Browsing by Subject "Proteinkonzentration"

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    Quality impact of nitrogen in wheat grain properties and protein development for higher baking quality
    (2022) Rekowski, Azin; Zörb, Christian
    Storage protein concentration and composition influence the baking quality of wheat. Traditionally, baking quality is correlated with the total protein concentration in flour. However, despite similar protein concentrations, the baking qualities of different cultivars can vary, and the variances may be related to differences in the storage protein composition (Zörb et al., 2018). Though both protein concentration and composition are affected by fertilization management (especially nitrogen) and water availability, it is not certain whether compositional changes will suffice to enhance the quality of final products. Additionally, there is a high risk for the environment, associated with nitrogen losses in wheat production. To increase nitrogen efficiency, minimize nitrogen losses and optimize the baking quality, it is crucial to improve nitrogen fertilizer management. To address the question whether nitrogen and water management induce changes in protein composition which result in altered baking qualities, several investigations were conducted in the present work. Total protein was extracted from wheat flour and SDS-PAGE (Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis) was used to detect proteins sub-fractions. To assess baking quality, the specific volume, freshness retention as well as the hardness of the bread were evaluated. In chapter two, as part of a pot experiment, two different levels of late nitrogen fertilizer were tested using two winter wheat cultivars of different quality classes (Discus and Rumor). Both cultivars produced more grain yield and total protein concentration as a result of late nitrogen supply. However, bread volume was only increased in Discus, possibly related to the greater changes in total gluten concentration and protein composition including HMW-GS and ω-gliadins. However, an increase of late nitrogen level did not further improve baking quality. Compared to Discus, an addition of late nitrogen did not result in significant changes in the protein composition of Rumor. Collectively these results indicate that late nitrogen management strategies are practical but need to be adjusted depending on the cultivar used. Chapter three describes a field experiment where three different nitrogen forms were used ((i)ammonium nitrate, (ii) urea with 46% total N, (iii) urea as before amended with urease inhibitor N-(2-nitro-phenyl) phosphoric triamide (2-NPT) and (iv) control (no nitrogen addition)). While no significant/only a slight effect was observed for urea alone, ammonium nitrate and urea plus urease inhibitor similarly increased total grain protein concentrations. Although both fertilizers boosted the levels of ω-gliadins and HMW-GS among the storage protein fractions, the influence was more pronounced in the ammonium nitrate application. In comparison to the urea treatment, the combination of urea plus urease inhibitor significantly influenced protein composition and generated higher specific baking volumes and the best fresh-keeping characteristics. Due to the strong enhancement in NUE and baking quality obtained with the urea plus urease inhibitor application, accompanied by reduced nitrogen losses and easy handling, this treatment could be considered as a substitute for urea alone or ammonium nitrate. Chapter four describes a field study conducted in Iran with different German (Impression, Discus, Rumor, Hybery) and Iranian (Alvand, Mihan) genotypes representing diverse quality classes and grain protein levels. Two different levels of water stress were applied during anthesis and grain filling period. Overall, no significant changes in total protein concentrations were recorded. In addition, the concentrations of different protein fractions were unchanged in five out of the six genotypes. However, German genotypes exhibited an increase in HMW-GS under severe drought conditions, and an increased severity of drought stress amplified the percentage of ω-gliadins in all genotypes. Even though drought stress did not alter the concentrations of the HMW-GS sub-fraction in Iranian genotypes, a high specific bread volume was still observed, most likely related to an increase in ω-gliadins. All in all, the protein composition should be considered in addition to yield and total grain protein concentration when developing new wheat varieties for challenging climatic conditions. In summary, late nitrogen and urea application, along with the addition of urease inhibitors, can enhance the gliadin and glutenin content and improve the baking quality. In addition, it may be possible to develop wheat genotypes with optimal baking properties by paying attention to the protein composition when drought stress exists. Although genetically determined subunits of the gluten fractions are known to be associated with bread-making quality, the studies presented here indicate that additional factors, such as the levels of nitrogen supply or water limitation, affect the composition of grain protein fractions and can be positively correlated with baking quality. Therefore, total grain protein concentration alone is not a reliable indicator of grain quality. Additionally, several individual proteins were altered by different management practices. Consequently, these proteins can have great effects on the quality of breads, so further studies should evaluate whether those individual proteins directly correlate with bread baking quality.