CO₂-mediated bloater defect can be induced by the uncontrolled growth of Enterobacteriaceae in cucumber fermentation

Enterobacteriaceae are known to proliferate in cucumber juice, deriving energy from the fermentation of sugars to organic acids and ethanol, and theoretically generating carbon dioxide (CO₂). We hypothesized that the CO₂ produced by the indigenous Enterobacteriaceae in the early stage of cucumber fermentation accumulates in the fermenting fruits causing bloater defect. The ability of seven Enterobacteriaceae, indigenous to cucumber, to grow and produce CO₂ in cucumber juice medium (CJM), a sterile model system for cucumber fermentation, was characterized. The induction of bloater defect in cucumber fermentation conducted with pasteurized and acidified fruits was also evaluated. The generation times of the seven Enterobacteriaceae in CJM ranged between 0.25 and 8.20 h and resulted in carbon dioxide (CO₂) production to estimated amounts of 7.22-171.5 mM. Enterobacter cancerogenus and Enterobacter nimipressuralis were among the bacteria that produced the most and the least CO₂ in CJM, respectively, at estimated mM concentrations of 171.58 ± 42.96 and 16.85 ± 6.53. Inoculation of E. cancerogenus and E. nimipressuralis in acidified and pasteurized cucumbers resulted in the production of 138 and 27 mM CO₂, respectively. Such Enterobacteriaceae produced 2% hydrogen in the model cucumber fermentations. A bloater index of 25.4 and 17.4 was calculated from the cucumbers fermented by E. cancerogenus and E. nimipressuralis, respectively, whereas no defect was observed in the fruits collected from uninoculated control fermentation jars. It is concluded that the metabolic activity of the Enterobacteriaceae indigenous to cucumber can produce sufficient CO₂ in cucumber fermentations to induce bloater defect.