Proanthocyanidin microcapsules:: preparation, properties and free radical scavenging activity

Microcapsules were prepared by interfacial cross-linking of grape proanthocyanidin (GPO) with terephthaloyl chloride (TC). Using 5% TC, 30-min reaction time and a stirring speed of 5000 rpm, batches were prepared from 10% GPO solutions in buffers pH 8, 9.8, and Il, respectively. Microcapsules were studied with respect to morphology (microscopy), size (laser diffraction technique), stability in water at 45 degrees C and, for stable batches, IR spectroscopy, degradation in human plasma, and free radical scavenging activity studied by electron paramagnetic resonance (EPR) using both extinction of the stable radical DPPH (2, 2-diphenyl-picryl-hydrazyl), and scavenging of OH degrees (evaluated using 5,5-dimethyl-pyrrolidine-N-oxide; DMPO). All particles had a mean size < 10 mu m. Microcapsules obtained at pH 8 were unstable (yellow supernatant after 8 days). Microcapsules obtained at pH 9.8 and 11 exhibited a high stability (> 5 months). Using a stirring speed of 3000 rpm at pH II provided 15-mu m particles which gave a yellow supernatant after 3 weeks. The IR spectra of the two stable batches (pH 9.8 and 11) showed bands at 1736 and 1267 cm(-1) reflecting the formation of esters. They were slowly degraded in plasma, and although less active than the initial GPO, they exhibited a significant antioxidant activity. The method appears to be an efficient means of stabilizing the polyphenol without suppressing the free radical scavenging activity. (C) 1998 Elsevier Science B.V. All rights reserved.