Vicilin-like storage globulin from buckwheat (Fagopyrum esculentum Moench) seeds

Present status and future perspectives of breeding for buckwheat quality

Buckwheat is an important crop globally. It has been processed into cereal grain, noodles, confectionery, bread, and fermented foods for many years. Buckwheat production and processing has supported local economies and is deeply related to the culture of some regions. Buckwheat has many unique traits as a food, with a good flavor and color. In addition, buckwheat is also a healthy food because it contains bioactive compounds that have anti-oxidative, anti-hypertensive, and anti-obesity properties. Therefore, breeding of buckwheat for quality is an important issue to be addressed. Compared to other crops, there is still a lack of basic information on quality, including bioactive compounds generation and enhancement. However, some mechanisms for modifying and improving the quality of buckwheat varieties have recently been identified. Further, some varieties with improved quality have recently been developed. In this review, we summarize the issues around buckwheat quality and review the present status and future potential of buckwheat breeding for quality.

Structural and antioxidant analysis of Tartary buckwheat (Fagopyrum tartaricum Gaertn.) 13S globulin

BACKGROUND

The main component of buckwheat seed storage proteins is 13S globulin. In this study, Tartary buckwheat 13S globulin was separated and its structural features were investigated using Edman sequencing and matrix-assisted laser desorption / ionization time of flight mass spectrometry (MALDI-TOF-MS). The protective effect of its enzymatic hydrolysates against oxidative stress induced by H₂ O₂ was also evaluated to elucidate the antioxidant mechanism.

RESULTS

Results showed that the isolated Tartary buckwheat 13S globulin contained one acidic and one basic subunit, which were linked by a disulfide bond. Six Tartary buckwheat active peptides were obtained from the enzymatic hydrolysates of Tartary buckwheat 13S globulin acidic subunit with a molecular weight of 38 kDa, namely Pep-1, Pep-2, Pep-3, Pep-4, Pep-5, and Pep-6. Pre-treatment of cells with Tartary buckwheat active peptides maintained the redox state balance of HepG₂ cells and protected the activity of antioxidant enzymes in HepG₂ cells. The Tartary buckwheat active peptides improved oxidative stress in HepG₂ cells via the PPAR-α/HO-1 pathway.

CONCLUSION

These results provide an insight into the antioxidant mechanism of Tartary buckwheat 13S globulin and suggest that Tartary buckwheat active peptides can be used as a functional ingredient in the food industry. © 2019 Society of Chemical Industry.

Composition, Protein Profile and Rheological Properties of Pseudocereal-Based Protein-Rich Ingredients

The objectives of this study were to investigate the nutrient composition, protein profile, morphology, and pasting properties of protein-rich pseudocereal ingredients (quinoa, amaranth, and buckwheat) and compare them to the more common rice and maize flours. Literature concerning protein-rich pseudocereal ingredients is very limited, mainly to protein profiling. The concentrations of macronutrients (i.e., ash, fat, and protein, as well as soluble, insoluble and total dietary fibre) were significantly higher for the protein-rich variants of pseudocereal-based flours than their regular protein content variants and the rice and maize flours. On profiling the protein component using sodium dodecyl sulfate⁻polyacrylamide gel electrophoresis (SDS-PAGE), all samples showed common bands at ~50 kDa and low molecular weight bands corresponding to the globulin fraction (~50 kDa) and albumin fraction (~10 kDa), respectively; except rice, in which the main protein was glutelin. The morphology of the starch granules was studied using scanning electron microscopy with quinoa and amaranth showing the smallest sized granules, while buckwheat, rice, and maize had the largest starch granules. The pasting properties of the ingredients were generally similar, except for buckwheat and amaranth, which showed the highest and lowest final viscosity, respectively. The results obtained in this study can be used to better understand the functionality and food applications of protein-rich pseudocereal ingredients.

Global transcriptome and coexpression network analyses reveal cultivar-specific molecular signatures associated with seed development and seed size/weight determination in chickpea

Seed development is an intricate process regulated via a complex transcriptional regulatory network. To understand the molecular mechanisms governing seed development and seed size/weight in chickpea, we performed a comprehensive analysis of transcriptome dynamics during seed development in two cultivars with contrasting seed size/weight (small-seeded, Himchana 1 and large-seeded, JGK 3). Our analysis identified stage-specific expression for a significant proportion (>13%) of the genes in each cultivar. About one half of the total genes exhibited significant differential expression in JGK 3 as compared with Himchana 1. We found that different seed development stages can be delineated by modules of coexpressed genes. A comparative analysis revealed differential developmental stage specificity of some modules between the two cultivars. Furthermore, we constructed transcriptional regulatory networks and identified key components determining seed size/weight. The results suggested that extended period of cell division during embryogenesis and higher level of endoreduplication along with more accumulation of storage compounds during maturation determine large seed size/weight. Further, we identified quantitative trait loci-associated candidate genes harboring single nucleotide polymorphisms in the promoter sequences that differentiate small- and large-seeded chickpea cultivars. The results provide a valuable resource to dissect the role of candidate genes governing seed development and seed size/weight in chickpea.

Proteins of Amaranth (Amaranthus spp.), Buckwheat (Fagopyrum spp.), and Quinoa (Chenopodium spp.): A Food Science and Technology Perspective

There is currently much interest in the use of pseudocereals for developing nutritious food products. Amaranth, buckwheat, and quinoa are the 3 major pseudocereals in terms of world production. They contain high levels of starch, proteins, dietary fiber, minerals, vitamins, and other bioactives. Their proteins have well-balanced amino acid compositions, are more sustainable than those from animal sources, and can be consumed by patients suffering from celiac disease. While pseudocereal proteins mainly consist of albumins and globulins, the predominant cereal proteins are prolamins and glutelins. We here discuss the structural properties, denaturation and aggregation behaviors, and solubility, as well as the foaming, emulsifying, and gelling properties of amaranth, buckwheat, and quinoa proteins. In addition, the technological impact of incorporating amaranth, buckwheat, and quinoa in bread, pasta, noodles, and cookies and strategies to affect the functionality of pseudocereal flour proteins are discussed. Literature concerning pseudocereal proteins is often inconsistent and contradictory, particularly in the methods used to obtain globulins and glutelins. Also, most studies on protein denaturation and techno-functional properties have focused on isolates obtained by alkaline extraction and subsequent isoelectric precipitation at acidic pH, even if the outcome of such studies is not necessarily relevant for understanding the role of the native proteins in food processing. Finally, even though establishing in-depth structure-function relationships seems challenging, it would undoubtedly be of major help in the design of tailor-made pseudocereal foods.

Physicochemical and conformational properties of buckwheat protein isolates: influence of polyphenol removal with cold organic solvents from buckwheat seed flours

The effects of polyphenol removal from common buckwheat seed flours with cold aqueous organic solvents (including 95% ethanol, 70% 2-propanol, and 80% methanol, v/v) on the physicochemical and conformational properties of their protein isolates (BPI) were investigated. The extraction resulted in considerable reduction in its polyphenol content, especially protein-bound polyphenol content, and concomitant increase in its protein content. The efficiency of the removal of the polyphenols was much better in the 2-propanol case than in other two cases. The surface hydrophobicity of the proteins changed slightly, while the disulfide bond contents remarkably increased, partially at the expense of free sulfhydryl group contents. The protein solubility in the pH range of 7.0-11.0 and the proportion of undenatured globulins in BPI products were variably improved by the organic solvent extraction, and the extent of the improvements was highest in the 2-propanol case. Intrinsic emission fluorescence and far-UV and/or near-UV CD spectra showed that polyphenol removal resulted in significant changes in tertiary and/or secondary conformations of the proteins in BPI, and the changes were also related to the efficiency of the removal of the polyphenols. These results suggest that the physicochemical and conformational properties of BPI are closely related to its polyphenol level, and there is also a close relationship between its physicochemical properties and tertiary and/or secondary conformations.

Heterologous expression of legumin gene in E. coli isolated from cDNA clones of immature seeds of pigeonpea (Cajanus cajan L.)

Proteins are one of the targets for improving the nutritional quality, and attempts are being made through manipulation of its native gene(s). Pigeonpea (Cajanus cajan L.) is one of the nutritionally important legumes of tropical and subtropical regions of the world, and studies of the structure of seed storage proteins and their interactions have been limited by the difficulty of isolating single-protein subunits in large amounts from a complex mixture of the seed endosperm. One way to overcome this problem is the expression of seed storage protein-encoded gene(s) in heterologous systems that have additional advantages wherein specific gene modifications can be made and the new gene constructs can quickly be expressed. Legumin protein was extracted from pigeonpea seeds of different developmental stages (5th to 25th day after flowering [DAF]) and characterized. The legumin gene (leg) of size 1.482 kb was screened, using the deoxygenin-labeled legumin probe, from the complementary deoxyribonucleic acid (cDNA) library, constructed from 18-day-old (DAF) immature seeds of pigeonpea and sequenced (accession no. AF3555403). The legumin gene was further characterized by DNA blotting, and its probable secondary structure was predicted using online ExPASy server. Significant Protein Data Bank (PDB) alignment of the deduced legumin protein by BLASTP was observed with proglycinin of soybean. Comparative 3D structural homology was predicted by Cn3D software, and the legumin protein showed the 3D structure alignment and interaction homology with proglycinin chain 1FXZA (PDB no. 1FXZ). The legumin gene was subcloned in vector pET-24a driven by the bacterial promoter, and its expression was detected in Escherichia coli by immunoblotting using polyclonal antibodies, raised against the purified legumin protein.

Buckwheat (Fagopyrum esculentum Moench) low molecular weight seed proteins are restricted to the embryo and are not detectable in the endosperm

Buckwheat (Fagopyrum esculentum Moench) proteins are nutritionally important because of their high and balanced content of essential amino acids making their biological value much higher than that of cereal proteins. We analyzed extracts of buckwheat endosperm and embryo proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). On electropherograms of endosperm proteins, six intense bands were detected. Two most intense bands were in the range of molecular weights (M.W.s) from 50 to 60 kDa. Protein of 57 kDa has been shown not to cross-react against antibodies raised against proteins of M.W. ranging between 23 and 25 kDa. There are no reports about the allergenicity of other endosperm proteins. On the electropherogram of buckwheat endosperm no low M.W. proteins could be detected. In this study we have demonstrated the tissue specific presence of proteins of different size classes of the endosperm and embryo tissues.

Isolation and computer analysis of the 5'-regulatory region of the seed storage protein gene from buckwheat (Fagopyrum esculentum Moench)

Using the modified rapid amplification of cDNA ends (5'-RACE) approach, a fragment containing the 955 bp long 5'-regulatory region of the buckwheat storage globulin gene (FeLEG1) has been amplified from the genomic DNA of buckwheat. The entire fragment was sequenced, and the sequence was analyzed by computer prediction of cis-regulatory elements possibly involved in tissue-specific and developmentally controlled seed storage protein gene expression. The promoter obtained might be interesting not only for fundamental research but also as a useful tool for biotechnological application.

Cloning and computer analysis of the promoter region of the legumin-like storage protein gene from buckwheat, Fagopyrum esculentum Moench

Using the modified 5?-RACE approach, a fragment containing the 955 bp long 5?- regulatory region of the buckwheat storage globulin gene (FeLEG1) has been amplified from the genomic DNA of buckwheat. The entire fragment was sequenced and the sequence analyzed by computer prediction of cis-regulatory elements possibly involved in tissue specific and developmentally controlled seed storage protein gene expression. The promoter obtained might be interesting not only for fundamental research, but also as a useful tool for biotechnological application.