VIEW ARTICLE    DOI: 10.1094/ASBCJ-36-0151

Genetic and Biochemical Studies on Yeast Strains Able to Utilize Dextrins. J. A. Erratt and G. G. Stewart, Labatt Breweries of Canada Ltd., London, Ontario N6A 4M3. J. Am. Soc. Brew. Chem. 36:0151, 1978.

Major carbohydrates in brewer's wort are sucrose, glucose, fructose, maltose, maltotriose and dextrin material. Normally, strains of ale (Saccharomyces cerevisiae) and lager (S. uvarum [carlsbergensis]) yeast can use only the sugars of hexose units 1-3, but some Saccharomyces strains use dextrin as sole carbon source for growth and fermentation; this is possible because an extracellular dextrinase or permease enzyme is excreted. Segregants of an S. diastaticus strain have at least one gene coding for dextrinase production. This gene (DEX 1) is on the right arm of chromosome III distal from the centromere. The enzyme coded by this gene hydrolyzes dextrin to glucose units and is considered to be amyloglucosidase. A nonbrewing Saccharomyces sp. haploid with ability to use dextrin as sole carbon source also has been found. The gene coding for this ability is unlinked (ie, in chromosome location) to DEX 1. Of the longer chain sugars, this system uses only maltotetraose and, to a lesser extent, maltopentose; it is regarded as a permease. The permease gene facilitates transport of maltotetraose and maltopentose across the cell membrane into the cytoplasm where α-glucosidase hydrolyzes these sugars to glucose. A MAL gene must "turn on" the maltose utilization system before a culture containing the permease gene can use maltotetraose and maltopentose.

Keywords: Brewing, Dextrin, Dextrinase, Fermentation, Genetics, Yeast