|ZHAI, YAWEN - North Carolina State University|
|Perez Diaz, Ilenys|
Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2021
Publication Date: 4/16/2021
Citation: Zhai, Y., Perez-Diaz, I.M. 2021. Identification of potential causative agents of the CO2-mediated bloater defect in low salt cucumber fermentation. International Journal of Food Microbiology. 344:109115. https://doi.org/10.1016/j.ijfoodmicro.2021.109115.
Interpretive Summary: The industrial fermentation of cucumbers, needed in the production of pickles, has suffered of bloater defect for decades. This defect can cause up to 20% production losses for pickle processors in the USA. While it is known that the defect is caused by the accumulation of the carbon dioxide gas in the fermentations, the sourcing microbes are unknown. This study aimed at identifying microbes able to produce carbon dioxide in cucumber fermentations and induce the defect so that prevention and control measures can be implemented. We identified three groups of bacteria naturally present in cucumbers as contributors of the defect and the target for control measures. We are relating the timing of the presence of the bacteria belonging to the Leuconostocaceae, Enterobacteriacea and Lactobacillaceae families in the fermentations with the time in which the gas is produced and bloater defect develops using microbiological and biochemical analyses. We aim at defining ways to prevent and control the activity of the three bacterial groups identified as potential contributors and eliminate the consequent bloater defect.
Technical 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.