brine and propionic-acid

To evaluate the interaction between selected yeasts and bacteria and associate their metabolic activity with secondary cucumber fermentation.. Selected yeast and bacteria, isolated from cucumber secondary fermentations, were inoculated as single and mixed cultures in a cucumber juice model system. Our results confirmed that during storage of fermented cucumbers and in the presence of oxygen, spoilage yeasts are able to grow and utilize the lactic and acetic acids present in the medium, which results in increased brine pH and the chemical reduction in the environment. These conditions favour opportunistic bacteria that continue the degradation of lactic acid. Lactobacillus buchneri, Clostridium bifermentans and Enterobacter cloacae were able to produce acetic, butyric and propionic acids, respectively, when inoculated in the experimental medium at pH 4.6. Yeast and bacteria interactions favoured the survival of Cl. bifermentans and E. cloacae at the acidic pH typical of fermented cucumbers (3.2), but only E. cloacae was able to produce a secondary product.. The methodology used in this study confirmed that a complex microbiota is responsible for the changes observed during fermented cucumber secondary fermentation and that certain microbial interactions may be essential for the production of propionic and butyric acids.. Understanding the dynamics of the development of secondary cucumber fermentation aids in the identification of strategies to prevent its occurrence and economic losses for the pickling industry.

Topics: Acetic Acid; Bacteria; Butyric Acid; Cucumis sativus; Fermentation; Food Preservation; Hydrogen-Ion Concentration; Lactic Acid; Microbial Interactions; Propionates; Salts; Yeasts

Calcium chloride fermentations represent an alternative to reduce chloride concentrations in the wastewaters generated from commercial cucumber fermentations, currently performed in cover brine solutions containing 6% to 12% sodium chloride. However, preliminary attempts to commercially ferment the cucumbers in the presence of oxygen led to the development of a secondary cucumber fermentation or spoilage. The development of cucumber secondary fermentation has also been occasionally reported by processors using cover brine solutions containing sodium chloride. This study focused on the development of a model system to characterize CaCl(2) and NaCl secondary cucumber fermentations under conditions similar to those present on the commercial scale. Cucumber fruits mixed with cover brine solutions, containing 100 mM CaCl(2) or 1.03 M NaCl, and 25 mM acetic acid, were fermented in 2 L fermentation vessels subjected to air-purging at a rate of 5 mL/min. Microorganisms and selected biochemical changes detected in the experimental cucumber fermentations had been previously observed in commercial spoilage samples, suggesting the successful reproduction of the secondary fermentation in the laboratory. Experimental secondary fermentations were characterized by the rapid oxidation of the lactic acid produced during the primary fermentation, which, in turn, increased pH. Lactic acid disappearance seemed to be the result of yeast metabolism that also led to the chemical reduction of the environment to levels at which other bacteria could become established and produce butyric, propionic, and acetic acids. This model system will be applied for the identification of strategies to prevent the initiation of the cucumber secondary fermentation and reduce economic losses in the pickling industry.. The study of secondary cucumber fermentation has represented a challenge for many years. The successful development of a model system for the study of this phenomenon in the laboratory is instrumental in furthering the study of the event and in optimizing the sodium-chloride-free fermentation at the commercial scale.

Topics: Acetic Acid; Butyric Acid; Calcium Chloride; Cucumis sativus; DNA, Bacterial; Fermentation; Food Contamination; Food Preservation; Food Storage; Fruit; Hydrogen-Ion Concentration; Lactic Acid; Lactobacillus plantarum; Models, Theoretical; Propionates; Salts; Sodium Chloride; Yeasts