Content of xylose, trehalose and L-citrulline in cucumber fermentations and utilization of such compounds by certain lactobacilli

Abstract

This research determined the concentration of trehalose, xylose and L-citrulline in fresh and fermented cucumbers and their utilization by Lactobacillus pentosus, Lactobacillus plantarum, Lactobacillus brevis and Lactobacillus buchneri. Targeted compounds were measured by HPLC and the ability of certain lactobacilli to utilize them was scrutinized in fermented cucumber juice. Fresh cucumber juice was supplemented with trehalose, xylose and L-citrulline to observed mixed culture fermentations. Changes in the biochemistry, pH and colony counts during fermentations were monitored. Trehalose was detected in fermentations to 15.51 {+/-} 1.68 mM. Xylose was found in a fresh cucumber sample to 36.05 mM. L-citrulline was present in fresh and fermented cucumber samples to 1.05 {+/-} 0.63 mM. Most of the lactobacilli tested utilized trehalose and xylose in FCJM at pH 4.7. L-citrulline was utilized by L. buchneri and produced by other LAB. L-citrulline (12.43 {+/-} 2.3 mM) was converted to ammonia (14.54 {+/-} 3.60 mM) and the biogenic amine ornithine (14.19 {+/-} 1.07 mM) by L. buchneri at pH 4.7 in the presence of 0.5 {+/-} 0.2 mM glucose enhancing growth by 0.5 log CFU/mL. The use of a mixed starter culture containing L. buchneri aided in the removal of L-citrulline and enhanced the fermentation stability. The utilization of L-citrulline by L. buchneri may be a cause of concern for the stability of cucumber fermentations at pH 3.7 or above. This study identifies the use of a tripartite starter culture as an enhancer of microbial stability for fermented cucumbers. ImportanceUtilization of trehalose, xylose and L-citrulline as energy sources by the indigenous cucumber microbiota was studied to determine if this was a cause for the spoilage of the fermented fruit. While the plant derived sugars, trehalose and xylose, were occasionally present in cucumber fermentations, they are readily utilized by the bacteria spearheading primary fermentation. L-citrulline, however, is an amino acid not naturally found in proteins, was detected in all the samples tested and was uniquely utilized by the spoilage associated bacterium, L. buchneri. Additionally, the bacteria involved in cucumber fermentation produced L-citrulline. It was observed that the use of L. pentosus, L. brevis and L. buchneri in a mixed starter culture aids in the removal of the alternate energy sources, including L-citrulline, and the generation of a stable cucumber fermentation for 55 days under anaerobiosis.