Identification of potential causative agents of the CO2-mediated bloater defect in low salt cucumber fermentation

Abstract

Development of bloater defect in cucumber fermentations is the result of carbon dioxide (CO2) production by the indigenous microbiota. The amounts of CO2 needed to cause bloater defect in cucumber fermentations brined with low salt and potential microbial contributors of the gas were identified. The carbonation of acidified cucumbers showed that 28.68 ± 6.04 mM (12%) or higher dissolved CO2 induces bloater defect. The microbiome and biochemistry of cucumber fermentations (n = 9) brined with 25 mM calcium chloride (CaCl2) and 345 mM sodium chloride (NaCl) or 1.06 M NaCl were monitored on day 0, 2, 3, 5, 8, 15 and 21 using culture dependent and independent microbiological techniques and High-Performance Liquid Chromatography. Changes in pH, CO2 concentrations and the incidence of bloater defect were also followed. The enumeration of Enterobacteriaceae on Violet Red Bile Glucose agar plates detected a cell density of 5.2 ± 0.7 log CFU/g on day 2, which declined to undetectable levels by day 8. A metagenomic analysis identified Leuconostocaceae in all fermentations at 10 to 62%. The presence of both bacterial families in fermentations brined with CaCl2 and NaCl coincided with a bloater index of 24.0 ± 10.3 to 58.8 ± 23.9. The prevalence of Lactobacillaceae in a cucumber fermentation brined with NaCl with a bloater index of 41.7 on day 5 suggests a contribution to bloater defect. This study identifies the utilization of sugars and malic acid by the cucumber indigenous Lactobacillaceae, Leuconostocaceae and Enterobacteriaceae as potential contributors to CO2 production during cucumber fermentation and the consequent bloater defect.