Effect of different levels of esterification and blockiness of pectin on the functional behaviour of pea protein isolate–pectin complexes

This research examines changes to the functional (solubility, emulsifying and foaming) properties of pea protein isolate when complexed with commercial citrus pectin of different structural attributes. Specifically, a high methoxy (P90; degree of esterification: 90.0%; degree of blockiness: 64.5%; galacturonic acid content 11.4%) and low methoxy (P29; degree of esterification: 28.6%; degree of blockiness: 31.1%; galacturonic acid: 70%) pectin at their optimum mixing ratios with pea protein isolate (4:1 pea protein isolate to P90; 10:1 pea protein isolate to P29) were assessed at the pHs associated with critical structure forming events during the complexation process (soluble complexation (pH_c), pH 6.7 and 6.1; insoluble complex formation (pH_ϕ1), pH 4.0 and 5.0; maximum complexation (pH_opt), pH 3.5 and 3.8; dissolution of complexes, pH 2.4 and 2.1; for admixtures of pea protein isolate–P90 and pea protein isolate–P29, respectively). Pea protein isolate solubility was improved from 41 to 73% by the presence of P90 at pH 6.0 and was also moderately increased at pH 4.0 and pH 5.0 by P90 and P29, respectively. The emulsion stability of both pea protein isolate–pectin complexes was higher than the homogeneous pea protein isolate at all critical pHs except pH_opt as well as pH_c for pea protein isolate–P29 only. P90, with the higher level blockiness and esterification, displayed better foaming properties at the maximal complexation pH when complexed with pea protein isolate than pea protein isolate–P29 or pea protein isolate alone. However at pH_ϕ2, pea protein isolate–P29 admixtures produced foams with 100% stability, increasing pea protein isolate foam stability by 85%. The enhanced functionality of pea protein isolate–pectin complexes based on the type of pectin used at critical pHs indicates they may be useful biopolymer ingredients in plant protein applications.