| The overall goal of this research is to better understand the mechanisms behind polysaccharide interactions during gelation in order to better control their use as food ingredients. The present research investigates polysaccharide structure and dynamics under dilute and semi-dilute conditions and during the sol-gel transition to better understand their behavior in food systems ranging from salad dressings to gelled desserts. In addition, the behavior of polysaccharides in high sugar systems is also studied, which is of importance in gelled-candy formulations.; The disordered (60°C) and ordered (25°C) state of dilute gellan and kappa-carrageenan were measured by static light scattering, circular dichroism and viscometry. The disordered-form of each polymer consists of random coils. Cations screened charges along gellan chains, increasing polymer spatial extensibility as described by an increased radius of gyration (R g). This was further supported by changes to the molecular ellipticity ([theta]). The Rg values for kappa-carrageenan decreased due to a salt induced transition. A temperature-induced transition occurred as temperatures were lowered to 25°C for both polymers, accompanied by an increase in [theta] and viscosity. Rg values decreased 15--36% for gellan depending on cations present, and 18% for kappa-carrageenan with and without K+. In the presence of Ca2+, R g for kappa-carrageenan decreased by 2.7%. The ordered state (25°C) for all polymer sols was hypothesized to consist of double helices, with the exception of kappa-carrageenan: Ca2+ systems, where it was proposed to consist of a cross-linked "dimer". All ordered conformations are suggested to form through intramolecular interactions as chains fold back onto themselves or undergo a hairpin turn.; Entanglement effects were investigated at initial stages of aggregation by studying the critical overlap (C*) and gelation (Co' ) concentration for gellan, kappa-carrageenan and alginate polysaccharides using steady shear rheometry. Both C* and Co' decreased for all polymer-cation systems, except in kappa-carrageenan: Ca 2+ sols where it remained unchanged. Aggregation was described by the site-bonded percolation theory to suggest individual clusters leading up to Co', where an infinite cluster forms. (Abstract shortened by UMI.)... |
