Influence of soy protein's structural modifications on their microencapsulation properties: α-Tocopherol microparticle preparation

Enzymatic and chemical modifications of soy protein isolate (SPI) were studied in order to improve SPI properties for their use as wall material for alpha-tocopherol microencapsulation by spray-drying. The structural modifications of SPI by enzymatic hydrolysis and/or N-acylation were carried out in aqueous media without any use of organic solvent neither surfactant. Emulsions from aqueous solutions of native or modified SPI and hydrophobic alpha-tocopherol, were prepared and spray-dried to produce alpha-tocopherol microparticles. The effect of protein modifications and the influence of the core/shell ratio on both emulsion and microparticle properties were characterized. The obtained results demonstrated that oil-in-water emulsions prepared with modified proteins had lower droplet size (0.5-0.9 mu m) and viscosity (3.6-14.8 mPa.s) compared to those prepared with native proteins (1.1 mu m and 15.0 mPa.s respectively). Efficiency of oil retention decreased after protein hydrolysis from 79.7 to 38.9%, but the grafting of hydrophobic chain by acylation improved efficiency of alpha-tocopherol retention up to 94.8%. Moreover, higher emulsion viscosity, particle size and process efficiency were observed with the increase of alpha-tocopherol amount. (C) 2012 Elsevier Ltd. All rights reserved.