Formation and stability of dairy emulsions prepared with gradually demineralized casein micelles
Résumé
Casein micelles are colloidal particles of 150 to 200 nm diameter constituted of casein molecules (αs1, αs2, β, κ) and minerals (calcium phosphate) [1]. Their composition and structure are altered by changes in their calcium content which modifies their physicochemical and functional properties [2], providing possibilities for developing better quality, natural and sustainable dairy products. The objective of our work was to investigate the emulsifying capacities and stabilities against flocculation of model dairy emulsions made with different suspensions of gradually calcium-demineralized casein micelles.
Several amount of sodium citrate (a calcium chelating agent) were added to suspensions of purified casein micelles (20 g L-1) to reach the final concentrations of 0, 5, 15 and 40 mmol kg-1 and induce an increasing casein micelles calcium-demineralization (with respective rates of 6, 23, 53 and 75%). The newly formed casein aggregates were characterised and then used to prepare and study model dairy oil-in-water (30:70) emulsions.
Results showed progressive dissociation of casein micelles with the increase in sodium citrate concentration producing smaller but similarly charged aggregates. The emulsion droplet size was decreasing from 28 to 12 µm, revealing higher emulsifying capacities for the most calcium-demineralized casein micelles. However, the stabilities of the emulsions decreased over 3 weeks and flocculation appeared in the emulsions made with the most demineralized particles, suggesting that the smallest aggregates enhanced the depletion flocculation phenomenon. Further investigations on the presence of casein aggregates at droplets interface, by confocal microscopy, and determination of casein concentration will help understand those new properties.