-systems. Combined thermomechanical and microscopy evidence argues for the development of phase separation phenomenon between protein and co-solute in high-solid preparations, where gelatin maintains helical conformation to provide network integrity as well as glassy consistency at subzero temperature. Again, that was distinct from the state of a single-phase system and “molecular dissolution” of polysaccharides in a high-content co-solute environment. At the high solids regime, glassy consistency was treated with theoretical frameworks from the synthetic polymer research to pinpoint the glass transition temperature of the gelatin/co-solute preparation.<br><br>The fourth system consisting of agarose, gelatin, and co-solute (polydextrose) was investigated from low to high levels of total solids, with a view to examining the phase behaviour of binary biopolymer mixtures that may lead to compositional adjustments in preparations. Agarose and gelatin form non-interactive bicontinuous phases in the aqueous environment. Systematic increase in the concentration of polydextrose prevents the formation of a stable agarose network, with the polysaccharide chains dispersing in the high-solid environment. Gelatin, on the contrary, retains its conformational stability even at a saturating co-solute environment through enhanced protein structuring. <br>