Complex coacervation of pea protein and pectin: Effect of degree and pattern of free carboxyl groups on biopolymer interaction

Abstract

In the field of microencapsulation, recently there has been an increasing interest in using plant-based biopolymers for complex coacervation. Since complex formation is based on electrostatic interactions, pectin and pea protein are generally considered as promising materials. However, electrostatic interactions are influenced by several biopolymer characteristics such as net charge and local charge density. Therefore, the aim of the study was to investigate the impact of degree of methoxylation (DM) and pattern of free carboxyl groups of pectin on complex coacervation with soluble pea protein fractions. Six pectin samples varying in DM 62%, 50%, 34% and local charge density (random or blockwise pattern) as well as soluble pea protein fractions were prepared under defined conditions. Interactions were qualitatively tested by turbidity measurement, by visual observation and microscopy. Isothermal titration calorimetry (ITC) allowed a quantitative evaluation of the interactions. A high protein share enhanced protein-pectin interactions, the optimum depended on pectin DM and was found for a mass ratio of 8:1 to 12:1. With respect to pectin, highest level of interaction was observed for pectin with a DM of 50%. The interaction was more pronounced for pectin with random than with blockwise pattern of free carboxyl groups. ITC measurements revealed a higher number of binding sites and a higher binding affinity with protein for pectin with random pattern of free carboxyl groups.