Screening of Freeze-Tolerant Yeasts and Their Bread Dough Fermentative Properties

Abstract

Freeze-tolerant yeasts were screened from natural sources and their characteristics for dough fermentative ability were studied. One-hundred and 44 strains of fermentable yeasts were isolated from various sources using Koji extract as a selection medium. Four strains of yeast, D₂_4, E₂, F₆ and A₂, which had relatively high freeze-tolerance and dough fermentative ability, were selected. Their freeze-tolerance rate ranged from 70 to 92%, which reflected the high fermentative ability of prefermented frozen doughs after storing at-30°C for several days. The D_2-4 strain also showed the highest fermentative ability in the sweet doughs, but in sponge doughs, CO₂ production in the later stage of fermentation tended to decrease due to the lack of maltose fermentation ability. The quality of bread from frozen dough with the D_2-4 strain was superior to that prepared by Saccharomyces cerevisiae, which was used as a control strain.