ROLE OF MALTOSE PERMEASE AND ALPHA-GLUCOSIDASE IN MALTOSE FERMENTATION AND DOUGH-LEAVENING OF TORULASPORA-PRETORIENSIS YK-1

The yeast Torulaspora pretoriensis YK-1 possesses both high potential leavening ability and freeze-thaw resistance, but its leavening abilit y in dough, without the addition of sugar, is much less than commercia l baking strains (Oda and Tonomura 1993) Institute for Fermentation, O saka, Japan (IFO) 0022, another strain of T. pretoriensis, previously found to leaven dough efficiently without the addition of sugar, showe d higher activities of both maltose permease and alpha-glucosidase and fermented maltose in an aqueous medium faster than YK-1. No significa nt difference was observed between the affinities of maltose permease and alpha-glucosidase from IFO 0022 and those from YK-1. MAL61 and MAL 62 genes of Saccharomyces cerevisiae were expressed in T. pretoriensis YK-1 and elevated the activities of maltose permease and alpha-glucos idase, respectively, when these genes were introduced on YCp-type plas mids under control of the glyceraldehyde 3-phosphate dehydrogenase pro moter. Maltose fermentation by cells harbouring the plasmids carrying either MAL61 or MAL62 genes was: slightly stimulated. introduction of both genes further enhanced the maltose fermentation rate but not leav ening ability in dough without the addition of sugar. These results su ggest that maltose permease and alpha-glucosidase determine the overal l velocity of maltose fermentation. (C) 1995 Academic Press Limited.