Novel quality features to expand durum wheat applications

Durum wheat represents a staple food in the human diet owing to its nutritional and technological features. In comparison to common wheat, durum wheat has higher tolerance to biotic and abiotic stresses. However, its production and culinary uses are limited compared to common wheat. Therefore, significant attention was attributed to upgrading the key quality of durum wheat (i.e., hardness, protein, starch and color). This review intends to put the spotlight on the modification of these properties to create new functionalities suiting a wider range of food applications based on critical compilation of scientific publications. Targeting specific genes has been shown to be a valuable strategy to design novel wheat varieties with higher nutritional value (e.g., high amylose), improved technological properties (e.g., higher glutenin content), attractive appearance (e.g., colored wheat) and new uses (e.g., soft durum wheat for breadmaking). Further efforts are still needed to find efficient ways to stabilize and maintain these properties. © 2022 Society of Chemical Industry.

The Use of a Non-Invasive Electrical Method to Assess the Chemical Composition, Hardness, and Color of Durum Wheat Grain Cultivated in an Integrated System

Electrical properties are the least known and described among the physical properties of food products. The most widespread practical directions of their use include moisture measurements as well as dielectric and microwave heating. Less frequently, they are used to assess the physicochemical parameters of food products, including the technological features of cereal grains. Earlier research by the authors of this paper demonstrated the possibility of using an RCC substitute model of food products (conductivity and capacitance parameters) to identify the grain variety, geometric features, level of grain damage as well as grain moisture content. This model can also be used to distinguish cereal species as well as to assess the proximate chemical composition of their grain. The promising results obtained in this area encouraged us to expand the research with a material important from the food market perspective—durum wheat, obtained in the conditions of sustainable cultivation in north-eastern Europe (temperate climate). The study material was obtained from a proprietary sustainable production technology designed in a strict field experiment. The aim of this research was: (1) to assess the effect of an integrated cultivation system of native durum wheat (six variants), differentiated by a nitrogen fertilization dose (0, 80, 120 kg·ha−1) and with and without growth regulator (GR, WGR) on changes in selected quality parameters (protein, lipid, and starch contents; hardness; color) and electrical parameters (Z, Cp, Cs) of the grain; and (2) to determine the correlations between the examined quality traits and electrical properties of the grain to indicate the possibility of using a non-invasive electrical method to assess grain quality. The highest contents of starch and total lipids and the highest grain hardness were obtained in the cultivation variants GR + 0N and WGR + 0N, whereas the highest protein content—upon wheat fertilization with 120N. The study demonstrated a different strength of the correlations between the tested parameters depending on the cultivation method. In the WGR + 0N variant (environmentally friendly), the strongest correlation between grain quality traits and electrical properties was obtained for both the conductive (Z) and capacitive (Cp, Cs) parameters in the entire analyzed range of current frequencies. The cultivation of durum wheat in the integrated system, especially in the WGR variant, facilitates grain quality modeling and enables using a non-invasive electrical method for a rapid assessment of the quality traits of the grain while raising no concerns over natural environment safety. The growth regulator (GR) application during native durum wheat cultivation hampers the use of the analyzed electrical method to assess its grain quality.

Toward the Genetic Basis and Multiple QTLs of Kernel Hardness in Wheat

Kernel hardness is one of the most important single traits of wheat seed. It classifies wheat cultivars, determines milling quality and affects many end-use qualities. Starch granule surfaces, polar lipids, storage protein matrices and Puroindolines potentially form a four-way interaction that controls wheat kernel hardness. As a genetic factor, Puroindoline polymorphism explains over 60% of the variation in kernel hardness. However, genetic factors other than Puroindolines remain to be exploited. Over the past two decades, efforts using population genetics have been increasing, and numerous kernel hardness-associated quantitative trait loci (QTLs) have been identified on almost every chromosome in wheat. Here, we summarize the state of the art for mapping kernel hardness. We emphasize that these steps in progress have benefitted from (1) the standardized methods for measuring kernel hardness, (2) the use of the appropriate germplasm and mapping population, and (3) the improvements in genotyping methods. Recently, abundant genomic resources have become available in wheat and related Triticeae species, including the high-quality reference genomes and advanced genotyping technologies. Finally, we provide perspectives on future research directions that will enhance our understanding of kernel hardness through the identification of multiple QTLs and will address challenges involved in fine-tuning kernel hardness and, consequently, food properties.

Effect of wheat grain protein composition on end-use quality

The quality of wheat products has been a new challenge next to wheat production which was achieved substantially during green revolution. The end-use quality of wheat is an essential factor for its commercial demand. The quality of wheat is largely based on the wheat storage proteins which extensively influences the dough properties. High molecular weight glutenin subunits (HMWGS), low molecular weight glutenin subunits (LMWGS) and gliadins significantly influence the end-use quality. Genomics and proteomics study of these gluten proteins of bread and durum wheat have explored new avenues for precise identification of the alleles and their role in end-use quality improvement. Secalin protein of Secale cereale encoded by Sec-1 loci and is associated with 1RS.1BL translocation has been known for deterioration of end-use quality. Chromosomal manipulations using various approaches have led to the development of new recombinant lines of wheat without secalin. Advanced techniques associated with assessment of end-use quality have integrated the knowledge of useful or deteriorating HMWGS/LMWGS alleles and their potential role in end-use quality. This review gives a comprehensive insight of different aspects of the end-use quality perspective for bread making in wheat along with some information on the immunological interference of gluten in celiac disease.

Expression of Puroindoline a in Durum Wheat Affects Milling and Pasting Properties

Durum wheat has limited culinary utilizations partly due to its extremely hard kernel texture. Previously, we developed transgenic durum wheat lines with expression of the wildtype Puroindoline a (Pina) and characterized PINA's effects on kernel hardness, total flour yield and dough mixing properties in durum wheat. The medium-hard kernel texture is potentially useful for exploring culinary applications of durum wheat. In the present study, we examined the milling parameters and flour attributes of the transgenic lines, including particle size distribution, damaged starch and water binding capacity. PINA expression results in increased break and reduction flour yield but decreased shorts. PINA expression also leads to finer flour particles and decreased starch damage. Interestingly, PINA transgenic lines showed increased peak viscosity and breakdown viscosity but leave other flour pasting parameters generally unaltered. PINA transgenic lines were associated with increased small monomeric proteins, appearing to affect gluten aggregation. Our data together with several previous results highlight distinct effects of PINs on pasting properties depending on species and variety. The medium-hard kernel texture together with improved pasting parameters may be valuable for producing a broader range of end-products from durum wheat.

Co-expression of high-molecular-weight glutenin subunit 1Ax1 and Puroindoline a (Pina) genes in transgenic durum wheat (Triticum turgidum ssp. durum) improves milling and pasting quality

BACKGROUND

Durum wheat is considered not suitable for making many food products that bread wheat can. This limitation is largely due to: (i) lack of grain-hardness controlling genes (Puroindoline a and b) and consequently extremely-hard kernel; (ii) lack of high- and low-molecular-weight glutenin subunit loci (Glu-D1 and Glu-D3) that contribute to gluten strength. To improve food processing quality of durum wheat, we stacked transgenic Pina and HMW-glutenin subunit 1Ax1 in durum wheat and developed lines with medium-hard kernel texture.

RESULTS

Here, we demonstrated that co-expression of Pina + 1Ax1 in durum wheat did not affect the milling performance that was enhanced by Pina expression. While stacking of Pina + 1Ax1 led to increased flour yield, finer flour particles and decreased starch damage compared to the control lines. Interestingly, Pina and 1Ax1 co-expression showed synergistic effects on the pasting attribute peak viscosity. Moreover, Pina and 1Ax1 co-expression suggests that PINA impacts gluten aggregation via interaction with gluten protein matrix.

CONCLUSIONS

The results herein may fill the gap of grain hardness between extremely-hard durum wheat and the soft kernel durum wheat, the latter of which has been developed recently. Our results may also serve as a proof of concept that stacking Puroindolines and other genes contributing to wheat end-use quality from the A and/or D genomes could improve the above-mentioned bottleneck traits of durum wheat and help to expand its culinary uses.

From ancient to old and modern durum wheat varieties: interaction among cultivar traits, management, and technological quality

Following the boom in durum wheat breeding, ancient wheat disappeared from the human diet and old durum wheat varieties were replaced by what is believed to be their better versions: higher yielding modern varieties grown in high-input systems. Breeders have worked intensely ever since to improve the quality of durum wheat traits - mainly gluten subunit alleles - to obtain superior technological quality in the main durum wheat end products (first pasta and then bread) but conflicts about predicting their quality still exist. This is because quality is neither governed by one trait alone nor conditioned by a single controllable factor. This review discusses the evolution of wheat varieties from ancient to old, and then modern durum wheat in terms of agronomy, genetics, technological, and end-product qualities. Environmental effects will not be discussed. Moving from ancient to modern durum wheat varieties, grain yield increased, grain protein concentration decreased, and gluten strength and dough toughness improved, ameliorating the quality of pasta but decreasing the durum wheat versatility. © 2018 Society of Chemical Industry.

Influence of Soft Kernel Texture on Fresh Durum Pasta

This study examined the quality of fresh pasta made from 3 varieties of a new type of durum wheat possessing soft kernel texture, as compared to fresh pasta made from commercial samples of durum semolina, durum flour, and bread flour, each at 3 levels of hydration (28%, 30%, and 32%, respectively). Soft durum possesses a small part of chromosome 5D that carries the Hardness locus and puroindoline genes. The soft durum lines were derived from the durum varieties Svevo, Alzada, and Havasu. The soft durum pasta exhibited low cooking weight increase (water uptake) (115% to 122%), the lowest cooking loss (∼3% to 4%), high firmness (269.3, 265.8, and 297.9 g, Soft Svevo, Soft Havasu, and Soft Alzada, respectively, versus 239.7 and 273.6 g, durum flour and semolina, respectively), low stickiness (4.17 to 4.96 g·s for the soft durums compared with 5.04 for the semolina), and raw and cooked pasta color comparable to or superior to those exhibited by the durum semolina (high L^* and b^* ). The soft durum samples also exhibited pasta quality superior to both the durum flour and bread flour samples. These results challenge the long-standing view that high-quality pasta must be made from durum semolina. PRACTICAL APPLICATION: This study illustrates the quality and potential applications of soft durum wheat in pasta manufacturing. As a new type of wheat, understanding these properties is crucial for manufacturers and others who may be interested in utilizing soft durum.

Structural consequences of the interaction of puroindolines with gluten proteins

The effect of puroindolines (PINs) on structural characteristics of wheat proteins was investigated in Triticum turgidum ssp. durum (cv. Svevo) and Triticum aestivum (cv. Alpowa) and in their respective derivatives in which PIN genes were expressed (Soft Svevo) or the distal end of the short arm of chromosome 5D was deleted and PINs were not expressed (Hard Alpowa). The presence of PINs decreased the amount of cold-SDS extractable proteins and the accessibility of protein thiols to specific reagents, but resulted in facilitated solvation of gluten proteins, as detected by tryptophan fluorescence measurements carried out on minimally mixed flour/water mixtures. We propose that PINs and gluten proteins are interacting in the grain or flour prior to mixing. Hydrophobic interactions between PINs and some of the gluten proteins modify the pattern of interactions among gluten proteins, thus providing an additional mechanistic rationale for the effects of PINs on kernel hardness.