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Downstream processes have great influences on bacterial starter production. Different modificatio... more 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, 1.96×10 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°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°C. At lower storage temperature (4°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°C whereas a heterogeneous population of cells with different respiration capacity emerged at 4°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'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.
Downstream processes have great influences on bacterial starter production. Different modificatio... more 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, 1.96×10 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°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°C. At lower storage temperature (4°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°C whereas a heterogeneous population of cells with different respiration capacity emerged at 4°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'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.