Extractable Condensed Tannins Research Articles

Microcosm study on fate and dynamics of mangrove tannins during leaf litter leaching

BackgroundMangrove tannins can participate in wetland biogeochemical cycling. However, their fate and dynamics during leaf litter leaching have yet to be elucidated in coastal aquatic environments.MethodsBy using a simulated microcosm experiment, changes in leaf litter mass and tannin compounds, including total phenolics (TP), extractable condensed tannins (ECT), and bound condensed tannins (BCT), were examined in the litters and leachates of four common mangrove species: Kandelia obovata (Ko), Aegiceras corniculatum (Ac), Sonneratia apetala (Sa), and Avicennia marina (Am).ResultsLeaching caused a notable decline in litter mass, TP, and ECT in the leaf litter of Ko, Ac, Sa, and Am, while BCT increased significantly in Ko and Ac. Loss in foliar TP was higher than in leaf litter mass, and loss in foliar ECT was higher than in TP of Ko and Ac, but Sa showed the opposite result. The temporal changes of TP and ECT concentrations in leachates followed a similar trend, with an initial increase followed by a decrease. ECT dynamics in Ko and Ac leachates correlated with their TP concentrations, while in Sa leachate, the peak ECT occurred 72 h later than its TP peak. The leachate ECT concentrations were highest in Ac, followed by Ko, and significantly lower in Sa. The peak TP and ECT proportions in leachates accounted for 9.2–23.9% and 7.7–9.4% of the total decreases in foliar TP and ECT, respectively.ConclusionDuring the leaching process, tannins’ fate was species-specific, while the dynamics were almost similar.

Antioxidant, Bacteriostatic and Preservative Effects of Extractable Condensed Tannins Isolated from Longan Pericarps and Seeds.

In the process of longan production and processing, a large amount of remnants is produced, such as dried longan pericarps and seeds, which have been reported to be rich in polyphenols but not effectively utilized. In this paper, the total phenolic contents in the remnants of longan pericarps and seeds were found to be 39.58 ± 3.54 and 69.53 ± 1.99 mg/g (DW), respectively, accounting for 60-80% of those in fresh samples. The contents of extractable condensed tannins (ECTs) in the remnants of longan pericarps and seeds were 19.25 ± 6.71 mg/g (DW) and 44.59 ± 2.05 mg/g (DW), respectively, accounting for 60-70% of the fresh samples. These data indicate that the polyphenols in the remnants of the sampled longan pericarps and seeds were effectively retained. The antioxidant capacity of ECTs from the longan pericarps and seeds was more than 60% of the fresh samples measured with the 1, 1-diphenyl-2-trinitrophenylhydrazine and ferric reducing ability of plasma methods. Further exploration showed that ECTs from the longan pericarps and seeds had significant inhibitory effects on Pseudomonas aeruginosa, Escherichia coli, Salmonella and Staphylococcus aureus. The minimum inhibitory concentration (MIC) of the longan pericarp ECTs on all four studied bacteria was 3 mg/mL. The MIC of longan seed ECTs on Salmonella was 3 mg/mL, and that of the other three bacteria was 1.5 mg/mL. In view of the good antioxidant and antibacterial activities of longan pericarps and seeds, we applied them to the preservation of fresh-cut lotus roots. When the concentration of ECTs in the longan pericarps and seeds was 2 mg/mL and 1 mg/mL, respectively, the two kinds of ECTs showed an obvious preservative effect. After the ECT treatment of the lotus roots, their browning degree was reduced, their color was better maintained, their respiration was inhibited and their nutrient loss was reduced. Bacterial reproduction was inhibited, and cell senescence was slowed. Accordingly, the shelf life of ECT-treated fruits and vegetables can be effectively extended. Overall, we can suggest that ECTs from the remnants of dried longan pericarps and seeds could be used as natural preservatives for fresh-cut fruits and vegetables.

Effects of decabromodiphenyl ether (BDE-209) on a mangrove plant, Kandelia obovata and the uptake, translocation and accumulation of BDE-209

Due to close proximity to urban development, mangroves exposed to the contamination of polybrominated diphenyl ethers (PBDEs). Decabromodiphenyl ether (BDE-209) is one of the most predominant PBDE congener. The present study aimed to investigate the toxic effects of BDE-209 on the antioxidative and non-antioxidative responses of Kandelia obovata, a very common mangrove species, under different concentrations of BDE-209, 0.1, 1, 5 and 10 mg l-1. BDE-209 did not exhibit any negative effects on the growth of K. obovata seedlings. The stimulatory effects of BDE-209 on the enzymes including superoxide dismutase, peroxidase and catalase only occurred in weeks 1 and 4 and diminished in week 8. The concentrations of total polyphenols (TP) and extractable condensed tannins (ECT) were not affected by BDE-209. The production of O2·- was induced only at the very high level of BDE-209 (10 mg l-1). H2O2 was induced only in weeks 1 and 4 under BDE-209 treatment. BDE-209 was taken up by the roots of K. obovata, translocated to above-ground tissues, and accumulated in plant tissues with the concentrations declined in the order of root > propagule > stem > leaf. Although BDE-209 has higher molecular weight and higher log Kow than other PBDE congeners, the K. obovata seedlings could absorb, translocate and accumulate BDE-209. These findings suggested that mangrove plants could take up, accumulate PBDEs, and BDE-209 are less toxic than other congeners but more difficult to be removed by mangrove systems.

Antioxidant and antityrosinase activity of extractable condensed tannins from durian shells with antibrowning effect in fresh-cut asparagus lettuce model

Inhibiting tyrosinase activity is considered as an effective strategy to prevent the enzymatic browning of fruits and vegetables. In this study, the extractable condensed tannins (ECTs) isolated from durian shells usually disposed as agricultural wastes were found to strongly inhibit on both monophenolase and diphenolase of tyrosinase, and the inhibition of diphenolase by ECTs was proved to be reversible and mixed-type. FT-IR, ESI-MS, MALDI-TOF-MS, reversed-phase thiolysis-HPLC-ESI-MS and normal-phase HPLC-ESI-MS revealed that ECTs were predominately constituted by B-type procyanidins with a small amount of propelargonidins and prodelphinidins as well as a low degree of 3-O-galloylation. Analyses of fluorescence quenching, metal-ion chelation and UV-scanning indicated that ECTs could bind with tyrosinase to form a complex, chelate copper ions and reduce the formation of dopaquinone, which in turn led to the decline of enzyme catalytic property. Besides, ECTs exhibited potent DPPH and ABTS radical scavenging activity, ferric reducing antioxidant power and inhibitory capacity against β-carotene bleaching. Also, antibrowning test demonstrated that ECTs effectively delayed the surface browning of fresh-cut asparagus lettuce. These results suggested that ECTs from durian shells were potential antioxidants and tyrosinase inhibitors and might provide a theoretical basis for the application of ECTs as novel antibrowning agents in food industry.

Seasonal variation and ecological importance of tannin and nutrient concentrations in Casuarina equisetifolia branchlets and fine roots

In this study, we investigated the effects of environmental factors on plant phenolic variability, seasonal dynamics of total phenolic content (TP), extractable condensed tannins (ECT), protein-bound condensed tannins (PBCT), fiber-bound condensed tannins (FBCT), total condensed tannins (TCT), protein precipitation capacity (PPC) and nutrient content in the branchlets and fine roots of Casuarina equisetifolia. TP and TCT concentrations in branchlets were lowest in the spring, then increased in summer and autumn, similar to the seasonal dynamics in air temperature. TP and TCT concentrations in fine roots were highest in summer, coinciding with heavy precipitation. In general, TP and TCT concentrations were higher in branchlets than in fine roots. No significant difference was found in C concentration among various seasons for either branchlets or fine roots. Branchlets had significantly higher N and P concentrations than fine roots in most seasons. The C/N and N/P ratios in branchlets were significantly lower than in fine roots in all seasons, except summer. The relationship between branchlets and fine roots was significant for C, P and FBCT, but no significant relationships were found for N, TP, ECT, PBCT and TCT. Additionally, TP and TCT content were each significantly correlated with PPC in branchlets and in fine roots. Both TP/N and TCT/N ratios were highest in the autumn for the branchlets and in the summer for fine roots. The results indicate that high temperatures lead to increased tannin production in branchlets, but that the tannin content in fine roots is mainly affected by precipitation. Tannin content was greater in branchlets than in fine roots, which may indicate that selective pressure is greater on branchlets than on fine roots.

Effects of conservation method on condensed tannin content, ruminal degradation, and in vitro intestinal digestion of purple prairie clover (Dalea purpureaVent.)

In situ and in vitro experiments were conducted to evaluate the effect of forage conservation method on the chemical composition, ruminal degradation, and intestinal digestion of purple prairie clover (PPC), which was conserved as freeze-dried forage (FD), silage (SIL), or hay (Hay). In situ dry matter (DM), neutral detergent fiber (NDF), and crude protein (CP) degradabilities were determined by incubating the forages in three rumen-cannulated heifers for 0, 1, 2, 4, 8, 24, 48, and 72 h. Intestinal DM and CP digestions were estimated by incubating 12 h ruminal in situ residues in a modified three-step in vitro procedure. Ensiling decreased (P < 0.001) extractable condensed tannins (CT) but increased (P < 0.001) protein- and fiber-bound CT compared with FD and Hay. The ruminal disappearance of CP at 8 and 24 h was affected by conservation method (P < 0.001), ranked as SIL > FD > Hay. The effective degradability of DM was lower (P < 0.001) for Hay than for FD and SIL. Ensiling lowered (P < 0.001) whereas haymaking increased (P < 0.001) intestinal digestion of CP compared with the fresh PPC. There were no differences in intestinal DM digestion among the three conserved forages. The results suggest that PPC conserved as Hay may conserve the biological activity of CT via preserving extractable CT more than as SIL, thus having the potential to improve protein utilization in ruminants.

Seasonal Variation of Tannin and Nutrient in Aegiceras corniculatum Leaves in Zhangjiang Mangrove Ecosystem

Seasonal dynamics of total phenolics (TP), extractable condensed tannins (ECT), protein-bound condensed tannins (PBCT), fiber-bound condensed tannins (FBCT), total condensed tannins (TCT) and nitrogen contents in sun and shade leaves of Aegiceras corniculatum were studied in the Zhangjiang Estuary, Fujian Province, China. The contents of TP, ECT and TCT in the sun leaves were significantly higher than those in the shade leaves through the season. The N content in sun leaves was higher than that in shade leaves in the autumn, while it was lower in the summer, and there was no significant difference in the winter and spring. With the respect to the P through the year, P content in the sun leaves was different between seasons, with the highest in winter and the lowest in summer. In addition, the TP:N and ECT:N ratios in sun leaves were significantly higher than those in shade leaves except in autumn. High tannin levels and TP:N and ECT:N ratios in the sun leaves not only can reduce oxidative stress, but also improve the ability of resisting plant diseases and insect pests.

Condensed tannins concentration of selected prairie legume forages as affected by phenological stages during two consecutive growth seasons in western Canada

Li, Y., Iwaasa, A. D., Wang, Y., Jin, L., Han, G. and Zhao, M. 2014. Condensed tannins concentration of selected prairie legume forages as affected by phenological stages during two consecutive growth seasons in western Canada. Can. J. Plant Sci. 94: 817–826. Studies have shown that condensed tannins (CT) at appropriate concentrations improve nutrient digestion in animals and influence ecosystem processes. However, knowledge of CT concentration in different phenological stages and different plant parts of non-conventional legumes growing in the western Canadian prairies is lacking for feed and grazing management. The research objectives were to determine the level and distribution of total CT (TCT), extractable CT (ECT) and protein-bound (PCT) or fiber-bound CT (FCT) concentrations in the whole plant of legume forages at different phenological (vegetative, flowering, seed maturity) stages and plant parts (leaves, stems, inflorescences and inflorescences+seedpods) using the Butanol-HCl procedure. Whole plant samples of purple prairie clover (Dalea purpurea Vent.), white prairie clover (D. candida Michx. ex Willd), sainfoin (Onobrychis viciifolia Scop.) and Canadian milkvetch (Astragalus canadensis L.) were collected in the 2011 and 2012 growing seasons from replicated small trial plots at vegetative, flowering and seed maturity stages. Species, phenological stages and their interactions all significantly affect the TCT, ECT, PCT and FCT concentrations in whole plant and plant parts (P<0.001). Concentrations of ECT and TCT increased for all species as they matured from vegetative to seed maturity, except for sainfoin where the vegetative stage had the highest ECT and TCT levels. The highest mean ECT and TCT concentrations for purple prairie clover and white prairie clover were found in the inflorescences part at flowering stage, while sainfoin had the highest ECT and TCT concentrations in the leaves at vegetative stage. There was little variation for PCT among different phenological stages in whole plant for species except for purple prairie clover and white prairie clover which had higher (P<0.05) PCT at seed maturity than at flowering stage. Only trace amounts of FCT were detected from either whole plant or different fractions of all plant species, except Canadian milkvetch. Condensed tannins were not observed in Canadian milkvetch except for trace amounts in the seed coat at seed maturity stage. The results demonstrate that legumes differ in their condensed tannin content which could potentially be used in pasture management.

Condensed tannins concentration of selected prairie legume forages as affected by phenological stages during two consecutive growth seasons in western Canada

Li, Y., Iwaasa, A. D., Wang, Y., Jin, L., Han, G. and Zhao, M. 2014. Condensed tannins concentration of selected prairie legume forages as affected by phenological stages during two consecutive growth seasons in western Canada. Can. J. Plant Sci. 94: 817-826. Studies have shown that condensed tannins (CT) at appropriate concentrations improve nutrient digestion in animals and influence ecosystem processes. However, knowledge of CT concentration in different phenological stages and different plant parts of non-conventional legumes growing in the western Canadian prairies is lacking for feed and grazing management. The research objectives were to determine the level and distribution of total CT (TCT), extractable CT (ECT) and protein-bound (PCT) or fiber-bound CT (FCT) concentrations in the whole plant of legume forages at different phenological (vegetative, flowering, seed maturity) stages and plant parts (leaves, stems, inflorescences and inflorescences seedpods) using the Butanol-HCl procedure. Whole plant samples of purple prairie clover (Dalea purpurea Vent.), white prairie clover (D. candida Michx. ex Willd), sainfoin (Onobrychis viciifolia Scop.) and Canadian milkvetch (Astragalus canadensis L.) were collected in the 2011 and 2012 growing seasons from replicated small trial plots at vegetative, flowering and seed maturity stages. Species, phenological stages and their interactions all significantly affect the TCT, ECT, PCT and FCT concentrations in whole plant and plant parts (P<0.001). Concentrations of ECT and TCT increased for all species as they matured from vegetative to seed maturity, except for sainfoin where the vegetative stage had the highest ECT and TCT levels. The highest mean ECT and TCT concentrations for purple prairie clover and white prairie clover were found in the inflorescences part at flowering stage, while sainfoin had the highest ECT and TCT concentrations in the leaves at vegetative stage. There was little variation for PCT among different phenological stages in whole plant for species except for purple prairie clover and white prairie clover which had higher (P<0.05) PCT at seed maturity than at flowering stage. Only trace amounts of FCT were detected from either whole plant or different fractions of all plant species, except Canadian milkvetch. Condensed tannins were not observed in Canadian milkvetch except for trace amounts in the seed coat at seed maturity stage. The results demonstrate that legumes differ in their condensed tannin content which could potentially be used in pasture management.

Changes of tannin and nutrients during decomposition of branchlets of Casuarina equisetifolia plantation in subtropical coastal areas of China

A litterbag experiment was conducted to investigate the changes of tannins and nutrients in branchlets at different decomposition stages of Casuarina equisetifolia in southern subtropical coastal zone, China, using the colorimetric assays. The time required for the loss of half of the initial dry weight (t&lt;sub&gt;50&lt;/sub&gt;) was 9.13 months. Total phenolics (TP), extractable condensed tannins (ECT), protein-bound condensed tannins (PBCT), total condensed tannins (TCT) and protein precipitation capacity (PPC) of branchlets litter decreased rapidly, while fibre-bound condensed tannins (FBCT) increased during decomposition. Nitrogen and phosphorus concentration of the branchlet litter both increased gradually during decay. Negative correlations between TP and nitrogen or phosphorus, as well as TCT and nitrogen or phosphorus were found. These chemical changes enhanced the current knowledge on the potential ecological role of nutrient transformation in tannins in C. equisetifolia plantations.

Effects of fertilization and drought stress on tannin biosynthesis of Casuarina equisetifolia seedlings branchlets

Nutrient, water, and their interactions influence the allocation of investment by plants to resistance and tolerance traits. We used a completely crossed randomized-block design experiment to examine the independent and interactive effects of nutrients and water availability on tannin production of C. equisetifolia seedlings. The results showed that nitrogen and phosphorus fertilizer have significant effects on total phenolics (TP) and extractable condensed tannins (ECT) concentrations of branchlets. TP and ECT concentrations decreased with fertilizer addition and increased in arid condition. This pattern lends to support source-sink hypothesis such as the carbon-nutrient balance (CNB) hypothesis and the growth-differentiation balance (GDB) hypothesis. Soluble sugars or starch concentrations were both inversely related to TP concentrations. However, there was no significant correlation between them and ECT concentrations. In addition, chlorophyll concentration had a positive linear correlation with TP and no significant correlation with ECT. On the contrary, chlorophyll a/b ratios were negatively correlated with TP and positively correlated with ECT. The discrepancy of relationship between carbohydrates and TP or ECT showed that the biosynthetic routes of different tannins were different. In this study, no significant correlation between TP and N, or ECT and N, did not support protein competition model (PCM). TP:N and ECT:N ratios were higher in nutrient deficiency and arid conditions, which were one of the important nutrient conservation strategies for C. equisetifolia.

Changes of condensed tannins during decomposition of leaves of Kandelia obovata in a subtropical mangrove swamp in China

Kandelia obovata, with abundant condensed tannins (CTs), is a typical mangrove species in China, but little is known about the chemical alterations and ecological roles of CTs during leaf litter decomposition. A litterbag experiment was conducted to investigate the changes of CTs in a subtropical mangrove swamp along Zhangjiang River Estuary, China, using the colorimetric assays, reversed/normal-phase HPLC–ESI-MS and MALDI–TOF-MS techniques. Total phenolics (TP), extractable CTs (ECT) and total CTs (TCT) decreased rapidly, while bound CTs (BCT), including protein- and fibre-bound CTs in leaves, increased during decomposition, and these temporal changes were well-expressed by exponential functions. Negative correlations between nitrogen (N) and TP, as well as N and ECT were found; however, a positive correlation between N and BCT was detected, suggesting that CTs played an important role in humification during N immobilization. The HPLC–ESI-MS analyses showed that the polymerization degree of CTs had an initial increase, due to leaching, followed by a decrease in the subsequent shift towards abiotic or/and biotic degradation. MALDI–TOF-MS confirmed the degradation processes for CTs. A decrease in the degree of hydroxylation, along with an increase in glycosylation-CTs, was obtained during litter decomposition. These chemical changes enhanced the current knowledge on the potential ecological role of N transformation in CTs in mangrove swamps.

Temporal changes of polyphenols and enzyme activities in seedlings of Kandelia obovata under lead and manganese stresses

The temporal responses of peroxidase (POD), superoxide dismutase (SOD), total polyphenols (TP), extractable condensed tannins (ECT) to different levels of lead (Pb) or manganese (Mn) stress, as well as the metal accumulation, in seedlings of Kandelia obovata were investigated. Both stress time and stress intensity had significant effects with significant accumulation of Pb and Mn in roots at Day 1. Pb and Mn showed no significant effects on root or leaf TP and ECT at Day 1. Prolonged exposure to metals caused significant drops of root TP and ECT but increased in leaves at Days 7 and 49. POD activities decreased in both roots and leaves at Day 1, while POD and SOD both increased under moderate levels of Pb and Mn at Day 7. The present study showed that antioxidative enzyme activities were more sensitive indicators to Pb or Mn stresses than phenolic compounds.

Tannin dynamics in hypocotyls and pericarps of Aegiceras corniculatum fruits during dry storage

In this study, we investigated the changes in total phenolics, extractable condensed tannins (ECT), protein noncovalent bound condensed tannins (PNBCT) and irreversible covalent bound condensed tannins (ICBCT) in the hypocotyls and pericarps of Aegiceras corniculatum fruits during dry storage. The loss of moisture content and survival rate, as indicators of the viability and quality of plant tissues, were also monitored during the dry storage. Great amount of free condensed tannins combined with proteins in the senescent pericarps during the process of deteriorative reactions associated with dry storage, which contributed to the rapid increase of PNBCT characterized by the sigmoid model. However, there was a rapid loss of total phenolics and ECT from pericarps during the first 9 days of the dry storage, with 37.3% loss of ECT due to the transformation of PNBCT. PNBCT of the hypocotyls also fitted a sigmoid model with dry storage time, and was related to the viability of the hypocotyls. During the dry storage, most of the disappeared ECT of hypocotyls formed complexes with protein, and the total condensed tannins (TCT) did not decline during the 27 days dry storage. The distribution of the oligomers and polymers in the condensed tannins was significantly different between the fresh and dried hypocotyls of A. corniculatum. The oligermers with lower degree of polymerization (DP) appeared to have higher capacity of binding to proteins than the polymers with high DP in plant tissues during the dry storage. The changes of hydroxy pattern of tetramers in the fresh and dried hypocotyls showed that the proteins would be selective binding those flavan-3-ol oligomers with more hydroxyl in plant tissues with deteriorative reactions during dry storage. However, the hydroxy pattern of nomamers was not significantly different between the fresh and dried hypocotyls. Our results indicated that few flavan3-ol polymers reacted with proteins in hypocotyls of A. corniculatum associated with the deteriorative reactions during the dry storage.

Seasonal changes in tannin and nitrogen contents of Casuarina equisetifolia branchlets

Seasonal dynamics of total phenolics (TP), extractable condensed tannins (ECT), protein-bound condensed tannins (PBCT), fiber-bound condensed tannins (FBCT), total condensed tannins (TCT), and protein precipitation capacity (PPC) in young, mature and senescent branchlets of Casuarina equisetifolia were studied at Chishan Forestry Center of Dongshan County, Fujian Province, China. In addition, nitrogen contents of branchlets at the different developmental stages were also determined. The contents of TP and ECT, and PPC in young branchlets were significantly higher than those in mature and senescent branchlets through the season. However, PBCT contents were significantly higher in senescent branchlets than those in young and mature branchlets; FBCT fluctuated with season. Young branchlets had the highest N content, which decreased during branch maturity and senescence. The highest contents of TP and the lowest contents of TCT and N in young and mature branchlets were observed in summer. There was a significant negative correlation between TP and N contents. In contrast, TCT contents were positively correlated to N contents. Nutrient resorption during senescence and high TCT:N ratios in senescent branchlets are the important nutrient conservation strategies for C. equisetifolia.

Tannin Dynamics of Propagules and Leaves of Kandelia candel and Bruguiera gymnorrhiza in the Jiulong River Estuary, Fujian, China

Changes in the total phenolics, condensed tannins (CT), protein-precipitable phenolics content and protein precipitation capacity were determined on a series of mangrove leaves from two true viviparous mangrove species (Kandelia candel and Bruguiera gymnorrhiza) at various stages of development and decomposition in the Jiulong River Estuary, Fujian, China. Similar measurements were also done for the propagules at different developmental stages. The results showed that the total phenolics, extractable condensed tannins, total condensed tannins, protein-precipitable phenolics content and protein precipitation capacity in young leaves were higher than those in mature and senescent leaves. Tannin dynamics during leaf decomposition varied with species, and the rapid loss of phenolics observed during decomposition can be ascribed to leaching and degradation. Protein-bound CT and fibre-bound CT tended to increase with leaf decomposition, with CT binding more strongly to protein than to fibre. Protein-bound CT was higher than fibre-bound CT with the exception of mature leaves. Total phenolics, extractable CT and protein-precipitable phenolics contents in flower tissues were relatively lower than those in hypocotyls at different developmental stages. Protein precipitation capacity fluctuated with the development of propagules. Increases in nitrogen in decaying litter, and declines in contents of total phenolics and total condensed tannins of detritus support the general conclusion that decomposing mangrove detritus can be a more palatable heterotrophic substrate than living leaves.

Forage quality and tannin concentration and composition of a collection of the tropical shrub legume Flemingia macrophylla

AbstractA collection of 23 Flemingia macrophylla (Willd.) Merrill accessions of different growth habits and contrasting digestibility and one Flemingia stricta reference accession were assessed for forage quality with particular emphasis on digestibility, condensed tannin concentration and fiber content. Large differences in in vitro dry matter digestibility (IVDMD) (356 to 598 g kg−1), content of crude protein (CP) (121 to 254 g kg−1) and extractable condensed tannins (CT) (0 to 268 g kg−1), protein‐binding capacity of extractable CT or astringency (1.7 to 7.9 protein‐binding entities) (PBE) and monomer composition of extractable CT were detected. IVDMD and extractable CT were negatively correlated and extractable CT was positively correlated with protein‐binding capacity. Prodelphinidin was positively and propelargonidin negatively correlated with protein‐binding capacity of extractable CT. The accessions CIAT 18438, CIAT 21083, CIAT 21090 and CIAT 22082 were superior to the most widely used accession CIAT 17403 in terms of forage quality and could be an option in production systems with acid infertile soils. In future evaluations, particular attention needs to be paid to chemical and structural features related to the composition of extractable CT and their effect on nitrogen utilization by ruminants. Copyright © 2006 Society of Chemical Industry