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

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 alpha-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 alpha-galactosidase, into a commercial mel 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 alpha-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 alpha-galactosidase than did a wild-type Mel strain and may prove useful for commercial production of alpha-galactosidase.