|FRANCO, WENDY - North Carolina State University|
|Perez Diaz, Ilenys|
|MCFEETERS, ROGER - Retired ARS Employee|
Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2012
Publication Date: 7/1/2012
Citation: Johanningsmeier, S.D., Franco, W., Perez Diaz, I.M., McFeeters, R.F. 2012. Influence of sodium chloride, pH, and lactic acid bacteria on anaerobic lactic acid utilization during fermented cucumber spoilage. Journal of Food Science. 77(7):M397-M404.
Interpretive Summary: Cucumbers preserved commercially by natural fermentations in salt brines occasionally spoil after the primary fermentation is complete. This spoilage has been characterized by decreases in lactic acid and rise in brine pH caused by microbial instability. Among several lactic acid bacteria species isolated from spoilage fermentations in this study, Lactobacillus buchneri was unique in its ability to initiate lactic acid degradation in fermented cucumbers and may play an important role in fermented cucumber spoilage. In the absence of oxygen, cucumbers fermented with 6% sodium chloride to a terminal pH of 3.2 were not subject to spoilage. However, lactic acid was degraded by spoilage microorganisms in cucumbers fermented with 0, 2, and 4% NaCl, even with a terminal pH as low as 3.2. Ongoing efforts to reduce sodium in commercial brining operations will need to include measures for controlling the increased susceptibility to spoilage of cucumbers fermented and stored with lower NaCl concentrations. L. buchneri may be an appropriate target for development of such control measures.
Technical Abstract: Cucumbers are preserved commercially by natural fermentations in 5% to 8% sodium chloride (NaCl) brines. Occasionally, fermented cucumbers spoil after the primary fermentation is complete. This spoilage has been characterized by decreases in lactic acid and a rise in brine pH caused by microbial instability. Objectives of this study were to determine the combined effects of NaCl and pH on fermented cucumber spoilage and to determine the ability of lactic acid bacteria (LAB) spoilage isolates to initiate lactic acid degradation in fermented cucumbers. Cucumbers fermented with 0%, 2%, 4%, and 6% NaCl were blended into slurries (FCS) and adjusted to pH 3.2, 3.8, 4.3, and 5.0 prior to centrifugation, sterile-filtration, and inoculation with spoilage organisms. Organic acids and pH were measured initially and after 3 wk, 2, 6, 12, and 18 mo anaerobic incubation at 25 ºC. Anaerobic lactic acid degradation occurred in FCS at pH 3.8, 4.3, and 5.0 regardless of NaCl concentration. At pH 3.2, reduced NaCl concentrations resulted in increased susceptibility to spoilage, indicating that the pH limit for lactic acid utilization in reduced NaCl fermented cucumbers is 3.2 or lower. Over 18 mo incubation, only cucumbers fermented with 6% NaCl to pH 3.2 prevented anaerobic lactic acid degradation by spoilage bacteria. Among several LAB species isolated from fermented cucumber spoilage, Lactobacillus buchneri was unique in its ability to metabolize lactic acid in FCS with concurrent increases in acetic acid and 1,2-propanediol. Therefore, L. buchneri may be one of multiple organisms that contribute to development of fermented cucumber spoilage.