Effect of package and storage conditions on viability and efficacy of the freeze-dried biocontrol agent Pantoea agglomerans strain CPA-2

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Abstract
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°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°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.
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