Mixed protein–polysaccharide interfacial layers: effect of polysaccharide charge distribution

Abstract

The influence of the polysaccharide charge distribution on the structure, thickness, and charge reversal of the interfacial layers, formed by adsorbed positively charged protein and oppositely charged polysaccharide, has been investigated using lattice-based self-consistent field (SCF) approach. We compare the adsorption behaviour of a uniformly charged polysaccharide model with that consisting of a short and a long block carrying different charge densities. For homogeneously charged 10 polysaccharide we observe a resulting interfacial layer that is closer to a mixed protein + polysaccharide film, rather than a multi-layer. We also find that the maximum adsorption of polysaccharide occurs at an optimal value of its charge, above and below which the adsorbed amount decreases. In contrast, for heterogeneously charged chains, as their charge is increasingly located on the shorter block, a much thicker interfacial layer results. In such cases the weakly charged longer blocks extend well away from 15 the surface into the solution. The interfacial film begins to resemble a multilayer with a primary protein and a distinct secondary polysaccharide layer. When the weakly charged long blocks still have a sufficient amount of negative charge, we also observe a reversal of the sign of surface potential from positive to a negative value. Our SCF calculated values for the reversed surface potential are of the order of −25 mV, in good agreement with several experimental results involving -potential measurements on 20 particles covered with such protein + polysaccharide films.

Influence of pH value and locust bean gum concentration on the stability of sodium caseinate-stabilized emulsions

“…If there is to be any adsorption of LBG this would have to be in the form of a secondary layer adsorbed on top of the primary caseinate layer. Adsorption of polysaccharides to hydrophobic-hydrophilic interfaces in this manner has been investigated both experimentally (Guzey & McClements, 2006;Guzey & McClements, 2007;Jourdain, Schmitt, Leser, Murray, & Dickinson, 2009) and through numerical theoretical calculations (Ettelaie, Akinshina, & Dickinson, 2008;Ettelaie, Akinshina, & Maurer, 2012). These studies have shown the need for strong favorable interactions between protein and polysaccharides before the formation of a secondary adsorbed layer by the latter can commence.…”

Colloidal interactions induced by overlap of mixed protein+polysaccharide interfacial layers

“…The aim is to relate the predicted interactions for different polysaccharides, having contrasting degrees of charge distribution along their back bone, to the interfacial structures that arise for each case. The influence of the charge distribution of polysaccharides on the structure of mixed interfacial films, formed by these and proteins molecules, has already been reported in a separate publication of our own (Ettelaie, et al, 2012) and those of others (Dobrynin, 2005;Patel, Jeon, Mather, & Dobrynin, 2005). …”

“…These are presented first, as they are of particular relevance to the discussion of the data we obtain in the current work. Next, we shall outline our methodology and the model, which again are largely based along the same lines as those reported before (Ettelaie, et al, 2012). In section 4 the results of the calculations showing the interactions mediated by the overlap of mixed layers, involving polysaccharides with a variety of charges and charge distributions, adsorbed on the surface of two approaching colloidal particles, are presented.…”

“…In the next section we shall first review and summarise some of the key results we found in our previous study (Ettelaie, et al, 2012) with regards to the structure of single isolated protein + polysaccharide interfacial layers. These are presented first, as they are of particular relevance to the discussion of the data we obtain in the current work.…”

“…It is a privilege for us to present the current work, which touches upon both of these two areas of research, in a special issue of the journal dedicated to Professor Dickinson. The work is the latest in a series of papers attempting to theoretically investigate the behaviour of mixed interfacial layers, resulting from the electrostatic interactions between proteins and oppositely charged polysaccharides , 2009Ettelaie, Akinshina, & Maurer, 2012). In particular, it is the nature of colloidal interactions arising from the overlap of two mixed protein + polysaccharide layers, formed during the simultaneous adsorption of these biopolymers, which is the focus of the attention here.…”