Composition and Structure of Whey Protein/Gum Arabic Coacervates

Abstract

Complex coacervation in whey protein/gum arabic (WP/GA) mixtures was studied as a function of three main key parameters: pH, initial protein to polysaccharide mixing ratio (Pr:Ps)(ini), and ionic strength. Previous studies had already revealed under which conditions a coacervate phase was obtained. This study is aimed at understanding how these parameters influence the phase separation kinetics, the coacervate composition, and the internal coacervate structure. At a defined (Pr:Ps)(ini), an optimum pH of complex coacervation was found (pH(opt)), at which the strength of electrostatic interaction was maximum. For (Pr:Ps)(ini) = 2:1, the phase separation occurred the fastest and the final coacervate volume was the largest at pH(opt) = 4.0. The composition of the coacervate phase was determined after 48 h of phase separation and revealed that, at pH(opt), the coacervate phase was the most concentrated. Varying the (Pr:Ps)(ini) shifted the pH(opt) to higher values when (Pr:Ps)(ini) was increased and to lower values when (Pr:Ps)(ini) was decreased. This phenomenon was due to the level of charge compensation of the WP/GA complexes. Finally, the structure of the coacervate phase was studied with small-angle X-ray scattering (SAXS). SAXS data confirmed that at pH(opt) the coacervate phase was dense and structured. Model calculations revealed that the structure factor of WP induced a peak at Q = 0.7 nm(-1), illustrating that the coacervate phase was more structured, inducing the stronger correlation length of WP molecules. When the pH was changed to more acidic values, the correlation peak faded away, due to a more open structure of the coacervate. A shoulder in the scattering pattern of the coacervates was visible at small Q. This peak was attributed to the presence of residual charges on the GA. The peak intensity was reduced when the strength of interaction was increased, highlighting a greater charge compensation of the polyelectrolyte. Finally, increasing the ionic strength led to a less concentrated, a more heterogeneous, and a less structured coacervate phase, induced by the screening of the electrostatic interactions.

Molecular interactions of plant and algal polysaccharides

“…We have undertaken studies on the phase behaviour of gum Arabic (GA) -bovine serum albumin (BSA) systems by monitoring the turbidity and scattering intensity as the pH was gradually reduced in situ by the slow hydrolysis of glucono delta lactone [38]. For systems containing BSA:GA in ratios between 1:1 and 6:1, the turbidity (monitored by absorbance) was found to increase between pH ~4.7 -5.2 depending on the ratio (Figure 15a).…”

Characterization of silk fibroin/hyaluronic acid polyelectrolyte complex (PEC) films

“…Protein-polyelectrolyte interactions often leading to coacervation and resulting in biopolymer complexes arises mainly from electrostatic interactions [16]. This complexation is dependent on the ionization degree of these macromolecules and thus the pH.…”

Coacervation in Biopolymers

“…In contrast during coacervation, the charge neutralization of complexes was achieved through lowering of acacia gum negative charges [8]. Weinbreck et al [9,10,64,65,94] have studied the complex coacervation phenomenon in whey protein and gum arabic solutions and examined the composition and structure of the coacervate phase. The rheological studies revealed the viscous nature of their complex coacervate where G'' dominated over G' .…”

“…The viscosity of the coacervate was observed to increase with electrostatic interaction between the two biopolymers. The intermolecular complexes were visualized as gum arabic chains crosslinked by electrostatic interactions with whey protein molecules [9]. Thus, it appears that for each coacervation process there exists signature interaction, rheological behaviour and phase stability road map though some broad observables are common to all.…”

“…In particular, protein-polysaccharide and protein-protein coacervates have attracted much attention because of their inherent potential in generating new biomaterials. In addition, such studies provide basic understanding of specific and non-specific interactions operating between complementary polyelectrolytes [1-6] or polyelectrolyte-polyampholyte [7][8][9][10][11][12][13][14][15] pairs. Normally, polysaccharides are strong polyelectrolytes whereas proteins, in addition, can be polyampholytes.…”