Mechanical properties of biopolymer composites and retardation of starch digestion in novel carbohydrate based products

Abstract

This report is divided into two parts which correspond to two different research projects. The earlier part of the work studied the mechanical properties of biocomposites comprising of a continuous gelatin matrix and a discontinuous phase of MCC fibers. Such binary blend represents a unique combination of protein and polysaccharide hydrogel which exhibits distinctive structural properties. Small-deformation dynamic oscillatory analysis was employed to probe for the mechanical properties of each individual component and their composites of different polymers concentrations. A cooling run with an iso-torque process was capable of orienting the MCC fibers in the suspending gelatin phase, giving rise to a composite with highly oriented filler particles. Enhancement of the gelatin network strength owing to MCC fibers orientation was further elucidated. Mechanical strength of composites reinforced with either isotropically ordered or highly oriented MCC fibers was modeled by existing and proposed mathematical models respectively. The second part of the thesis reports the research findings on starch digestion retardation in rice based food systems. Two approaches were investigated in this project with the ultimate aim of delaying starch digestion in a starch rich food system. The first approach was based on the notion of starch granules encapsulation by a three dimensional network of alginate set in the presence of calcium. Alginate network was supplemented into the formulation of a real food system, the rice dough. Structural strength imparted onto the dough was evaluated by small-deformation dynamic mechanical analysis and further probed by scanning electron microscopy. Resistance of this thermally stable network against enzymatic (a-amylase) digestion was then examined by an in-vitro study. Meanwhile, the second approach was based on the capability of tea polyphenols in inhibiting starch digestive enzymes. Six tea infusions representing black, oolong and green teas were utilized in this study. Their inhibitory activity against a-amylase (HSA) and a-glucosidase (AGH) was determined by IC50 measurement. The major polyphenols (catechins and theaflavins) present in these extracts were quantified by high performance liquid chromatography. Enzymatic inhibition potency of the extracts was then correlated to their polyphenols content. Black tea extract was identified to be most potent in delaying HSA and AGH digestion. Its capability in retarding rice noodle digestion by pancreatin was investigated with an in-vitro experimental set-up. In conjunction with this work, a new analytical technique based on refraction index measurement was proposed to be a convenient method for quantifying the degree of enzymatic starch digestion.