Strong and elastic pea protein hydrogels formed through pH-shifting method

Abstract

Pea protein has attracted attentions as an alternative for soy protein, but its weaker gelling properties has limited its applications in food formulations. This research reports a heat-induced strong and elastic gel from pea protein isolate (PPI) pre-treated by a modified pH-shifting method. The scanning electron microscopy (SEM) observation and rheological measurement revealed that the formation of three-dimensional (3D) coagulum for pea protein at pH 12 by extending the alkali holding time (1, 24 and 48 h) and such coagulum maintained their structure when adjusting pH back to neutral. Further heating the pH-shifted PPI suspension at 92 °C led to gels of densely cross-linked polymer-like network with thin connective walls and pore size of 1–2 μm. Such uniform polymer-like gel network microstructure obtained in this work might be related to a high level of pea protein unfolding during pH-shifting treatment, which made the protein chain flexible and created more active sites to promote molecular interactions including hydrogen bonds and hydrophobic interactions when the protein was neutralized and heated. Notably the gel mechanical strength was dramatically increased to 21 kPa, accompanied by excellent elasticity and water holding capacity (>95%). The modified method of pH-shifting process has provided a new approach for preparation of pea protein gels with superior strength, thus may enable wider applications of pea protein applications in food formulations where gelling and texturization functions are required.