Comparative behaviour of solutions and dispersions of amaranth proteins on their emulsifying properties

Abstract

In the present work the effect of the presence of soluble and insoluble protein on the stability of oil-water emulsions prepared with amaranth protein isolates (API) was analyzed. For this purpose, four types of emulsions were prepared: API-pH2 and API-pH6.3 dispersions and solutions. At pH 2.0 the amaranth proteins present higher solubility, are denatured and partially hydrolyzed; while at pH 6.3 its solubility is lower and its structure is more similar to the native protein. The soluble proteins present in API-pH2 and API-pH6.3 reduce with equal intensity the interfacial tension. However, the proteins present in API-pH2 are adsorbed twice as fast as those present in API-pH6.3, with equal rearrangement rate at the oil/water interface. Both, solutions and dispersions of API-pH2 and API-pH6.3 allow the formation of oil-in-water emulsions. Flocculation phenomena are evident, particularly in the case of API-pH6.3 dispersions. The calculated creaming-flocculation constant demonstrates that stability of emulsions increase with protein concentration and with the decrease of pH. The behaviour of API-pH2 and API-pH6.3 solutions was similar to that corresponding to the dispersions discarding a negative effect of the insoluble protein on the emulsifying properties of amaranth proteins.