Total content and speciation of aluminium in tea leaves and tea infusions

A total of 29 tea samples of different origin, 13 green tea samples, 13 black tea samples, two semi-fermented and one white tea, imported to the Czech Republic, were collected and analysed for total content of aluminium (Al) in tea leaves and tea infusions, as well as for Al compounds in these infusions. The total content of metals in tea leaves differs according to the type of tea (green or black) and is probably influenced by many factors, e.g., soil properties. The HPLC/IC speciation of Al in tea infusions was performed for all samples. The addition of Al³⁺ to the tea infusion proved that Al³⁺, Al(Y)²⁺ and Al(X)¹⁺ species can be determined in tea infusions. Increased extraction time did not show any affect on Al speciation, neither did the addition of sugar. After the addition of lemon juice, the speciation changed in one sample of black tea and five samples of green tea. These findings suggest that lemon juice as an additive can significantly influence Al speciation in tea infusions.     

Determination of flavonols in green and black tea leaves and green tea infusions by high-performance liquid chromatography

Tea flavonols are potent antioxidants and make up 2–3% of the water-soluble solids from tea leaves. In this paper, the conditions necessary for hydrolysing and analysing flavonols in tea leaves and tea infusions are optimised and an isocratic elution system for the determination of the hydrolysed flavonols by high-performance liquid chromotography is presented. Aqueous ethanol was selected as the best solution for hydrolysing flavonoids in tea leaves. The contents of flavonols on a dry weight base in green tea leaves ranged from 0.83–1.59, 1.79–4.05, and 1.56–3.31 g/kg, and in black tea leaves from 0.24–0.52, 1.04–3.03, and 1.72–2.31 g/kg for myricetin, quercetin, and kaempferol, respectively. It was observed that the particle size of ground tea leaves significantly influenced the yield of flavonols. The contents of flavonols in different green tea infusions are given.     

Availability of essential elements in Indian and US tea brands

Fifteen different brands of Indian tea leaves and seven US brands of flavoured tea were analysed for Na, K, Mn, Cu and Br by thermal neutron activation analysis (TNAA). Mn was also analysed by spectrophotometric and atomic absorption spectrometry (AAS) methods. In Indian tea, Mn concentration was found to be in the range 371–758 μg/g with a mean concentration of 575 ± 96 μg/g whereas in US tea it was in the range 79–768 μg/g with a mean concentration of 329 ± 231 μg/g. Na and Cu contents were also widely different in tea leaves from India and the USA but K contents were similar in the two tea leaves. Bromine was absent in tea leaves from the USA. Several standard or certified reference materials (SRMs/CRMs), including two tea leaves standards, were also analysed for data validation.     

Tracking residual organochlorine pesticides (OCPs) in green,herbal, and black tea leaves and infusions of commercially available tea products marketed in Poland

The content of residual organochlorine pesticides (OCPs) was examined in green, herbal, and black tea leaves as well as in their infusions prepared from tea products marketed in the main supermarkets in Poland. It was found that the detected mean levels of organochlorine residues in tea leaves ranged from ?1 dry weight. Among hexachlorocyclohexane isomers, γ-HCH in green tea occurred in the highest concentrations. Among dichlorodiphenyltrichloroethane (DDT) metabolites the highest level of p,p′DDT (1.96 ng g^?1 dw) was in green tea samples. The transfer of OCPs from tea leaves to brew was investigated. The present study revealed that during the infusion process, a significant percentage of the residues, particularly pesticides with high water solubility, were transferred to the infusions. The obtained results show that the percentage transfer of each pesticides from tea to the tea infusions ranged from 6.74% (heptachlor) to 86.6% (endrin). The detected residues were below current MRLs for these pesticides.     

高效液相色谱-二极管阵列法检测四川绿茶、黄茶、黑茶、红茶和青茶中甲基化儿茶素含量

采用高效液相色谱-二极管阵列检测法(HPLC-DAD)对四川省雅安、成都、乐山、宜宾、绵阳23家企业生产的绿茶、黄茶、黑茶、红茶和青茶中48个茶样的(-)-表没食子儿茶素-3-O(3-O-甲基)没食子酸酯(EGCG3″Me)含量进行了比较研究。结果表明:青茶EGCG3″Me含量最高,在3.14~6.08 mg/g之间,平均值为4.40 mg/g;黑茶EGCG3″Me含量在0~1.72 mg/g,平均值为0.35 mg/g;绿茶和黄茶中EGCG3″Me含量较低;绿茶中含量在0~0.39 mg/g之间,平均值为0.10 mg/g;黄茶中含量在0~0.09 mg/g之间,平均值为0.05 mg/g;红茶中未检出。各茶类间EGCG3″Me含量差异显著,主要原因在于加工所用鲜叶原料(品种、采摘标准等)及加工工艺等不同。建议易过敏人群应适当饮用青茶。     

Protein conversion efficiencies of four test diets based on milk, two milk and tea treatments, and casein

Milk consumption in 80 households in western Kenya averaged .25 to 1.00 L per family per day. Most of this milk was processed into a milk and tea beverage. Polyphenols, the major determinants of tea flavor and character, form soluble complexes with casein when black tea infusions are mixed with milk. Test diets were prepared from the following treatments: a) casein reference diet; b) milk, no tea leaves; c) milk added after heat treatment; and d) traditional Kenyan-style tea (i.e., milk and tea leaves heated together). Four groups of 10 male 21-day-old Sprague Dawley weanling rats were assembled and assigned to the test diets. Weight gain and protein intake (g/g) during a 28-d test period for the four diets were 1.94, 2.99, 2.93, and 2.77. The least significant difference test showed weight gain for protein intake was greater for rats on the milk-based diet and the diet with milk added after heating than for rats on the traditionally prepared milk and tea drink. Rats did most poorly when assigned to the casein reference diet. Modification of traditional Kenyan tea preparation practices (i.e., adding milk after tea leaves have been removed) might improve the nutritional value of the most popular milk product in western Kenya.     

Analysis of coumarin and its glycosidically bound precursor in Japanese green tea having sweet-herbaceous odour

Coumarin is a natural product well-known for its pleasant sweet-herbaceous and cherry flower-like odour. Despite coumarin being widely found in the plant kingdom, its occurrence in tea leaves is very poorly characterised. In this work, green tea made from the cultivars “Shizu-7132”, “Koushun” and “Tsuyuhikari” were found to have sweet-herbaceous odour. Application of the stable isotope dilution assay for the quantification of coumarin revealed that its levels in these Japanese green tea products ranged from 0.26 to 0.88 μg/g of green tea product, whereas concentrations were generally below 0.2 μg/g in common green tea products. In contrast to the leaf, the stem part contained much less coumarin. During the manufacturing process of the tea (Shizu-7132), the steaming time and drying temperature influenced the content of coumarin in the final product. Due to hydrolysis of glycosidically bound coumarin precursors, in fresh tea leaves most coumarin occurred in its free form. Tea leaves also contained small amounts of bound coumarin precursors, such as primeveroside.     

Cocoa tea (Camellia ptilophylla Chang), a natural decaffeinated species of tea – Recommendations on the proper way of preparation for consumption

Cocoa tea is a new natural decaffeinated tea. Three types of cocoa tea (green, oolong and black) were produced and their sensory evaluation scores accessed. Main components and their dissolution rates in ten infusions of the three teas were analyzed by HPLC and spectrophotometry. The comprehensive score of sensory evaluations was 85.1, 86.8 and 94.4, respectively. Upon fermentation the contents of water extract (46.67%, 41.8% and 40%), tea polyphenols (38.58%, 30.41% and 23.6%) and total catechins (23.51%, 17.68% and 4.02%) in green, oolong and black teas decreased gradually, and theaflavins (0.11%, 0.11% and 0.17%), thearubigins (4.29%, 5.00% and 9.71%), theabrownins (2.75%, 4.90% and 13.52%), water-soluble carbohydrates, flavonoid glycoside and gallic acid in the three teas increased gradually. Theobromine (3.52%, 3.43% and 3.71%) was the alkaloid present in cocoa tea and its content did not change upon fermentation. In the three teas, 9–25% of the main components dissolved in the first 10 s-infusion, more than 80% of most components dissolved in five infusions. A recommendation for consuming cocoa tea is to infuse tea leaves (g) with 50 times boiling water (ml) for 3 min, the first infusion should not be discarded and five infusions were sufficient.     

茶多酚水溶液浸提法生产低咖啡碱茶叶的研究

首次采用茶多酚水溶液浸提法脱除鲜茶叶与干茶叶中的咖啡碱,并保留其中的主要功能性成分茶多酚。鲜茶叶最佳浸提条件为:温度100℃,料液比1:10(g/mL),茶多酚水溶液质量体积分数5%,时间5min。此条件下咖啡碱脱除率达80.61%,比传统热水浸提法提高31.25%,且茶多酚无损失。干茶叶最佳浸提条件为:温度100℃,料液比1:20(g/mL),茶多酚水溶液质量体积分数15%,时间7min。此条件下咖啡碱脱除率达81.61%,且处理后的茶叶中茶多酚含量提高90.02%。研究结果表明,针对鲜茶叶和干茶叶原料,茶多酚水溶液浸提法均能有效脱除其咖啡碱,并有效保留或提高茶叶中的茶多酚,比传统热水浸提法有明显优势,是一种生产低咖啡碱茶叶的新方法。     

Content of various elements in different parts of the tea plant and in infusions of black tea from Southern India

Contents of various elements in dyferent parts of the tea plant (shoot, mature leaf, small stem, thick wood and root), black tea manufactured by the crush-tear-curl and orthodox processes, and tea brew after 1 and 5 min of infusion were determined by inductively coupled plasma atomic emission spectrometry. From these, the amount of each element assimilated in the production of 1000 kg of marketable tea, as well as the quantity of each element brought into infusion and thus possib f y taken up through drinking tea, were calculated and discussed. Among the various elements assimilated by the tea plant, the shoot jraction (economically important for manufacturing commercial tea) contained high concentrations of N, P, K and Mg while the mature leaf accumulated Al, Bu, Ca, Cd, Mn, Pb and Sr. Of the dgerent elements brought into infusion while brewing black tea, the amount of K was found to be the largest (> 10000 μg g⁻¹ tea) followed by P (700–1200 μg g⁻¹), Mg (300–700 μg g⁻¹), Ca and A1 (each 150–300 μg⁻¹), Mn (60–150 μg g⁻¹), Cu, Na, Si and Z n (each 6–50 μg g⁻¹), B, Ba, Cr, Fe, Ni and Pb (each Id μg g⁻¹), and Sr, Co and Gd (each <1μg g⁻¹). The proportion of the totalamount of an element brought into infusion showed that the elements Ba, Ca, Fe and Sr were less soluble (<10 % of total amount), Al, B, Cd, Co, Cr, Cu, Mg, Mn, P, Pb, Si and Zn were moderately soluble (10–50 %), and K, Nu and Ni were highly soluble (>50%). The overall mean of the extent of solubility of all elements in 1 and 5 min showed that, out of the amount soluble in 5 min, about 68% was dissolved within 1 min.     

Availability of aluminium from tea and coffee

 The amount of aluminium in different kinds of tea and ground coffee was analysed, the transfer of aluminium into the infusion was determined and aluminium intake via tea and coffee was calculated within the framework of our investigations. Aluminium concentrations amounted to (in μg/g dry matter): black tea, 899; flavoured black tea, 763; peppermint tea, 477; mountain herbal tea, 419; fruit tea, 292; ground coffee, 19. About 30% of the aluminium stored in black tea’s dry matter was transferred into the infusion, which contained 4.2 mg Al/l. In contrast, the availability of aluminium from peppermint and fruit tea as well as from ground coffee was very low (about 5%). The calculated aluminium intake via tea and coffee was 0.2 to 0.3 mg/day and contributed about 5% to the total aluminium intake. Only black tea infusions are a significant source of aluminium intake via beverages. Received: 9 January 1997     

The rôle of added carbohydrates in tea ‘cream’ solubilisation

The results of solubilisation studies of the ‘cream’ of tea infusions are reported. The addition of glucose, sucrose and maltodextrin to hot tea infusions was found to be ineffective. On the other hand, the incorporation of materials such as xylose, sorbitol, glucose, lactose, sucrose and maltodextrin at different levels into the distorted green leaves and subsequent fermentation for different periods resulted in solubilisation of the ‘cream’ to a large extent, in the following order of efficacy: monosaccharides > disaccharides > polysaccharides. This may be explained by the formation of tannin-carbohydrate-protein (enzyme) complexes in the fermenting leaf.     

Multi-element analysis of tea beverages by inductively coupled plasma atomic emission spectrometry

The metal content of several tea beverages, infusions, instant and tea soft drinks was determined. Eleven metals Al, Ba, Ca, Cu, Fe, K, Mg, Mn, Na, Sr and Zn were determined by inductively coupled plasma atomic emission spectrometry (ICP–AES). A study of the differences in the metal contents of tea beverages has been carried out. Pattern recognition techniques such as principal components analysis and linear discriminant analysis were used to discriminate between the tea beverages. The metal intake related to tea consumption has also been studied.     

N、P调控外源Se、Zn对茶叶元素含量及抗氧化能力的影响

选取以江西为代表的丘陵红壤区生长的茶树作为研究对象,通过在土壤中添加外源Se、Zn并进行N、P调控,研究一芽二叶和老叶中Se、Zn、Al、Mn四种元素含量、茶多酚含量以及茶叶抗氧化能力的变化。以期探寻在降低茶叶中Al、Mn含量的同时提高茶叶自然品质的新种植方法。实验结果表明,通过N、P调控外源Se、Zn进行种植后,一芽二叶和老叶中Se、Zn含量升高,最多分别提高255.65%和100.45%;Al、Mn含量降低,最多分别降低39.27%和35.85%;茶多酚含量提高,并且抗氧化能力增强。      

Leaching and bioavailability of aluminium, copper and manganese from tea (Camellia sinensis)

To assess human exposure to Al, Cu and Mn from tea drinking, eight tea samples were analysed for their ‘total’ and soluble elemental content. From this data, the percentage of ‘available’ element to the human system was calculated. Results for the samples showed that, compared to background levels for plants, concentrations of Al were highly elevated. The solubility of Al, Cu and Mn in infusions at 2, 5 and 10 min with boiling water showed that the solubility in the first infusion was the highest followed by the second and the third infusions in decreasing order. Calculation of percentage ‘available’ Al, Cu and Mn to the human system showed that tea is a rich source of dietary Mn, contributes towards our dietary copper intake, and is of no cause for concern in terms of Al toxicity in healthy individuals.     

Speciation of manganese in tea leaves and tea infusions

A speciation scheme was developed for identification of the chemical forms of manganese in tea leaves and tea infusions. The range of manganese in five different groups of tea leaves was found as 1107–2205 μg g⁻¹ on dry basis. It was noted that 30.0% of Mn was passed into the water that was present in the form of Mn(II), and also 2.5% of Mn was distributed in the total organic bound and was passed into the various solvents.     

茶叶中农药残留的检测

为了更好地解决茶叶中的农药残留问题,利用气相色谱仪(具电子捕获检测器)对茶叶中的α-HCH、β-HCH、γ-HCH、δ-HCH、ρ,ρ'-DDE、o,ρ'-DDT、ρ,ρ'-DDD和ρ,ρ'-DDT等农药的残留进行了测定,同时介绍了样品的处理方法,给出了测试的要求及部分样品测试的色谱图。结果表明:部分茶叶中有农药残留,总含量在100μg/L左右。     

不同干燥方式对黑茶品质的影响

目的 黑茶传统自然干燥工艺受天气、卫生、效率等因素局限,本文探讨黑茶采用现代机械干燥替代传统干燥的可行性。方法 以云南晒青毛茶渥堆叶为原料,采用不同干燥工艺(热风烘干、远红外干燥、炒干、微波干燥、光波干燥、微波光波混合干燥、晒干、晾干)制成黑茶。分析其感官品质、主要品质成分变化。结果 不同干燥方式加工的黑茶干茶色泽、汤色、叶底基本一致,香气和滋味相差较大。其中热风烘干的黑茶陈香突出,综合品质最高,其游离氨基酸含量较高。远红外干燥的黑茶滋味略带苦味,陈香较弱,其咖啡碱、儿茶素总量较低,滋味的浓度、协调度均不足。炒干的黑茶条索更紧结,香气带陈香较清新,滋味醇和,其可溶性糖、含量相对较高。微波干燥的黑茶滋味甜醇,稍带闷气,其可溶性糖、茶红素含量较高。光波干燥的黑茶茶滋味有甜醇风味及特殊香气,其游离氨基酸含量相对较高。微光波混合干燥的茶有甜醇味,香气略陈,其游离氨基酸、可溶性糖和咖啡碱的含量均介于微波与光波干燥之间,茶多酚的含量高于其他干燥方式。晒干的茶滋味涩,香气为日晒气,其游离氨基酸、可溶性糖含量较低,茶褐素含量高,儿茶素含量较高。晾干的茶滋味有涩味,口感低淡,其游离氨基酸、可溶性糖含量较低,茶褐素含量相对较高。 结论 结合感官品质和理化分析,黑茶加工干燥环节,热风烘干、炒干、微波干燥、光波干燥、微光波混合干燥等现代机械干燥方式可以取代传统的晒干和晾干方式。     

银杏草茶加工工艺

介绍以银杏叶、柿子叶、松针等为主要原料,通过杀青、脱水、干燥、粉碎和包装等过程,制成银杏草茶(袋泡茶)的工艺流程,并在外观、总黄酮含量、风味等方面与常规制茶工艺生产的银杏茶进行比较。银杏草茶口感和总黄酮含量优于常规工艺制作的银杏茶,是一种四季皆适于饮用的保健茶。     

Multielement analysis of Chinese tea (Camellia sinensis) by total-reflection X-ray fluorescence

 Total-reflection X–ray fluorescence (TXRF) was used for the simultaneous determination of 15 elements in tea samples which were produced either by acid digestion or acidified infusion of tea leaves (Camellia sinensis). The accuracy and precision of the method were checked by its application to a certified reference material (GBW 08505 : tea). A variety of 39 tea samples of different kinds and/or qualities produced in different regions of China were analysed. The range and mean of the concentrations of elements in the tea leaves (0.1–30.000 μg g^–1) and their solubility in infusions (0.5–85%) were determined and the influence of the origin, type and quality of the tea samples was studied. In some tea leaves produced in a Se-rich region, the content of Se was found to be very high (up to 7.5 μg g^–1), in contrast to a concentration of only about 0.1 μg g^–1 Se in most of the tea leaves examined. Received: 27 January 1998