Modulation of the bacterial population in commercial cucumber fermentations by brining salt type.

AIMS: Differences in the bacterial population of cucumber fermentations brined with no salt, 100 mmol l-1 (1·1%) calcium chloride (CaCl2 ) or 1·03 mol l-1 (6%) sodium chloride (NaCl) were studied. METHODS AND RESULTS: Changes in the microbiology and chemistry of commercial and laboratory scale cucumber fermentations occurring as a function of time were monitored using colony counts and metagenetic analysis, and a pH probe and high-performance liquid chromatography analysis respectively. Dissolved oxygen and carbon dioxide content were monitored in commercial fermentations. Fermentations brined with calcium chloride (CaCl2 ) or no salt sustained faster microbial growth and reduction in pH than those brined with 1·03 mol l-1 NaCl. Leuconostoc, Lactococcus and Weissella dominated in fermentations brined with no salt or 100 mmol l-1 CaCl2 on day 1 as compared to Weissella and enterobacteria in fermentations containing 1·03 mol l-1 NaCl. Lactobacilli dominated all fermentations by the third day, regardless of salt type, and was followed, in relative abundance by Pediococcus, Leuconostoc, Lactococcus and Weissella. From 84 to 96% of the population was composed of Lactobacillus by day 7 of the fermentations, except in the no salt fermentations in which a mixed population of LAB remained. The population of LAB found in commercial cucumber fermentations brined with 100 mmol l-1 CaCl2 (n = 18) or 1·03 mol l-1 NaCl (n = 9) mimicked that of laboratory fermentations. A declining population of aerobes was detected in commercial fermentations brined with CaCl2 on day 1. CONCLUSION: A reduced NaCl content in cucumber fermentation enhances microbial diversity. SIGNIFICANCE AND IMPACT OF THE STUDY: This study fills a knowledge gap and aids in the design of improved reduced NaCl cucumber fermentations.

Effect of high-pressure processing on strains of Enterobacter sakazakii.

Four strains of Enterobacter sakazakii were inoculated into tryptic soy broth and reconstituted powdered infant formula and exposed to high-pressure processing. Pressures of 200, 400, and 600 MPa were used for each medium for 1 min. E. sakazakii was reduced by more than 6 log (strains A and B) in both media at 600 MPa. Strain B was significantly (P < or = 0.05) more pressure resistant than the other strains, with just more than a 3-log reduction at 600 MPa in both media. The reconstituted infant formula has a significant (P < or = 0.05) protective effect for certain strains and pressures (strain B at 400 MPa and strain D at 400 and 600 MPa). Differences in log reductions between media (milk and broth) were also observed for certain strains and specific pressures (strain B at 400 MPa and strain D at 400 and 600 MPa; P < or = 0.05). This research showed that E. sakazakii, when present in reconstituted powdered infant formula, can be submitted to high-pressure processing (600 MPa for 1 min) and achieve log reductions ranging from 3 to 6.84, depending on the strain.

Determination of 5-log reduction times for Escherichia coli O157:H7, Salmonella enterica, or Listeria monocytogenes in acidified foods with pH 3.5 or 3.8 3.

A critical factor in ensuring the safety of acidified foods is the establishment of a thermal process that assures the destruction of acid-resistant vegetative pathogenic and spoilage bacteria. For acidified foods such as dressings and mayonnaises with pH values of 3.5 or higher, the high water phase acidity (acetic acid of 1.5 to 2.5% or higher) can contribute to lethality, but there is a lack of data showing how the use of common ingredients such as acetic acid and preservatives, alone or in combination, can result in a 5-log reduction for strains of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in the absence of a postpackaging pasteurization step. In this study, we determined the times needed at 10° C to achieve a 5-log reduction of E. coli O157:H7, S. enterica, and L. monocytogenes in pickling brines with a variety of acetic and benzoic acid combinations at pH 3.5 and 3.8. Evaluation of 15 different acid-pH combinations confirmed that strains of E. coli O157:H7 were significantly more acid resistant than strains of S. enterica and L. monocytogenes. Among the acid conditions tested, holding times of 4 days or less could achieve a 5-log reduction for vegetative pathogens at pH 3.5 with 2.5% acetic acid or at pH 3.8 with 2.5% acetic acid containing 0.1% benzoic acid. These data indicate the efficacy of benzoic acid for reducing the time necessary to achieve a 5-log reduction in target pathogens and may be useful for supporting process filings and the determination of critical controls for the manufacture of acidified foods.