Evaluation of factors influencing the growth of non-toxigenic Clostridium botulinum type E and Clostridium sp. in high-pressure processed and conditioned tender coconut water from Thailand

Bacterial spores survive high pressure processing (HPP). Group II Clostridium botulinum is an obligate anaerobe spore-forming pathogen that can produce the botulinum neurotoxin under refrigeration. This study assessed nontoxigenic type E C. botulinum and Group II Clostridium sp. growth in raw and HPP (550 MPa, 3 min, 10 degrees C) Thai coconut water (CCW; pH 5.2). No spore germination or growth occurred in HPP CCW inoculated with 10(5) CFU/ml after 61 days regardless of oxygen concentration (< 0.5 - 11 mg/l) or storage temperature (4 and 20 degrees C). Spore concentration decreased by 3.0 +/- 0.1 log CFU/ml in a worst-case scenario consisting of non-HPP filter-sterilized CCW (pH 7.0) under anoxic incubation at 30 degrees C during 61 days, suggesting spore germination followed by cellular death. Supplementing filter-sterilized CCW (pH 7.0) with selected germinants and free amino acids did not support spore development, but the addition of nutrient-rich laboratory media (TPGY broth) at low concentrations (6.25%) promoted growth, suggesting that a lack of nutrients prevents C. botulinum development in CCW. Further risk assessment will require evaluating other CCW varieties and toxin production.