Abstract
ABSTRACT The effect of sodium chloride concentration (3, 4, 5, 6, 8, 10 and 12%) and storage temperatures (4°C, 10°C, 15°C and 30°C) on toxin production by Clostridium botulinum isolated from tropical fish was studied in anaerobic cooked meat medium. The combined effect of sodium chloride (3, 5%), low pH (5.5) and low temperature (15°C) on toxin production by C. botulinum was also examined. The toxicity was tested by mouse bioassay. An increase in lag phase was noticed by increasing the salt concentration. At 30°C, spores of C. botulinum type E were able to grow and produce toxin up to 3% salt (aw = 0.976), whereas for types C and D the limiting salt concentration was 4–5% (aw = 0.97–0.974) and for types A and B it was 8% (aw = 0.952). By lowering the storage temperature, an increase in lag phase and time to toxicity was noticed for type E at 3% salt and for types A, C and D at 5% salt level. The probability of growth and toxin production at 5% salt decreased as the pH and storage temperature (combined stress) was decreased.
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