Ultra-fast separation of wheat glutenin subunits by reversed-phase HPLC using a superficially porous silica-based column

Comprehensive analysis of alkenones by reversed-phase HPLC-MS with unprecedented selectivity, linearity and sensitivity

Alkenones are among the most widely used paleotemperature biomarkers. Traditionally, alkenones are analyzed using gas chromatography-flame ionization detector (GC-FID), or GC-chemical ionization-mass spectrometry (GC-CI-MS). However, these methods encounter considerable challenges for samples that exhibit matrix interference or low concentrations, with GC-FID requiring tedious sample preparations and GC-CI-MS suffering from nonlinear response and a narrow linear dynamic range. Here we demonstrate that reversed-phase high pressure liquid chromatography-mass spectrometry (HPLC-MS) methods provide excellent resolution, selectivity, linearity and sensitivity for alkenones in complex matrices. We systematically compared the advantages and limitations of three mass detectors (quadrupole, Orbitrap, and quadrupole-time of flight) and two ionization modes (electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)) for alkenone analyses. We demonstrate that ESI performs better than APCI as response factors of various unsaturated alkenones are similar. Among the three mass analyzers tested, orbitrap MS provided the lowest limit of detection (0.4, 3.8 and 8.6 pg injected masses for Orbitrap, qTOF and single quadrupole MS, respectively) and the widest linear dynamic range (600, 20 and 30 folds for Orbitrap, qTOF and single quadrupole MS, respectively). Single quadrupole MS operated in ESI mode provides accurate quantification of proxy measurements over a wide range of injection masses, and with its modest instrument cost, represents an ideal method for routine applications. Analysis of global core-top sediment samples confirmed the efficacy of HPLC-MS methods for the detection and quantification of paleotemperature proxies based on alkenones and their superiority over GC-based methods. The analytical method demonstrated in this study should also allow highly sensitive analyses of diverse aliphatic ketones in complex matrices.

Avenanthramides: Unique Bioactive Substances of Oat Grain in the Context of Cultivar, Cropping System, Weather Conditions and Other Grain Parameters

Our study was focused on the evaluation of the content of a wider spectrum of eight avenanthramides (AVNs) as unique components of oat grain under the effects of four selected factors (cultivar, locality, cropping system, and year). The weather effects on changes in the AVN content and their relationship to other important parameters of oat grain were further evaluated in more detail. A sensitive UHPLC system coupled with a QExactive Orbitrap mass spectrometer was used for AVN quantification. AVNs confirmed a high variability (RDS = 72.7–113.5%), which was dominantly influenced by the locality and year factors. While most AVN types confirmed mutually high correlations (r = 0.7–0.9), their correlations with the other 10 grain parameters were lower (r ≤ 0.48). Their significant correlations (0.27–0.46) with β-D-glucan could be used in perspective in breeding programs for the synergetic increase of both parameters. PCA analysis and Spearman correlations based on individual cultivars confirmed a significant effect of June and July precipitation on the increase of Σ AVNs. However, the results also indicated that higher precipitation can generate favorable conditions for related factors, such as preharvest sprouting evoking a direct increase of AVNs synthesis in oat grain.

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.

Fundamental to achieving fast separations with high efficiency: A review of chromatography with superficially porous particles

Types of particles have been fundamental to LC separation technology for many years. Originally, LC columns were packed with large-diameter (>100 μm) calcium carbonate, silica gel, or alumina particles that prohibited fast mobile-phase speeds because of the slow diffusion of sample molecules inside deep pores. During the birth of HPLC in the 1960s, superficially porous particles (SPP, ≥30 μm) were developed as the first high-speed stationary-phase support structures commercialized, which permitted faster mobile-phase flowrates due to the fast movement of sample molecules in/out of the thin shells. These initial SPPs were displaced by smaller totally porous particles (TPP) in the mid-1970s. But SPP history repeated when UHPLC emerged in the 2000s. Stationary-phase support structures made from sub-3-μm SPPs were introduced to chromatographers in 2006. The initial purpose of this modern SPP was to enable chromatographers to achieve fast separations with high efficiency using conventional HPLCs. Later, the introduction of sub-2-μm SPPs with UHPLC instruments pushed the separation speed and efficiency to a very fast zone. This review aims at providing readers a comprehensive and up-to-date view on the advantages of SPP materials over TPPs historically and theoretically from the material science angle.

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.

Wheat storage proteins: changes on the glutenins after wheat infection with different isolates of Fusarium graminearum

Wheat gluten proteins are decisive for the industrial properties of flour, so alterations resulting from grain infection with Fusarium graminearum produce changes in the glutenin content that affect the baking properties. This work analyzes the high-molecular-weight glutenin changes from wheat flour with different degrees of F. graminearum infection at field, since these proteins are determinant for the quality properties of flour. Wheat cultivars-on field trials-infected with F. graminearum isolates of diverse aggressiveness showed severity values between 9.1 and 42.58% and thousand kernel weight values between 28.12 and 32.33 g. Negative correlations between severity and protein content and positive correlations between yield and protein content were observed, employing reversed-phase high-performance liquid chromatography and polyacrylamide gel electrophoresis. Furthermore, the protein signal changes were in agreement for both methodological approaches. Also, the degree of disease observed and the protein changes on infected wheat cultivars varied in relation with the aggressiveness of the isolate responsible for the infection. The principal component analysis showed a close arrangement among protein values obtained by HPLC. For each cultivar, two principal components were obtained, which explained 80.85%, 88.48%, and 93.33% of the total variance (cultivars Sy200, AGP Fast, and Klein Tigre respectively). To our knowledge, the approaches employed for the analysis of protein changes according to the degree of disease, as well as the thorough statistical analysis, are novel for the study of Fusarium Head Blight.

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.

Engineering high α-amylase levels in wheat grain lowers Falling Number but improves baking properties

Late maturity α-amylase (LMA) and preharvest sprouting (PHS) are genetic defects in wheat. They are both characterized by the expression of specific isoforms of α-amylase in particular genotypes in the grain prior to harvest. The enhanced expression of α-amylase in both LMA and PHS results in a reduction in Falling Number (FN), a test of gel viscosity, and subsequent downgrading of the grain, along with a reduced price for growers. The FN test is unable to distinguish between LMA and PHS; thus, both defects are treated similarly when grain is traded. However, in PHS-affected grains, proteases and other degradative process are activated, and this has been shown to have a negative impact on end product quality. No studies have been conducted to determine whether LMA is detrimental to end product quality. This work demonstrated that wheat in which an isoform α-amylase (TaAmy3) was overexpressed in the endosperm of developing grain to levels of up to 100-fold higher than the wild-type resulted in low FN similar to those seen in LMA- or PHS-affected grains. This increase had no detrimental effect on starch structure, flour composition and enhanced baking quality, in small-scale 10-g baking tests. In these small-scale tests, overexpression of TaAmy3 led to increased loaf volume and Maillard-related browning to levels higher than those in control flours when baking improver was added. These findings raise questions as to the validity of the assumption that (i) LMA is detrimental to end product quality and (ii) a low FN is always indicative of a reduction in quality. This work suggests the need for a better understanding of the impact of elevated expression of specific α-amylase on end product quality.

Separation of kafirins on surface porous reversed-phase high-performance liquid chromatography columns

Surface porous high-performance liquid chromatography (HPLC) columns were investigated for the separation of kafirins, storage proteins of grain sorghum. Kafirins were successfully separated using C3, C8, and C18 surface porous stationary phases in less than 17 min. Separations using a monolithic C18 stationary phase were also developed and were slightly faster than those achieved on the surface porous C18 stationary phase. However, the resolution was higher on the latter column. Using an ammonium hydroxide/acetonitrile mobile phase, separations were performed on a novel, alkaline stable surface porous C18 stationary phase. The resolution at alkaline pH was not as high, however, as with the traditional acidic acetonitrile mobile phases. In comparison to fully porous stationary phases, the surface porous phases provided higher resolution with much lower separation times (17 versus 40 min). Total peak areas were correlated to total protein content of sorghum (r(2) = 0.96; n = 10), and a method to measure in vitro pepsin digestibility using reversed-phase (RP)-HPLC peak areas showed good correlation to the traditional nitrogen combustion method (r(2) = 0.82; n = 20). Thus, the surface porous stationary phases could be used not only for more rapid separations but also to provide simultaneous information on total protein content and digestibility.

Solid core column technology applied to HPLC-FD of paralytic shellfish toxins

Pre-column oxidation liquid chromatography with fluorescence detection is a chemical method for analyzing paralytic shellfish toxins. In order to improve the sample throughput and efficiency of AOAC Method 2005.06, solid core particle column technology was evaluated. We demonstrate that supplanting the original fully porous particle column with a solid core particle column reduces sample analysis time from 15 to 5 min per sample and improves resolution.

Effects of overexpression of high molecular weight glutenin subunit 1Dy10 on wheat tortilla properties

Wheat (Triticum aestivum L.) flour properties necessary for optimal tortilla production have not been identified. Transgenic wheats (Triticum aestivum L.) overexpressing high molecular weight glutenin subunit (HMW-GS) 1Dy10 were used to make tortilla and their quality was evaluated. The level of HMW-GS 1Dy10 in flours derived from transgenic wheats was 2.5-5.8-fold greater than in controls. Polymeric proteins in the transgenic samples had a molecular weight distribution shifted toward larger polymers as indicated by increased levels of polymeric proteins present and greater M(w) averages of the largest fractions in the insoluble polymeric proteins. Dough derived from transgenic wheats had greater resistance to extension and lower extensibility than controls. Tortilla quality evaluation revealed that tortillas originated from transgenic wheats had decreased diameter, greater thickness and rupture force, and lower rollability scores and stretchability than controls. The presence of 1RS chromosomal translocations from rye (Secale cereale L.) in transgenic wheat decreased the negative effects of overexpression of HMW-GS 1Dy10, as tortillas made with this flour mostly exhibited quality properties similar to those made from control flour. Results suggested that the negative effects of overexpression of HMW-GS 1Dy10 on tortilla properties were derived from a nonideal gluten matrix formation.

Evolutionary origin of the segmental duplication encompassing the wheat GLU-B1 locus encoding the overexpressed Bx7 (Bx7OE) high molecular weight glutenin subunit

Sequencing of a BAC clone encompassing the Glu-B1 locus in Glenlea, revealed a 10.3 Kb segmental duplication including the Bx7 gene and flanking an LTR retroelement. To better understand the evolution of this locus, two collections of wheat were surveyed. The first consisted of 96 diploid and tetraploid species accessions while the second consisted of 316 Triticum aestivum cultivars and landraces from 41 countries. The genotypes were first characterized by SDS-PAGE and a total of 40 of the 316 T. aestivum accessions were found to display the overexpressed Bx7 phenotype (Bx7OE). Three lines from the 96 diploid/tetraploid collection also displayed the stronger intensity staining characteristic of the Bx7(OE) subunit. The relative amounts of the Bx7 subunit to total HMW-GS were quantified by RP-HPLC for all Bx7OE accessions and a number of checks. The entire collection was assessed for the presence of four DNA markers namely an 18 bp indel of the coding region of Bx7 variant alleles, a 43 bp indel of the 5'-region and the left and right junctions of the LTR retrotransposon borders and the duplicated segment. All 43 accessions found to have the Bx7OE subunit by SDS-PAGE and RP-HPLC produced the four diagnostic PCR amplicons. None of the lines without the Bx7OE had the LTR retroelement/duplication genomic structure. However, the 18 and 43 bp indel were found in accessions other than Bx7OE. These results indicate that the overexpression of the Bx7 HMW-GS is likely the result of a single event, i.e., a gene duplication at the Glu-B1 locus mediated by the insertion of a retroelement. Also, the 18 and 43 bp indels pre-date the duplication event. Allelic variants Bx7*, Bx7 with and without 43 bp insert and Bx7OE were found in both tetraploid and hexaploid collections and shared the same genomic organization. Though the possibility of introgression from T. aestivum to T. turgidum cannot be ruled out, the three structural genomic changes of the B-genome taken together support the hypothesis of multiple polyploidization events involving different tetraploid progenitors.