Dry bean tannins: A review of nutritional implications

Tannins are one of several antinutritional factors present in dry beans and are located mainly in the seed coat or testa. The tannin content of dry beans ranges from 0.0 to 2.0% depending on the bean species and color of the seed coat. Many high tannin bean varieties are of lower nutritional quality than low tannin varieties of beans. Naturally occurring food legume tannins are reported to interact with proteins (both enzyme and nonenzyme proteins) to form tannin-protein complexes resulting in inactivation of digestive enzymes and protein insolubility. Both in vitro and in vivo studies indicate that bean tannins decrease protein digestibility, either by inactivating digestive enzymes or by reducing the susceptibility of the substrate proteins after forming complexes with tannins and absorbed ionizable iron. Other deleterious effects of tannins include a lowered feed efficiency and growth depression in experimental animals. The antinutritional activity of bean tannins can be reduced by processing (1 or a combination of 2 or more methods), for example dehulling, soaking, cooking and germination. Genetic selection also may help in breeding varieties low in tannins. Potential chemical treatments such as use of tannin complexing agents are discussed. Presented at the AOCS Meeting, Dallas, Texas, April 1984.     

Gelatin/tannin complex nanospheres via molecular assembly

Nanospheres were produced by molecular assembly between tannin and gelatin because of the synergistic interaction of the hydrophobic effect and hydrogen bonding. The factors that influenced the production of nanospheres, such as sample concentration, mass ratio between tannin and gelatin, reaction temperature, pH, and reaction time, were studied. Moreover, the nanospheres were analyzed and characterized by a particle size analyzer, UV–vis spectrophotometer, and TEM. It was concluded that the critical point was important for the assembled nanospheres. The tannin/protein mass ratio should be lower than the critical point. The concentration of tannin should be confined to a relatively low level. The proper range of the reaction temperatures was usually between 10°C and 50°C. It was steady for nanospheres assembled when the pH value of the gelatin solution was within ±1 IEP of the gelatin. After the reaction had gone on for more than 48 h, the assembled nanospheres became stable. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3125–3130, 2006     

Effect of reheating on iron availability and the protein nutritive value of cooked black bean (Phaseolus vulgaris)]

In Guatemala, at the rural level, beans are prepared for family consumption every two days. Beans are cooked again every 12 hours for 15 minutes prior to their consumption. Due to the adverse effect that the process causes on nutritive value, the present study evaluated the method and preparation practice of beans on protein value; tannin and soluble and ionizable iron content. As to the effect of re-cooking on protein level, findings revealed that there were no significant statistical effects on net protein ratio (NPR) or in protein efficiency ratio (PER) and number of bean cooking. Nevertheless, a constant effect in quality in the first and second cooking procedure was detected. The second cooking gave a similar value as the first. Also, the first and second heating reduced protein digestibility, but the third gave a value similar to the initial one. No changes were observed in the digestibility of dry matter. Relatively high amounts of protein were found in the cooking broth, which was not affected by the number of heating. It was also found that the bean broth contained high levels of tannins in the initial heating, decreasing later significantly. The same was observed in the cooked beans alone and in beans with their broth. With respect to iron, findings showed a relatively high transference of beans to broth, in total iron as well as in soluble, ionizable and insoluble iron. No changes were observed in whole beans without broth caused by number of heatings, on total, soluble or ionizable iron. In beans with their broth, a similar effect was observed, although a slight increase in insoluble iron was detected at the end of heating. A decrease in soluble and insoluble iron was observed in broth with number of heatings. Correlations were calculated among the parameters studied, which suggested an effect of tannins on the bioavailability of iron caused by tannins.     

High performance liquid chromatography study of water‐soluble complexes and covalent conjugates of polyacrylic acid with bovine serum albumin

Polycomplex formation of bovine serum albumin (BSA) and polyacrylic acid (PAA) was studied by pH titration, fluorescence, and HPLC methods in water solutions. It was shown that the complex formation and the solubility (phase state) of the polycomplexes depended on pH of the solutions and ratio of the components. The stability of PAA‐BSA complexes was negligibly weak when pH = 6.0–7.0 [pH > pI (isoelectric pH)]. Stable water‐soluble polycomplexes formed at pH = pI (pH 5.0) in a wide range of n_BSA/n_PAA ratios (0.05–50) and coexisted with free protein molecules at the higher ratios of components. Existence of water‐soluble and insoluble PAA‐BSA complexes has been observed at pH ≤ 4.5. The soluble to insoluble state transition of polycomplexes has been confirmed and binding mode of polyelectrolytes to proteins was assumed dependent on the ratio of components as a result of formation of soluble polycomplexes, complex coacervation, or amorphous precipitates. Soluble complexes were formed as fully homogenized mixtures. Fraction composition of the mixtures and insoluble complexes depended on the protein/polymer ratio and over the critical protein/polymer ratio, the soluble polycomplexes coexisted with free BSA molecules. On the other hand, the comparision of covalent conjugate formation and complexation of PAA with BSA has been revealed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Phlorotannin-protein interactions

Tannins are one of the most broadly distributed types of plant secondary compounds, and have been the focal point for many studies of plant/herbivore interactions. Tannins interact strongly with proteins, so that the fate and effects of ingested tannins are in part dependent on the mode of interaction of the tannin with dietary and endogenous proteins in an herbivore's gut. We investigated the factors affecting the precipitation of proteins by phlorotannins from three species of marine brown algae:Carpophyllum maschalocarpum, Ecklonia radiata, andLobophora variegata. Phlorotannins were precipitated by proteins in a pH-dependent and concentration-dependent fashion. Precipitation also varied as a function of the presence of reducing agent, the type of phlorotannin or protein used, and the presence of organic solvents such as hydrogen bond inhibitors. Of particular significance was the ability of some phlorotannins to oxidize and form covalent bonds with some proteins. In contrast, under similar experimental conditions three types of terrestrial tannins (procyanidins, profisetinidins, and gallotannins) apparently did not form covalent complexes with proteins. Our results suggest several ways in which the biological activity of phlorotannins may vary as a function of the properties of the gut environment of marine herbivores. Moreover, we identify specific structural characteristics of phlorotannins which affect their tendency to oxidize, and thus, their potential effects on marine herbivores.     

Effects of Toasting Time on Digestive Hydrolysis of Soluble and Insoluble 00-Rapeseed Meal Proteins

Thermal damage to proteins can reduce their nutritional value. The effects of toasting time on the kinetics of hydrolysis, the resulting molecular weight distribution of 00‐rapeseed meal (RSM) and the soluble and insoluble protein fractions separated from the RSM were studied. Hydrolysis was performed with pancreatic proteases to represent in vitro protein digestibility. Increasing the toasting time of RSM linearly decreased the rate of protein hydrolysis of RSM and the insoluble protein fractions. The extent of hydrolysis was, on average, 44% higher for the insoluble compared with the soluble protein fraction. In contrast, the rate of protein hydrolysis of the soluble protein fraction was 3–9‐fold higher than that of the insoluble protein fraction. The rate of hydrolysis of the insoluble protein fraction linearly decreased by more than 60% when comparing the untoasted to the 120 min toasted RSM. Increasing the toasting time elicited the formation of Maillard reaction products (furosine, N^ε‐carboxymethyl‐lysine and N^ε‐carboxyethyl‐lysine) and disulfide bonds in the insoluble protein fraction, which is proposed to explain the reduction in the hydrolysis rate of this fraction. Overall, longer toasting times increased the size of the peptides resulting after hydrolysis of the RSM and the insoluble protein fraction. The hydrolysis kinetics of the soluble and insoluble protein fractions and the proportion of soluble:insoluble proteins in the RSM explain the reduction in the rate of protein hydrolysis observed in the RSM with increasing toasting time.     

Radial diffusion method for determining tannin in plant extracts

Tannin in plant extracts can be determined by reacting the tannin with a protein and quantitating the precipitated complex. In the new assay described here, a tannin-containing solution is placed in a well in a protein-containing agar slab. As the tannin diffuses into the gel and complexes with protein, a visible ring of precipitation develops. The area of the ring is proportional to the amount of tannin in the extract. The detection limit of the method is 0.025 mg tannic acid or condensed tannin and the precision is 6% (relative standard deviation). Tests with extracts of a variety of plants show that the new method gives results comparable to other precipitation methods and that the new method is superior for samples of unusual composition, such as aspen buds. The method has several advantages over other methods for determining tannin: The new method is very simple and requires neither complex reagents nor instruments. Components of the plant extract such as non-tannin phenolics or water-insoluble compounds do not interfere with the method. The assay is not subject to interference from the organic and aqueous solutions which are commonly used to extract tannin from plants.     

Bioartificial materials based on blends of collagen and poly(acrylic acid)

The interactions between soluble collagen (C) from calf skin and poly(acrylic acid) (PAA) were studied. Mixing aqueous solutions of collagen and PAA, at various pH values (2.5–4), leads to the formation of complexes that precipitate in the form of insoluble aggregates. The effects of mixture composition, pH, and ionic strength on C/PAA complex formation were investigated by gravimetric, turbidimetric, and conductometric analysis. The experimental results indicate that the complexes form through electrostatic interactions. Homogeneous solid films with variable C/PAA ratios were obtained by casting from solutions in which the pH was adjusted just over the isoelectric point of collagen, thus avoiding the attractive ionic interactions responsible for the complexation of collagen and PAA molecules. A relevant result obtained is related to the possibility of restoring the ionic interactions between the two polymers inside the solid films. Mixture composition and pH appear to influence the thermal properties of both complexes and films. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 971–976, 1999     

Soluble and insoluble ternary complexes of serum proteins with polyanions in the presence of Cu2+ in water

Complex formation between polyacrylic acid (PAA) and bovine serum albumin (BSA), human serum albumin (HSA), hemoglobin (Hb), globin (Gl), and, respectively, transferrin (Tr), were studied in neutral water. Water-soluble and insoluble complexes are formed upon addition of divalent copper ions to the solution. The contacts between proteins and PAA are achieved via chelate unit formation in which the copper ions are located at the center. The solubility of the polycomplexes depends on the nature of proteins and correlates with their isoelectric points (pI). In the mixtures of Hb–Cu²⁺–PAA and Gl–Cu²⁺–PAA, insoluble complexes are formed at pH = pI starting with very low concentrations of Cu²⁺ (n_cu/n_AA ≤ 0.01). On the other hand, these polycomplexes remain soluble at pH > pI. BSA, HSA, and Tr form soluble ternary polycomplexes at neutral water (pH 7). The formation of the polycomplexes in the mixture BSA&–Cu²⁺–PAA was intensively studied by titration, HPLC, electrophoretic, and spectrophotometric methods. The solubility, composition, and stability of these polycomplexes depend on metal/polymer and protein/polymer ratio. Insoluble polycomplexes are formed when concentration of Cu²⁺ reaches a critical value (n_Cu/n_AA ≥ 0.25). At this concentration of Cu²⁺, phase separation takes place, starting with very low concentration of protein in the system. Over the critical ratio of the protein/polymer, the mixture again exhibits water-soluble character. The pattern of distribution of Cu²⁺ between PAA coils and of protein globules between polymer-metal complex particules appeared to follow the self-assembly principle. A hypothetical structural scheme for the formation of soluble and insoluble ternary polycomplexes is proposed. © 1996 John Wiley & Sons, Inc.     

Failure of tannic acid to inhibit digestion or reduce digestibility of plant protein in gut fluids of insect herbivores

The rate of hydrolysis of the abundant foliar protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPC), in enzymatically active gut fluid ofManduca sexta larvae is very rapid and is unaffected by the presence of tannic acid, even when tannic acid is present in the incubation mixture in amounts in excess of the amount of RuBPC. When this protein is dissolved in the denatured gut fluids ofM. sexta larvae orSchistocerca gregaria nymphs, large amounts of tannic acid must be added to bring about the precipitation of significant quantities of protein. The ability of insect gut fluid to prevent the formation of insoluble tannin-protein complexes is due to the presence of surfactants. On the basis of our results and a review of the findings of other investigators, we argue that there is no evidence that tannins reduce the nutritional value of an insect's food by inhibiting digestive enzymes or by reducing the digestibility of ingested proteins and, further, that the failure of tannins to interfere with digestion is readily explained on the basis of well-documented characteristics of the digestive systems of herbivorous insects. In challenging the currently popular notion that tannins are digestibility-reducing substances, we do not challenge the general utility of either the apparency theory or resource availability theory of plant defense. In debating the merits of these two analyses of plant-herbivore interactions, however, the demise of tannins as all-purpose, dose-dependent, digestibility-reducing defensive substances must be taken into account.     

Iron(III) chelating resins. VI. Stability constants of iron(III)–ligand complexes on insoluble polymeric matrices

A method is presented for the determination of stability constants of iron(III)–ligand complexes on insoluble polymeric matrices based on a competition chelation reaction for iron(III) of the resin with a soluble chelator. Stability constants (K') were calculated for iron(III)–ligand complexes on DFO–Sepharose gel, HMP–Sepharose gel, AHMP–HEMA resin, and AHMP–DMAA resin. In these resins, desferrioxamine B (DFO, hexadentate ligand) or the 3-hydroxy-2methyl-4(1H)-pyridinone (HMP, bidentate ligand) was bound on insoluble polymeric matrices. The average values (log K') were: 26.6 (DFO–Sepharose); 37.9 (HMP–Sepharose); 27.2 (AHMP–HEMA); and 39.9 (AHMP–DMAA). The stability constants of the insoluble iron(III) complexes on the resins were compared with those of the corresponding soluble iron(III) complexes. The effect of immobilization on the constants was discussed, and it was found that a higher hydrophilicity and stability of a resin resulted in an increase of the stability constant, whereas steric hindrance decreased the stability constant. © 1995 John Wiley & Sons, Inc.     

Reassessment of interaction between gut detergents and tannins in lepidoptera and significance for gypsy moth larvae

Surface-active lysophospholipids are thought to interfere with tannin-protein interactions and may comprise an adaptation in Lepidoptera to tannin-rich diets. We found several lysophospholipids and phospholipids at about eight times the critical micelle concentration (CMC) in the midguts of gypsy moth larvae, which exhibited appropriately reduced surface tensions. We confirmed the interfering activity of lysophosphatidylcholine (lysolecithin) in a model astringency assay using tannic acid and hemoglobin (hemanalysis), but discovered that tannic acid and red oak tannin extracts precipitate the lipid from simulated midgut solutions quantitatively, even at pH 10. Leaf tannin extracts from trees on which gypsy moths grew and reproduced poorly precipitated lysolecithin more effectively than did extracts from trees on which gypsy moths performed well. Adding tannic acid to midgut fluid elevated surface tension, and about 25% of larvae feeding on oak leaves exhibited elevated midgut surface tension, suggesting a loss of surfactants. Larvae appear able to replace lost surfactants to a limited degree. An important effect of leaf tannins, and perhaps other phenolics, may be to reduce concentrations of surface-active phospholipids in the midgut and produce lipid or other dietary deficiencies in insects.     

Vegetable tannin composition and its association with the leather tanning effect

Abstract

The increasing environmentally friendly approach of using renewable materials has led to vegetable tannins having an important role as tanning agents in the leather industry. Tannins are complex phenolic structures, and the literature shows that a considerable amount of chemical parameters measured through analytical techniques can be associated with their tanning ability. In the present study, five types of vegetable tannins highly used in the tanning industry were chosen for the evaluation of some of their relevant chemical parameters and the correlation with their cross-sectional penetration in the hide. Black wattle (Acacia mearnsii), quebracho (Schinopsis lorentzii), chestnut (Castanea sativa), tara (Caesalpinia spinosa), and myrobalan (Terminalia chebula) were tested. The chemical properties of the total tannin polyphenols, non-tannin polyphenols, insoluble solids, soluble solids, total solids, total phenols, non-tannin polyphenols:total phenols ratio, and residual tanning float concentration were measured and associated with the leather cross-sectional penetration results. The statistical Mann–Whitney-U test showed that the insoluble solids, non-tannin polyphenols, soluble solids, and total tannin polyphenol percentages distinguished the groups of tannins that crossed the hide from those that did not well. Hence, since the analysis of insoluble solids is the simplest and the most direct among them, it would be recommended to use this parameter to define a cutoff to distinguish the performance of tannins for leather application.     

铝阳极氧化废水浸出废旧阴极的动力学

采用水浸?酸性废水浸出两步法,水浸溶出铝电解槽废旧阴极中可溶氟化物,对难溶电解质进行了废水浸出,考察了搅拌速率、液固比、温度对浸出率的影响,并建立了反应动力学方程. 结果表明,废旧阴极酸性废水浸出过程符合未反应收缩核模型,难溶电解质的浸出控制环节为内扩散,提高反应温度、延长反应时间均能提高浸出率,浸出过程反应表观活化能为12.71 kJ/mol. 在浸出温度80℃、搅拌速率300 r/min、液固比8 mL/g的条件下浸出180 min,碳纯度可提升至95.83%. 浸出后碳粉可按比例配入原厂阴极中.     

Synthesis of cyclodextrin‐based polymers and their use as debittering agents

Cyclodextrins (CDs) and their derivatives are used to suppress unpleasant tastes and odors or to achieve a controlled release of certain food constituents. This article describes the synthesis by nonconventional methods of (1) crosslinked, insoluble CD polymers and (2) water‐soluble, CD‐grafted carboxymethylchitosan and carboxymethylcellulose. The CD polymers were obtained by the reaction of β‐CD with one of the following crosslinking agents: epichlorohydrin, diphenyl carbonate, or hexamethylene diisocyanate. Their preparations were usually carried out under high‐intensity ultrasound, which resulted in much shorter reaction times and narrower distributions of particle size (as determined by scanning electron microscopy measurements). A novel, insoluble CD polymer was obtained by reticulation under microwaves of propargyl‐β‐CD with 1,3‐bis(azidomethyl)benzene through Huisgen 1,3‐dipolar cycloaddition. Short columns packed with the insoluble polymers were found to efficiently sequester naringin from aqueous solutions; successively, they could be easily regenerated by a counter‐current ethanol wash that also achieved an excellent recovery of the flavonoid. Differential scanning calorimetry thermograms showed that the crosslinked CD polymers formed inclusion complexes with naringin. The soluble polymers also interacted with bitter flavonoids of citrus fruits (naringin and limonin), as shown by the results of sensorial panel tests, in which they behaved as bitter‐masking agents. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Interspecific Differences in Tannin Intakes of Forest-Dwelling Rodents in the Wild Revealed by a new Method Using Fecal Proline Content

Mammalian herbivores adopt various countermeasures against dietary tannins, which are among the most widespread plant secondary metabolites. The large Japanese wood mouse Apodemus speciosus produces proline-rich salivary tannin-binding proteins in response to tannins. Proline-rich proteins (PRPs) react with tannins to form stable complexes that are excreted in the feces. Here, we developed a new method for estimating the tannin intake of free-living small rodents, by measuring fecal proline content, and applied the method to a field investigation. A feeding experiment with artificial diets containing various levels of tannic acid revealed that fecal proline content was clearly related to dietary tannin content in three species (A. speciosus, Apodemus argenteus, and Myodes rufocanus). We then used fecal proline content to estimate the tannin intakes of these three forest-dwelling species in a forest in Hokkaido. In the autumn, estimated tannin intakes increased significantly in the Apodemus species, but not in M. rufocanus. We speculated that an increase in tannin intake during autumn may result from consumption of tannin-rich acorns. This hypothesis was consistent with population fluctuation patterns of the three species, which were well-synchronized with acorn abundance for the Apodemus species but not for M. rufocanus.     

The Clicked Pyridyl‐Triazole Ligand: From Homogeneous to Robust,Recyclable Heterogeneous Mono‐ and Polymetallic Palladium Catalysts for Efficient Suzuki–Miyaura,Sonogashira, and Heck Reactions

Various mono‐ and polymetallic palladium complexes containing a 2‐pyridyl‐1,2,3‐triazole (pyta) ligand or a nonabranch‐derived (nonapyta) ligand have been synthesized by reaction of palladium acetate with these ligands according to a 1:1 metal‐ligand stoichiometry and used as catalysts for carbon‐carbon cross‐coupling including the Suzuki–Miyaura, Sonogashira and Heck reactions. The unsubstituted monopalladium and nonapalladium complexes were insoluble in all the reaction media, whereas tri‐ and tetranuclar palladium complexes were soluble, which allowed conducting catalysis under either homogeneous or heterogeneous conditions. The organopalladium complexes were characterized by standard analytical and spectroscopic methods and by thermogravimetry showing decomposition above 110 °C. Both types of catalysts showed excellent activity for these cross carbon‐carbon bond formations involving aryl halides including activated aryl chlorides or acyl chloride. Besides the comparison between homogeneous and heterogeneous catalysis, the key feature of these catalysts is their remarkable robustness that allowed recycling at least ten times in the example of the Heck reaction with excellent yields and without significant reduction of the conversion.     

Verlustfreie Katalysatorrezirkulation durch ein neuartiges Verfahrensprinzip bei der Hydroformylierung höhermolekularer Olefine

Free-of-loss Catalyst Recycling in the Hydroformylation of Higher Molecular Olefins by a Novel Process Technology In this paper a novel homogenous-heterogeneous procedure for the hydroformylation reaction of higher molecular olefins is presented, at which the reaction itself is homogeneously catalyzed and only after the reaction the catalyst complex is heterogenized only for separation. This procedure is achieved by using the lithium salt of triphenylphosphine monosulfonic acid (Li-TPPMS) as complex ligand for the hydroformylation catalyst and methanol as solubilizer. Li-TPPMS and its complexes with metal carbonyls are highly soluble in water and methanol, but completely insoluble in almost all other organic solvents. After the reaction the methanol is distilled off. The catalyst system becomes insoluble and can be separated from the reaction product by filtration or by extraction with water. The aqueous catalyst solution is evaporated to dryness and the catalyst system dissolved in methanol for a new reaction.     

Evaluation of Methods for Measuring Polyphenols in Conifer Foliage

There is a resurgence of interest in the quantification of polyphenols in plant tissues because of their presumed ecological importance in plant–litter–soil and plant–animal interactions. The influence of sample preparation, extracting solvent, foliage quality, and assay method was investigated for the quantification of total phenols and condensed tannins in conifer foliage. Our results suggest that it is not possible to recommend a single optimal protocol for quantification of total phenol and condensed tannin fractions from plant materials. In general, the use of aqueous acetone (50–70% v/v) with freeze-dried materials gave the highest recovery. The Folin-Ciocalteau method for total phenols and the butanol–HCl hydrolysis method for condensed tannins appear superior to other common assays tested. There were large differences (1.4–2.2 times) in the reactivity of purified condensed tannins among species, indicating the importance of an appropriate standard for polyphenol quantification. A solid-state ¹³C NMR method with an improved "interrupted decoupling" pulse sequence yielded the highest concentrations for condensed tannins. Assuming that ¹³C NMR provides an accurate measure of total condensed tannin, the other extraction/assay methods used in this study recovered 50–86% of the condensed tannin fraction. The recovery rate is correlated with the nitrogen content of the foliage, which suggests that the formation of protein–tannin complexes may limit the extractability of condensed tannins. While ¹³C NMR condensed tannin values may give the best value for total condensed tannin concentrations, the water-soluble fraction may have the greatest physiological and/or ecological significance.     

煤焦油精制软沥青非等温热转化动力学研究

用热重(TG)-微分热重(DTG)-差热分析(DTα)法分析煤焦油精制软沥青及其族组成在氮气保护下,从室温到800℃的热转化过程。采用Freeman-Carroll的非等温微分法对煤焦油精制软沥青及其族组成的TG-DTG曲线进行处理。煤焦油精制软沥青各族组分的热转化动力学方程证明,自制煤焦油精制软沥青的热转化的三段反应可看成是庚烷可溶族(HS),庚烷不溶甲苯可溶族(HI-TS)和甲苯不溶喹啉可溶族(TI-QS)混合组分的连串反应;HS族段的热转化动力学属二级反应,HI-TS和TI-QS族段都属一级;其活化能和频率因子分别为:48.512,28.575,60.210 kJ/mol和3.110×107,2.328×106,1.483×107。