Potato Protein Isolate as a Solubility Enhancer of Poorly Water-Soluble Curcumin

Limited aqueous solubility, often associated with low drug bioavailability, represents one of the greatest challenges in the clinical translation of numerous drugs currently on the market or in development. New and safer strategies are needed to unlock the full potential of poorly water-soluble compounds. Here, we report the ability of potato protein isolate (PPI), a valorized side-stream product of the potato starch industry, to arrest precipitation of curcumin in aqueous-based solutions in a concentration-dependent manner, leading to a manifold improvement in the solubility of curcumin as compared to pure water. High concentrations of PPI and presolubilization of curcumin (in pure ethanol) before mixing with the protein isolate were necessary to achieve complete solubilization of 0.1 mg/mL curcumin in 90% (v/v) water. The effect of PPI as a solubility enhancer was found to be limited by its propensity to undergo gel transition when exposed to higher concentrations of ethanol. Finally, PPI was non-toxic to HeLa cells, as demonstrated by an in vitro cell viability study, whereas dispersions of curcumin induced a cytotoxic effect. Our findings highlight the potential of less conventional plant protein isolates, such as PPI, as a strategy to improve the aqueous solubility of poorly water-soluble compounds.