Monday, August 2, 2010
Pacific Concourse (Hyatt Regency San Francisco)
Dry powders obtained by spray drying, are the best way for conditioning biofungicides. However, spores of T. harzianum, a biological control agent, are heat-sensitive. One strategy to avoid heat damage is microencapsulation. In this process, the proper selection of the wall material is very important. Activation energy (Ea), defined as the energy required for evaporating one mol of water from the material to be dried, could provide a quantitative discriminating parameter to qualitatively evaluate commonly used materials for microencapsulation. The aim of this study was the evaluation of the effect of the activation energy of different wall materials, as well as the inlet (IT) and outlet (OT) drying temperatures on the survival of T. harzianum during spray drying process. We evaluated the polymers: maltodextrin 10DE, maltodextrin 20DE, gum arabic and the 1:1 (w/w) mixture of maltodextrin 10DE and gum arabic (Ea = 29, 24, 19 and 31 kJ mol-1, respectively), inlet temperature (120 - 150°C) and outlet temperature (70 - 90ºC) using a 33 factorial design. The wall material that resulted in the best survival (%) was the mixture 50:50 (w/w) of maltodextrin and gum arabic, which was dried at IT=140ºC and OT=90ºC. The use of this mixture allowed a eleven fold in terms of the spores survival in relation to non-microencapsulated spores. Our results indicate that the use of a material with high Ea, as well as the highest inlet and outlet temperatures, increase cell survival due to the formation of a fine, dense wall as seen by SEM.