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Spray drying could be a suitable method for preserving microorganisms, as it allows large quantities of cultures to be dried at low cost. The aims of this paper were to evaluate the effects of spray-drying conditions on survival of the biocontrol agent Pantoea agglomerans CPA-2, which has shown antifungal activity against Penicillium expansum and Penicillium digitatum on citrus fruits. Various compounds cited in the bibliography as carriers were tested in our spray drying, and some salts (MgSO4, K2SO4. and Na2CO3) and dairy products (lactoserum or nonfat skimmed milk [NFSM]) showed the best results in terms of recovered powder. Outlet temperature had more influence on the death of bacteria than inlet temperature. P. agglomerans was heat sensitive, and the activation energy was around 6 kcal/mol K when MgSO4 (10%) or NFSM (10%) were used as carriers and only 3 kcal/mol K when the combination of MgSO4 (10%) and NFSM (10%) was used. The highest powder recovery was obtained when NFSM was used as the rehydration medium. Although the percentage of powder recovery was not high (around 50%) and viability was low, the results suggest that with bigger spray dryers, we could expect a lower outlet temperature and probably an increased viability. Further research into spray-dryer design is needed in order to demonstrate this.

Viability of the postharvest biocontrol agent Candida sake CPA-1 stored as liquid formulation was evaluated by studying the effect of growth, preservation medium, and temperature. C. sake was grown in molasses medium with unmodified water activity (a(w)) and in the same with a(w) modified to 0.98 with the addition of several solutes. Cells were preserved with isotonic solutions of different substances. Efficacy of liquid formulations stored for different periods was tested against infection by Penicillium expansum on apples. The best growth media were the (unmodified one and those modified to 0.98 a(w) with the addition of glycerol or sorbitol. For all growth media, the best preservation medium was the isotonic solution prepared with trehalose. When the effect of trehalose concentration in the preservation medium was studied, generally, at trehalose concentrations below the isotonic one, C. sake viabilities increased with increased trehalose. However, the best results were obtained when cells were preserved with the trehalose solution which was isotonic with cells. After 7 months of storage at 4 degrees C, cells that were grown in the sorbitol-modified medium and preserved with the isotonic solution of trehalose (0.96 M) maintained their viability and efficacy against P. expansum infection of apples.

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