Gelatin vs Polysaccharide in Mixture with Sugar Stefan Kasapis* and Insaf M. Al-Marhoobi Department of Food Science & Nutrition, College of Agricultural & Marine Sciences, Sultan Qaboos University, PO Box 34, Al-Khod 123, Sultanate of Oman Marcin Deszczynski and John R. Mitchell Division of Food Sciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, U.K. Rukmal Abeysekera Institute for Applied Biology, University of York, Yorkshire YO1 5DD, U.K. Received November 12, 2002 The structural behavior of a well-characterized gelatin sample has been revisited to investigate the morphology of its network in the presence of sugar. This was then contrasted with the corresponding properties of the gelling polysaccharides agarose, κ-carrageenan, and deacylated gellan. Small deformation dynamic oscillation, differential scanning calorimetry in plain and modulated mode, visual observations, and transmission electron microscopy were used to identify the structural characteristics of the biopolymers from the rubbery plateau through the transition region to the glassy state. In contrast to the collapse of the polysaccharide gels at intermediate levels of co-solute, gelatin forms reinforced networks. The drop in polysaccharide network strength is accompanied by a decline in the enthalpy of the coil-to-helix transition, whereas the transition enthalpy is more pronounced in gelatin gels in accordance with their strengthening. Tangible evidence of the molecular transformations was obtained using microscopy, with polysaccharides disaggregating and dissolving in the saturated sugar environment. Gelatin, on the other hand, is visualized in an aggregated form thus producing a phase-separated topology with sugar. Introduction Over the last 20 years, we have witnessed the development of a materials science approach to food structure in high solids formulations. 1-3 This has involved the construction of state diagrams and the use of these diagrams to understand the kinetics of physicochemical changes occurring on storage of materials. Central to this development is the idea of molecular mobility governing the kinetics of phase/state transitions and chemical reactions. Molecular mobility is often, though not invariably, associated with the macroscopic viscosity of the material, 4 and the approach is relevant to the low water conditions of confectionery and ice cream products. The science governing the behavior of hydrocolloids in these sugar, low water systems is much less understood than in the high water environment where they are widely employed. 5,6 In the former, the most frequently used hydro- colloids are gelatin, starch, or pectin. The structural attributes imparted by these molecules are different, though starch manufacturers are putting considerable effort into developing ingredients that can match the functional properties of gelatin. There is also substantial research effort in developing gelatin alternatives from other hydrocolloids such as pectin, carra- geenan, agarose, or gellan gum. Confectionery manufacturers, ingredient suppliers, and academics consider how to extend the sophisticated synthetic polymer approach with the intention of obtaining a better understanding of hydrocolloid behavior in high-solid systems. 7-9 Thus, ideas of polymer physics which form the backbone of the materials science were used to interpret the mechanical, thermal, and spectroscopic characteristics of biological glasses and melts. Three critical scientific issues were addressed, as summarized below: The transition from the rubbery to the glassy state was clearly identified allowing definition of the glass transition temperature (T g ) as the conjunction of two molecular mechanisms. In terms of the temperature dependence of relaxation processes, 10 these were based on the configurational rearrangements of segments of the polymeric backbone occurring in the glass transition region and the energetic barrier to rotation of submolecular groups in the glassy state. Second, the glass transition temperature measured by calorimetry remains unaltered by the presence of low levels of polysaccharide suggesting that the mobility of the sugar is unaffected by the presence of the macromolecule. How- ever, the mechanical profile of the rubber-to-glass transition is strongly influenced by the polysaccharide particularly if it is network forming. Thus, it is possible to represent the magnitude of this polysaccharide contribution to rheology by a “network T g ”, the greater the extent to which this differs * To whom correspondence should be addressed: Fax: + 968 513 418. E-mail: stefan@squ.edu.om. 1142 Biomacromolecules 2003, 4, 1142-1149 10.1021/bm0201237 CCC: $25.00 © 2003 American Chemical Society Published on Web 07/26/2003