Characterisation of biopolymer/co-solute composites for the design of high-solid biomaterials with improved structural properties

The field of structure/function relationships in protein and polysaccharide systems of low solids has been extensively researched. In contrast, there is scant information in the literature on the subject of structure/function relationships in high-solid biopolymer mixtures with immediate applications in the confectionery industry. The overall aim of this research study is to draw attention to this scarcity of data by examining the structure-function relationships of model systems incorporating materials of industrial interest and viability, like agarose, gelatin, whey protein isolate (WPI) and glucose syrup. The Chapter 1 of this study covers, a comprehensive literature review on the subject of the properties of these ingredients in solutions and gels in relation to a widespread range of applications in the dairy and other food industries. Chapter 2 talks about the extended methodology of the techniques utilised in this work to assess the functional properties of our preparations. These include small-deformation dynamic oscillation on shear, modulated differential scanning calorimetry and confocal laser scanning microscopy. Theoretical principles in terms of constitutive equations governing the operational procedures of the instruments, and equations covering the thermodynamics and kinetics aspect of analysis are discussed. Chapter 3 deals with the binary composites of agarose and gelatin in the presence of increasing amounts of glucose syrup, the sugar phase which acts as the co-solute for the polymeric materials. <br><br>Agarose/gelatin mixtures in an aqueous low-solid environment form non-interactive bicontinuous networks. Fundamental contributions to the underlying physical chemistry of the structural relationship in high-solid mixtures is made by reporting for the first time: i) addition of glucose syrup to the polymeric blend prevents the formation of stable double helices in the agarose network, which is increasingly “dissolved” in the high-solvent environment, and ii) gelatin, on the other hand, withstands better the co-solute induced change in solvent quality. In addition, estimates of the mechanical glass transition temperature are distinct from the DSC counterparts in the agarose/gelatin/co-solute system and interpret this result in relation to the distinct property and distance scale being probed by the two techniques of rheology and calorimetry. The single value of Tg estimated by this working protocol argues in accordance with experimental observations for the predominance of the gelatin network in the high-solid mixture. Chapter 4 is a treatise of the structural properties of WPI, which were made by heat denaturing the protein. Furthermore, solvent quality was manipulated by increasing the glucose syrup concentration in the presence of 10 mM calcium chloride. Mechanical analysis shows considerable changes in the structural properties of the gels formed by varying the level of co-solute, which relates to distinct interactive patterns in the mixtures. The nature and extent of these interactive patterns or molecular forces were further examined calorimetrically. Tangible evidence of the aggregation patterns of whey protein molecules is recorded using laser microscopy. This part of the work clearly demonstrates that the protein molecules are able to cluster in a high sugar environment by utilising a limited layer of hydration as compared to aqueous systems. Chapter 5 is a way forward giving a brief account of a range of related topics that can be analysed in future in order to further advance the understanding of the subject of high-solid biomaterials.