The acid-neutralization treatment caused structural modifications on all the proteins. The soybean proteins suffered some conformational changes and dissociation whereas the amaranth proteins were partially hydrolyzed by an endogenous aspartic protease, activated at acid pH. M showed the equivalent presence of S and A proteins, but TM, presented characteristics more similar to the TA proteins suggesting that the amaranth protease acted on the soybean proteins.
The acid treatment did not modify the S tensioactivity while TA and TM increased their tensioactivity compared to A and M. Amaranth proteins showed to be faster and more efficient than S in decreasing the surface tension, and present the higher velocity of foam formation. The acid treatment improved the foam formation capacity of all samples. Foam stabilization was also enhanced by the acid treatment, though in this case S proteins were better foam stabilizers than A. Although M showed an intermediate behavior between S and A, the TM showed a foam stability nearer the TS.
The mixture of amaranth and soybean proteins subjected to acid treatment make up an ingredient with improved surface and foam properties compared with its non treated components.