Effect of acid treatment on structural and foaming properties of soy amaranth protein mixtures

Abstract

To obtain a food ingredient composed of soybean and amaranth proteins with better functionality, the proteins were subjected to an acid treatment followed by neutralization. The native and treated proteins, amaranth (A and TA), soybean (S and TS) and the 1:1 mixture (M and TM) were studied. The structural characteristics and surface tension and foaming properties of the proteins were analyzed.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.