Flow behaviour of biopolymer solutions and effect on saltiness perception

• Main Author: Koliandris, Anne-Laure
• Published: University of Nottingham 2011
• Subjects: 664; TX Home economics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542143

In order to improve public health, active measures are taken to lower the salt (sodium chloride) consumption of the population. However, significant effort is required to reduce salt content in processed foods without adversely affecting taste, flavour and consumer preference. This research aimed at investigating how the saltiness efficiency of sodium chloride could be improved. The first approach investigated the relationship between rheology and taste perception to evaluate whether it is possible to enhance saltiness perception through careful design of product rheology. The objective was to identify the flow parameters correlating to saltiness perception. The shear rate relevant to saltiness perception was investigated using a range of typical solution flow behaviour (Newtonian, shear-thinning, yield behaviour). It was found that saltiness perception is related to viscosity measured at low shear (1-10 s-1) and not to zero shear or high shear viscosity. An enhancement of saltiness perception was found for very high polymer concentrations, which could be explained by the increased osmolality of these solutions. Subsequently, food grade Boger fluids (Newtonian fluids of high elasticity) were formulated and characterised to investigate whether extensional viscosity impacts saltiness perception. As no clear effect was reported, hypothesised to be due to the unfavourable mouthfeel of the relatively thick fluids, an alternative approach using low viscosity polysaccharide solutions of identical shear behaviour but of different extensional behaviour was taken. Extensional behaviour of polysaccharide solutions in large deformation flow has received very little attention compared to shear flow behaviour and was characterised here using the techniques of filament break-up and microfluidics as preliminary work for future sensory studies. Large differences in elasticity among polysaccharides and singularities of polysaccharides compared to synthetic polymers were found. As a second approach it was investigated whether duplex emulsions could be stabilised by chemical cross-linking of proteins adsorbed at the oil-water interface. The interest in duplex emulsions is based on the hypothesis that increase in the salt concentration in the continuous product phase of an emulsion-based food may increase saltiness perception. Formulation of stable food duplex emulsions is challenging and here it was shown that chemical cross-linking of Bovine Serum Albumin (BSA) adsorbed at the oil-water interface improved stability towards coalescence and emptying out of the internal water phase. The interface of single oil-in-water emulsions was also successfully cross-linked. Both the industrial impact and fundamental interest of this research were discussed.