Art Bettge, Megazyme, Moscow, ID, U.S.A.
Coauthor(s): David Mangan,
Enzymes, Extracts, Other Ingredients
The combined action of a range of carbohydrate hydrolases endogenous to barley is responsible for starch mobilization and hydrolysis into fermentable sugars during the mashing stage of the brewing process. Endo-(1,3:1,4)-β-glucanase (EC 188.8.131.52) and endo-1,4-β-xylanase (EC 184.108.40.206) are the two major hydrolytic enzymes involved in the breakdown of the endosperm cell wall, which is composed of approximately 75% (w/w) β-glucan and 20–25% (w/w) arabinoxylan. The extent of cell wall hydrolysis by these two enzymes is crucial, not only because it affects wort viscosity and filterability, which have a major impact on processing times, but also because it allows the amylolytic enzymes α-amylase (EC 220.127.116.11), β-amylase (EC 18.104.22.168), and limit-dextrinase (EC 22.214.171.124) to hydrolyze the starch within the endosperm into fermentable sugars. This poses the question of whether the importance of the cell wall degrading enzymes could have been overlooked in previous studies of their impact on the apparent attenuation limit (AAL). The relevant parameters commonly measured for a given malt sample are diastatic power and β-glucan content, which indirectly quantify the overall amylolytic activity and β-glucanase activity respectively. The development of novel, rapid, specific, highly reproducible assays for endo-(1,3:1,4)-β-glucanase, endo-1,4-β-xylanase, α-amylase, β-amylase, and limit-dextrinase in a series of barley malt samples will be discussed here. Defined colorimetric oligosaccharide substrates have been synthesised and employed in enzyme-coupled assay formats that remain in solution throughout the assay, making them ideally suited to high throughput automated analysis systems. These new assays are a powerful tool for malt quality assessment and should allow for accurate batch blending, more predictable brews, and consistent fermentability expectations. It is proposed that this approach could also be applied to the analysis of the endogenous enzyme activity of other cereals and could find extensive use in plant breeding and evolution based studies.
Art currently works as a consultant in cereal chemistry, having retired from 32 years with the USDA Agricultural Research Service at Western Wheat Quality Laboratory. In his capacity there as research lab manager, he investigated the biochemical underpinnings of wheat functionality in end uses, determining how endogenous proteins, lipids, and carbohydrates combine and interact to enable wheat to be milled and subsequently economically produce the diversity of products consumed by people globally. He also worked to produce testing methods and instrumentation to rapidly evaluate the quality of wheat and flour and used the resulting information to provide genetic information and molecular markers to wheat breeders. He has authored more than 40 peer-reviewed publications and book chapters and has been active with the AACCI for more than 25 years, serving on the board of directors and chair of the Milling and Baking Division and is currently serving as an associate editor for the journal Cereal Chemistry.