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

Abstract

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 (10¹⁰ cfu ml⁻¹) was used; the opposite occurred with non‐fat skim milk. The use of 10¹⁰ 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.