Presence and persistence of Pseudomonas sp. during Caspian Sea-style spontaneous milk fermentation highlights the importance of safety and regulatory concerns for traditional and ethnic foods

Bruna Leal Maske,Luiz Alberto Júnior Letti,Maria Giovana Pagnoncelli,Dão Pedro De Carvalho Neto,Juliano De Dea Lindner,Gilberto Vinícius De Melo Pereira,Carlos Ricardo Soccol

doi:10.1590/fst.15620

Abstract

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.

Highlights

The emergence of dairying was a critical step in early agriculture, with considerable importance in the human diet (Panesar, 2011)
Rarefaction curve analysis showed a trend to level-off at the genus level, indicating that the majority of bacterial communities were covered (Supplementary Material, Figure S1)
The results of this study demonstrated that Caspian Sea-style spontaneous milk fermentation is not an efficient tool to overcome poor microbiological quality of the milk used as raw material

Summary

Introduction

The emergence of dairying was a critical step in early agriculture, with considerable importance in the human diet (Panesar, 2011). As a rich nutritional source for microbial growth, prehistoric farmers used lactic acid fermentation to prolong the shelf life of milk (Carrer et al, 2016). Caspian Sea-style spontaneously fermented milk is widespread as an traditional product. It is usually produced by natural fermentation (12-24 h) of raw cow’s milk at ambient temperature (approximately 25 °C) (Kiryu et al, 2009). In Brazil, a similar fermented milk is produced by different families (private households) that believe the “mother inoculum” is originated from Caucasus region, so-called Caspian Sea-style fermented milk. There are no studies of this traditional product circulated in Brazil

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Conclusion