Nitrogen regulates the synthesis of hydrophobic amino acids to improve protein structural and gel properties in common buckwheat.

Nitrogen (N) fertilizer impacts the grain quality of common buckwheat, but the effects and regulatory mechanisms of N on various protein parameters of buckwheat are not fully understood. The purpose of this study was to investigate the particle morphology, structural and gel properties, and regulation mechanism of buckwheat protein under four N levels. The bulk density, surface hydrophobicity, particle size, and thermal properties of the buckwheat protein were maximized through the optimal N application (180 kg N/ha), further enhancing the thermal stability of the protein. N application increased the ß-sheet content and reduced the random coil content. Appropriate N fertilizer input enhanced the tertiary structure stability and gel elasticity of buckwheat protein by promoting hydrophobic interactions, disulfide bonds, ionic bonds, storage modulus and loss modulus. The differentially expressed proteins induced by N are primarily enriched in small ribosomal subunit and ribosome, improving protein quality mainly by promoting the synthesis of hydrophobic amino acids. Future agriculture should pay attention to the hydrophobic amino acid content of buckwheat to effectively improve protein quality. This study further advances the application of buckwheat protein in the field of food processing and provides a theoretical basis for the extensive development and utilization of buckwheat protein.

Effects of biochar coupled with chemical and organic fertilizer application on physicochemical properties and in vitro digestibility of common buckwheat (Fagopyrum esculentum Moench) starch.

Common buckwheat starch, a functional ingredient, has wide food and non-food applications. Excessive chemical fertilizer application during grain cultivation decreases quality. This study examined the effects of different combinations of chemical fertilizer, organic fertilizer, and biochar treatment on the physicochemical properties and in vitro digestibility of starch. The amendment of both organic fertilizer and biochar was observed to have a greater impact on the physicochemical properties and in vitro digestibility of common buckwheat starch in comparison to organic fertilizer amendment solely. The combined application of biochar, chemical, and organic nitrogen in an 80:10:10 ratio significantly increased the amylose content, light transmittance, solubility, resistant starch content, and swelling power of the starch. Simultaneously, the application reduced the proportion of amylopectin short chains. Additionally, this combination decreased the size of starch granules, weight-average molecular weight, polydispersity index, relative crystallinity, pasting temperature, and gelatinization enthalpy of the starch compared to the utilization of chemical fertilizer alone. The correlation between physicochemical properties and in vitro digestibility was analyzed. Four principal components were obtained, which accounted for 81.18 % of the total variance. These findings indicated that the combined application of chemical fertilizer, organic fertilizer, and biochar would improve common buckwheat grain quality.

Suitable nitrogen fertilizer application drives the endosperm development and starch synthesis to improve the physicochemical properties of common buckwheat grain.

The effects of nitrogen (N) fertilizer on endosperm development, starch component, key enzyme activity and grain quality of common buckwheat were investigated in this study. The results showed that N fertilization significantly enhanced the number and area of endosperm cells, and significant increases were also observed in the contents of amylose, amylopectin and total starch. With increasing N level, the activities of key enzyme significantly increased showing the maximum under the N2 level (180 kg N ha-1), and then decreased under high N level. As N level increased, the ash, crude protein and amylose content varied from 1.36 to 2.25 %, from 7.99 to 15.84 % and from 22.69 to 27.64 %, respectively. The gelatinization enthalpy significantly increased with the range of 3.46-5.66 J/g, while no change was found in crystalline structure of common buckwheat flour. These results indicated that appropriate N application could effectively improve the endosperm development, starch synthesis and accumulation, and grain properties of common buckwheat, with the best effect under the level of 180 kg N ha-1.

Proteomics characterization of the synthesis and accumulation of starch and amino acid driven by high-nitrogen fertilizer in common buckwheat.

The accumulation of starches and amino acid content of common buckwheat is promoted by Nitrogen (N), but the molecular mechanism is not clear. N applications with 0 (control group) and 180 kg/ha were designed. High-N significantly improved grain fullness and increased the starch, amylopectin and amylose content. The number of upregulated differentially expressed proteins (DEPs) induced by N gradually increased with the filling progress. N resulted in 139, 341 and 472DEPs significant upregulation at 10d, 20d and 30d and they were mainly related to the 'Starch and sucrose metabolism', 'Protein processing in endoplasmic reticulum' and 'Ribosome' by kyoto encyclopedia of genes and genomes analysis. High-N induced one sucrose synthase, two alpha-amylases and six alpha-glucan phosphorylases significant upregulation at 30d and one alpha-amylases upregulation at 10d, and the expression levels of these proteins showed a significant linear relationship with starch and amylose contents. N promoted the arginine and lysine biosynthesis at the late filling stage. These results elucidated that the mechanism of N promoted common buckwheat starches and amino acid accumulation. The identified crucial proteins may improve buckwheat quality.

Relationship between nitrogen fertilizer and structural, pasting and rheological properties on common buckwheat starch.

Nitrogen is an essential element for the yield and quality of grain. In this study, the structural and physicochemical properties of two common buckwheat varieties under four nitrogen levels (0, 90, 180, 270 kg N ha-1) at one location in two years were investigated. With increasing nitrogen level, the contents of moisture and amylose decreased but the contents of ash and crude protein increased. Excessive nitrogen application significantly increased the granule size, but reduced the light transmittance, water solubility, swelling power, absorption of water and oil. All the samples showed a typical A - type pattern, while high relative crystallinity and low order degree were observed under high nitrogen level. The samples under high nitrogen level had lower textural properties, pasting properties and rheological properties but higher pasting temperature and gelatinization enthalpy. These results indicated that nitrogen fertilizer significantly affected the structural and physicochemical properties of common buckwheat starch.

Proteomics characterization nitrogen fertilizer promotes the starch synthesis and metabolism and amino acid biosynthesis in common buckwheat.

Nitrogen (N) affects common buckwheat quality by affecting starch and amino acids (AAs) content, but its molecular mechanism is still unclear. We selected two common buckwheat varieties with high and low starch content, and designed two treatments with 180 and 0 kg N/ha. Application of high-N led to significant increases in starch, amylose and amylopectin content. Of 1337 differentially expressed proteins (DEPs) induced by high-N conditions. 472DEPs were significantly upregulated and 176DEPs downregulated for Xinong9976. 239DEPs were significantly upregulated and 126DEPs downregulated for Beizaosheng. The six alpha-glucan phosphorylases, three alpha-amylases, one granule-bound starch synthase 1 and one sucrose synthase exhibited higher expression at the 180 kg N/ha than at the 0 kg N/ha. In addition, high-N application promoted arginine, leucine, isoleucine and valine biosynthesis. This study revealed the effect of N on the starch and AA content of common buckwheat and its mechanism. The crucial proteins identified may develop the quality of common buckwheat.

Diverse effects of nitrogen fertilizer on the structural, pasting, and thermal properties of common buckwheat starch.

At present, the yield of common buckwheat, which is mainly grown in northern Shaanxi of China, is low and the grain quality is poor. Nitrogen is an important nutrient for the growth of common buckwheat, and appropriate nitrogen application can improve the grain quality. Nitrogen fertilizer could alter the starch granule morphology shapes and the granule size distribution. With increasing nitrogen levels, branch number, flower clusters number, grain number per plant, contents of protein and fat, size distribution of "C" granules, and percentages of light transmittance significantly increased, whereas amylose content and retrogradation decreased. All the samples displayed typical A-type X-ray diffraction patterns. Starch showed higher pasting temperature and gelatinization enthalpy but lower trough and final viscosities under high nitrogen levels. These results suggested N2 treatment was more suitable for common buckwheat growth, principal components and correlation analysis revealed that nitrogen fertilizer significantly affected the physicochemical properties of common buckwheat starches.

Structural, pasting and thermal properties of common buckwheat (Fagopyrum esculentum Moench) starches affected by molecular structure.

Common buckwheat starch (CBS) has extensive using value in the human diet. In this study, the molecular structure and physicochemical properties of CBS isolated from five cultivars collected from three regions of China were studied. Variations in molecular structure, crystalline structure, complexity, water solubility (WS), swelling power (SP), pasting properties, and thermal characteristics were recorded among the starches. The CBS had both similarities and differences in its properties by comparison with maize starch (MS) and potato starch (PS). The average molecular weight (MW) and amylopectin average chain length (ACL) of CBS ranged from 3.86 × 107 g/mol to 4.68 × 107 g/mol and from 21.29% to 22.68%, respectively. CBS and MS were divided into one subgroup and showed typical A diffraction patterns, while PS was divided into two subgroups and exhibited a typical B polymorphic pattern. The WS and SP of all the starches significantly increased with increasing temperature and had great variation at 70 °C and 90 °C. Pearson's correlation analysis showed that the molecular structure of starches greatly affected the physicochemical properties. This study revealed that the physicochemical properties of CBS could be affected by the molecular structures.