Location: Food Science ResearchTitle: Gentiobiose and cellobiose content in fresh and fermenting cucumbers and utilization of such disaccharides by lactic acid bacteria in fermented cucumber juice medium
Submitted to: Food Science and Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2020
Publication Date: 11/24/2020
Citation: Ucar, R.A., Perez Diaz, I.M., Dean, L.L. 2020. Gentiobiose and cellobiose content in fresh and fermenting cucumbers and utilization of such disaccharides by lactic acid bacteria in fermented cucumber juice medium. Food Science and Nutrition. 8(11):5798-5810. https://doi.org/10.1002/fsn3.1830.
Interpretive Summary: Like many fermented healthy foods, cucumber fermentations are microbiologically unstable as a function of time. This research aimed at studying a potential cause of fermented cucumbers spoilage. We investigated if fresh and fermented cucumbers naturally contain free cellobiose and gentiobiose, which are sugars derived from plant tissue. If so, it was of interest to understand if such sugars could be utilize as energy source by the same bacteria that spearhead cucumber fermentations and a bacterium known to cause spoilage of fermented cucumbers. We found that cellobiose and gentiobiose are not potential energy sources in cucumber fermentations as their level in the fresh fruit are not of biological significance and they are not produced as the result of the fermentation itself. Additionally we determined that the bacteria that lead cucumber fermentations are capable of utilizing both sugars and derive energy for growth. So, should the sugars be present in cucumber fermentations as the result of factors not considered in this study, the bacteria responsible for the fermentation could convert them to acids and preclude spoilage bacteria from using them as an energy source.
Technical Abstract: The content of cellobiose and gentiobiose, cellulose-derived dissacharides, in fresh and fermented cucumber was evaluated along with the ability of Lactobacillus plantarum, Lactobacillus pentosus, Lactobacillus buchneri and Lactobacillus brevis to utilize them during and after fermentation. The disaccharide content in fresh and fermenting cucumbers was below the detection level (10 µM) using HPLC for analysis. Utilization of cellobiose and gentiobiose by lactic acid bacteria (LAB) was tested in fermented cucumber juice medium (FCJM), a model system for the bioconversion and postfermentation lacking glucose and fructose. Changes in the fermentation metabolites were followed using HPLC and pH measurements as a function of time. The disaccharides were utilized by L. plantarum, L. pentosus, and L. buchneri in FCJM at pH 4.7 ± 0.1, representative of the active fermentation period, and converted to lactic acid. The disaccharides were not utilized in FCJM at pH 3.7 ± 0.1, representative of the end of fermentation. While L. brevis was unable to utilize cellobiose efficiently in FCJM, they were able to remove gentiobiose at pH 4.7 ± 0.1. Some strain level differences in cellobiose utilization were observed. It is concluded that the disaccharides are absent in the fresh cucumber and the typical fermentation. The LAB prevalent in the bioconversion utilizes cellobiose and gentiobiose, if available, at pH 4.7 ± 0.1. The LAB would not remove the disaccharides, which could become available from cellulose degradation by the acid resistant indigenous microbiota, after the pH is reduced to 3.7 ± 0.1.