Temperature dependence of copper,iron, nickel and chromium transfers into various black and green tea infusions

Transfer ratios of copper, iron, nickel and chromium from 10 blended, unblended, instant and green tea samples of Turkish or British origin into the infusions have been determined at different brewing temperatures (18, 40, 60 and 80°C). The transfer ratio of each metal into the infusion appeared to be dependent on both temperature and strength of infusions as well as the kind of tea. Ingested metal amounts were calculated and discussed. © 1998 SCI.     

The chemical oxidation of catechins and other phenolics: A study of the formation of black tea pigments

The chemical oxidation of polyphenols has been used to produce black tea pigments. (+)-Catechin, (?)-epicatechin, (?)-epicatechin gallate and (?)-epigallocatechin gallate were isolated from convenient sources, their identity being confirmed by mass spectrometry and HPLC. The oxidation of a mixture of (?)-epicatechin gallate and gallic acid gave an oxidation product of (?)-epicatechin gallate in addition to epitheaflavic acid 3-gallate. The catechins were oxidised chemically and the products analysed by HPLC, the chromatograms being compared with a black tea chromatogram. The reactions gave both resolved and unresolved pigments, and many of the resolved pigments had HPLC retention times close to black tea pigments. Each catechin behaved differently, the chromatograms of the oxidation products from each starting material being clearly distinguishable. Resolved pigments were obtained by the chemical oxidation of other phenolic compounds. This work provides a convenient method for studying the formation of resolved and unresolved black tea pigments.     

In vitro human skin permeation and cutaneous metabolism of catechins from green tea extract and green tea extract-loaded chitosan microparticles

Catechins are major antioxidants in green tea (Camellia sinensis or Camellia assamica), but because they do not permeate the skin well, the application of green tea in cosmetic products has so far been limited. This study aims to evaluate the cutaneous absorption of catechins from an extract of green tea and from a green tea extract-loaded chitosan microparticle. The catechin skin metabolism was also examined. The results suggest that chitosan microparticles significantly improve the ability of catechins to permeate skin. The cutaneous metabolism of the catechins significantly affected their permeation profiles. Epicatechin (EC) and epigallocatechin (EGC) penetrated the skin more than epigallocatechin gallate (EGCG) and epicatechin gallate (ECG). The galloyl groups in EGCG and ECG were enzymatically hydrolysed to EGC and EC, respectively. Dehydroxylation of catechins was also observed. Chitosan microparticles effectively prevented enzymatic changes of the catechins; therefore, chitosan microparticles are here found to be the promising carriers for enhancing the skin permeation.     

Comparative study on composition and antioxidant properties of mint and black tea extract

The antioxidant properties of plants could be correlated with oxidative stress defence in different human diseases. The present study was undertaken to evaluate and compare the antioxidant potential and the phytochemical composition in the aqueous extracts of mint leaves, black tea and black tea enriched with mint extract. All the three preparations exhibited free radical‐scavenging potential for nitric oxide (NO) radical, superoxide anion radical and hydroxyl radical, and the values were lesser than those of the antioxidants which acted as standards. In comparison, the mint extract exhibited higher free radical and NO scavenging effect. Hydroxyl radical and superoxide scavenging effects were more pronounced in tea with the mint extract, while the reducing power was exhibited more significantly by the black tea extract. The phytochemical compounds were identified and the total phenols and flavonoids were quantified and compared between these extracts.     

Comparison of the relative dissipation rates of endosulfan pesticide residues between oolong and green tea

The dissipation behaviour of endosulfan in dry made-tea leaves of oolong and green tea was compared to establish whether there was any difference in dissipation rates between the two teas. The dissipation of endosulfan in oolong and green tea corresponded with a first-order kinetics curve. The average half-life of endosulfan (n = 12) was 1.60 ± 0.44 days in green tea and 2.01 ± 0.55 days in oolong tea, showing a statistically significant difference, and indicating that the dissipation of the pesticide was significantly slower in oolong tea than that in green tea. Although the initial levels of residual endosulfan were lower in oolong tea, due to the slower dissipation rate, the residues 5-7 days after application were higher in oolong than in green tea. It is suggested that the minimum interval between endosulfan application and tea leaf harvesting is 7 days for green tea and 10 days for oolong tea in the case where the maximum residue limit of endosulfan in made-tea is fixed as 10 mg kg^-1.     

Comparison of the relative dissipation rates of endosulfan pesticide residues between oolong and green tea

The dissipation behaviour of endosulfan in dry made-tea leaves of oolong and green tea was compared to establish whether there was any difference in dissipation rates between the two teas. The dissipation of endosulfan in oolong and green tea corresponded with a first-order kinetics curve. The average half-life of endosulfan (n = 12) was 1.60 ± 0.44 days in green tea and 2.01 ± 0.55 days in oolong tea, showing a statistically significant difference, and indicating that the dissipation of the pesticide was significantly slower in oolong tea than that in green tea. Although the initial levels of residual endosulfan were lower in oolong tea, due to the slower dissipation rate, the residues 5–7 days after application were higher in oolong than in green tea. It is suggested that the minimum interval between endosulfan application and tea leaf harvesting is 7 days for green tea and 10 days for oolong tea in the case where the maximum residue limit of endosulfan in made-tea is fixed as 10 mg kg^?1.     

Comparison of the dissipation behaviour of three neonicotinoid insecticides in tea

The dissipation behaviour of three neonicotinoids – thiamethoxam, imidacloprid and acetamiprid – was compared in tea shoots, in Chinese green and black tea, and after tea infusion in hot water. The simple and rapid analytical procedures for the quantification of these three residues in these matrices were developed using HPLC with ultraviolet (UV) detection. Degradation rates in tea shoots of neonicotinoids applied in either recommended or double dosages followed first-order kinetics, with half-lives of 1.62 or 1.58 days for thiamethoxam, of 2.45 or 2.67 days for imidacloprid, and of 3.24 or 3.85 days for acetamiprid, respectively. Through harvest and processing the residue retentions for thiamethoxam, imidacloprid and acetamiprid were 85.0%, 84.1% and 70.6% of the initial dosages in green tea, and 77.1%, 52.4% and 57.4% in black tea. These three residues all showed high transfer rates through green or black tea brewing of 80.5% or 81.6% for thiamethoxam, of 63.1% or 62.2% for imidacloprid, and of 78.3% or 80.6% for acetamiprid. Waiting periods between the last application and harvest of at least 12, 17 and 20 days were suggested for thiamethoxam, imidacloprid and acetamiprid, respectively, after application at their recommend dosages to ensure levels below a maximum residue limit (MRL) of 0.05 mg kg^?1.     

云南红茶加工过程中香气成分的变化

为提高云南红茶品质和指导实际生产,采用同时蒸馏萃取法(SDE)提取香气物质并用GC-MS检测香气成分,研究加工过程中云南工夫红茶主要香气成分组成的变化规律。结果表明:云南工夫红茶在发酵结束后挥发油含量达到最高,经过干燥过程后挥发油含量则大幅降低;不同阶段过程样的香气成分组成和含量上有明显差异;红茶在加工过程中,挥发性香气成分中的萜类化合物中的芳樟醇、芳樟醇氧化物、α-松油醇的相对含量大幅减少,而醛类化合物中的苯甲醛、苯乙醛,芳香族醇类化合物中的苯甲醇、苯乙醇的相对含量则大幅增加。萎凋、发酵、干燥工序是影响红茶香气形成的关键工序,对云南红茶香气的形成至关重要。     

绿茶汁澄清工艺的研究

比较池明矾、硅胶、高岭土、碱式氯化铝和聚丙烯酰胺５种物质对绿茶汁的洽效果,发现碱式氯化铝的澄清效果较好;通过Ｌ９（３＾４）正交实验优化,碱式氯化铝澄清绍茶汁适宜的条件为：ＰＨ＝６,用量０．１％和温度１５℃。     

菊花绿茶复合饮料的研制

以绿茶、菊花为主要原料,研究了菊花茶饮料加工工艺中的最佳浸提方法和条件,确定了饮料的最佳调配比例。结果表明,采用微波辅助水浴法浸提得到的浸提液品质较常规水浴法的好,微波辅助水浴法浸提绿茶的最佳工艺条件为：茶水比1∶100、pH5、微波功率为400W条件下处理4min、90℃水浴锅中浸提10min;菊花浸提最佳工艺条件为：料水比1∶180、微波功率为175W条件下处理10min、80℃水浴锅中浸提15min。饮料最佳调配比例为绿茶汁40%、菊花汁50%、白砂糖2%、柠檬酸0.02%。     

壳聚糖与黄原胶对绿茶汁澄清效果的研究

壳聚糖分子链上具有氨基、羟基官能团,与酸或酸性化合物结合后,便成为带正电荷的聚电解质,和溶液中存在的带负电荷的蛋白质、纤维素等微粒相互作用,能够使引起果汁和酒液混浊的蛋白质、单宁等胶态颗粒絮凝沉淀下来而达到澄清目的。黄原胶可以将食品分散体系中的颗粒物絮凝出来。本文以浊度和色差为指标,壳聚糖和黄原胶为澄清剂,研究了壳聚糖/黄原胶对绿茶汁的澄清效果,确定了最佳的工艺参数,并在单因素试验的基础上,通过多因素正交试验,得出澄清绿茶汁的最适工艺为时间55min,壳聚糖(10g/L)黄原胶(10g/L)比例7∶3,绿茶汁pH4.1,验证试验结果表明此时浊度为0.63NTU,绿茶汁的色差L*=40.08,b*=20.19,此工艺条件不但能得到满意的澄清效果还能呈现绿茶原汁的亮黄色。     

Comparison of bioactive components in GABA tea and green tea produced in Taiwan

The aim of this study is to investigate the bioactive components of GABA (γ-aminobutyric acid) tea as compared with green tea produced in Taiwan. Using in total 56 tea samples (28 green tea and 28 GABA tea), moisture content, Hunter L, a and b values, phenolic compounds, amino acids including GABA, fatty acids and ascorbic acid were determined. The results showed that moisture, total free amino acids, crude fat, Hunter L value, total nitrogen, free fatty acids and reducing sugar did not differ significantly between GABA tea and green tea. However, GABA tea had higher Hunter a and b values, while green tea had higher total catechin and ascorbic acid contents (p < 0.05). Of major catechins, epicatechin and epigallocatechin gallate were found to be lower in GABA tea than in green tea. For free amino acids, GABA, alanine, ammonia, lysine, leucine and isoleucine were found to be significantly higher in GABA tea, while the glutamic acid, aspartic acid, and phenylalanine were higher in green tea (p < 0.05). Theanine, tryptophan, valine, threonine and methionine were not found to be different between the two kinds of tea.     

Effects of lipophillic pigments on colour of the green tea infusion

Studies about effect of pigments on colour of green tea infusion will help for quality evaluation and adopting suitable measure for prevention from non‐enzyme browning. HPLC results showed that concentrations of chlorophylls and pheophytin a in green tea infusions were higher than their thresholds, and that lutein and β‐carotene were near or above the thresholds. Significant correlation between pigments concentration and colour difference index in green tea infusion was also found. Therefore, lipophillic pigments did affect the colour of green tea infusion markedly, and the ratio of chlorophylls to pheophytins could be used as an indicator of infusion colour and quality of green tea.     

葛根绿茶酸奶的工艺研究

以葛根、绿茶、全脂奶粉、蔗糖为主要原料,通过保加利亚乳酸杆菌和嗜热链球菌发酵,研制出一种新型的葛根绿茶酸奶.采用正交实验法筛选出最佳工艺条件为：葛根汁20%,蔗糖量7.5%,接种量2.5%,茶叶量0.4%,发酵时间5h,发酵温度43℃.实验结果表明,产品风味独特,色泽嫩绿,营养丰富,是一种新型的优良保健饮品.     

超滤法生产罐装红茶饮料的研究

采用超滤法除去红茶汁中的鞣质，辅以砂糖、果汁等生产罐装红茶饮料，呈透明状态；同时，茶中的营养成分、风味物质得到保留。证明了超滤法生产罐装红茶饮料的可行性。     

灰树花固体发酵茶青的研究

以茶青为发酵培养基质,对灰树花固体发酵过程中的各种内含物含量的变化及其品质进行了研究。结果表明,灰树花的最佳发酵培养基成分及培养条件:中叶茶,2%大豆粉,接种量1%,培养温度25℃,培养时间9d。发酵后其菌质的有效成分为:茶多酚1.78%,游离氨基酸0.77%,酚氨比2.3,多糖4.69%。与发酵前比较其多糖含量增加了31.7%,茶多酚降解了77.8%,游离氨基酸降低了26.7%,酚氨比降低了69.9%,茶叶品质得到很大改善。     

超滤膜分离对绿茶茶水处理效果的影响

研究了超滤膜对绿茶茶水的分离效果 ,为超滤分离技术应用于绿茶饮料和茶多酚的工业生产提供了有关依据。研究结果表明 ,截留分子量小于 2 0 0 0 0的超滤膜 ,对茶水中的固形物、茶多酚的截留率分别高达 89%、 87% ;截留分子量高于 10 0 0 0 0的超滤膜可有效截留茶水中的大分子蛋白质和果胶类物质 ,改善了茶水的溶液特性 ,有利于茶多酚的工业生产 ;操作温度对茶水的超滤效果有显著影响。     

Mixed extracts of green tea and orange peel encapsulated and impregnated on black tea bag paper to be used as a functional drink

Herbal drinks have been considered among the known groups of functional drinks. The aim of this study was to encapsulate green tea and orange peel extracts using double emulsion followed by complex coacervation to be used in the preparation of a functional drink. All of the microcapsule formulations were spherically prepared without cracks in the walls and their sizes increased by decreasing the ratio of the core to the wall. Microcapsules under the best conditions of this study were used to coat the paper of a bag containing black tea. The results showed that theaflavin and its ratio to thearubigin as the quality indices for black tea have increased in comparison with the sample without encapsulation. This study resulted in the production of encapsulated mixed extracts of green tea and orange peel that can be used later for the preparation of a functional drink.     

柠檬红茶酸奶的加工工艺研究

以柠檬、红茶和鲜奶为主要原料,以嗜热性链球菌和保加利亚乳杆菌为发酵剂,经发酵制成一种新型固体酸奶。通过正交试验方法和感官评定,确定该产品的最佳配方和生产工艺为：柠檬红茶汁5%,蔗糖和蜂蜜4%,保加利亚乳杆菌和嗜热性链球菌3％,发酵温度42℃、发酵时间5h。     

Effect of black tea, garlic and onion on corn oil stability and fatty acid composition under accelerated oxidation

Fresh black tea, garlic bulbs and onion skin were macerated in refined corn oil to evaluate their antioxidant properties and the effect of heat on oil stability and fatty acid composition in accelerated oxidation experiments at 55 ° and 140 °C. At the lowest temperature control and onion treatments showed an induction time of 3 days with maximum peroxide values of 62 and 45 meq kg^?1, respectively. Addition of black tea and garlic increased oil stability with peroxide values of 5 meq kg^?1, without appreciable changes in the fatty acid composition. Heating at 140 °C for 48 h produced an accelerated deterioration of corn oil in all treatments. A reduction of polyunsaturated fatty acids of about 40% was observed, with high concentrations of non‐eluted materials which contained thermo‐oxidized substances. It was found that natural extract of black tea and garlic were effective to preserve corn oil under accelerated oxidation at 55 °C which simulates oil behaviour during storage, but cannot reduce the rate of oxidation at frying temperatures.