MICROENCAPSULATION OF RHIZOBACTERIA BY SPRAY-DRYING - FORMULATION ANDSURVIVAL STUDIES

This research deals with the microencapsulation of the bacteria Pseudo monas fluorescens-putida, using the spray-drying technique. These bact eria act as a plant growth stimulator and the microparticles are subse quently included in the seed coating or pelleting material. The object ive was to maintain living encapsulated bacteria for a minimum of 5-6 months. Three polymers were tested: a methacrylic copolymer from the E udragit(R) range, an ethylcellulose and a modified starch. A silica ad ditive to the spraying food was also examined. The granulometric distr ibution and the morphology of the microparticles were studied and the residual moisture was measured after each bacteria survival control te st. The best results were obtained with the methacrylic copolymer Eudr agit(R), particularly for microparticles collected in the cone of the spray-drying chamber. The mean diameter of the microspheres was 44.6 m u m, 85% of these particles having a size between 6.2 and 84.4 mu m. T he bacterial survival time of a particular strain incorporated in thes e microparticles, strain M3.1, was one year. A relationship was found between the bacterial survival and the microspheres' residual moisture , the best survival of the stored bacteria being observed when the res idual moisture was around 25%.