13,696
edits
Changes
no edit summary
''Brettanomyces'' strains may possess both alpha and beta-glucosidases. Beta-glucosidase is intracellular (works on sugars that are passed into the cell through the cell wall), while alpha-glucosidase is both intracellular and extracellular (released into the environment by the cell). <ref name="Daenen1">[http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2007.03566.x/full Screening and evaluation of the glucoside hydrolase activity in Saccharomyces and Brettanomyces brewing yeasts. L. Daenen, D. Saison, F. Sterckx, F.R. Delvaux, H. Verachtert, G. Derdelinckx. 2007.]</ref><ref name="Kumara_1993">[http://aem.asm.org/content/59/8/2352.short Localization and Characterization of α-Glucosidase Activity in Brettanomyces lambicus. H. M. C. Shantha Kumara, S. De Cort and H. Verachtert. 1993.]</ref> These enzymes allow ''Brettanomyces'' strains to break down a broad range of sugars, including long-chain carbohydrate molecules (polysaccharides, dextrins, and cellulose/cellobiose), and to liberate glycosidically bound sugars which are unfermentable to ''Saccharomyces'' yeasts. <ref name="Steensels"></ref><ref>[http://www.scribd.com/doc/277758178/Insight-into-the-Dekkera-anomala-YV396-genome Insight into the Dekkera anomala YV396 genome. Samuel Aeschlimann. Self-published on Eureka Brewing Blog. Spet 2015.]</ref>.
Extracellular and intracellular alpha-glucosidase activity has been shown to break down sugars up to 9-12 chain carbons in one strain of ''B. lambicus'' (now classified as ''B. bruxellensis''), which is partly responsible for the slow, over-attenuation of wort that some strains of ''Brettanomyces'' an achieve in beers such as lambic and American sour beers <ref name="yakobson_introduction"></ref><ref name="smith_divol_2016"></ref>. Alpha-glucosidases are the enzymes that allow them to break down maltose, turanose, melezitose, and trehalose, as well as dextrins such as maltotetraose and maltopentaose. These enzymes work by cleaving off glucose that can be directly consumed by the cell, leaving a shorter chain sugar behind which is then further broken down. In the case of extracellular alpha-glucosidase activity, this breakdown of complex sugars occurs outside of the cell and may benefit other microorganisms if present such as lactic acid bacteria. These dextrins are left over after a normal ''Saccharomyces'' fermentation <ref name="Steensels"></ref>. Some other polysaccharides can be fermented by ''Brettanomyces'', including starch, laminarin, and pectin <ref name="Crauwels1"></ref>. The more complex the starch or sugar, the slower it is hydrolyzed by the alpha-glucosidase enzymes. The optimal pH for the alpha-glucosidase enzyme produced by one strain of ''B. bruxellensis'' was 6 and at a temperature of 39-40°C (102-104°F), and its activity was greatly reduced below a pH of 4.5 and above 8 (although citric acid was used as a buffer, and its effects on the enzyme was not compared to other acids), which might contribute to slower ''Brettanomyces'' fermentation in acidic beers <ref name="Kumara_1993" />. A survey of 84 strains from several species of ''Brettanomyces'' showed that there is a wide variability in the ability of different strains to ferment maltose, with some strains not being able to ferment it at all and others fermenting it very slowly, suggesting that alpha-glucosidase is not functional or poor in some strains . Additionally, when maltose is present instead of just glucose, the researchers saw an increased lag during the growth phase <ref name="colomer_2020_genome" />.
''B. bruxellensis'' and ''B. nanus'' can also produce oligo-1,6-glucosidase, which hydrolyze the alpha-1,6 linkages in starch and glycogen to produce oligosaccharides, and then further break down these oligosaccharides to produce sugars with alpha-1,4 linkages (for example, maltose, in the case of starches from malted barley <ref>[https://www.ncbi.nlm.nih.gov/books/NBK22396/ Complex Carbohydrates Are Formed by Linkage of Monosaccharides. Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. 2002.]</ref>). These alpha-1,4 linkages (maltose) are then further broken down by the maltose enzyme by strains of ''Brettanomyces'' or other present microbes that produce this enzyme <ref name="Crauwels_2014" />. Unlike for some domesticated diastatic ''S. cerevisiae'' strains, this ability for ''Brettanomyces'' to break down starches has occurred in the wild without domestication <ref name="roach_2019" /><ref>"Amylases". H. Taniguchi, Y. Honnda, in Encyclopedia of Microbiology (Third Edition), 2009.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/3049768678384659/ Ben Sykes. Milk The Funk Facebook post on ''Brettanomyces'' evolution to ferment dextrins. 11/13/2019.]</ref>.