The potential value of succinylated soy protein (SPS) as a wall material for the encapsulation of ibuprofen (IBU), a model hydrophobic drug, by spray-drying was investigated. A succinylation rate of 93% was obtained for soy protein isolate, with a molar ratio of 1/1.5 (NH2/succinic anhydride). The solubility profile at 37°C showed that this chemical modification decreased the solubility of the protein below its isoelectric point, whereas solubility increased in alkaline conditions. Various SPS/IBU ratios (90/10, 80/20, and 60/40) were studied and compared with the same ratio of soy protein isolate (SPI/IBU). High encapsulation efficiency was achieved (91-95%). Microparticles were spherical and between 4 and 8 μm in diameter. The spray-drying of protein/IBU solutions appeared to be beneficial, as it resulted in an amorphous solid dispersion of IBU within the microparticles, coupled with an increase in the thermal stability of IBU. In vitro release was evaluated in acidic (pH 1.2 in the presence of pepsin) and neutral (pH 6.8) conditions similar to those in the gastrointestinal (GI) tract. IBU was released significantly more slowly at pH 1.2, for both proteins. However, this slowing was particularly marked for SPS, for which rapid (within 2 h) and complete release was observed at pH 6.8. These results validate the hypothesis that SPS is suitable for use as a coating material for hydrophobic active pharmaceutical ingredients (APIs) due to its pH sensitivity, which should delay IBU release in the gastrointestinal tract.
Keywords: green excipient; microencapsulation; modified release; oral route; pH sensitivity; plant protein; succinylation.