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

- Amaranth proteins can form stable emulsions at both pH2 and pH6.3 at protein concentrations greater than 0.1% w/w.
- The presence of insoluble proteins in the emulsion does not affect their emulsifying properties.
- The formation of a flocs network increases the quicient stability of emulsions.

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.

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