IDENTIFICATION OF YEAST ISOLATED FROM LABORATORY SOURDOUGHS PREPARED WITH GRAPE, APPLE, AND YOGURT

Yeast strains collected from three spontaneous laboratory sourdoughs, prepared over 10 days and using a traditional Spanish protocol, and formulated with (non-essential) different ingredients were identified and described. In addition to wheat flour (Triticum aestivum) and water, organic apples (5 days juice fermented at 40 degrees C), or plain yogurt, or organic white grapes (2 days must fermented at 20 degrees C) were used at the beginning of each sourdough production. One-hundred-eighteen yeast colonies were collected from the different phases of sourdoughs (ingredients preparation, pre-sourdough, and ripe sourdough propagation) using WL agar and Lysine agar media. Yeast isolates were clustered into 8 groups using PCR-RFLP analysis of the 5.8S-ITS rRNA region. One strain of each group was chosen for sequencing to confirm yeast identification at species level. The specifically prepared fruit ingredients, apple and grape, provided diversity of non-Saccharomyces yeast to the respective sourdoughs. The dominant species in the pre-sourdough phase were Meyerozyma guilliermondii for apple sourdough and Hanseniaspora uvarum for grape sourdough. For yogurt sourdough, Saccharomyces cerevisiae was already the dominant yeast in the pre-sourdough phase with a low proportion of Meyerozyma guilliermondii and Wickerhamomyces anomalus. In the three sourdoughs, regardless of the different ingredients used, Saccharomyces cerevisiae was the dominant yeast in the ripe phase.