LEAVENING ABILITY AND FREEZE TOLERANCE OF YEASTS ISOLATED FROM TRADITIONAL CORN AND RYE BREAD DOUGHS

Strains of Saccharomyces cerevisiae and Torulaspora delbrueckii isolat ed from traditional bread doughs displayed dough-raising capacities si milar to the ones found in baker's yeasts, During storage of frozen do ughs, strains of T. delbrueckii (IGC 5321, IGC 5323, and IGC 4478) pre sented approximately the same leavening ability for 30 days. Cell viab ility was not significantly affected by freezing, but when the dough w as submitted to a bulk fermentation before being stored at -20 degrees C, there was a decrease in the survival ratio which depended on the y east strain, Furthermore, the leavening ability after 4 days of storag e decreased as the prefermentation period of the dough before freezing increased, except for strains IGC 5321 and IGC 5323, These two strain s retained their fermentative activity after 15 days of storage and 2. 5 h of prefermentation, despite showing a reduction of viable cells un der the same conditions, The intracellular trehalose content was highe r than 20% (wt/wt) in four of the yeasts tested: the two commercial st rains of baker's yeast (S, cerevisiae IGC 5325 and IGC 5326) and the t wo mentioned strains of T. delbrueckii (IGC 5321 and IGC 5323), Howeve r, the strains of S. cerevisiae were clearly more susceptible to freez ing damages, indicating that other factors may contribute to the freez e tolerance of these yeasts.