Factors influencing the clarification of apple juice with honey

Six apple cultivars were studied to determine the effect of pH, degree of browning and polyphenol composition on clarification of apple juice by addition of honey. The optimum pH for all apple cultivars was about 3·5. Only browned apple juices, those prepared with no ascorbic acid, flocculated with the honey and consequently clarified. The flocculation time was inversely related to the degree of browning of all apple cultivars except Golden Delicious. The clarification rate did not correlate well with the different phenolic groups present in the juices.     

Degradation of tannic acid by cell-free extracts of Lactobacillus plantarum

The ability of Lactobacillus plantarum CECT 748^T to degrade hydrolysable tannins was evaluated. Three commercial tannic acids were incubated in presence of cell-free extracts containing soluble proteins from L. plantarum. By HPLC analyses, almost a complete tannic acid degradation was observed in the three samples assayed. By using HPLC-DAD/ESI-MS, we partially determined the composition of tannic acid from Quercus infectoria galls. This tannic acid is a gallotannin mainly composed of monomers to tetramers of gallic acid. We studied the mechanism of its degradation by L. plantarum. The results obtained in this work indicated that L. plantarum degrades gallotannins by depolymerisation of high molecular weight tannins and a reduction of low molecular weight tannins. Gallic acid and pyrogallol were detected as final metabolic intermediates. Due to the potential health beneficial effects, the ability to degrade tannic acid is an interesting property in this food lactic acid bacteria.     

Factors affecting in vitro formation of tannin-protein complexes

In interaction of condensed tannins from Desmodium intortum and Lotus pedunculatus and tannic acid (hydrolysable tannin) with salivary mucoproteins (from sheep and goats), plant leaf proteins and bovine serum albumin were evaluated. These studies were carried out over a pH range of 2-0-9-0 and different inorganic ion conditions to simulate conditions in which dietary proteins would interact with tannins in a ruminant digestive tract. Insoluble tannin-protein interactions were found at pH 4–5–5–5 for bovine serum albumin and 3–5–5–5 for plant leaf protein. The present study showed that pH alone was not the sole determinant for tannin-protein complex formation, since tannin-protein complexation was found in the pH range 6-0–6-5 when different inorganic ions were added to the solutions. Insoluble complexes were not formed with salivary proteins, although precipitation by tannic acid was achieved at 5°C. This suggests that tannins may form soluble rather than insoluble complexes with salivary proteins. It was concluded that purified F1 leaf protein (the major protei occurring in leaf tissue) ought to be used as the test protein for evaluating tannin-protein interactions for in vitro assay procedures. Using this method it was calculated that 27–43% and 19–40% of available plant protein may interact with condensed tannins from Desmodium intortum and Lotus pedunculatus, respectively.     

Sorghum kafirin interaction with various phenolic compounds

The ability of various phenolic compounds to bind and precipitate kafirin, the prolamin protein of sorghum, was investigated with regard to effects on its nutritional and functional uses. The protein–phenolic compound interaction was quantified by haze formation and colorimetric determination of total polyphenol bound. Ferulic acid, catechin and extracted phenolics (flavonoids) from condensed tannin‐free sorghum did not complex kafirin. Only tannic acid and sorghum‐condensed tannins had the ability to complex kafirin. The sorghum‐condensed tannins interacted more strongly than tannic acid. The haze of sorghum‐condensed tannins–kafirin was permanent, indicating a strong interaction. The fact that sorghum‐condensed tannins can bind irreversibly to kafirin indicates that this may play a role in decreasing protein digestibility in high‐tannin sorghum and can cause haze formation in lager beer made from high‐tannin sorghum. However, in condensed tannin‐free sorghum, phenolic compounds may not appear to play a major role in decreasing protein digestibility, as these endogenous phenolics may not bind with kafirin. Copyright © 2003 Society of Chemical Industry     

Measurement of protein in tannin-protein precipitates using ninhydrin

A method was tested for quantifying protein in precipitated tannin-protein complexes in which protein was hydrolysed with acid and the amino acids released were measured with ninhydrin. Unlike previously published methods, this technique requires no prior separation of tannin and protein and can be used to compare the binding of different soluble proteins to tannins under identical conditions. The method was used to compare the precipitation of bovine serum albumin, porcine pancreatic protease, β-glucosidase and γ-globulin by tannic acid. The amount of tannic acid required to precipitate maximal amounts of protease and β-glucosidase was approximately 7–8 times that required to cause maximal precipitation of albumin and γ-globulin when tested with 2 mg ml^?1 protein. All protein preparations contained a fraction (10–40% of total protein) which was not precipitated by tannic acid. Protein in tannin-protein precipitates produced in a standard haemanalysis assay were also measured with ninhydrin. Per cent precipitation at each tannic acid concentration as measured with ninhydrin was identical to that determined by haemanalysis within the linear portions of the binding curves produced by the two methods. These results confirm that the ninhydrin method accurately measures precipitation of protein by tannin.     

Gravimetric determination of tannins and their correlations with chemical and protein precipitation methods

Abstract. A method for gravimetric determination of tannins based on binding with insoluble polyvinylpyrrolidone (PVP) is presented. The gravimetric method gives the absolute amount of tannins and avoids problems of standards associated with spectrophotometric methods. The method was applied to nine browse and tree leaves. The values obtained correlate significantly with tannins determined spectrophotometrically, protein precipitation capacities and protein precipitable phenotics. This method together with other tannin assays will be useful in nutritional studies. The present study also demonstrates the different behaviour of tannic acids from different commercial sources towards PVP suggesting the presence of different moieties in tannic acids from different commercial sources and even among batches from the same source thereby affecting the results obtained using the spectrophotometric methods. Use of well-defined tannic acid as a standard in spectrophotometric methods is suggested which will allow meaningful comparison of values obtained from different laboratories.     

Response of a Lactobacillus plantarum human isolate to tannic acid challenge assessed by proteomic analyses

Scope : To gain insight on the mechanisms used by intestinal bacteria to adapt and resist the antimicrobial action of dietary tannins and identify targets for tannic acid in Lactobacillus plantarum. Methods and results : A proteomic analysis of an L. plantarum human isolate exposed to the tannic acid challenge was undertaken. Tannic acid targeted proteins involved in outstanding processes for bacterial stress resistance including cyclopropanation of membrane lipids, stress response at population scale and maintenance of cell shape. To respond to this aggression, tannic acid‐misfit cells of L. plantarum challenged with tannic acid reorganized their metabolic capacity to economize energy and express proteins involved in oxidative stress defense and cell wall biogenesis, indicating that the injury incurred by tannic acid was based on oxidative damage and disruption of the cell envelope. The induction of 3‐octaprenyl‐4‐hydroxybenzoate carboxy‐lyase, which is sensitive to changes in redox conditions and involved in ubiquinone biosynthesis in other bacteria, suggests for a tannic acid‐induced redox imbalance. Conclusion : The results reveal the adaptation of a gastrointestinal isolate of L. plantarum to tannic acid and identify antibacterial targets for this dietary compound. This provides the basis for the selection of tannin‐resistant microorganisms and their use to obtain health benefits from tannin‐containing diets.     

Changes of contents and antioxidant activities of polyphenols during fruit development of four apple cultivars

Polyphenols are functional components in apples and can be separated into four groups by Sephadex LH-20 as epicatechin, procyanidolic oligomers, chlorogenic acid and procyanidolic polymers. Antioxidant activities of each group were determined by FRAP and DPPH radical scavenging assay. It was found that procyanidolic oligomers and procyanidolic polymers influenced the total polyphenols content (measured by Folin–Ciocalteu method) much more in Jonagold, Golden Delicious, Fuji and Guoguang four apple cultivars. The Fe-reducing activity of procyanidolic oligomers in the four apple cultivars increased significantly during the development while the other three compounds changed irregularly. And the Fe-reducing activities of epicatechin and procyanidin contributed much more to the total Fe-reducing activities during the fruit development in the four apple cultivars. The DPPH scavenging activities of four compounds in Jonagold and Golden Delicious decreased during fruit development and that of Fuji and Guoguang changed irregularly. Chlorogenic acid was the main contributor in Jonagold, Golden Delicious and Fuji to the total scavenging activity. In Guoguang, it was procyanidolic oligomers that contributed much to the total scavenging activity.     

Tannins and Human Health: A Review

Tannins (commonly referred to as tannic acid) are water-soluble polyphenols that are present in many plant foods. They have been reported to be responsible for decreases in feed intake, growth rate, feed efficiency, net metabolizable energy, and protein digestibility in experimental animals. Therefore, foods rich in tannins are considered to be of low nutritional value. However, recent findings indicate that the major effect of tannins was not due to their inhibition on food consumption or digestion but rather the decreased efficiency in converting the absorbed nutrients to new body substances. Incidences of certain cancers, such as esophageal cancer, have been reported to be related to consumption of tannins-rich foods such as betel nuts and herbal teas, suggesting that tannins might be carcinogenic. However, other reports indicated that the carcinogenic acitivity of tannins might be related to components associated with tannins rather than tannins themselves. Interestingly, many reports indicated negative association between tea consumption and incidences of cancers. Tea polyphenols and many tannin components were suggested to be anticarcinogenic. Many tannin molecules have also been shown to reduce the mutagenic activity of a number of mutagens. Many carcinogens and/or mutagens produce oxygen-free radicals for interaction with cellular macromolecules. The anticarcinogenic and antimutagenic potentials of tannins may be related to their antioxidative property, which is important in protecting cellular oxidative damage, including lipid peroxidaton. The generation of superoxide radicals was reported to be inhibited by tannins and related compounds. The antimicrobial activities of tannins are well documented. The growth of many fungi, yeasts, bacteria, and viruses was inhibited by tannins. We have also found that tannic acid and propyl gallate, but not gallic acid, were inhibitory to foodborne bacteria, aquatic bacteria, and off-flavor-producing microorganisms. Their antimicrobial properties seemed to be associated with the hydrolysis of ester linkage between gallic acid and polyols hydrolyzed after ripening of many edible fruits. Tannins in these fruits thus serve as a natural defense mechanism against microbial infections. The antimicrobial property of tannic acid can also be used in food processing to increase the shelf-life of certain foods, such as catfish fillets. Tannins have also been reported to exert other physiological effects, such as to accelerate blood clotting, reduce blood pressure, decrease the serum lipid level, produce liver necrosis, and modulate immunoresponses. The dosage and kind of tannins are critical to these effects. The aim of this review is to summarize and analyze the vast and sometimes conflicting literature on tannins and to provide as accurately as possible the needed information for assessment of the overall effects of tannins on human health.     

单宁酸对小麦醇溶蛋白结构及功能性质的影响

采用荧光分光光度计、紫外分光光度计(UV-visible)、傅立叶红外光谱仪(FTIR)等探究单宁酸与小麦醇溶蛋白通过非共价与共价方式结合的机理以及蛋白结构与功能特性的改变。结果表明,在非共价作用下,单宁酸对小麦醇溶蛋白的淬灭类型为生成复合物的静态淬灭作用,两者以氢键作用驱动结合,且以1:1摩尔比结合。同时,在碱性环境下,单宁酸与小麦醇溶蛋白上的自由氨基发生席夫碱反应以共价方式形成复合物。此外,不同条件下,复合物的形成会使得小麦醇溶蛋白三级结构发生去折叠现象、二级结构展开。碱性环境下复合物的形成导致小麦醇溶蛋白二级结构展开程度更高。单宁酸的加入使复合物的抗氧化能力提高,且非共价复合物抗氧化活性更高。在热稳定性方面,两者共价结合使小麦醇溶蛋白的热稳定性提升1.03℃,而两者非共价结合使小麦醇溶蛋白热稳定性降低5.39℃。     

Preliminary studies on acidity-astringency interactions in model solutions and wines

Intensity of astringency in model solutions and wines varying in total acid and total phenols was evaluated by paired comparisons by 10 trained judges. Model solutions consisted of tannic (500, 1000, 2000 mg litre^?1) and tartaric (0, 2, 4, 6 g litre^?1) acids dissolved in aqueous solutions of ethanol (120 ml litre^?1) and sucrose (5 g litre^?1). Wine solutions were prepared by addition of citric acid (0, 0.5, 1, 2, 3 g litre^?1 as tartaric acid) to a high phenol-red wine (2645 mg litre^?1 GAE) and a moderate phenol-white wine (800 mg litre^?1 GAE). At all three levels of tannic acid, astringency of model solutions increased significantly (P<0.001) with tartaric acid concentration. Astringency of white wine also increased significantly (P<0.05) with citric acid concentration. A negative linear relation was found between relative astringency and pH at a given tannin level for both model solutions and white wine. As pH was reduced, more phenolic molecules were in the phenol form thereby increasing the likelihood of hydrogen bonding between hydroxyl groups of wine tannins and ketoimide groups of mouth proteins. The preliminary hypothesis that hydrogen bonding is the main reaction involved in the formation of protein-tannin complexes resulting in the sensation of astringency was reinforced.     

Comparison of the polyphenol profiles of apple fruit cultivars by correspondence analysis

Concentrations of the major flavonoids and phenolic acids in the peel and cortex of fruit of eight commercial apple cultivars were determined by HPLC. The multivariate statistical technique of correspondence analysis was applied to the polyphenol profiles to describe distinctive groups of cultivars and of polyphenols, and their joint correspondences. Cultural and growing conditions had a limited effect on the polyphenol profiles of the cortex and peel. Chlorogenic acid was the principal polyphenol in the cortex with the lowest levels being in Red Delicious and the highest in Jerseymac, which were compensated by changes in phlorizin. Cortland had low levels of chlorogenic acid and Gravenstein had high levels, but these were offset by the levels of catechins. The quercetin, rhamnoside, was the principal phenolic compound for the peel data with low levels in Red Delicious, Cortland, Spartan and Jerseymac and high levels in Golden Delicious, Gravenstein and Northern Spy. Levels of chlorogenic acid, offset by levels of phlorizin and catechins, distinguished between Red Delicious and Cortland. Rutin was important in distinguishing between Jerseymac and Spartan.     

Ruminal degradation of tannin‐treated legume meals

The inefficiency of protein utilisation by ruminants fed protein concentrates (based on legume meals) causes serious economic loss and environmental damage owing to their rapid hydrolysis and deamination in the rumen. Thus efforts aimed at slowing the ruminal fermentation of such feeds are needed, and recent studies have observed potentially positive effects of tannins on ruminant nutrition under certain circumstances. Tannins are a complex group of naturally occurring plant polyphenols characterised by their ability to bind with proteins. This property of tannins is considered responsible for the decreased ruminal digestibility of forages both in vivo and in vitro. Under that perspective, commercial tannic acid was added at three proportions (10, 25 and 50 g kg^?1 on a dry matter basis) to four different legume meals (horse bean, kidney bean, soybean and pea), and the effect on in situ dry matter and crude protein ruminal disappearance was assessed. The results confirmed the dose‐dependent (although not persistent after 48 h) slowing of in situ digestibility, this effect being significant at the highest tannin treatment when compared with untreated samples. Scanning electron microscopy revealed that soybean seed endosperm cell walls were protected from digestion by the ruminal microbiota, while the digestion of starch granules was relatively unaffected by tannic acid. Electrophoresis of the protein fractions confirmed the lower digestibility of tannin‐treated seeds as well as the relative lack of alteration of the electrophoretic profile of individual proteins. Implications for the digestion of concentrates in ruminants are discussed. Copyright © 2004 Society of Chemical Industry     

蓝靛果单宁的提取及对酵母发酵能力的影响

为确定酵母菌发酵蓝靛果果汁中的最适单宁含量,采用单因素实验及正交试验优化超声辅助法提取蓝靛果单宁工艺,将此条件下获得的单宁粗提液纯化、浓缩后得到单宁酸样品.将其添加到模拟蓝靛果果汁中,研究不同浓度单宁酸对酵母菌的影响,并验证最适单宁含量对发酵蓝靛果果汁的影响.结果 表明,蓝靛果单宁最优提取条件为:乙醇体积分数50％,料...     

Selective removal of tannins from medicinal plant extracts using a collagen fiber adsorbent

A novel adsorbent, used for the selective removal of tannins from medicinal plant extracts, was prepared from bovine skin collagen fiber. Some typical active constituents of medicinal plants were selected as probe molecules to investigate the adsorption selectivity of the collagen fiber adsorbent to tannins. In batch adsorption experiments, the extent of adsorption of condensed tannins, including larch tannin, black wattle tannin and bayberry tannin, was 100%. The extent of adsorption of tannic acid and the hydrolyzable tannins was also 100%. In contrast, for the most active constituents of medicinal plants, their amounts adsorbed by collagen fiber adsorbent were limited. For procyanidin, the common active constituents in medicinal plant extracts, its extent of adsorption was also low, although it has a similar basic structure to condensed tannins. In comparison with traditionally used polyamide adsorbent, the collagen fiber adsorbent exhibited an obvious advantage in adsorption selectivity over tannins. Therefore, this study provides a novel and effective method for selective removal of tannins from medicinal plant extracts. Copyright © 2005 Society of Chemical Industry     

Behaviour of tannic acid from various commercial sources towards redox,metal complexing and protein precipitation assays of tannins

Tannic acid is the most commonly used standard for quantitation of tannins. Tannic acid from five commercial sources (Merck, Sigma, Aldrich, Fluka and Apin chemical companies) was tested towards a redox (Folin-Ciocalteu method) and a metal complexing (ferric chloride method) assay, and three protein precipitation assays. Tannic acid from various commercial sources behaved differently towards these tannin assays showing that (i) tannic acid preparation differed from source to source, and (ii) tannic acid from different sources as a standard results in different tannin values for a given sample. It is suggested that the source of tannic acid used as a standard should be stated, and the assay values obtained by different workers should be compared with caution.     

聚苯乙烯/铁-单宁酸配合物微球在棉织物上的结构生色

针对目前基于多巴胺制备结构色织物的过程耗时及成本高的问题,采取单宁酸替代多巴胺快速实现结构色效果,制备了聚苯乙烯/铁-单宁酸配合物(PS/TA-Fe³⁺)微球,并通过重力沉积法在棉织物表面构建无规密堆积的非晶胶体阵列。采用马尔文纳米粒度分析仪、场发射电子显微镜、透射电子显微镜和显微角分辨光谱仪对聚苯乙烯(PS)微球、PS/TA-Fe³⁺微球和结构色织物进行了表征,探究了适宜的单宁酸和Fe³⁺用量,表征了结构色织物表面PS/TA-Fe³⁺微球的排列、结构生色效果及PS/TA-Fe³⁺涂层的结构稳定性。结果表明:当单宁酸用量为10%、单宁酸与Fe³⁺的量比为10:1时,制备的PS/TA-Fe³⁺微球粒径均匀、单分散性较好,结构色织物颜色柔和明亮,不具备角度依赖性,且具有良好的耐洗涤和耐摩擦性能。     

Effect of adding an anaerobic fungal culture isolated from a wild blue bull (Boselophus tragocamelus) to rumen fluid from buffaloes on in vitro fibrolytic enzyme activity,fermentation and degradation of tannins and tannin‐containing Kachnar tree (Bauhinia variegata) leaves and wheat straw

The study investigated the effects of adding an anaerobic fungus (Piromyces sp FNG5; isolated from the faeces of a wild blue bull) to the rumen fluid of buffaloes consuming a basal diet of wheat straw and concentrates on in vitro enzyme activities, fermentation and degradation of tannins and tannin‐rich tree leaves and wheat straw. In experiment 1, strained rumen fluid was incubated for 24 and 48 h, in quadruplicate, with or without fungal culture using condensed tannin‐rich Bauhinia variegata leaves as substrates. In experiment 2, in vitro incubation medium containing wheat straw and different concentrations of added tannic acid (0–1.2 mg mL^?1) were incubated for 48 h, in quadruplicate, with strained buffalo rumen fluid with or without fungal culture. In experiment 3, tolerance of the fungal isolate to tannic acid was tested by estimating fungal growth in pure culture medium containing different concentrations (0–50 g L^?1) of tannic acid. In in vitro studies with Bauhinia variegata tree leaves, addition of the fungal isolate to buffalo strained rumen liquor resulted in significant (P < 0.01) increase in neutral detergent fibre (NDF) digestibility and activities of carboxymethyl cellulase (P < 0.05) and xylanase (P < 0.05) at 24 h fermentation. There was 12.35% increase (P < 0.01) in condensed tannin (CT) degradation on addition of the fungal isolate at 48 h fermentation. In in vitro studies with wheat straw, addition of the fungus caused an increase in apparent digestibility (P < 0.01), true digestibility (P < 0.05), NDF digestibility (P < 0.05), activities of carboxymethyl cellulase (P < 0.001), β‐glucosidase (P < 0.001), xylanase (P < 0.001), acetyl esterase (P < 0.001) and degradation of tannic acid (P < 0.05). Rumen liquor from buffaloes which had never been exposed to tannin‐containing diet had been found to have substantial inherent tannic acid‐degrading ability (degraded 55.3% of added tannic acid within 24 h of fermentation). The fungus could tolerate tannic acid concentration up to 20 g L^?1 in growth medium. The results of this study suggest that introduction of an anaerobic fungal isolate with superior lignocellulolytic activity isolated from the faeces of a wild herbivore may improve fibre digestion from tannin‐containing feeds and degradation of tannins in the rumen of buffaloes. Copyright © 2005 Society of Chemical Industry     

Levels of nutritional constituents and antinutritional factors in black gram (Vigna mungo L. Hepper)

A study was conducted on nutritional constituents (total sugars, total proteins, total lipids and starch content) and antinutritional factors such as phenolic compounds, tannins, saponins, phytic acid, trypsin inhibitors and enzymes related to them such as acid- and alkaline phosphatases, ??-galactosidase in eleven recommended cultivars and twenty one advance breeding lines of black gram (Vigna mungo L. Hepper) with an aim to identify genotypes containing high nutritional quality and low antinutritional content. The average content of starch, total soluble sugars, proteins and lipids was around 43.5, 4.84, 22.0 and 1.1%, respectively. Seven genotypes had higher levels of bound fructose contributed by sucrose and raffinose series oligosaccharides. A significant positive correlation was observed among total phenols, o-dihydroxy phenols and flavonols; and among trypsin inhibitors and saponins. The content of phytic acid and activity of trypsin inhibitors showed significant variation among these genotypes. However, not much variation was observed in the content of tannins and saponins. Activities of ??-galactosidase, acid- and alkaline phosphatase were found to be related to the content of bound fructose of raffinose series oligosaccharides and phytic acid respectively. Genotypes having higher activity of these enzymes showed lower content of these antinutritional factors. The results showed that the observed diversity in developed cultivars and advance breeding lines could be further used by plant breeders.     

Effects of tannic acid on gluten protein structure,dough properties and bread quality of Chinese wheat

BACKGROUND: The effects of tannic acid, which is present in many plants, on the structure of gluten proteins and the properties of dough and bread were studied. Tannic acid was added at levels of 0.01, 0.02 and 0.03 g kg^?1 during the dough‐making process. RESULTS: The added tannic acid acted negatively on disulfide bond formation but interacted with gluten proteins via other covalent bonds, as detected by UV spectroscopy and dynamic rheometry. Rheological properties and texture of the bread were measured by farinograph, extensograph and texture profile analyser. Texture analysis indicated little change in adhesiveness and resilience of the bread at all three levels of tannic acid compared with the control, but changes in hardness and chewiness of the bread made with added tannic acid indicated that tannic acid could delay bread staling. CONCLUSION: The effect of tannic acid on flour and dough is different from that of other flour redox agents. It breaks down disulfide bonds but also has positive effects on dough properties and bread quality. Disulfide bonds are commonly considered to be the most important factor affecting changes in the quality of bread. However, this study presents the new concept that other covalent bonds can also improve the quality of flour and bread and uses this property to investigate new, safe and efficient flour additives. Copyright © 2010 Society of Chemical Industry