Complex coacervation of pea protein and pectin: Contribution of different protein fractions to turbidity

Turbidity measurement is commonly used to determine interactions of biopolymers during complex coacervation. However, to investigate the influence of biopolymers with plant-based proteins, results may become affected when turbidity is additionally caused by protein self-aggregation of individual protein fractions. Therefore, the aim of the study was to distinguish between pea protein fractions that mainly are involved in protein-protein interactions and those that are involved in complex formation with pectin. To approach the aim, soluble pea protein (SPP) with low turbidity was fractionated from pea protein concentrate (PP) by isoelectric precipitation. Turbidity development of SPP with pectin was investigated in comparison to the PP with pectin. In mixture, pea protein and pectin, form complex coacervates mainly via electrostatic interactions. The pH-dependent complex formation between pectin and both protein samples respectively was investigated via turbidity measurement. The maximum turbidity of SPP-pectin mixtures was lower in comparison to PP-pectin mixtures. It was shown, that pea globulins influence the turbidity development due to protein self-aggregation, while the SPP fractions showed no influence on turbidity, resulting only in protein-pectin complexes. Analysis of the molecular weight distribution revealed that pea albumin (PA2) and another protein fraction with a low molecular weight (<20 kDa) are the main fractions interacting with pectin. Results from our study showed that protein self-aggregation should not be neglected when investigating the interaction between plant-based proteins and polysaccharides.