It was observed that the elemental concentrations in the four types of tea and their infusions showed wide variability. It was demonstrated that 25 min was appropriate for tea extraction, and the elements of Mn, Mg, K, and Sr were extracted easier than Ca, Cu, Al, and Ni in the first time infusion. Generally, Tea could be an important source of Mn and the large amount of K could be beneficial for hypertensive patients.
124 Reference
Cao, H., Qiao, L., Zhang, H., & Chen, J. (2010). Exposure and risk assessment for aluminium and heavy metals in Puerh tea. Science of The Total Environment, 408(14), 2777-2784.
Chan, E. W. C., Lim, Y. Y., & Chew, Y. L. (2007). Antioxidant activity of Camellia sinensis leaves and tea from a lowland plantation in Malaysia. Food Chemistry, 102(4), 1214-1222.
Karak, T., & Bhagat, R. M. (2010). Trace elements in tea leaves, made tea and tea infusion: A review. Food Research International, 43(9), 2234-2252.
Lv, H.-P., Lin, Z., Tan, J.-F., & Guo, L. (2013). Contents of fluoride, lead, copper, chromium, arsenic and cadmium in Chinese Pu-erh tea. Food Research International, 53(2), 938-944.
Mossion, A., Potin-Gautier, M., Delerue, S., Le Hécho, I., & Behra, P. (2008). Effect of water composition on aluminium, calcium and organic carbon extraction in tea infusions. Food Chemistry, 106(4), 1467-1475.
Pytlakowska, K., Kita, A., Janoska, P., Połowniak, M., & Kozik, V. (2012). Multi-element analysis of mineral and trace elements in medicinal herbs and their infusions. Food Chemistry, 135(2), 494-501.
Salahinejad, M., & Aflaki, F. (2009). Toxic and Essential Mineral Elements Content of Black Tea Leaves and Their Tea Infusions Consumed in Iran. Biological Trace Element Research, 134(1), 109-117.
Sofuoglu, S. C., & Kavcar, P. (2008). An exposure and risk assessment for fluoride and trace metals in black tea. Journal of Hazardous Materials, 158(2-3), 392-400.
Street, R., Drabek, O., Szakova, J., & Mladkova, L. (2007). Total content and speciation of aluminium in tea leaves and tea infusions. Food Chemistry, 104(4), 1662-1669.
Welna, M., Szymczycha-Madeja, A., & Pohl, P. (2013). A comparison of samples preparation strategies in the multi-elemental analysis of tea by spectrometric methods. Food Research
125
International. 53(2), 922-930
126 General conclusion
As tea is traded all over the world and so large mount, some trade disputes with regard to tea types occur. Meanwhile, teas from different geographical origins, tea fermentation processes (Tea type) or picking methods (Buds or old leaves) have significant differences in the composition and activity capacity resulting in different health-promoting properties and market selling prices. Therefore, an accurate analytical method is required to discriminate both the geographical origins and difference in process techniques for the quality control of tea.
Stable isotopic ratio as a natural attribute in biology, was used as on kind of
“Natural fingerprint”, distinguish origins of tea. Isotopic composition analysis in food provided scientific, independent, immutable identity identification information for its origin traceability. A discriminant analysis of data obtained from element composition (C and N) analysis in combination with stable isotope data (δ15N‰, δ13C‰ and δ18O‰) were used to determine the growing region as EC, MC and SC with a high degree of confidence. Moreover, this method can be used for discriminating tea types.
Nevertheless, the three stable isotope ratios and both element contents considered here have already correctly classified around 80% of tea samples because the similar geological and climatic conditions as well as natural variability. The tea traceability may not enough only based on the stable isotope ratios fingerprint, so more pertinence and accuracy technique for food authenticity was required.
In chapter 3, sample preparation is a critical step in ICP-MS analysis because systematic errors, such as contamination or analyte loss, may occur in the process.
The method that used glass tubes in the digestion block gave the highest recovery results of all the three treatments in this study. The influence of operating parameters, such as heating temperature, heating time, and amount of liquid, on the concentration
127
of Mn in sample digestion was evaluated using RSM. RSM analysis revealed that the optimum conditions for digestion were as follows: heating time of 6.1 h, heating temperature of 132.3 ℃, and liquid amounting to1.6 ml. Based on the optimum conditions, we present the results of determination of 23 elements in Chinese tea using ICP-MS for searching the authenticity markers, especially in the context of geographical origins and types. Trace elements in tea samples from Chinese were determined using ICP-MS. The scatter plot of the samples against two first discrimination functions (Function1 vs function 2) indicates that five groups of different areas and types of tea are separated with using LDA. The recognition ability for five classes of tea was highly satisfactory. 100% of original grouped cases were correctly classified. Ni and Mn are variables which play the most important role in the discrimination of tea samples. The oolong tea group has higher concentrations of Al, Mn and Pb than the other groups, suggesting that most of the oolong tea buds had a longer growth time and the leaves were much older than the other types of tea. The differences in methods used for processing as well as the storage methods of teas used could be the contributory factors to variations of Cr, Ni and Cu content. Ni mainly comes through the foliar and soil application of low quality fertilizers and micro nutrients.
Tea plant was a cross-pollinated with highly heterogeneous and difference in isotope fractionating and element accumulation between different cultivars. The adsorption process of elements may differ between cultivars within one species. These results shown that the ranges of element concentrations in leaves of the seven cultivars were in good agreement with the levels obtained in previous studies and the level of most elements in tea leaves was significant different among cultivars. The classifications of seven tea cultivars were 100% accurate in total by PCA, HCA, LDA.
128
In a word, each cultivar presented a distinctive element fingerprint and the elements in tea leaves can be significant predictors in differentiating tea cultivars.
Meanwhile, these parameters were also found regularity and differences in different parts of tea tree because of the isotopic fractionation and, such as in buds, aging leaves, branch, and roots. The aging leaves were the principal place occurs of photosynthesis and nitrogen assimilation, caused the lowest C and N isotope ratio in the aging leaves. Element concentrations and N isotope were variety with the soil from the different areas. The difference from the area was greater than the differences among cultivars.
Finally, the elemental concentrations in the four types of tea and their infusions were detected to reveal the dependence of the extraction time, temperature and the number of infusions. The results showed wide variability. It was demonstrated that 25 min was appropriate for tea extraction, and the elements of Mn, Mg, K, and Sr were extracted easier than Ca, Cu, Al, and Ni in the first time infusion. Generally, Tea could be an important source of Mn and the large amount of K could be beneficial for hypertensive patients.