Reentrant condensation of a multicomponent cola/milk system induced by polyphosphate

Highlights

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  A mixture of multicomponent cola and milk yielded reentrant condensation (RC).

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  Casein in milk and polyphosphate (polyP) in cola also exhibited reentrant behavior.

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  The critical points of RC depended on the length of the polyP chain.

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  Electrostatic interaction between casein and polyP induces RC in cola/milk system.

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  Introducing the concept of RC could enhance the strategy for designing food additive.

Abstract

Reentrant condensation (RC) is a protein behavior in which the protein solution shifts between the one- and two-phase state more than twice by increasing a single parameter. Although RC would be a candidate mechanism for the physicochemical design of food additives, no realistic model has been established under diverse contaminants like food materials. Here, we found that a mixture of cola and milk yielded RC. At pH 3.2–3.6, cola induced milk condensation at 30–40%, while lower or higher concentrations of cola did not. Furthermore, we reduced this cola/milk system to two pure components, casein in milk and polyphosphate (polyP) in cola, and investigated the characteristics of casein concentration and zeta potential. This was the first experimental demonstration of RC occurrence in a multicomponent system. The well-characterized cola/milk system would explore both the universal nature of proteins and the industrial application of RC.