PH-DEPENDENT MICROSPHERES FROM MODIFIED SOYBEAN PROTEIN HYDROLYSATE

Soybean hydrolysate is a hydrophilic mixture of amino acids and low mo lecular peptides which are soluble over the whole pH range. Chemical m odification of soybean hydrolysate with aromatic acyl chlorides result ed in a product that yielded pi-I-dependent microspheres. Investigatio n into the physicochemical properties of the microsphere forming mater ial indicated that acylation had altered the hydrophobic/hydrophilic r atio as evidenced by an increased column retention time on reverse pha se HPLC. This was further confirmed by analysis of the amino acid comp osition of the modified material. The data indicated that the hydropho bic/hydrophilic ratio and low molecular weight were critical factors i n the formation of this supramolecular complex. An estimation based on sedimentation rate revealed an average molecular weight of these micr ospheres as 10(7)-10(8) Daltons. Light scattering experiments indicate d that the microspheres have discrete chambers in the interior. Includ ed among the properties of the microspheres that have been determined are the pH range of the phase transition, size distribution and zeta-p otential. The physicochemical characteristics of the microspheres prep ared from modified soybean protein are similar to the microsphere form ing material produced by thermal condensation of amino acids. Formatio n of microspheres in solution containing either porcine insulin or sal mon calcitonin resulted in the encapsulation of nearly 60% of the diss olved proteins. Oral gavage of encapsulated porcine insulin or salmon calcitonin into the stomach of rats resulted in significant titers of either protein in the systematic circulation.