Impact of ingredient interactions on the physico-chemical stability of milk protein-stabilised oil-in-water emulsions

Besides an oil phase and an aqueous phase, emulsions also contain an emulsifier (e.g. protein). In addition, most food emulsions contain other ingredients, which are intended to adjust the macroscopic appearance, rheology or gravitational stability. Thickeners are used to slow down creaming or sedimentation phenomena. Using a model system including guar gum in a sodium caseinate stabilised oil-in-water emulsion, it was shown that intermediate concentrations may have the opposite effect: in fact, faster creaming may occur due to depletion flocculation effects when adding a neutral polysaccharide to these protein-stabilised emulsions. This macroscopic demixing could be reduced by formation of a sufficiently strong three-dimensional network, which could be realised by further increasing the guar gum concentration and/or the ionic strength. Hence, the macroscopic behaviour is dependent on a complex interplay of electrostatic and depletion interactions on the one hand, and bulk viscosity effects on the other hand. Anionic polysaccharides, such as pectins, were used to improve the stability of protein-stabilised emulsions around the protein’s iso-electric point by adsorption onto the interfacial protein layer, resulting in a beneficial combination of electrostatic and steric effects. However, rather large amounts of pectin were required since electrostatic interactions are weak around the iso-electric point. Our experiments revealed that covalent coupling of polysaccharides to proteins by mild heat treatment of dry mixtures is a promising technique to largely improve the emulsion stability around the protein’s iso-electric point. In this particular case, the surface-active protein transports the bound highly charged and hydrophilic polysaccharide towards the O/W interface and hence gives rise to a pronounced electrosteric stabilisation. As a last example, heat-induced coagulation in a coffee cream simulant has been studied. Heat coagulation may lead to an excessive increase of the viscosity of sterilised concentrated milk. It was observed that hydrolysed lecithin led to a heat-stabilising effect. Addition of such lecithin significantly reduced the additional protein adsorption upon sterilisation. It is suggested that the heat-stabilising effect of lecithin is due to the fact that it largely reduces attractive protein-protein interactions, such as interactions between whey proteins or between (aggregated) whey proteins and casein micelles, upon severe heating.

Grantor dc:publisher

Ghent University, Faculty of Bioscience Engineering

Year dc:date

2009

Author dc:creator

• Neirynck, Nico

Contributors dc:contributor

• Van der Meeren, Paul

• Agriculture and Food Sciences

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://biblio.ugent.be/publication/720670
urn:isbn:9789059892958
https://biblio.ugent.be/publication/720670/file/1886245

OAI identifier oai:identifier

oai:archive.ugent.be:720670