A study on the thermally induced gelation of quinoa protein isolate (QPI) dispersions : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Auckland, New Zealand
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Date
2022
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Massey University
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Abstract
Plant proteins is an alternate option for animal proteins. In the last decade, the market trend towards plant-based protein is significantly accelerated. To meet market demand, plant-based protein ingredients must compete with or outperform traditional animal protein sources in terms of techno-functional properties. Plant proteins typically have extremely different molecular, chemical, and physical properties than animal proteins. Due to this the main challenge is to stimulate the desirable appearance, texture, mouthfeel, and functionality of the products manufactured from plant proteins as compared with animal proteins. We choose quinoa as they can reduce the risk of several diseases such as anti-depressants, anti-inflammatory, and anti-cancer. High amount of flavonoids such as quercetin and kaempferol, and antioxidants are present in quinoa seeds. However, understanding the underlying characteristics of plant proteins and how they might be built into structures similar to those found in animal products is therefore crucial. So, to understand the gelation property of quinoa plant protein, this study aims to investigate the physicochemical and rheological behaviour of quinoa protein with different NaCl and CaCl₂ concentration, different polysaccharides concentration and to compare the heat-induced gelation behaviour between quinoa protein isolate and whey protein isolate. The rheological properties and microstructural changes in the quinoa protein were monitored when addition of salt (NaCl and CaCl₂), polysaccharide, and comparison of plant protein and dairy protein at various pH and protein concentrations were performed. The changes in the storage modulus and microstructure of the suspension and gels were examined. This research evaluated the effect of addition of NaCl (0 mM to 200 mM) and CaCl₂ (20 mM and 50 mM) at various concentrations; addition of guar gum, locust bean gum, and xanthan gum at 0.05 %, 0.1 % and 0.2 % concentrations; and to assess and compare the gelation behaviour of the quinoa protein isolate, and whey protein isolate at pH 7, pH 5 and pH 3 with different protein concentration. Addition of NaCl and CaCl₂ illustrated sol-gel transition using small and large deformation rheology, although all protein gels displayed weak gel characteristics. It was discovered that with addition of NaCl from 0 mM to 200 mM, gelation temperature decreased from 73 °C to 40 °C and complex modulus (G*) increased from ~67 Pa to ~125 Pa. As the NaCl concentration increased, heterogenous and larger aggregates of the gel microstructure developed. But for gel microstructure without salt addition, homogenous structure existed. In the case of CaCl₂ (20 mM and 50 mM), rheology showed weak gel rigidity. And from CLSM images, larger aggregates with big voids were observed in the case of 50 mM CaCl₂, probably exhibiting phase separation. From SAXS and SANS, a particle size of ~32 Å and ~57 Å, was observed for QPI gels containing 0 to 200 mM NaCl, respectively. Polysaccharide addition at low concentration can increase the viscoelastic property of thermally induced QPI gels. For each polysaccharide (guar gum, locust bean gum, xanthan gum), as concentration increased (0.05 % to 0.2 %), gelation temperature decreased from 64 °C to 50 °C approximately for guar gum, and 46 °C to 31 °C for locust bean gum. Addition of xanthan gum revealed the maximum storage modulus (Gʹ), as compared with other polysaccharides. In comparison with guar gum and locust bean gum, xanthan gum did not confirm gelation temperature due to high viscosity of the suspension at all the concentrations. Complex modulus (G*) (1 Hz) increased as the concentration of each polysaccharide increased from 664 Pa to 1797 Pa for Xanthan gum. The CLSM microstructure was also in corelation with the rheological characterisation. The highest water holding capacity was also seen for highest xanthan gum concentration (0.2 %). The protein concentration (3 wt% to 10 wt%) and various pH (pH 3, pH 5 and pH 7) affects the gelation behaviour and microstructural characteristics of quinoa protein and whey proteins. At all the pH values, whey protein shows high viscoelasticity as compared with quinoa protein. Highest viscoelasticity for QPI is achieved at pH 5. Hydrophobic bonds and electrostatic interactions are responsible for the gelation of quinoa protein isolate. The highest viscoelasticity for WPI is determined at pH 7. The thiol disulphide interchange reactions are responsible for the gelation behaviour of whey protein isolate. The increase in protein concentration for QPI and WPI gel formation increased. The gelation temperature decreased as the protein concentration increased (3 wt% to 10 wt%) for QPI and WPI at all the pH values (pH 3, pH 5 and pH 7).
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The following Figures have been removed for copyright reasons: 2.1 (=Garcia et al., 2015 Fig 3.1); 2.6 (=Warnakulasuriya & Nickerson, 2018 Fig 1); 2.9 (=Bansal & Bhandari, 2016 Fig 3.9); 2.11 (=Totosaus et al., 2002 Fig 1) & 2.12 (=Nicolai & Chassenieux, 2019 Fig 1).