Gluten, starch, lipids, and water‐soluble material were separated from seven wheat samples with a range of protein contents and breadmaking quality. The isolated glutens were further partitioned into gliadin‐ and gluteninrich fractions using pH precipitation. Protein content and glutenin‐togliadin ratio were systematically altered by blending these fractions into the original flours in calculated amounts. Mixing properties, extension‐tester parameters, and baking performance of composite flours were determined using small‐scale techniques. Results of dough testing with blends of constant glutenin‐to‐gliadin ratio showed increases in the mixing time, mixograph peak resistance, maximum resistance to extension, extensibility, and loaf volume as the protein content increased. At constant protein content, increases in glutenin‐to‐gliadin ratio were associated with increases in mixing time, mixograph peak resistance, maximum resistance to extension, and loaf volume, and with decreases in extensibility. Thus, total protein content and glutenin‐to‐gliadin ratio independently affected dough and baking properties. The results have allowed the separation of the effects of flour protein quantity and composition on breadmaking properties.

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Balla K., Rakszegi M., Li Z., Békés F., Bencze S., Veisz O. (2011): Quality of winter wheat in relation to heat and drought shock after anthesis. Czech J. Food Sci., 29: 117-128.Raw material quality, which is influenced not only by the protein content, insoluble protein polymers, and gluteninto-gliadin ratio but also by the starch granule size, is very important for the quality of bakery products. This study investigated the effect of high temperature and drought (during grain-filling) on the quality and components yield of five winter wheat varieties. Drought and drought + heat were found to have a much greater influence on the yield and quality than heat stress alone. Averaged over the varieties, the yield losses were 57% after drought, 76% after drought + heat, and only 31% after heat stresses. The reductions in the unextractable polymeric protein fraction and glutenin-to-gliadin ratio indicated a poorer grain yield quality, despite the higher protein content. Quality deterioration was observed after drought or drought + heat, while high temperatures alone resulted in no change or in a better ratio of protein components. A significant negative correlation was observed between starch granule size and relative protein content after drought, demonstrating that this parameter contributes, together with protein, to the baking quality of the flour. Wheat varieties with satisfactory genetic traits are essential for the production of high quality wheat. Certain quality parameters vary over a very wide range in individual breeding lines. This broad genetic variability is demonstrated by the fact that the protein content ranges from 10-17%, the gluten content from 20-45%, the grain hardness from 10-85, the falling number from 60-450, and the farinograph index from C2 to A1. These differences in quality also depend on the soil, nutrient supplies, standard of plant protection, and other agronomic factors. The weather conditions during the growing season, especially the rainfall quantity and temperature, have a substantial influence on the plant metabolic processes, and thus on wheat quality.

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High-molecular-weight glutenin subunits (HMW-GS) are important determinants of wheat dough quality as they confer visco-elastic properties to the dough required for mixing and baking performance. With this important role, the HMW-GS alleles are key markers in breeding programs. In this work, we present the use of a PCR marker initially designed to discriminate Glu1 Bx7 and Glu1 Bx17 HMW-GS. It was discovered that this marker also differentiated two alleles, originally both scored as Glu1 Bx7, present in the wheat lines CD87 and Katepwa respectively, by a size polymorphism of 18 bp. The marker was scored across a segregating doubled-haploid (DH) population (CD87 x Katepwa) containing 156 individual lines and grown at two sites. Within this population, the marker differentiated lines showing the over-expression of the Glu1 Bx7 subunit (indicated by the larger PCR fragment), derived from the CD87 parent, relative to lines showing the normal expression of the Glu1 Bx7 subunit, derived from the Katepwa parent. DNA sequence analysis showed that the observed size polymorphism was due to an 18 bp insertion/deletion event at the C-terminal end of the central repetitive domain of the Glu1 Bx 7 coding sequence, which resulted in an extra copy of the hexapeptide sequence QPGQGQ in the deduced amino-acid sequence of Bx7 from CD87. When the DH population was analysed using this novel Bx7 PCR marker, SDS PAGE and RP HPLC, there was perfect correlation between the Bx7 PCR marker results and the expression level of Bx7. This differentiation of the population was confirmed by both SDS-PAGE and RP-HPLC. The functional significance of this marker was assessed by measuring key dough properties of the 156 DH lines. A strong association was shown between lines with an over expression of Bx7 and high dough strength. Furthermore, the data demonstrated that there was an additional impact of Glu-D1 alleles on dough properties, with lines containing both over-expressed Bx7 and Glu-D1 5+10 having the highest levels of dough strength. However, there was no statistically significant epistatic interaction between Glu-B1 and Glu-D1 loci.

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The uniaxial elongational and shear rheology of doughs varying in either the protein content or glutenin‐to‐gliadin ratio were investigated. Increasing the protein content at constant glutenin‐to‐gliadin ratio increased the strain‐hardening properties of the dough, as shown by increasing elongational rupture viscosity and rupture stress. Glutenin and gliadin had a more complex effect on the elongational properties of the dough. Increased levels of glutenin increased the rupture viscosity but lowered the rupture strain, while elevated gliadin levels lowered the rupture viscosity but increased the rupture strain. These observations provide rheological support for the widely inferred role of gliadin and glutenin in shaping bread dough rheology, namely that gliadin contributes the flow properties, and glutenin contributes the elastic or strength properties. The shear and elongational properties of the doughs were quite different, reflecting the dissimilar natures of these two types of flow. Increasing protein content lowered the maximum shear viscosity, while increasing the glutenin‐to‐gliadin ratio increased maximum shear viscosity. Strong correlations between the results of basic and empirical rheology were found. These basic, or fundamental, rheological measurements confirmed prior empirical studies and supported baking industry experience, highlighting the potential of basic rheology for bread and wheat research.

The effects of α‐ + β‐, γ‐, ω‐ and total gliadins on mixing, extension baking, and techno‐functional properties of doughs from hard and soft flours were measured using small‐scale techniques. The addition of all gliadin fractions resulted in decreased mixing time, peak resistance, maximum resistance to extension, and loaf height, and in increased resistance breakdown and extensibility. The various gliadin fractions showed differences in functional properties, with γ‐gliadin reducing the mixing time and maximum resistance to extension to the greatest extent, ω‐gliadin contributing to the greatest reduction in loaf height, and α‐ + β‐gliadins having the least effect on reducing loaf height. The effects of gliadin fractions on loaf height were correlated with molecular mass, and effects on mixing time, maximum resistance to extension, and extensibility were correlated with hydrophobicity.