Growth phenomena in biopolymer complexes composed of heated WPI and pectin

Abstract

An unusual growth behaviour of biopolymer complexes composed of whey protein isolate (WPI) and pectin with various degrees of esterification (DE) was investigated. The formation and stability of complexes was studied at the isoelectric point (pI) of the protein since most likely hydrophobic rather than electrostatic interaction forces dominate the complexation process. As such, biopolymer particles were generated under slightly acidic conditions (pH 4.6) which had been subjected to various heat treatments (ϑ = 25–80 °C). Dynamic light scattering and ζ-potential measurements were utilized to examine the formation and stability of pectin-protein complexes. The results revealed that the initial size and surface charge of biopolymer particles depended on the pectins DE. Use of low-methoxylated pectins (DE 10%) led to the formation of small-sized complexes with narrow particle size distributions and a higher magnitude of surface charge. All biopolymer samples showed a time-dependent increase in size. A linear regression analysis revealed that the particle volume (r3) increased linearly with time. It was demonstrated that the growth rates increased with decreasing temperatures, increasing DE, and decreasing pectin concentrations, respectively. However, the ζ-potential remained unchanged over the entire storage time tested. These results suggest that the control over processing conditions, biopolymer characteristics, and physicochemical interactions might lead to the fabrication of particles with specific particle sizes and surface charges.