Effect of high moisture extrusion on the structure and physicochemical properties of Tartary buckwheat protein and its in vitro digestion

Tartary buckwheat is rich in nutrients and its protein supports numerous biological functions. However, the digestibility of Tartary buckwheat protein (TBP) poses a significant limitation owing to its inherent structure. This study aimed to assess the impact of high moisture extrusion (HME, 60 % moisture content) on the structural and physicochemical attributes, as well as the in vitro digestibility of TBP. Our results indicated that TBP exhibited unfolded and amorphous microstructures after HME. The protein molecular weight of TBP decreased after HME, and a greater degradation was observed at 70 °C than 100 °C. In particular, HME at 70 °C caused an almost complete disappearance of bands near 35 kDa compared with HME at 100 °C. In addition, compared with native TBP (NTBP, 44.53 µmol/g protein), TBP subjected to HME at 70 °C showed a lower disulfide bond (SS) content (42.67 µmol/g protein), whereas TBP subjected to HME at 100 °C demonstrated a higher SS content (45.70 µmol/g protein). These changes endowed TBP with good solubility (from 55.96 % to 83.31 % at pH 7), foaming ability (20.00 %-28.57 %), and surface hydrophobicity (8.34-23.07). Furthermore, the emulsifying activity (EA) and in vitro digestibility are closely related to SS content. Notably, extruded TBP (ETBP) obtained at 70 °C exhibited higher EA and digestibility than NTBP, whereas ETBP obtained at 100 °C showed the opposite trend. Consequently, HME (especially at 70 °C) demonstrated significant potential as a processing technique for improving the functional and digestive properties of TBP.

Tartary buckwheat protein-phenol conjugate prepared by alkaline-based environment: Identification of covalent binding sites of phenols and alterations in protein structural and functional characteristics

Tartary buckwheat protein-rutin/quercetin covalent complex was synthesized in alkaline oxygen-containing environment, and its binding sites, conformational changes and functional properties were evaluated by multispectral technique and proteomics. The determination of total sulfhydryl and free amino groups showed that rutin/quercetin can form a covalent complex with BPI and could significantly reduce the group content. Ultraviolet-visible spectrum analysis showed that protein could form new characteristic peaks after binding with rutin/quercetin. Circular dichroism spectrum analysis showed that rutin and quercetin caused similar changes in the secondary structure of proteins, both promoting β-sheet to α-helix, β-ture and random coil transformation. The fluorescence spectrometry results showed that the combination of phenols can cause the fluorescence quenching, and the combination of rutin was stronger than the quercetin. Proteomics showed that there were multiple covalent binding sites between phenols and protein. Rutin had a high affinity for arginine, and quercetin and cysteine had high affinity. Meanwhile, the combination of rutin/quercetin and protein had reduced the surface hydrophobic ability of the protein, and improved the foaming, stability and antioxidant properties of the protein. This study expounded the mechanism of the combination of BPI and rutin/quercetin, and analysed the differences of the combination of protein and phenols in different structures. The findings can provide a theoretical basis for the development of complexes in the area of food.

Identification of binding sites for Tartary buckwheat protein-phenols covalent complex and alterations in protein structure and antioxidant properties

To investigate the effects of structure, multiple binding sites and antioxidant property of Tartary buckwheat protein-phenols covalent complex, protein was combined with different concentrations of phenolic extract. Four kinds of phenols were identified by UPLC-Q/TOF-MS, which were rutin, quercetin, kaempferol and myricetin. UV-vis absorption spectroscopy and X-ray diffraction showed that the phenols can successfully bind to BPI. Fourier-transform infrared, circular dichroism and fluorescence emission spectroscopy showed that the binding of phenol can change the secondary/tertiary structure of protein. The particle distribution indicated that the binding of phenols could reduce the particle size (from 304.70 to 205.55 nm), but cross-linking occurred (435.35 nm) when the bound phenol content was too high. Proteomics showed that only rutin, quercetin and myricetin can covalently bind to BPI. Meanwhile, 4 peptides covalently bound to phenols were identified. The DPPH· scavenging capacity of complexes were from 8.38 to 33.76 %, and the ABTS·⁺ binding activity of complexes were from 19.35 to 63.99 %. The antioxidant activity of the complex was significantly higher than that of the pure protein. These results indicated that protein-phenol covalent complexes had great potential as functional components in the food field.

Effects of Microwave Treatment on Structure, Functional Properties and Antioxidant Activities of Germinated Tartary Buckwheat Protein

Tartary buckwheat protein (TBP) has promise as a potential source of novel natural nutrient plant protein ingredients. The modulating effects of microwave pretreatment at varying powers and times on the structure, functional properties, and antioxidant activities of germinated TBP were investigated. Compared with native germinated TBP, after microwave pretreatment, the content of free sulfhydryl groups in the germinated TBP increased, and the secondary structure changes showed a significant decrease in α-helix and an increase in random coil contents, and the intensity of the ultraviolet absorption peak increased (p < 0.05). In addition, microwave pretreatment significantly improved the solubility (24.37%), water-holding capacity (38.95%), emulsifying activity index (17.21%), emulsifying stability index (11.22%), foaming capacity (71.43%), and foaming stability (33.60%) of germinated TBP (p < 0.05), and the in vitro protein digestibility (5.56%) and antioxidant activities (DPPH (32.35%), ABTS (41.95%), and FRAP (41.46%)) of germinated TBP have also been improved. Among different treatment levels, a microwave level of 300 W/50 s gave the best results for the studied parameters. Specifically, microwave pretreatment could be a promising approach for modulating other germinated plant protein resources, as well as expanding the application of TBP.

Effects of Tartary Buckwheat Protein on Gut Microbiome and Plasma Metabolite in Rats with High-Fat Diet

The prevalence of lipid metabolism diseases, mainly obesity, fatty liver, and hyperlipidemia, is increasing in the world. Tartary buckwheat is a kind of medicinal and edible crop, and clinical experiments have also confirmed that dietary Tartary buckwheat can effectively regulate lipid metabolism disorders. Tartary buckwheat protein (TBP), as the main active ingredient of Tartary buckwheat, has an effect of blood lipid reduction that has been widely reported. In this paper, we investigated the constituents of TBP and then evaluated the hypolipidemic effect of TBP in hyperlipidemia rats. Male Sprague–Dawley rats were fed a high-fat diet for six weeks to induce hyperlipidemia and then given TBP orally for five weeks. The effects of TBP on body weight, serum lipids, liver lipids, liver oxidative stress, pathological organization, gut microbiota, and plasma metabolites were analyzed. At the serum level, TBP supplement significantly decrease the level of LDL-C and increase the level of HDL-C. At the liver level, it can reduce the levels of TC, TG, and LDL-C. The potential mechanism of action is, on the one hand, to increase the abundance of the Lachnospiraceae and the Ruminococcaceae by modulating the gut microbiota, facilitating the productivity of short-chain fatty acids, and increasing fecal bile acid excretion and, on the other hand, may be related to the improvement of bile acid metabolism.

Cholesterol-Lowering Activity of Tartary Buckwheat Protein

Previous research has shown that Tartary buckwheat flour is capable of reducing plasma cholesterol. The present study was to examine the effect of rutin and Tartary buckwheat protein on plasma total cholesterol (TC) in hypercholesterolemia hamsters. In the first animal experiment, 40 male hamsters were divided into four groups fed either the control diet or one of the three experimental diets containing 8.2 mmol rutin, 8.2 mmol quercetin, or 2.5 g kg^-1 cholestyramine, respectively. Results showed that only cholestyramine but not rutin and its aglycone quercetin decreased plasma TC, which suggested that rutin was not the active ingredient responsible for plasma TC-lowering activity of Tartary buckwheat flour. In the second animal experiment, 45 male hamsters were divided into five groups fed either the control diet or one of the four experimental diets containing 24% Tartary buckwheat protein, 24% rice protein, 24% wheat protein, or 5 g kg^-1 cholestyramine, respectively. Tartary buckwheat protein reduced plasma TC more effectively than cholestyramine (45% versus 37%), while rice and wheat proteins only reduced plasma TC by 10-13%. Tartary buckwheat protein caused 108% increase in the fecal excretion of total neutral sterols and 263% increase in the fecal excretion of total acidic sterols. real-time polymerase chain reaction and Western blotting analyses showed that Tartary buckwheat protein affected the gene expression of intestinal Niemann-Pick C1-like protein 1 (NPC1L1), acyl CoA:cholesterol acyltransferase 2 (ACAT2), and ATP binding cassette transporters 5 and 8 (ABCG5/8) in a down trend, whereas it increased the gene expression of hepatic cholesterol-7α -hydroxylase (CYP7A1). It was concluded that Tartary buckwheat protein was at least one of the active ingredients in Tartary buckwheat flour to lower plasma TC, mainly mediated by enhancing the excretion of bile acids via up-regulation of hepatic CYP7A1 and also by inhibiting the absorption of dietary cholesterol via down-regulation on intestinal NPC1L1, ACAT2 and ABCG5/8.