| Abstract: | In wort fermentations, production of extracellular amyloglucosidase (AMG) by Saccharomyces diastaticus was greatest, and initiated earliest, when the requirement of yeast for oxygen or unsaturated lipid was incompletely satisfied. During such fermentations, maltotriose disappeared before maltose, glucose, the product of AMG action, accumulated and the wort was inadequately attenuated. In all circumstances examined, commencement of dextrin breakdown coincided with initiation of AMG excretion. Prior to excretion, active enzyme was associated with yeast cells but was located externally to the plasma-membrane. Dextrin or starch was not required to induce AMG production which is initiated, we conclude, when the carbon and energy-source becomes growth-limiting. S. diastaticus strains hydrolysed only a small proportion of wort dextrine and AMG produced in beer was unable to release glucose from pullulan. For production of low carbohydrate beer, strains which (i) synthesise significant amounts of a ‘debranching’ enzyme and (ii) are catabolite-derepressed for AMG production would be advantageous. |
