Acidity Of Different Samples Of Tea Leaves.pdf
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Acidity Of Different Samples Of Tea Leaves.pdf
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Mean oxalate content of loose-packed black tea infusions after different brewing time (2g/240 ml)/ All analytical data are the mean of triplicate measurements of three independent samples SEM/ A one-factor ANOVA and the post hoc test showed that there were significant differences between the oxalate content of different brewing times (P
Mean oxalate content of loose-packed black tea infusions after different dilutions (2g/240 ml)/ All analytical data are the mean of triplicate measurements of three independent samples SEM/The results of independent t-test showed that there were significant differences between the mean oxalate content of different dilutions (P
As shown in Fig. 1, the range of oxalate in Iranian consumed loose-packed black tea after different brewing times was from 4.4 to 6.3 mg/240 ml. The brewing of tea in hot water extracts that portion of total oxalate that is soluble, leaving the insoluble oxalate (mainly oxalate bound to calcium) in the tea leaves [25]. The oxalate contents of black tea samples from tea bags for 1 and 5 min infusions were 10.8 and 20.8 mg oxalate/250 ml, respectively, for one brand and 10.8 and 12.0 mg oxalate/250 ml for another brand [26]. By contrast, no significant increase in oxalate content of Chinese green teas was observed by longer brewing time (5 vs. 10 min) [27]. The results of present study revealed incremental increases in soluble oxalate with increased brewing times all the way up to 60 min although after the 15 min time point, there was a marked decrease in the magnitude of this increase per unit of time.
Concentrations of selected metals (Cu, Mn, Zn, Cd) in tea leaves were investigated. Samples included black, green, and other (red, white, yellow, and oolong) teas. They were purchased on a local market but they covered different countries of origin. Beverages like yerba mate, rooibos, and fruit teas were also included in the discussion. Metal determinations were performed using atomic absorption spectrometry. In black teas, Mn/Cd ratio was found to be significantly higher (48,091 35,436) vs. green (21,319 16,396) or other teas (15,692 8393), while Cd concentration was lower (31.4 18.3 μg/kg) vs. other teas 67.0 (67.0 24.4). Moreover, Zn/Cu and Cu/Cd ratios were, respectively, lower (1.1 0.2 vs. 2.2 0.5) and higher (1086 978 vs. 261 128) when comparing black teas with other teas. Intake of each metal from drinking tea was estimated based on the extraction levels reported by other authors. Contributions to recommended daily intake for Cu, Mn, and Zn were estimated based on the recommendations of international authorities. Except for manganese, tea is not a major dietary source of the studied elements. From the total number of 27 samples, three have shown exceeded cadmium level, according to local regulations.
Manganese concentration in the samples varied from 457 4 to 2210 35 mg/kg (mean SD 962 388 mg/kg). Similar results were published by Street et al. [1], where manganese concentration in 30 samples of different types of teas varied from 511 to 2220 mg/kg. The authors did not notice a major difference between manganese concentration in black and green teas (nor they did for other elements: iron, zinc, and copper).
Comparing black and green teas, Mn/Cd ratio was found to be significantly different between these two groups. When comparing black teas to the others, four parameters showed significant differences: Cd concentrations, Mn/Cd