There is increased interest in utilizing pea [P. sativum L.] protein as a kind of food ingredients. In our previous work 1, we had indicated that pea proteins exhibited better emulsifying properties at acidic pH values, suggesting a good potential of these proteins in acidic food formulations. In the present work, we further reported a novel behavior of pea protein isolate (PPI) to be applied to stabilize the oil-in-water emulsions at pH 3.0. At pH 3.0, most of the proteins in PPI were present in the nanoparticle form, with the hydrodynamic radius ranging from approximately 67 to 82 nm, and zeta potential from 55 to 47 mV, respectively, as the concentration (c) increased from 0.25 to 3.0 wt%. When all the emulsions at a specific oil fraction of 0.2 and varying c values of 0.25-3.0% were formed by a microfluidization emulsification, we found that upon increasing the c from 0.25 to 3.0%, the emulsion size considerably decreased, while the creaming stability of the emulsions progressively increased. Especially for the emulsions at c values higher 2%, no creaming occurred even after storage of 20 days. Confocal laser scanning microscopy analyses showed that increasing the c resulted in a progressive increase in extent of droplet flocculation, and at higher c values, a gel-like network could be observed, suggesting that the improvement of creaming stability was due to formation of gel-like network. Droplet size analyses indicated that the emulsions stabilized by PPI at c values above 1% were stable against coalescence upon storage. The gel-like network formation in the emulsions was closely associated with the increased interfacial protein concentration. The results suggest that at acidic pH PPI could produce a kind of highly creaming-stable emulsions with fine droplets, by varying the c or oil fraction. The underlying mechanism for the extraordinary stability against creaming might be largely associated with the formation of gel-like Pickering emulsions.
References
1. H. N. Liang & C. H. Tang, 2013, Food Hydrocolloids, 33, 309-319.
