A process for producing microparticles, in which an aqueous solution of purified
amylopectin-based starch of reduced molecular weight is prepared, the solution
is combined with biologically active substance, an emulsion of starch droplets
is formed in an outer phase of polymer solution, the starch droplets are made to
gel, the gelled starch particles are dried, and a release-controlling shell is
optionally applied to the particles, wherein at least one buffer substance having
the ability of keeping the pH of the produced microparticles above 3 if exposing
the microparticles to an aqueous evironment is added at any stage during the process.
Microparticles which essentially consist of said starch, have an amino
acid content of less than 50 g and have no covalent chemical cross-linking
and which have the aktivity of keeping the pH above 3 if exposed to a aqueous environment.