Helen M. Collins

REVIEW: Variability in Fine Structures of Noncellulosic Cell Wall Polysaccharides from Cereal Grains: Potential Importance in Human Health and Nutrition

ABSTRACTNoncellulosic polysaccharides from the cell walls of cereal grains are not digested by human small intestinal enzymes and so contribute to total dietary fiber intake. These polysaccharides are becoming recognized increasingly for their potential to lower the risk of serious diet-related conditions such as type II diabetes, cardiovascular disease, colorectal cancer, and diverticular disease. The effectiveness of noncellulosic cell wall polysaccharides in improving health outcomes is related to the fine structure and associated physicochemical properties. The two most nutritionally relevant wall polysaccharides of cereal grains are the arabinoxylans and the (1-3,1-4)-β-d-glucans. These polysaccharides have high molecular mass values but are nevertheless soluble in aqueous media, at least in part, where they adopt highly asymmetrical conformations and consequently form high viscosity solutions. Thus, arabinoxylans and (1-3,1-4)-β-d-glucans contribute to the soluble fiber component of human diets. The...

Over-expression of specific HvCslF cellulose synthase-like genes in transgenic barley increases the levels of cell wall (1,3;1,4)-β-D-glucans and alters their fine structure

Cell walls in commercially important cereals and grasses are characterized by the presence of (1,3;1,4)-β-d-glucans. These polysaccharides are beneficial constituents of human diets, where they can reduce the risk of hypercholesterolemia, type II diabetes, obesity and colorectal cancer. The biosynthesis of cell wall (1,3;1,4)-β-d-glucans in the Poaceae is mediated, in part at least, by the cellulose synthase-like CslF family of genes. Over-expression of the barley CslF6 gene under the control of an endosperm-specific oat globulin promoter results in increases of more than 80% in (1,3;1,4)-β-d-glucan content in grain of transgenic barley. Analyses of (1,3;1,4)-β-d-glucan fine structure indicate that individual CslF enzymes might direct the synthesis of (1,3;1,4)-β-d-glucans with different structures. When expression of the CslF6 transgene is driven by the Pro35S promoter, the transgenic lines have up to sixfold higher levels of (1,3;1,4)-β-d-glucan in leaves, but similar levels as controls in the grain. Some transgenic lines of Pro35S:CslF4 also show increased levels of (1,3;1,4)-β-d-glucans in grain, but not in leaves. Thus, the effects of CslF genes on (1,3;1,4)-β-d-glucan levels are dependent not only on the promoter used, but also on the specific member of the CslF gene family that is inserted into the transgenic barley lines. Altering (1,3;1,4)-β-d-glucan levels in grain and vegetative tissues will have potential applications in human health, where (1,3;1,4)-β-d-glucans contribute to dietary fibre, and in tailoring the composition of biomass cell walls for the production of bioethanol from cereal crop residues and grasses.

Assessing the impact of the level of diastatic power enzymes and their thermostability on the hydrolysis of starch during wort production to predict malt fermentability.

In this study, commercially produced malts were used for small-scale simulated mashing trials to investigate the impact of differences in the level and thermostability of malt diastatic power (DP) enzymes on the resultant wort fermentability. A modified European Brewery Convention/American Society Brewing Chemists mashing protocol was used with mash-in temperatures ranging between 45 and 76°C for full-malt and 30% rice adjunct mashes. Malt extract yield varied little with mashing temperature for most varieties in this temperature range. However, the fermentability, maltose content, and free amino nitrogen of that extract was considerably affected by mashing temperature with 65°C achieving the highest fermentability for all malt varieties. Multilinear regression analysis of full-malt and rice adjunct mashing trials at 65°C using 43 commercial malts showed that the level of α-amylase and total limit dextrinase activity, Kolbach Index, and the total β-amylase activity level and thermostability were the most important malt quality predictors of wort fermentability. These conclusions suggest that the conventional DP assessment could be replaced with the measurement of its component enzymes outlined above so that maltsters could better satisfy brewers malt quality expectations by blending and defining their malt quality in terms of these fermentability predicting factors. This information would be particularly useful to brewers who brew with multiple varieties and blends from different suppliers. The focus on individual enzyme characteristics by barley breeders is likely to provide selection targets that are more accurate and achievable.

Mapping and validation of chromosome regions associated with high malt extract in barley (Hordeum vulgare L.)

Malt extract represents the soluble material extracted from malt during the mashing process of barley. The measurement of malt extract is used by maltsters and brewers to assess the quality of the barley they are purchasing and is therefore one of the most important parameters used by breeders to assess the quality of new barley varieties before release. This paper identifies and investigates several regions (quantitative trait loci, QTLs) found to be associated with malt extract and discusses the uses of these regions for marker assisted selection (MAS). Eight regions of the barley genome were found to be associated with malt extract in 3 mapping populations. Five regions were found in the Sloop/Alexis and Sloop-sib/Alexis mapping populations on chromosomes 1H, 2H, 3H, 4H, and 5H. Two regions were found in the Chebec/Harrington population on chromosomes 1H and 5H and a single region was found on chromosome 2H in the Galleon/Haruna Nijo mapping population. Markers from 6 of these regions were investigated using several breeding populations with a high malt extract variety as a parent. The allele from the high malt extract parent was found to be associated with a significant increase in malt extract in 4 regions, 2 regions on chromosome 2H and 2 regions on chromosome 5H.

QTL analysis of malting quality traits in two barley populations

Selection for malting quality traits is a major breeding objective for barley breeding programs. With molecular markers linked to loci affecting these traits, this selection can be undertaken at an earlier stage of the breeding program than is possible using conventional tests. Quantitative trait loci (QTLs) associated with malting quality traits were mapped in 2 populations derived from parents with elite malting quality. Progeny from an Arapiles/Franklin population grown in 4 environments and an Alexis/Sloop population grown in 5 environments were tested for grain protein percentage, α-amylase activity, diastatic power, hot water extract, wort viscosity, wort β-glucan, β-glucanase, and free α-amino acids. QTL analysis was performed using a one-stage approach, which allowed for modelling of spatial variation in the field, and in each phase of the malting quality analysis in the laboratory. QTLs for malting quality traits were detected on all chromosomes and for both populations. Few of these QTLs were significant in all of the environments, indicating that QTL × environment interactions were important. There were many coincident QTLs for traits that are expected to be related such as diastatic power and α-amylase activity, wort β-glucan and wort viscosity and for some traits that are not expected to be related such as hot water extract and malt viscosity.

Mapping and QTL analysis of the barley population Chebec × Harrington

A doubled haploid population of 120 individuals was produced from the parents Chebec, an Australian 2-row barley of feed quality with resistance to the cereal cyst nematode, and Harrington, a 2-rowed, Canadian variety of premium malting quality. This paper describes 18 field and laboratory experiments conducted with the population and summarises the traits mapped and analysed. The genomic location of 25 traits and genes is described and marker–trait associations for 5 traits (malt extract, diastatic power, resistance to cereal cyst nematode, early flowering, resistance to pre-harvest sprouting) important to Australian efforts to improve malting barley varieties have been used in practical breeding programs. Detailed maps for these populations are shown in this paper, while a consensus map incorporating these maps and further experiments on the populations are described elsewhere in this issue.

Use of putative QTLs and structural genes in marker assisted selection for diastatic power in malting barley (Hordeum vulgare L.)

The usefulness of marker assisted selection (MAS) to improve diastatic power was demonstrated by selecting quantitative trait loci (QTLs) and structural gene alleles involved in enhanced diastatic power and activity of its component hydrolytic enzymes from Alexis, Amagi Nijo, Harrington, Haruna Nijo, and Sloop. Six unmapped breeders populations involving these donor sources of malting quality were used for MAS. For each population, individual lines were pooled into classes separated on the basis of either the presence or absence of malting quality parent marker alleles at each of 9 identified loci (QTLs or structural genes). Diastatic power, β-amylase, and α-amylase activities were determined for each line, and used to compare alternative marker allele class means. Lines carrying malting parent marker alleles at a chromosome 5H locus abg463 were associated with 21–44% higher α-amylase activity levels, depending on the cross. The malting parent alleles at the chromosome 4H Bmy1 locus were associated with increased diastatic power and β-amylase activity. A simple PCR marker detecting the Bmy1 locus was found to be effective in screening for improved diastatic power, β-amylase activity, and thermostability. Lines carrying malting parent alleles at the chromosome 2H Bmy2 locus produced differences in diastatic power and β-amylase activity that, after adjusting for the correlated effect of malt protein, became non-significant. The Alexis allele of the chromosome 1H EBmac501 locus was associated with significant differences in all traits for a population carrying this source. The implication of these results to the improvement of diastatic power through MAS is discussed.

Mapping and QTL analysis of the barley population Galleon × Haruna Nijo

A genetic linkage map consisting of 435 molecular markers has been constructed using a doubled-haploid mapping population derived from a cross between the Australian barley feed variety Galleon and Haruna Nijo, a Japanese barley cultivar of high malting quality. This map was used to locate the genes conferring CCN and SFNB resistance from Galleon and to locate malting and brewing quality genes from Haruna Nijo. Closely linked markers to the trait loci have been identified and are now being widely implemented in Australian breeding programs.

Separation and purification of soluble polymers and cell wall fractions from wheat, rye and hull less barley endosperm flours for structure-nutrition studies

The nutritional values associated with the cell walls of cereal endosperm flours are due to a combination of solubilized arabinoxylan and (1-3,1-4)-β-d-glucan as well as residual nonsolubilized cell wall material. In order to investigate structure-nutrition relationships, an appropriate method for the complete functional and structural characterization of cell wall polysaccharides in various cereal endosperm flours is described. This involves the separation of soluble polymers and the residual cell wall fraction without using organic solvents, and the fractionation of soluble polymers into arabinoxylan- and (1-3,1-4)-β-d-glucan-rich fractions for subsequent analysis. This methodology is applied to endosperm flours from wheat, hull-less barley and rye, and could be extended to include studies on the effects of food processing with respect to yield and characteristics of the three fractions in order to better understand the structural basis for nutritional functionality.

Mapping and QTL analysis of the barley population Alexis × Sloop

Two populations between the German malting variety Alexis and the Australian malting variety Sloop were constructed, mapped, phenotyped, and subjected to quantitative trait loci analysis. One population consisted of 153 F4-derived recombinant inbred lines and the other of 111 doubled haploid lines. This paper describes 18 field and laboratory experiments conducted with the populations and summarises the traits mapped and analysed. The genetic basis of 5 traits (malt extract, resistance to leaf rust, resistance to powdery mildew, early flowering, plant stature) important to Australian efforts to improve malting barley varieties was elucidated. Detailed maps for these populations are shown in this paper, while a consensus map incorporating these maps and further experiments on the populations are described elsewhere in this issue.