Construction of a Stable α-Galactosidase-Producing Baker's Yeast Strain

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Abstract
Molasses is widely used as a substrate for commercial yeast production. The complete hydrolysis of raffinose, which is present in beet molasses, by Saccharomyces strains requires the secretion of α-galactosidase, in addition to the secretion of invertase. Raffinose is not completely utilized by commercially available yeast strains used for baking, which are Mel − . In this study we integrated the yeast MEL1 gene, which codes for α-galactosidase, into a commercial mel 0 baker's yeast strain. The Mel + phenotype of the new strain was stable. The MEL1 gene was expressed when the new Mel + baker's yeast was grown in molasses medium under conditions similar to those used for baker's yeast production at commercial factories. The α-galactosidase produced by this novel baker's yeast strain hydrolyzed all the melibiose that normally accumulates in the growth medium. As a consequence, additional carbohydrate was available to the yeasts for growth. The new strain also produced considerably more α-galactosidase than did a wild-type Mel + strain and may prove useful for commercial production of α-galactosidase.

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