Molecular understanding of functionality and utilisation of whey protein in novel product concepts with chitosan and starch
Creators: name: Yang, Natasha
Publisher: name: RMIT University
Year: 2024

description: The PhD research examines network formation of thermally treated composite biopolymer systems of whey protein isolate (WPI), native wheat starch (WS) and chitosan (CHT). The work builds from the understanding of binary biopolymer systems and moves through investigation of low to intermediate concentrations to bridge the gap in understanding low and high solid tertiary polymer systems. Subsequently, WPI and CHT networks in the presence of gelatinised starch are manipulated and investigated for the potential of reducing the glycemic index at conditions imitating in vivo the human gastrointestinal tract. <br><br>Aqueous systems consisting of a constant 15% WPI, i.e. over the minimum critical gelling concentration of the protein, and increasing concentrations of up to 15% WS were heated from 25-85°C, followed by cooling from 85-5°C. Following understanding of binary mixtures, various levels of calcium chloride and CHT were incorporated. The experiments conducted include small deformation dynamic oscillation in shear, differential scanning calorimetry (DSC), texture profile analysis, environmental scanning electron microscopy and in vitro starch digestion.<br><br>The studies on WPI-WS systems argue for the formation of micro phase separated networks that are WPI continuous and WS discontinuous. For example, from the DSC studies endothermic peaks reflecting starch gelatinisation and protein denaturation were resolved and the absence of other events exemplifies associative physicochemical interactions lacking between the two polymers. In the rheological experiments the mixtures exhibited dramatic increases in G’ temperatures more closely related to those observed for individual WPI (73°C) rather than WS (60°C) systems. This pattern prevailed even at high additions of WS (15%), whereby intense G’ values were detected at 70°C. <br><br>The second set of experiments examined the formation of heat induced WPI and WS gels in the presence of CaCl2 (5-192mM). As followed by rheological experiments, the presence of the salt clearly affected WPI network formation and the influence was concentration dependent. At intermediate levels of incorporation, WPI-WS gels were the least vulnerable to amylolytic attack during digestion experiments. The investigation proves that CaCl2 promotes the aggregation of WPI and incorporation at 48mM provides the optimum spatial structure for maximum reduction in starch degradation.<br><br>The incorporation of medium molecular weight CHT in WPI-WS preparations at pH 5.5 also exemplifies significant changes on protein aggregation. From the ATR-FTIR work, an increased intensity of the absorbance peak at the amide II region was apparent, with samples containing the heteropolysaccharide, which represents a higher degree of morphological arrangement in the system. Results of the study evidenced electrostatic interactions as the driving force between the CHT and WPI which led to augmentation of infrared spectra. The in vitro starch digestion work on CHT involved comparison between 2% low molecular weight (LMW) and 2% medium molecular weight (MMW) under a digestion model with pH and volume adjustments according to those applicable to the human gastrointestinal tract (mouth, stomach, small intestine). The incorporation of both MMW and LMW CHT assisted in the reduction of starch degradation with the former being of greater effect. <br><br><br>