Black-carrot drink şalgam as a habitat for spoilage yeasts

Abstract

Şalgam is a traditional drink produced via the lactic-acid fermentation of vegetables (black carrot and turnip), sourdough, and bulgur flour; with rock salt also added. During storage, an additional yeast-mediated fermentation can occur, causing changes in organoleptic properties, as evidenced by the microbe-mediated release of gases. Here, we characterise şalgam as a microbial habitat, identify the yeasts that cause spoilage, and characterise yeast-induced changes of the şalgam. The total acidity of the spoiled şalgam, in terms of lactic acid, ranged from 5.33 to 8.36 g/L with pH values from 3.86 to 4.10. Nine different spoilage fungi were isolated and then identified using molecular techniques (combination of PCR-RFLP of the 5.8 S-rRNA region and sequencing of the D1/D2 domain of the 26 S-rRNA gene). The highest frequencies of species were for the (apparently dominant) Saccharomyces cerevisiae, Galactomyces candidum, and Pichia kudriavzevii. Notably, two of these yeasts—P. kudriavzevii and Saccharomyces cerevisiae—are known to be acid-tolerant, have a robust stress biology, and can dominate various microbial habitats including those of fermented foods and drinks. Şalgam is a nutrient-rich, high-water-activity habitat that can favour the growth of various microbes and becomes less acidic (so more ecologically open) after the proliferation of yeasts.