The impact of barley alpha-glucosidases on mashing and the production of fermentable sugars

Authors: IM, HANNA - Sejong University; Henson, Cynthia

Submitted to: Journal of the American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2021
Publication Date: 3/3/2021
Citation: Im, H., Henson, C.A. 2021. The impact of barley alpha-glucosidases on mashing and the production of fermentable sugars. Journal of the American Society of Brewing Chemists. https://doi.org/10.1080/03610470.2021.1880222.
DOI: https://doi.org/10.1080/03610470.2021.1880222

Interpretive Summary: Starch present in barley malts is the source of most or all, depending on the brewing method, of the fermentable sugars that are converted to alcohol by brewers' yeast. One of the four proteins responsible for fermentable sugar production is also one of the most susceptible to the high temperatures used by brewers during the generation of alcoholic beverages. The work presented here demonstrates how much of the fermentable sugars are actually produced by this one protein even though it is not functional at the highest temperatures used in the industrial production of alcoholic beverages. As this work determined that there is a significant amount of two of the three main sugars used by yeast by just this one protein, this work demonstrates the value of developing improved sources of this protein either by traditional plant breeding methods or other gene manipulation methods. The impact of such efforts would result in higher yield of usable product from the raw materials used during industrial processing.

Technical Abstract: The independent and interactive contributions of alpha-glucosidase to the degradation of raw starch isolated from barley and to the degradation of Lintner starch have been mathematically evaluated, but its contributions to the production of fermentable sugars during the actual mashing process have not been previously determined. Here we report the evaluation of those contributions through the use of an active site inhibitor, conduritol B epoxide, that specifically inhibits only alpha-glucosidase and has no effects on either alpha-amylase or beta-amylase activities. Introduction of the inhibitor at the beginning of mashing resulted in the reduction of glucose produced by 20-30% throughout mashing and the reduction maltotriose by 15-30%. Maltose levels were less influenced by alpha-glucisdase activities than were the levels of glucose and maltotriose. Hence, even though alpha-glucosidases are considerably thermolabilie at themperatures often used for starch conversion, they can contribute significantly to the production of two of the three fermentable sugars generated from starch degradation during mashing. Additionally, we demonstrate that kilning resulted in a 12-34% loss of alpha-glucosidase activity, that most activity was solubilized during mashing, most activity solubilized survived until mashing temperatures reached 55 C, and that when mash temperatures reached 72 C alpha-glucosidase activity was rapidly inactivated.