|MCFEETERS, ROGER - Retired ARS Employee|
Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2013
Publication Date: 9/1/2013
Citation: Johanningsmeier, S.D., McFeeters, R.F. 2013. Metabolism of lactic acid in fermented cucumbers by Lactobacillus buchneri and related species, potential spoilage organisms in reduced salt fermentations. Food Microbiology. 35(2):129-135.
Interpretive Summary: It is known that lactic acid degradation during spoilage-associated secondary fermentation of cucumbers is influenced by processing variables such as salt concentration (sodium chloride), pH, and presence of oxygen. Certain lactic acid bacteria, specifically Lactobacillus buchneri, may play an important role in initiating this spoilage. This research investigated the ability of this bacterium to degrade lactic acid in fermented cucumbers under varying conditions of salt, pH, and in the presence and absence of oxygen. Metabolic breakdown of lactic acid by L. buchneri was compared to that carried out by spoilage organisms from industrial and reduced salt fermentations. We found that L. buchneri was capable of initiating lactic acid degradation at an acidic pH (3.8) in 0-6% salt in both the presence and absence of oxygen, covering a wide range of conditions that may occur in commercial fermentations. The highest rate and greatest extent of lactic acid degradation occurred in 2% salt, which may explain the increased incidence of spoilage that has been observed in reduced salt fermentations. Other lactic acid bacteria isolated from spoilage brines, Lactobacillus parafarraginis and Lactobacillus rapi, may also be contributing to the spoilage that is observed. L. parafarraginis degraded lactic acid similarly to L. buchneri. L. rapi did not metabolize lactic acid, but had complementary metabolic activity and may work together with L. buchneri to produce the commonly observed spoilage compounds. This increased knowledge of the ability of spoilage-associated lactic acid bacteria to degrade lactic acid in fermented cucumbers will assist us in developing appropriate practices for carrying out reduced salt fermentations.
Technical Abstract: 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.