Effect of protective agents, rehydration media and initial cell concentration on viability of Pantoea agglomerans strain CPA-2 subjected to freeze-drying

The effect of initial cell density, protective agents and rehydration media on the viability of biocontrol agent Pantoea agglomerans CPA-2 when subjected to freeze-drying was studied. Several additives were tested as protective agents against freeze-drying injury. Maximum viability of the bacterial cells was obtained with disaccharides (survival levels > 60%). Freeze-dried samples were rehydrated with several media; the highest percentage viability was obtained with 10% non-fat skim milk (100%+). The effect of initial bacterial load on the final recovery was dependent on protectant but not on rehydration media. Sucrose was an effective protectant when a high initial concentration (10(10) cfu ml(-1)) was used; the opposite occurred with non-fat skim milk. The use of 10(10) cfu ml(-1) as an initial concentration, sucrose as a protectant and non-fat skim milk as a rehydration medium enabled 100% of P. agglomerans viability to be conserved after freeze-drying. Results suggest the possibility of achieving a good formulation system for the studied biocontrol agent with a high number of viable cells to be used toward pathogens, which is desirable for the industrial development of the product.