Tannin levels in leaves of some oak species at different stages of maturity

Total phenolics, condensed tannins, degree of polymerisation, protein precipitation capacity, protein precipitable phenolics and specific activity (protein bound per unit tannins) were determined in the leaves of four oak species at different stages of maturation (4 days old to 1 year old). The content of total extractable phenols was higher in younger leaves in Quercus ilex Linn, Quercus semecarpifolia Sm and Quercus serrata Roxb, whereas in Quercus glauca Thumb the content was higher in the mature leaves. In all species studied, condensed tannins increased with maturation. Protein precipitation capacity had a trend similar to that of total phenols. In Q serrate and Q semecarpifolia the apparent degree of polymerisation increased, and the content of protein precipitable phenolics and specific activity decreased as the leaves matured. The decrease in protein precipitation capacity with maturation in these two species may be explained by both the decrease in the content and the change in the nature of phenols capable of binding proteins. Protein precipitation capacity was not detectable in Q ilex leaves. Protein precipitation capacity in the mature leaves decreased in the order of Q serrata > Q semecarpifolia > Q glauca > Q ilex.     

Effect of drying conditions on tannin,fibre and lignin levels in mature oak (Quercus incana) leaves

Oak (Quercus incana Roxb) leaves are rich in tannins and produce adverse effects when fed to livestock. The effects of shade and sun drying and oven drying at 60°C and 90°C for different lengths of time (24 to 72 h) on total phenolics, condensed tannins, protein precipitation capacity, degree of polymerisation, specific activity (protein bound per unit tannins), fibre-linked proanthocyanidins, acid and neutral detergent fibres and lignin levels in mature oak leaves were studied. Removal/inactivation of tannins was not observed on wilting or drying under several conditions. Similarly the drying conditions had no effect on fibre composition. The adverse effects on feeding fresh or dried oak leaves are expected to be of similar magnitude.     

Comprehensive study of the phenolic composition of the edible parts of jambolan fruit (Syzygium cumini (L.) Skeels)

Jambolan fruit has been used in traditional Indian medicine and has recently attracted interest as a functional food. The comprehensive study by HPLC–DAD-ESI-MS/MS has revealed the occurrence of around 74 individual phenolic compounds in the edible parts of jambolan, including 9 anthocyanins (mainly based on delphinidin, petunidin and malvidin), 9 flavonols (myricetin, laricitrin and syringetin glycosides), 19 flavanonols (dihexosides of dihydromyricetin and its methylated derivatives), 8 flavan-3-ol monomers (mainly gallocatechin), 13 gallotanins and 13 ellagitanins, together with some proanthocyanidins (highly galloylated prodelphinidins) and free gallic and ellagic acids. No hydroxycinnamic acid derivatives were detected. The skin of the jambolan fruit accumulated great amounts of phenolic compounds, almost all of the non-tannin phenolics. In contrast, condensed tannins (proanthocyanidins) and hydrolyzable tannins (gallotannins and ellagitannins) were present in both edible parts, accounting for greater amounts in the skin. Overall, the main phenolics of jambolan were anthocyanins and hydrolyzable tannins (similar amounts of gallotannins and ellagitanins), followed by flavanonols, flavonols and flavan-3-ols.     

Insights into the metabolism and microbial biotransformation of dietary flavan-3-ols and the bioactivity of their metabolites

Flavan-3-ols, occurring in monomeric, as well as in oligomeric and polymeric forms (also known as condensed tannins or proanthocyanidins), are among the most abundant and bioactive dietary polyphenols, but their in vivo health effects in humans may be limited because of their recognition as xenobiotics. Bioavailability of flavan-3-ols is largely influenced by their degree of polymerization; while monomers are readily absorbed in the small intestine, oligomers and polymers need to be biotransformed by the colonic microbiota before absorption. Therefore, phenolic metabolites, rather than the original high molecular weight compounds found in foods, may be responsible for the health effects derived from flavan-3-ol consumption. Flavan-3-ol phenolic metabolites differ in structure, amount and excretion site. Phase II or tissular metabolites derived from the small intestine and hepatic metabolism are presented as conjugated derivatives (glucuronic acid or sulfate esters, methyl ether, or their combined forms) of monomeric flavan-3-ols and are preferentially eliminated in the bile, whereas microbial metabolites are rather simple conjugated lactones and phenolic acids that are largely excreted in urine. Although the colon is seen as an important organ for the metabolism of flavan-3-ols, the microbial catabolic pathways of these compounds are still under consideration, partly due to the lack of identification of bacteria with such capacity. Studies performed with synthesized or isolated phase II conjugated metabolites have revealed that they could have an effect beyond their antioxidant properties, by interacting with signalling pathways implicated in important processes involved in the development of diseases, among other bioactivities. However, the biological properties of microbe-derived metabolites in their actual conjugated forms remain largely unknown. Currently, there is an increasing interest in their effects on intestinal infections, inflammatory intestinal diseases and overall gut health. The present review will give an insight into the metabolism and microbial biotransformation of flavan-3-ols, including tentative catabolic pathways and aspects related to the identification of bacteria with the ability to catabolize these kinds of polyphenols. Also, the in vitro bioactivities of phase II and microbial phenolic metabolites will be covered in detail.     

Antioxidant composition and activity of barley (Hordeum vulgare) and malt extracts and of isolated phenolic compounds

Phenolics have been identified and quantified in nine varieties of barley and their corresponding malts as flavan-3-ols, flavonols, phenolic acids and apolar esters. Flavan-3-ols are monomers, (+)-catechin and (−)-epicatechin, and polymers constituted mainly by units of (+)-catechin and (+)-gallocatechin. The most abundant compounds were the dimers procyanidin B3 and prodelphinidin B3. The main trimeric procyanidin was procyanidin C2. After malting, the phenolic content decreased for all varieties. Catechin monomers were the most affected. Beside polyphenols, barley and malt extracts contained other antioxidants: carotenoids (lutein and zeaxanthin) and tocopherols (α, δ and γ). The antioxidant activity was measured using three methods: capacity to react with DPPH^. (ARP), inhibition of lipoxygenase activity (LoxI) and inhibition of cooxidation of β-carotene in a linoleate model system (AOP). The inhibition of cooxidation of β-carotene in a linoleate model system did not allow varieties to be discriminated. They all have high antioxidative properties. Using this assay, tocopherols were the best antioxidants. The ARP (antiradical power) was correlated positively with the amount of total flavan-3-ols (r = 0.89) and increased with the degree of polymerisation. The LoxI assay allowed discrimination of the nine varieties of barley and their corresponding malts but was not correlated with any compound, although flavan-3-ols were good inhibitors of lipoxygenase activity. © 1999 Society of Chemical Industry     

Condensed tannins in horse bean seeds: Chemical structure and apparent effects on poultry

The seed-coats of numerous varieties of horse beans contain condensed tannins of the proanthocyanidin type. These polymers consist of molecules of flavan-3-ols (catechin, gallocatechin) and flavan-3,4-diols (leucocyanidin, leucodelphinidin). Condensed tannins of horse bean seeds appear to depress the growth of muscovy ducklings, to cause a reduction in the weight of eggs produced by laying hens and to decrease the digestibility of nitrogen compounds in growing chicks.     

橡木桶陈酿对红葡萄酒中黄烷-3-醇和原花色素的影响

本文以华夏酿酒有限公司2004年度赤霞珠为试材,研究了美洲、欧洲和欧美三种类型橡木桶陈酿对黄烷-3-醇和原花色素含量及组成的影响。结果表明,橡木桶陈酿过程中,(-)-表儿茶素((-)-epicatechin,EC)、(-)-表儿茶素没食子酸酯((-)-epicatechingallate,ECG)、(-)-表棓儿茶素没食子酸酯((-)-epgallocatechingallate,EGCG)含量上升,(+)-儿茶素((+)-catechin,CAT)保持相对稳定,而(-)-表棓儿茶素((-)-epigallocatechin,EGC)略有下降。原花色素含量下降,平均聚合度降低。不同类型的橡木桶对两者含量的影响不同。     

Antioxidant gallocatechins,dimeric and trimeric proanthocyanidins from sea buckthorn (<Emphasis Type="Italic">Hippophaë rhamnoides</Emphasis>) pomace

Residues such as peels and seeds that result from fruit juice production may contain substantial amounts of valuable natural antioxidants. In order to isolate the potential antioxidants gallocatechins and proanthocyanidins, pomace from sea buckthorn (Hippophaë rhamnoides) berries was extracted by acetone-water (75:25, v/v) and fractionated by Sephadex LH-20 gel chromatography and semipreparative HPLC. The structures of the monomeric flavan-3-ols isolated, (+)-gallocatechin and (–)-epigallocatechin, were elucidated by electrospray mass spectrometry (ESI-MS) and ¹H and ¹³C NMR spectroscopy. Five dimeric proanthocyanidins were identified by HPLC-ESI-MS(-MS) and by acid-catalyzed cleavage in the presence of phloroglucinol. Moreover, nine trimeric proanthocyanidins were tentatively identified by HPLC-ESI-MS(-MS) in the Sephadex fractions of sea buckthorn pomace. The isolated flavan-3-ols and proanthocyanidins were potent in scavenging Fremys salt, a synthetic free radical. They possessed antioxidant capacities that were higher or comparable to that of ascorbic acid or Trolox. On comparing the antioxidant capacities of monomeric flavan-3-ols and dimeric proanthocyanidins, no significant influence from the degree of polymerization (DP) was observed.     

Flavan-3-ols: nature, occurrence and biological activity

Representing the most common flavonoid consumed in the American diet, the flavan-3-ols and their polymeric condensation products, the proanthocyanidins, are regarded as functional ingredients in various beverages, whole and processed foods, herbal remedies and supplements. Their presence in food affects food quality parameters such as astringency, bitterness, sourness, sweetness, salivary viscosity, aroma, and color formation. The ability of flavan-3-ols to aid food functionality has also been established in terms of microbial stability, foamability, oxidative stability, and heat stability. While some foods only contain monomeric flavan-3-ols [(-)-epicatechin predominates] and dimeric proanthocyanidins, most foods contain oligomers of degree of polymerization values ranging from 1-10 or greater than 10. Flavan-3-ols have been reported to exhibit several health beneficial effects by acting as antioxidant, anticarcinogen, cardiopreventive, antimicrobial, anti-viral, and neuro-protective agents. This review summarizes the distribution and health effects of these compounds.     

Influence of phenolics in finger millet on grain and malt fungal load,and malt quality

Phenolic type, fungal load, germinative energy (GE) and malt quality of finger millet grain types of varied kernel colour and phenolic content were analysed, to determine if phenolics in finger millet grain influence its malt quality. The fungal load (total fungal count (TFC) and infection levels) of the unmalted grain and malt were negatively correlated (p < 0.05) with total phenolics (TP) and amount of phenolic type (condensed tannins, anthocyanins and flavan-4-ols). High-phenol finger millet types had much higher malt quality than the low-phenol types, with respect to diastatic power (DP), and α- and β-amylase activities. GE, DP and α-amylase activity were positively correlated with TP and amount of phenolic type (p < 0.05) and negatively correlated with TFC (p < 0.01). Phenolics in finger millet grain influence its malt quality positively by contributing to attenuation of the fungal load on the germinating grain.     

圆叶葡萄种子发育过程中多酚积累特性

以栽培于广西地区2 个圆叶葡萄品种‘Noble’和‘Carlos’为实验材料,以真葡萄品种‘赤霞珠’和‘雷司令’为对照,使用超高效液相色谱-串联三重四极杆飞行时间质谱,分析其种子发育过程中多酚组成和积累特性。结果表明：在4种葡萄发育过程的种子样品中共检测到106种多酚,包括48种鞣花酸及前体物、24种黄酮醇、20种羟基苯甲酸、9种黄烷-3-醇、3种芪类和2种羟基肉桂酸。鞣花酸及前体物（主要是前体物）和黄烷-3-醇（主要是没食子酰化体和单体）分别是圆叶葡萄和真葡萄种子中最主要的多酚类型,但其含量在不同年份和品种间具有较大差异。前体物含量在圆叶葡萄‘Noble’幼果期种子中较高,然后逐渐下降,完全转色后再次上升;‘Carlos’则在浆果转色前种子中含量较高,随后略有下降。黄烷-3-醇在真葡萄‘雷司令’种子中2013年随着浆果发育含量显著升高,转色时含量达到最高,随后有所下降,2014年不受发育期的影响;‘赤霞珠’则分别在2013年幼果期和2014年果实完熟时的种子中含量最高。     

Antioxidant compounds and antioxidant capacity of Peruvian camu camu (Myrciaria dubia (H.B.K.) McVaugh) fruit at different maturity stages

The antioxidant capacities of ascorbic acid and phenolic compounds present in camu camu fruit were screened during ripening. Ascorbic acid decreased, and anthocyanin, flavonol and flavanol contents, and DPPH antioxidant capacity increased during ripening. Antioxidant compounds from camu camu were fractionated in two fractions: an ascorbic acid-rich fraction (F-I) and a phenolics-rich fraction (F-II). F-I was the major contributor to the DPPH antioxidant capacity (67.5–79.3%) and F-II played a minor role (20.7–32.5%). A total of 30 different phenolic compounds were detected by HPLC-PAD. The presence of catechin, delphinidin 3-glucoside, cyanidin 3-glucoside, ellagic acid and rutin was elucidated. Other phenolic compounds, such as flavan-3-ol, flavonol, flavanone and ellagic acid derivatives, were also present. For the three ripening stages the flavan-3-ols and ellagic acid group were the most representative phenolic compounds in this fruit. Acid hydrolysis of F-II revealed the presence mainly of gallic and ellagic acids, suggesting that camu camu fruit possesses important quantities of hydrolysed tannins (gallo- and/or ellagitannins). These results confirm that camu camu fruit is a promising source of antioxidant phenolics.     

Phenolic composition of Merlot and Cabernet-Sauvignon grapes from Bordeaux vineyard for the 2009-vintage: Comparison to 2006, 2007 and 2008 vintages

Cabernet-Sauvignon and Merlot skin and seed extracts from Bordeaux grapes were investigated to determine both grape variety and vintage effect on phenolic composition. The total content of polyphenols and tannins in Merlot seeds was higher than that of Cabernet-Sauvignon allowing to discriminate the varieties. HPLC analyses underlined significant differences in the absolute concentration of proanthocyanidins amongst the two varieties and in their composition: mean degree of polymerisation (mDP) and percentage of galloylation of seed extracts were good indicators of grape variety. The vintage effect on the phenolic composition was confirmed for 2009 in comparison to previous vintages. Low values of mDP and concentrations of proanthocyanidins and anthocyanins were found in 2009 seeds and skins. The climatic conditions of 2009 (high rainfall before flowering followed by a strong hydric stress during berries development until ripening) let us hypothesise a lower activation of flavonoid pathway.     

Determination of free radicals and flavan-3-ols content in fermented and unfermented teas and properties of their infusions

The objective of this study was to analyse selected brands of fermented (red and black) and unfermented (white and green) teas for free radical content with the use of electron paramagnetic resonance (EPR) spectroscopy and for contents of flavan-3-ols by means of high-performance liquid chromatography. Analyses were also conducted for the polyphenolic profile of infusions of the analysed teas (with the Folin–Ciocalteu’s method) and their antioxidant activity (in reaction with a DPPH radical) at three brewing times (5, 10 and 15 min). The obtained results showed the possibility of using rapid spectroscopic method EPR to evaluate the oxidative changes in tea leaves caused by enzymatic fermentation. The number of free radicals in teas was negatively correlated with contents of flavan-3-ols, (?)-EGCG in particular. The main signals observed in EPR spectra of teas were attributed to semiquinone radicals; however, also signals attributed to carbohydrate radicals were detected. Regarding unfermented teas, it was ascertained that teas with the highest content of flavan-3-ols, (?)-EGCG in particular, were characterised by the lowest content of semiquinone radicals and a high content of carbohydrate radicals. The group of fermented teas demonstrated to contain mainly semiquinone radicals. The total phenolic content and antioxidant activity of the tea infusions were strongly diversified depending on the kind and brand of tea as well as on the extraction time. The predominating flavan-3-ol in the analysed teas was epigallocatechin gallate (?)-EGCG, the content of which was additionally highly correlated with the antioxidant activity of the tea infusions.     

Roasting enhances antioxidant effect of bitter melon (Momordica charantia L.) increasing in flavan-3-ol and phenolic acid contents

Bitter melon (BM, Momordica charantia L) has various biological functions including antidiabetic, anticancer, anti-inflammatory, antiviral, and antioxidant activities. In this study, the antioxidant effects of BM fruits, leaves, stems, and roots after roasting using DPPH, ABTS, reducing power, and ferric reducing/antioxidant power (FRAP) assays were compared. The roasted BM exhibited significantly higher antioxidant activity than unroasted BM in the test methods used. Particularly, the roasted BM roots showed the highest antioxidant activity compared to any other extracts. Antioxidant compounds including flavan-3-ols and phenolic acids increased, whereas flavanols decreased in the BM following roast processing. Moreover, the total phenolic contents and flavan-3-ol and phenolic acid contents were markedly increased, leading to a general increase in antioxidant activities after roasting. These results suggest that the roasting BM extracts could be used as a potential source of natural antioxidants in certain food and medicinal applications.     

Chemical constituents of the leaves of rabbiteye blueberry (Vaccinium ashei) and characterisation of polymeric proanthocyanidins containing phenylpropanoid units and A-type linkages

Chemical constituents of the leaves of rabbiteye blueberry (Vaccinium ashei READE) were investigated in detail. The major phenolic components were caffeoyl quinic acids, flavonol glycosides, flavan-3-ols and proanthocyanidins. Catechins and proanthocyanidins having additional phenylpropanoid units, such as cinchonains, kandelins and mururins, characterised the polyphenols of this plant. Among them, vaccinin A, an isomer of mururin A, was found to be a new compound, and the structure was characterised by spectroscopic methods. The most abundant polyphenols (11.3% of freeze-dried leaves) were oligomeric proanthocyanidins. Thiol degradation with mercaptoethanol indicated that the polymer was constituted of (+)-catechin and (−)-epicatechin as the terminal units and (−)-epicatechin, procyanidin A-2, and cinchonains Ia and Ib as the extension units. Mass spectral analysis suggested the presence of at least dodecamers with A-type linkages and phenylpropanoid moieties.     

Effect of frozen storage on the phenolic content of vacuum impregnated Granny Smith and Stark Delicious apple <Emphasis Type="Italic">cvv</Emphasis>.

The phenolic fraction modification was evaluated in untreated vacuum impregnated frozen apple slices from two varieties (Granny Smith and Stark Delicious) a few days after freezing and after 12 months of frozen storage. After 12 months the phenolic content of both fresh and vacuum impregnated apple slices varied greatly. The most important change was the increase of many polymeric flavan-3-ols, which may be due to hydrolysis of polymeric procyanidins. Furthermore, there was significant correlation (r ² = 0.52, P < 0.05) between the increase in flavan-3-ols and the decrease in pH. In fact, control Stark slices presented the highest pH, and had no statistically significant increase in flavan-3-ols. Other classes of phenolic compounds were decreased in apple slices following frozen storage.     

The structure of tannins of some edible fruits

The tannins of 20 species of edible fruits are described. The majority contain condensed tannins (polymeric proanthocyanidins) whose structural units and number average molecular weight have been determined. Some fruits contain both condensed and hydrolysable, or hydrolysable tannins alone—notably those in the genus Rubus. The structures of tannins in the fruit and leaves are compared in several cases.     

不同品种茶叶单宁的含量与结构测定

测定了本山、黄旦和铁观音三个品种茶树成熟叶片的总酚及可溶缩合单宁含量,并通过基质辅助激光解吸附飞行时间质谱(MALDI-TOF MS)研究了茶叶缩合单宁的基本结构。结果显示,三种茶叶均具有较高的总酚含量,大约为200mg/g;三种茶叶的缩合单宁是以(表)儿茶素(EC/C)和(表)棓儿茶素(EGC/GC)为基本结构单元的均聚物和杂聚物,且大部分聚合物的结构单元之间存在A 型和B 型两种连接方式,其中本山和黄旦缩合单宁的最高聚合度要大于铁观音。     

原花青素的研究进展

原花青素是一类广泛存在于自然界中的黄烷-3-醇类化合物。本文详细整理国内外有关原花青素的报道,就其化学结构、生物活性、吸收代谢和毒理学特性做详细综述。其中,原花青素的化学结构根据其聚合度分类,结合结构单元、连接方式、空间构型和取代基的不同,并配结构图列举说明每种类型;原花青素有很强的生物活性,如抗氧化活性、防治心血管疾病、抗癌、抗高血压、降血脂、降血糖等;原花青素的吸收代谢包括体外Caco-2细胞模型和体内代谢的研究;毒理学研究表明原花青素的安全性很高。本文结合国内外的最新文献,较为全面地介绍生物活性强、食源性和低毒性的原花青素类成分,为该类成分的进一步研究提供参考。