C. W. Wrigley

Biochemical, Genetic, and Molecular Characterization of Wheat Glutenin and Its Component Subunits

Of all the cereal grains, wheat is unique because wheat flour alone has the ability to form a dough that exhibits the rheological properties required for the production of leavened bread and for the wider diversity of foods that have been developed to take advantage of these attributes. The unique properties of the wheat grain reside primarily in the gluten-forming storage proteins of its endosperm. It is these dough-forming properties that are responsible for wheat being the most important source of protein in the human diet. The bread and durum wheats are polyploid species containing three (AABBDD) and two (AABB) related genomes, respectively. The genetic constitution of wheat is important because all quality traits result from the expression of genes and their interaction with the environment. The full spectrum of wheat-endosperm proteins has been exhibited in proteome studies involving the two-dimensional fractionation of the polypeptides (after disulfide-bond rupture), followed by dissection of the individual components for identification. This display (Fig. 1) shows that there are at least 1,300 polypeptides, over 300 of which have been identified by N-terminal amino

Sources of Variation for Starch Gelatinization, Pasting, and Gelation Properties in Wheat

ABSTRACT The starch of wheat (Triticum aestivum L.) flour affects food product quality due to the temperature-dependent interactions of starch with water during gelatinization, pasting, and gelation. The objective of this study was to determine the fundamental basis of variation in gelatinization, pasting, and gelation of prime starch derived from seven different wheat cultivars: Kanto 107, which is a partial waxy mutant line, and six near-isogenic lines (NILs) differing in hardness. Complete pasting curves with extended 16-min hold at 93°C were obtained using the Rapid Visco Analyser (RVA). Apparent amylose content ranged from 17.5 to 23.5%; total amylose content ranged from 22.8 to 28.2%. Starches exhibited significant variation in onset of gelatinization. However, none of the parameters measured consistently correlated with onset or other RVA curve parameters that preceded peak paste viscosity. Peak paste viscosity varied from 190 to 323 RVA units (RVU). Higher peak, greater breakdown, lower final visc...

Changes in polypeptide composition and grain quality due to sulfur deficiency in wheat

Qualitative and quantitative differences in protein composition were examined in 12 samples of flour milled from wheat (cultivar Olympic) grown under a wide range of sulfur and nitrogen inputs. Two-dimensional fractionation, comprising isoelectric focusing in one dimension and electrophoresis at pH 3 in the other, indicated that the changes in gliadin composition associated with sulfur deficiency involved the proportions of individual gliadins but not their charge, size or isoelectric point characteristics. Quantitative Polyacrylamide gel electrophoresis in the presence of SDS showed that sulfur deficiency resulted in increases in the proportions of polypeptides in the mol.wt. ranges 51,000 to 80,000 and above, but decreases in the proportions of lower mol.wt. polypeptides (8000 to 28,000, mainly albumins). The proportions of polypeptides in five size ranges were highly correlated with the sulfur to nitrogen ratios in the flour samples and also with their dough quality characteristics, particularly as measured with the Extensograph. Doughs produced from the variety, Olympic, usually are extensible but the increased proportion of high mol.wt. polypeptides, found in the sulfur-deficient samples, was associated with an increase in the toughness and a decrease in the extensibility of the dough.

The diversity of allergens involved in bakers' asthma

Sera from 35 individuals with suspected allergies to inhaled flour were screened for the presence of immunoglobulin E (IgE) specific for wheat‐flour proteins. Sera from nine asthmatic bakers with high wheat RAST scores were selected for further study with the aim of purifying the allergen(s) involved in bakers’ asthma and related conditions. However, each of the different techniques applied–ion exchange chromatography, preparative isoelectric focusing and the electrophoretic transfer, or‘Western blotting’ technique, showed that serum IgE from different individuals have markedly different specificities and bind to numerous wheat proteins. When three purified wheat proteins were tested–wheat germ agglutinin; a fraction purified using a concanavalin‐A affinity column and a putative trypsin inhibitor–all were identified as allergens for some but not all of the allergic bakers.

Gluten polypeptides as useful genetic markers of dough quality in Australian wheats

Seed proteins of 28 Australian bread wheat cultivars were analysed by gel electrophoresis to indicate variations in the composition of their gliadins and glutenin polypeptides (both low- and high-molecular-weight). Composition was indicated according to allelic blocks of genes for each protein class and for each chromosome involved. Relationships were studied between gluten-protein alleles, pedigrees and dough properties (in the Extensograph). Overall, gliadins and low-molecular-weight (LMW) subunits of glutenin controlled by group 1 chromosomes showed closest relationships with each other. LMW subunits were most highly correlated with dough resistance and extensibility. Gliadins controlled by chromosomes 6A and 6D also had highly significant relationships to dough resistance and extensibility, respectively. Among high-molecular-weight subunits of glutenin, however, only those controlled by chromosome 1B showed a significant relationship with resistance to dough extension.

Monoclonal antibodies to gliadin proteins used to examine cereal grain protein homologies

Monoclonal antibodies were prepared to a gliadin protein extract of bread wheat (Triticum aestivum cv. Timgalen) and specific antibody-cereal protein interactions were detected using horseradish peroxidase-coupled second antibodies after transfer of proteins to nitrocellulose following electrophoresis. Whilst some antibodies had broad specificity for gliadin proteins, other antibodies of narrower specificity were investigated further. The latter antibodies were selective for ω-gliadins and bound neither high molecular weight glutenin subunits albumin and globulin wheat proteins, nor a wide variety of other proteins. However, certain related cereal species such as durum wheat, barley and rye contained endosperm proteins recognised by these monoclonal antibodies. This observation confirms that sequence homologies exist between prolamins from wheat and related cereal species as well as between certain gliadins from hexaploid wheat.

Alteration to grain, flour and dough quality in three wheat types with variation in soil sulfur supply

Shortim, a hard bread wheat, Egret, a soft biscuit wheat and Olympic, a multi-purpose wheat, were grown at a field site, where yield responses to both sulfur and nitrogen fertilizer application had been obtained previously. By varying the sulfur and nitrogen treatments applied, grain ranging in sulfur content from 0·10 to 0·21 % (w/w; dry basis) was produced. From a grain sulfur content of 0·1 %, grain became softer as the sulfur content increased. As with Olympic grown in 1978, so the three cultivars grown in 1980 showed close relationships between flour sulfur content and dough extensibility, and inverse relationships with resistance to stretching. From 0·08 to 0·17% flour sulfur content, these relationships remained linear. Flour colour improved with increasing sulfur content in each case. Mixing responses were variable, and showed no uniform trend either in water absorption or dough development time. Both measurement of the sulfur content of grain, and of the colour developed when grain is treated with glutaraldehyde, appear useful in assessment of grain quality for baking. The results presented confirm that sulfur supply has an important role in altering the processing and product quality of wheat.

The wheat-grain proteome as a basis for more efficient cultivar identification.

The wheat‐grain proteome was investigated, as a basis for devising more efficient methods of cultivar identification or discrimination. Australian wheats (Halberd, Cranbrook, CD87 and Katepwa) were used as the basis of this study. These cultivars were selected on the basis of differences in the quality types represented, in terms of dough‐processing attributes that can suit one cultivar better than another for specific types of industrial utilisation. Total wheat endosperm (flour) protein extracts were prepared from mature wheat for two‐dimensional electrophoresis, across both acidic (pH 4–7) and basic (pH 6–11) pH ranges. Three particular regions of the proteome maps were chosen for close comparison, involving two sets of gluten proteins and a nongluten protein region (involving small heat shock proteins), based on previous protein characterisation. Differences in the nongluten protein regions (heat shock proteins and other unidentified polypeptides) are of particular interest as being possible targets for use in developing new approaches to cultivar discrimination, such as the development of simple immunoassays.

Lupin Flours as Additives: Dough Mixing, Breadmaking, Emulsifying, and Foaming

ABSTRACT The nutritional quality of various food products could be improved by supplementation with grain legumes to increase protein content and to improve the balance of essential amino acids. The lupin grain is a good candidate for this role, given its yield potential in a range of climatic environments and soil types. To establish the practicality of extending the use of lupins as food additives, the functional properties of various species and cultivars of lupin were studied for their effect as additives to baked products and their ability to provide foaming and emulsifying properties. Of the two lupin species that are commonly cultivated commercially, Lupinus albus showed the greater potential as a bread additive; loaf height and structure were maintained when lupin flour was substituted for wheat flour at levels up to 5%. This level of substitution offered the advantage of reducing mixing time. The detrimental effects at higher substitution levels appeared to be associated with the nonprotein compo...

Quality-related endosperm proteins in sulfur-deficient and normal wheat grain

Specific groups of proteins associated with the baking properties of flour were identified by extracting flour from normal and sulfur-deficient wheat with a sodium dodecylsulfate (SDS)-Tris buffer either with or without reducing agent. Total proteins (with reducing agent), extract proteins (without reducing agent), and residue proteins (re-extraction of sediment with reducing agent) were fractionated by SDS-polyacrylamide gel electrophoresis (with reducing agent present for all fractions). Significant correlations were obtained between the proportions of certain groups of polypeptides and flour-quality characteristics. The proportion of high molecular weight (HMW) components (Mr 80,000; corresponding to HMW-glutenin subunits) in the residue was strongly positively correlated with resistance to extension and negatively correlated with dough extensibility and breakdown. Of the proteins extracted mainly by SDS without reduction, ω-gliadins in the Mr range 51,000 to 80,000 showed the same correlations as the HMW-glutenin subunits, whereas proteins inthe Mr range 38,000 to 50,000 and 28,000 to 39,000 were positively correlated with dough extensibility. The proteins of these latter ranges correspond mainly to α-, β-, and γ-gliadins and LMW-glutenin subunits. The proteins of the lowest Mr range (Mr