Water uptake in barley grain: Physiology; genetics and industrial applications.

Water uptake by mature barley grains initiates germination and is the first stage in the malting process. Here we have investigated the effects of starchy endosperm cell wall thickness on water uptake, together with the effects of varying amounts of the wall polysaccharide, (1,3;1,4)-ß-glucan. In the latter case, we examined mutant barley lines from a mutant library and transgenic barley lines in which the (1,3;1,4)-ß-glucan synthase gene, HvCslF6, was down-regulated by RNA interference. Neither cell wall thickness nor the levels of grain (1,3;1,4)-ß-glucan were significantly correlated with water uptake but are likely to influence modification during malting. However, when a barley mapping population was phenotyped for rate of water uptake into grain, quantitative trait locus (QTL) analysis identified specific regions of chromosomes 4H, 5H and 7H that accounted for approximately 17%, 18% and 11%, respectively, of the phenotypic variation. These data indicate that variation in water uptake rates by elite malting cultivars of barley is genetically controlled and a number of candidate genes that might control the trait were identified under the QTL. The genomics data raise the possibility that the genetic variation in water uptake rates might be exploited by breeders for the benefit of the malting and brewing industries.

The fungal community structure of barley malts from diverse geographical regions correlates with malt quality parameters.

Malt is a preferred base for fermentations that produce beer or whisky. Barley for malt is grown under diverse environments in different geographical locations. Malt provides an ecological niche for a varied range of microorganisms with both positive and negative effects on its quality for brewing. Little information exists in the literature on the microbial community structure of Australian malt as well as broader global geographical differences in the associated fungal and bacterial communities. The aims of the present study were to compare the bacterial and fungal community structures of Australian commercial malt with its international counterparts originating from different geographical regions using terminal restriction fragment length polymorphism (TRFLP) fingerprinting and clone library analyses of ribosomal RNA genes. Further, the relationship between malt associated microbial communities and conventional malt quality parameters was also compared. Results showed that differences in fungal communities of malts from different geographical location were more pronounced than bacterial communities. TRFLP analysis discriminated high quality commercial malts with low fungal loads from malts deliberately infected with fungal inocula (Fusarium/Penicillium). Malt moisture, beta-amylase, α-amylase and limit dextrinase contents showed significant correlations with fungal community structure. This investigation concluded that fungal community structure was more important to subsequent malt quality outcomes than bacteria.

TRFLP analysis reveals that fungi rather than bacteria are associated with premature yeast flocculation in brewing.

Premature yeast flocculation (PYF) is a sporadic fermentation problem in the brewing industry that results in incomplete yeast utilization of fermentable sugars in wort. Culture-independent, PCR-based fingerprinting techniques were applied in this study to identify the associations between the occurrence of the PYF problem during brewery fermentation with barley malt-associated microbial communities (both bacteria and fungi). Striking differences in the microbial DNA fingerprint patterns for fungi between PYF positive (PYF +ve) and negative (PYF -ve) barley malts were observed using the terminal restriction fragment length polymorphism (TRFLP) technique. The presence of terminal restriction fragments (TRFs) of 360-460 bp size range, for fungal HaeIII restriction enzyme-derived TRFLP profiles appeared to vary substantially between PYF +ve and PYF -ve samples. The source of the barley malt did not influence the fungal taxa implicated in PYF. TRFLP analysis indicates bacterial taxa are unlikely to be important in causing PYF. Virtual digestion of fungal sequences tentatively linked HaeIII TRFs in the 360-460 bp size range to a diverse range of yeast/yeast-like species. Findings from this study suggest that direct monitoring of barley malt samples using molecular methods could potentially be an efficient and viable alternative for monitoring PYF during brewery fermentations.