Tailoring of whey protein isoalte stabilized oil-water interfaces for improved emulsification
Date
2014-08-29
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Journal ISSN
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Publisher
ORCID
Type
Degree Level
Doctoral
Abstract
In this thesis, mechanisms for enhancing the stability of whey protein emulsions using two approaches were investigated. First, the physicochemical and emulsifying properties of whey protein isolate (WPI), and its two main proteins, alpha-lactalbumin (ALA) and beta-lactoglobulin (β-LG), were investigated in response to changes in pH and temperature pre-treatments. Solvent conditions which inhibit protein aggregation, such as pHs away from the isoelectric point, were found to form stable emulsions. In contrast, thermal treatments were found to negatively affect emulsion stability, where the most stable emulsions for WPI, ALA and β-LG were formed at room temperature (i.e. 25°C) at pH 7.0. It was also determined that emulsions formed using WPI, ALA and β-LG were stabilized by electrostatically repulsive forces which prevent flocculation and creaming. Secondly, the use of tailored protein-polysaccharide interactions involving WPI and carrageenan (CG) were explored as a means of enhancing emulsion stability. Carrageenan (CG) partakes in electrostatic attraction with WPI when acidified, leading to the formation of coupled gel networks. CG was selected for its anionic properties and for its well-characterized structure in that kappa-, iota- and lambda-type CG contain 1-, 2- and 3-sulfated groups per disaccharide repeating unit respectively. WPI-CG mixtures formed gel networks once acidified, where WPI-kappa-CG and WPI-iota-CG mixtures formed stiff networks, whereas WPI-lambda-CG formed a weak fluid network. WPI-CG complexes were found to be surface active, causing changes to the interfacial tension and interfacial rheology at pHs corresponding to where electrostatic attraction occurs upon acidification. Electrostatically coupled gel networks were formed in an emulsion, where oil droplets became entrapped within the biopolymer matrix. WPI-CG mixtures were sensitive to WPI-CG mixing ratio as stiffer gels were formed at higher CG content. Furthermore, WPI-iota-CG gels were stiffer than those made with WPI-kappa-CG gels presumably due to the higher number of sulfated groups lending greater opportunities for iota-CG to form bonds with neighboring polymers compared to kappa-CG.
Description
Keywords
Whey, emulsion, gel, carrageenan, rheology, beta-lactoglobulin, alpha-lactalbumin, oil-in-water
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Food and Bioproduct Sciences
Program
Food Science