植物单宁的结构改性研究进展

植物单宁作为一种天然多酚类物质,广泛存在于多种植物的各组织部位中。单宁的结构复杂多样,含有大量的酚羟基、酯基、醚基等活性基团,可以和多种物质结合从而具有抗氧化、离子吸附及皮革鞣制等作用。这使得植物单宁这一功能材料,在医药加工、食品生产、污水处理等行业中应用广泛。然而天然的单宁类成分也存在着其结构上的固有不足之处,如分子量大、脂溶性差等。基于此,国内外的学者一直在探索寻找合适的单宁结构改性方法,从而改善单宁的渗透性、溶解性及反应活性等,使其能更加充分地用于工业生产中。以单宁的组成结构为基础,综述了近年来有关单宁的结构改性方法,并对其进行了展望,以期为单宁的结构修饰及高值化利用提供有益参考。     

黑荆树皮单宁不同级分的抑菌性能

通过对黑荆树皮单宁进行醇沉纯化 ,可以使单宁质量分数提高 1 0 %。在此基础上进行萃取分级 ,可得到相对分子质量分布范围不同的单宁级分。各级分的抑菌性能与其浓度和pH有关。根据最低抑菌浓度 (MIC)测试结果 ,黑荆树皮单宁各级分在适宜pH条件下的抑菌性能依次为 :乙酸乙酯级分 >乙醚级分 >纯化后单宁 >水级分 >未纯化单宁。各级分在 1 0g dL质量浓度下对所选霉菌和酵母菌无抑制作用。     

Methods and pitfalls of extracting condensed tannins and other phenolics from plants: Insights from investigations onEucalyptus leaves

Optimal conditions for extraction of tannins and other phenolics from tree foliage and their subsequent storage rarely have been investigated. We investigated methods of drying leaves, optimal solvents, and the effects of light and temperature on the extractability and stability of condensed tannins (proanthocyanidins) and total phenolics from leaves ofEucalyptus trees. Aqueous acetone was a better solvent than aqueous methanol for condensed tannins and total phenolics, but condensed tannins were less stable in aqueous acetone than aqueous methanol. Stability of condensed tannins also was decreased substantially by room temperature versus 4°C and by exposure to indirect sunlight, although the assay for total phenolics was unaffected. For quantitative estimation of condensed tannins, extraction with 50% acetone was better than methods of direct analysis of leaf tissue. The highest estimates of total condensed tannins were obtained by exhaustive extraction with 50% acetone followed by direct analysis of the residue. Lyophilization of fresh leaf increased yield of condensed tannin (although usually by less than 10%). Lyophilization and subsequent storage of extracts had little effect on assays for condensed tannins or total phenolics.     

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.     

Salivary Proteins as a Defense Against Dietary Tannins

Tannins, a diverse group of water-soluble phenolics with high affinity to proteins, are widely distributed in various parts of plants, and have negative effects in herbivores after ingestion. Some mammalian species are thought to counteract tannins by secreting tannin-binding salivary proteins (TBSPs). Several types of TBSPs are found in the saliva of laboratory animals, livestock, and wildlife. Among them, proline-rich proteins (PRPs) and histatins are effective precipitators of tannins. It is widely accepted that, at the least, PRPs act as a first line of defense against tannins. Many observations support this idea: in vitro affinity of PRPs to tannins is far higher than that of other proteins such as bovine serum albumin; complexes formed between PRPs and tannins are stable even under the conditions in the stomach and intestine; and PRP production is induced by ingesting tannins. It is believed that species that usually ingest tannins as part of their natural diets produce high levels of PRPs, whereas species not exposed to tannins produce little or no PRPs. This hypothesis is generally supported, although studies on TBSPs in wildlife are limited. This work stresses the importance of gathering basic information on such items as the characteristics of unidentified TBSPs, and seasonal and geographical variations in PRP production.     

Effects of the Hydroxylation Patterns and Degrees of Polymerization of Condensed Tannins on their Metal-Chelating Capacity

Abstract

We studied the effects of the hydroxylation patterns and the degrees of polymerization of condensed tannins on their metal-chelating capacity. These effects were evaluated by the relative stability of aluminium complexes with proanthocyanidin. The relative stability of aluminium complexes was determined qualitatively in methanol solution by the competition with the metallochromic reagent (chrome azurol S). A comparison of these capacities indicates the following results: 1) phenolic hydroxy groups in tannins are essential sites for the chelation with metal. 2) the sites of tannins interacting with metal ions are mainly o-dihydroxyphenyl groups in B-ring. 3) increasing degrees of polymerization of tannins tends to increase the relative stability of condensed tannin-aluminium chelate.     

Structural Features and Biological Properties of Ellagitannins in Some Plant Families of the Order Myrtales

Plant tannins, including hydrolysable and condensed varieties, are well known antioxidants in medicinal plants, foods, and edible fruits. Their diverse biological properties and potential for disease prevention have been demonstrated by various in vitro and in vivo assays. A number of ellagitannins, the largest group of hydrolysable tannins, have been isolated from dicotyledoneous angiosperms and characterized. This diverse class of tannins is sub-grouped into simple ellagitannins, C-glycosidic ellagitannins, complex tannins (condensates of C-glycosidic tannins with flavan-3-ol), and oligomers up to pentamers. This review outlines and describes the chemotaxonomic significance of structural features in various types of ellagitannins found in plants belonging to the Myrtaceae, Onagraceae, and Melastomataceae families, which are all included in the order Myrtales. Any biological activities that have been reported, including antitumor and antibacterial effects as well as enzyme inhibition, are also reviewed.     

Nanoencapsulation of capsaicin by complex coacervation of gelatin,acacia, and tannins

Using gelatin and acacia as wall and capsaicin as core substance, nanocapsules were prepared by mixing two solutions of oppositely charged polymers, and then treated by hydrolysable tannins. The morphology and size distribution of the nanocapsules were analyzed by transmission electron microscope and laser particle size analyzer, respectively. The nanocapsules had a mean diameter of 300–600 nm, with mean drug loading content (20.81%) and encapsulation efficiency (81.17%) with good dispersion and spherical morphology. The interaction between gelatin and tannins is discussed in the article. Moreover, the addition of hydrolysable tannins in the system had an important influence on the morphology and particle distribution of the nanocapsules because of the synergistic actions of hydrogen bonding and hydrophobic effects. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2225–2229, 2005     

Comparison of Chemical Compositions and Antioxidant Activities of Condensed Tannins From Different Parts of Calliandra haematocephala

In this study, the condensed tannins in 70% acetone extracts of leaf, twig, and stem bark of Calliandra haematocephala were purified by a Sephadex LH-20 column, and their structures were identified using MALDI-TOF-MS and thiolysis-HPLC-ESI-MS analyses. The results showed that the condensed tannin structures varied significantly among C. haematocephala organs. The condensed tannins from leaf were essentially of prodelphinidins, consisting mainly of (epi)gallocatechin and (epi)gallocatechin-3-O-gallate units; the condensed tannins from twig and stem bark were predominately of procyanidins, with catechin, epicatechin, and (epi)catechin-3-O-gallate as the main constitutive units for the former and epicatechin as the main constitutive unit for the latter, respectively. Furthermore, in vitro antioxidant activities of these condensed tannins were evaluated using the ABTS^·+ and FRAP methods. All of the condensed tannins exhibited stronger antioxidant activities compared to those of synthetic antioxidant BHA. For all organs, the two tested activities were found to be the highest in leaf condensed tannins, followed by that in twig condensed tannins and stem-bark condensed tannins. The results suggested that the number of hydroxyl groups on the B-ring and the level of 3-O-galloylation in condensed tannins were closely related with their antioxidant activities, and that the condensed tannins from different parts of C. haematocephala could be used as a natural additive in the food and cosmetic industries.     

Chemical and Biological Assays to Evaluate Bacterial Inhibition by Tannins

The interactions among purified tannins from three different plants with five strains of ruminal bacteria were investigated. Tannins were purified from crude quebracho (Schinopsis balansae spp.), desmodium (Desmodium ovalifolium), and myrtle (Mirtus communis). The ruminal bacteria studied were Streptococcus bovis JB1, Ruminococcus albus 8, Fibrobacter succinogenes S85, Prevotella ruminicola H₁4, and a recently isolated tannin-tolerant bacterium. Bacterial binding to tannins, rate of tannin binding, and the inhibitory concentrations for each bacterium to each tannin were evaluated. The effects of tannins on glucose utilization and fermentation product formation also were studied. Tannin binding was rapid with little additional binding occurring 10 min after tannin addition. There was variation among bacteria in the amount of tannins bound and in the amount of tannin required to inhibit growth. Condensed tannins from myrtle and desmodium had the highest binding capacity and were most inhibitory to microbes. Absorbance readings from the total phenolics assay were highest for myrtle and lowest for quebracho. Similarly, readings for condensed tannins were highest for desmodium, which also had the largest polymer size. Myrtle and quebracho gave the largest precipitate rings in the radial diffusion assay, a biological assay that measures precipitation of bovine serum albumin by tannins. The relative absorbance values obtained from the total phenolics assay were the most useful predictor of tannin inhibition of microbial growth. The acid–butanol assay and the radial diffusion assay using bovine serum albumin as the precipitable protein were much less useful predictors of tannin biological activity against the bacteria studied.     

Tannins, peptic ulcers and related mechanisms

This review of the current literature aims to study correlations between the chemical structure and gastric anti-ulcer activity of tannins. Tannins are used in medicine primarily because of their astringent properties. These properties are due to the fact that tannins react with the tissue proteins with which they come into contact. In gastric ulcers, this tannin-protein complex layer protects the stomach by promoting greater resistance to chemical and mechanical injury or irritation. Moreover, in several experimental models of gastric ulcer, tannins have been shown to present antioxidant activity, promote tissue repair, exhibit anti Helicobacter pylori effects, and they are involved in gastrointestinal tract anti-inflammatory processes. The presence of tannins explains the anti-ulcer effects of many natural products.     

巨尾桉单宁的提取分离及其抗菌抗氧化性能

采用超声波辅助法提取了巨尾桉叶中的单宁,大孔树脂吸附法纯化了粗提物,考察了提取物对8种常见菌种的抑制作用和对H2O2、DPPH.和.OH的清除作用。结果表明,巨尾桉单宁的提取得率为4.01%;经树脂分离纯化后单宁质量分数达到53.12%;巨尾桉单宁对除大肠杆菌外的供试菌种均有较强的抑制作用,纯化后的单宁对金黄色葡萄球菌、酵母菌和痢疾杆菌的最低抑菌质量浓度(MIC)均为1.0 g/L,对蜡状芽孢杆菌和沙门氏菌的抑制作用优于阳性对照物;粗提物、纯化物在质量浓度为0.50 g/L时对H2O2有最大清除率,分别为80.00%、89.12%,其IC50分别为0.11、0.12 g/L;抗坏血酸、粗提物和纯化物均在质量浓度为1.50 g/L时对DPPH.有最大清除率,分别为98.43%、88.97%和92.21%。在清除.OH体系中,粗提物、纯化物均在质量浓度为4.00 g/L时有最大清除率,分别为87.52%和94.32%,各试样对.OH的清除能力依次为抗坏血酸>纯化物>粗提物。     

Tannin antioxidant characteristics in leather versus leather light stability: Models

The variation of leather color as a function of aging time on prolonged irradiation with UV light of the leather produced by tanning with different polyflavonoid and hydrolyzable vegetable tannins is reported. A predictive model and two equations for the variation of leather color as a function of UV‐irradiation time and as a function of the different vegetable tannins used was also established. This technique appears to describe well the overall phenomenon of oxidation and color change in situ observable in vegetable‐tanned leathers. The variation of leather color as a function of aging time on prolonged irradiation with UV light of the leather produced based on different vegetable tannins was found to be composed of two main effects: The first one of these is the darkening reaction of the leather. This is due to the formation of quinones on the phenolic structure of the vegetable tannin. The second one is the leather‐lightening reaction due to the photodegradation of the system. These two phases were equated and correlated with the radical uptake reaction and radical stabilization/decay reaction observed by ESR for UV‐irradiation of pure tannin in the solid form and of the leather produced using the same. Thus, correlation among the antioxidant capability of tannins in the solid form, their antioxidant capability once included in the leather, and the color variation (darkening and lightening) of leather by colorimetry was established. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1030–1040, 2004     

An overview of the phenolics of canola and rapeseed: Chemical,sensory and nutritional significance

Utilization of rapeseed meal in human foods has been thwarted by the presence of antinutritional factors such as glucosinolates, phenolics, phytates and hulls. The content of phenolics in rapeseed flour is nearly 30 times higher than that of soybean. Phenolic compounds contribute to the dark color, bitter taste and astringency of rapeseed meals. They may also interact with amino acids, enzymes and other food components, thus influencing the nutritional value of rapeseed meal and its products. Therefore, phenolic compounds are important factors when considering rapeseed meal as a protein source in food formulations. Available literature data on phenolic compounds and tannins of rapeseed/canola are fragmentary and diverse. Furthermore, developing a standardized method for analysis and quantitation of these compounds is warranted. Interaction of rapeseed phenolics/tannins with proteins and their effects on enzymes and other food components remain to be studied.     

Study on the antimicrobial activities of the capsaicin microcapsules

In this study, capsaicin microcapsules were prepared by the complex coacervation of gelatin, acacia, and tannins. The antimicrobial activities of these microcapsules on the common microorganisms of food preservation, Botrytis cinerea and Aspergillus niger, were investigated. The factors affecting their antimicrobial effects, including the microcapsule concentrations, pH values, and release behavior were also examined. The results showed that the optimum pH for the antimicrobial effect was about 5.0, which might be related to the strongest protein‐precipitating ability of tannins at this pH value. The inhibitory activity of the system originated from the synergistic actions of both capsaicin and tannins. The release behavior of the microcapsules had an important influence on the antimicrobial effect for the long shelf‐life storage of foods. The present study indicated that the capsaicin microcapsules displayed potential antimicrobial applications in the food storage. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1318–1321, 2006     

The Influence of Condensed Tannin Structure on Rate of Microbial Mineralization and Reactivity to Chemical Assays

We examined how tannin structure influences reactivity in tannin assays and carbon and nitrogen mineralization. Condensed tannins from the foliage of ten tree and shrub species and from pecan shells (Carya illinoensis) had different proportions of: (a) epicatechin (cis) and catechin (trans) isomers, (b) procyanidin (PC) and prodelphinidin (PD) monomers, and (c) different chain lengths. The response of each tannin to several widely used tannin assays was determined. Although there was some variation in response to proanthocyanidin (butanol/HCl) and Folin Ciocalteu assays, we did not deduce any predictable relationship between tannin structure and response to either assay. There was little variation in protein precipitation among the different tannins. To assess biological activity, six of the tannins were incubated with forest humus for 22 days. We determined that, while PC-based tannins remained at least partly extractable for the duration of the incubation, tannins with a high proportion of PD subunits rapidly became unextractable from soil. There was a positive correlation between net nitrogen mineralization and cis chemical structure. Carbon mineralization was enhanced initially by the addition of tannins to humus, but after 22 days, a negative correlation between the proportion of cis subunits and respiration was determined. Overall, we were not able to demonstrate consistent effects of structure on either microbial mineralization or reactivity to chemical assays; such relationships remain elusive.     

Tannin Composition Affects the Oxidative Activities of Tree Leaves

We examined whether tannin composition plays an important role in explaining the oxidative activities of tree leaves of Acer saccharum (sugar maple) and Quercus rubra (red oak). Sugar maple leaves contained substantial amounts of ellagitannins, condensed tannins, and galloyl glucoses, whereas red oak leaves contained almost exclusively condensed tannins. Oxidative activities of the crude phenolics from both species, and the phenolic fractions from sugar maple, were measured with electron paramagnetic resonance (EPR) spectrometry and UV-visible spectrophotometry. The two assays produced similar results: (1) sugar maple phenolics produced larger semiquinone radical concentrations,and higher semiquinone decay rates and browning rates than did red oak phenolics;(2) ellagitannin levels were positively associated with the three measures of oxidative activity; and (3) condensed tannin and galloyl glucose levels were negatively associated with these measures. The negative relationship between condensed tannin levels and oxidative activity resulted from the antioxidant effects of condensed tannins on hydrolyzable tannins; several purified condensed tannins significantly decreased the concentrations of semiquinone radicals and browning rates of pedunculagin (an ellagitannin) and pentagalloyl glucose. As expected, whole-leaf extracts from sugar maple produced elevated levels of semiquinone radicals, but none were observed in red oak extracts when the two species were compared with an EPR time-course assay. We conclude that the oxidative activities of tree leaves may be affected by tannin composition, and that the prooxidant activity of ellagitannins may be decreased by co-occurring condensed tannins.     

Effect of dehulling on the composition of antinutritive compounds in various cultivars of rapeseed

Eight different rapeseed cultivars (Brassica napus L.) have been dehulled by hand. The contents of glucosinolates, sinapine, condensed tannins and inositol phosphates have been investigated in the resulting fractions of dehulled seeds and hulls as well as in the whole seeds by HPLC methods and a spectroscopical method for condensed tannins. After dehulling the content of glucosinolates as well as the content of sinapine and inositol phosphates increased significantly (P = 0.01) in the seeds of the different cultivars by 2.0 to 35.0%, 14.1 to 57.1% and 11.9 to 38.2%, respectively. The content of condensed tannins decreased by 26.0 to 81.2% after the dehulling process. In most of the cultivars the enrichment of antinutritive compounds corresponded to the share of hulls separated from the seeds. Only in the case of condensed tannins unproportional losses in the dehulled seeds were observed.     

Selection for Small Amounts of Hydrolysable Tannins by a Concentrate-Selecting Mammalian Herbivore

Although herbivores usually avoid plants with high concentrations of tannins, roe deer in natural habitats select tannin-rich plants. We tested the hypotheses that: (H1) roe do not seek tannins, rather they select for other (unmeasured) factors such as minerals or vitamins; and (H2) roe do select for tannins. Tame roe deer were offered a choice of food pellets to which hydrolyzable chestnut tannins had been added or control pellets. The daily consumption of pellets containing a high level of tannins (9.1%) was lower than consumption of control pellets. However, when offered medium level tannin pellets (3.8%), roe deer ate more tannin than control pellets. Moreover, the roe regulated their intake of these tannins closely. The regression of tannin intake versus total pellet intake across all the tests was linear and precise (r ² = 0.94): intake was about 28 g of tannin per kilogram of pellets eaten. We therefore reject H1 and suggest that roe can monitor tannin concentrations in their food, and regulate their intake precisely. The results suggest that a certain level of tannins induces no costs or that they provide a nutritional benefit for roe deer.     

Chelation of Cu(II), Zn(II), and Fe(II) by Tannin Constituents of Selected Edible Nuts

The tannin fractions isolated from hazelnuts, walnuts and almonds were characterised by colorimetric assays and by an SE-HPLC technique. The complexation of Cu(II) and Zn(II) was determined by the reaction with tetramethylmurexide, whereas for Fe(II), ferrozine was employed. The walnut tannins exhibited a significantly weaker reaction with the vanillin/HCl reagent than hazelnut and almond tannins, but the protein precipitation capacity of the walnut fraction was high. The SE-HPLC chromatogram of the tannin fraction from hazelnuts revealed the presence of oligomers with higher molecular weights compared to that of almonds. Copper ions were most effectively chelated by the constituents of the tannin fractions of hazelnuts, walnuts and almonds. At a 0.2 mg/assay addition level, the walnut tannins complexed almost 100% Cu(II). The Fe(II) complexation capacities of the tannin fractions of walnuts and hazelnuts were weaker in comparison to that of the almond tannin fraction, which at a 2.5 mg/assay addition level, bound Fe(II) by ~90%. The capacity to chelate Zn(II) was quite varied for the different nut tannin fractions: almond tannins bound as much as 84% Zn(II), whereas the value for walnut tannins was only 8.7%; and for hazelnut tannins, no Zn(II) chelation took place at the levels tested.