Aims: To reduce concentrations of protective and rehydrating media and to evaluate the effect of storage temperature, packaging and atmosphere conditions on the stability of freeze-dried Pantoea agglomerans cells. Efficacy against Penicillium digitatum of freeze-dried cells in orange fruits was also evaluated.
Methods and results: Several concentrations of protective and rehydration media were tested to reduce processing costs. Freeze-dried cells were packed in glass vials or plastic bags under vacuum or nitrogen conditions at 4 and 25 degrees C. After 1 and 3 months, efficacy of freeze-dried P. agglomerans against P. digitatum was tested.
Conclusions: The results indicate that it is possible to reduce the concentration of non-fat skimmed milk as a rehydration medium from 10% to 1%, maintaining viabilities of 100%. Moreover, freeze-dried cells could be stored in glass vials or in high barrier plastic bags at 4 degrees C for 3 months while maintaining high viabilities and efficacy against P. digitatum.
Significance and impact of the study: The major obstacle in the commercialization of biocontrol products is the development of a shelf-stable formulated product that retains biocontrol activity at a level similar to that of fresh cells. This study suggests that it is possible to maintain viability and efficacy of freeze-dried P. agglomerans cells for at least 3 months.