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Title: Physical and enzymatic stability of emulsions containing complexes of casein and anionic polysaccharide
Author: Jourdain, Laureline Sophie
ISNI:       0000 0001 3593 2623
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2008
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Proteins and polysaccharides are widely used as food ingredients because of their ability to improve the shelf-life stability and texture of food products. Under conditions where positively charged residues are present on the protein molecules, negatively charged polysaccharides can interact with the protein to fonn electrostatic complexes. This study reports on the effect of the use of a highly sulfated polysaccharide, dextran sulfate or t-carrageenan, on model oil-in-water emulsions containing sodium caseinate, with respect to the stability of the emulsions towards two environmental stresses to which foods are exposed during digestion: acidification and trypsin hydrolysis. Two routes were investigated for preparation of the emulsions. Bilayer emulsions were prepared by a layer-by-Iayer deposition technique, in which the polysaccharide was added to a protein-stabilized emulsion. Mixed emulsions were prepared by a one-step method, in which soluble complexes were present during homogenization of the emulsions. In bilayer emulsions at pH = 6, bridging flocculation was observed at low polysaccharide concentration, and polymeric restabilization at high concentration. No flocculation was observed in the mixed emulsions at any polysaccharide concentration. The presence of 1 wt% dextran sulfate in the mixed or bilayer emulsion was found to protect the emulsion against acid-induced precipitation and enhance its shelf-life stability. The presence of ~ 0.1 wt% polysaccharide in both types of emulsions was found to reduce significantly the extent of trypsinolysis, as detennined by chromatogniphy. A different set of peptide fragments was produced in the presence of the polysaccharide (hydrophilic ~-casein peptIde), as compared in the absence of polysaccharide (hydrophobic ~-casein peptide). Surface dilatational and shear rheology at the oil-water interface revealed that the bilayer system had weaker viscoelastic properties than the mixed system. The different physical and enzymatic properties of the bilayer and mixed emulsions can be explained in tenns ofthe interfacial structures ofthe systems. Keywords: casein, amomc polysaccharide, complex coacervation, emulsion, aggregation, stability, acidification, trypsin hydrolysis, surface rheology.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available