A Modified Brewing Procedure Informed by the Enzymatic Profiles of Gluten-Free Malts Significantly Improves Fermentable Sugar Generation in Gluten-Free Brewing

The mashing step underpins the brewing process, during which the endogenous amylolytic enzymes in the malt, chiefly β-amylase, α-amylase, and limit dextrinase, act concurrently to rapidly hydrolyze malt starch to fermentable sugars. With barley malts, the mashing step is relatively straightforward, due in part to malted barley’s high enzyme activity, enzyme thermostabilities, and gelatinization properties. However, barley beers also contain gluten and individuals with celiac disease or other gluten intolerances should avoid consuming these beers. Producing gluten-free beer from gluten-free malts is difficult, generally because gluten-free malts have lower enzyme activities. Strategies to produce gluten-free beers commonly rely on exogenous enzymes to perform the hydrolysis. In this study, it was determined that the pH optima of the enzymes from gluten-free malts correspond to regions already typically targeted for barley mashes, but that a lower mashing temperature was required as the enzymes exhibited low thermostability at common mashing temperatures. The ExGM decoction mashing procedure was developed to retain enzyme activity, but ensure starch gelatinization, and demonstrates a modified brewing procedure using gluten-free malts, or a combination of malts with sub-optimal enzyme profiles, that produces high fermentable sugar concentrations. This study demonstrates that gluten-free malts can produce high fermentable sugar concentrations without requiring enzyme supplementation.

Genes That Mediate Starch Metabolism in Developing and Germinated Barley Grain

Starch is synthesized in the endosperm of developing barley grain, where it functions as the primary source of stored carbohydrate. In germinated grain these starch reserves are hydrolyzed to small oligosaccharides and glucose, which are transported to the embryo to support the growth of the developing seedling. Some of the mobilized glucose is transiently stored as starch in the scutellum of germinated grain. These processes are crucial for early seedling vigor, which is a key determinant of crop productivity and global food security. Several starch synthases (SS), starch-branching enzymes (SBEs), and starch debranching enzymes (isoamylases, ISA), together with a limit dextrinase (LD), have been implicated in starch synthesis from nucleotide-sugar precursors. Starch synthesis occurs both in the developing endosperm and in the scutellum of germinated grain. For the complete depolymerization of starch to glucose, α-amylase (Amy), β-amylase (Bmy), isoamylase (ISA), limit dextrinase (LD), and α-glucosidase (AGL) are required. Most of these enzymes are encoded by gene families of up to 10 or more members. Here RNA-seq transcription data from isolated tissues of intact developing and germinated barley grain have allowed us to identify the most important, specific gene family members for each of these processes in vivo and, at the same time, we have defined in detail the spatio-temporal coordination of gene expression in different tissues of the grain. A transcript dataset for 81,280 genes is publicly available as a resource for investigations into other cellular and biochemical processes that occur in the developing grain from 6 days after pollination.

The expression of the gene associated with β-glucan content, β-amylase and limit dextrinase synthesis as affected by post-heading heat stress in barley

Background: Malt barley shows a dramatic deterioration of malt quality when exposed to heat or high temperature stress during grain-filling stage (post heading), and global change results in the more frequent occurrence of high temperature, posing a severe threat to high-quality malt barley production. In a previous study, we found heat stress during grain-filling stage caused the significant reduction of kernel weight, and the significant increase of protein and β-glucan content, and β-amylase and limit dextrinase (LD) activities, and the effect varied with barley genotypes and the time of heat stress exposure.Results: In this study, we determined the relative expressions of HvCslF6 and HvCslF9 for β-glucan, HvBmy1 for β-amylase and LD gene for limit dextrinase of two barley cultivars（ZU9 and Hua30）under the two heat stress (HS) treatments (32/26℃, day/night), initiated from the 7th day (early grain-filling stage) and the14th day (middle grain-filling stage) after heading. In comparison with normal temperature (24/18℃, day/night), HS treatments significantly up-regulated the relative expression of all four genes, and Hua30 being larger than ZU9. The change pattern of each examined gene for the two barley genotypes under heat stress treatments is completely consistent with that of corresponding malt quality trait as affected by heat stress.Conclusion: The results indicate that the enhancement of β-glucan content, and β-amylase and limit dextrinase activities under high temperature during grain filling stage is at least in part attributed to increased expression of the relevant genes.