Optimization of a freeze-drying process for the biocontrol agent Pseudomonas spp. and its influence on viability, storability and efficacy
Our objective was to investigate the practicability of freeze-drying to formulate and stabilize pseudomonads. Using a not optimized freeze-drying protocol the viability of five Pseudomonas strains after freeze-drying ranged only between 2% and 10%. To improve the viability, three different freezing rates, three drying temperatures and 20 cryo-protective agents (CPAs) were compared. The viability after freeze-drying was particularly influenced by the CPAs. Especially, saccharose, glucose, lactose, skimmed milk and ligninosulfonic acid protected vegetative cells within the freeze-drying process. After optimizing the process the viability of the tested P. fluorescens strain Pf153 before and after freeze-drying was not anymore reduced. Within storability tests of four Pseudomonas strains with the best five CPAs, lactose, saccharose and skimmed milk performed the highest viability. When the efficacy of freshly produced and freeze-dried pseudomonads was compared in two different plant-pathogen systems, no significant differences were obtained. But CPAs were influencing the efficacy of strain Pf153 against Botrytis cinerea. The same efficacy was obtained when strain Pf153 was freezedried with lactose or skimmed milk whereas formulation with saccharose had a negative effect. Our results demonstrate that freeze-drying is a realistic drying technology for pseudomonads. For the development of the best freeze-drying protocol beside viability, the efficacy and storability are important additional selection criteria.
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