Amaranth proteins foaming properties: Film rheology and foam stability - Part 2.

In this work the influence of pH and ionic strength on the stability of foams prepared with amaranth protein isolate was analyzed. The behaviour observed was related to the physico-chemical and structural changes undergone by amaranth protein as a result of those treatments. The results obtained show that foams prepared at acidic pH were more stable than the corresponding to alkaline pH. At pH 2.0 the foams presented higher times and more volumes of drainage. This behaviour is consistent with the characteristics of the interfacial film, which showed a higher viscoelasticity and a greater flexibility at acidic pH than alkaline pH value, which in turn increased by increasing the concentration of proteins in the foaming solution. It is also important to note that the presence of insoluble protein is not necessarily detrimental to the properties of the foam. Detected changes in the characteristics of the interfacial film as in the foam stability have been attributed to the increased unfolding, greater flexibility and net charge of amaranth proteins at acidic conditions.

Amaranth proteins foaming properties: adsorption kinetics and foam formation--part 1.

This work has focused on the study of the relationships between the structural changes in proteins of amaranth under different conditions of pH and ionic strength and the ability to form foam, also taking into consideration the kinetics of adsorption of proteins at the interface. Results showed that treatment at pH 2.0 significantly improves the foaming properties of amaranth proteins. The structural studies performed indicate that amaranth proteins at acidic pH are denatured, dissociated and undergo partial hydrolysis due to the existence of an endoprotease. They also present a lower content of ß-sheet and random coil secondary structures. Diffusion-adsorption studies of proteins at the air:water interface allowed to determine that the acidic pH favors adsorption thereof (higher values of kdiff and ka) and reduces the need for a rearrangement (higher values of γr). The interfacial behavior of amaranth proteins is a direct consequence of the structural changes they undergo at acidic pH, changes that also were reflected on the increased foaming capacity (higher vo) thus forming more dense and homogeneous foams. The behavior of the soluble proteins as surfactants was not altered by the presence of protein aggregates and insoluble proteins.