Comparison of melibiose utilizing baker's yeast strains produced by genetic engineering and classical breeding

Yeast strains currently used in the baking industry cannot fully utilize th e trisaccharide raffinose found in beet molasses due to the absence of meli biase (alpha-galactosidase) activity. To overcome this deficiency, the MEL1 gene encoding melibiase enzyme was introduced into baker's yeast by both c lassical breeding and recombinant DNA technology. Both types of yeast strai ns were capable of vigorous fermentation in the presence of high levels of sucrose, making them suitable for the rapidly developing Asian markets wher e high levels of sugar are used in bread manufacture. Melibiase expression appeared to be dosage-dependent, with relatively low expression sufficient for complete melibiose utilization in a model fermentation system.