Effect of drying conditions on tannin,fibre and lignin levels in mature oak (Quercus incana) leaves

Oak (Quercus incana Roxb) leaves are rich in tannins and produce adverse effects when fed to livestock. The effects of shade and sun drying and oven drying at 60°C and 90°C for different lengths of time (24 to 72 h) on total phenolics, condensed tannins, protein precipitation capacity, degree of polymerisation, specific activity (protein bound per unit tannins), fibre-linked proanthocyanidins, acid and neutral detergent fibres and lignin levels in mature oak leaves were studied. Removal/inactivation of tannins was not observed on wilting or drying under several conditions. Similarly the drying conditions had no effect on fibre composition. The adverse effects on feeding fresh or dried oak leaves are expected to be of similar magnitude.     

Changes in tannin content,polymerisation and protein precipitation capacity in oak (Quercus incana) leaves with maturity

Changes in the content of total phenolics, condensed tannins, proanthocyanidins and flavan-4-ols, the degree of polymerisation, the protein precipitation capacity, the protein-precipitable phenolic content and the specific activity (protein: tannin in the complex) were determined in Quercus incana leaves with maturity. Total phenolic content and protein precipitation capacity decreased whereas the levels of condensed tannins, proanthocyanidins, flavan-4-ols and degree of polymerisation increased with maturation. The protein-precipitable phenolic content was highest in young leaves and decreased as leaves matured. The specific activity decreased slightly. The results suggest that young leaves would be more toxic to livestock than mature leaves.     

Changes with maturity in fibre composition and levels of extractable polyphenols in Greek browse: Effects on in vitro gas production and in sacco dry matter degradation

Neutral and acid detergent fibre (NDF, ADF), lignin, crude protein (CP), total extractable phenols (TEPH), tannins (TETa), condensed tannins (vanillin assay TECTa; proanthocyanidins TEPAs) in the leaves of spring Phyllirea media (SPRG) or early summer (ESUM) and early autumn (EAUT) Carpinus duinensis, Quercus coccifera and Fraxinus ornus were studied. Gas production (in vitro) and dry matter (DM) degradation (in sacco) were also studied after incubation for up to 96 h. Concentrations of TEPH, TETa, TECTa, TEPAs and the fibre components were variable (P < 0·05) among species and except for CP were not consistently changed with degree of maturity. CP content varied from 70·5 to 132·9 (g kg^?1 DM) but was always decreased by 15–25% at maturity, whereas levels of TECTa and TEPAs were increased (P < 0·05) in C duinensis and Q coccifera but not in F ornus (P > 0·05). Concentrations of phenolics were related negatively but more significantly to gas production than to DM degradation (in sacco). Therefore, the gas test was considered to be more efficient than the nylon bag technique for the identification of feeds with antinutritive factors. Based on their phenolic content and gas production or DM degradation, the nutritive value of P media = F ornus (ESUM and EAUT) > C duinensis = Q coccifera (ESUM) > C duinensis = Q coccifera (EAUT). It was concluded that the decline in CP with maturity could make nitrogen the factor limiting intake and digestibility. This would be accentuated with an increase in the concentration of phenolics, particularly tannins.     

Nutrient content,in vitro ruminal fermentation characteristics and methane reduction potential of tropical tannin‐containing leaves

BACKGROUND: Plant tannins as rumen modifiers are better than chemicals or antibiotic‐based modifiers since these compounds are natural products which are environmentally friendly and therefore have a better acceptance with regard to feed safety issues. Tropical plants containing phenols such as tannins were found to suppress or eliminate protozoa from the rumen and reduce methane and ammonia production. The screening of these plants is an important step in the identification of new compounds and feed additives which might contribute to mitigate rumen methanogenesis. The present study was carried out to determine the efficacy of tannins from tropical tree leaves for their methane reduction properties. RESULTS: Activity of tannins, as represented by the increase in gas volume with the addition of polyethylene glycol (PEG)‐6000 as a tannin binder (tannin bioassay) was highest in Ficus bengalensis (555%), followed by Azardirachta indica (78.5%). PEG addition did not alter (P > 0.05) methane percentage in Ficus racemosa, Glyricidia maculata, Leucena leucocephala, Morus alba and Semaroba glauca, confirming that tannins in these samples did not affect methanogenesis. The increase (P < 0.05) in protozoa population with PEG was maximal in Ficus religiosa (50), followed by Moringa oleifera (31.2), Azardirachta indica (29.9) and Semaroba glauca (27.5). There was no change (P > 0.05) in the protozoa population in Autocarpus integrifolia, Ficus bengalensis, Jatropha curcus, Morus alba and Sesbania grandiflora, demonstrating that methane reduction observed in these samples per se was not due to defaunation effect of the tannin. The increase in total volatile fatty acid concentration in samples with PEG ranged from 0.6% to > 70%. The highest increase (%) in NH₃‐N was recorded in Azardirachta indica (67.4), followed by Ficus mysoriensis (35.7) and Semaroba glauca (32.6) leaves, reflecting strong protein binding properties of tannin. CONCLUSION: The results of our study established that in vitro methanogenesis was not essentially related to the density of protozoa population. Tropical tree leaves containing tannins such as Autocarpus integrifolia, Jatropha curcus and Sesbania grandiflora have the potential to suppress methanogenesis. Therefore tannins contained in these plants could be of interest in the development of new additives in ruminant nutrition. Copyright © 2012 Society of Chemical Industry     

Antioxidant activity and genotoxic effect on HeLa cells of phenolic compounds from infusions of Quercus resinosa leaves

Water infusions of mature and fresh Quercus resinosa leaves were evaluated for antioxidant activity and genotoxic effects on HeLa cells. Native Mexicans used to drink Q. resinosa leaves tea as a refreshing beverage. The air dried leaves were pulverised and boiled in water, then their phenolic content and condensed tannins were determined. The chromatographic profile of 15 phenolic components in Quercus leaves infusions was also determined by HPLC. In vitro analysis of antioxidant capacity of leaves infusion extracts were performed by the DPPH method and the deoxyribose assay. The genotoxicity of Q. resinosa leaves extracts was evaluated on HeLa cells as well as its underlying mechanism by the single-cell electrophoresis assay (comet assay). Results show that fresh leaves infusions increase the oxidative process and other damage to DNA in transformed human cells. Fresh leaves from Q. resinosa may serve as a potential source of phenolics with anticancer activity.     

Influence of thermal treatment on phenolic compounds and antioxidant properties of oak acorns from Serbia

The aim of the present work was to investigate and compare phenolic compounds and antioxidant activity of methanol extracts of Quercus robur and Quercus cerris acorn kernels obtained before and after thermal treatment. Content of total phenolics, tannins, non-tannin phenolics and flavonoids was determined spectrophotometrically and content of gallic acid with HPLC. Antioxidant activity of the samples was assayed through FRAP (Ferric Reducing Antioxidant Power), DPPH scavenging test and inhibition of Fe²⁺/ascorbate induced lipid peroxidation. Extracts of native and thermally treated kernels showed high antioxidant activity, with extracts of thermally treated kernels being more active than extracts of native ones. Hydrolysable tannins and gallic acid were identified in all samples. Non-tannin phenolics, including gallic acid, were present in significantly higher quantities in thermally treated samples, whilst tannin content decreased. This indicates that during thermal treatment hydrolysable tannins were degraded. As the result of this degradation and consequent increase of non-tannin phenolics content, and amongst them especially gallic acid, thermally treated samples possess higher antioxidant activity than do the native ones. The obtained results have provided further grounds for establishing Q. robur and Q. cerris acorn kernels as a source for functional food preparation.     

Gravimetric determination of soluble phenolics including tannins from leaves by precipitation with trivalent ytterbium

A method for the gravimetric determination of soluble phenolics based on precipitation with trivalent ytterbium is described. Solutions of ytterbium-precipitated phenolics can be prepared in order to study u.v. absorbance, colorimetric assays for phenolics, protein precipitation and cellulase inhibition. The method was applied to mature leaves of 10 East African browse species in the diets of goats and camels. There was a large range in ytterbium-precipitated phenolics (Yb-ppt), from 50% dry matter (DM) in Acacia nilotica to less than 15% in Acacia brevispica and Cadaba farinosa. Results from u.v. absorbance and the Folin-Ciocalteu assay on solutions of ytterbium-precipitated phenolics indicated that ytterbium precipitates many types of phenolics including proanthocyanidins. The vanillin-HCl and n-butanol-HCl assays for proanthocyanidins separated the samples into two groups with high or low levels. The group with high levels of proanthocyanidins had greater protein precipitation capacity and cellulase inhibition at similar amounts of Yb-ppt. The results indicate that the method may be useful in nutritional studies involving browse and other forages. Gravimetric analysis avoids problems associated with colorimetric assays because it does not rely on the use of standards. The preparation of solutions of Yb-precipitated phenolics allows direct comparison between amount and nutritional effects such as protein precipitation and enzyme inhibition.     

Phenolic Contents and Antioxidant Activities of Date Palm (Phoenix dactylifera L.) Leaves

The antioxidant capacity and phenolic content of three varieties of Phoenix dactylifera leaves, namely Deglet Nour, Medjhoul, and Barhee, were studied. The antioxidant activities of extracts of different leaf varieties obtained with solvents of different polarity were investigated using assays of 2, 2-diphenyl-2-picrymhydrasyl hydrate radical-scavenging activity, total phenolics and flavonoids amount, condensed tannins, reducing power, and total antioxidant capacity. The results showed that all the extracts exhibited antioxidant and radical-scavenging activities at different magnitudes and potency. The decreasing order of antioxidant and radical-scavenging activities among the extracts assayed were found to be methanol (MeOH) fraction > ethyl acetate fraction > hexane fraction > water extract. Correlation analysis indicated that there is a linear relationship between antioxidant potency, free radical-scavenging ability, and the content of phenolic and flavonoids compounds of Phoenix dactylifera leaf extracts. These results showed that Phoenix dactylifera leaf extracts are a valuable natural antioxidant, which can be applied in both healthy medicine and food industry and biotechnology.     

Chemical composition and in vitro digestibility of some Spanish browse plant species

Samples of leaves, flowers and fruits of four browse species were collected from uplands in the province of León (northwestern Spain) at different sampling times (from spring till autumn). The browse species were Erica australis (Spanish heath), Cistus laurifolius (laurel‐leaved rock rose), Quercus pyrenaica (hoary oak) and Rosa canina (wild dog rose). A large variability in chemical composition and in vitro digestibility and gas production kinetics was observed among species and among sampling times within each species. The ranking order of the browse plants according to their in vitro digestibility and gas production kinetics was R canina > Q pyrenaica > C laurifolius > E australis. In the leaves of R canina and Q pyrenaica, crude protein content, digestibility and parameters of gas production tended to decrease throughout the growing season (P < 0.05 in most cases), whereas cell wall contents followed the opposite trend. Seasonal variations were less pronounced in the other browse species. There were significant (P < 0.05) correlations between in vitro digestibility and chemical composition of the browse plants, positive with the crude protein content and negative with the fibre fractions. Copyright © 2004 Society of Chemical Industry     

Maderisation of white wines: I.—Influence of pressing on the susceptibility of the grapes to oxidative browning

The oxidative browning of white wines (maderisation) obtained by fermenting musts derived from progressive pressing cycles, was studied in relation to the phenolic concentration. A picture of the distribution of the various phenolics was obtained by combining the total phenolics determination with selective precipitation of flavonoids with formaldehyde and tannins with cinchonine. Both enzymic and non-enzymic browning are directly related to the flavonoids concentration in the wines; a progressive insolubilisation of tannic flavonoids and a polymerisation of the non-tannic flavonoids accompanies the colour change. The concentration of non-flavonoid phenolics does not vary significantly during oxidative degradation and therefore they tend to become the most representative phenolic fraction in the maderised wines.     

Quercetin,Hyperin, and Chlorogenic Acid Improve Endothelial Function by Antioxidant,Antiinflammatory, and ACE Inhibitory Effects

In recent years, the blueberry cultivation and processing industry developed quickly because blueberries are super‐fruit with healthy function. Blueberry leaves are byproducts of the blueberry industry, which are rich in bioactive phenolics, such as quercetin (Q), hyperin (H), and chlorogenic acid (C). This study investigated protective effects of 3 phenolics (Q, H, and C) from leaves of rabbiteye blueberry Vaccinium ashei on human umbilical vein endothelial cells. The results showed that all these 3 phenolics could improve endothelial function by inhibiting oxidative damage and proinflammatory cytokines caused by tumor necrosis factor‐α (TNF‐α). The cell vitalities of endothelial cells pretreated with Q, H, and C were higher than those stimulated with TNF‐α only. These phenolics could decrease reactive oxygen species and xanthine oxidase‐1 levels and increase superoxide dismutase and heme oxygenase‐1 levels in endothelial cells. They also could decrease the protein expressions of intercellular adhesion molecule‐1, vascular cell adhesion molecule‐1, and monocyte chemotactic protein‐1 induced by TNF‐α. In addition, Q, H, and C also exhibited vasodilatory effect by reducing the angiotensin I–converting enzyme (ACE) protein levels in endothelial cells. Mostly 3 phenolics exhibited bioactivities as a function of concentration, but the effects not always depended on the concentration. The antioxidant and antiinflammatory effects of Q seemed to be more pronounced than H; however, H exhibited higher cell vitalities. The results indicated that phenolics from rabbiteye blueberry leaves could be potential antioxidants, inflammation and ACE inhibitors, and rabbiteye blueberry leaves provide a new resources of phytochemicals beneficial for cardiovascular health.     

Nutritional composition and antioxidant activity in hazelnut shells from US‐grown cultivars

The hard shell of a hazelnut is a major waste of the hazelnut industry. The chemical composition, phenolic compounds (total phenolics, tannins and condensed tannins), antioxidant activity (DPPH and ABTS free‐radical scavenging assays), and the relationships between phenolic compounds and antioxidant activities of the hazelnut shells from twelve US grown cultivars were investigated to for potential commercial development. Crude fibre accounted for over 85% of total carbohydrate. The shells contained high concentrations of phenolic compounds. Concentrations of phenolic constituents and ABTS^?+ ‐scavenging capacities were significantly higher (P > 0.05) in the Oregon cultivars than their Nebraska counterparts. There were significant positive correlations between ABTS^?+ scavenging capacities and the phenolic compounds, whereas DPPH^? ‐scavenging capacity demonstrated a weak negative correlation with ABTS^?+ scavenging capacity and the phenolics. The results suggest that hazelnut hard shell may serve as a potential source of natural antioxidants for food applications.     

Impact of exogenous tannin additions on wine chemistry and wine sensory character

Tannins are an important part of wine quality and are frequently added during winemaking. Tannin additives and their impact on wine are poorly documented. This work sought to characterize a range of enological tannins and their contribution to wine quality. Enological tannins were analysed for protein precipitable tannins and iron reactive phenolics. One tannin product was added to a Merlot wine during barrel ageing, at a range of concentrations from 60 to 300 mg/l. Condensed and hydrolysable tannins were added to Cabernet Sauvignon wine post-pressing at a recommended and excessive rate. Wines were analysed for anthocyanin, small and large polymeric pigment, precipitable tannin, iron reactive phenolics and sensory character. Enological tannins contained 12-48% tannin and recommended additions had little impact on wine tannin. High tannin additions were readily measured in the wines and were discriminated in sensory analysis with lower intensities of most parameters except brown colour, bitterness and earthy character. Recommended addition rates are too low to impact the measured tannin concentration of Merlot and Cabernet Sauvignon wines from Washington (USA). High enological tannin additions had a measureable impact on final wine had a negative impact on sensory character. Tannins are added to wines for a range of reasons and represent one of many input costs in an industry increasingly seeking efficiencies in response to global economic circumstances, over-supply and an ongoing price point squeeze. This research suggests many tannin additions may be unjustified and have limited or negative impacts on quality.     

Gravimetric determination of tannins and their correlations with chemical and protein precipitation methods

Abstract. A method for gravimetric determination of tannins based on binding with insoluble polyvinylpyrrolidone (PVP) is presented. The gravimetric method gives the absolute amount of tannins and avoids problems of standards associated with spectrophotometric methods. The method was applied to nine browse and tree leaves. The values obtained correlate significantly with tannins determined spectrophotometrically, protein precipitation capacities and protein precipitable phenotics. This method together with other tannin assays will be useful in nutritional studies. The present study also demonstrates the different behaviour of tannic acids from different commercial sources towards PVP suggesting the presence of different moieties in tannic acids from different commercial sources and even among batches from the same source thereby affecting the results obtained using the spectrophotometric methods. Use of well-defined tannic acid as a standard in spectrophotometric methods is suggested which will allow meaningful comparison of values obtained from different laboratories.     

Comparison of the Precipitation of Alfalfa Leaf Protein and Bovine Serum Albumin by Tannins in the Radial Diffusion Method

The precipitation of protein by condensed and hydrolysable tannins was evaluated with the radial diffusion method of Hagerman (1987) using bovine serum albumin (BSA) and isolated leaf protein from fresh alfalfa (Medicago sativa). Alfalfa leaf protein (AALP) was included at two concentrations, 25 and 156 mg N litre^-1, at pH 6·8 and 39°C to simulate rumen conditions. The condensed tannins were purified from lyophilised samples of Arachis pintoi, Desmodium ovalifolium, Gliricidia sepium, Manihot esculenta and quebracho (Schinopsis balansae). Hydrolysable tannins from tannic acid (TA) were used as well. There was a significant interaction (P<0·001) between tannin and protein source, and protein level on protein precipitation. Most purified condensed tannins (CTs) precipitated more AALP than BSA when protein was included at the same level. Purified CT from quebracho and hydrolysable tannin from TA failed to precipitate AALP at both protein levels. In a second experiment, tannins from crude plant extracts were studied in the radial diffusion method using BSA and two levels of AALP. The crude plant extracts were obtained from lyophilised plant samples of A pintoi, Centrosema macrocarpum, Clitoria ternatea, D ovalifolium, Erythrina berteroana, E poepigiana, G sepium, M esculenta, Pueraria montana and P phaseoloides. The protein precipitated by soluble tannins in the plant samples was correlated to the total phenolic content and to the soluble CT estimated by the acid butanol assay or by the radial diffusion method. Tannins from different plant species precipitated different amounts of BSA and AALP. Therefore, the measures of the biological activity of tannins based on BSA precipitation may not reflect the ability of tannins to precipitate proteins of plant origin such as those commonly found in the diets of herbivores. The present study offers the possibility of using the radial diffusion method with plant proteins at precipitation conditions similar to those in the rumen. © 1997 SCI.     

Comparison of analytical methods for the determination of condensed tannins in grape skin

Background and Aims: Condensed tannins extracted from grapes are an important organoleptic component of wine. Assessing tannin level in grapes requires an effective analytical method. This study compared the efficacy of three analytical methods. Methods and Results: Condensed tannin levels were measured in 38 grape skin samples by protein and methylcellulose precipitation and by high‐performance liquid chromatography (HPLC)‐phloroglucinolysis. Total phenolics were determined by absorbance at 280 nm. Tannin levels by protein and methylcellulose precipitation were of similar magnitude, while levels determined by HPLC‐phloroglucinolysis were generally higher. No correlation was found between the level of phenolics and tannins by any of the methods employed. Neither was there a correlation between tannin levels determined by HPLC‐phloroglucinolysis and by precipitation, although previously a strong correlation had been reported between protein precipitation and HPLC‐phloroglucinolysis in wine. Conclusions: The ratio of tannin to non‐tannin phenolics is highly variable between cultivars. Each analytical method measures a different fraction of the tannin extracted from grape skin. Significance of the Study: The disparity between analytical methods requires that method selection reflect the decision‐making that will utilise the information produced. For example, protein precipitation of tannins by bovine serum albumin (BSA) has been correlated with perceived astringency; consequently this may be the best indicator of potential mouthfeel.     

Effect of heat treatment on antinutrients and precaecal crude protein digestibility in broilers of four tropical crop seeds

Four tropical crop seeds, namely Vigna unguiculata (Cowpea), Mucuna pruriens, Manihot esculenta and Centrosema pubescens were thermally processed for 1 h at 100 °C and analysed for their antinutritional factors (ANF). Four hundred and forty‐eight 1‐day‐old broilers were used to determine the effect of heating the seeds on their precaecal crude protein (CP) digestibility. Total phenols, protein precipitable tannins and l ‐dopa were higher in the mucuna and centrosema seeds and diets than in the vigna and manihot seeds and diets. Phytic acid was of similar occurrence in all the raw seeds. Heat treatment resulted in reduction in all the ANF in the seeds. Precaecal CP digestibility, feed intake and growth rate were significantly (P < 0.01) increased in the heat‐treated mucuna and centrosema diets. There was no significant effect on the digestibility of CP, feed intake and growth rate in birds on the vigna and manihot diets owing to heat treatment of the seeds. The results showed that heating improved the nutritive quality of mucuna and centrosema seeds but was not of significant advantage with vigna and manihot seeds when used at levels of up to 150 g kg^?1 in diets.     

Microassay for the quantitation of protein precipitable polyphenols: use of bovine serum albumin–benzidine conjugate as a protein probe

A simple, sensitive and indirect spectrophotometric method for the determination of protein precipitable polyphenols (tannins) has been developed, based on the ability of the polyphenols to precipitate the synthetic, brown coloured azo-protein, bovine serum albumin–benzidine conjugate (BSA–benzidine, mole ratio 1:7), which shows an absorption maxima at 405 nm. The amount of unprecipitated BSA–benzidine is measured directly at 405 nm, which is inversely related to the polyphenol concentration. Tannic acid was used as a reference standard. The microassay was performed in citrate/phosphate buffer (0.1 m), pH 4.8. The method was found to be linear in the range of 5–150 μg (3–88 nmol) of tannic acid (y=1.0+(−0.007)x; r=−0.989). Spiking studies carried out with various levels of tannic acid (0.01, 0.1 and 1.0%) indicated a recovery in the range of 94–101% and 94–98% in rice and sorghum samples, respectively. Free phenolics, when added in the range of 50–150 μg (catechin, chlorogenic acid, ferulic acid, caffeic acid and p-coumaric acid) had no influence on the protein precipitation in the microassay. Also spectral analysis of free phenolics and acid-methanolic sorghum extracts showed no interference in the present method. The conjugate was found to be stable over a period of 24 weeks in a freeze-dried condition and at 4°C, with <5% deterioration in aqueous condition. The microassay method developed has been used for the quantitation of protein precipitable polyphenols in various sorghum (Sorghum bicolor L. Moench) genotypes and compared with the widely used Folin–Denis chemical method of analysis.     

Dried fruits: phytochemicals and their fate during in vitro digestion

Mediterranean dried fruits that are cultivated and produced in Greece; that is, Corinthian currants, figs, prunes, cherries, apricots and peaches were evaluated in terms of total polar phenols, individual simple phenolics, anthocyanins and antioxidant capacity in vitro. The potential release of dried fruit polar phenols among the different fractions of an in vitro digestion model was also determined. Total polar phenol, flavanol, flavone/flavonol content and antioxidant capacity was in the range 86–551 mg GAE/100g, 0.2–57 mg CE/100g, 9–71 mg RE/100g and 6–47 mg AAE/100g, respectively. A 12–82% release of total phenolics was observed post-mastication, which further increased post-gastric digestion. The same trend was also followed in the case of total flavanols and flavones/flavonols. Total polar phenols and flavones/flavonols were found to enter the simulated epithelial cell wall. Simple polar phenolics and anthocyanins were identified and quantified in all dried fruit extracts and in some of the digestion fractions.