Stimulatory effects of tannins and cholic acid on tryptic hydrolysis of proteins: Ecological implications

The biochemical basis for considering tannins as digestion inhibitors has been reexamined. Both stimulatory and inhibitory effects of tannins on tryptic hydrolysis are reported. We show how stimulation may result from tannin-induced structural changes in the substrate protein, effectively denaturing it. The surfactant and bile constituent cholic acid also produced similar stimulatory effects. These results have considerable implications for normal digestive physiology as well as for the impact of tannins on argicultural and natural herbivore populations.     

Taste thresholds and suprathreshold responses to tannin-rich plant extracts and quinine in a primate species (Microcebus murinus)

Theories of plant chemical defenses discriminate between quantitative digestibility reducers (e.g., tannins) and qualitative toxins (e.g., alkaloids). Since the differential effect on taste of these compounds is poorly known, we recorded ingestive responses of a primate species, Microcebus murinus, to four tannin-rich plant extracts and to quinine, by using the behavioral method of the two-bottle test. The efficiency of tannic extracts at precipitating protein was measured with the blue BSA method. Inhibition taste thresholds for tannins added to a moderately sweet solution varied between 0.25 and 2 g/l. The threshold for quinine hydrochloride was 0.32 g/l. The profiles of the response/concentration curves established for these astringent and bitter substances were similar, with maximal inhibition of consumption occurring for near-threshold concentrations. The large amounts of quinine required to deter this small-bodied species from feeding were unexpected, given its unspecialized frugivorous/insectivorous diet. We propose that the taste responses of Microcebus to tannins have been shaped in relation to the widespread occurrence of efficient polyphenols in food plants, while low responsiveness to quinine reflects a low risk of ingesting toxic alkaloids when feeding on ripe fruits and insects.     

Obtaining phenolic compounds from jatoba (Hymenaea courbaril L.) bark by supercritical fluid extraction

The extraction of polyphenol compounds from jatoba (Hymenaea courbaril L. var stilbocarpa) bark using supercritical fluid extraction (SFE) with CO₂ and cosolvents has been investigated. Among the solvent systems studied, SFE using CO₂ and water (9:1, v/v), at 323 K and 35 MPa, presented the best results, with extract yield of 24%, and with high antioxidant activity (IC₅₀ of 0.2 mg/cm³). This solvent system was used to determine global yield isotherms, which were built at 323 and 333 K, and 15, 25, and 35 MPa, using a second lot of jatoba. The highest yield was 11.5% at 15 MPa and 323 K, with maximum total phenolic compounds (TPC) of 335.00 mg TAE/g extract (d.b.) and total tannins content of 1.8 g/100 g raw material. A kinetic experiment was performed using optimized conditions, yielding 18% extract, and the kinetic parameters were used to scale-up the process from laboratory to pilot scale. Chemical analyses showed high content of phenolic compounds in the extracts of jatoba bark mostly due to the presence of procyanidins.     

The efficacy of protective effects of tannic acid, gallic acid, ellagic acid, and propyl gallate against hydrogen peroxide-induced oxidative stress and DNA damages in IMR-90 cells

There is increasing evidence that reactive oxygen species (ROS) are intimately involved in the oxidative damage of tissues for a wide variety of pulmonary diseases. Thus, it is desirable to search for chemopreventive agents that can counteract ROS-mediated injury to the pulmonary tissues. Using a human lung fibroblast IMR-90 cells as the experimental model, we first demonstrated that nearly 90% of intracellular ROS could be removed when H(2)O(2)-treated cells (200 microM) simultaneously incubated with 10 microg/mL of tannic acid (TA), gallic acid (GA), ellagic acid (EA), and propyl gallate (PA). Using C(11)-BODIPY(581/591 )as a lipid peroxidation probe, we also attested that all these compounds examined (10 microg/mL) could alleviate H(2)O(2)-evoked lipid peroxidation phenomena. Next, we examined the protective effects of these compounds on the depletion of intracellular glutathione (iGSH) in H(2)O(2)-treated cells using CMF-DA probe. Interestingly, PA was demonstrated to be the only compound that could effectively protect the integrity of iGSH from being depleted by this system. Finally, the protective effects of these compounds against oxidative DNA damage were evaluated using 8-oxoguanine formation as a marker. Our data indicated that all four compounds suppressed the formation of 8-oxoguanine effectively. Taken together, our data suggested that TA, GA, EA, and PA can protect cells from oxidative stress.     

Content of polyphenolic constituents and antioxidant activity of some Stachys taxa

Seven Croatian Stachys taxa (S. alpina, S. officinalis, S. palustris, S. recta subsp. recta, S. recta subsp. subcrenata, S. salviifolia and S. sylvatica) have been investigated in order to determine their content of biologically active compounds (polyphenols, tannins, phenolic acids and flavonoids) as well as their antioxidant activity. All taxa tested had a high content of total polyphenols, medium content of total phenolic acids, and a rather low content of tannins and flavonoids. The total phenolic acids content correlated significantly with total polyphenols content and the content of polyphenols unadsorbed on hide powder. A low correlation between plant phenolic acids and tannins was observed. Methanolic, ethanolic and dichloromethane extracts were investigated using DPPH, lipid peroxidase and xanthine oxidase assays. The extracts showed no inhibitory effects against lipid peroxidation and xanthine oxidase, but they had the ability to scavenge DPPH. The most effective in the DPPH assay were methanolic extracts of S. recta sub. recta and S. palustris whose radical scavenging activity was higher then that of the reference rutin. A low correlation between radical scavenging capacities of extracts with total flavonoids content was observed. The results indicate that investigated Stachys taxa exhibit potent antiradical activity and therefore could be a potential material for extracting free radical scavengers.     

Use of antioxidants in extraction of tannins from walnut plants

The radial diffusion assay was applied to estimate the amount of total tannins in extracts from walnut plant materials. We found that the protein-precipitating activity of the tannin extracts were increased by 30–75 % when antioxidants (ascorbic acid or sodium metabisulfite, 5.5 mM) were added in extraction solvents (50% aqueous methanol). The extracts obtained with Na₂S₂O₅ were much less brown than control. Moreover, two-dimensional thin-layer chromatography revealed some additional polyphenolic compounds in the extracts made with Na₂S₂O₅. These results suggest that the amount of tannins and/or their protein-precipitating property may be strongly affected by oxidation events during extraction procedure. The addition of antioxidants in the extraction solvents is useful to limit this problem.     

Analysis of phenolic compounds including tannins,gallotannins and flavanols of Uapaca kirkiana fruit

Tannins and phenolic acids were extracted from Uapaca kirkiana unripe pulp, seed coat, peel and embryo, as well as from ripe pulp, seed coat, embryo and peel portions of the fruit. Extraction was done using 50% methanol. More tannins were detected in the embryos of both ripe and raw fruit. Both ripe and raw seed coat contained the least amounts of tannins. The flavanoids and gallotannins also followed the same trend, with most of them in the embryos of both, the ripe and raw, fruit portions whilst the least were found in the seed coat. Tannins were, however lost during sun-drying compared to oven-drying, even though the differences were not very large. Also, raw fruits showed high concentrations of tannins compared to the ripe fruits. Hydroxybenzoic acid was found in the peel and pulp but none was detected in the seed coat or in the embryo. Similar phenolic acids were detected in the seed coat, except for caffeic acid and protocatechuic acid, detected in the embryo by both the UV florescence and Folin spray.     

In‐vitro study on the efficacy of tannin fractions of edible nuts as antioxidants

Tannin fractions were isolated from crude acetonic extracts of defatted walnut, hazelnut and almond kernels using Sephadex LH‐20 column chromatography. The obtained material was characterized by content of total phenolics and electrophoretic separations using capillary zone electrophoresis (CZE). The antioxidant activities of the tannin fractions were analyzed by several methods: DPPH and ABTS assays, photochemiluminescence (PCL) method, as well as in two lipid model systems: emulsion with β‐carotene‐linoleic acid and L ‐α‐lecithin liposomes. The contents of total phenolics in the tannin fractions of walnuts, hazelnuts and almonds were 550, 329 and 83 mg catechin eq/g, respectively. The electrophoretic profiles of hazelnut and almond tannin fractions were similar, in contrast to the walnut profile. All analyzed fractions exhibited strong antioxidant properties. The antioxidant capacity of lipid‐soluble (ACL) compounds determined by PCL method was the highest for the fraction isolated from walnuts – 7.35 mmol Trolox eq/g. The DPPH radical and the ABTS radical cation were scavenged by the walnut tannin fraction with a higher efficacy than by the two other fractions. EC₅₀ values of the DPPH method were 1.8 times higher for the hazelnut fraction and 2.3 times higher for the almond fraction when compared to the walnut tannins. In turn, the total antioxidant activity values were 8.17, 2.82 and 1.98 mmol Trolox eq/g for the walnut, hazelnut and almond fractions, respectively. On the other hand, in both lipid models applied, lower antioxidant activity of walnut tannins than of hazelnut tannins was noted. The antioxidant effect of almond tannins was weaker or similar than that of walnut tannins in the β‐carotene‐linoleic acid emulsion and the L ‐α‐lecithin liposomal system, respectively.     

Antioxidant and cardioprotective activities of phenolic extracts from fruits of Chilean blackberry Aristotelia chilensis (Elaeocarpaceae), Maqui

The methanol extract from mature fruits of Aristotelia chilensis (Mol) Stuntz (Elaeocarpaceae) showed antioxidant activities and cardioprotective effects on acute ischemia/reperfusion performed in rat heart in vivo. This extract protected animals from heart damage by the incidence of reperfusion dysrythmias, and the no-recovery of sinus rhythm. On the other hand, the MeOH extract of the fruit was able to prevent these harmful events in the animal’s heart by diminishing lipid oxidation and reducing the concentration of thiobarbituric acid reactive substances (TBARS), a lipid peroxidation index. In addition, MeOH extract of A. chilensis was evaluated for DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging, crocin radical scavenging, oxygen radical absorption capacity (ORAC), ferric reducing antioxidant power (FRAP), an estimation of lipid peroxidation in liposomes through the inhibition of formation of TBARS. MeOH extract was found to have IC₅₀ of 1.62 ppm against DPPH and 2.51 ppm against TBARS, compared with the juice, whose IC₅₀ was 12.1 ppm and 9.58 ppm against DPPH and TBARS formation, respectively. Antioxidant activities of MeOH extract were strongly correlated with total polyphenol content. Consistent with this finding, MeOH had the greatest ORAC and FRAP values as percentage of activity. These results show that these fruits could be useful as antioxidant, cardioprotective and nutraceutical sources.     

Characterisation of Bobal and Crujidera grape cultivars,in comparison with Tempranillo and Cabernet Sauvignon: Evolution of leaf macronutrients and berry composition during grape ripening

We present characterisation data for two Spanish autochthonous grapevines, Bobal and Crujidera, in comparison with the well-known cultivars Tempranillo and Cabernet Sauvignon. Microsatellite markers were used for the molecular characterisation of Crujidera grapevines. Leaf macronutrient contents of the four cultivars were evaluated, as well as their changes at different vine developmental stages, and veraison was seen as the most suitable time to evaluate the nutritional status. Quantitative changes in some physiological parameters and the phenolic composition of the four grape varieties were measured during the last month of ripening. Polyphenols, tannins and anthocyanins increased with grape maturation, although the accumulation of these phenolic compounds and their patterns of evolution varied considerably with the cultivar. The biosynthetic potential of these grapes to produce resveratrol largely depended on the grape variety, with a remarkably high content found in Bobal berry skins.