Extraction methods significantly impact pea protein composition, structure and gelling properties

Abstract

Pea protein has been processed by many methods, however, a systematic understanding of pea protein functionalities as impacted by extraction methods is limited. This study found that protein recovery methods determine the protein composition. Those obtained by ultrafiltration and dialysis contained albumins, whereas the alkaline-isoelectric precipitation (AI) and micellar precipitation (MP) methods specifically retained globulins. Pea proteins prepared by alkaline solution had higher 11S/7S ratio than those extracted by salt solution. Moreover, alkaline extraction had more profound impacts on protein conformation than salt solution and exposed protein hydrophobic region. The protein isolateed by different methods showed large variation in gelling properties due to their compositions and structures. Pea proteins extracted by MP or ultrafiltration from alkaline (AU) or salt extraction (SU) formed superior gels with a compressive strength of 60–80 kPa, comparable to soy protein gels (11 kPa). AU, SU, MP experienced high degree of unfolding upon heating, resulting in the exposure of interaction regions. The appropriate level of 7S allowed unfolded proteins to aggregate in a more organized manner through intra-floc links. These together led to homogeneous percolating-like microstructure with greater strength. Instead, the aggregates triggered by extraction through salt-dialysis (SD) method prevented protein unfolding, leading to coarse particulate structure, and weak gels. The AI method resulted in protein with loose conformation which promoted aggregation during gelling, hindering further protein unfolding, leading to weak gels. Results of this study demonstrated that by modulating the composition through extraction methods, stronger gels can be achieved for wider applications of pea protein.