Wheat GSPs and Processing Quality Are Affected by Irrigation and Nitrogen through Nitrogen Remobilisation

The rheological properties and end-use qualities of many foods are mainly determined by the types and levels of grain storage proteins (GSPs) in wheat. GSP levels are influenced by various factors, including tillage management, irrigation, and fertiliser application. However, the effects of irrigation and nitrogen on GSPs remain unclear. To address this knowledge gap, a stationary split-split block design experiment was carried out in low- and high-fertility (LF and HF) soil, with the main plots subjected to irrigation treatments (W0, no irrigation; W1, irrigation only during the jointing stage; W2, irrigation twice during both jointing and flowering stages), subplots subjected to nitrogen application treatments (N0, no nitrogen application; N180, 180 kg/ha; N240, 240 kg/ha; N300, 300 kg/ha), and cultivars tested in sub-sub plots (FDC5, the strong-gluten cultivar Fengdecun 5; BN207, the medium-gluten cultivar Bainong 207). The results showed that GSP levels and processing qualities were significantly influenced by nitrogen application (p < 0.01), N240 was the optimal nitrogen rate, and the influence of irrigation was dependent on soil fertility. Optimal GSP levels were obtained under W2 treatment at LF conditions, and the content was increased by 17% and 16% for FDC5 and BN207 compared with W0 under N240 treatment, respectively. While the optimal GSP levels were obtained under W1 treatments at HF conditions, and the content was increased by 3% and 21% for FDC5 and BN207 compared with W0 under N240 treatment, respectively. Irrigation and nitrogen application increased the glutenin content by increasing Bx7 and Dy10 levels in FDC5, and by increasing the accumulation of Ax1 and Dx5 in BN207. Gliadins were mainly increased by enhancing α/β-gliadin levels. Correlation analysis indicated that a higher soil nitrate (NO3-N) content increased nitrogen remobilisation in leaves. Path analysis showed that Dy10, Dx5, and γ-gliadin largely determined wet glutenin content (WGC), dough stability time (DST), dough water absorption rate (DWR), and sedimentation value (SV). Therefore, appropriate irrigation and nitrogen application can improve nitrogen remobilisation, GSP levels, and processing qualities, thereby improving wheat quality and production.

Control of wheat starch rheological properties and gel structure through modulating granule structure change by reconstituted gluten fractions

Reconstituted gluten fractions (RGF) varying in glutenin/gliadin (glu/gli) ratios was applied to change the property of wheat starch. The addition of RGF, irrespective of glu/gli ratio, significantly decreased the gelatinization enthalpy, viscosity, storage modulus (G'), and gel strength of starch. Starch particle size and leached amylose decreased by 4.5% and 22.2%, respectively, as the ratio of glu/gli changed from 1:0 to 0:1, indicating that the increase in gliadin ratio could inhibit swelling and rupturing of starch granules to a larger extent. Confocal laser scanning micrographs showed that gliadin could surround starch granules more effectively, thereby stabilizing the granule structure better than glutenin. With the increasing of gliadin ratio, the storage modulus (G') and loss modulus (G″) of the starch paste declined, accompanied by more loose gel structure and weaker gel strength. By varying the ratios of glu/gli in RGF, the change of wheat starch granule structure could be modulated, and therefore the rheological properties and gel structure could be regulated.

In vitro digestibility of proteins from historical and modern wheat cultivars

BACKGROUND

Previous research has suggested that proteins and other quality parameters of wheats may have changed over a century of wheat breeding. These changes may affect protein digestibility. The in vitro protein digestibility of breads made with 21 cultivars of wheat introduced or released in the USA between 1870 and 2013 was therefore evaluated.

RESULTS

Protein digestibility increased with release year, but was not normally distributed; three older cultivars had significantly lower digestibility than the other cultivars: 42.0 ± 0.3 mol% (primary amino N/total N) versus 34.7 ± 0.7 mol%; P < 0.001. High molecular weight (MW) protein fractions increased and low MW protein fractions decreased with release year, but these changes were not related to protein digestibility. Thus, other differences in protein composition or other flour components may contribute to diminished digestibility of the three older cultivars.

CONCLUSIONS

This study identified differences in protein digestibility among wheat cultivars that may have important implications for human nutrition. Further investigation is required to determine the specific characteristics that differentiate high- and low-digestibility wheat cultivars. © 2020 Society of Chemical Industry.

Relationship of molecular weight distribution profile of unreduced gluten protein extracts with quality characteristics of bread

A statistical correlation was established among the molecular weight distribution patterns of unreduced gluten proteins and physicochemical, rheological and bread-making quality characteristics of wheat varieties. Size exclusion chromatography fractionated the gluten proteins apparently into five peaks. Peak I signified glutenins (30-130kDa), peak II as gliadins (20-55kDa), peak III as very low molecular weight monomeric gliadins (10-28kDa), peak IV and V, collectively, as albumins and globulins (<10kDa). Peaks I and II had appreciable effects on dough development time (r=0.830(∗∗) and r=-0.930(∗∗)) and dough stability (r=0.901(∗∗) and r=-0.979(∗∗)). Peak I was associated with R/E ratio (r=0.745(∗∗)), gluten index (r=0.959(∗∗)), and gliadin/glutenin ratio (r=-0.952(∗∗)), while peak II influenced inversely as expected. Peak I exhibited positive statistical significance with bread loaf volume (r=0.848(∗∗)); however, peak II had negative (r=-0.818(∗∗)) impact. Bread firmness increased with increment in peak II (r=0.625(∗∗)), and decreased with accretion in peak I (r=-0.623(∗∗)).

Biochemical and functional properties of wheat gliadins: a review

Gliadins account for 40-50% of the total storage proteins of wheat and are classified into four subcategories, α-, β-, γ-, and ω-gliadins. They have also been classified as ω5-, ω1, 2-, α/β-, and γ-gliadins on the basis of their primary structure and molecular weight. Cysteine residues of gliadins mainly form intramolecular disulfide bonds, although α-gliadins with odd numbers of cysteine residues have also been reported. Gliadins are generally regarded to possess globular protein structure, though recent studies report that the α/β-gliadins have compact globular structures and γ- and ω-gliadins have extended rod-like structures. Newer techniques such as Mass Spectrometry with the development of matrix-assisted laser desorption/ionization (MALDI) in combination with time-of-flight mass spectrometry (TOFMS) have been employed to determine the molecular weight of purified ω- gliadins and to carry out the direct analysis of bread and durum wheat gliadins. Few gliadin alleles and components, such as Gli-B1b, Gli-B2c and Gli-A2b in bread wheat cultivars, γ-45 in pasta, γ-gliadins in cookies, lower gliadin content for chapatti and alteration in Gli 2 loci in tortillas have been reported to improve the product quality, respectively. Further studies are needed in order to elucidate the precise role of gliadin subgroups in dough strength and product quality.