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Li, Xinxin (2021) Interactions between rod-like biopolymer solutions and saliva. PhD thesis, University of Nottingham.

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Abstract

This thesis aims to evaluate underpinning mechanisms of oral processing of polysaccharide thickeners with a rod-like conformation. Xanthan gum (XG) and scleroglucan (SG) are identified as key research targets, with the view to identify the differences and similarities between XG and SG and to assess the potential of SG utilisation as XG analogue in specialised nutrition applications, such as in oropharyngeal dysphagia. Specifically, hydrodynamic properties of SG have been investigated, including hydrodynamic and thermodynamic non-ideality, as well as molecular weight distribution. Furthermore, rheological and lubrication properties have been studied to elucidate complex rheological behaviour of both polysaccharides, as well as to probe their interactions with human whole saliva and bovine submaxillary mucin, used as a saliva-mimicking model. The rheological behaviour was probed using a combination of the steady shear flow, small amplitude oscillatory shear, first normal stress difference and capillary break-up rheometry techniques, whilst lubrication and friction behaviour was examined using the soft-contact tribology method.

Sedimentation velocity in analytical ultracentrifuge (AUC) showed SG preparation was unimodal when concentration is higher than 0.75 mg/ml. However, it was resolved into two main components at lower concentrations with partial reversibility between two components. Sedimentation equilibrium experiments revealed that SG exhibits partially reversible self-association behaviour. The molecular weight ranges from ~3 × 106 g/mol to ~5 × 106 g/mol after thermodynamic non-ideality correction. The results of SEC-MALS showed that the rod-shape structure of SG may transfer into a structure with more flexibility at higher masses. When XG solution or SG solution are mixed with mucin, sedimentation velocity experiment showed no apparent interactions at low concentrations.

At higher concentrations, XG and SG solutions of the same concentration have comparable steady shear flow profile and linear viscoelasticity spectra. At the same time, they show marked differences in the elongational flow behaviour, normal stress difference and lubrication behaviour. When XG and SG are dissolved in viscosified matrix (40% sucrose solution), the differences were minimised, confirming that chain relaxation dynamics at longer characteristic time is similar between XG and SG. The influence of saliva (or mucin) on complex rheological behaviour and lubrication of XG and SG was found to be minimal, which is consistent with the results of the sedimentation analysis showing no effect in low concentration solutions. The examined sets of rheological and tribological behaviour show new opportunities for the use of SG as a XG-replacing thickener in medical nutrition applications.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Harding, Stephen Yakubov, Gleb
Keywords:	Xanthan gum, Scleroglucan, Rheology, Small amplitude oscillatory shear, Capillary break-up, First normal stress difference, Soft-contact tribology, Bovine submaxillary mucin, Saliva
Subjects:	Q Science > QP Physiology > QP501 Animal biochemistry
Faculties/Schools:	UK Campuses > Faculty of Science > School of Biosciences
Item ID:	66258
Depositing User:	Li, Xinxin
Date Deposited:	31 Dec 2021 04:40
Last Modified:	01 Sep 2022 04:30
URI:	https://eprints.nottingham.ac.uk/id/eprint/66258

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