Influence of Competitive Adsorption on Flocculation and Rheology of High-Pressure-Treated Milk Protein-Stabilized Emulsions

Abstract

The effect of high-pressure treatment (HPT) on the droplet-size distribution and small-deformation rheology of oil-in-water emulsions containing beta-lactoglobulin and a nonionic surfactant or sodium caseinate has been investigated at neutral pH. Addition of Tween 20 (polyoxyethylenesorbitan monolaurate) to a beta-lactoglobulin-stabilized emulsion results in competitive displacement of the adsorbed globular protein film and, following HPT, the formation of a less flocculated emulsion. The age of the beta-lactoglobulin-stabilized emulsion prior to addition of sodium caseinate influences the competitive adsorption behavior. The strengthening of the beta-lactoglobulin layer with time makes it more resistant to disruption by sodium caseinate. The level of pressure-induced flocculation of beta-lactoglobulin-coated oil droplets depends on the intensity of processing conditions and on the degree of interfacial displacement. In contrast, beta-lactoglobulin added after emulsification appears to show little evidence of competitive adsorption behavior at the caseinate oil-water interface. Changes in the rheological properties of these latter systems following HPT can be attributed to pressure-induced denaturation and gelation of beta-lactoglobulin in the continuous phase of the emulsion.

Flocculation of protein-stabilized oil-in-water emulsions

“…Liquidlike emulsions can be converted into solid-like emulsion gels on heating [111]. Static high-pressure treatment of ␤-lactoglobulin in emulsions can also have a significant influence on protein aggregation and emulsion stability [112][113][114].…”

High pressure versus heat treatments for pasteurisation and sterilisation of model emulsions

“…A considerable amount of research has been performed on the stability of WPI and β-lactoglobulin emulsions under high pressure (Dickinson & James, 1998;Dickinson & James, 1999;Galazka, Dickinson, & Ledward, 1996;Galazka, Ledward, Dickinson, & Langley, 1995). It has been shown that HP treatment of emulsions under relatively severe pasteurisation conditions (800 MPa, 30 min) is less destabilising for an emulsion made with β-lactoglobulin than a mild heat treatment (Dickinson & James, 1999) and has little effect on the stability of a whey protein stabilised emulsion (Galazka et al, 1995). High-pressure sterilisation is a relatively novel development in this field where pressure and heat together result in sterilisation of food products.…”

Interactions of some amino acids and glycine peptides with aqueous sodium dodecyl sulfate and cetyltrimethylammonium bromide at T=298.15 K: a volumetric approach

“…Surfactant-protein interactions have been studied using conductivity [5,6], chromatography [5], axisymmetric drop shape analysis [7], FTIR [8][9][10], circular dichroism [11,12], fluorescence [13,14], and direct calorimetry [15][16][17][18]. It has been proposed that surfactants may interact with proteins directly by competing for oil-water or air-water interfaces [19,20] and by binding to them thereby leading to substantial changes in the protein conformation [21,22]. Alterations in the molecular characteristics of globular proteins due to their interactions with surfactants may lead to changes in their ability to bind other molecules; i.e.…”