Microbiological survey of spontaneous vegetable fermentations: A food safety perspective

A survey of 75 commercially available, unpasteurised, spontaneously fermented vegetables was conducted, focusing on the culturable microbiota. Foodborne pathogens (Listeria monocytogenes, Salmonella sp.), indicator bacteria (generic E. coli, Enterobacteriaceae), and lactic acid bacteria (LAB) were analysed both at the day of purchase and at the end of shelf life. Selected samples were further examined for biogenic amines, and dominant culturable LAB were isolated and identified. Challenge tests evaluated the growth potential of L. monocytogenes during white cabbage fermentation. Results showed considerable variation in pH (3.1-4.3) and LAB counts (<1.0-8.8 log CFU/g), reflecting the spontaneous nature of the vegetable fermentations. No Salmonella sp. (detection in 25 g), L. monocytogenes (LOD 10 CFU/g), or E. coli (LOD 10 CFU/g) were detected, indicating no immediate food safety or hygiene concerns, although Enterobacteriaceae were present (LOD 10 CFU/g) in six samples, suggesting an inadequate (spontaneous) fermentation process to ensure die-off of enteric pathogens. LAB isolates were dominated by Pediococcus parvulus, Lactiplantibacillus plantarum, Levilactobacillus brevis, and Lentilactobacillus buchneri. High biogenic amine levels highlight an increased risk for adverse health effects related to spontaneous vegetable fermentations. Challenge tests confirmed that rapid acidification to pH <4.4, followed by a minimum 14-day holding period under optimal fermentation conditions, effectively limits pathogen outgrowth and/or survival. Good fermentation practices, together with a sensory evaluation are essential to ensure the microbiological safety, quality, and consistency of spontaneous vegetable fermentations.