Secondary fermentations during the bulk storage of fermented cucumbers can result in spoilage that causes a total loss of the fermented product, at an estimated cost of $6,000 to $15,000 per affected tank. Previous research has suggested that such fermentations are the result of microbiological utilization of lactic acid and the formation of acetic, butyric, and propionic acids. The objectives of this study were to characterize the chemical and environmental conditions associated with secondary cucumber fermentations and to isolate and characterize potential causative microorganisms. Both commercial spoilage samples and laboratory-reproduced secondary fermentations were evaluated. Potential causative agents were isolated based on morphological characteristics. Two yeasts, Pichia manshurica and Issatchenkia occidentalis , were identified and detected most commonly concomitantly with lactic acid utilization. In the presence of oxygen, yeast metabolic activities lead to lactic acid degradation, a small decline in the redox potential (E _h , Ag/AgCl, 3 M KCl) of the fermentation brines, and an increase in pH to levels at which bacteria other than the lactic acid bacteria responsible for the primary fermentation can grow and produce acetic, butyric, and propionic acids. Inhibition of these yeasts by allyl isothiocyanate (AITC) resulted in stabilization of the fermented medium, while the absence of the preservative resulted in the disappearance of lactic and acetic acids in a model system. Additionally, three Gram-positive bacteria, Lactobacillus buchneri , a Clostridium sp., and Pediococcus ethanolidurans , were identified as potentially relevant to different stages of the secondary fermentation. The unique opportunity to study commercial spoilage samples generated a better understanding of the microbiota and environmental conditions associated with secondary cucumber fermentations.

Quinoa, a nutritional grain, can be used as an ingredient in gluten-free sourdoughs. This study characterizes quinoa flour spontaneous fermentation with emphasis in the isolation of exopolysaccharide (EPS) producer bacteria. Real, red and black grains were studied. Dough yield, microbiota composition and fermentation biochemistry were determined for a total of 36 quinoa flour fermentations. The fermentation biochemistry was monitored by high-performance liquid chromatography (HPLC) analysis, pH measurement and titratable acidity. Changes in the microbiota were monitored by plating on deMann Rogosa and Sharp 5 agar (MRS5) and yeast and mold agar (YMA) plates and with metagenetic analysis. The ability to produce exopolysaccharides was screened in selected lactic acid bacteria (LAB) isolates. Production of organic acids in the spontaneous fermentation dropped the pH to 4.0 ± 0.3. The community of presumptive LAB reached 8.37 ± 0.01 log colony forming units (CFU)/mL by day 8 of back-slopped fermentations. The microbiota was composed of Lactobacillus, Enterococcus, Leuconostoc, Lactococcus, Pediococcus and Weissella. P. pentosaceous, L. citreum and W. cibaria were able to produce EPS in a starch-rich medium. P. pentosaceous showed higher exopolysaccharide yield, rapid acidifying kinetics and was able to drop the dough broth pH to values below 4.0 and a positive fermentation quotient after 24 h of incubation. Therefore, the bacterium might be a potential candidate for quinoa sourdough production.