Modulation of the bacterial population in commercial cucumber fermentations by brining salt type

Authors: Perez Diaz, Ilenys; DICKEY, ALLISON - North Carolina State University; FITRIA, RASI - North Carolina State University; RAVISHANKAR, NIVEDITHA - North Carolina State University; Hayes, Janet; CAMPBELL, KEVIN - Mount Olive Pickle Company; ARRITT, FLETCHER - Mount Olive Pickle Company

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2020
Publication Date: 6/1/2020
Citation: Perez Diaz, I.M., Dickey, A., Fitria, R., Ravishankar, N., Hayes, J.S., Campbell, K., Arritt, F. 2020. Modulation of the bacterial population in commercial cucumber fermentations by brining salt type. Journal of Applied Microbiology. 128(6):1678-1693. https://doi.org/10.1111/jam.14597.
DOI: https://doi.org/10.1111/jam.14597

Interpretive Summary: The fermentation of cucumbers, a centuries-old process to extent the shelf-life of such fruit, is known to improve sensorial characteristics as compared to the fresh produce and popularly believe to enhance beneficial microbes content and bioactivity. This research focused in defining the microbiome of cucumber fermentations brined with 0% sodium chloride, 6% sodium chloride and 1% calcium chloride to fill a knowledge gap and determine if significant differences in the fermentative microbiota exist as a function of salt type and/or content. Addition of calcium chloride to the fermentation brines resulted in an accelerated preservation in which beneficial microbes dominated. The presence of sodium chloride in the fermentation brine enabled the survival of Enterobacter for a prolong period of time as compared to the no salt and the calcium chloride containing fermentations. Beneficial microbes belonging to the lactic acid bacteria group prevail in all fermentations by day 7, regardless of salt content and/or type.

Technical Abstract: Aims: Differences in the bacterial population of cucumber fermentations brined with no salt, 100 mmol 1-1 (1-1%) calcium chloride or 1-03 mol l-1 (6%) sodium chloride (NaCl) were studied. Methods and Results: Changes in the microbiology and chemistry of commercial and laboratory scale cucumber fermentations occurring as a function of time were monitored using colony counts and metagenetic analysis, and a pH probe and high-performance liquid chromatography analysis respectively. Dissolved oxygen and carbon dioxide content were monitored in commercial fermentations. Fermentations brined with calcium chloride or no salt sustained faster microbial growth and reduction in pH than those brined with 1-03 mol l-1 NaCl. Leuconostoc, Lactococcus and Weissella dominated in fermentations brined with no salt or 100 mmol l-1 calcium chloride on day 1 as compared to Weissella and enterobacteria in fermentations containing 1-03 mol l-1 NaCl. Lactobacilli dominated all fermentations by the third day, regardless of salt type, and was followed, in relative abundance by Pediococcus, Leuconostoc, Lactococcus and Weissella. From 84 to 96% of the population was composed of Lactobacillus by day 7 of the fermentations, except in the no salt fermentations in which a mixed population of LAB remained. The population of LAB found in commercial cucumber fermentations brined with 100 mmol l-1 calcium chloride (n = 18) or 1-03 mol l-1 NaCl (n = 9) mimicked that of laboratory fermentations. A declining population of aerobes was detected in commercial fermentations brined with CaCl2 on day 1. Conclusion: A reduced NaCl content in cucumber fermentation enhances microbial diversity. Significance and Impact of the Study: This study fills a knowledge gap and aids in the design of improved reduced NaCl cucumber fermentations.