Increasing calcium solubility from whey mineral residues by combining gluconate and δ-gluconolactone

Abstract Insoluble milk mineral residues from whey processing, dominated by hydroxyapatite and calcium hydrogen phosphate, dissolved isothermally in aqueous gluconate/δ-gluconolactone, spontaneously forming solutions supersaturated in both calcium hydrogen phosphate and calcium gluconate. Calcium concentration of maximally supersaturated solutions was proportional to gluconate concentration, indicating gluconate assisted dissolution, while gluconolactone increased calcium available for dissolution and supersaturation. Precipitation of calcium gluconate, rather than of calcium hydrogen phosphate, was critical for supersaturation robustness. For calcium gluconate ionic product:solubility product of calcium gluconate ratios 100 times compared with equilibrium calcium hydrogen phosphate solubility, may be exploited for increasing calcium availability of whey mineral based functional foods.