Formation and stability of emulsions made with proteins and peptides

P.E.A. Smulders

Research output: Thesisinternal PhD, WU

Abstract

<p>The formation and stabilization of oil-in-water emulsions using well-defined and well-characterized proteins and peptides was studied in order to elucidate the relation between their molecular and functional properties. The emulsions were formed with a high-pressure homogenizer. To study the effect of the homogenizer scale on the emulsion properties, emulsions were prepared with a laboratory and a small industrial homogenizer. The flow in the industrial homogenizer was shown to be turbulent. In the laboratory homogenizer, droplet break-up was found to occur in a bounded laminar type of flow, resulting in a poor operating efficiency. The effect of the flow type on the emulsion properties, however, appeared to be small, if the number of passes through the laboratory homogenizer was sufficiently high.</p><p>Proteins appeared to have good emulsion forming properties as long as protein aggregation was absent. In those cases, the recoalescence rate during homogenization was found to be similar and only small differences in the droplet size of emulsions could be determined. The surface excess of the emulsion droplets appeared to be governed by the conformational stability and the aggregated state of the proteins. Globular proteins with a high conformational stability yielded relatively low surface excesses, while a flexible random coil protein, likeβ-casein, yielded a relatively high surface excess. Protein aggregation may be due to physicochemical conditions and surface or heat denaturation. If protein aggregates were present, the emulsion droplets were also often aggregated. The droplet size, surface excess, and rate of recoalescence of these aggregated emulsions were usually found to be relatively high.</p><p>The emulsion forming properties ofβ-casein peptides appeared to be comparable or superior to those of intact proteins. Amphiphilic peptides without the hydrophobic C-terminal domain ofβ-casein yielded a relatively low surface excess, likely due to strong electrostatic interactions between the highly charged groups of the N-terminal end. The surface excess of emulsions made with hydrophobic peptides with a removed N-terminal domain was comparable to those of emulsions made with intactβ-casein. The peptides were due to their relatively small molar mass more readily desorbed from the oil/water interface than intact proteins.</p><p>The coalescence stability of emulsions made with proteins was high even at low protein concentrations and appeared to be mainly determined by the surface excess of the droplets. The emulsion stabilizing properties ofβ-casein peptides were inferior to those of intact proteins probably due to their relatively low molar mass. Comparison of the stability of emulsions made with amphiphilic peptides with an intact or partially removed N-terminal domain showed that this domain was of great importance for providing stability against coalescence. The coalescence stability of emulsions made with hydrophobic peptides was relatively high, which was attributed to the high surface excess of the droplets. The electrostatic and steric interactions appeared to be of great importance for stabilizing emulsions made with peptides against coalescence as was indicated by the effect of changes in pH and ionic strength on the stability.</p><p><strong>Keywords:</strong> emulsions, formation, stability, molecular properties,β-casein,β-lactoglobulin,α-lactalbumin, lysozyme, ovalbumin, peptides.</p>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • Walstra, P., Promotor
Award date4 Dec 2000
Place of PublicationS.l.
Publisher
Print ISBNs9789058083135
Publication statusPublished - 2000

Keywords

  • emulsions
  • formation
  • stability
  • casein
  • lactalbumin
  • lysozyme
  • ovalbumin
  • peptides

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