Rapid determination of tannins in tanning baths by adaptation of BSA method

A rapid and reproducible method for the determination of tannins in vegetable tanning baths is proposed as a modification of the BSA method for grain tannins existing in literature. The protein BSA was used instead of leather powder employed in the Filter Method, which is adopted in Italy and various others countries of Central Europe. In this rapid method the tannin contents is determined by means a spectrophotometric reading and not by means a gravimetric analysis of the Filter Method. The BSA method, which belongs to mixed methods (which use both precipitation and complexation of tannins), consists of selective precipitation of tannin from a solution containing also non tannins by BSA, the dissolution of precipitate and the quantification of free tannin amount by its complexation with Fe(III) in hydrochloric solutions. The absorbance values, read at 522 nm, have been expressed in terms of tannic acid concentration by using a calibration curve made with standard solutions of tannic acid; these have been correlated with the results obtained by using the Filter Method.     

Mimosa and chestnut tannin extracts reacted with hexamine in solution

Autocondensation reactions of mimosa and chestnut tannin extracts solutions have been analysed at several pH by differential scanning calorimetry (DSC). Alkaline pH promotes autocondensation reaction of these tannins. Curing reactions between these tannins and hexamine at acid and not strongly alkaline pH have been proved by DSC. Thermal analysis gives insights not only on reactions between tannin and hexamine, but also about water presence on solutions and degradation reactions of tannins. Products obtained from reactions between tannins and hexamine have been analysed by Fourier transform infrared spectroscopy (FTIR). The obtained chemical structures are influenced by both chemical structure of tannin and pH of solution. For mimosa tannin amine and ether groups are obtained while for hydrolysable chestnut tannin amide groups have been detected.     

Thermal properties of tannin extracted from Anacardium occidentale L. using TGA and FT-IR spectroscopy

The chemical nature of the polyphenols of cashew kernel testa has been determined. Testa contains tannins, which present large molecular complexity and has an ancient use as tanning agents. The use of tannins extracted from cashew testa, considered in many places as a waste, grants an extra value to the cashew. In this work we have analysed through high performance liquid chromatography, infrared spectroscopy (FT-IR) and thermo gravimetric analysis the average molecular weight, main functional groups and thermal properties of tannins extracted from Anacardium occidentale L. The results of these analyses are compared with the commercial grade tannic acid. The FT-IR spectra showed bands characteristic of C = C, C–C and OH bonds. This important bioactive compound present in the cashew nut kernel testa was suggested as an interesting economical source of antioxidants for use in the food and nutraceutical industry.     

UPLC‐ESI‐MS study of the oxidation markers released from tannin depolymerization: toward a better characterization of the tannin evolution over food and beverage processing

Condensed tannins take an important part in the sensory quality of food and beverage. Sensory analyses are usually carried out with various tannin fractions isolated from food or beverage, and their interpretation are limited by the lack of knowledge in the fine and accurate molecular composition of the tannin fractions. Besides, the studies of the chemical reactivity conducted in model solutions with ‘simple’ flavanols allow a better understanding of their evolution pathways, but they cannot take into account their reactivity as polymers, specifically regarding oxidation. In particular, competition between intramolecular and intermolecular reactions may strongly impact on the tannin structures (size, branching and conformation) and consequently on their properties. An ultra‐performance liquid chromatography‐mass spectrometry electrospray ionization mass spectrometer analytical method was thus developed in order to identify oxidized tannins generated by autoxidation. Given the difficulties to separate and detect tannins with high DP, samples were depolymerized by chemical depolymerization prior to analysis. Since the linkages created by oxidation are not cleavable in the usual depolymerization conditions (contrarily to the original interflavanic linkages), specific oxidation residues are released from tannins structures after their autoxidation. Oxidation markers of both intermolecular and intramolecular mechanisms have been identified; these are mainly dimers and trimers, more or less oxidized, and some contain additional hydroxyl groups. Furthermore, the nature of the subunits (extension vs terminal) making up these dimers and trimers was clearly established. Copyright © 2012 John Wiley & Sons, Ltd.     

Simultaneous metal adsorption on tannin resins

Vegetable tannin sorbent is evaluated as ion exchange resin using a multitracer study on the adsorption behavior of various elements. Lisiloma latisiliqua L. tannins, polycondensated into spherical pellets were chosen as sorbent resin material. Sorption evaluation of Ce, Cu(II), U(VI), Eu, Fe(III), Th, Nd as representatives of different classes of metal ions were done at different pH values. The distribution ratio of the studied elements was calculated from laboratory experiments. Tannic ion exchange material shows excellent ability for actinides and rare earth elements adsorption from waters. Using radiotracers, the number of catechins subunits involve in each tannin-metal complex was determined.     

Flow nephelometric analysis of protein-tannin interactions

The interaction of tannins from different sources (grape skin, grape seed and wine) with bovine serum albumin (BSA) was studied using a continuous flow method with nephelometric detection. The tannin samples were mixed in a reaction chamber with increasing BSA concentration and the resulting tannin-BSA insoluble aggregates passed through a flow cell where the turbidity was monitored. Based on this technique, the tannin specific activity (TSA) of wine can be directly determined from different wine flows without previous dilutions or any other treatment. The maximum amount of insoluble aggregates formed with BSA and wine or grape skin tannins seemed to remain constant even with the addition of an excess of protein, whereas a decrease in the amount of insoluble aggregates with an excess of BSA was observed in the case of grape seed tannins. It should be noted that BSA was used in these experiments as a model protein and only as an analytical reagent since bovine additives are not allowed in wine.     

Thermomechanical analysis of the tannins of <Emphasis Type="Italic">Acacia Nilotica</Emphasis> spp. <Emphasis Type="Italic">Nilotica</Emphasis> as a rapid tool for the evaluation of wood–based adhesives

In this article, autocondensation reactions of Acacia nilotica spp. nilotica (Ann) tannin extracts solutions have been studied at several pH values by thermomechanical analyzer (TMA). TMA has been chosen for this study as it has been shown to give results more rapidly and more precisely than panels. It also tends to exaggerate the differences in results which render it an excellent tool for comparison. Therefore, autocondensation reactions were studied and compared with its polycondensation reactions upon addition of different hardeners such as paraformaldehyde, urea, and PMDI at same pH values. The aim was to evaluate the tannin’s reactivity and therefore its suitability for the production of commercially and technically viable tannin adhesives for wood products. The results of autocondensation showed that the maximum Young’s modulus values (3300 and 3600 MPa) were obtained at pH 4. However, these values have been achieved at high temperature (160 and 208 °C). Results of copolymerization reaction of the tannins with different hardeners revealed that some of these co-reactants were found to depress tannins autocondensations, while others appear to enhance the formation of the final networking. Polycondensation of the Ann tannins with 8% paraformaldehyde and 10% PMDI gave the maximum Young’s modulus values at lower temperature (91–101 °C) and acidic pH5. However, the addition of 20 and 30% PMDI achieved the best Young’s modulus values 2300 and 3300 MPa, respectively, at pH 4. Furthermore, the obtained values were comparable to those obtained by the addition of urea and the self condensation reactions. This is very important for particleboard production from economical and technical point of view. It has been noticed that the addition of hardeners lowered the temperature of hardening, and the obtained values were more consistent with the pH acidity. The study concluded that the tannins of Ann were very reactive, and therefore, it could be a potential precursor for particleboard adhesives. The results also indicated that the tannins can be used alone, and it would possibly produce zero emission environmentally friendly particleboard.     

植物多酚研究与利用的意义及发展趋势*

植物多酚(植物单宁) 是一类广泛存在于植物体内的重要的天然产物。多年来它们一直用于许多传统工业领域如制革、石油开采和木材胶粘剂的生产。近30 年来, 随着植物多酚化学的发展, 植物多酚的化学结构和性质已被深入揭示。根据美国化学文摘(CA ) 近30 年相关文献资料的统计分析, 阐述了植物多酚化学的发展状况及其作为一类丰富的可再生绿色资源的利用情况, 讨论了植物多酚化学的研究发展趋势和广阔的应用前景。     

Association of tannins and related polyphenols with the cyclic peptide gramicidin S

The association of 10 different tannins and related polyphenols with gramicidin S, a cyclic peptide having a rigid beta-turn structure, has been examined using 1H-NMR spectroscopy. In the presence of pentagalloylglucose and epigallocatechin-3-O-gallate, the proton signals due to proline and the adjacent phenylalanine moieties selectively shifted to up field, suggesting a regioselective association with the beta-turn structure. The association was also supported by the observation of intermolecular nuclear Overhauser effects between epigallocatechin-3-O-gallate and the peptide. In contrast, ellagitannins, biogenetically derived from pentagalloylglucose, showed small and non-selective chemical shift changes, suggesting that interaction with these tannins is relatively weak. The hydrophobicity of the tannin molecules and the steric hindrance of the interaction site are thought to be important in the association.     

Formaldehyde Condensation Products of Model Phenols for Conifer Bark Tannins

Abstract

Gel permeation chromatography of the condensation products of phenols and formaldehyde proved effective in understanding the reactions of condensed tannins with formaldehyde. Rates of condensation of phloroglucinols, resorcinols, catechols, (+)catechin, and (-)epicatechin were examined to determine if methylol-tannins from southern pine bark could be prepared as resin intermediates. The phloroglucinols (models for the A-ring of pine bark tannins) were so much more reactive than were the resorcinols (models for the A-ring of wattle tannins), that preparation of methylol-tannins from pine bark tannins seems unlikely even though this approach has been applied successfully to synthesis of resins from wattle tannins. The methylol content of catechin-formaldehyde condensation products was very low. The catechol B-ring was unreactive under conditions in which condensations of pine bark tannins could be controlled. Although there is much less steric hindrance of the A-ring of (-)epicatechin than of (+)catechin, differences in the rates of condensation of these isomers were not detected. GPC and H-NMR spectra of (+)catechin condensation products showed that a dimer formed rapidly and that further condensation occurred more slowly.     

植物油中真菌毒素检测技术的研究进展

真菌毒素是由丝状真菌或霉菌产生的结构多样的小分子次级代谢产物，常见于粮油中，具有致畸性、肝毒性、肾毒性、致癌性、出血性、免疫抑制及破坏生殖系统等毒性。真菌毒素在基体中存在浓度低、种类多、极性范围广、同族类化合物结构类似、性质接近，定性信息缺乏。植物油是易受真菌毒素污染的食品之一，并且含有大量的油脂、脂肪酸和色素，可能增加基质效应，降低灵敏度，并损坏仪器。因此，建立高效样品前处理方法及高灵敏度、高通量、多种真菌毒素检测技术成为植物油基体中真菌毒素准确测定面临的巨大挑战。该文综述了溶剂提取（LLE）、固相萃取（SPE）、凝胶渗透色谱（GPC）、动态共价化学肼（DCHC）、QuEChERS方法在油中真菌毒素前处理中的应用，分析了气相色谱、液相色谱、液相色谱-串联质谱及免疫传感器等检测技术的特点，并对植物油中真菌毒素污染检测的发展应用进行了展望。     

Characterization of Acacia mangium polyflavonoid tannins by MALDI-TOF mass spectrometry and CP-MAS C NMR

The MALDI-TOF mass spectrometry (MS) and solid state CP-MAS ¹³C Nuclear Magnetic Resonance (NMR) spectroscopic technique were introduced to characterize Acacia mangium tannin (condensed tannins). The MALDI-TOF MS illustrated a series of peaks corresponding to oligomers of condensed tannins of up to 11 flavonoid units (3200 Da). A. mangium condensed tannins were found to consist predominantly of prorobinetinidin combined with profisetinidin and prodelphinidin. Both the MALDI-TOF mass spectra and the solid state CP-MAS ¹³C NMR indicated that the A. mangium tannins obtained from Kudat, had an almost completely linear structure; In addition, Lembah Beringin, consist of “angular” polymer structure; and Tawau, has included “twice-angular” polymer structures present in oligomers type of up to 7 flavonoid units. The high degree of polymerization of linear, angular type, twice-angular structures and longer oligomer (3200 Da) chains have not been observed in previous studies of condensed tannins. The spectra also indicated that A. mangium tannins are more heavily branched and have higher degree of polymerization (>7.0) compared to commercial mimosa (A. mearnsii) tannin (4.9). Because tannins are phenolic, it was expected that they can be used to replace phenol-formaldehyde (PF) adhesives.     

Broom fibers as reinforcement for thermoplastic matrices

Vegetable fibers deriving from the basts of broom plants have been used as reinforcement for two polypropylenic matrices: a conventional isotactic polypropylene (iPP) and a maleate modified one (iPPMA). Before mixing the fibers were subjected to two different extraction procedures: a conventional alkaline treatment and an innovative steam explosion process. Afterwards, the composites obtained by compression moulding were thermally, morphologically, and mechanically characterized. Moreover, water absorption tests, to examine the behaviour of these materials in wet conditions, were also performed.     

Regulation of Selenium/Sulfur Interactions to Enhance Chemopreventive Effects: Lessons to Learn from Brassicaceae

Selenium (Se) is an essential trace element, which represents an integral part of glutathione peroxidase and other selenoproteins involved in the protection of cells against oxidative damage. Selenomethionine (SeMet), selenocysteine (SeCys), and methylselenocysteine (MeSeCys) are the forms of Se that occur in living systems. Se-containing compounds have been found to reduce carcinogenesis of animal models, and dietary supplemental Se might decrease cancer risk. Se is mainly taken up by plant roots in the form of selenate via high-affinity sulfate transporters. Consequently, owing to the chemical similarity between Se and sulfur (S), the availability of S plays a key role in Se accumulation owing to competition effects in absorption, translocation, and assimilation. Moreover, naturally occurring S-containing compounds have proven to exhibit anticancer potential, in addition to other bioactivities. Therefore, it is important to understand the interaction between Se and S, which depends on Se/S ratio in the plant or/and in the growth medium. Brassicaceae (also known as cabbage or mustard family) is an important family of flowering plants that are grown worldwide and have a vital role in agriculture and populations’ health. In this review we discuss the distribution and further interactions between S and Se in Brassicaceae and provide several examples of Se or Se/S biofortifications’ experiments in brassica vegetables that induced the chemopreventive effects of these crops by enhancing the production of Se- or/and S-containing natural compounds. Extensive further research is required to understand Se/S uptake, translocation, and assimilation and to investigate their potential role in producing anticancer drugs.     

A rapid screening technique for vegetable oil identity by sub-ambient DSC

Vegetable oils are widely used in the food industry. Labeling requirements have alerted the consuming public to the presence of vegetable oils and to the wide variety of oils used. Vegetable oils are selected commercially for their physical properties, price and availability, and many ingredient labels contain the ‘and/or’ clause reflecting the interchangeability of food grade vegetable oils.A ‘fingerprinting’ method has been developed utilizing the characteristic sub-ambient liquid—solid and solid—solid transitions of vegetable oils. The DSC was used in the temperature range 320 to 220 K. The cooling curves and their first derivatives were recorded for a pattern recognition library of pure vegetable oils, mixtures of oils, and oils present in standard cookie dough. This pattern library will serve as the basis for rapid verification of identity for vegetable oils, mixtures of oils and oils in commercially prepared food products.     

Preparation of immobilized tannins for protein adsorption

Preparation and adsorption specificity of tannins immobilized by covalent binding on water-insoluble matrices were investigated. Immobilized tannins were prepared by condensing cyanogen bromide activated tannins with aminohexyl derivatives of several kinds of matrices. The most suitable matrix for the immobilization of tannin was alkali-treated cellulose powder. The concentration of sodium hydroxide solution for alkali treatment influenced the adsorption capacity of immobilized tannin for a protein, but temperature and time for alkali treatment did not. Immobilized tannins having spacers of long chain length exhibited high adsorption capacity for a protein. Chinese gallotannin was the most favorable ligand for protein adsorption. The immobilization of tannin on aminohexyl matrices was also possible by using epichlorohydrin instead of cyanogen bromide. The maximum adsorption capacity of the immobilized tannin for a protein was about 50 mg/ml of the absorbent. Immobilized tannin adsorbed proteins specifically but did not absorb low molecular weight compounds.     

Retention of tannic acid and condensed tannin by Fe-oxide-coated quartz sand

This paper intends to shed light on the interactions between tannin and mineral soil particles. For that purpose, aqueous solution of condensed tannin (CT) (derived from Black pine (Pinus nigra var. maritima)) and commercially available tannic acid (TA) were added to purified quartz (Qtz) sand and quartz sand coated with either goethite (Gt) or ferrihydrite (Fh). After solvent removal by evaporation the samples were extracted by water. The extracts were analysed for organic carbon, total phenolics and CT. The extractability of the two tannins was small and increased in the order Qtz-Fh < Qtz-Gt < Qtz. For all mineral samples, TA was more extractable than CT. Bonding of tannins to the mineral samples and the partial peptisation of the Fe oxide coatings upon the binding resulted in complex tannin release curves. Our results suggest that the inextractability of tannins from natural soils and the absence of tannins in soil leachates might be caused by strong adsorption on soil minerals such as Qtz and Fe (oxy)(hydr)oxides. The results of competition experiments with mixtures of both tannins demonstrate that the CTs, and TA in particular, can release large amounts of Fe (oxides), suggesting that the tannins are excellent metal-mobilising agents. We therefore suggest that the fate of tannins in the mineral soil environment is highly dependent on the abundance of weakly bonded secondary oxides.     

Isolation and Purification of Condensed Tannins from Flamboyant Tree and Their Antioxidant and Antityrosinase Activities

Flamboyant tree, a kind of medicinal plant, was studied as a source of condensed tannins. The antioxidant activities of the condensed tannins from the leaf, fruit, and stem bark of flamboyant tree were screened by ABTS radical and hydroxyl radical scavenging activity methods. The results indicated that these compounds possessed potent antioxidant activity. Their structures were then characterized by high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) after thiolytic degradation. The results showed that the leaf condensed tannins were composed of afzelechin/epiafzelechin, catechin/epicatechin, and gallocatechin/epigallocatechin, while the fruit and stem bark condensed tannins had afzelechin/epiafzelechin and catechin/epicatechin. In addition, the condensed tannins were evaluated for their antityrosinase ability. They were found to have significant antityrosinase activity. The IC₅₀ values were 35 ± 2.0 and 40 ± 0.5 μg/ml for the condensed tannins of fruit and stem bark, respectively. Further, fluorescence quenching and copper interacting techniques were utilized to unravel the molecular mechanisms of the inhibition. The results showed that the hydroxyl group of the condensed tannins could chelate the dicopper center of the enzyme and interact with tryptophan residues. Our studies revealed that condensed tannins might be suitable for use in food, agriculture, cosmetic, nutraceutical, and pharmaceutical applications.