Dietary Tannins Research Articles

Tannins — a dietary problem for hand-reared grey partridge Perdix perdix after release?

A 4-week feeding trial on 22 grey partridges Perdix perdix was conducted in this study. Seven birds were fed commercial poultry food, seven natural food and eight commercial poultry food containing 6% of quebracho–tannin. Our results suggest that 6% dietary tannin, when added to a commercial food with high protein content, effects the grey partridge only slightly. No difference was seen in food consumption and body mass remained stable. However, birds fed tannin had longer small intestines, which most probably indicate gastrointestinal detoxication. They also excreted a high amount of tannin in their faeces. In addition, no between-group variation was seen in cytochrome P450 enzymes. Birds fed natural food had high concentration of nitrogen in intestinal excreta and high plasma alanine concentrations. They also suffered a rapid decrease in body mass after the change in diet and their body mass remained low. This may indicate increased protein excretion and/or catabolism of endogenous nutrient reserves. Potential short-term effects of the change in diet were seen in plasma. These findings coincide with the high mortality period of birds released into the wild.

The molecular interaction of human salivary histatins with polyphenolic compounds

Dietary tannins are polyphenols that are effectively precipitated by salivary histatins (Hsts), a novel family of tannin binding proteins. Epigallocatechin gallate (EGCG), a flavan-3-ol ester related to condensed tannins (polymerized products of flavan-3-ols), and pentagalloyl glucose (PGG), a hydrolyzable tannin, were used to evaluate the molecular nature of Hst-polyphenol interaction. NMR demonstrated that Hst5, a representative Hst, bound to EGCG in a hydrophobic manner via basic and aromatic residues. In contrast, proline plays a dominant role in polyphenol binding to other tannin precipitating proteins. The role of basic and aromatic amino acids in EGCG binding was investigated using a series of modified Hsts in each of which one type of amino acid was substituted by Ala. EGCG bound to all modified Hsts, but the binding was diminished. Optimal EGCG binding also depended on the primary structure, as a polypeptide with randomised Hst5 sequence showed significantly diminished interaction with EGCG. Soluble EGCG/Hst5 complexes containing up to seven molecules of EGCG per mol of Hst5 had a 1-mM dissociation constant. In contrast to EGCG, PGG formed small soluble complexes with Hst5 consisting of only one molecule each of PGG and Hst5, as demonstrated by analytical ultracentrifugation. These complexes became insoluble upon binding of additional molecules of PGG. Diminished PGG binding was seen to a peptide with a Hst5 randomized sequence showing the importance of the primary structure. Hsts may serve to form insoluble complexes with tannins thereby preventing their absorption from the intestines and potentially harmful biological effects. In contrast the much weaker interaction with EGCG may allow its uptake into the organism and exploitation of its antioxidant effect.

Desempenho do piauçu (Leporinus macrocephalus) arraçoado com dietas contendo diferentes teores de tanino

Este estudo foi conduzido com o objetivo de avaliar o efeito dos taninos sobre o desempenho produtivo e a composição da carcaça do piauçu. Utilizaram-se 21 aquários (80 L) num sistema de fluxo fechado com circulação continua (vazão de 1 L/min), filtro biológico e temperatura controlada. Empregaram-se 84 peixes com peso médio inicial de 5,06 g, na densidade de quatro por aquário, num delineamento inteiramente casualizado com sete tratamentos e três repetições. As rações foram formuladas de forma a apresentarem-se isoenergéticas (3200 kcal ED/ kg de ração) e isoprotéicas (30% PB), com as seguintes composições de tanino total: 0,00; 0,23; 0,46; 0,69; 0,92; 1,37 e 1,82. Avaliou-se a influência do tanino sobre o desempenho produtivo: ganho de peso, conversão alimentar aparente e taxa de eficiência protéica; a composição corporal dos peixes: proteína bruta da carcaça, extrato etéreo da carcaça, proteína bruta e extrato etéreo dos fígados e gordura visceral; e a relação hepatossomática: índice hepatossomático. Concluiu-se que, embora a presença de até 0,69% de taninos na ração não tenha comprometido os índices de conversão alimentar aparente e taxa de eficiência protéica das rações, níveis iguais ou superiores a 0,46% resultaram em ganho de peso significativamente inferior para o piauçu e que a espécie se mostrou sensível à presença de taninos condensados, os quais prejudicaram significativamente o metabolismo e o valor biológico dos nutrientes presentes nas rações.

Proteolytic processing of a human salivary proline-rich protein precursor by proprotein convertases.

Salivary proline-rich proteins (PRPs) are synthesized as precursors that are cleaved before secretion giving rise to glycosylated PRPs which have lubricating function and basic PRPs which are potent precipitators of dietary tannins. The putative cleavage sites in the precursors for basic and glycosylated PRPs all conform to the sequence RSXR downward arrowS (X can be A, S or P) in agreement with the recognition sequence (RXXR downward arrow) for various proprotein convertases. PRB4S, a proprotein giving rise to a basic PRP (IB-5) as well as a glycosylated PRP (II-1) was synthesized by in vitro transcription-translation. It was cleaved by furin at RSAR downward arrowS(173-178) giving rise to two proteins II-1 and IB-5. Similarly another precursor with the sequence RSAR downward arrowS(173-178) was also cleaved by furin. This together with previous results show that in vitro furin can cleave all RSXR downward arrowS sequences in the proproteins that give rise to glycosylated and basic PRPs. To demonstrate cellular cleavage, a human submandibular cell line (HSG) was transfected with a vector encoding PRB4S. This resulted in secretion of II-1 and IB-5. The degree of cleavage was enhanced by coexpressing furin and PRB4S. No cleavage occurred if the cells expressed a mutant PRB4S, R177Q, where the furin cleavage site had been destroyed. Cleavage was also inhibited if a furin inhibitor was coexpressed with PRB4S. Incubating the cells at 20 degrees C which blocks exit of proteins from the trans-Golgi network demonstrated that cleavage occurs before exit of the proteins from this network. These results show that furin may be responsible for in vivo cleavage of PRP precursors. Transfecting furin-deficient RPE.40 cells with a vector encoding PRB4S also led to secretion of II-1 and IB-5 showing that convertases other than furin can also cleave PRB4S in tissue culture.

The effects of tannin and protein on food preference in eastern grey squirrels

Although some mammalian generalist herbivores avoid foods high in plant secondary compounds, it has not been adequately shown that eastern grey squirrels (Sciurus carolinensis), who regularly encounter tannin in acorns, avoid high tannin diets. Dietary tannin can inhibit nitrogen assimilation; hence herbivores that eat tannin should seek high protein diets to compensate. I presented freeranging grey squirrels with four types of dough balls that differed in tannin and protein content. Squirrels consistently preferred low to high tannin foods but did not distinguish between low and high protein foods. Intensity of preference for low tannin foods was greatest during early to mid autumn, when food is relatively abundant, and declined into the spring and early summer, when food is relatively scarce. Food availability, partitioning foraging effort between eating and scatterhoarding, physiological competence, and nutrient complementarity may explain why squirrels consume tannin in natural diets, in spite of preference for low tannin dough balls demonstrated here.

Preference for polyethylene glycol by sheep fed a quebracho tannin diet.

Tannins decrease food intake by reducing digestion and by causing illness, whereas polyethylene glycol (PEG) attenuates the aversive effects of tannins. Our objective was to determine whether sheep recognize the benefits of ingesting substances such as PEG when consuming tannins. If so, then ingestion of PEG should be 1) PEG-specific, 2) a function of previous experience with recovery from tannin-toxicosis, and 3) dependent on the presence/absence of tannins. During conditioning, lambs in Group 1 (n = 10) were offered a meal of high-tannin food, which presumably caused malaise, and then offered PEG (molecular weight, 3,350), which presumably led to recovery from malaise. Subsequently, lambs ingested a control food (wheat straw) that did not have the "medicinal" effects of PEG in the absence of the tannin diet. In contrast, lambs in Group 2 (n = 10) ingested PEG in the absence of the tannin diet, and they ingested the tannin diet only in association with wheat straw. Ingestion of PEG and straw by both groups of lambs increased as a function of the presence of tannins in the diet (P < 0.05). However, when offered a choice among the tannin diet, PEG and straw, or when given the tannin diet and then offered a choice between PEG and straw, lambs trained to associate PEG with tannins ate more PEG than lambs that ingested PEG without tannins (P < 0.05). The responses were apparently PEG-specific; straw intake did not differ between groups of lambs during testing (P > 0.05), and differences in PEG intake disappeared in the absence of tannins (P > 0.05). In summary, our results suggest that lambs fed high-tannin diets discriminated the effects of PEG from those provided by a "nonmedicinal" food (straw). Thus, it may be possible to formulate PEG supplements that allow herbivores to self-regulate intake of PEG under extensive management conditions.

Differential long-term effects of tannic acid on adenyl cyclase activity and lipolysis in rat adipocytes.

Plants elaborate a variety of secondary metabolites such as hydrolysable tannins which are relatively abundant in fruits, vegetables and beverages in the human diet. We have studied the in vivo long-term effect consumption of tannic acid-supplemented drinking water (0.05%, w/v) on the rat adipocyte adenyl cyclase system and on lipolysis. We found that 14-day tannic acid supplementation did not significantly affect either body growth or food consumption, while fat pads weight was higher than that of the control, although the difference was not significant. On the other hand, tannic acid supplementation decreased both basal and isoproterenol-stimulated lipolysis significantly whereas cyclic AMP production as well as adenyl cyclase activity increased significantly. These results are at a first glance contradictory as cyclic AMP accumulation and lipolysis are positively correlated in rat adipocytes. They suggest at least that the tannic acid diet led to an inhibition of cyclic AMP-dependent protein kinase activity followed by a decrease in lipolysis in rat adipocytes, and to an increased activity of the type VI adenyl cyclase subunit of rat fat cells. This subunit is known to be negatively regulated under phosphorylation by cyclic AMP-dependent protein kinase. More in-depth studies are required to examine whether tannic acid could at least modify the expression of the catalytic subunit of adenyl cyclase, G-proteins and cyclic AMP-dependent protein kinase and/or alter their activities.

Response of silvereyes (Zosterops lateralis) to dietary tannins: the paradox of secondary metabolites in ripe fruit

There are many secondary metabolites in ripe fruit that are toxic to vertebrate consumers. The most prevalent explanation for their presence in ripe fruit is to protect the fruit against consumers that do not disperse viable seeds. It has been hypothesised that seed dispersers are not deterred by, or can tolerate, the consumption of secondary metabolites in ripe fruit. We tested whether silvereyes (Zosterops lateralis), which are known seed dispersers, were deterred by quebracho (condensed tannins) presented in two different food types. In the first experiment, silvereyes were given artificial fruit containing either 0% or 5% quebracho and their fruit consumption was measured. A second experiment recorded consumption of a cereal-based, long-term maintenance diet containing either 0% or 5% quebracho. Silvereyes did not exhibit a significant preference for artificial fruit that did not contain quebracho: 39.9% of the fruit consumed did contain quebracho. However, silvereyes strongly avoided the cereal diet containing quebracho, consuming, on average, only 0.36 g (0.06 g) of cereal per 5 h compared with 17.3 g (0.23 g) of cereal that did not contain quebracho. We suggest that because the artificial fruit were swallowed whole by silvereyes, the quebracho may not have been detected as easily in the time available as it would have been in the aqueous cereal diet. Consumption of fruit containing secondary metabolites by wild silvereyes is likely to depend on factors such as food availability, nutrient content of the fruit and the degree of diet mixing.

Secondary Plant Products. Antinutritional and beneficial actions in animal feeding

Introduction *Overview of secondary plant products *Tannins: their nature and biological significance *Tannins: implications for non-ruminants *Effects of dietary tannins on ruminants *Protein protease inhibitors from plants *Plant breeding: what is being, can be and should be done *Plant lectins *Discussion and conclusion *Index

Differential Sensitivity to Vegetable Tannins in Planktonic Crustacea from Alpine Mosquito Breeding Sites

The differential capability to detoxify dietary tannins from the leaf litter of the vegetation surrounding alpine mosquito communities was experimentally investigated in different strains of planktonic crustacean taxa (Daphnia pulex, Simocephalus vetulus, and Eucypris virens) associated with the culicine populations. Tannic acid, used as an experimental standard, had differential biocidal effects in strains associated with various surrounding vegetation with different phenolic contents. Such a differential sensitivity to tannic acid was correlated with qualitative and quantitative features of cytochromes P-450, esterases, and glutathione S-transferases activities measured in these strains. This suggests that these enzymes are involved in the detoxification of vegetable tannins by these crustacean taxa. Contribution of cytochromes P-450, esterases, and glutathione S-transferases in the resistance of Crustacea to those xenobiotics was also implied by the synergistic effect in vivo of piperonyl butoxide and S,S,S, tributyl phosphorotrithioate on the toxicity of tannins.

Differential Toxicity of Leaf Litter to Dipteran Larvae of Mosquito Developmental Sites

The relative toxicity of leaf litter to nematocerous dipteran larvae characteristic of mosquito developmental sites was investigated. Culicidae, Chironomidae, and Simuliidae taxa originating from alpine hydrosystems were tested together with two laboratory nonindigenous culicid taxa. Bioassays indicate that ingestion of 10-month-old decaying leaves from Alnus glutinosa, Populus nigra, and Quercus robur by larvae is more deleterious for Aedes aegypti, A. albopictus, Culex pipiens, Simulium variegatum, and Chironomus annularius than for A. rusticus. Histopathological observations reveal that the midgut epithelium is the main target organ of the toxic effect of dietary leaf litter, which appears to be stronger than that of previously reported tannic acid. There is a general response of the nematocerous larval midgut epithelium to dietary tannins–phenolic compounds: clear cells of the anterior midgut showing symptoms of intoxication before dark cells of the posterior midgut.

Self-regulation of intake of polyethylene glycol by sheep fed diets varying in tannin concentrations.

Tannins occur in many plant species, and they often suppress intake by reducing nutrient availability or by causing malaise. Polyethylene glycol (PEG) binds to tannins and may thereby increase the availability of macronutrients and decrease malaise. Supplemental PEG increases intake of tannin-containing plants by sheep, goats, and cattle. Given the strong response to supplemental PEG, we speculated that animals might self-regulate their intake of PEG when offered foods high in tannins. The objective of the first experiment was to determine if the amount of supplemental PEG (0, 25, 50, 75, or 100 g; molecular weight, 3,350) affected intake by lambs of a food (milo-tannin mix) containing 20% quebracho tannin. There was a linear relationship (Y = 272 + 1.2X; R2 = .86; P = .023) between the amount of supplemental PEG ingested and the subsequent intake of milo-tannin food by lambs. The objective of the second experiment was to determine whether lambs self-regulated intake of PEG when fed a ration that contained 0, 5, 10, 15, or 20% quebracho tannin and whether they adjusted their intake of PEG when tannin was removed from the diet. There was a positive relationship between the amount of PEG ingested and intake of food and tannin (P = .0001). Lambs fed high-tannin diets ate more PEG than controls (P = .03). Lambs fed the 20% tannin diet ate the most PEG, and controls ate the least PEG. Tannin limited intake of the diets, but PEG attenuated the response to a great degree (P = .065). Immediately after tannin was removed from the ration, lambs that formerly had been fed the 20% tannin ration ate more PEG than lambs fed the other rations (P = .0075). Ten of the lambs (5 from the 20% tannin group, 1 from the 15% tannin, and 2 each from the 10 and 5% groups) continued to eat PEG for 7 d after tannin was removed from their ration. When they were tested again 6 wk after the trial and offered tannin-free diets, their intake of PEG had decreased.

Antibody to H(+) V-ATPase subunit E colocalizes with portasomes in alkaline larval midgut of a freshwater mosquito (Aedes aegypti).

The pH profile, gross structure, ultrastructure and immunolabeling of the mosquito (Aedes aegypti) larval midgut are described as a first step in analyzing the role of plasma membrane H(+ )V-ATPase in the alkalization of the gut, nutrient uptake and ionic regulation. Binding of an antibody to H(+ )V-ATPase subunit E colocalizes with 'portasomes' (approximately 10 nm in diameter), which are thought to correspond to the V(1) part of the H(+) V-ATPase. In gastric caeca (pH 8), both antibody-binding sites and portasomes are located apically; in the anterior midgut (pH 10-11), they are located basally; and in the posterior midgut (pH approximately equal to 8) they are again located apically. The hypothesis that the energization of alkalization is mediated by an H(+) V-ATPase is supported by the inability of larvae to maintain the high pH after 72 h in 10 (micro)M bafilomycin B1. Confirming earlier reports, the two principal epithelial cell types are designated as 'columnar' and 'cuboidal' cells. The apical plasma membranes (microvilli) of epithelial cells in the gastric caeca and basal infoldings of anterior midgut are invaded by mitochondria that lie within approximately 20 nm of the portasome-studded plasma membranes. The colocalization of V-ATPase-immunolabeling sites and portasomes to specific plasma membranes within so-called 'mitochondria-rich' cells of gastric caeca and anterior midgut suggests that midgut alkalization in mosquitoes is achieved by molecular mechanisms similar to those that have been described in caterpillars, even though the gross structure of the midgut and the localization of the V-ATPase are dissimilar in the two species. In caterpillars, the high alkalinity is thought to break down dietary tannins, which block nutrient absorption; it may play a similar role in plant-detritus-feeding mosquito larvae. The colocalization of immunolabeling sites and portasomes, together with the presence of long, 'absorptive-type' microvilli in the posterior midgut, suggest that the V-ATPase energizes nutrient uptake there.

Effects of ruminal inoculations with tannin-tolerant bacteria on fibre and nitrogen digestibility of lambs fed a high condensed tannin diet

The goal of this study was to evaluate the effects of dosing unadapted lambs with tannin-tolerant bacteria to improve the digestibility of a high condensed tannin (CT) diet. During the initial phase (metabolism study), a diet containing 30% peanut skins was fed to two groups of Suffolk × Finn-Dorset ram lambs that were about three months old and weighed an average of 24.2 ± 1.4 kg. All animals received 150 ml of a culture (A 600 of 1.0) of a Gram positive rod (a close relative of Eubacterium cellulosolvens) that was able to tolerate 0.5 g/l of purified CT from Desmodium ovalifolium. The control group (7 animals) was inoculated with autoclaved bacteria. The treatment group (6 animals) was inoculated with actively growing bacteria. Inoculations were made daily during a three-week period. Dry matter intake (DMI) was 55.4 and 64.9 g/kg 0.75/day for the control and treatment group, respectively, ( P = 0.13). Digestibility of DM, crude protein (CP) and neutral detergent fibre (NDF) was similar between treatments. Crude protein intake ( P = 0.10) and CP retention ( P = 0.07) were higher for animals inoculated with live bacteria. The CP retention/CP intake ratio was also higher for animals inoculated with the live bacteria ( P = 0.07). To investigate carry-over effects on animal performance due to the bacterial inoculations after the metabolism study, the animals were kept in metabolism cages, but they received no supplemental bacteria. During a subsequent two-week period, the animals continued to receive the high CT diet. Dry matter and CP intake, as well as the feed : gain ratio, were similar between the groups of animals. Finally, for a second two-week period, the animals were fed a low CT (normal) diet without peanut skins. Dry matter intake was 92.9 and 88.6 g/kg 0.75/day for the control and treatment groups, respectively ( P = 0.14). Crude protein intake and feed : gain ratio were similar between the two groups of animals.

Effects of feeding quebracho tannin diets, with or without a dietary modifier, on rumen function in sheep

AbstractThe effect of quebracho tannin (QT) on the activities of rumen microbes was studied both in vivo and in vitro. The in vivo study was carried out in four rumen environments created by feeding four fistulated sheep a basal diet of chopped grass hay, grass cubes and whole barley (control) with or without the addition of QT and the dietary modifier Browse Plus (BP). The active ingredients in BP are polyethylene glycol (PEG, more than 0·95 of the dry material), polyvinyI pyrrolidone (PVP) and calcium hydroxide. The diets offered were control, control plus 50 g QT per kg diet (CQT), control plus 50 g QT per kg and 0·1 (CQT+ 0·1) or 1.0 g BP per kg (CQT + 1·0). The experiment was a 4 X 4 Latin-square design with periods of 4 weeks. Rumen liquor samples were collected at 0, 2, and 8 h after feeding, 18 and 25 days after commencement of each period. Changes in free and bound proanthocyanidin (PA) concentrations, rumen pH, ammonia, volatile fatty acids (VFA), soluble protein concentrations, particle-bound cellulase and xylanase activities and rumen protozoal counts were used as indices of microbial activities. The same diets were incubated with rumen contents in vitro, except that the 0.1 g/kg level of BP was replaced by a fourth treatment made up of control plus 1·0 g BP per kg DM of hay (CBP). In vivo, bound PA concentrations in the rumen liquor of all the sheep given QT-containing diets were higher than those of the free PAs. The bound PA was higher (V &lt; 0·05) in the rumen liquor of sheep given CQT in comparison with those containing BP. There were reductions in ammonia (P &gt; 0·05), soluble protein (P &lt; 0·05) and total VFA (P &gt; 0·05) concentrations in the rumen liquor of sheep given CQT in comparison with those given the control and BP-containing diets. Reductions (P &gt; 0·05) were also observed in the cellulase and xylanase activities of the rumen microbes and in protozoal counts (P &lt; 0·05) in the presence of QT in the diet. In vitro, QT reduced (P &gt; 0·05) the viable bacterial counts, gas production and the total VFA concentrations after incubation. In both the in vivo and in vitro experiments, BP was able to alleviate some but not all of the depression in microbial activities. The main constituent (PEG) in BP binds to some of the tannins in solution and may displace tannins from tannin-protein complexes.

Effects of dietary quebracho tannin on nutrient utilisation and tissue metabolism in sheep and rats

The effect of feeding quebracho tannin, a mixture of condensed tannins, on dietary nutrient utilisation and nitrogen (N) retention and its effects on the gastrointestinal (GI) tract was investigated in sheep and rats. Sheep (n = 24) were fed on a pelleted diet of dried grass alone (controls) or containing quebracho tannin at 50 g kg−1 diet dry matter (DM) (tannin-fed animals) at a level sufficient to achieve a daily liveweight gain (DLWG) of 100 g day−1. Complete collections of faeces and urine were made for two seven-day periods after two and six weeks of feeding these diets (n = 6 per group). Apparent digestibilities of dry matter, N and neutral detergent fibre (NDF) were significantly (P < 0.001) reduced in tannin-fed animals at both measurement periods. No evidence was obtained to suggest that rumen micro-organisms can adapt to the presence of dietary tannins with prolonged feeding. Tannin-fed animals excreted significantly (P < 0.01) more N in faeces and less in urine than controls suggesting an alteration in N metabolism. Histological examination of samples of the GI tract obtained from pairs of sheep slaughtered after two, five and seven weeks of feeding the diets indicated ulceration and an increase in mucosal histiocytes, particularly in the jejunum and ileum of most tannin-fed animals. In a subsequent experiment, rats were fed ad libitum a ground chow containing either cellulose or quebracho tannin at 40 g kg−1 DM. Tannin-fed rats had significantly (P < 0.05) reduced feed intakes, DLWG, N retention and body fat deposition compared to controls. Protein synthesis rates in the duodenal mucosa were not increased in tannin-fed rats suggesting that enterocyte proliferation was not stimulated in this region of the GI tract. These studies indicate that feeding quebracho tannin to ruminants has both ruminal and post-ruminal effects that, together, result in reduced nutrient utilisation and impaired animal performance. © 1999 Society of Chemical Industry

Chemopreventive activity of very low dose dietary tannic acid administration in hepatoma bearing C3H male mice

Tannins are plant polyphenols comprising a heterogeneous group of compounds. Tannic acid is a common tannin found in tea, coffee, immature fruits, etc. and it has also been used as a food additive. An increasing body of experimental evidence supports the hypothesis that tannins exert anticarcinogenic activity in chemically induced cancers in animal models. In the present study, tannic acid was administered in very low doses in the drinking water of C3H male mice divided into three groups (75 mg/l, 150 mg/l and 300 mg/l). These animals carry a genetic defect and show a high incidence of spontaneous liver tumors (>50%) at an age older than 12 months. The results showed a decrease in the overall incidence of hepatic neoplasms (adenomas plus carcinomas): 53.3% of animals in the control group developed hepatic neoplasms versus 33.3% in the group given a low dose of tannic acid, 26.6% in the group given a medium dose and 13.3% in the high dosage group. The difference was more pronounced in the animals with carcinomas: 4.44% of mice who received tannic acid developed carcinomas versus 33.3% of those in the control group. Tannic acid administration did not affect the PCNA labeling index of normal hepatocytes. It is concluded that tannic acid dietary intake in low doses can exert a strong dose-dependent chemoprotective activity against spontaneous hepatic neoplasm development in C3H male mice, most probably through antipromoting mechanisms.

Interaction of Tannin with Human Salivary Histatins

The ability of all major human salivary histatins to precipitate condensed tannin was demonstrated, and it was found that histatins 3 and 5 share the same condensed tannin-binding region but less tannin bound to histatin 1. The condensed tannin-binding region of histatin 5 includes both the N- and the C-terminal parts, although more tannin binding occurs in the C-terminal region. Epigallocatechin gallate (EGCG) showed similar binding characteristics as condensed tannin, but much less EGCG was precipitated. Pentagalloyl glucose (PGG) was precipitated equally well by histatins 1, 3, and 5 and bound equally well to the N- and C-terminal regions of histatin 5. In contrast to condensed tannin, cleaving histatin 5 into N- and C-terminal fragments increased their ability to precipitate PGG. Together, these results show a number of differences in the nature of interaction of histatins with condensed tannin, EGCG, and PGG. Most of the condensed tannin-protein complexes remained insoluble under conditions similar to those in the stomach and the small intestine, suggesting that histatins may act as a defense against dietary tannin in humans.

Effects of dietary tannic acid and quebracho tannin on growth performance and metabolic rates of common carp ( Cyprinus carpio L.)

The effects of tannic acid (a hydrolysable tannin) and quebracho tannin (a condensed tannin) on common carp at a level of 2% in a soybean and fish meal-based diet containing about 40% crude protein have been studied. Quebracho tannin did not affect feed intake, body weight gain, average metabolic growth rate and oxygen consumption during the experimental period (84 days). The carp grew from an initial body weight of about 30 g to a final body weight of 150 g, and the carcass composition was also not affected by quebracho tannin. On the other hand, tannic acid produced adverse effects after day 28. The rejection of diet started on day 28 and a complete rejection of the diet was observed on day 40. The feeding of this diet was discontinued after day 42. The average metabolic growth rate for days 35–42 was significantly lower ( P<0.05) in this group. The oxygen consumption of carp fed a diet containing tannic acid also decreased although non-significantly for this period. It is concluded that the toxicity of tannic acid is higher to carp compared to that of quebracho tannin, and that protein sources of plant origin containing high amounts of tannins and in particular hydrolysable tannins should be used with caution as fish meal substitutes in carp diets.

Effect of Acacia saligna with and without administration of polyethylene glycol on dietary intake in desert sheep

AbstractThe study was designed to measure (i) dry-matter intake (DMT) of sheep when diets including different tannins were offered and (ii) the effect of administration of polyethylene glycol (PEG), a tannin-binding agent, on DMI of tannin-rich diets. Acacia saligna phyllodes, a potential food for sheep, quebracho powder or tannic acid were added to a concentrate diet that served as a control and were offered to 16 ewe lambs (34·6 (s.d. 3·3) kg) that is, four lambs per diet. A. saligna has high levels of tannins; quebracho is a complex mixture of phenolic compounds in which condensed tannins predominate while tannic acid is a relatively pure example of a hydrolysable tannin. Intake was measured during four periods (I to IV) of 10 days each in which PEG was offered during periods II and IV. Food and water were available ad libitum. The DMI of the concentrate diet ranged between 925 glday and 1050 glday which was higher than for the other three diets (P &lt; 0·05). The lambs consumed approximately 600 g dry matter (DM) of the diet that included 400 g A. saligna phyllodes per kg, and 500 g DM of the diets that included 100 glkg quebracho or 150 glkg tannic acid. With the quebracho and tannic acid diets, there was a distinct increase in intake when PEG was added and a decrease without PEG. This was not so with the Acacia diet when the intake remained high in period III without PEG and increased again in period IV with PEG. Body mass of control lambs increased in all periods and the increase was greater than in the other diets (P &lt; 0·05). With the quebracho and tannic acid diets, there was an increase in body mass when PEG was added and a decrease without PEG. With the Acacia diet, there was a decrease in body mass in period I and an increase thereafter, even without PEG in period III.