Inhibitory mechanism of epicatechin gallate on α-amylase and α-glucosidase and its combinational effect with acarbose or epigallocatechin gallate

Phytochemicals from fractioned dark tea water extract enhance the digestive enzyme inhibition, antioxidant capacities and glucose-lipid balance

Dark tea has long been recognized for its health-promoting benefits, attributed to its complex phytochemical composition. However, the specific bioactive compounds responsible for these beneficial effects remain inadequately characterized. This study aimed to explore the impact of dark tea water extract (DTE) on digestive enzyme activity, antioxidant capacity, and glucose-lipid balance. DTE was fractioned into four fractions using gel separation, followed by analysis with high-performance liquid chromatography and quasi-targeted metabolomics. The 30 % ethanol elution (EEA) and 50 % ethanol elution (EEB) fractions showed stronger antioxidant and enzyme inhibition effects compared to the whole DTE. The EEA fraction was rich in 5 catechins and 26 additional phytochemicals, while the EEB fraction contained high levels of caffeine, ECG, and 29 other phytochemicals. Notably, significant correlations were observed between quercetin-3,4'-O-di-β-glucopyranoside and 3-(2-Naphthyl)-L-alanine with digestive enzyme inhibition. Cellular studies revealed the ability of EEA and EEB to reduce lipid accumulation, improve glycolipid metabolism, and alleviate oxidative stress by increasing SOD, CAT, and GSH levels while decreasing MDA and ROS in HepG2 cells. Furthermore, 34 flavonoids, 2 alkaloids, 2 terpenes, 2 alcohols and polyols, 2 phenylpropanoids and polyketides, 1 organoheterocyclic compound were directly linked to the antioxidant activity and the modulation of glucose and lipid levels. These findings offer valuable insights into the phytochemical profiles of dark tea and its potential health benefits.

Inhibition of coreopsin against α-amylase/α-glucosidase and synergy with acarbose

Coreopsin is a flavonoid from Coreopsis tinctoria. The inhibition of coreopsin and synergy with acarbose against α-amylase (PPA) or α-glucosidase (SCG) were explored. As a result, coreopsin exhibited stronger inhibition on PPA/SCG than that of acarbose. Combination of coreopsin (4.11 μM) with acarbose (132.77 μM) had significant synergistic effect on PPA, while combination of coreopsin (5.76 μM) and acarbose (121.7 μM) had significant synergy on SCG. Coreopsin, acarbose and acarbose-coreopsin inhibited PPA in mixed-type mode. Acarbose competitively inhibited SCG, whereas coreopsin and acarbose-coreopsin inhibited SCG in mixed-type mode. Fluorescence analysis conformed that coreopsin could synergize with acarbose by increasing the binding ability of acarbose to PPA/SCG. Compared with acarbose or coreopsin, acarbose-coreopsin complexes resulted in more conformational changes of PPA/SCG, revealing that the complexes had stronger inhibitory ability than acarbose or coreopsin alone. The detail binding information of coreopsin, acarbose or acarbose-coreopsin to PPA /SCG was revealed by computer simulation.

Inhibitory Effect and Mechanism of Dancong Tea from Different Harvesting Season on the α-Glucosidase Inhibition In Vivo and In Vitro

Tea polyphenols have been reported to decrease the rate of starch hydrolysis by inhibiting α-glucosidase. However, the effect of the tea harvesting season and the structure of catechin monomers on the inhibitory activity of α-glucosidase is not understood. In this study, the inhibitory effect and underlying mechanism of four seasons of Dancong tea against α-glucosidase were investigated by in vivo and in vitro experiments, multi-spectroscope and molecular dynamic. The Dancong tea harvested in spring and winter showed a stronger inhibitory effect on α-glucosidase due to a higher content of catechin, especially EGCG ((-)-epigallocatechin-3-gallate). The results of in vivo and in vitro experiments showed that EGCG and ECG ((-)-epicatechin-3-gallate) with a higher content of gallate and hydroxyl groups exhibited a stronger inhibitory effect on starch hydrolysis, rise of postprandial blood glucose and activities of α-glucosidase compared to EGC ((-)-epigallocatechin) and EC ((-)-epicatechin). These gallate and hydroxy groups were more effective in interacting with the amino acid residues in the active site of α-glucosidase, leading to structural changes in the enzyme. Certainly, the inhibitory effect of Dancong tea on α-glucosidase explains one of the mechanisms by which it helps alleviate diabetes; the other hypoglycaemic mechanisms of Dancong tea will be further explored.

Preparation and Characterization of Calcium-Chelated Sea Cucumber Ovum Hydrolysate and the Inhibitory Effect on α-Amylase

α-amylase can effectively inhibit the activity of digestive enzymes and alter nutrient absorption. The impact of ovum hydrolysates of sea cucumbers on α-amylase activity was investigated in this study. The protein hydrolysates generated using different proteases (pepsin, trypsin, and neutral protease) and molecular weights (less than 3000 and more than 3000) were investigated. The results showed that all three different hydrolysates demonstrated calcium-chelating activity and induced a fluorescence-quenching effect on α-amylase. The sea cucumber ovum hydrolysate with a molecular weight of less than 3000 Da, isolated using trypsin, showed the most effective inhibitory effect on α-amylase, with an inhibition rate of 53.9%, and the inhibition type was identified as mixed forms of inhibition. In conclusion, the generation and utilization of protein hydrolysates from sea cucumber ovum as a functional food ingredient could be a potential approach to add value to low-cost seafood by-products.

Pectin enhances the inhibition of α-amylase via the mixture of rutin and quercetin

The human dietary system, which contains a variety of compounds such as polyphenols and polysaccharides, is very complex. Whether polysaccharides affect the inhibitory of polyphenol mixtures on α-amylase needs to be further investigated. The aim of this study was to analyze the effect and mechanism of pectin on the inhibition of α-amylase by a mixture of rutin and quercetin (R-Q). Results revealed that the inhibition and quenching affinity of R-Q for α-amylase was enhanced by pectin. The Stern-Volmer quenching constant of R-Q-α-amylase was increased by pectin from (6.08 ± 0.453) × 103 mL/mg to (9.80 ± 0.285) × 103 mL/mg. Pectin enhanced the ability of R-Q to inhibit α-amylase for two main reasons. On the one hand, it was owing to the binding of pectin to rutin, which increased the opportunity for quercetin to bind to the active center of α-amylase, thus enhancing the inhibitory effect of R-Q on α-amylase. On the other hand, pectin and quercetin simultaneously bound to different sites of α-amylase by noncovalent interactions to form the ternary complex of pectin-α-amylase-quercetin. The conformation of α-amylase and the hydrophobicity of amino acid residues were altered by the ternary complex, thereby enhancing the hydrogen bonding in the reaction system.

Inhibition mechanisms of α-glucosidase by eight catechins: Kinetic, molecular docking, and surface plasmon resonance analysis

α-Glucosidase is considered to be one of the effective targets for the treatment of type 2 diabetes. This study examined the inhibitory mechanisms of eight catechins on α-glucosidase, including both the free forms (C, EC, GC, EGC) and esterified forms (CG, ECG, GCG, EGCG). Enzyme kinetics and molecular docking studies demonstrated that catechins primarily inhibit α-glucosidase by binding through hydrogen bonds and hydrophobic interactions, with esterified catechins exhibiting stronger inhibitory effects. The structural changes of the proteins following binding were further explored using fluorescence spectroscopy and atomic force microscopy (AFM). Fluorescence spectroscopy revealed that catechins altered the microenvironment around the fluorescent amino acids within the enzyme (such as tyrosine and tryptophan), resulting in slight unfolding of the protein structure. AFM further confirmed that catechin binding to α-glucosidase induced protein aggregation, with esterified catechins exhibiting a more pronounced effect. All of the above findings were based on static model studies. Moreover, the binding kinetics of catechins with α-glucosidase were innovatively investigated using surface plasmon resonance (SPR), revealing that esterified catechins bound more rapidly and displayed higher affinity. The presence of the gallate group in esterified catechins was identified as crucial for their binding to α-glucosidase, resulting in a more significant inhibitory effect. These findings suggested that dietary intake of catechins, especially esterified form, may more effectively inhibit the activity of α-glucosidase.

Study on the effects of endogenous polyphenols on the structure, physicochemical properties and in vitro digestive characteristics of Euryales Semen starch based on multi-spectroscopies, enzyme kinetics, molecular docking and molecular dynamics simulation

Euryales Semen (ES) is a highly nutritious food with low digestibility, which is closely associated with its endogenous phenolic compounds. In this study, five phenolic compounds (naringenin, isoquercitrin, gallic acid, epicatechin and quercetin) with high concentrations in ES were selected to prepare starch-polyphenol complexes. Subsequently, the effects of endogenous polyphenols on the structure, physicochemical properties and digestion characteristics of ES starch were studied using multiple techniques. The addition of phenolic compounds markedly reduced the in vitro digestibility, swelling power, gelatinization enthalpy, while increased the solubility of ES starch. Fourier-transform infrared spectroscopy and X-ray diffraction analysis showed that phenolic compounds interacted with the starch through non-covalent bonds. Five phenolic compounds inhibited α-amylase activity through a mixed competitive inhibition mechanism, with the inhibition potency ranked as follows: quercetin > epicatechin > gallic acid > isoquercitrin > naringenin. The spectroscopic analysis and molecular dynamics simulations confirmed that five phenolic compounds interacted with the amino acid residues of α-amylase through hydrogen bonding and hydrophobic interactions, caused α-amylase static fluorescence quenching, and altered its conformation and microenvironment. This study provides a better understanding of the interaction mechanisms between ES starch and polyphenols, and supports the development of ES as a food that lowers sugar levels.

Epicatechin Isolated from Litchi chinensis Sonn. (Litchi) Fruit Peel Ethyl Acetate Extract Modulated Glucose Uptake in Chang Cells and Suppressed ROS Production in RAW 264.7 Macrophages

Bioactive flavonoid epicatechin has been reported in the peel of litchi fruit but isolated from its hydroalcoholic extracts. This study isolated epicatechin with cellular glucose uptake modulatory and ROS production inhibitory properties from the ethyl acetate (EtOAc) extract using a bioassay-guided approach. The fruit peel was defatted with hexane and sequentially extracted using dichloromethane (DCM), EtOAc, methanol (MeOH) and water. In vitro phytochemical models, namely antioxidant (Fe3+ reducing, radical scavenging and anti-linoleic acid peroxidative) and glycaemic control (α-glucosidase and α-amylase inhibitory and glucose uptake modulatory), were employed for the bioassay-guided isolation, while the isolated compound was characterised using NMR and mass spectrometry and assessed for dose-dependent inhibition of α-glucosidase and lipopolysaccharide (LPS)-induced cellular ROS production, as well as modulation of cellular glucose uptake. Relative to the other extracts, the EtOAc extract had appreciable phenol and flavonoid contents, which perhaps influenced its potent anti-lipid peroxidative (65.0%) and α-glucosidase inhibitory (52.4%) effects. The α-glucosidase inhibitory potency of the fractions (1-8) from the EtOAc extracts correlated with their flavonoid contents, with fraction 5 outperforming other fractions. The fraction comprised a pool of fractions obtained from the DCM:MeOH:water (7:3:0.281 v/v/v) solvent system. LC-MS revealed the predominant presence of epicatechin in fraction 5, which was later isolated from one of the sub-fractions (sub-fraction 4) of fraction 5. This sub-fraction had stronger anti-lipid peroxidative (65.5%), α-glucosidase inhibitory (65.8%) and glucose uptake modulatory (38.2%) effects than the other sub-fractions from fraction 5, which could have been influenced by the isolated epicatechin. Moreover, the isolated epicatechin inhibited α-glucosidase (IC50 = 35.3 µM), modulated cellular glucose uptake (EC50 = 78.5 µM) and inhibited LPS-induced ROS production in RAW 264.7 macrophages in a dose-dependent fashion [IC50 = 18.9 µM; statistically comparable (p > 0.05) to ascorbic acid, IC50 = 9.57 µM]. Epicatechin from litchi peel EtOAc extract could potentiate glucose uptake modulatory, α-glucosidase inhibitory and ROS suppressive capacities, which could be influential in the use of litchi fruit peel for managing diabetes and associated oxidative damage.

UHPLC-PDA-Q-TOF-MS-α-amylase-FLD activity detection system and molecular docking

INTRODUCTION

Traditional and some scientific literature document the antidiabetic effects of the Ziziphi Spinosae Semen (ZSS). However, the bioactive compounds of ZSS responsible for the antidiabetic effects are not well known.

OBJECTIVES

This study aimed to investigate the material basis of the antidiabetic effects of ZSS by inhibiting α-amylase.

METHODOLOGY

An online analysis platform was established and optimized using an ultra-performance liquid chromatography-photo-diode array-quadrupole-time-of-flight-mass spectrometry-α-amylase-fluorescence detector (UHPLC-PDA-Q-TOF-MS-α-amylase-FLD) system to screen α-amylase inhibitors in ZSS rapidly. The inhibitory effect of these compounds was confirmed by molecular docking screening. and the molecular interactions between α-amylase and active compounds were evaluated, which strongly supported the experimental results.

RESULTS

Seventy-eight compounds were identified in the ZSS extract, eleven of which were screened to have significant α-amylase binding activity.

CONCLUSION

This study demonstrated the feasibility of using an established platform to screen for effective components in ZSS, providing a practical method for the rapid screening of potential antidiabetic active ingredients in traditional Chinese medicine.

Identification and characterization of a calcium-binding peptide from salmon bone for the targeted inhibition of α-amylase in digestion

α-Amylase, essential for carbohydrate digestion, relies on calcium (Ca) for its structural integrity and enzymatic activity. This study explored the inhibitory effect of salmon bone peptides on α-amylase activity through their interaction with the enzyme's Ca-binding sites. Among the various salmon bone hydrolysates, salmon bone trypsin hydrolysate (SBTH) exhibited the highest α-amylase inhibition. The peptide IEELEEELEAER (PIE), with a sequence of Ile-Glu-Glu-Leu-Glu-Glu-Glu-Glu-Leu-Glu-Ala-Glu-Arg from SBTH, was found to specifically target the Ca-binding sites in α-amylase, interacting with key residues such as Asp206, Trp203, His201, etc. Additionally, cellular experiments using 3 T3-L1 preadipocytes indicated PIE's capability to suppress adipocyte differentiation, and decreases in intracellular triglycerides, total cholesterol, and lipid accumulation. In vivo studies also showed a significant reduction in weight gain in the group treated with PIE(6.61%)compared with the control group (33.65%). These findings suggest PIE is an effective α-amylase inhibitor, showing promise for obesity treatment.

Spectroscopic and in silico evaluation of hesperetin, aglycone flavanone, as a prospective regulatory ligand for human salivary α-amylase

The insight into the binding mechanism of hesperetin, an aglycone flavanone, with human salivary α-amylase (HSAA), simulated under physiological salivary condition, was explored using various spectroscopic approaches and in silico method. Hesperetin effectively quenched the intrinsic fluorescence of HSAA and the quenching was mixed quenching mechanism. The interaction perturbed the HSAA intrinsic fluorophore microenvironment and the enzyme global surface hydrophobicity. The negative values of ΔG for thermodynamic parameters and in silico study revealed the spontaneity of HSAA-hesperetin complex while the positive values of enthalpy change (ΔH) and entropy change (ΔS) showed noticeable involvement of hydrophobic bonding in the stabilization of the complex. Hesperetin was a mixed inhibitor for HSAA with a KI of 44.60 ± 1.63 μM and having apparent inhibition coefficient (α) of 0.26. Macromolecular crowding, given rise to microviscosity and anomalous diffusion, regulated the interaction. Sodium ion (Na+) created high ionic strength, also, modulated the interaction. The in silico study proposed the preferential binding of hesperetin at the active cleft domain of HSAA with the least energy of -8.0 kcal/mol. This work gives a novel insight on the potentials of hesperetin as a future prospective medicinal candidate in the management of postprandial hyperglycemic condition.Communicated by Ramaswamy H. Sarma.

Inhibition effect of epicatechin gallate on acid phosphatases from rainbow trout (Oncorhynchus mykiss) liver by multispectral and molecular docking

Inhibition of acid phosphatase, which significantly contributes to inosine 5'-monophosphate (IMP) degradation, is crucial for preventing flavor deterioration of aquatic products during storage. In this study, the inhibitory effect of epicatechin gallate (ECG) on the activity of acid phosphatase isozymes (ACPI and ACPII) was analyzed using inhibition kinetics, fluorescence spectroscopy, isothermal titration calorimetry, and molecular simulation. ACPI and ACPII with molecular weights of 59.5 and 37.3 kDa, respectively, were purified from rainbow trout liver. ECG reversibly inhibited ACPI and ACPII activities via mixed-type inhibition, with half maximal inhibitory concentration (IC50) of 0.24 ± 0.01 mmol/L and 0.27 ± 0.03 mmol/L, respectively. Fluorescence spectra indicated that ECG statically quenched the intrinsic fluorescence of ACPI and ACPII. ECG could spontaneously bind to ACPI and ACPII through hydrogen bonding and van der Waals forces and exhibited a higher affinity for ACPI than for ACPII. In addition, molecular dynamic simulation revealed that ECG-ACPI and ECG-ACPII complexes were relatively stable during the entire simulation process. Our findings provide a theoretical basis for the use of ECG as an inhibitor of ACP to improve the flavor of aquatic products.

Flavonoids as dual-target inhibitors against α-glucosidase and α-amylase: a systematic review of in vitro studies

Diabetes mellitus remains a major global health issue, and great attention is directed at natural therapeutics. This systematic review aimed to assess the potential of flavonoids as antidiabetic agents by investigating their inhibitory effects on α-glucosidase and α-amylase, two key enzymes involved in starch digestion. Six scientific databases (PubMed, Virtual Health Library, EMBASE, SCOPUS, Web of Science, and WHO Global Index Medicus) were searched until August 21, 2022, for in vitro studies reporting IC50 values of purified flavonoids on α-amylase and α-glucosidase, along with corresponding data for acarbose as a positive control. A total of 339 eligible articles were analyzed, resulting in the retrieval of 1643 flavonoid structures. These structures were rigorously standardized and curated, yielding 974 unique compounds, among which 177 flavonoids exhibited inhibition of both α-glucosidase and α-amylase are presented. Quality assessment utilizing a modified CONSORT checklist and structure-activity relationship (SAR) analysis were performed, revealing crucial features for the simultaneous inhibition of flavonoids against both enzymes. Moreover, the review also addressed several limitations in the current research landscape and proposed potential solutions. The curated datasets are available online at https://github.com/MedChemUMP/FDIGA .

Preparation of Ribes nigrum L. polysaccharides-stabilized selenium nanoparticles for enhancement of the anti-glycation and α-glucosidase inhibitory activities

Seven kinds of selenium nanoparticles (RP-SeNPs) were prepared by using the polysaccharides extracted from Ribes nigrum L. (RP) as the stabilizer and dispersant. Among them, RP-SeNPs-1 (94.2 nm), RP-SeNPs-2 (101.2 nm) and RP-SeNPs-3 (107.6 nm) with relatively smaller mean particle size exhibited stronger α-glucosidase inhibitory activity than other RP-SeNPs (115.3-164.2 nm) and SeNPs (288.9 nm). Ultraviolet-visible spectrophotometry, Fourier transform-infrared, X-ray diffraction, energy dispersive X-ray and X-ray photoelectron spectroscopy analyses confirmed that SeNPs were ligated with RP to form nanocomposites and displayed amorphous form. Electron microscopy images revealed that RP-SeNPs-1 - RP-SeNPs-3 were regular shape spherical nanocomposites with much better dispersion than SeNPs. Compared with SeNPs, RP-SeNPs displayed relatively high thermal, storage, pH and salt ion stability. Moreover, RP-SeNPs-1-RP-SeNPs-3 showed significantly better anti-glycation and α-glucosidase inhibitory activity than SeNPs, especially RP-SeNPs-1 with the smallest particle size. Inhibitory kinetics analysis indicated that SeNPs and RP-SeNPs inhibited α-glucosidase with competitive type and reversible mechanism. In addition, the conformation of the α-glucosidase was changed after binding with the SeNPs and RP-SeNPs-1. Fluorescence quenching and isothermal titration calorimetry assays revealed that these two nanoparticles could interact with α-glucosidase to form non-fluorescent complexes through hydrogen bonding, and the formation was spontaneously driven by enthalpy.

Fermentation of Murta (Ugni molinae) Juice: Effect on Antioxidant Activity and Control of Enzymes Associated with Glucose Assimilation

Berries are rich in bioactive compounds, including antioxidants and especially polyphenols, known inhibitors of starch metabolism enzymes. Lactic acid fermentation of fruits has received considerable attention due to its ability to enhance bioactivity. This study investigated the effect of fermentation with L. mesenteroides of juice from the Chilean berry murta on antioxidant activity, release of polyphenols, and inhibitory activity against α-amylase and α-glucosidase enzymes. Three types of juices (natural fruit, freeze-dried, and commercial) were fermented. Total polyphenol content (Folin-Ciocalteu), antioxidant activity (DPPH and ORAC), and the ability to inhibit α-amylase and α-glucosidase enzymes were determined. Fermented murta juices exhibited increased antioxidant activity, as evidenced by higher levels of polyphenols released during fermentation. Inhibition of α-glucosidase was observed in the three fermented juices, although no inhibition of α-amylase was observed; the juice from freeze-dried murta stood out. These findings highlight the potential health benefits of fermented murta juice, particularly its antioxidant properties and the ability to modulate sugar assimilation by inhibiting α-glucosidase.

Mechanism of Anti-Diabetic Activity from Sweet Potato (Ipomoea batatas): A Systematic Review

This study aims to provide an overview of the compounds found in sweet potato (Ipomoea batatas) that contribute to its anti-diabetic activity and the mechanisms by which they act. A comprehensive literature search was conducted using electronic databases, such as PubMed, Scopus, and Science Direct, with specific search terms and Boolean operators. A total of 269 articles were initially retrieved, but after applying inclusion and exclusion criteria only 28 articles were selected for further review. Among the findings, four varieties of sweet potato were identified as having potential anti-diabetic properties. Phenolic acids, flavonols, flavanones, and anthocyanidins are responsible for the anti-diabetic activity of sweet potatoes. The anti-diabetic mechanism of sweet potatoes was determined using a combination of components with multi-target actions. The results of these studies provide evidence that Ipomoea batatas is effective in the treatment of type 2 diabetes.

Microwave-Induced Behavior and Digestive Properties of the Lotus Seed Starch-Chlorogenic Acid Complex

The effect of chlorogenic acid (CA) on the dielectric response of lotus seed starch (LS) after microwave treatment, the behavior and digestive characteristics of the resulting starch/chlorogenic acid complex (LS-CA) at different degrees of gelatinization and the inhibition of α-amylase by chlorogenic acid were investigated. The variation in dielectric loss factor, ε″, and dielectric loss tangent, tanδε, of the microwave thermal conversion indicated that LS-CA had a more efficient microwave-energy-to-thermal-energy conversion efficiency than LS. This gelatinized LS-CA to a greater extent at any given temperature between 65 and 85 °C than LS, and it accelerated the degradation of the starch crystalline structure. The greater disruption of the crystal structure decreased the bound water content and increased the thermal stability of LS-CA compared to LS. The simulated in vitro digestion found that the presence of the LS-CA complex improved the slow-digestion property of lotus seed starch by increasing its content of resistant and slowly digested starch. In addition, the release of chlorogenic acid during α-amylase hydrolysis further slowed starch digestion by inhibiting α-amylase activity. These findings provide a foundation for understanding the correlation between the complex behavior and digestive properties of naturally polyphenol-rich, starch-based foods, such as LS, under microwave treatment, which will facilitate the development of starch-based foods with tailored digestion rates, lower final degrees of hydrolysis and glycemic indices.

Metabolites of Geum aleppicum and Sibbaldianthe bifurca: Diversity and α-Glucosidase Inhibitory Potential

α-Glucosidase inhibitors are essential in the treatment of diabetes mellitus. Plant-derived drugs are promising sources of new compounds with glucosidase-inhibiting ability. The Geum aleppicum Jacq. and Sibbaldianthe bifurca (L.) Kurtto & T.Erikss. herbs are used in many traditional medical systems to treat diabetes. In this study, metabolites of the G. aleppicum and S. bifurca herbs in active growth, flowering, and fruiting stages were investigated using high-performance liquid chromatography with photodiode array and electrospray ionization triple quadrupole mass spectrometric detection (HPLC-PDA-ESI-tQ-MS/MS). In total, 29 compounds in G. aleppicum and 41 components in S. bifurca were identified including carbohydrates, organic acids, benzoic and ellagic acid derivatives, ellagitannins, flavonoids, and triterpenoids. Gemin A, miquelianin, niga-ichigoside F1, and 3,4-dihydroxybenzoic acid 4-O-glucoside were the dominant compounds in the G. aleppicum herb, while guaiaverin, miquelianin, tellimagrandin II₂, casuarictin, and glucose were prevailing compounds in the S. bifurca herb. On the basis of HPLC activity-based profiling of the G. aleppicum herb extract, the most pronounced inhibition of α-glucosidase was observed for gemin A and quercetin-3-O-glucuronide. The latter compound and quercetin-3-O-arabinoside demonstrated maximal inhibition of α-glucosidase in the S. bifurca herb extract. The obtained results confirm the prospects of using these plant compounds as possible sources of hypoglycemic nutraceuticals.

Hesperetin-Cu(II) complex as potential α-amylase and α-glucosidase inhibitor: Inhibition mechanism and molecular docking

Inhibition of α-amylase and α-glucosidase activity is an effective way for controlling postprandial blood glucose-related diabetes. The study found that hesperetin-Cu(II) complex (Hsp-Cu(II)) exhibited a stronger inhibitory ability on α-amylase and α-glucosidase compared to hesperetin (Hsp), with smaller IC₅₀ values of Hsp-Cu(II) (60.3 ± 0.9 µM for α-amylase; 1.25 ± 0.03 µM for α-glucosidase) than Hsp (115.6 ± 1.1 µM for α-amylase; 55.2 ± 0.1 µM for α-glucosidase). Interestingly, Hsp-Cu(II) and acarbose exerted a synergistic effect on inhibition of α-glucosidase. The binding affinities of Hsp-Cu(II) to α-amylase and α-glucosidase were strong with the Ka values (binding constant) in the magnitude order of 10⁵, which was 9 times larger than Hsp. After interacting, Hsp-Cu(II) reduced α-helix contents of α-amylase and α-glucosidase, resulting in a looser conformation of these two enzymes. Molecular simulations manifested that Hsp-Cu(II) bound to the active center of enzymes driven by hydrogen bonds and interacted with the key catalytic amino acids (α-amylase: Gln63, Asp300 and His305; α-glucosidase: Tyr158, Asp215, Glu277 and Glu411), altering the conformation of enzymes, blocking the entrance of substrates, ultimately reducing the activities of α-glucosidase and α-amylase. This study has demonstrated that Hsp-Cu(II) may be a promising candidate of functional nutritional additive and medicine for the prevention of diabetes.

Isolation and identification of dipeptidyl peptidase-IV inhibitory peptides from Sacha inchi meal

BACKGROUND

Sacha inchi meal (SIM) is a by-product of oil processing. Our previous studies showed that SIM hydrolysates exhibited dipeptidyl peptidase-IV (DPP-IV) inhibition activity. The objective of the present work was to identify and characterize the bioactive peptides from protein hydrolysates of SIM; enzyme kinetics and peptide-enzyme interaction were also investigated.

RESULTS

From SIM hydrolysates, ten peptides responsible for the activity were identified: GPSRGF (GF-6), FPILSPDPA (FA-9), APYRRGGKI (AI-9), WPYH (WH-4), DPATWLALPT (DT-10), NPEDEFRQQ (NQ-9), APESKPVGV (AV-9), LEWRDR (LR-6), APVYWVQ (AQ-7) and LLMWPY (LY-6). The IC₅₀ values of five peptides (GF-6, WH-4, AQ-7, AV-9 and LY-6) with better inhibitory activity on DPP-IV were within the range of 23.43-128.40 μmol L^-1 . AQ-7 had the best activity, with an IC₅₀ value of 23.43 μmol L^-1 . Enzyme kinetics indicated the presence of various inhibition types (mixed, non-competitive and competitive). Isothermal titration microcalorimetry showed that the main forces of the binding sites between peptide (GF-6 or AQ-7) and DPP-IV were hydrogen bond, hydrophobic interaction and van der Waals force. The key residues involved in peptide-enzyme interaction were determined by molecular docking. Furthermore, at a concentration of 800 μmol L^-1 , GF-6 was found to significantly increase the glucose consumption in insulin-resistant HepG2 cells (P < 0.05) compared with the model group.

CONCLUSION

Sacha inchi meal-derived peptides displayed potent DPP-IV inhibition activity and could be used in the health food industry and as lead compounds for diabetes therapy. © 2023 Society of Chemical Industry.

Possible Side Effects of Polyphenols and Their Interactions with Medicines

Polyphenols are an important component of plant-derived food with a wide spectrum of beneficial effects on human health. For many years, they have aroused great interest, especially due to their antioxidant properties, which are used in the prevention and treatment of many diseases. Unfortunately, as with any chemical substance, depending on the conditions, dose, and interactions with the environment, it is possible for polyphenols to also exert harmful effects. This review presents a comprehensive current state of the knowledge on the negative impact of polyphenols on human health, describing the possible side effects of polyphenol intake, especially in the form of supplements. The review begins with a brief overview of the physiological role of polyphenols and their potential use in disease prevention, followed by the harmful effects of polyphenols which are exerted in particular situations. The individual chapters discuss the consequences of polyphenols’ ability to block iron uptake, which in some subpopulations can be harmful, as well as the possible inhibition of digestive enzymes, inhibition of intestinal microbiota, interactions of polyphenolic compounds with drugs, and impact on hormonal balance. Finally, the prooxidative activity of polyphenols as well as their mutagenic, carcinogenic, and genotoxic effects are presented. According to the authors, there is a need to raise public awareness about the possible side effects of polyphenols supplementation, especially in the case of vulnerable subpopulations.

Structural changes and molecular mechanism study on the inhibitory activity of epigallocatechin against α-glucosidase and α-amylase

In this study, the inhibition and mechanism of epigallocatechin (EGC) on two key glycoside hydrolases (α-glucosidase, α-amylase) were explored from the molecular structure level. The chemical structure of EGC was characterized by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and proton nuclear magnetic resonance spectroscopy. EGC's inhibition on these enzymes was colorimetrically determined. The effects of EGC on the chemical structure and spatial configuration of the enzymes were explored via FTIR spectroscopy, fluorescence spectroscopy, and molecular docking techniques. The results showed that EGC exhibited the inhibition of α-glucosidase and α-amylase in a non-competitive manner, showing a continuous upward trend as EGC's concentration increased. There was a fluorescence quenching effect of EGC on α-glucosidase and α-amylase. Molecular docking confirmed that EGC can bind to amino acid residues in the enzyme through intermolecular hydrogen bonds and hydrophobic interactions, resulting in the changed chemical structure and spatial conformation of the enzymes. This decreased enzyme activity. This result suggested that EGC has the potential to inhibit two key glycoside hydrolases, and it would be beneficial to incorporate EGC into functional foods for diabetics.

The Inhibition of α-Glucosidase, α-Amylase and Protein Glycation by Phenolic Extracts of Cotoneaster bullatus, Cotoneaster zabelii, and Cotoneaster integerrimus Leaves and Fruits: Focus on Anti-Hyperglycemic Activity and Kinetic Parameters

Cotoneaster species have gained significant importance in traditional Asian medicine for their ability to prevent and treat hyperglycemia and diabetes. Therefore, in this study, some aspects of the beneficial health effects of hydromethanolic extracts of C. bullatus, C. zabelii, and C. integerrimus leaves and fruits were evaluated, including their influence on α-glucosidase, α-amylase, and nonenzymatic protein glycation. The activity was investigated in relation to the polyphenolic profile of the extracts determined by UV-spectrophotometric and HPLC-PDA-fingerprint methods. It was revealed that all leaf and fruit extracts are a promising source of biological components (caffeic acid pseudodepsides, proanthocyanidins, and flavonols), and the leaf extracts of C. bullatus and C. zabelii contain the highest levels of polyphenols (316.3 and 337.6 mg/g in total, respectively). The leaf extracts were also the most effective inhibitors of digestive enzymes and nonenzymatic protein glycation. IC50 values of 8.6, 41.8, and 32.6 µg/mL were obtained for the most active leaf extract of C. bullatus (MBL) in the α-glucosidase, α-amylase, and glycation inhibition tests, respectively. In the kinetic study, MBL was displayed as a mixed-type inhibitor of both enzymes. The correlations between the polyphenol profiles and activity parameters (|r| > 0.72, p < 0.05) indicate a significant contribution of proanthocyanidins to the tested activity. These results support the traditional use of Cotoneaster leaves and fruits in diabetes and suggest their hydrophilic extracts be promising in functional applications.

Inhibition Mechanism of α-Amylase/α-Glucosidase by Silibinin, Its Synergism with Acarbose, and the Effect of Milk Proteins

As a natural flavonolignan, silibinin is reported to possess multiple biological activities, while the inhibitory potential of silibinin on carbohydrate-hydrolyzing enzymes is still unclear. Therefore, in this study, the inhibitory effect and underlying mechanism of silibinin against α-amylase/α-glucosidase were investigated. The results indicated that silibinin showed a strong inhibitory efficiency against α-amylase/α-glucosidase in noncompetitive manners and exhibited synergistic inhibition against α-glucosidase with acarbose. However, interestingly, the inhibitory effect of silibinin was significantly hindered in various milk protein-rich environments, but this phenomenon disappeared after simulated gastrointestinal digestion of milk proteins in vitro. Furthermore, silibinin could combine with the inactive site of α-amylase/α-glucosidase and change the microenvironment and secondary structure of the enzymes, thereby influencing the catalytic efficiency of enzymes. This research suggested that silibinin could be used as a novel carbohydrate-hydrolyzing enzyme inhibitor, and milk beverages rich in silibinin had the potential for further application in antidiabetic dietary or medicine.

Epicatechin Gallate as Xanthine Oxidase Inhibitor: Inhibitory Kinetics, Binding Characteristics, Synergistic Inhibition, and Action Mechanism

Epicatechin gallate (ECG) is one of the main components of catechins and has multiple bioactivities. In this work, the inhibitory ability and molecular mechanism of ECG on XO were investigated systematically. ECG was determined as a mixed xanthine oxidase (XO) inhibitor with an IC50 value of 19.33 ± 0.45 μM. The promotion of reduced XO and the inhibition of the formation of uric acid by ECG led to a decrease in O2- radical. The stable ECG-XO complex was formed by hydrogen bonds and van der Waals forces, with the binding constant of the magnitude of 104 L mol-1, and ECG influenced the stability of the polypeptide skeleton and resulted in a more compact conformation of XO. Computational simulations further characterized the binding characteristics and revealed that the inhibitory mechanism of ECG on XO was likely that ECG bound to the vicinity of flavin adenine dinucleotide (FAD) and altered the conformation of XO, hindering the entry of substrate and the diffusion of catalytic products. ECG and allopurinol bound to different active sites of XO and exerted a synergistic inhibitory effect through enhancing their binding stability with XO and changing the target amino acid residues of XO. These findings may provide a theoretical basis for the further application of ECG in the fields of food nutrition and functional foods.

Effect of gamma irradiation on growth, proline content, bioactive compound changes, and biological activity of 5 popular Thai rice cultivars

Gamma irradiation is the technique used to induce plant mutation and it has affected both the physiological and biochemical compounds of the plant. Some new rice lines are also created through the gamma-irradiation technique. We investigated the effect of gamma irradiation on plant growth, volatile compounds, and the biological activity of gamma-irradiated rice extract compared to non-gamma-irradiated rice extract. The results reveal that the gamma-irradiated rice growth was related to the proline content, as the low gamma dose induced rice growth and proline accumulation in gamma-irradiated rice. We induced the bioactive compounds, including the flavonoid content and phenolic content of gamma-irradiated rice, through the low gamma irradiation dose at 60-100 Gy. Interestingly, bioactive compounds were stimulated by a gamma dose similar to that of the biological activity (antioxidant activity and enzyme inhibition) of gamma-irradiated rice. The results suggest that gamma-irradiated rice extract's biological activity was closely related to the flavonoid and phenolic content of rice. We also identified the variety of volatile compounds in gamma-irradiated rice and they were also reported for the biological activity. Our results can generate a new rice line that exhibits high plant growth and is rich with bioactive compounds such as flavonoid and phenolic compounds which are related to the improvement of human health.

Insights into the multi-scale structural properties and digestibility of lotus seed starch-chlorogenic acid complexes prepared by microwave irradiation

By inspecting starch hierarchical structural evolution, this work explored how microwave irradiation tailored the digestion characteristics of lotus seed starch-chlorogenic acid mixtures. The results showed that after microwave treatment, the granular structure, short-range ordered structure, helical conformation, and lamellar structure of starch exhibited different degrees of disorganization. In this procedure, chlorogenic acid interacted with starch molecules to form lotus seed starch-chlorogenic acid complexes and participated in the reorganization of the matrixes of the starch substrate in three forms: V-type inclusion complex, non-inclusion complex, and simply physically entrapped. These structural changes, coupled with the inhibition of chlorogenic acid on carbohydrate hydrolyzing enzymes, contributed to the slowly digestible features of lotus seed starch-chlorogenic acid complexes. This study provided a basis for understanding the multi-scale structure-digestibility relationship of starchy foods rich in phenolic acids under microwave treatment.

Tanacetum vulgare L. (Tansy) as an effective bioresource with promising pharmacological effects from natural arsenal

The Tanacetum genus is a big treasure with the presence of biologically-active compounds and members of this genus are widely used for the treatment of several diseases in traditional medicine system. Considering this fact, we aimed to analyze the extracts from Tanacetum vulgare L. in case of chemical profiles and biological effects. Chemical characterization was performed by using UHPLC-HRMS technique and showed the presence of several phytochemical groups (107 compounds were identified, including phenolic acids, flavonoids, terpenoids and fatty acids. Biological abilities were examined by using antioxidant (DPPH, ABTS, FRAP, CUPRAC, metal chelating and phosphomolybdenum assays) and enzyme inhibition (tyrosinase, amylase, glucosidase and cholinesterase) properties. Pharmaco-toxicological investigations were also performed with the aim to identify limits of biocompatibility, anti-oxidant and neuromodulatory effects, in hypothalamic HypoE22 cells. A bioinformatic analysis was also carried to unravel the putative protein-targets for the observed biological effects. Generally, the tested hexane and hydroalcoholic extracts displayed stronger activities in antioxidant and enzyme inhibitory assays, when compared with water. In addition, multivariate analysis was performed to understand the differences in both solvents and plant parts and we clearly observed the separation of these parameters. The extracts (10 μg/mL) also stimulated DAT and inhibited TNFα and BDNF gene expression, in HypoE22 cells. In parallel, the extracts were also able to stimulate norepinephrine release from this cell line. By contrast, in the concentration range 50-100 μg/mL, the extracts reduced the HypoE22 viability, thus demonstrating cytotoxicity at concentrations 5-10 fold higher compared to those effective as neuromodulatory. Our observations manifested that T. vulgare has several beneficial effects and it can be used as a potential natural raw material for designing further health-promoting applications in nutraceutical, cosmeceutical, and pharmaceutical areas.

Effect of quercetin on the in vitro Tartary buckwheat starch digestibility

Tartary buckwheat is one of the few pseudocereals with abundant flavonoids and starch. However, there are different views on the digestibility of Tartary buckwheat starch (TBS) because of its particle size and structure. In this study, fluorescence spectrum methods and enzymatic kinetics were used to investigate the interaction between TBS /two glycosidase (α-amylase and α-glucosidase) and quercetin to explore its digestive properties and provide a perspective regarding the application of TBS in functional starch products. The results showed that the interaction between TBS and quercetin was probably weak hydrophobic force and hydrogen bonding. The inhibitory effect of quercetin on α-amylase was better than that on α-glucosidase. The half inhibitory concentrations (IC₅₀) of quercetin to α-amylase and α- glucosidase was (270 ± 3.31) and (544 ± 9.01) μg/mL, respectively. The intrinsic fluorescence of two enzymes was statically quenched by forming a complex with quercetin. Quercetin also increased the microenvironment hydrophilicity of tryptophan residues in glycosidase. In vitro digestion experiment demonstrated that quercetin and TBS co-gelatinized together was more effective to inhibit TBS hydrolysis than quercetin itself alone. In the first-order kinetic and LOS model, quercetin-starch gel structure and quercetin inhibitory activity against enzymes had synergistic effects of the TBS digestion.

Preparation of phytic acid modified α-Glucosidase/Cu3(PO4)2·3H2O hybrid nanoflower and its application

A simple, convenient and efficient enzyme immobilization method through phytic acid (PA) modified α-Glucosidase (α-Glu)/Cu₃(PO₄)₂·3H₂O hybrid nanoflower was developed. The structural properties of the materials were studied by several characterization techniques. Subsequently, the enzymatic reaction conditions such as the pH value and temperature were optimized, and the enzyme kinetics and inhibition parameters were determined. The PA modified α-Glu/Cu₃(PO₄)₂·3H₂O hybrid nanoflower had better enzymatic activity under a wide pH range and high temperature than the free one. After seven successive cycles, the PA modified α-Glu/Cu₃(PO₄)₂·3H₂O hybrid nanoflower could still maintain approximately 63.0 % of its initial immobilized enzyme activity. The Michaelis-Menten constant (K_m) and the half-maximal inhibitory concentration (IC₅₀) of acarbose were determined as 0.77 mM and 15.01 μM, respectively. In addition, the material was applied to evaluate the inhibitory activity of ten phenolic compounds on α-Glu, and epicatechin gallate, gallocatechin gallate, epigallocatechin gallate and rosmarinic acid showed good inhibitory activity with % of inhibition of (53.42 ± 2.39)%, (37.28 ± 1.32)%, (37.08 ± 0.63)% and (35.53 ± 0.23)%, respectively. These results indicate that the PA modified hybrid nanoflower is an efficient method of α-Glu immobilization.

Characterization of selenized polysaccharides from Ribes nigrum L. and its inhibitory effects on α-amylase and α-glucosidase

The polysaccharide from Ribes nigrum L. (RCP) was modified by nitric acid-sodium selenite method. After purification by Sepharose-6B, high purity native (PRCP) and three selenized polysaccharides (PRSPs) with different selenium contents were obtained. Compared with PRCP, PRSPs possessed the lower molecular weight, better water-solubility, physical stability and rheological properties. FT-IR and NMR spectra confirmed PRSPs had the characteristic absorption peaks of polysaccharides and the glycosidic bond types were not changed after selenylation modification, whereas the selenyl groups existing in PRSPs were mainly introduced at the C-6 position of sugar residue →4)-β-d-Manp-(1→. Moreover, PRSPs displayed obviously smoother and smaller flaky structure than PRCP, and their inhibitory effects on α-amylase and α-glucosidase also were greater than PRCP. PRSPs exhibited a reversible inhibition on two enzymes in competitive manner and quenched their fluorescence through the static quenching mechanism. The polysaccharide-enzyme complex was spontaneously formed mainly driven by the hydrophobic interaction and hydrogen bonding.

Structural and kinetic insights into HIV-1 reverse transcriptase inhibition by farnesiferol C

Human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) is the key enzyme for the virus gene replication and the most important target for antiviral therapy. Toxicity, drug resistance and side effects have led to search for new antiviral agents. Farnesiferol C (FC) is a well-known biologically active sesquiterpene coumarin derivative from genus Ferula. The current study was designed to examine the impacts of FC on the structure and function of HIV-1 RT, using some theoretical and experimental methods. FC inhibited HIV-1RT activity via mixed inhibition mechanism (IC₅₀ = 30 μM). Spectroscopic data showed some conformational changes in the secondary as well as tertiary structure of HIV-1RT following the interaction with FC. Results showed that FC could quench the intrinsic fluorescence emission of HIV-1RT through static quenching mechanism. Thermodynamic parameters revealed that hydrogen bondings and van der Waals forces are the major forces in the binding reaction and the low equilibrium constants (K_D) value obtained from surface plasmon resonance data, confirmed the high affinity of FC for HIV-1RT. Molecular docking studies indicated that FC interacts with enzyme through hydrophobic pocket. Taken together, the outcomes of this research revealed that, sesquiterpene coumarines can be used to design natural remedies as anti-HIV agents.

Comparing the inhibitory abilities of epigallocatechin-3-gallate and gallocatechin gallate against tyrosinase and their combined effects with kojic acid

Inhibition of tyrosinase activity contributes to the control of food browning and skin pigmentation diseases. Herein, the inhibitory mechanism of epigallocatechin-3-gallate (EGCG) and gallocatechin gallate (GCG) on tyrosinase were investigated. Both EGCG and GCG inhibited tyrosinase in a mixed manner with the IC₅₀ values of 39.4 ± 0.54 μM and 36.8 ± 0.21 μM, and showed a synergism with their combination, while EGCG and GCG combined with kojic acid (IC₅₀ = 19.2 ± 0.26 μM) exhibited antagonism and additive effect, respectively. EGCG and GCG interacted with tyrosinase mainly by hydrogen bonding and hydrophobic interactions and induced a looser conformation of tyrosinase. Molecular docking indicated that EGCG and GCG bound to the active center of tyrosinase and interacted with copper ions and key amino acid residues. Molecular dynamics simulation further characterized the structure and property of EGCG/GCG-tyrosinase complex. This study provides novel insights into the mechanism of catechins as tyrosinase inhibitors.

Three flavanols delay starch digestion by inhibiting α-amylase and binding with starch

The study aimed to reveal the different mechanisms of delaying starch digestion by ECG, EGCG and Procyanidin based on the perspective of α-amylase-flavanol interaction and starch-flavanol interaction. The interaction characteristics of flavanols with α-amylase were studied from five aspects: enzyme inhibition, kinetics, fluorescence quenching, circular dichroism (CD) and computer simulation. The IC50 of flavanols (ECG, EGCG and Procyanidin) against α-amylase were 172.21 ± 0.22, 732.15 ± 0.13 and 504.45 ± 0.19 μg/mL according to the results of α-amylase inhibition experiment, respectively. ECG and Procyanidin showed mixed inhibition against α-amylase, while EGCG showed non-competition against α-amylase. However, thermodynamic parameters，computer-based docking and dynamic simulation proved that ECG and EGCG-α-amylase complexs were mainly driven by van der Waals and hydrogen bonds, while Procyanidin-α-amylase complexs was driven by hydrophobic interaction. In addition, it was indicated, by means of starch‑iodine complex spectroscopy, that flavanols inhibited the digestion of starch not only through bind with α-amylase but also through bind with starch. Thus, flavanols as a starch-based food additive have the potential to be employed as adjuvant therapy for diabetes.

Insight into interaction mechanism between theaflavin-3-gallate and α-glucosidase using spectroscopy and molecular docking analysis

To elucidate the α-glucosidase (α-GC) inhibitory mechanism of theaflavin-3-gallate (TF-3-G), their interaction mechanism was investigated using spectroscopy and molecular docking analysis. The inhibition ratio of TF-3-G against α-GC was determined to be 92.3%. Steady fluorescence spectroscopy showed that TF-3-G effectively quenched the intrinsic fluorescence of α-GC through static quenching, forming a stable complex through hydrophobic interactions. Formation of the TF-3-G/α-GC complex was also confirmed by resonance light scattering spectroscopy. Synchronous fluorescence spectroscopy and circular dichroism spectroscopy indicated that the secondary structure of α-GC was changed by TF-3-G. Molecular docking was used to simulate TF-3-G/α-GC complex formation, showing that TF-3-G might be inserted into the hydrophobic region around the active site of ɑ-GC, and bind with the catalytic Asp215 and Asp352 residues. The ɑ-GC inhibitory mechanism of TF-3-G was mainly attributed to the change in ɑ-GC secondary structure caused by the complex formation. PRACTICAL APPLICATIONS: α-Glucosidase (α-GC) can hydrolyze the glycosidic bonds of starch and oligosaccharides in food and release glucose. Therefore, the inhibition of α-GC activity has been used to treat postprandial hyperglycemia and type 2 diabetes mellitus. Theaflavin-3-gallate (TF-3-G), a flavonoid found in the fermentation products of black tea, exhibits strong inhibition of α-GC activity. However, the α-GC inhibitory mechanism of TF-3-G is unclear. This study aids understanding of this mechanism, and proposed a possibly basic theory for improving the medicinal value of TF-3-G in diabetes therapy.

Screening and identifying of α-amylase inhibitors from medicine food homology plants: Insights from computational analysis and experimental studies

There is a growing interest in screening α-amylase inhibitors from natural products for application in the development of new antidiabetic drugs or functional foods. In this study, a structure-based virtual screening was applied to rapidly identify the α-amylase inhibitors from medicine food homology (MFH) plants. Similarity search, docking & scoring were used for further filter small molecules. As a result, 21 corresponding potential α-amylase inhibitors from MFH plants were obtained. And, six polyphenol compounds (curcumin, procyanidins, epicatechin gallate (ECG), epigallocatechin gallate (EGCG), hesperidin, and puerarin) were highlighted for further verification after a thorough assessment of the classification of hit molecules as well as docking scores. The results of the enzyme inhibition test showed that ECG, EGCG, and procyanidins had the better binding ability of α-amylase among these six polyphenols. The Ki values of ECG, EGCG, and procyanidins on α-amylase were 0.70, 1.68, and 0.24, respectively. The CD spectra results indicated that the three polyphenols can cause conformational changes in α-amylase. PRACTICAL APPLICATIONS: A structure-based virtual screening method for rapid identifying α-amylase inhibitors from MFH plants was developed successfully in this study. These findings suggested that natural polyphenols such as ECG, EGCG, and procyanidins may be a potential inhibitor of α-amylase which could be used as a nutrient supplement for the prevention of diabetes mellitus or can be further used in the development of hypoglycemic drugs. At the same time, it can provide theoretical guidance for the better utilization and development of medicine food homology plants containing these potential α-amylase inhibitors. Moreover, this work may provide ideas and references for the screening of other target protein inhibitors.