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Downstream processes have great influences on bacterial starter production. Different modifications occur to cellular compounds during freeze-drying process and storage of bacterial starters. Consequently, viability and culturability (multiplication capacity) undergo some changes. In this study, the effects of freeze-drying process and storage conditions were examined on cell envelope integrity, respiration and culturability of  Acetobacter senegalensis . Freezing of cells protected with mannitol (20% w/w) did not affect cell multiplication and respiration considerably; however, 19% of cells showed compromised cell envelope after freezing. After drying, 1.96&amp;times;10 11  CFU/g were enumerated, indicating that about 34% of the cells could survive and keep their culturability. Drying of the cells induced further leakage in cell envelope and finally 81% of cells appeared as injured ones; however, 87% of the dried cells maintained their respiration capacity. Storage temperature had significant effect on cell multiplication ability; higher storage temperature (35&amp;deg;C) caused 8.59-log reduction in cell culturability after nine-month period of storage. Collapse of cell envelop integrity and respiration was observed at 35&amp;deg;C. At lower storage temperature (4&amp;deg;C), the culturability decreased about one-log reduction after nine months. Cell envelope integrity was subjected to minor changes during a period of nine month-storage at 4&amp;deg;C whereas a heterogeneous population of cells with different respiration capacity emerged at 4&amp;deg;C. These results indicate that a major part of cells undergone drying process and storage entered into viable but non-culturable state. In addition, usage of different culture media didn&amp;rsquo;t improve resuscitation. Besides, it seems that sub-lethal damages to cell envelope caused uptake of propidium iodide, however these kinds of injuries could not impress cell multiplications and respiration.

Flow-cytometric assessment of damages to Acetobacter senegalensis during freeze-drying process and storage