Metabolism of lactic acid in fermented cucumbers by Lactobacillus buchneri and related species, potential spoilage organisms in reduced salt fermentations

• d- and l-lactic acid were degraded by Lactobacillus buchneri in fermented cucumber media.
• The highest rate of lactate metabolism occurred in the presence of 2% sodium chloride.
• Lactobacillus parafarraginis behaved similarly to L. buchneri in fermented cucumber media.
• Lactobacillus rapi was able to convert 1,2-propanediol to propionic acid and propanol.
• Lactate metabolism by L. buchneri was indicated as the source of pH rise in FC spoilage.

Recent evidence suggests that Lactobacillus buchneri may play an important role in spoilage-associated secondary fermentation of cucumbers. Lactic acid degradation during fermented cucumber spoilage is influenced by sodium chloride (NaCl) concentration, pH, and presence of oxygen. Objectives were to evaluate these factors on lactic acid utilization by L. buchneri, and to compare the biochemical changes to those which occur during fermented cucumber spoilage. Effects of NaCl (0, 2, 4, and 6% w/w), pH (3.8 vs 5.0), and aerobic environment were investigated using fermented cucumber media (FC) inoculated with spoilage microorganisms. At pH 3.8, L. buchneri degraded lactic acid in all NaCl concentrations. The highest rate of lactic acid utilization occurred in FC with 2% NaCl (P < 0.05). Lactic acid utilization was nearly identical under aerobic and anaerobic conditions, indicating that oxygen does not influence lactate metabolism by L. buchneri. Lactic acid utilization was accompanied by increases in acetic acid and 1,2-propanediol, and Lactobacillus rapi was able to convert 1,2-propanediol to propionic acid and propanol. L. buchneri initiated spoilage in a wide range of environmental conditions that may be present in commercial cucumber fermentations, and L. rapi may act syntrophically with L. buchneri to produce the commonly observed spoilage metabolites.