Lignin binding to pancreatic lipase and its influence on enzymatic activity

Effects of air flow micro pulverized wheat bran dietary fiber on physicochemical, structural, and digestive properties of wheat starch

The effects of wheat bran dietary fiber (WBDF) treated by air flow micro-pulverization on gelatinization, thermal, rheological, structural properties, and in vitro digestion of wheat starch (WS) were investigated. Different particle sizes of WBDF were obtained by conventional knife grinding and airflow micro-grinding. Compared with conventional knife grinding, the particle size of WBDF treated by air flow micro-pulverization decreased, the particle size distribution was concentrated at small particle sizes, the specific surface area increased, and the hydraulic and oil-holding power decreased, which was mainly related to the change of WBDF spatial structure and the increase of solubility. At the same time, the peak viscosity, setback, breakdown, and resistant starch content short-range order degree and relative crystallinity of WS were increased by adding WBDF treated by air flow micro-pulverization, whereas the gelatinization enthalpy value and apparent viscosity were decreased. This indicated that the air micro pulverized WBDF promoted gelatinization and inhibited digestion while reducing the thermal stability of WS, leading to short-term recovery. This study provides a theoretical reference for the production and processing of gluten-containing flour products. PRACTICAL APPLICATION: In this study, the physical and chemical properties and spatial structure of air flow micro pulverized dietary fiber of wheat bran were analyzed, and its effects on the properties of wheat starch were studied. Therefore, this study provides a theoretical basis for the industrial application of gluten-containing flour products.

Organic acid treatments on citrus insoluble dietary fibers and the corresponding effects on starch in vitro digestion

Three environmentally friendly organic acids, acetic acid, citric acid and oxalic acid, were used to treat citrus insoluble dietary fiber (CIDF) in present study, aiming to explore the changes in structural properties as well as their inhibitory effects on starch digestion. The results showed that organic acid treatment significantly reduced the particle size of all three CIDFs, with rougher and folded surfaces, improved crystallinity and thermal stability. During in vitro digestion, it was found that organic acid treatment could increase the particle size and viscosity of digestion, and also effectively enhance the inhibitory ability of α-glucosidase activity, resulting in a further blockage of starch digestion. The starch digestion in oxalic acid-treated group (with 3 wt% addition) was significantly reduced by 18.72 % compared to blank group and 9.05 % compared to untreated. These findings provide evidence of the potential of organic acid-treated insoluble dietary fiber as a functional food.

Inhibitory effects of nobiletin-mediated interfacial instability of bile salt emulsified oil droplets on lipid digestion

Previous lipase inhibitors studies mainly focus on the binding between inhibitors and lipase, ignoring the impact of inhibitors on the oil-water interface of lipid droplets. This study aimed to investigate the effect of nobiletin (NBT) from Citri Reticulatae Pericarpium on the oil-water interface properties and lipid digestion. Here, we found that NBT could destroy bile salt (BS)-stabilized lipid droplets and thus inhibited free fatty acid release, owing to the interaction between NBT and BS at the oil-water interface, and reducing the stability of the oil-water interface (the stability index decreased from 91.15 ± 2.6 % to 66.5 ± 3.6 %). Further, the molecular dynamics simulation and isothermal titration calorimetry revealed that NBT could combine with BS at oil-water interface through intermolecular interactions, including hydrogen bonds, Van der Waals force, and steric hindrance. These results suggest that the interfacial instability of NBT mediated BS emulsified oil droplets may be another pathway to inhibit lipid digestion.

Thermal treatment of alkali lignin to eliminate its inhibition of pancreatic proteases in vitro

This study aims to investigate how alkali lignin inhibits protein digestion and explore thermal treatment as a potential solution. Solid alkali lignin species pre-heated at different temperatures (150, 200, and 250 °C) and soluble acid-differentiated fractions are subjected to in vitro protein digestion. A range of techniques, including Thermogravimetric Analysis (TGA), Size-Exclusion Chromatography (SEC), Zeta Potential Analyzer, 1H NMR, Isothermal Titration Calorimetry (ITC), and Molecular Docking, were used to investigate the inhibitory mechanism of alkali lignin on pancreatic proteases hydrolysis. Our results suggest that soluble alkali lignin inhibits pancreatic trypsin and chymotrypsin, with the acid-differentiated soluble fraction (LgpH<1) displaying the strongest inhibition and proteases' binding affinity due to the abundance of polar groups (e.g., -OH, -CHO), which facilitate hydrogen-bond formation. Furthermore, pre-heating lignin (200 °C) was confirmed effective for removing LgpH<1 and its negative nutritional influence, providing a feasible strategy for overcoming the negative impact of alkali lignin on protein digestion.

Virtual screening, activity evaluation, and stability of pancreatic lipase inhibitors in the gastrointestinal degradation of nattokinase

Nattokinase is an alkaline serine protease secreted by natto during fermentation. Despite its good thrombolytic effect, it is intolerant to gastrointestinal conditions and is easily digested and degraded into polypeptides, oligopeptides, and amino acids. However, whether these peptides inhibit fat-digesting enzymes and other biological activities remains unknown. To explore the bioactivity of peptides produced through nattokinase degradation, nattokinase was subjected to simulated digestion in the gastrointestinal tract, and 41 small peptides were obtained through the enzymolysis of gastric enzymes, pancreases, and chymotrypsin. Four pancreatic lipase (PL) inhibitory peptides (SW, ASF, GAY, and PGGTY) were selected based on their activity scores, water solubility, and toxicity predictions. The molecular docking results revealed that hydrogen bonds and electrostatic interactions were the main forces for inhibiting PL activity. The results of enzyme activity verification revealed that all four peptides inhibited PL activity. Among them, GAY exhibited the strongest inhibitory effect, with an inhibitory rate of 10.93 % at a concentration of 1 mg/mL. Molecular dynamics simulations confirmed that the GAY-1ETH complex demonstrated good stability. Natto foods containing nattokinase own the activity of inhibiting fat-digesting enzymes and show antiobesity potentials.

Preparation of water-insoluble lignin nanoparticles by deep eutectic solvent and its application as a versatile and biocompatible support for the immobilization of α-amylase

As one of the most abundant biopolymers, lignin is a widely available resource. However, its potential largely remains untapped, with most of it ending up as waste from industries like paper production, pulp processing, and bio-refining. The research undertaken in this study focused on the extraction of lignin from agroforestry waste using a deep eutectic solvent (DES) as a carrier for α-amylase immobilization, resulting in high stability and reusability. Several techniques, including Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and the Brunauer-Emmett-Teller (BET) method were employed to examine the structure and morphology of both the extracted lignin and the immobilized enzyme. The temperature used to recover lignin by DES would affect immobilization efficiency and enzyme loading by influencing its specific surface area, pore size, and volume distribution. Investigations using Nuclear Overhauser Effect Spectroscopy (NOESY) uncovered that the hydroxyl groups in G, H, and S units and the β-O-4 structure of lignin primarily serve as binding sites for enzyme molecules. Immobilized α-amylase demonstrated a higher pH and thermal stability level, with an optimal pH of 7.0 and temperature of 100 °C, compared to the free enzyme, which exhibited optimal activity at a pH of 6.5 and temperature of 90 °C. Importantly, immobilized α-amylase retained >80 % of its initial activity even after 28 days at room temperature, and it maintained 70 % of its activity after being reused 12 times. These findings strongly suggest that lignin derived from agroforestry residues holds promising potential as a future versatile immobilization material, a prospect integral to society's sustainable development.

Proanthocyanidins as the main pancreatic lipase inhibitors in chokeberry fruits

Pancreatic lipase inhibitors are recognized as important in strategies for the management of overweight and obesity. The phytocompounds in chokeberry fruit show multidirectional pro-health effects, including anti-obesity activity. The aims of this study were to fractionate and identify the phenolic compounds of chokeberry fruit phenolic-rich extract that are active as pancreatic lipase inhibitors. Phenolic compounds were fractionated using Sephadex LH-20 resin, followed by polyphenol profile analysis using chromatographic and spectrophotometric methods, while pancreatic inhibitory activity was determined using 4-methylumbelliferyl oleate and emulsified triolein as enzyme substrates. Among the six fractions isolated from extract, two fractions rich in highly polymerized proanthocyanidins showed the greatest ability to inhibit pancreatic lipase activity. In comparison, fractions containing mainly low-molecular-weight phenolic compounds, such as phenolic acids, flavonols and anthocyanins, were 11-64 times less active. The most active fraction showed a mixed mode of pancreatic lipase inhibition, as determined by Lineweaver-Burk plot analysis, and exhibited a cumulative effect with orlistat. This study shows that black chokeberry polyphenols, particularly highly polymerized procyanidins, can effectively inhibit pancreatic lipase activity determined by in vitro methods.

Binding mechanism of lipase with Lentinus edodes mycelia polysaccharide by multi-spectroscopic methods

It is an effective strategy to avoid obesity by inhibiting the activity of lipase. In this study, the binding mechanism of lipase and Lentinus edodes mycelia polysaccharide (LMP) were explored with multi-spectral methods, for example, three-dimensional (3D) fluorescence, Fourier-transformed infrared (FT-IR), and Raman spectra. At 290 K, the binding constant was 2.44 × 10⁵  L/mol, there was only one binding site between LMP and lipase. Static quenching was the quenching mechanism. The major forces were hydrogen bonding and van der Waals force. The binding of LMP to lipase impacted the microenvironment around tyrosine and tryptophan residues. The polarity around these residues was decreased and hydrophobicity was enhanced. This study not only revealed the binding mechanism of LMP on lipase but also provided scientific evidence for expanding the application of LMP in functional food industries.

Longan seed polyphenols inhibit α-amylase activity and reduce postprandial glycemic response in mice

The effects of longan seed polyphenols (LSPs) on postprandial glycemic response in mice were investigated, enzyme inhibition kinetics of LSPs against α-amylase were studied using an inhibition assay in vitro, and the underlying mechanisms were discussed by analyzing the impacts of LSPs on the structure of α-amylase using multispectral approaches. The results showed LSPs significantly suppressed blood glucose response in a dose-dependent manner. Enzyme inhibition analysis demonstrated LSPs inhibited α-amylase activity in a mixed type (IC₅₀ 3.02 mg mL^-1). UV-vis absorption spectroscopy and fluorescence quenching spectroscopy suggest LSPs tend to bind with α-amylase through static interaction at one binding site, mainly through hydrogen bonding and van der Waals forces. The secondary structure of α-amylase was changed by LSPs as reviewed by circular dichroism, showing a more compact skeleton and more flexible loop of α-amylase. This hinders the substrate from reaching the binding site of the enzyme, resulting in reduced enzyme activity. These suggest the potential application of LSPs as a hypoglycemic agent in functional foods.

Unlocking the secret of lignin-enzyme interactions: Recent advances in developing state-of-the-art analytical techniques

Bioconversion of renewable lignocellulosics to produce liquid fuels and chemicals is one of the most effective ways to solve the problem of fossil resource shortage, energy security, and environmental challenges. Among the many biorefinery pathways, hydrolysis of lignocellulosics to fermentable monosaccharides by cellulase is arguably the most critical step of lignocellulose bioconversion. In the process of enzymatic hydrolysis, the direct physical contact between enzymes and cellulose is an essential prerequisite for the hydrolysis to occur. However, lignin is considered one of the most recalcitrant factors hindering the accessibility of cellulose by binding to cellulase unproductively, which reduces the saccharification rate and yield of sugars. This results in high costs for the saccharification of carbohydrates. The various interactions between enzymes and lignin have been explored from different perspectives in literature, and a basic lignin inhibition mechanism has been proposed. However, the exact interaction between lignin and enzyme as well as the recently reported promotion of some types of lignin on enzymatic hydrolysis is still unclear at the molecular level. Multiple analytical techniques have been developed, and fully unlocking the secret of lignin-enzyme interactions would require a continuous improvement of the currently available analytical techniques. This review summarizes the current commonly used advanced research analytical techniques for investigating the interaction between lignin and enzyme, including quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy (FLS), and molecular dynamics (MD) simulations. Interdisciplinary integration of these analytical methods is pursued to provide new insight into the interactions between lignin and enzymes. This review will serve as a resource for future research seeking to develop new methodologies for a better understanding of the basic mechanism of lignin-enzyme binding during the critical hydrolysis process.

Dietary fibers fractionated from gardenia (Gardenia jasminoides Ellis) husk: structure and in vitro hypoglycemic effect

BACKGROUND

Gardenia (Gardenia jasminoides Ellis) husk rich in dietary fiber is a byproduct of fructus processing, and commonly discarded as waste. The husk was fractionated by sequential extraction into four fractions: water-soluble fiber (W-SF), acid-soluble fiber (Ac-SF), alkali-soluble fiber (Al-SF) and insoluble residue fiber (IRF). The aim of this study was to investigate the differences in structure and in vitro hypoglycemic effect of these fibers.

RESULTS

Monosaccharide composition and Fourier transform infrared spectra showed that the major component might be pectin for W-SF and Ac-SF, xylan as well as pectin for Al-SF and cellulose for IRF. These fibers offered excellent water-holding capacity and swelling capacity, except that IRF was only slightly swellable in water. W-SF exhibited significantly higher capacities to adsorb glucose (2.408 mmol g^-1 at a glucose concentration of 200 mmol L^-1 ) and inhibit α-amylase activity (29.48-49.45% inhibition rate at a concentration of 4-8 mg mL^-1 ), probably caused by the higher viscosity and hydration properties; while Ac-SF, Al-SF and IRF (especially Al-SF) were more effective in retarding the glucose diffusion across a dialysis membrane (34.97-41.67% at 20-30 min), which might be attributed to particle size and specific surface area. All the fibers could quench the intrinsic fluorescence of α-amylase to some degree.

CONCLUSIONS

Dietary fiber from gardenia husk, especially W-SF, can be used as a potential hypoglycemic ingredient in diabetic functional foods. © 2020 Society of Chemical Industry.

Inhibitory effect of lignin from Canna edulis Ker residues on trypsin: kinetics and molecular docking studies

BACKGROUND

Lignin extracted from Canna edulis Ker residues shows a strong inhibitory effect on α-glucosidase and a promoting effect on α-amylase. Protease activity inhibition may play a key role in disease processes, such as metastasis, tumor invasion and bacterial colonization. Hence, in the present study, the inhibitory mechanism of lignin on trypsin was examined, including the interaction type, thermodynamic parameters, structure, reaction site and molecular docking.

RESULTS

The isolated lignin presented an inhibitory effect on trypsin activity with an IC₅₀ value of 1.35 μmol L^-1 . This inhibition was a mixed linear type with a constant K_i of 3.92 μmol L^-1 . The lignin could bind with the key amino acid residue Ser195 on the active site of the trypsin molecule to inhibit its activity, and the phenolic hydroxyl group and -OH on the β-O-4 structure of the lignin molecule were the major groups bound with trypsin.

CONCLUSION

These results illustrate the inhibitory effects of Canna edulis residue lignin on protease, which helps with respect to understanding the possible application of lignin in the food industry in functional foods. © 2020 Society of Chemical Industry.

Thermally processed lignin reduces the apparent hydrolysis rate of pancreatic α-amylase in starchy foods

Lignin, despite being the second most abundant constituent of plant cell walls, is thought to be chemically inert during gastrointestinal digestion and therefore attracts little attention for its role in the human diet. This study explores the heat modifications of lignin to derive species capable of slowing starch digestion in vitro. We applied various advanced biochemical (e.g. enzymic digestion, solubility) and physio-chemical (e.g. scanning electron microscopy, Fourier-Transform-Infrared Spectroscopy, ¹³C-NMR) analyses to characterize the structure-function of lignin induced by heat treatment. It was found that lignin thermally processed above 300 °C reduced the apparent hydrolysis rate of pancreatic α-amylase, which is ascribed mainly to the insoluble lignin with a modified particle surface morphology. Further kinetic experiments showed that lignin species derived by thermal processing slowed in vitro digestion rates of potato starch and pasta. These findings highlight the potential for utilizing thermally processed lignin in slowing digestion of starchy foods.

Inhibition of glutathione and s-allyl glutathione on pancreatic lipase: Analysis through in vitro kinetics, fluorescence spectroscopy and in silico docking

Inhibition of pancreatic lipase (PL) is considered one of the important therapeutic interventions against obesity. In the present study, the inhibition of porcine (mammalian) PL (PPL) by two tripeptides glutathione (GSH) and s-allyl glutathione (SAG) was studied. In vitro kinetic analysis was done to determine the inhibition of GSH and SAG against PPL. The binding of GSH and SAG with PPL was elucidated by fluorescence spectroscopy analysis. Docking and molecular dynamics (MD) simulation analysis was carried out to understand the intermolecular interaction between both GSH and SAG with PPL as well as human PL (HPL). Both GSH and SAG inhibited PPL in mixed non-competitive manner. The IC₅₀ value for GSH and SAG against PPL was found to be 2.97 and 6.4 mM, respectively. Both GSH and SAG quenched the intrinsic fluorescence of PPL through static quenching that is through forming complex with the PPL. SAG and GSH interacted with amino acids involved in catalysis of both PPL and HPL. MD simulation showed interactions of SAG and GSH with both PPL and HPL were stable. These results would lead to the further studies and application of GSH and SAG against obesity through inhibition of PL.

The Use of Lignin as a Microbial Carrier in the Co-Digestion of Cheese and Wafer Waste

The aim of the article was to present the effects of lignin grafted with polyvinylpyrrolidone (PVP) as a microbial carrier in anaerobic co-digestion (AcoD) of cheese (CE) and wafer waste (WF). Individual samples of waste cheese and wafers were also tested. The PVP modifier was used to improve the adhesive properties of the carrier surface. Lignin is a natural biopolymer which exhibits all the properties of a good carrier, including nontoxicity, biocompatibility, porosity, and thermal stability. Moreover, the analysis of the zeta potential of lignin and lignin combined with PVP showed their high electrokinetic stability within a wide pH range, that is, 4-11. The AcoD process was conducted under mesophilic conditions in a laboratory by means of anaerobic batch reactors. Monitoring with two standard parameters: pH and the VFA/TA ratio (volatile fatty acids-to-total alkalinity ratio) proved that the process was stable in all the samples tested. The high share of N-NH4+ in TKN (total Kjeldahl nitrogen), which exceeded 90% for WF+CE and CE at the last phases of the process, proved the effective conversion of nitrogen forms. The microbiological analyses showed that eubacteria proliferated intensively and the dehydrogenase activity increased in the samples containing the carrier, especially in the system with two co-substrates (WF+CE/lignin) and in the waste cheese sample (CE/lignin). The biogas production increased from 1102.00 m3 Mg-1 VS (volatile solids) to 1257.38 m3 Mg-1 VS in the WF+CE/lignin sample, and from 881.26 m3 Mg-1 VS to 989.65 m3 Mg-1 VS in the CE/lignin sample. The research results showed that the cell immobilization on lignin had very positive effect on the anaerobic digestion process.

Investigating inhibitory activity of novel synthetic sericin peptide on α-D-glucosidase: kinetics and interaction mechanism study using a docking simulation

BACKGROUND

We synthesised a novel sericin peptide (SP-GI) with α-d-glucosidase inhibitory activity, which has a sequence of SEDSSEVDIDLGN. The kinetics of its peptide-induced inhibition on α-d-glucosidase activity and its interaction mechanism merging with molecular docking were both investigated.

RESULTS

SP-GI exhibited significant inhibitory activity with an IC₅₀ of 2.9 ± 0.1 µmol L^-1 and this inhibition was reversible and non-competitive with a K_i value of 1.0 ± 0.1 µmol L^-1 . An interaction study with SP-GI revealed it bound to α-d-glucosidase at a single binding site, resulting in alterations in α-d-glucosidase secondary structure. This led to quenching of intrinsic α-d-glucosidase fluorescence by a static quenching mechanism. Molecular docking results showed that the SP-GI binding site on α-d-glucosidase differed from acarbose, with hydrogen bonding and van der Waals forces being the main binding drivers.

CONCLUSION

These findings suggest the potential use for SP-GI or other natural sericin peptides as dietary supplements for the treatment of type 2 diabetes. © 2017 Society of Chemical Industry.

In vitro Inhibition of Pancreatic Lipase by Polyphenols: A Kinetic, Fluorescence Spectroscopy and Molecular Docking Study

The inhibitory activity and binding characteristics of caffeic acid, p-coumaric acid, quercetin and capsaicin, four phenolic compounds found in hot pepper, against porcine pancreatic lipase activity were studied and compared to hot pepper extract. Quercetin was the strongest inhibitor (IC50=(6.1±2.4) µM), followed by p-coumaric acid ((170.2±20.6) µM) and caffeic acid ((401.5±32.1) µM), while capsaicin and a hot pepper extract had very low inhibitory activity. All polyphenolic compounds showed a mixed-type inhibition. Fluorescence spectroscopy studies showed that polyphenolic compounds had the ability to quench the intrinsic fluorescence of pancreatic lipase by a static mechanism. The sequence of Stern-Volmer constant was quercetin, followed by caffeic and p-coumaric acids. Molecular docking studies showed that caffeic acid, quercetin and p-coumaric acid bound near the active site, while capsaicin bound far away from the active site. Hydrogen bonds and π-stacking hydrophobic interactions are the main pancreatic lipase-polyphenolic compound interactions observed.

Identification of critical genes associated with lignin biosynthesis in radish (Raphanus sativus L.) by de novo transcriptome sequencing

Radish is an important root vegetable crop with high nutritional, economic, and medicinal value. Lignin is an important secondary metabolite possessing a great effect on plant growth and product quality. To date, lignin biosynthesis-related genes have been identified in some important plant species. However, little information on characterization of critical genes involved in plant lignin biosynthesis is available in radish. In this study, a total of 71,148 transcripts sequences were obtained from radish root, of which 66 assembled unigenes and ten candidate genes were identified to be involved in lignin monolignol biosynthesis. Full-length cDNA sequences of seven randomly selected genes were isolated and sequenced from radish root, and the assembled unigenes covered more than 80% of their corresponding cDNA sequences. Moreover, the lignin content gradually accumulated in leaf during the developmental stages, and it increased from pre-cortex to cortex splitting stage, followed by a decrease at thickening stage and then increased at mature stage in root. RT-qPCR analysis revealed that all these genes except RsF5H exhibited relatively low expression level in root at thickening stage. The expression profiles of Rs4CL5, RsCCoAOMT1, and RsCOMT genes were consistent with the changes of root lignin content, implying that these candidate genes may play important roles in lignin formation in radish root. These findings would provide valuable information for identification of lignin biosynthesis-related genes and facilitate dissection of molecular mechanism underlying lignin biosynthesis in radish and other root vegetable crops.

Lignin from bamboo shoot shells as an activator and novel immobilizing support for α-amylase

This study examined the feasibility of α-amylase activation and immobilization, using lignin from bamboo shoot shells (BSS). Our results demonstrated that BSS lignin is an excellent α-amylase activator and it elevated α-amylase activity more than two-fold at a concentration of 5mg/ml. For immobilization of α-amylase via adsorption, BSS lignin was incubated in an α-amylase solution (5mg/ml) for 20min, and the maximum specific activity, amount of loaded protein and activity recovery were 92.4U/mg, 19.0mg/g and 111%, respectively. In contrast to its free counterpart, immobilized α-amylase improved the catalytic efficiency and storage stability, under comparable working conditions (temperature and pH). Regarding its convenient usage, immobilized enzyme can be suspended in advance, but a suspension incubated at 60°C should be used within 30min. The residual activity after 14 re-uses remained at a reasonable level (53.2%). In conclusion, this study reveals a novel support for enzyme immobilization.

Inhibitory mechanism of morin on α-glucosidase and its anti-glycation properties

It is important to investigate the inhibition of α-glucosidase due to its correlation with type 2 diabetes. Morin was found to exert significant inhibition activity on α-glucosidase in a reversible mixed-type manner with an IC50 value of (4.48 ± 0.04) μM. Analyses of fluorescence and circular dichroism spectra indicated that the formation of the morin-α-glucosidase complex was driven mainly by hydrophobic forces and hydrogen bonding, and caused the conformational changes of α-glucosidase. The phase diagrams of fluorescence showed that the conformational change process was monophasic without intermediates. Molecular docking indicated that morin mainly interacted with amino acid residues located close to the active site of α-glucosidase, which may move to cover the active pocket to reduce the binding of the substrate and then inhibit the catalytic activity. Morin was also found to exhibit inhibition in the generation of advanced glycation end products which was related to the long term complications of diabetes.