Interaction between four flavonoids and trypsin: effect on the characteristics of trypsin and antioxidant activity of flavonoids

Chymotrypsin and Trypsin Inhibitory Activity of Some Medicinal Plants Collected from Rize (Türkiye)

In this research, the evaluation of in vitro chymotrypsin and trypsin inhibitory activities of ten plant species collected from Rize were aimed, and fractions that showed strong activity were analyzed through HPLC. Daphne pontica L. and Mentha longifolia (L.) L. were found to have the highest chymotrypsin inhibitory activities (87.75 and 84.24 % inhibition). Similarly, the highest trypsin inhibitory activity was observed in D. pontica (%99.93 inhibition), followed by Sambucus ebulus L. flowers (87.47 % inhibition). Extracts showing strong enzyme inhibition were fractioned and subjected to activity tests. The highest chymotrypsin inhibitory activity was observed in the n-hexane fraction of D. pontica (%80.70 inhibition), while the highest trypsin inhibitory activity was found in the n-butanol fraction of S. ebulus (%86.81 inhibition). HPLC studies determined that the 80 % ethanol extract of D. pontica and its dichloromethane and ethyl acetate fractions contained umbelliferone. It was found that chlorogenic acid was present in the 80 % ethanol extracts of S. ebulus flowers. M. longifolia was found to contain chlorogenic acid, caffeic acid, luteolin-7-glucoside, and rosmarinic acid. M. longifolia has been identified as the plant exhibiting the highest antioxidant activity in ABTS and CUPRAC tests, consistent with its high phenolic and flavonoid content.

Spermidine improves the antioxidant capacity and morphology of intestinal tissues and regulates intestinal microorganisms in Sichuan white geese

Introduction

Intestinal health is very important to the health of livestock and poultry, and is even a major determining factor in the performance of livestock and poultry production. Spermidine is a type of polyamine that is commonly found in a variety of foods, and can resist oxidative stress, promote cell proliferation and regulate intestinal flora.

Methods

In this study, we explored the effects of spermidine on intestinal health under physiological states or oxidative stress conditions by irrigation with spermidine and intraperitoneal injection of 3-Nitropropionic acid (3-NPA) in Sichuan white goose.

Results and discussion

Our results showed that spermidine could increase the ratio of intestinal villus to crypt and improve intestinal morphology. In addition, spermidine can also reduce malondialdehyde (MDA) accumulation caused by 3-NPA by increasing superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) enzyme activity, thus alleviating intestinal damage. Furthermore, spermidine can regulate intestinal digestive enzyme activities and affect intestinal digestion and absorption ability. Spermidine can also promote an increase in intestinal microbial diversity and abundance and alleviate the change of microflora structure caused by 3-NPA. In conclusion, spermidine promotes the production of beneficial intestinal metabolites such as Wikstromol, Alpha-bisabolol and AS 1-5, thus improving the level of intestinal health. Taken together, these results indicate that spermidine can improve intestinal health by improving intestinal morphology, increasing antioxidant capacity and regulating intestinal flora structure.

A critical examination of human data for the biological activity of quercetin and its phase-2 conjugates

This critical review examines evidence for beneficial effects of quercetin phase-2 conjugates from clinical intervention studies, volunteer feeding trials, and in vitro work. Plasma concentrations of quercetin-3-O-glucuronide (Q3G) and 3'-methylquercetin-3-O-glucuronide (3'MQ3G) after supplementation may produce beneficial effects in macrophages and endothelial cells, respectively, especially if endogenous deglucuronidation occurs, and lower blood uric acid concentration via quercetin-3'-O-sulfate (Q3'S). Unsupplemented diets produce much lower concentrations (<50 nmol/l) rarely investigated in vitro. At 10 nmol/l, Q3'S and Q3G stimulate or suppress, respectively, angiogenesis in endothelial cells. Statistically significant effects have been reported at 100 nmol/l in breast cancer cells (Q3G), primary neuron cultures (Q3G), lymphocytes (Q3G and3'MQ3G) and HUVECs (QG/QS mixture), but it is unclear whether these translate to a health benefit in vivo. More sensitive and more precise methods to measure clinically significant endpoints are required before a conclusion can be drawn regarding effects at normal dietary concentrations. Future requirements include better understanding of inter-individual and temporal variation in plasma quercetin phase-2 conjugates, their mechanisms of action including deglucuronidation and desulfation both in vitro and in vivo, tissue accumulation and washout, as well as potential for synergy or antagonism with other quercetin metabolites and metabolites of other dietary phytochemicals.

Food Antioxidants and Their Interaction with Human Proteins

Common to all biological systems and living organisms are molecular interactions, which may lead to specific physiological events. Most often, a cascade of events occurs, establishing an equilibrium between possibly competing and/or synergistic processes. Biochemical pathways that sustain life depend on multiple intrinsic and extrinsic factors contributing to aging and/or diseases. This article deals with food antioxidants and human proteins from the circulation, their interaction, their effect on the structure, properties, and function of antioxidant-bound proteins, and the possible impact of complex formation on antioxidants. An overview of studies examining interactions between individual antioxidant compounds and major blood proteins is presented with findings. Investigating antioxidant/protein interactions at the level of the human organism and determining antioxidant distribution between proteins and involvement in the particular physiological role is a very complex and challenging task. However, by knowing the role of a particular protein in certain pathology or aging, and the effect exerted by a particular antioxidant bound to it, it is possible to recommend specific food intake or resistance to it to improve the condition or slow down the process.

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.

Screening of trypsin inhibitors in Cotinus coggygria Scop. extract using at-line nanofractionation coupled with semi-preparative reverse-phase liquid chromatography

In this study, an at-line nanofractionation (ANF) platform was successfully fabricated in parallel with mass spectrometry and trypsin inhibitory bioactivity assessment for rapid screening of trypsin inhibitors (TIs) from natural products for the first time. After systematic optimization, the ANF platform was applied to screen and identify TIs in the extract of a traditional Chinese herb, i.e., Cotinus coggygria Scop. The semi-preparative reverse-phase liquid chromatography was used subsequently to further simplify and enrich the insufficiently separated components. After comprehensive evaluation and validation, the ANF platform successfully identified 12 compounds as potential TIs, including 8 flavonoids and 2 organic acids. Additionally, a comparison study was conducted using two other ligand fishing approaches, i.e., capillary monolithic and magnetic beads-based trypsin-immobilized enzyme microreactors, which successfully identified 8 identical flavonoids as TIs. Importantly, the molecular docking study showed the molecular interactions between enzymes and inhibitors, thus strongly supporting the experimental results. Overall, this work has fully demonstrated the feasibility of the established ANF platform for screening TIs from Cotinus coggygria Scop., and proved its great prospects for screening bioactive components from natural products.

Transcriptome analyses and virus-induced gene silencing identify HuWRKY40 acting as a hub transcription factor in the preservation of Hylocereus undatus by trypsin

Trypsin can significantly improve the storage quality of Hylocereus undatus (H. undatus). To verify the hub WRKY gene of H. undatus in trypsin preservation, joint analysis of transcriptome and protein-protein interaction (PPI) network was carried out, and virus-induced gene silencing (VIGS) was conducted. In the transcriptome of H. undatus, GO directed acyclic graph (DAG) showed that the GO terms of 55 WRKY genes were mainly enriched in sequence-specific DNA binding, DNA binding transcription factor activity, and so on. The GO enrichment chord diagram showed that HuWRKY40 was significantly up-regulated in the enriched top10 GO terms. KEGG enrichment analysis showed that 55 WRKY genes were mainly enriched in plant-pathogen interaction and MAPK pathway. The results of PPI network showed that HuWRKY40 was a hub protein of WRKY transcription factors (TFs) family regulated by trypsin, which was consistent with the results of transcriptome analysis. Bioinformatics analysis showed that HuWRKY40 of H. undatus had the highest homology with Beta vulgaris L. and Spinacia oleracea L. The function of the core regulatory protein HuWRKY40 was further clarified by VIGS technology. The results of VIGS showed that there was a big difference between the phenotype of the pTRV2-HuWRKY40 group and that of the control group. Finally, it was confirmed that HuWRKY40 accelerated the synthesis of flavonoids and improved the fruit quality during the storage of H. undatus. This study found that trypsin may regulate HuWRKY40 activity through the MAPK cascade pathway, affect the participation of flavonoid synthesis, and then delay fruit corruption. PRACTICAL APPLICATIONS: With attention of people to the safety and freshness of fruits and vegetables, biological preservation technology has become one of the hotspots in the field of preservation in recent years. Trypsin can significantly improve the antioxidant capacity of fruits and vegetables. As a new biological preservative, it is convenient to operate and economical. In the current work, the mechanism of trypsin on the WRKY TFs during H. undatus storage was investigated. The application of trypsin would provide a new strategy for the storage quality control of fruits and vegetables.

Effects of taxifolin from enzymatic hydrolysis of Rhododendron mucrotulatum on hair growth promotion

Flavonoid aglycones possess biological activities, such as antioxidant and antidiabetic activities compared to glycosides. Taxifolin, a flavonoid aglycones, is detected only in trace amounts in nature and is not easily observed. Therefore, in this study, to investigate the hair tonic and hair loss inhibitors effect of taxifolin, high content of taxifolin aglycone extract was prepared by enzymatic hydrolysis. Taxifolin effectively regulates the apoptosis of dermal papilla cells, which is associated with hair loss, based on its strong antioxidant activities. However, inhibition of dihydrotestosterone (DHT), which is a major cause of male pattern hair loss, was significantly reduced with taxifolin treatment compared with minoxidil, as a positive control. It was also confirmed that a representative factor for promoting hair growth, IGF-1, was significantly increased, and that TGF-β1, a representative biomarker for hair loss, was significantly reduced with taxifolin treatment. These results suggest that taxifolin from enzymatic hydrolysis of RM is a potential treatment for hair loss and a hair growth enhancer.

Omics analyses indicate the routes of lignin related metabolites regulated by trypsin during storage of pitaya (Hylocereus undatus)

The storage quality of Hylocereus undatus was significantly improved by trypsin, a novel preservative. The transcriptomic results revealed that antioxidant signal pathways were induced, while lignin catabolic process was impeded by trypsin. In addition, the results of protein-protein interaction (PPI) network networks suggested that flavone 3'-O-methyltransferase 1 (OMT1), ferulic acid 5-hydroxylase 1 (CYP84A1), cellulose synthase isomer (CEV1), and 4-coumarate-CoA ligase 3 (4CL3) act as hubs of peroxidases, lignin related proteins, and proteins involved in the phenylpropanoid metabolism (PLPs) induced by trypsin. Trypsin also regulated the biosynthesis of lignin, chlorogenic acid, and flavonoids. Caffeic acid might be the hub in the metabolic network of the early pathways of phenylpropanoid biosynthesis. It has been hypothesized that trypsin might quickly induce lignin biosynthesis and then up-regulated bioactive metabolites to enhance storage quality of H. undatus.

Relationships between Structure and Antioxidant Capacity and Activity of Glycosylated Flavonols

The antioxidant capacity (AC) and antioxidant activity (AA) of three flavonols (FLV), aglycones and their glycosylated derivatives were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays in various solvents. Findings confirmed that the glycosylation at the 3-position (3-glycosylation) always decreased the AC under most conditions due to substitution of the 3-position hydroxyl group and glycoside disruption in the molecular planarity. The 7-glycosylated derivatives did not have the above effects, thus generally exhibited ACs similar to their aglycones. Glycosylation decreased the AA of kaempferol and isorhamnetin for both assays in methanol, 3-glycosylation inhibited quercetin AA in the ABTS assay. In the DPPH assay, the AA of 3-glycosylated quercetin was significantly higher than quercetin. Using LC–MS/MS analysis, we found that quercetin and quercetin-7-glucoside underwent dimerization during the antioxidant reaction, potentially leading to a decline in AAs. However, 3-glycoside substitution may have hindered dimer formation, thereby allowing the FLVs to retain strong free radical scavenging abilities.

Real-Time Analysis of Polyphenol-Protein Interactions by Surface Plasmon Resonance Using Surface-Bound Polyphenols

A selection of bioactive polyphenols of different structural classes, such as the ellagitannins vescalagin and vescalin, the flavanoids catechin, epicatechin, epigallocatechin gallate (EGCG), and procyanidin B2, and the stilbenoids resveratrol and piceatannol, were chemically modified to bear a biotin unit for enabling their immobilization on streptavidin-coated sensor chips. These sensor chips were used to evaluate in real time by surface plasmon resonance (SPR) the interactions of three different surface-bound polyphenolic ligands per sensor chip with various protein analytes, including human DNA topoisomerase IIα, flavonoid leucoanthocyanidin dioxygenase, B-cell lymphoma 2 apoptosis regulator protein, and bovine serum albumin. The types and levels of SPR responses unveiled major differences in the association, or lack thereof, and dissociation between a given protein analyte and different polyphenolic ligands. Thus, this multi-analysis SPR technique is a valuable methodology to rapidly screen and qualitatively compare various polyphenol-protein interactions.

Counter-Current Fractionation-Assisted Bioassay-Guided Separation of Active Compound from Blueberry and the Interaction between the Active Compound and α-Glucosidase

An efficient strategy for the selection of active compounds from blueberry based on counter-current fractionation and bioassay-guided separation was established in this study. Blueberry extract showed potential α-glucosidase inhibitory activity. After extraction by different solvents, the active components were enriched in water. The water extract was divided into six fractions via high-speed counter-current chromatography to further track the active components. Results indicated that the α-glucosidase inhibition rate of F4 was remarkable higher than the others. Cyanidin-3-glucoside (C3G) with a purity of 94.16% was successfully separated from F4 through column chromatography, and its structure was identified by ultraviolet spectral, Fourier-transformed infrared spectroscopy, high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry, ¹H nuclear magnetic resonance (NMR), and ¹³C NMR. The interaction mechanism between C3G and α-glucosidase was clearly characterized and described by spectroscopic methods, including fluorescence and circular dichroism (CD) in combination with molecular docking techniques. C3G could spontaneously bind with α-glucosidase to form complexes by hydrogen bonds. The secondary structure of α-glucosidase changed in varying degrees after complexation with C3G. The α-helical and β-turn contents of α-glucosidase decreased, whereas the β-sheet content and the irregular coil structures increased. Molecular docking speculated that C3G could form hydrogen bonds with α-glucosidase by binding to the active sit (Leu 313, Ser 157, Tyr 158, Phe 314, Arg 315, and two Asp 307). These findings may be useful for the development of functional foods to tackle type 2 diabetes.

Catechin gallate acts as a key metabolite induced by trypsin in Hylocereus undatus during storage indicated by omics

Trypsin is a novel superoxide scavenger. The storage quality of H. undatus was significantly improved by trypsin. To investigate the mechanism of flavonoid metabolism regulated by trypsin, combined analysis of widely targeted metabolomic and transcriptome were performed. GO and KEGG enrichment analyses of the transcriptome profiles of H. undatus revealed that some of the flavonoid related biosynthesis pathways were regulated by up or down patterns with the treatment of trypsin. Correlation analysis of flavonoid related genes expression in H. undatus provided a rationale for the functional significance of them. Furthermore, it has been revealed that the most significantly regulated flavonoid was catechin gallate in metabolomic profiles of H. undatus. The major route of flavonoid biosynthesis regulated by trypsin was also illustrated by both transcriptomic and metabolomic data. Finally, the results of PPI network revealed that C4H, HCT, and CYP75B1 acted as hub proteins involved in flavonoid metabolism regulated by trypsin.

Hub genes and sub-networks of stoma-related genes in Hylocereus undatus through trypsin treatment during storage revealed by transcriptomic analysis

To further investigate the preservation mechanisms of trypsin, the synergistic mechanisms of trypsin and stoma-related genes were evaluated in Hylocereus undatus. Trypsin significantly induced the stoma closure and improved the storage quality of H. undatus. Transcriptomic analyses of H. undatus revealed that important antioxidant signal pathway, such as SREBP signaling pathway, cellular response to H₂ O₂ or cellular response to molecule of bacterial origin, were induced; while responses to water deprivation were impeded by trypsin. These results indicated that trypsin relieved pitaya of pressure of water deprivation and exhibited the protection on pitaya during storage. Furthermore, the analyses of networks of protein-protein interaction suggested that OST1, HK5, AT4G27585, and HIR1 act as hubs of stoma-related proteins induced by trypsin during storage of H. undatus. PRACTICAL APPLICATIONS: Preservation of fruit is becoming increasingly important to the world. Keep the balance of production and scavenging of reactive oxygen species is efficient to improve the storage quality of fruit. Trypsin had a novel superoxide anion scavenging activity and protect fruit cells from cellular injury induced by excess ROS. This article investigates the hub genes and interaction mechanisms of stoma closure induced by trypsin during the storage of H. undatus. The application of trypsin provides a new strategy for the quality control of fruit storage. Trypsin will have a broad market and development potential in the area of food additives.

Comparative studies on the interaction of nine flavonoids with trypsin

In this study, the interaction between nine classic flavonoids (including baicalin, quercetin, myricetin, rutin, puerarin, daidzein, liquiritin and isoliquiritin) and trypsin was investigated by fluorescence spectroscopy and molecular modeling methods. The results reveal that all flavonoids can interact with trypsin to form flavonoid-trypsin complexes. The binding parameters obtained from the data at different temperatures indicate that all flavonoids can spontaneously bind with trypsin with one binding site. The binding constants of trypsin with nine classic flavonoids are in the following order as: baicalin > myricetin > rutin > isoliquiritin > hesperidin > puerarin > quercetin > daidzein > liquiritin. The interaction forces between flavonoids and trypsin may be electrostatic forces (except for rutin/puerarin/daidzein), hydrophobic interactions as well as van der Waals forces. Synchronous fluorescence spectroscopy shows that the interaction between flavonoids and trypsin changes the hydrophobicity of the microenvironment of tryptophan (Trp) residues. All flavonoids close to tyrosine (Tyr) residues but have no effect on the microenvironment around Tyr residues except for hesperidin and liquiritin. Molecular modeling displays that all flavonoids bind directly into trypsin cavity site and lead to a decrease in enzyme activity.

Transcriptomic analysis reveals hub genes and subnetworks related to ROS metabolism in Hylocereus undatus through novel superoxide scavenger trypsin treatment during storage

BACKGROUND

It was demonstrated in our previous research that trypsin scavenges superoxide anions. In this study, the mechanisms of storage quality improvement by trypsin were evaluated in H. undatus.

RESULTS

Trypsin significantly delayed the weight loss and decreased the levels of ROS and membrane lipid peroxidation. Transcriptome profiles of H. undatus treated with trypsin revealed the pathways and regulatory mechanisms of ROS genes that were up- or downregulated following trypsin treatment by gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) enrichment analyses. The current results showed that through the regulation of the expression of hub redox enzymes, especially thioredoxin-related proteins, trypsin can maintain low levels of endogenous active oxygen species, reduce malondialdehyde content and delay fruit aging. In addition, the results of protein-protein interaction networks suggested that the downregulated NAD(P) H and lignin pathways might be the key regulatory mechanisms governed by trypsin.

CONCLUSIONS

Trypsin significantly prolonged the storage life of H. undatus through regulatory on the endogenous ROS metabolism. As a new biopreservative, trypsin is highly efficient, safe and economical. Therefore, trypsin possesses technical feasibility for the quality control of fruit storage.

Transcriptomic Analysis Reveals Cu/Zn SODs Acting as Hub Genes of SODs in Hylocereus undatus Induced by Trypsin during Storage

It has been revealed by us that superoxide scavenging is a new activity of trypsin. In this study, the synergistic mechanisms of trypsin and superoxide dismutases (SODs) were evaluated in Hylocereus undatus (pitaya). Trypsin significantly improved the storage quality of H. undatus, including weight loss impediment and decrease of cellular injury. The regulatory mechanisms of 16 SOD genes by trypsin were revealed using transcriptomic analysis on H. undatus. Results revealed that important physiological metabolisms, such as antioxidant activities or metal ion transport were induced, and defense responses were inhibited by trypsin. Furthermore, the results of protein–protein interaction (PPI) networks showed that besides the entire ROS network, the tiny SODs sub-network was also a scale-free network. Cu/Zn SODs acted as the hub that SODs synergized with trypsin during the storage of H. undatus.

Transcriptomic analysis reveals key genes related to antioxidant mechanisms of Hylocereus undatus quality improvement by trypsin during storage

The synergistic effect of trypsin with antioxidant enzymes can improve the storage quality of H. undatus. Transcriptomic analysis and PPI network indicated that CAT is the key one among the enzymes of the complicated antioxidant system.

Green Tea Polyphenols Mitigate Gliadin-Mediated Inflammation and Permeability in Vitro

SCOPE

Green tea, a polyphenol-rich beverage, has been reported to mitigate a number of inflammatory and hypersensitivity disorders in laboratory models, and has been shown to moderate pathways related to food allergies in vitro. The present study investigates the impact of decaffeinated green tea extract (GTE) on the digestion of gliadin protein in vitro and the effect of physical interactions with GTE on the ability of gliadin to stimulate celiac disease-related symptoms in vitro.

METHODS AND RESULTS

Complexation of GTE and gliadin in vitro is confirmed by monitoring increases in turbidity upon titration of GTE into a gliadin solution. This phenomenon is also observed during in vitro digestion when gliadin is exposed to the digestive proteases pepsin and trypsin. SDS-PAGE and enzymatic assays reveal that GTE inhibits digestive protease activity and gliadin digestion. In differentiated Caco-2 cell monolayers as a model of the small intestinal epithelium, complexation of gliadin with GTE reduces gliadin-stimulated monolayer permeability and the release of interleukin (IL)-6 and IL-8.

CONCLUSION

There are potential beneficial effects of GTE as an adjuvant therapy for celiac disease through direct interaction between gliadin proteins and green tea polyphenols.

Trypsin Binding with Copper Ions Scavenges Superoxide: Molecular Dynamics-Based Mechanism Investigation

Trypsin is a serine protease, which has been proved to be a novel superoxide scavenger. The burst of superoxide induced by polychlorinated biphenyls can be impeded by trypsin in both wild type and sod knockout mutants of Escherichia coli. The experimental results demonstrated that the activities of superoxide scavenging of trypsin were significantly accelerated by Cu ions. Also, with the addition of Cu ions, a new β-sheet (β7) transited from a random coil in the Cu(II)-trypsin (TP) system, which was favorable for the formation of more contacts with other sheets of trypsin. Residue–residue network analysis and the porcupine plots proved that the Cu ion in trypsin strengthened some native interactions among residues, which ultimately resulted in much greater stability of the Cu(II)-TP system. Moreover, compact and stable trypsin structures with Cu ions might be responsible for significantly provoking the activity of superoxide scavenging.

The Role of Dietary Phenolic Compounds in Protein Digestion and Processing Technologies to Improve Their Antinutritive Properties

Digestion is the key step for delivering nutrients and bioactive substances to the body. The way different food components interact with each other and with digestive enzymes can modify the digestion process and affect human health. Understanding how food components interact during digestion is essential for the rational design of functional food products. Plant polyphenols have gained much attention for the bioactive roles they play in the human body. However, their strong beneficial effects on human health have also been associated with a negative impact on the digestion process. Due to the generally low absorption of phenolic compounds after food intake, most of the consumed polyphenols remain in the gastrointestinal tract, where they then can exert inhibitory effects on enzymes involved in the degradation of saccharides, lipids, and proteins. While the inhibitory effects of phenolics on the digestion of energy-rich food components (saccharides and lipids) may be regarded as beneficial, primarily in weight-control diets, their inhibitory effects on the digestion of proteins are not desirable for the reason of reduced utilization of amino acids. The effect of polyphenols on protein digestion is reviewed in this article, with an emphasis on food processing methods to improve the antinutritive properties of polyphenols.

Polyphenolic Compounds and Digestive Enzymes: In Vitro Non-Covalent Interactions

The digestive enzymes–polyphenolic compounds (PCs) interactions behind the inhibition of these enzymes have not been completely studied. The existing studies have mainly analyzed polyphenolic extracts and reported inhibition percentages of catalytic activities determined by UV-Vis spectroscopy techniques. Recently, pure PCs and new methods such as isothermal titration calorimetry and circular dichroism have been applied to describe these interactions. The present review focuses on PCs structural characteristics behind the inhibition of digestive enzymes, and progress of the used methods. Some characteristics such as molecular weight, number and position of substitution, and glycosylation of flavonoids seem to be related to the inhibitory effect of PCs; also, this effect seems to be different for carbohydrate-hydrolyzing enzymes and proteases. The digestive enzyme–PCs molecular interactions have shown that non-covalent binding, mostly by van der Waals forces, hydrogen binding, hydrophobic binding, and other electrostatic forces regulate them. These interactions were mainly associated to non-competitive type inhibitions of the enzymatic activities. The present review emphasizes on the digestive enzymes such as α-glycosidase (AG), α-amylase (PA), lipase (PL), pepsin (PE), trypsin (TP), and chymotrypsin (CT). Existing studies conducted in vitro allow one to elucidate the characteristics of the structure–function relationships, where differences between the structures of PCs might be the reason for different in vivo effects.

Interaction of phenolic acids with trypsin: Experimental and molecular modeling studies

Trypsin is a kind of protease for digestion and food processing, whose activity can be inhibited by phenolic acids in plant foods. However, most reports explained the inhibitory difference of phenolic acids based on the number and position of substituent groups, which failed to reveal the comprehensive inhibitory mechanism. In this work, the inhibitory effects of 11 common phenolic acids on trypsin were investigated. Amongst the tested cinnamic and benzoic acid derivatives, caffeic acid and gallic acid showed the strongest anti-trypsin activity with a noncompetitive inhibition pattern, respectively. The fluorescence analysis displayed that both the quenching rate constant (K_q) and binding constant (K_A) of caffeic acid were higher than those of gallic acid. Molecular docking illustrated their different binding modes with trypsin. The ONIOM calculations revealed that the binding capacity of caffeic acid was higher than that of gallic acid, which could explain their difference in their inhibitory behaviors.

Effects of bisphenol S on the structures and activities of trypsin and pepsin

The effects of bisphenol S on the structures and activities of trypsin and pepsin were investigated by various methods like UV-visible absorbance, fluorescence, circular dichroism, and molecular docking. The secondary and tertiary structures of trypsin and pepsin were altered by bisphenol S binding, which resulted in the loosening of the skeletons of trypsin and pepsin. In addition, bisphenol S induced microenvironmental changes around tyrosine and tryptophan residues of trypsin and pepsin. The activity experimental results showed that the activity of pepsin decreases obviously with the increasing concentration of BPS, while the activity of trypsin does not change remarkably. The binding and thermodynamic parameters obtained by molecular docking and fluorescence spectroscopy showed that the bindings of bisphenol S to trypsin and pepsin were spontaneous processes and hydrogen bonding and hydrophobic interactions played a vital role in stabilizing the bisphenol S-trypsin and bisphenol S-pepsin complexes. The binding constants (K(A)) of bisphenol S with trypsin were 7.42 × 10(4) (298 K) and 5.91 × 10(4) L/mol (310 K), and those of pepsin were 5.78 × 10(4) (298 K) and 4.44 × 10(4) L/mol (310 K). Moreover, there was one main kind of binding site for bisphenol S on trypsin or pepsin.