A respiratory-deficient mutant,
Zygosaccharomyces rouxii Y-72, was induced from
Z.rouxii Y-7 by treating with ethidium bromide.The mutant was distinguished from the wild strain by culturing on glycerol medium and or color plate medium.Oxygen absorption was not observed in this strain using a Warburg's manometer.The reason for respiration deficiency was revealed to be lacking of cytochrome a and a
3 by modified opal glass method.There was no remarkable difference in growth progress between the two strains by static culture, whereas viable cells of the mutant decreased drastically after the peak at 40 hours of shaking culture.After the stationary phase of shaking culture, mutant cells were half the size of the wild strain cells.Though the mutant cell mass was only 80% that of the wild one's, fermentation efficiency was 12% higher in static culture.
Miso fermented by the mutant (mutnat miso) showed 13% higher fermentation efficiency and less sugar consumption than that by the wild strain (wild miso). Panels of sensory evaluation were divided into two groups; one group recognized no difference between the two misos, and the other pointed that mutant
miso had better quality. Mutant
miso could be preserved under 0.5% less alcohol concentration in comparison with the wild
miso.
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