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1.
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. 相似文献
2.
The effects of sample preparation, cultivar, leaf age and tea processing on melatonin content of mulberry (Morus spp.) leaves were investigated. Sample preparation using ultrasonic technique in combination with solid phase extraction resulted in high recovery rate (76%), when compared to homogenisation in combination with liquid–liquid extraction procedure (12% recovery rate). The melatonin contents in mulberry leaves harvested from three major cultivars (Buriram 60, Sakonnakhon and Khunphai) grown in Thailand were identified and quantified using high-performance liquid chromatography combined with fluorescence detector. The average melatonin content of the mulberry leaves cv. Buriram 60 (279.6 ng/g dry weight (DW)) was higher than those of cv. Sakonnakhon (100.5 ng/g DW) and cv. Khunphai (40.7 ng/g DW). The melatonin contents of all cultivars tested were highest in the tip of the leaves, followed by that in the young leaves, whereas the lowest was found in the old leaves. The melatonin contents of the two types of tea produced from mulberry leaves cv. Buriram 60 were also determined. Heat treatment during tea processing decreased the melatonin content in mulberry leaves cv. Buriram 60 by approximately 87%, when compared to that of the fresh leaves. However, there were no significant differences between the melatonin contents of the mulberry leaf tea produced with blanching (mulberry green tea) and those produced without blanching (mulberry black tea). 相似文献
3.
目的 建立了桑叶茶中1-脱氧野尻霉素(1-deoxynojirimycin,1-DNJ)含量的高效液相色谱-串联质谱测定方法。方法 样品经70%甲醇水超声提取,用xbridge amide柱(2.1 mm×100 mm, 3.5 μm)分离, 以含0.1%(V/V)甲酸溶液和乙腈作为流动相进行梯度洗脱, 采用大气压化学电离(Atmosphere Pressure Chemical Ionization, APCI)和多离子检测模式(multiple reaction monitoring, MRM)进行检测,外标法定量。方法 目标物在0.01~0.2mg/L范围内线性相关系数大于0.99; 1-脱氧野尻霉素的定量限为5mg/kg;在5~50mg/kg浓度范围内加标回收试验, 平均回收率在94.2%~98.7%, 相对标准偏差为3.2%~4.7%。结论 该方法具有分析速度快、操作简便等优点,可用于桑叶茶中1-脱氧野尻霉素的含量测定。 相似文献
4.
Aurélie Mossion Martine Potin-Gautier Sébastien Delerue Isabelle Le Hécho Philippe Behra 《Food chemistry》2008
Tea infusion is the second world wide consumed beverage. In this study, total aluminium and calcium concentrations, total organic carbon and total polyphenol content were determined and compared with respect to the origin of tea leaves, their particle size (broken or whole leaves) and also the mineral composition of four waters. It appeared that the higher the mineral content, the lower the extraction yield of aluminium, total organic carbon and total polyphenols. This could be due to calcium uptake by leaves. Calcium present in mineral waters could be complexed with pectins present in cell walls thus leading to a decrease in the element extraction. 相似文献
5.
Acetamiprid, a new-generation, highly active neonicotinoid insecticide has been used to control mites and insect pests. In the present study, the disappearance trend of acetamiprid residue in tea under field conditions was studied at two dosages for two seasons (dry and wet), and transfer of residues from made tea to infusion was also determined. Acetamiprid dissipation rate was found to be faster in the wet season. Half-life of acetamprid was found to be 1.82–2.33 days in green tea shoots and 1.84–2.25 days in made tea for both dry and wet seasons. The percent transfer of acetamiprid residues from made tea to infusion was 36.84–50.00%; however, 31.11–44.40% of the residues remained stuck to the spent leaves during both the dry and wet seasons. On the basis of transfer of residues from made tea to infusion, a waiting period of 15 days for tea plucking after pesticide application at recommended dose may be suggested. 相似文献
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Imidacloprid is a systemic insecticide used widely in controlling mites, mealy bugs and other related pests in fruits, vegetables and tea. The dissipation behaviour of imidacloprid residues in green tea shoots, made tea and its transfer potential from made tea to infusion in hot water was studied. Analysis in tea matrices of imidacloprid was carried out using high-performance liquid chromatography with diode array detection. Under field conditions, imidacloprid dissipation rate was found to be faster in the wet season than the dry season. Half lives in green shoots were in the range 1.14–1.23 and 1.03–1.09 days, and 1.14–1.25, 1.04–1.07 days in made tea, for the dry and wet season, respectively. The percent transfer of imidacloprid residue from made tea to infusion was in the range of 29.2–42.0% during the dry and wet season; however, 38.2% and 57.9% of the residues remained stuck to the spent leaves during the dry and wet seasons, respectively. On the basis of transfer of residues from made tea to hot water infusion, a waiting period of 7 days after pesticide application at a recommended dose for tea plucking is suggested. 相似文献
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Márcia Reto Maria E. Figueira Helder M. Filipe Cristina M.M. Almeida 《Food chemistry》2007,100(1):405-411
The usual methods for determination vitamin K are laborious. With the aim of replace them by a simpler method that requires fewer solvents, lower analytical levels and allows reporting of results in a smaller period of time, a procedure based on solid-phase microextraction (SPME) and gas chromatography with flame ionization detector (GC-FID) was developed. This method was used to analyse vitamin K in green tea leafs and infusions from nine brands of green tea commercialised in Portugal. 相似文献
10.
Wine is a prolific, but complex and information-intensive product, so it is important for marketers to understand the behaviors and characteristics of different wine market segments, in order to better target their marketing strategies to these different segments’ needs. Yet little is known about how the characteristics of consumers’ subjective and objective knowledge of wine impact their variety seeking purchasing behavior. As variety seeking behavior affects customer retention and loyalty, a better understanding of this behavior is important to wine marketers. Results of a survey show that wine knowledge types are a significant predictor of variety seeking purchasing behavior of wine. Wine consumers who think they know a lot about wine, tend to engage in more variety seeking behavior in their wine purchasing. This suggests that marketers should adapt their segmentation, targeting and channel strategies to individual knowledge types to be more successful. 相似文献
11.
Ali Reza Khanchi Mohamad Khayatzadeh Mahani Majid Hajihosseini Mohamad Ghanadi Maragheh Marzieh Chaloosi Farhad Bani 《Food chemistry》2007,103(3):1062-1068
In order to determine the amount of caffeine and theobromine, spectrophotometry was used as a simple, rapid and economical method. Because of severe overlapping between these components, artificial neural network was used. The 230–300 nm spectral window with 1 nm interval was used for data acquisition. An artificial neural network (5-5-3) with linear transfer function between input-hidden and hidden-output layers was trained and applied for prediction of concentration of these methylxanthines in four Iranian tea samples. The model was compared with PLS modeling method. HPLC technique was used as a standard method. 相似文献
12.
This study showed the relationship between tea leaf age, bud and first two leaves, and shade levels, on the relative concentrations of six major compounds of tea leaf, namely l-theanine, caffeine, and the major tea catechins; (−)-epigallocatechin gallate (EGCG), (−)-epigallocatechin (EGC), (−)-epicatechin (EC), and (−)-epicatechin gallate (ECG), all of which are reported to have positive effects on human health, as well as at the ferric reducing antioxidant power of bud and leaf extracts. The concentration of l-theanine and caffeine decreased as leaf age increased moving from bud to first and then second leaf, while the concentration of the four catechins increased from the bud to first and second leaves. In most cases this increase was generally relatively small but in the case of EGC it was 7 to 10-fold. Certain chemical components of freshly picked, minimally processed and essentially unoxidised tea may potentially be used as markers for age, quality, authenticity and area of growth. 相似文献
13.
Emma K. Keenan Mike D.A. Finnie Paul S. Jones Peter J. Rogers Caroline M. Priestley 《Food chemistry》2011
Recent interest into the possible benefits of l-theanine found in tea has raised the issue that there are few data available on amounts of l-theanine contained in cups of commercially-available teas, prepared by a standard method. HPLC along with a standard method of preparing tea was employed here to determine amounts of l-theanine in cups of tea and the effects that various preparation factors have on amounts of l-theanine extracted. Brewing time was found to be a major determinant of the amount of l-theanine extracted, while the addition of small amounts of milk and sugar made no significant difference. High levels of milk resulted in a marked lowering of the level of detectable l-theanine. Contrary to previous research, a standard (200 ml) cup of black tea was found to contain the most l-theanine (24.2 ± 5.7 mg) while a cup of green tea contained the least (7.9 ± 3.8 mg). 相似文献
14.
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. 相似文献
15.
Aurlie Couzinet-Mossion Stphane Balayssac Vronique Gilard Myriam Malet-Martino Martine Potin-Gautier Philippe Behra 《Food chemistry》2010,119(1):107-181
Black tea infusions of Camellia sinensis leaves were studied for the influence of water composition, especially calcium content, on the amount of extracted organic matter and on the interactions between caffeine and polyphenols. The higher the calcium content, the lower the extraction of caffeine and polyphenols in acidic media. In alkaline media, besides the calcium effect, polyphenols are oxidized. Caffeine NMR chemical shifts varied depending on the water used showing modified interactions. Using model solutions, polyphenols seem to be responsible for these changes in the case of ultra pure water, but in the case of alkaline solutions, the data in model solutions are different from tea infusions implying that other compounds should interact. Moreover, epigallocatechin gallate (EGCg) and epigallocatechin are the polyphenols interacting most strongly with caffeine in infusions and not EGCg and epicatechin gallate as thought before. 相似文献
16.
Tarun Ch. Sarmah Mahinath Dev Choudhury Monoranjan Goswami 《Journal of the science of food and agriculture》1987,41(2):107-113
Assay conditions in vivo for determination of nitrate reductase activity (NRA) in leaf and feeder root tissues of tea bushes (Camellia sinensis L.) were studied. The composition of the incubation mixture, pH, temperature, period of incubation and tea shoot components were varied. Maximum NRA was obtained in leaf with a medium containing 300 mg Polyclar AT with 300 mg leaf disc in 0.1 M phosphate buffer at pH 7-5, 0.02 M KNO3 in a total volume of 5 ml and incubated for 4 hat 30°C in the dark. Propan-1-ol inhibited NRA in tea leaf and root. Highest activity was found in the first leaf. 相似文献
17.
William E. Price Michael Spiro 《Journal of the science of food and agriculture》1985,36(12):1303-1308
Concentrations of theaflavin and caffeine were determined in whole Kapchorua Pekoe Fannings and in six of its sieved fractions, as well as in Kapchorua Pekoe Dust, Betjan Flowery Broken Orange Pekoe and Rupai Flowery Orange Fannings and in one sieved fraction of each. The partition constants of theaflavin and caffeine between these leaves and water at 80°C were also determined. Neither property varied significantly with leaf size but did depend on leaf origin and manufacture. The concentration and partition constants for caffeine were greater than for theaflavin. As a corollary, the ratio of caffeine to theaflavin is larger in tea initially drawn from the teapot than in the beverage prepared after topping up with fresh hot water. 相似文献
18.
Makoto Kondo Kazumi Kita Hiro‐omi Yokota 《Journal of the science of food and agriculture》2004,84(7):721-727
This study evaluated the fermentation characteristics and in vitro gas production of sudangrass (Sorghum sudanese) silage with tea leaf waste of green tea, oolong tea and black tea added. All types of tea leaf waste contain large amounts of nitrogen (N) and tannins, and a small amount of low‐water‐soluble carbohydrates. Sudangrass was preserved without (control) and with green tea waste (GTW), oolong tea waste (OTW) or black tea waste (BTW) at rates of 50, 100 and 200 g kg?1 fresh matter in laboratory silos. The pH and butyric acid levels were significantly lower in GTW at all rates and in OTW at the 200 g kg?1 rate, whereas those levels were high in the control and BTW‐treated silage. Lactic acid level was appreciably higher in GTW‐ and OTW‐treated silage than the control and BTW‐treated silage. The addition of all types of tea waste increased the total N and tannins of the silage, whereas the acid detergent insoluble N was increased in the OTW‐ and BTW‐treated silage. GTW treatment increased gas production within a 96‐h period compared with the control, whereas OTW and BTW additions at 200 g kg?1 rates caused lower gas production. It is concluded that the fermentation characteristics and feed value of the silage incorporating with tea leaf wastes are different for these types of tea leaf. Among the three kinds of tea waste, GTW is the most valuable material as a silage additive. Copyright © 2004 Society of Chemical Industry 相似文献
19.
William E. Price Michael Spiro 《Journal of the science of food and agriculture》1985,36(12):1309-1314
The rates of infusion of theaflavin and caffeine into water at 80°C have been measured for Kapchorua Pekoe Fannings, Kapchorua Pekoe Dust, Betjan Flowery Broken Orange Pekoe and Rupai Flowery Orange Fannings whole teas and sieved fractions. For Kapchorua PF fractions the rates of theobromine infusion were also determined. Caffeine always infused faster than theobromine, and both infused faster than theaflavin. Rate constants were obtained from the slopes of first order kinetic plots which yielded straight lines with small intercepts. The rate constants for all three constituents increased by a factor of 2.2 as leaf size decreased from 850–1000μm to 500–600μm. The rates of extraction from whole teas varied more than fourfold. Kapchorua PD gave the most rapid rates and Betjan FBOP the slowest. Comparisons of similarly sized fractions of teas showed that leaf size distributions accounted for half these differences and the intrinsic properties of the leaf for the remaining factor of two. The Kenyan CTC teas gave higher rate constants than the Indian orthodox teas. From the rate constants, the effective diffusion coefficients for theaflavin and caffeine in Betjan FBOP leaf were calculated and found to be some 100 times smaller than in water. This shows the diffusion processes within the leaf to be complex ones. 相似文献
20.
Effects of tea polyphenols on the activities of α-amylase,pepsin, trypsin and lipase 总被引:1,自引:0,他引:1
Tea polyphenols (TP) possess many beneficial properties, such as reducing the risk of cancer and heart diseases, and acting as natural antioxidants for the food industry. At the same time, tea polyphenols might inhibit digestive enzymes and reduce food digestibility. To explore this possible antinutritional property, the effects of tea polyphenols on the activity of four typical digestive enzymes were investigated. HPLC analysis of the tea polyphenols extracted from Chinese green tea indicated that their catechin content was 93.6% (w/w), and that the content of ester bond-containing polyphenols was more than 82%. Measurement of the interaction of gelatin with tea polyphenols was first carried out, in order to model enzyme protein–TP interaction. It proved that tea polyphenols were capable of binding and precipitating protein, suggesting a potential ability of TP to denature digestive enzymes. In addition, the inhibitory effects of tea polyphenols on α-amylase, pepsin, trypsin and lipase were studied. In the presence of 0.05 mg/ml tea polyphenols, the inhibition ratios of α-amylase, pepsin, trypsin and lipase were, respectively, 61%, 32%, 38% and 54%, suggesting that TP might possess antinutritional properties. 相似文献