Haemanalysis of tannins: The concept of relative astringency

The astringency of tannins, that is their efficiency as precipitants of proteins, is determined by their reaction with the proteins of haemolysed blood and calorimetric determination of residual haemoglobin. The method is accurate and sensitive because of the narrow range of concentration of tannin between that required to initiate precipitation (the threshold concentration) and that for complete precipitation. ‘Relative astringency’ (RA) is the ratio of the concentration of the tannic acid to that of the tannin which effects the same degree of precipitation. The RA of certain esters of hexahydroxydiphenic acid and of certain procyanidins of known constitution has been determined and the results applied to the ellagitannins and/or leucoanthocyanins present in species of Shorea, Geranium and other plants. The homology of each of these classes of tannins is discussed in the light of the results.     

Degradation of condensed tannins byCalvatia gigantea

Summary Calvatia gigantea, an edible puffball, was grown well on simple phenolic compounds and hydrolysable and condensed tannins as sole carbon sources. A new enzymic system was found to be involved in the degradation of catechin, the building unit of condensed tannins. This enzymic system was induced by catechin and displayed no phenoloxidase activity. Crude enzymic preparation functioned optimally at pH 7.5–8.0 and 40–45°C and had an apparentK _m , 2.96 × 10⁻⁵ M at pH 8.0. The results of this work makeC. gigantea a potential microorganism for the degradation of toxic phenolic and polyphenolic compounds and particularly condensed tannins.     

Effect of condensed tannins on bacterial diversity and metabolic activity in the rat gastrointestinal tract

The effect of dietary condensed tannins (proanthocyanidins) on rat fecal bacterial populations was ascertained in order to determine whether the proportion on tannin-resistant bacteria increased and if there was a change in the predominant bacterial populations. After 3 weeks of tannin diets the proportion of tannin-resistant bacteria increased significantly (P < 0.05) from 0.3% +/- 5.5% to 25.3% +/- 8.3% with a 0.7% tannin diet and to 47.2% +/- 5.1% with a 2% tannin diet. The proportion of tannin-resistant bacteria returned to preexposure levels in the absence of dietary tannins. A shift in bacterial populations was confirmed by molecular fingerprinting of fecal bacterial populations by denaturing gradient gel electrophoresis (DGGE). Posttreatment samples were generally still distinguishable from controls after 3.5 weeks. Sequence analysis of DGGE bands and characterization of tannin-resistant isolates indicated that tannins selected for Enterobacteriaceae and Bacteroides species. Dot blot quantification confirmed that these gram-negative bacterial groups predominated in the presence of dietary tannins and that there was a corresponding decrease in the gram-positive Clostridium leptum group and other groups. Metabolic fingerprint patterns revealed that functional activities of culturable fecal bacteria were affected by the presence of tannins. Condensed tannins of Acacia angustissima altered fecal bacterial populations in the rat gastrointestinal tract, resulting in a shift in the predominant bacteria towards tannin-resistant gram-negative Enterobacteriaceae and Bacteroides species.     

Interactions of condensed tannins with selected proteins

The relative affinities of condensed tannins purified from sorghum, pinto bean, quebracho and wattle for six dissimilar proteins have been determined by a competitive binding assay. The results indicate that tannin/protein interactions may be specific for different tannins as well as for different proteins. The highly specific interactions suggest that the differences in affinity are functionally significant.     

The condensed tannins of pasture legume species

Condensed tannins have been isolated from legume pasture species and purified by gel chromatography on Sephadex G-50 and LH-20 media. Molecular size di     

Extraction of condensed tannins from Mexican plant sources

Contents of total polyphenols, condensed tannins and proanthocyanidins, and their stability to various pH values and temperatures were studied in Mexican blueberry, cuautecomate fruit, garambullo fruit, aubergine, coffee pulp and residues of black grapes. Several aqueous extracts, obtained through a one-pass-extraction process, were analyzed using liquid chromatography in order to quantify the condensed tannin (proanthocyanidin) content responsible for their antioxidant activity and colour. All tested samples included high proanthocyanidin contents demonstrating that these Mexican fruits and vegetables are good sources of natural antioxidants, and they all could be considered as excellent functional foods due to their bioactivity measured as the condensed tannin level.     

Effect of lucerne saponins and Lotus condensed tannins on survival of grass grub,Costelytra zealandica

Abstract

Crude extracts of lucerne (Medicago sativa) and Lotus pedunculatus root were toxic when administered orally to third-instar Costelytra zealandica larvae. Purified saponins from lucerne root were alone found sufficiently toxic to account fully for the activity of the crude extract. Condensed tannins extracted from L. pedunculatus and L. corniculatus had no effect on larval survival when administered at levels equivalent to those present in crude extracts.     

Effect of condensed tannins in rations of lactating dairy cows on production variables and nitrogen use efficiency

The objective of this study was to evaluate the effect of supplemented condensed tannins (CT) from the bark of the Black Wattle tree (Acacia mearnsii) on production variables and N use efficiency in high yielding dairy cows. A feeding trial with 96 lactating German Holstein cows was conducted for a total of 169 days, divided into four periods. The animals were allotted to two groups (control (CON) and experimental (EXP) group) according to milk yield in previous lactation, days in milk (98), number of lactations and BW. The trial started and finished with a period (period 1 and 4) where both groups received the same ration (total-mixed ration based on grass and maize silage, ensiled sugar beet pulp, lucerne hay, mineral premix and concentrate, calculated for 37 kg energy-corrected milk). In between, the ration of EXP cows was supplemented with 1% (CT1, period 2) and 3% of dry matter (DM) (CT3, period 3) of a commercial A. mearnsii extract (containing 0.203 g CT/g DM) which was mixed into the concentrate. In period 3, samples of urine and faeces were collected from 10 cows of each group and analyzed to estimate N excretion. Except for a tendency for a reduced milk urea concentration with CT1, there was no difference between groups in period 2 (CON v. CT1; P>0.05). The CT3 significantly reduced (P<0.05) milk protein yield, the apparent N efficiency (kg milk N/k feed N) and milk urea concentration; but total milk yield and energy-corrected milk yield were not affected by treatment. Furthermore, as estimated from 10 cows per group and using urinary K as a marker to estimate the daily amount of urine voided, CT3 caused a minor shift of N compounds from urine to faeces, as urea-N in urine was reduced, whereas the N concentration in faeces increased. As an improvement in productivity was not achieved and N use efficiency was decreased by adding the CT product it can be concluded that under current circumstances the use in high yielding dairy cows is not advantageous.     

Methane emission by goats consuming different sources of condensed tannins

Twenty-four yearling Boer × Spanish wethers (7/8 Boer; initial body weight (BW) of 37.5 ± 0.91 kg) were used to assess effects of different condensed tannin (CT) sources on methane (CH₄) emission. Diets were Kobe lespedeza (Lespedeza striata; K), K plus quebracho providing CT at 50 g/kg dry matter (DM) intake (KQ), Sericea lespedeza (Lespedeza cuneata; S), and a 1:1 mixture of K and S (KS). Forages harvested daily were fed at 1.3 times the maintenance metabolizable energy requirement. The experiment was 51 days divided into two phases. In phase A forage diets were fed alone, and in phase B, 25 g/day of polyethylene glycol (PEG) was given mixed with 50 g/day of ground maize grain. Adaptation periods were 28 and 7 days in phases A and B, respectively. After adaptation there were 8 days for feces and urine collections, with gas exchange measured on the last 2 days. Ruminal fluid was collected at the end of the experiment via stomach tube for microbiology assays. The N concentration was 22.8 and 23.6 g/kg DM, in vitro true DM digestibility was 0.698 and 0.648, and the level of CT was 140 and 151 g/kg DM for S and K, respectively. DM intake was similar among treatments in both phases (phase A: 720, 611, 745, and 719 g/day (S.E. = 59.0); phase B: 832, 822, 867, and 880 g/day (S.E. = 55.3) for K, KQ, S, and KS, respectively). N digestibility was affected by treatment in phase A (P<0.05) but not in phase B (phase A: 0.514, 0.492, 0.280, and 0.413 (S.E. = 0.0376); phase B: 0.683, 0.650, 0.638, and 0.662 (S.E. = 0.0203) for K, KQ, S, and KS, respectively). Gross energy digestibility was similar among treatments in phase A (0.475, 0.407, 0.393, and 0.411 (S.E. = 0.0353)) but differed among treatments in phase B (0.449, 0.373, 0.353, and 0.409 for K, KQ, S, and KS, respectively (S.E. = 0.0221)) CH₄ emission was 9.6, 6.8, 10.6, and 8.9 l/day (S.E. = 1.44) in phase A and 19.0, 16.6, 21.8, and 19.2 l/day (S.E. = 1.51) in phase B for K, KQ, S, and KS, respectively (S.E. = 1.25). When data of both phases were pooled, supplementation with PEG in phase B markedly increased (P<0.05) CH₄ emission (9.0 l/day versus 19.1 l/day). In accordance, there was a substantial difference (P<0.05) between phases in in vitro CH₄ emission by ruminal fluid incubated for 3 weeks in a methanogenic medium and with other conditions promoting activity by methanogens (11.5 and 22.9 ml in phases A and B, respectively). Counts of total bacteria and protozoa were similar among treatments in both phases, but values were greater (P<0.05) in phase B versus phase A. In summary, CT from different sources had a disparate influence on N digestion, but similar effects on ruminal microbial CH₄ emission by goats, possibly by altering activity of ruminal methanogenic bacteria though change in actions of other bacteria and/or protozoa may also be involved.     

The quantification of condensed tannins in African savanna tree species

We compared Quebracho with Sorghum tannin as standards for condensed tannin (CT) quantification in selected African savanna tree species in relation to the acid-butanol assay for CTs. Without exception, the use of Quebracho tannin as standard overestimated CTs, ranging from 0.7 to as much as 8.3 times. Sorghum tannin underestimated CTs by 0.26–0.79 times, except in one species where there was no difference in the CT concentration. Condensed tannins in African savanna trees showed qualitative and quantitative differences in chemical composition which may explain the variable reactivity in the acid-butanol assay. We propose the use of condensed tannins purified from the plant under investigation be used as standard since it will closely represent the CT structure and presumably chemical reactivity in the acid-butanol assay.     

Effect of molecular weight of condensed tannins from warm-season perennial legumes on ruminal methane production in vitro

The objectives of the present study were to determine if the molecular weight of condensed tannins (CT) from warm-season perennial legumes affects the biological activity of CT relative to suppression of methane (CH₄) production by ruminants, and to identify potential North American native forage plants to use for mitigation of enteric CH₄ emission. Eight North American native warm-season perennial legumes were evaluated: Leucaena retusa Benth. (littleleaf leadtree), Desmanthus illinoensis (Michx.) MacMill. Ex B.L. Rob. & Fernald (Illinois bundleflower), Lespedeza stuevei Nutt. (tall lespedeza), Mimosa strigillosa Torr. & A. Gray (powderpuff), Neptunia lutea (Leavenworth) Benth. (yellow puff), two ecotypes of Acacia angustissima var. hirta (Nutt.) B.L. Rob (prairie acacia), and Desmodium paniculatum (L.) DC. var. paniculatum (panicledleaf ticktrefoil). Two introduced legumes were also included: Arachis glabrata Benth. (rhizoma peanut) and Lespedeza cuneata (Dum. Cours.) G. Don (sericea lespedeza). Forages were fermented with cattle rumen fluid for 48 h anaerobically using an in vitro gas production technique. D. paniculatum, L. stuevei, and M. strigillosa were high in CT, ranging from 11.7 to 12.5%. D. illinoensis, L. cuneata, N. lutea, and two ecotypes of A. angustissima var. hirta had less CT (P < 0.05), ranging from 8.1 to 8.9%, whereas L. retusa and A. glabrata had the least CT (P < 0.05), measuring 3.2 and 0.5%, respectively. Weight-average molecular weight (M_W) of CT ranged from 1483 Da for L. cuneata to 552 Da for L. stuevei. In vitro CH₄ production was greatest for L. retusa and A. glabrata at 40.7 mg/g DM and 38.2 mg/g DM, respectively. The least amount of in vitro CH₄ was produced by fermentation of two ecotypes of A. angustissima var. hirta, which measured 0.8 and 0.6 mg/g DM, respectively. In vitro CH₄ production regressed on CT M_W resulted in a R² of 0.0009 (P = 0.80), strongly suggesting that CT M_W does not explain the biological activity of in vitro CH₄ production by the forage legumes surveyed. Five of the seven North American native warm-season perennial legumes have promise for use in ruminant diets for the purpose of CH₄ emission mitigation.     

Effects of condensed tannins on behavior and performance of a specialist aphid on aspen

Genes involved in plant defences against herbivores and pathogens are often highly polymorphic. This is a putative sign that balancing selection may have operated reciprocally on the hosts and their herbivores. Spatial and temporal variations (for example, in soil nutrients and the plants'' ontogenetic development) may also modulate resistance traits, and thus selection pressures, but have been largely overlooked in theories of plant defences. Important elements of defences in Populus tremula (hereafter aspen) are phenolic compounds, including condensed tannins (CTs). Concentrations of CTs vary considerably with both variations in external factors and time, but they are also believed to provide genotype‐dependent resistance, mainly against chewing herbivores and pathogens. However, evidence of their contributions to resistance is sparse. Detailed studies of co‐evolved plant–herbivore associations could provide valuable insights into these contributions. Therefore, we examined correlations between CT levels in aspen leaves and both the feeding behavior and reproduction of the specialist aspen leaf aphid (Chaitophorus tremulae) in varied conditions. We found that xylem sap intake and probing difficulties were higher on genotypes with high‐CT concentrations. However, aphids engaged in more nonprobing activities on low‐CT genotypes, indicating that CTs were not the only defence traits involved. Thus, high‐CT genotypes were not necessarily more resistant than low‐CT genotypes, but aphid reproduction was generally negatively correlated with local CT accumulation. Genotype‐specific resistance ranking also depended on the experimental conditions. These results support the hypothesis that growth conditions may affect selection pressures mediated by aphids in accordance with balancing selection theory.     

Consequences of long-term feeding with condensed tannins on sheep parasitised with Trichostrongylus colubriformis

Naive wethers were used to investigate the long-term effects of dietary condensed tannins from Quebracho extract, during an intestinal parasitic infection in sheep. Sheep were allocated to eight groups; seven groups were daily infected with 3000 L(3) Trichostrongylus colubriformis for 10 weeks and the eighth group was the uninfected control. The 10-week experiment was divided into two periods; Period 1 (P(1), week 1-5) corresponded to high worm establishment and acquisition of immunity, whereas Period 2 (P(2), week 6-10) to the established worm population and expression of host immunity. Three experimental foods with similar composition were formulated: Q0, Q3 and Q6. Their difference was in the content of Quebracho extract which was 0, 30 and 60 g per kg fresh matter, respectively. All foods were offered at an allowance of 3.5% of sheep liveweight. During P(1), parasitised sheep were offered one of the three experimental foods and during P(2) they either remained on the same food or changed food according to the design (P(1)-P(2)): Q0-Q0, Q0-Q3, Q0-Q6, Q3-Q0, Q3-Q3, Q6-Q0, Q6-Q6. Control sheep were offered the allowance of Q0 throughout. Sheep that consumed Q3 and Q6 reduced their faecal egg counts (FEC) compared to sheep offered Q0, during both periods (P<0.05). No differences were observed in the FEC between sheep offered Q3 and Q6. The changeover from Q0 in P(1) to either Q3 or Q6 during P(2), was accompanied by a reduction in FEC (P<0.05), whereas an increase in FEC was observed when food changed from Q3 or Q6 to Q0 (P<0.05). Worm burdens and fecundity at the end of the experiment were reduced in sheep offered foods Q3 and Q6 compared to sheep offered Q0. A significant decrease in liveweight gain and in food conversion efficiency of parasitised sheep offered Q3 and Q6 compared to sheep offered Q0, was observed in P(1) (P<0.05) but not in P(2). By the end of the experiment control sheep had achieved higher liveweight and converted food more efficiently than parasitised sheep (P<0.05). In conclusion, evidence for a long-term effect of Quebracho extract, during both the initial establishment and on the established T. colubriformis population in sheep, was provided by the present study. It is suggested that the effect observed was a direct anthelmintic effect of the condensed tannins included in sheep diets.     

Structural properties of colloidal complexes between condensed tannins and polysaccharide hyaluronan

Interactions of plant tannins with polysaccharide hyaluronan are studied by means of light scattering and small-angle X-ray scattering (SAXS). In this paper, we show that (1) the tannin-polysaccharide complexes remain stable in colloidal suspension; (2) the masses and structures of colloidal tannin-polysaccharide objects depend on the tannin degree of polymerization; and (3) the densities of tannin-polysaccharide aggregates are about 7 times lower than the density of a single solvated polysaccharide molecule. Short tannins and polysaccharides are aggregated in loose oligomeric structures whose sizes are comparable to a single polysaccharide molecule. Tannins longer than 10 nm and polysaccharides are aggregated in larger microgel-like particles whose sizes exceed 200 nm.