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The aim of this study was to evaluate the performance of Caspian Sea-style spontaneous milk fermentation to improve the quality of pasteurized milk containing high levels of Pseudomonas contamination, with a focus on microbiological safety and stability of the final product. Bacterial diversity of pasteurized milk, fermentation process, and after 60 days of storage was analyzed by Illumina-based sequencing, and presence of viable taxa was confirmed by culturing on selective media. Low quality pasteurized milk harbored mainly Gram-negative bacteria, markedly dominated by Pseudomonas. Following fermentation, lactic acid bacteria rapidly became dominant with maximum population of 10.15 log CFU/mL at 18 h, represented mainly by Lactococcus. However, sequences related to Pseudomonas, and to a lesser extent for enterobacteria, remained constant throughout the fermentation process. The cultured-dependent approach confirmed the presence of viable Pseudomonas, with a final population of 5.60 log CFU/mL. Biochemical transformations were further analyzed, indicating lactic acid as the main end-metabolite produced (maximum concentration of 5.93 g/L at 24 h). In addition, the increase of 2-nonanone can be correlated as a volatile biomarker of P. aeruginosa and related species. Altogether, the results demonstrated that natural milk fermentation may often not inhibit the development of pathogens and food spoilage microorganisms.

The emergence of Coronavirus disease 2019 as a global pandemic has increased popular concerns about diseases caused by viruses. Fermented foods containing high loads of viable fungi and bacteria are potential sources for virus contamination. The most common include viruses that infect bacteria (bacteriophage) and yeasts reported in fermented milks, sausages, vegetables, wine, sourdough, and cocoa beans. Recent molecular studies have also associated fermented foods as vehicles for pathogenic human viruses. Human noroviruses, rotavirus, and hepatitis virus have been identified in different fermented foods through multiple routes. No severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) virus or close members were found in fermented foods to date. However, the occurrence/persistence of other pathogenic viruses reveals a potential vulnerability of fermented foods to SARS-CoV-2 contamination. On the other side of the coin, some bacteriophages are being suggested for improving the fermentation process and food safety, as well as owing potential probiotic properties in modern fermented foods. This review will address the diversity and characteristics of viruses associated with fermented foods and what has been changed after a short introduction to the most common next generation sequencing platforms. Also, the risk of SARS-CoV-2 transmission via fermented foods and preventive measures will be discussed.

The use of yeasts as starter cultures was boosted with the emergence of large-scale fermentations in the 20th century. Since then, Saccharomyces cerevisiae has been the most common and widely used microorganism in the food industry. However, Candida species have also been used as an adjuvant in cheese production or as starters for coffee, cocoa, vegetable, meat, beer, and wine fermentations. A thorough screening of candidate Candida is sometimes performed to obtain the best performing strains to enhance specific features. Some commonly selected species include C. pulcherrima (teleomorph Metschnikowia pulcherrima) (wine), C. parapsilosis (teleomorph Monilia parapsilosis) (coffee), C. famata (teleomorph Debaryomyces hansenii) (cheese), and C. zeylanoides (teleomorph Kurtzmaniella zeylanoides) and C. norvegensis (teleomorph Pichia norvegensis) (cocoa). These species are associated with the production of key metabolites (food aroma formation) and different enzymes. However, safety-associated selection criteria are often neglected. It is widely known that some Candida species are opportunistic human pathogens, with important clinical relevance. Here, the physiology and metabolism of Candida species are addressed, initially emphasizing their clinical aspects and potential pathogenicity. Then, Candida species used in food fermentations and their functional roles are reported. We recommended that Candida not be used as food cultures if safety assessments are not performed. Some safety features are highlighted to help researchers choose methods and selection criteria.