Spectrophotometric determination of yellow pigment content and evaluation of carotenoids by high-performance liquid chromatography in durum wheat grain

The so-called "yellow pigment" content of durum wheat has been used for a long time as an indicator of the color quality of durum wheat and pasta products. For decades the chemical nature of these pigments has been assigned to carotenoids, mainly to the xanthophyll lutein and its fatty acid esters. The chemical composition of the yellow pigments of eight German durum wheat cultivars was studied. Grains were milled on a laboratory mill. Pigment extraction of millstream fractions was performed according to the optimized ICC standard method 152 procedure, and the chemical composition of the extract was analyzed by isocratic reversed phase high-performance liquid chromatography. all-trans-Lutein ranged from 1.5 to 4 mg kg(-1), and zeaxanthin was found in traces. No lutein esters and carotenes were detected. Surprisingly, the fraction of carotenoids of the complete yellow pigment content amounted to only 30-50% of the yellow pigment quantities, so there are still compounds in durum wheat not yet identified that contribute considerably to the yellow color of the grain extracts. The isolation and chemical identification of those pigments are under investigation.     

Hydration Dynamics of Durum Wheat Endosperm as Studied by Magnetic Resonance Imaging and Soaking Experiments

The precise knowledge of the kinetics of water transport in durum wheat endosperm is a prerequisite for the optimization of wheat processing techniques like pasta dough mixing on a fundamental basis. Pieces of endosperm were cylindrically cut, prepared from durum wheat kernels, and used to study the water uptake by applying a gravimetric method and magnetic resonance imaging (MRI). The total water uptake of endosperm cylinders at different soaking times was determined by gravimetric soaking experiments and revealed a swelling limit of ≈40 g/100 g wb after 60 min. With these results it was possible to estimate an apparent diffusion coefficient of water in durum endosperm by using numerical simulation based on a diffusion model (D_25°C ~ 0.76 × 10^–10 m²/sec). MRI was used to quantify the water distribution in the endosperm cylinders over time at excess and limited water conditions. The calibration of MRI for the quantification of local and time‐dependent water contents was successful by correlating the spin‐spin relaxation time (T₂) with the water content of calibration samples at intermediate moisture levels (19–45 g/100 g wb). Water content maps were generated and showed the kinetics of water distribution inside the endosperm cylinders up to equilibrium conditions. The water uptake of the endosperm cylinders over time, as measured by MRI, fitted well to the water uptake as determined gravimetrically in soaking tests, which validated the applied MRI calibration and measurement procedures. The results allow the quantitative prediction of water transport properties of durum wheat endosperm during moistening procedures.     

Alkylresorcinol content and homologue composition in durum wheat (Triticum durum) kernels and pasta products

The total alkylresorcinol (AR) content and relative homologue composition of 21 durum wheat (Triticum durum) kernel samples, as well as 5 pasta products and the corresponding flour mixtures, were determined. Durum wheat contained on average 455 microg/g ARs, and the average relative homologue composition was C17:0 (0.4%), C19:0 (14%), C21:0 (58%), C23:0 (21%), and C25:0 (6.5%). The homologue composition was found to be relatively consistent among samples, with durum wheat being different from common wheat by having a higher proportion of the longer homologues. No differences in content or homologue composition were observed in pasta products compared to flour ingredients, showing that alkylresorcinols are stable during pasta processing. The ratio of the homologues C17:0 to C21:0 was < or =0.02 for whole grain durum wheat products, which is different from those of common wheat (0.1) and rye (0.9).     

Genetic variability of carotenoid concentration and degree of esterification among tritordeum (xTritordeum Ascherson et Graebner) and durum wheat accessions

The higher carotenoid content (commonly referred as "yellow pigment content") of tritordeum seeds as compared to wheat and the potential of this species as a donor of useful traits to wheat led us to investigate the detailed carotenoid composition of 53 accessions of hexaploid tritordeums originating from different stages of the tritordeum breeding program developed at IAS-CSIC. In addition, seven durum wheat accessions were also studied for comparison. Lutein was the unique carotenoid detected, either free or esterified with fatty acids. On average, tritordeum had 5.2 times more carotenoids than durum wheat, which suggests a high potential of this species to become a functional food. In addition, the most outstanding result of this work is the high esterification degree of lutein found in tritordeums as compared to durum wheat. This difference may indicate the differential esterification ability between tritordeum and durum wheat species. The implications of this high level of lutein esterification on both carotenoid accumulation and stability are discussed.     

Structure and dynamics of high molecular weight glutenin subunits of durum wheat (Triticum durum) in water and alcohol solutions studied by electron paramagnetic resonance and circular dichroism spectroscopies

Complementary information on the structure and dynamics of high molecular weight glutenin subunits (HMW-GS) of durum wheat (Triticum durum) was obtained by means of two spectroscopic techniques. Electron paramagnetic resonance was used to investigate the dynamics of the HMW-GS hydrated with two 2-propanol/water mixtures at temperatures between 268 and 308 K by specific spin labeling of their cysteine residues. Spectra were of a composite type, resulting from two populations of spin labels differing in molecular mobility, both undergoing isotropic rotational diffusion. Diffusional coefficients and populations of the fast- and slow-moving spin labels, determined by an accurate spectral line shape analysis, are discussed as a function of temperature and water content in the solvent systems. Far-UV circular dichroism was employed to provide information on the secondary structure of the HMW-GS in three different solvents [aqueous 50% (v/v) 2-propanol, aqueous 0.1% (v/v) trifluoroacetic acid, and trifluoroethanol]. For the first one, the influence of temperature on HMW-GS structure was also investigated.     

Front-surface absorbance spectra of wheat flour: determination of carotenoids

Front-surface absorbance spectra of wheat flours in the 250-650 nm region can be obtained by measuring reflectance spectra with a conventional spectrofluorometer suitably set to detect light scattered from powder samples. The spectra recorded on flour samples, obtained from seeds of four bread and five durum wheats, show high-intensity absorption bands due to aromatic amino acids of wheat proteins and low-intensity bands due to chromophores bound to low-molecular-weight compounds. The intensity of these last bands is proportional to the concentration of the corresponding chromophores present in the flour; thus, it can be used to measure the content of the compounds containing the chromophore(s). In particular, a quantitative determination of the carotenoids actually present in the flours is made, obtaining information on the original content of the seeds. This determination is important, as, for example, xanthophylls are well-known antioxidants and free-radical scavengers involved in aging processes of seeds. Reflectance measurements on powder samples are far more economic in terms of time and materials consumption than methods such as extraction and HPLC analysis of extracts and, in addition, give an evaluation of the overall content of carotenoids with absorption bands in the spectral range 450-500 nm. Application of the technique to other food powders with low-intensity absorption bands in the near-UV and vis region is possible.     

Occurrence of Fusarium spp. and fumonisin in durum wheat grains

A survey was carried out to determine Fusarium species and fumonisin contamination in 55 durum wheat (Triticum turgidum L. var. durum) samples collected during two harvest seasons (2007 and 2008) using HPLC and further LC-MS/MS confirmation. All samples showed Fusarium contamination with infection levels ranging from 8 to 66%, F. proliferatum being the species most frequently isolated during 2007 and the second most frequently isolated one during the 2008 harvest season, respectively. Natural contamination with fumonisins was found in both harvest seasons. In 2007, 97% of the samples showed total fumonisin (FB(1) + FB(2)) levels ranging from 10.5 to 1245.7 ng/g, while very low levels of fumonisins were detected in samples collected during 2008. These results could be explained by differences in the amount of rainfall during both periods evaluated. A selected number (n = 48) of F. proliferatum isolates showed fumonisin production capability on autoclaved rice. This is the first report of the presence of natural fumonisins in durum wheat grains.     

Analysis and stability of carotenoids in the flowers of daylily (Hemerocallis disticha) as affected by various treatments

The analysis and stability of carotenoids in the flowers of daylily (Hemerocallis disticha) as affected by soaking and drying treatments were studied. The various carotenoids in the flowers of daylily were analyzed using a reversed-phase C(30) HPLC column and a mobile phase of methanol/methylene chloride/2-propanol (89:1:10, v/v/v) with methanol/methylene chloride (45:55, v/v) as sample solvent. Twenty-one pigments were resolved, of which 14 carotenoids were identified, including neoxanthin, violaxanthin, violeoxanthin, lutein-5,6-epoxide, lutein, zeaxanthin, beta-cryptoxanthin, all-trans-beta-carotene, and their cis isomers, based on spectral characteristics and Q ratios. Prior to hot-air-drying (50 degrees C) or freeze-drying, some of the daylily flowers were subjected to soaking in a sodium sulfite solution (1%) for 4 h. Under either the hot-air- or the freeze-drying treatment, the amounts of most carotenoids were higher in the soaked daylily flowers than in those that were not soaked. With hot-air-drying, the amount of cis carotenoids showed a higher yield in soaked samples than in nonsoaked samples. However, with freeze-drying, only a minor change of each carotenoid was observed for both soaked and nonsoaked samples. Also, air-drying resulted in a higher loss of carotenoids than freeze-drying.     

Improved normal-phase high-performance liquid chromatography procedure for the determination of carotenoids in cereals

Besides the health benefits associated with whole-grain consumption, cereals are recognized sources of health-enhancing bioactive components such as carotenoids, which are a group of yellow pigments involved in the prevention of many degenerative diseases and which have been used for a long time as indicators of the color quality of durum wheat and pasta products. This work reports a fast, sensitive, and selective procedure for the extraction and determination of carotenoids from cereals and cereal byproducts. The method involves sample saponification and extraction followed by normal-phase high-performance liquid chromatography, allowing the separation of the main carotenoids pigments of cereals, especially lutein and zeaxanthin. An application of the established method to various species of cereals and cereal byproducts is also shown. The highest carotenoid levels were found in maize (approximately 11.14 mg/kg of dry weight), which contains high amounts of beta-cryptoxanthin (2.40 mg/kg of dry weight), and, among the cereals considered, has the highest content of zeaxanthin (6.43 mg/kg of dry weight) and alpha+beta-carotene (1.44 mg/kg of dry weight). With the exception of maize, lutein is the main compound found (from 0.23 to 2.65 mg/kg of dry weight in oat and durum wheat, respectively). Moreover, whereas alpha+beta-carotene and zeaxanthin are principally localized in the germ, lutein is equally distributed along the kernel.     

Extraction and separation of water-soluble proteins from different wheat species by acidic capillary electrophoresis

Optimization of protein extraction and a capillary zone electrophoresis method for water-soluble protein analysis in wheat is described. The optimal separation was obtained with a 50 microm i.d. x 27 cm (20 cm to detector) uncoated capillary filled with 0.1 M phosphoric acid/beta-alanine, pH 2.5, buffer containing urea (1 M), 0.05% (w/v) hydroxypropylmethylcellulose, and 20% (v/v) acetonitrile. Separation was carried out at 15 kV and 35 degrees C for 9 min. Extract stability was also investigated within 2 h from the extraction. Good visual peak parameters and a higher sensitivity can be obtained when 30% ethanol is used as an extraction medium. The method was successfully used to analyze extracts obtained from whole and refined meals of six Triticum spp. Moreover, the described methodology could be applied to the discrimination of species with different ploidy levels and to the detection of durum wheat adulteration, as well as to screen wheat collections for enzymes involved with the quality of wheat derivatives.     

Inheritance of manganese efficiency in durum wheat

Manganese (Mn) deficiency is a widespread problem on the alkaline soils, particularly for durum wheat (Triticum turgidum L. var. durum), which is more sensitive than either bread wheat or barley. The existence of considerable genetic variation in current germplasm of durum wheat (a relative yield of 58% in Stojocri 2 compared to 15% in check cv Yallaroi) and the development of a consistent selection criterion (Mn content of 35‐day‐old seedlings) has made breeding for Mn efficiency feasible. The development of Mn‐efficient durum wheat would be facilitated if the mode of inheritance was well understood. F1 hybrid, F2, and F2‐derived families from a cross between Stojocri 2 (moderately efficient) and Hazar (inefficient) were studied under controlled‐environment conditions. F1 hybrid was intermediate to the parents, indicating incomplete dominance and dependence on external Mn concentration. Analysis of 110 F2 and 220 F3 single plants (including 20 F2‐derived F3 families) showed that the observed variance was in agreement with the expected variance of a population segregating for two genes. Chi‐square analysis of the segregation ratios of F3 families also supported the digenic segregation hypothesis. Currently Stojocri 2 is used in a breeding program for the transfer of Mn efficiency to commercial varieties, by backcrossing (two backcrosses retain about 88% of recurrent parent genotype).     

Starch Characteristics of Waxy and Nonwaxy Tetraploid (Triticum turgidum L. var. durum) Wheats

Manufacture of pasta products is paramount for durum wheat (Triticum turgidum L. var. durum). The recent development of waxy durum wheat containing starch with essentially 100% amylopectin may provide new food processing applications and present opportunities for value‐added crop production. This investigation was conducted to determine differences in some chemical and functional properties of waxy durum starch. Starch was isolated from two waxy endosperm lines and four nonwaxy cultivars of durum wheat. One of the waxy lines (WX‐1) was a full waxy durum wheat whereas the other line (WX‐0) was heterogeneous, producing both waxy and nonwaxy seed. Effects on starch swelling, solubility, pasting, gelatinization, and retrogradation were examined. The full waxy starch had four times more swelling power than the nonwaxy durum starches at 95°C, and was also more soluble at three of the four temperatures used. Starch pasting occurred earlier and peak viscosities were greater for starches from both waxy lines than for the nonwaxy starches, but their slurries were less stable with continued stirring and heating. Greater energy was required to melt gelatinized waxy starch gels, but no differences were found in either refrigerated storage or freeze‐thaw retrogradation, as determined by differential scanning calorimetry. The results of this investigation showed some significant differences in the starch properties of the waxy durum wheat lines compared to the nonwaxy durum wheats.     

Plant part selection and evaluation of factors affecting analysis and recovery of nitrate in irrigated durum wheat tissue

Abstract

Periodic nitrate tissue tests are used to determine nitrogen (N) fertility status of a variety of crops. Data on the importance of plant part selection, sample handling techniques, grinding criteria and extraction conditions in N0₃‐N analysis of wheat tissue are essential if the procedure is to achieve widespread adoption and use. Detailed partitioning of field grown durum spring wheat (Triticum durum) plants at the Feekes 2 (3–4 leaf), 6 (joint) and 10 (boot) growth stages was conducted to document which plant part exhibits the greatest accumulation of NO₃‐N. Sample handling, fineness of tissue grinding, different tissue: extractant ratios and extraction times were examined to determine their effects on NO₃‐N recovery. Partitioning data confirmed previous findings which identified the basal stem between ground level and the seed prior to jointing and the 5 cm of stem just above ground level thereafter as the plant parts showing the greatest accumulation of NO₃‐N. Therefore, these plant parts have the greatest potential as indicators of the ? nutritional status of durum spring wheat. Optimal recovery of tissue NO₃‐N was obtained when stem tissue was separated immediately in the field and dried within 8 hours of sampling, ground to pass a 0.55 mm mesh screen, and extracted for at least 30 minutes when using a sample size of 0.1000 g in conjunction with 25 ml of extractant (i.e. 1: 250 plant tissue to extractant ratio)     

Influence of Soft Kernel Texture on the Flour,Water Absorption,Rheology, and Baking Quality of Durum Wheat

Durum wheat (Triticum turgidum subsp. durum ) production worldwide is substantially less than that of common wheat (T. aestivum ). Durum kernels are extremely hard; thus, most durum wheat is milled into semolina, which has limited utilization. Soft kernel durum wheat was created by introgression of the puroindoline genes via homoeologous recombination. The objective of this study was to determine the effects of the puroindoline genes and soft kernel texture on flour, water absorption, rheology, and baking quality of durum wheat. Soft Svevo and Soft Alzada, back‐cross derivatives of the durum varieties Svevo and Alzada, were compared with Svevo, a hard durum wheat, Xerpha, a soft white winter wheat, and Expresso, a hard red spring wheat. Soft Svevo and Soft Alzada exhibited soft kernel texture; low water, sodium carbonate, and sucrose solvent retention capacities (SRCs); and reduced dough water absorptions similar to soft wheat. These results indicate a pronounced effect of the puroindolines. Conversely, SDS flour sedimentation volume and lactic acid SRC of the soft durum samples were more similar to the Svevo hard durum and Expresso samples, indicating much less effect of kernel softness on protein strength measurements. Alveograph results were influenced by the inherent differences in water absorption properties of the different flours and their genetic background (e.g., W and P were markedly reduced in the Soft Svevo samples compared with Svevo, whereas the puroindolines appeared to have little effect on L ). However, Soft Svevo and Soft Alzada differed markedly for W and L . Soft durum samples produced bread loaf volumes between the soft and hard common wheat samples but larger sugar‐snap cookie diameters than all comparison samples. The soft durum varieties exhibited new and unique flour and baking attributes as well as retaining the color and protein characteristics of their durum parents.     

Influence of Structural Characteristics of Aleurone Layer on Milling Behavior of Durum Wheat (Triticum durum Desf.)

The structure of the aleurone layer was considered for many years as a potential factor influencing wheat milling efficiency. Eight durum wheat samples of different milling values, including distinct cultivars and harvesting conditions, were employed to investigate the structural characteristics of the aleurone layer through image analysis of kernel sections. Particular attention was paid to tissue thickness and structural irregularity of its interface with the starchy endosperm. Wheat cultivar, agricultural conditions, and location of measurement within the grain had an influence similar to both thickness and irregularity of the aleurone layer. Conversely, grain weight and morphology showed no effect on these parameters. Statistical investigation demonstrated no correlation between structural characteristics and wheat milling behavior. However, the negative correlation between the extraction rate of semolina and starch content in the bran fraction, which was used as an indicator of the endosperm‐aleurone dissociation extent, demonstrated the relevance of the tissue adhesion on milling efficiency.     

Distribution of Peroxidases in Durum Wheat (Triticum durum)

A biochemical study of the main durum wheat milling fractions (bran, embryo, and semolina) showed that peroxidases (POD) were present in multiple forms in the kernel and appeared to be tissue specific: one form for the embryo, one for the endosperm, one for the subaleuronic layer, and one for the outer layers. Large varietal differences were found regarding both the composition and the POD activity. POD activity, detected by diaminobenzidine, was found mainly in the cell wall of the subaleurone layer and inside some specific, differentiated cells of the embryo. Immuno‐localization with antibodies of durum wheat POD showed the presence of POD in several layers of the pericarp (epidermis) and the seed coat (testa), in the embryo, and also in the endosperm. In this latter tissue, the staining intensity decreased gradually from the outer layers toward the center of the kernel. The localization of POD in durum wheat kernel suggests specific functions for different forms.     

First source of resistance in durum wheat to Hessian fly (Diptera: Cecidomyiidae) in Morocco

Hessian fly, Mayetiola destructor (Say), is the major pest of wheat in North Africa. In Morocco, durum wheat (Triticum turgidum L. subsp. durum (Desf). Husn.) losses due to this pest have been estimated at 32%. Genetic resistance is the only economical and practical means of controlling this insect. Field and greenhouse screening of durum wheat genotypes resulted in the identification of one source of resistance to Hessian fly in Morocco. This is the first source of durum wheat Hessian fly-resistance identified in Morocco. This source of resistance expresses a medium level of antibiosis against first-instar Hessian fly larvae; about 25% of the larvae survive on resistant plants. The deployment of varieties that allow for larval survival on resistant plants should reduce selection for biotype development. This source of resistance is being used by CIMMYT/ICARDA and Moroccan breeders to develop resistant durum wheat varieties.     

Bioaccessibility of carotenoids and vitamin e from pasta: evaluation of an in vitro digestion model

The present investigation aimed to expand the knowledge of bioaccessibility of carotenoids, tocopherols, and tocotrienols from cereal products such as pasta. Because most of the published approaches assessing the bioaccessibility of lipophilic micronutrients dealt with fruits and vegetables, a prevalent in vitro digestion procedure was modified. Additionally, several digestion parameters were evaluated with regard to their impact on the bioaccessibility of carotenoids and vitamin E from pasta. Overall, the estimated values were highly dependent on the amount of bile extract present in the digestive medium and to a lesser extent on the simulated gastric pH and the incubation time with digestive enzymes. The bioaccessibility of carotenoids and vitamin E from durum wheat pasta was quite high (71 ± 5 and 70 ± 4%, respectively), whereas these micronutrients were considerably less accessible from pasta containing 10% eggs (57 ± 1 and 49 ± 5%, respectively).     

Preparation and characterization of durum wheat (Triticum durum) straw cellulose nanofibers by electrospinning

Cellulose nanofibers from durum wheat straw ( Triticum durum ) were produced and characterized to study their potential as reinforcement fibers in biocomposites. Cellulose was isolated from wheat straw by chemical treatment. Nanofibers were produced via an electrospinning method using trifluoroacetic acid (TFA) as the solvent. The nanofibers were 270 ± 97 nm in diameter. Analysis of the FT-IR spectra demonstrated that the chemical treatment of the wheat straw removed hemicellulose and lignin. XRD revealed that the crystallinity of the cellulose was reduced after electrospinning, but nanofibers remained highly crystalline. The glass transition temperature (T(g) value) of the fibers was 130 °C, higher than that of cellulose (122 °C), and the degradation temperature of the fibers was 236 °C. Residual TFA was not present in the nanofibers as assessed by the FT-IR technique.     

Study of Viscoelastic Properties of Wheat Kernels Using Compression Load Method

The method to measure hardness and other viscoelastic properties of intact wheat kernels is presented. Wheat with 9.3% moisture showed high elastic behavior compared with wheat tempered at 22.5% moisture that showed a plastic behavior. Load‐deformation curves showed that bread wheat behaves as a more plastic material than durum wheat, which is a more elastic material. Yield point of all the wheat samples was ≈18.5 N, independent of wheat type and moisture content. The height of the wheat kernel increased linearly, and the compression area increased exponentially, with increasing moisture content. The modulus of elasticity of wheat ranged from 99.2 MPa for 22.5% moisture content to 394.8 MPa for 9.3% moisture content. Young's modulus range for soft wheat such as Salamanca, Saturno, and Cortazar cultivars was 232.2–308.5 MPa, as compared with Rayón bread wheat at 321.5 MPa and the Altar, Sofía, and Rafi cultivars of durum wheat that had elastic moduli of 438.7–485.8 MPa. The compression force and final stress decreased from 69.9 N and 40.1 MPa in soft wheat to 90 N and 78.9 MPa in durum, respectively. Total work range was 14.7 MPa/sec in soft wheat to 19.7 MPa/sec for durum wheat and, as expected, was higher in the durum and bread wheat than in soft wheat. The plastic part ranged from 2.4 MPa/sec in soft wheat to 0.6 MPa/sec in durum wheat.