Antioxidant properties of ferulic acid dimers

A wide array of lignin-related phenolics are oxidized by an evolved bacterial dye-decolourising peroxidase

Lignin is the second most abundant natural polymer next to cellulose and by far the largest renewable source of aromatic compounds on the planet. Dye-decolourising peroxidases (DyPs) are biocatalysts with immense potential in lignocellulose biorefineries to valorize emerging lignin building blocks for environmentally friendly chemicals and materials. This work investigates the catalytic potential of the engineered PpDyP variant 6E10 for the oxidation of 24 syringyl, guaiacyl and hydroxybenzene lignin-phenolic derivatives. Variant 6E10 exhibited up to 100-fold higher oxidation rates at pH 8 for all the tested phenolic substrates compared to the wild-type enzyme and other acidic DyPs described in the literature. The main products of reactions were dimeric isomers with molecular weights of (2 × MWsubstrate - 2 H). Their structure depends on the substitution pattern of the aromatic ring of substrates, i.e., of the coupling possibilities of the primarily formed radicals upon enzymatic oxidation. Among the dimers identified were syringaresinol, divanillin and diapocynin, important sources of structural scaffolds exploitable in medicinal chemistry, food additives and polymers.

Thermal-assisted synthesis of ferulic acid-chitosan complex in water and its application as safe antioxidant

Safe antioxidants are highly demanded in food preservation, yet existing preparation methods of typical bio-based antioxidants all suffer from either toxic catalysts or poor water solubility of the products. Herein, a water-soluble safe antioxidant, ferulic acid-chitosan complex, was facilely prepared in water with the assistance of mild-temperature heating. The chemical structure of ferulic acid-chitosan complex was determined by spectroscopy, and its thermal stability and rheological properties were studied in detail. Different from its precursors, the ferulic acid-chitosan complex exhibits much improved water solubility, thanks to its ionic structure. The as-prepared chitosan-ferulic acid complex displays higher antioxidative property than free ferulic acid, which was illustrated by the good preservation of freshly prepared apple juice. Such thermal-assisted synthesis strategy is demonstrated as an effective approach to prepare hydrophilic chitosan complex bearing hydrophobic organic acid, which enables great feasibility to the development of chitosan-based functional biomaterials.

Characterization of brewer's spent grain extracts by tandem mass spectrometry and HPLC‐DAD : Ferulic acid dehydrodimers, phenolamides, and oxylipins

Brewer's spent grain (BSG) is a major by-product of the brewing industry which is generated in high amounts. In recent years, sustainable food production has become more and more important. BSG mainly used as cattle feed has gained high interest due to not only its valuable ingredients such as fiber and proteins but also secondary metabolites remaining in BSG after the brewing process and known for many biological effects. In the present study, various methods were applied, such as acetone extraction (A), alkaline hydrolysis followed by ethyl acetate extraction (HE), and acetone extraction of alkaline hydrolysis residue (HA). Compounds present in the respective bioactive extracts were characterized by mass spectrometry to identify the active compounds. Various hydroxycinnamic acid derivatives as well as oxylipins and some dicarboxylic acids, such as azelaic acid, were present in HE and HA extracts. In contrast, some catechins and phenolamides, such as numerous hordatines, as well as oxylipins and phospholipids were detected in A extracts. Quantification using HPLC-DAD revealed hordatine contents up to 172.2 ± 2.1 μg p-coumaric acid equivalents/mg extract. Hydroxycinnamic acid derivatives content accounted for up to 48% of the total extract (HE extracts) but only around 3% of the total HA extracts. In summary, all extracts contained secondary plant metabolites belonging to different classes, ranging from hydroxycinnamic acids to phenolamides, such as not only hordatines but also oxylipins, which were identified for the first time in BSG.

Anticholinesterase Activities of Different Solvent Extracts of Brewer's Spent Grain

Cholinesterases, involved in acetylcholine catabolism in the central and peripheral nervous system, have been strongly linked with neurodegenerative diseases. Current therapeutic approaches using synthetic drugs present several side effects. Hence, there is an increasing research interest in naturally-occurring dietary polyphenols, which are also considered efficacious. Food processing by-products such as brewer’s spent grain (BSG) would be a potential bio-source of polyphenols. In this study, polyphenol-rich BSG extracts using 60% acetone and 0.75% NaOH solutions were generated, which were further subjected to liquid–liquid partitioning using various organic solvents. The water-partitioned fractions of the saponified extracts had the highest total polyphenol content (6.2 ± 2.8 mgGAE/g dw) as determined by Folin–Ciocalteu reagent, while the LC-MS/MS showed ethyl acetate fraction with the highest phenolics (2.9 ± 0.3 mg/g BSG dw). The best inhibitions of acetyl- (37.9 ± 2.9%) and butyryl- (53.6 ± 7.7%) cholinesterases were shown by the diethyl ether fraction of the saponified extract. This fraction contained the highest sum of quantified phenolics (99 ± 21.2 µg/mg of extract), and with significant (p < 0.01) inhibitory contribution of decarboxylated-diferulic acid. Amongst the standards, caffeic acid presented the highest inhibition for both cholinesterases, 25.5 ± 0.2% for acetyl- and 52.3 ± 0.8% for butyryl-cholinesterase, respectively, whilst the blends insignificantly inhibited both cholinesterases. The results showed that polyphenol-rich BSG fractions have potentials as natural anti-cholinesterase agents.

Methyl divanillate: redox properties and binding affinity with albumin of an antioxidant and potential NADPH oxidase inhibitor

Vanillic acid is a widely used food additive (flavouring agent, JECFA number: 959) with many reported beneficial biological effects. The same is true for its ester derivative (methyl vanillate, JECFA number: 159). Based on the increasing evidence that diapocynin, the dimer of apocynin (NADPH oxidase inhibitor), has some improved pharmacological properties compared to its monomer, here the dimer of methyl vanillate (MV), i.e., methyl divanillate (dimer of methyl vanillate, DMV) was synthesized and studied in the context of its redox properties and binding affinity with human serum albumin (HSA). We found that the antioxidant potency of DMV was significantly increased compared to MV. In this regard, the reduction of 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical by DMV was 30-fold more effective compared to MV. Ferric ion reduction was 4-fold higher and peroxyl radical reduction was 2.7-fold higher. The interaction with HSA was significantly improved (Stern–Vomer constants, 3.8 × 10⁵ mol⁻¹ L and 2.3 × 10⁴ mol⁻¹ L, for DMV and MV, respectively). The complexation between DMV and HSA was also evidenced by induced circular dichroism (ICD) signal generation in the former due to its fixation in the asymmetric protein pocket. Density-functional calculations (TD-DFT) showed that the ICD spectrum was related to a DMV conformation bearing a dihedral angle of approximately −60°. Similar dihedral angles were obtained in the lowest and most populated DMV cluster poses obtained by molecular docking simulations. The computational studies and experimental displacement studies revealed that DMV binds preferentially at site I. In conclusion, besides being a powerful antioxidant, DMV is also a strong ligand of HSA. This is the first study on the chemical and biophysical properties of DMV, a compound with potential beneficial biological effects.

Methyl divanillate, a derivative of the vanillic acid (flavouring agent, JECFA number: 959) with promising beneficial biological effects.

The structure-antioxidant activity relationship of dehydrodiferulates

In this study, 11 dehydrodiferulic acids (DFAs) and 8 diethyl dehydrodiferulates (DEFs) were synthesized and evaluated by Trolox equivalent antioxidant capacity (TEAC) and 2,2'-diphenyl-1-picrylhydrazyl (DPPH) assays for their antioxidant properties to understand the Structure-Antioxidant Activity Relationship (SAR) of these dehydrodiferulates. In both assays, the order of antioxidant activity for all tested ferulic acid dimers were consistent except for 3-(4-Hydroxy-3-methoxy-benzylidene)-5-(4-hydroxy-3-methoxy-phenyl)-3H-furan-2-one (2, 8-8-lactone DC DFA, not occurred naturally) being the best antioxidant by TEAC test. The order of antioxidant activity of diferulic acid ethyl esters, evaluated by both assays, was not consistent; however, TEAC and DPPH assays provided consistent results for certain set of ethyl diferulates. In this study most of dimeric ferulates, with three exceptions, showed higher radical-scavenging efficacy than the monomers. Comparing the antioxidant activities of the tested diferulates suggested that the phenolic hydroxyl group, electron donating methoxyl group, and stable conjugated transient structures dictate the antioxidant activity of diferulates.

Antioxidant activity-guided fractionation of blue wheat (UC66049 Triticum aestivum L.)

Antioxidant activity-guided fractionation based on three in vitro antioxidant assays (Folin-Ciocalteu, TEAC, and leucomethylene blue assays) was used to identify major antioxidants in blue wheat (UC66049 Triticum aestivum L.). After consecutive extractions with solvents of various polarities and multiple chromatographic fractionations, several potent antioxidants were identified by NMR spectroscopy and mass spectrometry. Anthocyanins (delphinidin-3-glucoside, delphinidin-3-rutinoside, cyanidin-3-glucoside, and cyanidin-3-rutinoside), tryptophan, and a novel phenolic trisaccharide (β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl-(1→6)-(4-hydroxy-3-methoxyphenyl)-β-D-glucopyranoside) were the most active water-extractable constituents. However, anthocyanins were found to be major contributors to the overall blue wheat antioxidant activity only when the extraction steps were performed under acidic conditions. Alkylresorcinols were among the most active antioxidants extractable with 80% ethanol in the TEAC assay. However, this may be due to a color change instead of a bleaching of the ABTS radical. Ferulic acid was found to be the major antioxidant in alkaline cell-wall hydrolysates. The contents of the most active antioxidants were determined.

Novel effects of a single administration of ferulic acid on the regulation of blood pressure and the hepatic lipid metabolic profile in stroke-prone spontaneously hypertensive rats

We studied the effects of a single oral administration of ferulic acid (FA) on the blood pressure (BP) and lipid profile in stroke-prone spontaneously hypertensive rats (SHRSP). Male 12-week-old SHRSP were administered FA (9.5 mg/kg of body weight) and distilled water as the control (C) (1 mL) via a gastric tube. The hypotensive effect of FA was observed at the lowest value after 2 h administration. A decrease in the angiotensin-1-converting enzyme (ACE) activity in the plasma corresponded well with the reduction of BP. Plasma total cholesterol and triglyceride levels were lower after 2 h administration. The mRNA expression of genes involved in lipid and drug metabolism was downregulated in the FA group. These results suggest that oral administration of FA appears beneficial in improving hypertension and hyperlipidemia.

Phenolics in cereals, fruits and vegetables: Occurrence, extraction and analysis

Consumption of plant foods, particularly fruits, vegetables and cereal grains is encouraged because they render beneficial health effects. Phenolics and polyphenolics are among the most desirable food bioactives because of their antioxidant activity, brought about by a number of pathways, or due to other mechanisms. The analysis of phenolics and polyphenolics requires their extraction possible purification and structure elucidation. This overview provides a cursory account of the source, extraction and analysis of phenolics in fruits, vegetables and cereals.

Antioxidant and antigenotoxic effects of plant cell wall hydroxycinnamic acids in cultured HT-29 cells

We demonstrate that two hydroxycinnamic acids, (E )-ferulic acid and (E )-p-coumaric acid, have the ability to protect against oxidative stress and genotoxicity in cultured mammalian cells. They also show the ability to reduce the activity of the xenobiotic metabolising enzyme, cytochrome P450 1A, and downregulate the expression of the cyclooxygenase-2 enzyme. At equitoxic doses, their activities are equal to or superior to that of the known anticarcinogen, curcumin. The hydroxycinnamic acids are both important components of plant cell walls in certain plant foods. It is known that the action of microbial hydroxycinnamoyl esterases can lead to the release of hydroxycinnamic acids from ester-linkages to cell wall polysaccharides into the human colon. Thus, providing they can reach effective levels in the colon, they could provide an important mechanism by which dietary fibres of food plants, such as spinach or cereal, protect against colon cancer.

Photo-irradiated curcumin supplementation in streptozotocin-induced diabetic rats: effect on lipid peroxidation

BACKGROUND

Diabetes mellitus is one of the most common endocrine disorders. A large number of studies are in progress to identify natural substances that are effective in reducing the severity of diabetes. Although a number of drugs are currently marketed, their long-term use can cause a number of adverse effects.

MATERIALS AND METHODS

In the present study, we examined the effect of photo-irradiated curcumin on experimental diabetes in order to evaluate the antihyperglycaemic effects of this compound on streptozotocin (40 mg/kg bodyweight)-induced diabetes. Photo-irradiated curcumin was given at a dose of 10, 30 and 80 mg/kg bodyweight. The level of blood glucose was elevated in the diabetic animals. The liver, kidney and brain were assayed for the degree of lipid peroxidation, reduced glutathione content and the activity of enzymic and levels of non-enzymic antioxidants.

RESULTS

Antioxidant status decreased in the diabetic animals. Oral administration of photo-irradiated curcumin for 45 days resulted in a significant decrease in the levels of blood glucose, together with near normalisation of enzymic activity and the markers of lipid peroxidation. The best results were obtained in rats treated with 30 mg/kg bodyweight of photo-irradiated curcumin.

The bioavailability of ferulic acid is governed primarily by the food matrix rather than its metabolism in intestine and liver in rats

The physiologic importance of ferulic acid (FA), and notably its antioxidant properties, depends upon its availability for absorption and subsequent interaction with target tissues. Because FA is widely present in cereals, the aim of the present study was to investigate its intestinal and hepatic metabolism in rats by in situ intestinal perfusion model (from 10 to 50 nmol/min), and its bioavailability in supplemented diets (from 10 to 250 micromol/d) or in a complex cereal matrix, i.e., whole flours from Valoris (Triticum aestivum) or Duriac (T. durum) cultivars and bran or white flour from the Valoris cultivar. In perfused rat intestine, net FA absorption was proportional to the perfused dose (R2 = 0.997); once absorbed, FA was completely recovered as conjugated forms in plasma and bile secretion (representing 5-7% of the perfused dose). In rats fed FA-enriched semipurified diets, FA absorption was quite efficient because approximately 50% of the ingested dose was recovered in urine. This extensive elimination by kidneys limited FA accumulation in plasma (typically 1 micromol/L in rats fed 50 micromol FA/d). In contrast, in rats fed cereal diets providing 56-81 micromol FA/d, urine excretion was 90-95% lower than in rats fed FA-enriched semipurified diets, and plasma concentrations were approximately 0.2-0.3 micromol/L. Thus, the cereal matrix appears to severely limit FA bioavailability. This inherently low bioavailability of FA in cereals likely reflects FA association with the fiber fraction through cross-linking with arabinoxylans and lignins.

Intestinal release and uptake of phenolic antioxidant diferulic acids

Diferulic acids are potent antioxidants and are abundant structural components of plant cell walls, especially in cereal brans. As such, they are part of many human and animal diets and may contribute to the beneficial effect of cereal brans on health. However, these phenolics are ester-linked to cell wall polysaccharides and cannot be absorbed in this form. This study provides the first evidence that diferulic acids can be absorbed via the gastrointestinal tract. The 5-5-, 8-O-4-, and 8-5-diferulic acids were identified in the plasma of rats after oral dosing with a mixture of the three acids in oil. Our study also reveals that human and rat colonic microflora contain esterase activity able to release 5-5-, 8-O-4-, and 8-5-diferulic acids from model compounds and dietary cereal brans, hence providing a mechanism for release of dietary diferulates prior to absorption of the free acids. In addition, cell-free extracts from human and rat small intestine mucosa exhibited esterase activity towards diferulate esters. Hence, we have shown that esterified diferulates can be released from cereal brans by intestinal enzymes, and that free diferulic acids can be absorbed and enter the circulatory system. Our results suggest that the phenolic antioxidant diferulic acids are bioavailable.

Initial steps of ferulic acid polymerization by lignin peroxidase

The major products of the initial steps of ferulic acid polymerization by lignin peroxidase included three dehydrodimers resulting from beta-5' and beta-beta'coupling and two trimers resulting from the addition of ferulic acid moieties to decarboxylated derivatives of beta-O-4'- and beta-5'-coupled dehydrodimers. This is the first time that trimers have been identified from peroxidase-catalyzed oxidation of ferulic acid, and their formation appears to be favored by decarboxylation of dehydrodimer intermediates. After initial oxidation, the coupling reactions appear to be determined by the chemistry of ferulic acid phenoxy radicals, regardless of the enzyme and of whether the reaction is performed in vitro or in vivo. This claim is supported by our finding that horseradish peroxidase provides a similar product profile. Furthermore, two of the dehydrodimers were the two products obtained from laccase-catalyzed oxidation (Tatsumi, K. S., Freyer, A., Minard, R. D., and Bollag, J.-M. (1994) Environ. Sci. Technol. 28, 210-215), and the most abundant dehydrodimer is the most prominent in grass cell walls (Ralph, J., Quideau, S., Grabber, J. H., and Hatfield, R. D. (1994) J. Chem. Soc. Perkin Trans. 1, 3485-3498). Our results also indicate that the dehydrodimers and trimers are further oxidized by lignin peroxidase, suggesting that they are only intermediates in the polymerization of ferulic acid. The extent of polymerization appears to be dependent on the ionization potential of formed intermediates, H(2)O(2) concentration, and, probably, enzyme stability.

A cinnamoyl esterase from Aspergillus niger can break plant cell wall cross-links without release of free diferulic acids

A cinnamoyl esterase, ferulic acid esterase A, from Aspergillus niger releases ferulic acid and 5-5- and 8-O-4-dehydrodiferulic acids from plant cell walls. The breakage of one or both ester bonds from dehydrodimer cross-links between plant cell wall polymers is essential for optimal action of carbohydrases on these substrates, but it is not known if cinnamoyl esterases can break these cross-links by cleaving one of the ester linkages which would not release the free dimer. It is difficult to determine the mechanism of the reaction on complex substrates, and so we have examined the catalytic properties of ferulic acid esterase A from Aspergillus niger using a range of synthetic ethyl esterified dehydrodimers (5-5-, 8-5-benzofuran and 8-O-4-) and two 5-5-diferulate oligosaccharides. Our results show that the esterase is able to cleave the three major dehydrodiferulate cross-links present in plant cell walls. The enzyme is highly specific at hydrolysing the 5-5- and the 8-5-benzofuran diferulates but the 8-O-4-is a poorer substrate. The hydrolysis of dehydrodiferulates to free acids occurs in two discrete steps, one involving dissociation of a monoesterified intermediate which is negatively charged at the pH of the reaction. Although ferulic acid esterase A was able to release monoesters as products of reactions with all three forms of diesters, only the 5-5- and the 8-O-4-monoesters were substrates for the enzyme, forming the corresponding free diferulic acids. The esterase cannot hydrolyse the second ester bond from the 8-5-benzofuran monoester and therefore, ferulic acid esterase A does not form 8-5-benzofuran diferulic acid. Therefore, ferulic acid esterase A from Aspergillus niger contributes to total plant cell wall degradation by cleaving at least one ester bond from the diferulate cross-links that exist between wall polymers but does not always release the free acid product.

Ferulic acid dehydrodimers from wheat bran: isolation, purification and antioxidant properties of 8-O-4-diferulic acid

Wheat bran contains several ester-linked dehydrodimers of ferulic acid, which were detected and quantified after sequential alkaline hydrolysis. The major dimers released were: trans-5-[(E)-2-carboxyvinyl]-2-(4-hydroxy-3-methoxy-phenyl)-7-methoxy-2, 3- dihydrobenzofuran-3-carboxylic acid (5-8-BendiFA), (Z)-beta-[4-[(E)-2-carboxyvinyl]-2-methoxyphenoxy]-4-hydroxy-3-methox ycinnamic acid (8-O-4-diFA) and (E,E)-4,4'-dihydroxy-5,5'-dimethoxy-3,3'-bicinnamic acid (5-5-diFA). trans-7-hydroxy-1-(4-hydroxy-3methoxyphenyl)-6-methoxy-1,2-dihydro - naphthalene-2,3-dicarboxylic acid (8-8-diFA cyclic form) and 4,4'-dihydroxy-3,3'-dimethoxy-beta,beta'-bicinnamic acid (8-8-diFA non cyclic form) were not detected. One of the most abundant dimers, 8-O-4-diFA, was purified from de-starched wheat bran after alkaline hydrolysis and preparative HPLC. The resultant product was identical to the chemically synthesised 8-O-4-dimer by TLC and HPLC as confirmed by 1H-NMR and mass spectrometry. The absorption maxima and absorption coefficients for the synthetic compound in ethanol were: lambda max: 323 nm, lambda min: 258 nm, epsilon lambda max (M-1 cm-1): 24,800 +/- 2100 and epsilon 280 (M-1 cm-1): 19,700 +/- 1100. The antioxidant properties of 8-O-4-diFA were assessed using: (a) inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine liposomes and; (b) scavenging of the radical cation of 2,2'-azinobis (3-ethyl-benzothiazoline-6-sulphonate) (ABTS) relative to the water-soluble vitamin E analogue, Trolox C. The 8-O-4-diFA was a better antioxidant than ferulic acid in both lipid and aqueous phases. This is the first report of the antioxidant activity of a natural diferulate obtained from a plant.