Separation of cereal proteins by reversed-phase high-performance liquid chromatography

Determining the Impact of Genotype × Environment on Oat Protein Isolate Composition Using HPLC and LC-MS Techniques

The effect of genotype and environment on oat protein composition was analyzed through size exclusion-high-performance liquid chromatography (SE-HPLC) and liquid chromatography-mass spectrometry (LC-MS) to characterize oat protein isolate (OPI) extracted from three genotypes grown at three locations in the Canadian Prairies. SE-HPLC identified four fractions in OPI, including polymeric globulins, avenins, glutelins, and albumins, and smaller proteins. The protein composition was dependent on the environment, rather than the genotype. The proteins identified through LC-MS were grouped into eight categories, including globulins, prolamins/avenins, glutelins, enzymes/albumins, enzyme inhibitors, heat shock proteins, grain softness proteins, and allergenic proteins. Three main globulin protein types were also identified, including the P14812|SSG2-12S seed storage globulin, the Q6UJY8_TRITU-globulin, and the M7ZQM3_TRIUA-Globulin-1 S. Principal component analysis indicated that samples from Manitoba showed a positive association with the M7ZQM3_TRIUA-Globulin-1 S allele and Q6UJY8_TRITU-globulin, while samples from Alberta and Saskatchewan had a negative association with them. The results show that the influence of G × E on oat protein fractions and their relative composition is crucial to understanding genotypes' behavior in response to different environments.

Wheat grain proteins: Past, present, and future

Background and Objectives

Research on wheat grain proteins is reviewed, including achievements over the past century and priorities for future research. The focus is on three groups of proteins that have major impacts on wheat quality and utilization: the gluten proteins which determine dough viscoelasticity but also trigger celiac disease in susceptible individuals, the puroindolines which are major determinants of grain texture and the amylase/trypsin inhibitors which are food and respiratory allergens and are implicated in triggering celiac disease and nonceliac wheat sensitivity.

Findings

Although earlier work focused on protein structure and properties, the development of genomics and high-sensitivity proteomics has resulted in the availability of a vast amount of information on the amino acid sequences of individual wheat proteins, including allelic variants of gluten proteins which are associated with good processing quality and of puroindolines, which are associated with a hard or soft grain texture, and on protein expression and polymorphism.

Conclusions

However, our ability to exploit this knowledge is limited by a lack of detailed understanding of the structure:function relationships of wheat proteins. In particular, we need to understand how the three-dimensional structures of the individual proteins determine their interactions with other grain components (to determine functional properties) and with the immune systems of susceptible consumers (to trigger adverse responses), how these interactions are affected by allelic variation, and how they can be manipulated.

Significance and Novelty

The article, therefore, identifies priorities for future research which should enable the adoption of a more rational approach to improving the quality of wheat grain proteins.

Gluten proteins: Enzymatic modification, functional and therapeutic properties

Glutens are potential proteins with multifunctional therapeutic effects. Their covalence network structures with and without protease inhibitors are expected to enhance or to serve further properties and further technological points such as increased bioactive surfaces, gelatinization, gelation and pasting properties. The depletion of the allergic peptide sequences of gluten proteins comprising sometimes protease inhibitors are valid via the enzymatic ingestion using proteolytic enzymes that might enhance these functional and technological processes by producing active peptides having osmoregulation and regular glass transitions, surface activity for coating and encapsulation properties. In addition to further therapeutic functions such as immunoregulatory, antithrombin and opioidal activities, particularly in eradicating most of the free radicals, suppressing diabetes Mellitus II complications and inhibiting angiotensin converting enzyme cardiovascular growth diseases.

A Rapid, Reliable RP-UPLC Method for Large-Scale Analysis of Wheat HMW-GS Alleles

High-molecular-weight glutenin subunits (HMW-GS) account for only 10% of total wheat storage proteins, but play an important role in the processing quality of wheat flour. Therefore, identifying HMW-GS alleles associated with good end-use quality provides important information for wheat breeders. To rapidly, accurately and reproducibly identify HMW-GS, we established an optimized reversed-phase ultra-performance liquid chromatography (RP-UPLC) method. Separation parameters were optimized using an ACQUITY UPLC Protein BEH C4 column and stepwise ACN gradient, and the separation patterns and retention times (RTs) of 22 subunits were comparatively analyzed in 16 standard wheat cultivars. All HMW-GS proteins were well separated within about 5.5 min, and all analyses were complete within 12 min. We distinguished the 16 subunits based on RT, although three subunits in 1Bx (1Bx7/1Bx7OE and 1Bx17) and three subunits in 1By (1By8*, 1By9 and 1By15) had overlapping RTs; these were differentiated by SDS-PAGE. To distinguish 1Bx7 and 1Bx7OE, which differ in protein abundance, RP-UPLC was combined with PCR analysis of DNA junction markers. The optimized method was successfully applied to determine HMW-GS alleles in a large collection of bread wheat germplasm (1787 lines). This protocol is an appropriate option for selecting lines harboring favorable HMW-GS alleles in wheat breeding.

Research on the influences of two alcohol soluble glutenins on the retrogradation of wheat amylopectin/amylose

Two alcohol soluble glutenins (ASGLUs) were extracted from gluten and further separated by column chromatography. The ASGLUs with Mw lower than 20,000 (ASGLU 1) and Mw higher than 70,000 (ASGLU 2) show the total amino acid contents of 86.71 g/100 g and 62.847 g/100 g respectively. Both of them are rich in Glu (45.574% and 43.224%) and Pro (15.447% and 16.370%) while poor in cys-s, met and lys (less than 1%). When wheat amylopectin/amylose retrogrades with those ASGLUs, the retrogradation rate of amylopectin with ASGLU 1 enhances significantly. UV-Vis, X-ray diffraction, FT-IR, DSC, CD and solid ¹³C NMR suggest that the double helixes of amylopectin short-chain branching are unwound during gelatinization. The hydrogen bonds of ASGLU 1 between amide and carbonyl oxygen are destroyed, meanwhile, β-sheets are unfolded. During retrogradation, ASGLU 1 with less steric hindrance gets into the crevice of amylopectin and combines with the short-chain branching by hydrogen bond. The retrogradation dynamics show that the nucleation type of amylopectin-ASGLU 1 changes from instantaneous to rod-like growth during the process of retrogradation. β-sheet of ASGLU 1 changes to β-turn and random conformations at the meantime. The results provide a key targeting to control retrogradation of dough.

Proteomic analysis of 2-chloroethanol extracts of rice (Oryza sativa L.) seeds

Ethanol-soluble proteins, including prolamins, are one of the most important seed proteins in rice (Oryza sativa L.). However, little is known about the proteomic profile of ethanol-soluble protein fraction extracted from rice grain. In this work, the differential profile of ethanol-soluble proteins extracted by 2-chloroethanol and ethanol has been documented. Proteome analysis utilizing LC-MS/MS identified a total of 64 unique proteins in the 2-chloroethanol extract of rice seeds. The majority of these proteins had low molecular weight ranging from 10 to 25 kD and isoelectric point (pI) in mid-acidic (pH 5-pH 7) and mid-basic (pH 7-pH 9) ranges. Database searches combined with transmembrane domain (TMD) analysis revealed that >70% of identified proteins were hydrophobic, i.e., had at least one TMD. Gene ontology classification and enrichment analysis showed that the identified proteins were involved in13 types of biological processes, 5 types of cell components, and 17 types of molecular functions. These results were significant based on the hyper p-value of <0.05. The most frequent categories of biological processes, cell components, and molecular functions were, respectively, type I hypersensitivity, extracellular space and extracellular region, and serine-type endopeptidase inhibitor activity. Interestingly, in addition to seed storage proteins such as prolamins and glutelins, certain allergen proteins, protease inhibitors, and lipid transfer proteins were identified in the extracts. Together, the collected data provide novel insights into the protein profile of 2-chloroethanol extract of rice seeds.

Development of an Optimized MALDI-TOF-MS Method for High-Throughput Identification of High-Molecular-Weight Glutenin Subunits in Wheat

Because high-molecular-weight glutenin subunits (HMW-GS) are important contributors to wheat end-use quality, there is a need for high-throughput identification of HMW-GS in wheat genetic resources and breeding lines. We developed an optimized method using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to distinguish individual HMW-GS by considering the effects of the alkylating reagent in protein extraction, solvent components, dissolving volume, and matrix II components. Using the optimized method, 18 of 22 HMW-GS were successfully identified in standard wheat cultivars by differences in molecular weights or by their associations with other tightly linked subunits. Interestingly, 1Bx7 subunits were divided into 1Bx7 group 1 and 1Bx7 group 2 proteins with molecular weights of about 82,400 and 83,000 Da, respectively. Cultivars containing the 1Bx7 group 2 proteins were distinguished from those containing 1Bx7OE using well-known DNA markers. HMW-GS 1Ax2* and 1Bx6 and 1By8 and 1By8*, which are difficult to distinguish due to very similar molecular weights, were easily identified using RP-HPLC. To validate the method, HMW-GS from 38 Korean wheat varieties previously evaluated by SDS-PAGE combined with RP-HPLC were analyzed by MALDI-TOF-MS. The optimized MALDI-TOF-MS method will be a rapid, high-throughput tool for selecting lines containing desirable HMW-GS for breeding efforts.

Comparison of MALDI-TOF-MS and RP-HPLC as Rapid Screening Methods for Wheat Lines With Altered Gliadin Compositions

The wheat gliadins are a complex group of flour proteins that can trigger celiac disease and serious food allergies. As a result, mutation breeding and biotechnology approaches are being used to develop new wheat lines with reduced immunogenic potential. Key to these efforts is the development of rapid, high-throughput methods that can be used as a first step in selecting lines with altered gliadin contents. In this paper, we optimized matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and reversed-phase high-performance liquid chromatography (RP-HPLC) methods for the separation of gliadins from Triticum aestivum cv. Chinese Spring (CS). We evaluated the quality of the resulting profiles using the complete set of gliadin gene sequences recently obtained from this cultivar as well as a set of aneuploid lines in CS. The gliadins were resolved into 13 peaks by MALDI-TOF-MS. α- or γ-gliadins that contain abundant celiac disease epitopes and are likely targets for efforts to reduce the immunogenicity of flour were found in several peaks. However, other peaks contained multiple α- and γ-gliadins, including one peak with as many as 12 different gliadins. In comparison, separation of proteins by RP-HPLC yielded 28 gliadin peaks, including 13 peaks containing α-gliadins and eight peaks containing γ-gliadins. While the separation of α- and γ-gliadins gliadins achieved by RP-HPLC was better than that achieved by MALDI-TOF-MS, it was not possible to link peaks with individual protein sequences. Both MALDI-TOF-MS and RP-HPLC provided adequate separation of ω-gliadins. While MALDI-TOF-MS is faster and could prove useful in studies that target specific gliadins, RP-HPLC is an effective method that can be applied more broadly to detect changes in gliadin composition.

Improved Method for Reliable HMW-GS Identification by RP-HPLC and SDS-PAGE in Common Wheat Cultivars

The accurate identification of alleles for high-molecular weight glutenins (HMW-GS) is critical for wheat breeding programs targeting end-use quality. RP-HPLC methods were optimized for separation of HMW-GS, resulting in enhanced resolution of 1By and 1Dx subunits. Statistically significant differences in retention times (RTs) for subunits corresponding to HMW-GS alleles were determined using 16 standard wheat cultivars with known HMW-GS compositions. Subunits that were not identified unambiguously by RP-HPLC were distinguished by SDS-PAGE or inferred from association with linked subunits. The method was used to verify the allelic compositions of 32 Korean wheat cultivars previously determined using SDS-PAGE and to assess the compositions of six new Korean cultivars. Three cultivars contained subunits that were identified incorrectly in the earlier analysis. The improved RP-HPLC method combined with conventional SDS-PAGE provides for accurate, efficient and reliable identification of HMW-GS and will contribute to efforts to improve wheat end-use quality.

Ultrasound-based protein determination in maize seeds

The need for a simple and accurate method for protein estimation in alcoholic extracts led to the reexamination of the optimum conditions of a colorimetric assay based on the biuret reaction. Sonication time and the other experimental parameters were optimized after kinetics study on the extraction of either zein or total proteins. Zein extraction and purity were investigated by (1)H and (13)C NMR spectroscopy, SDS-PAGE electrophoresis, and UV-visible spectrophotometry (UV-vis). A zein assay was proposed, which involves the reaction of copper ions in copper phosphate powder with zein extracted in ethanolic solutions under strong alkaline environment. Furthermore, we extended this procedure to determine total proteins in maize samples simultaneously with their ultrasonic-assisted (US) extraction with an alkaline-alcoholic solution. Proteins in both types of extracts were well characterized by UV-vis spectroscopy. However, the 545 nm absorbance of the violet-colored supernatants which is proportional to the protein content was found to be the key parameter of the improved biuret-based protein assay. Comparison of values obtained by this procedure and by Micro-Kjeldahl method was in excellent agreement. A scaled-down procedure agreed well with the standard procedure. Enhanced accuracy and repeatability was found in protein determination in maize using the modified biuret method. The optimization of reagent concentrations and incubation times were studied as well.

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.

Characterization and comparative analysis of wheat high molecular weight glutenin subunits by SDS-PAGE, RP-HPLC, HPCE, and MALDI-TOF-MS

High molecular weight glutenin subunits (HMW-GS) from 60 germplasms including 30 common wheat cultivars and 30 related species were separated and characterized by a suite of separation methods including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), reversed-phase high-performance liquid chromatography (RP-HPLC), high-performance capillary electrophoresis (HPCE), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Comparative analysis demonstrated that each methodology has its own advantages and disadvantages. The main drawback of SDS-PAGE was its overestimation of molecular mass and incorrect identification of HMW-GS due to its low resolution. However, it had the advantages of technical simplicity and low requirements of equipment; thus, it is suitable for large-scale and high-throughput HMW-GS screening for breeding programs, especially when the glutenin composition is clear in the breeding material. MALDI-TOF-MS clearly expressed many technical advantages among the four methods evaluated, including high throughput, high resolution, and accuracy; it was, however, associated with high equipment cost, thus preventing many breeding companies from accessing the technology. RP-HPLC and HPCE were found to be intermediate between SDS-PAGE and MALDI-TOF-MS. Both RP-HPLC and HPCE demonstrated higher resolution and reproducibility over SDS-PAGE but lower detection power than MALDI-TOF-MS. Results demonstrated that MALDI-TOF-MS is suitable for analyzing HMW-GS for routine breeding line screening and for identifying new genotypes.

Fractionation of zein by size exclusion chromatography

Zein is a group of alcohol-soluble corn proteins, which consists of several individual proteins. A single-step gel filtration chromatography method was developed to fractionate individual zeins from ethanol extracts of whole corn. A Superdex prep 75 column was used with different mobile phases to fractionate the zeins, which were analyzed by SDS-PAGE and UV spectrophotometry. With 70% aqueous ethanol as the mobile phase, fractions containing a mixture of alpha-zein/beta-zein and alpha-zein/delta-zein were obtained. With ammonium bicarbonate added to the 70% ethanol mobile phase, it was possible to obtain beta-zein and delta-zein fractions devoid of other proteins. However, all fractions containing alpha-zein also contained minor amounts of delta-zein and/or beta-zein. Almost all fractions also contained non-protein impurities.

Intra-specific genetic relationship analyses of Elaeagnus angustifolia based on RP-HPLC biochemical markers

Elaeagnus angustifolia Linn. has various ecological, medicinal and economical uses. An approach was established using RP-HPLC (reversed-phase high-performance liquid chromatography) to classify and analyse the intra-specific genetic relationships of seventeen populations of E. angustifolia, collected from the Xinjiang areas of China. Chromatograms of alcohol-soluble proteins produced by seventeen populations of E. angustifolia, were compared. Each chromatogram of alcohol-soluble proteins came from a single seed of one wild plant only. The results showed that when using a Waters Delta Pak. C18, 5 microm particle size reversed phase column (150 mm x 3.9 mm), a linear gradient of 25%-60% solvent B with flow rate of 1 ml/min and run time of 67 min, the chromatography yielded optimum separation of E. angustifolia alcohol-soluble proteins. Representative peaks in each population were chosen according to peak area and occurrence in every seed. The converted data on the elution peaks of each population were different and could be used to represent those populations. GSC (genetic similarity coefficients) of 41% to 62% showed a medium degree of genetic diversity among the populations in these eco-areas. Cluster analysis showed that the seventeen populations of E. angustifolia could be divided into six clusters at the GSC=0.535 level and indicated the general and unique biochemical markers of these clusters. We suggest that E. angustifolia distribution in these eco-areas could be classified into six variable species. RP-HPLC was shown to be a rapid, repeatable and reliable method for E. angustifolia classification and identification and for analysis of genetic diversity.

Identification of Rhodiola species by using RP-HPLC

An approach was established using RP-HPLC (reversed-phase high-performance liquid chromatography) to identify ten species of Rhodiola, R. coccinea A. Bor, R. junggarica C.Y. Yang et N.R. Cui spn., R. heterodonta A. Bor, R. linearifolia A. Bor, R. pamiro alaiucm A. Bor, R. kaschgarica A. Bor, R. litwinowii A. Bor, R. gelida schrenk, R. rosea L. and R. quadrifide Fisch et Mey collected from the Tianshan Mountains areas of China. Chromatograms of alcohol-soluble proteins, generated from these ten Rhodiola spp. were compared. Each chromatogram of alcohol-soluble proteins came from a single seed of one wild species only. The results showed that when using a Waters Delta Pak. C18, 5 microm particle size reversed phase column (150 mm x 3.9 mm), a linear gradient of 22%-55% solvent B with a flow rate of 1 ml/min and a run time of 67 min, the chromatography gave optimum separation of Rhodiola alcohol-soluble proteins. Chromatogram of each species was different and could be used to identify those species. Cluster analysis of genetic similarity coefficients of 37% to 60% showed a medium degree of genetic diversity among the species in these eco-areas. Cluster analysis showed that the ten species of Rhodiola can be divided into four clusters and yielded the general and unique biochemical markers of these species. RP-HPLC was shown to be a rapid, repeatable and reliable method for Rhodiola species identification and analysis of genetic diversity.

Compared use of HPLC and FZCE for cluster analysis of Triticum spp and for the identification of T. durum adulteration

Wheat quality criteria continually evolve in response to market pressure and consumer preference. Characterization of cereal cultivars for quality and agronomic properties, have widely shown the importance of the protein content to ensure good quality products. The aim of this work is a comparison of reversed-phase high performance liquid chromatography (RP-HPLC) and free zone capillary electrophoresis (FZCE) in the identification of Italian wheat cultivars and detection of durum wheat flour adulteration. Mainly alcohol soluble (gliadins) and water soluble (albumins) proteins were extracted from 14 common wheat cultivars and from 9 durum wheat cultivars. In RP-HPLC chromatograms, wheat albumins and gliadins eluted between 3 and 9 min and between 10 and 42 min, respectively. Even if the chosen chromatographic conditions (reversed phase) did not permit a complete resolution of hydrophilic proteins such as albumins, a good reproducibility was observed for both albumins and gliadins. In FZCE electropherograms, wheat albumins and gliadins migrated between 8 and 14 min and 16-25 min, respectively. A good reproducibility was found for wheat albumins, while the relatively poor reproducibility of gliadin fractions was a consequence of the selected separation conditions aimed to separate in the same run either hydrophilic (albumins) and alcohol-soluble (gliadins) proteins. The principal component analysis (PCA) of HPLC and FZCE data evidenced that both techniques allowed the univocal identification of the great proportion of investigated wheat cultivars. Three peaks were exclusively detected in RP-HPLC chromatograms of common wheat cultivars, while three unique peaks were found in FZCE electropherograms of common wheat cultivars. These peaks were investigated as a basis for detecting and estimating the adulteration of durum wheat flour with flour from common wheat. The direct relationship between the area of the peaks and adulteration level enabled standard curves to be constructed. The standard curves showed that adulteration may be quantified by either RP-HPLC or FZCE.

Uptake and distribution of rare earth elements in rice seeds cultured in fertilizer solution of rare earth elements

The uptake behavior of rare earth elements (REEs) under pot conditions using deionized water and a REE fertilizer solution as the culture media as well as the distribution of REEs in rice proteins were studied. The uptake of REEs in rice seeds increased dramatically after a lag period of approximately three days. Roots can accumulate a much higher content of REEs than germs and the resting seeds. The REE content in each water-soluble (albumin) and salt-soluble (globulin) component of the rice seeds accounted for 5-8% and 4-6% of the total REEs, respectively. However, there are less than 1.5% of the total REEs were found in the alcohol-soluble (prolamin) and acetic acid-soluble (glutelin) components. The high performance liquid chromatography (HPLC) in the gel permeation and the reserved-phase were used to monitor changes in the molecular weight distribution changes of the soluble proteins of rice seeds during germination after having been cultured in the same solution for seven days. No changes occurred in the prolamin, while a slight change occurred in the albumin, globulin and glutelin. Fractionation of the albumin of rice seeds cultured in a REE fertilizer solution on the Sephadex G-100 column indicated that REEs, especially Ce, La, Pr and Nd, were associated mainly with biological compounds of a molecular weight between 10,000 and 12,000.

High-performance capillary electrophoresis of cereal proteins

Cereal grains are widely used of human foods and animal feed throughout the world. Cereals provide dietary protein, which also often has a functional role, as wheat gluten does in bread. Cereal proteins are unique in many ways: they are highly complex and heterogeneous, are often difficult to extract, and aggregate readily, making them difficult to characterize. Because of the economic importance and widespread use of cereal proteins, however, many techniques have been used for their analysis. High-performance capillary electrophoresis (HPCE) is one of the newest techniques to be so used. This review describes the development of charge- and size-based HPCE methods for analysis of cereal grain proteins, and the use of these methods for cultivar identification, classification, and prediction of quality. HPCE is versatile, rapid, easily automated, readily quantified, and provides high-resolution separations. Clearly, HPCE is a valuable addition to other methods of cereal protein analysis and should, in time, be applicable to all protein classes from all cereals.

Wheat cultivar discrimination by capillary electrophoresis of gliadins in isoelectric buffers

A modified method is reported for screening of wheat cultivars: capillary zone electrophoresis of gliadins in isoelectric buffers. Previously published procedures recommended a 100 mM phosphate buffer, supplemented with 0.05% hydroxypropylmethylcellulose and 20% acetonitrile, in uncoated capillaries. Due to the very high conductivity of such a buffer (4.7 mmhos at 25 degrees C) high speed separations (10-12 min analysis time at 800 V/cm) could only be elicited in 20 microm internal diameter (ID) capillaries, at the expense of sensitivity. In the present report, we optimized the background electrolyte as follows: 40 mM aspartic acid (pH=pI=2.77) in the presence of 7 M urea and 0.5% short-chain hydroxyethylcellulose (Mn 27000 Da; apparent pH 3.9 in 7 M urea). As an alternative recipe, the same isoelectric buffer can be supplemented with a mixed organic solvent composed of 4 M urea and 20% acetonitrile (apparent pH 3.66). Due to the much lower conductivity (0.7 mmhos), separations can be carried out at 1000 V/cm in only 10 min, but in larger bore capillaries (50 microm ID), ensuring a five-times higher sensitivity. The gliadin patterns thus obtained are species-specific and allow easy identification of all cultivars tested of both durum and bread wheat. No adsorption of proteins to the silica wall seems to occur and high reproducibility in peak areas and transit times is obtained.

Characterization of distinct alpha- and gamma-type gliadins and low molecular weight components from wheat endosperm as coeliac immunoreactive proteins

Distinct alpha- and gamma-type gliadins, as well as a few low molecular weight components have been identified as coeliac immunoreactive proteins from a chloroform/methanol extract from wheat endosperm. Characterization of these components involved the combination of reverse-phase high-performance liquid chromatography, immunoblotting following SDS-PAGE using a coeliac serum and microsequencing analysis. This has allowed the identification of a group of gliadins with different molecular weights, according to their N-terminal amino-acid sequence: five alpha-type gliadins of 31, 35, 38 and two of 45 kDa, one gamma 2-type gliadin of 40 kDa, two gamma 3-type gliadins of 31, and 50 kDa, and two gamma-type gliadins with an atypical gliadin N-terminal of 31, and 40 kDa, as well as a few unidentified low molecular weight components and three N-terminal blocked proteins, all exhibiting similar antigenicity.

Characterization of soybean proteins by HPLC

Proteins extracted from five soybean cultivars were separated by reversed-phase (RP) and size exclusion (SE) high performance liquid chromatography (HPLC). A RP-HPLC method was developed that permits protein separation of nondefatted flours from soybean cultivars. RP-HPLC showed that protein of these cultivars could be classified into two groups, one of which contained intermediate component peaks under identical conditions. Genetically closely related cultivars exhibited only small differences in their RP-HPLC chromatograms. Size exclusion high performance liquid chromatography (SE-HPLC) resolved extracts of nondefatted flours from various soybean cultivars into six common peaks which accounted for 80 to 94% of the total peak area. Soybean cultivars were primarily identified by the percent area of their fifth peak (fraction F5) which had the highest variability of the total peak area. Seed protein of the cultivars was closely related with the area percent of peak F2 (r = 0.91). SE-HPLC proved to be a rapid one step quantitative method with potential for assessing soybean cultivars on the basis of protein content.

Electrophoresis and chromatography of wheat proteins: available methods, and procedures for statistical evaluation of the data

Analysis of gluten proteins from the wheat grain endosperm has long challenged the analytical chemist. Several hundred unique polypeptides are present, many in large polymers. This complexity, plus useful relationships of composition to genotype and quality, encouraged development and application of electrophoresis and chromatography for gluten analysis. We review the methods of polyacrylamide gel electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, isoelectric focusing and high-performance liquid chromatography available for study of wheat proteins. Singly and in combination, they provide rapid, reproducible, high-resolution separations based on size, charge, or surface hydrophobicity. As challenging and important as the analyses themselves, however, is interpretation of data. Subjective evaluation is sometimes possible, but statistical methods such as similarity scores, clustering, principal components, multiple linear regression, and partial least squares now are increasingly used for data analysis. We review the use of these procedures, and precautions necessary to avoid misinterpretation of data. Optimal evaluation of protein analytical data will enhance the value of such analyses in wheat breeding, marketing, and processing.