Biopolymer Co-solute Systems - Theory and Applications

Abstract

The thesis aims to study the physicochemical properties of various biopolymers. It contains two parts, progressing from intermediate to high solid biopolymer systems. The first part of the thesis attempts to reveal the relaxation mechanism and molecular architecture of intermediate solid gluten system at subzero temperatures. In doing so, techniques of modulated differential scanning calorimetry, small-deformation dynamic oscillation on shear, and transmission electron microscopy were employed. The shallow and broad relaxation observed calorimetrically due to the polydispersity of the material was not seen in mechanical response of the material; instead, ice melting was the most important factor controlling the mechanical stability. In the absence of a distinct glass transition region, ice melting was proposed to be a valid indicator of molecular mobility and quality control for frozen hydrated gluten. The supramolecular morphology of the protein is made of cohesive sheets or thin films, and the molecular interactions of the gluten network are severely affected by ice formation as well as recrystallization. The second part of the thesis deals with characterization of high solid systems, and three different types of systems were studied. First type of system consists of gelatin and co-solute (glucose syrup), and the effect of molecular weight difference of gelatin on the vitrification of the system was studied. Vitrification behavior of the systems was characterized using small-deformation dynamic oscillation and transient stress relaxation experiments, and was further modeled according to the scheme of Williams, Landel, and Ferry (WLF) equation in conjunction with the concept of free volume, as well as the coupling model in the form of the Kohlrausch, Williams and Watts (KWW) function, which provided the glass transition temperature (Tg), fractional free volume (f), relaxation time (t), and coupling constant (n). Finally, molecular weight of gelatin was related to the coupling constant of the system. Second type of system utilizes gelling polysaccharides instead of gelatin, together with glucose syrup. The same techniques were used to evaluate the relaxation dynamics of the systems, and the data obtained were modeled with WLF and KWW equations to find out the Tg, f, t, and n. Molecular interactions in these polysaccharide/co-solute systems were found to be stronger compared to those of gelatin/co-solute systems, due to their distinct microstructures. Building on the understanding of polysaccharide/co-solute system, the translational mobility of a small molecular compound in high solid glucose syrup system with/without ¿-carrageenan at the vicinity of Tg was examined using UV spectroscopy and correlated with vitrification of the matrices. Translational diffusion diminishes as the temperature approaches their respective Tg, and becomes minimal at Tg. In addition, for both systems, translational mobility can be directly related to mechanical Tg of the systems. Furthermore, the diffusing compound was found to have a much higher translational mobility compared to the molecules composing the matrices. In the last type of system, eight different polysaccharides, both gelling and non-gelling, were incorporated into starch based system to make a commercially applicable product, instant noodle. Characterization of both the raw ingredients and the noodle systems employed a variety of techniques, including small-deformation dynamic oscillation, tensile test, texture profile analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. Propylene glycol alginate and xanthan gum was shown to produce noodles with the best textural properties, and this was postulated to be due to the more extensive release of amylose from the starch by addition of the gums.