Method of producing microparticles of the type having a crosslinked, aggregated protein matrix by spray drying

A method of producing microparticles by spray drying, the method comprising the steps of:

• providing a food-grade spray-drying feedstock solution comprising water, a volatile divalent metal salt, a weak acid, 5-15% dairy or vegetable protein (w/v), and an active agent, the feedstock solution having a pH at which the volatile divalent metal salt is substantially insoluble;
• spray drying the feedstock solution at an elevated temperature to provide atomised droplets whereby the volatile divalent metal salt disassociates at the elevated temperature to release divalent metal ions which crosslink and aggregate the protein in the atomised droplets to produce microparticles having a crosslinked aggregated protein matrix and the active agent dispersed throughout the matrix, wherein the spray-drying feedstock solution is prepared by the steps of:
• preparing an aqueous solution of the weak acid;
• preparing an aqueous dispersion of the volatile divalent metal salt;
• mixing the aqueous solution and the aqueous dispersion to provide a weak acid/volatile divalent metal salt dispersion and adjusting the pH such that the volatile divalent metal salt is substantially insoluble in the dispersion;
• preparing an aqueous dispersion of the protein;
• admixing the active agent with the aqueous dispersion of the protein to provide an active agent/protein dispersion;
• and
• admixing the active agent/protein dispersion and the weak acid/volatile divalent metal salt dispersion at a ratio of 1.0:1.5 to 1.5:1.0 to form the spray-drying feedstock solution.