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Abstract
Freeze-dried spores of Bacillus megaterium, B. stearothermophilus, Clostridium bifermentans and C. botulinum type E suffered little or no loss in viability after storage at 25° at water activity (aw ) values between 0.2 and 0.8. When stored over P2O5 (0.00 aw ) the spores of all four species showed a marked loss in viability. The above results were similar for spores whether stored in air or in vacuum. With spores stored over distilled water (1.00 aw ) the Bacillus spores underwent a large loss of viability in vacuum, but not in air; for spores of the clostridia the reverse was true. The addition of DL-glyceraldehyde, diacetyl or ribose (0.05 M) to the spore suspensions before drying caused increased death during storage at 0.50 aw and to a lesser extent at 0.20 aw. Death was greater at 30° than at 10°. The addition of sucrose, glutamate or semi-carbazide did not decrease the viability. When the dried spores were resuspended in dilute phosphate buffer after storage for 2.6 years their resistance to heating was greatest after storage at aw values of 0.4, 0.6 and 0.8.
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