Beauveria brongniartii subjected to spray-drying in a composite carrier matrix system

The negative aspects of chemical pesticides are of growing concern to the public. Thus, there is a strong effort to exploit environmentally friendly possibilities for pest management. One strategy is the application of biocontrol agents such as the fungus Beauveria brongniartii. In this context, the central objective of the research presently described is to investigate spray drying as a preservation method for fungal conidia to obtain a practical formulation for spray application. An aqueous binary mixture composed of skim milk (SM) and polyvinylpyrrolidone (PVP K90) was examined as encapsulation matrix. The influence of different inlet/outlet temperature adjustments, the composition of the carrier system and the conidia concentration were examined with respect to their influence on spore viability. Results indicate that air outlet temperatures up to 53 +/- 2 degrees C resulted in a slight reduction of conidial viability (approximately 3%). Microencapsulated conidia have been subjected to storage tests with and without the addition of silica gel capsules at various temperatures. Results show that survival is inversely related to storage temperatures and residual moisture levels of the spray dried powders. The highest survival rates were observed at moisture contents of 3% and a temperature of 10 degrees C. Moreover, production characteristics like entrapment efficacy, shape and size were investigated. Furthermore, the composition of the carrier matrix was optimised to result in production yields of 25%. Results show that spray drying is a useful, economic encapsulation technology for aerial conidia of Beauveria brongniartii resulting in highly concentrated, spray dried powders of 92% viability.