The Uptake and Incorporation of 14C-labelled Sugars into Polysaccharides during Wort Fermentation by a Synchronous Culture of Brewer's Yeast

Abstract

SUMMARY: The incorporation of [U-14C]glucose, -maltose and -maltotriose into the polysaccharides of a brewer's yeast, Saccharomyces cerevisiae (NCYC240), in synchronous culture was followed during the fermentation of brewer's wort. The synchrony was induced by repeated subculture in brewer's wort at regular intervals, using cells skimmed from the surface of previous brews. The 14C-labelled sugars were assimilated simultaneously by the yeast and small but significant amounts of each incorporated into cellular polysaccharides. The low molecular weight acid-soluble fraction exhibited a cyclic fluctuation attributable to changes in enzymic activity associated with the synchronous behaviour of the yeast. Cyclic changes were also observed in the incorporation of labelled sugars into the mannan fraction of the walls, the uptake rising to successive maxima at the same stage of each budding cycle, followed by a rapid loss as the next cycle began. The incorporation of 14C into glycogen exhibited a stepwise character, in which brief periods of glycogen buildup alternated with longer periods of stability. The periods of glycogen biosynthesis coincided with the periods of most intensive budding. Incorporation of 14C into the glucan of the walls was a continuous process and could not be correlated with any particular phase of the cell cycle. Incorporation of 14C into glycogen and glucan was stable.