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References [65] [79] [63, 64] [69] [70] [80] Tea Black Black Black Black Green Black Black Green Ti —^a – – – 4–70 15–52 n/d^b–10 3–30 2–19 Cr – – <2–3.4 <2–4.7 – – n/d–0.26 n/d–4.6 0.8–10 Mn – 43–724 213–1228 28–730 160–1500 548–1500 — 162–1000 174–1130 Fe 1600–12 200 14–234 99–617 144–993 50–1800 18–752 0.2–107 79–1140 63–1040 Co — — <1–1.3 <1 — — н/о–0.12 — — Ni — — 1.2–8.1 1.4–4.3 2–23 5.1–8.9 0.06–3.2 1–5.3 2.7–13 Cu 100–250 12–27 15.4–30.2 4.6–12 8–40 13–20 0.2–2.7 10–56 10–17.6 Zn 130–280 20–149 20–85 15–37 20–60 30–54 н/о‐4.5 25–450 29–61 Rb 50–190 11–129 2.6–71 2.7–38.2 25–150 82–130 — 23–95 14–73 Sr 20–90 2–18 12–38 3.9–17.6 3.5–24 8.4–15 — 9–45 2.6–35 Pb 20–100 0.5–4.3 0.4–2.3 0.3–8.3 0.9–4 — 0.5–1.8 0.8–3.1

      ^a ‐ Not determined.

      ^b ‐ n/d: not detected.

      Our estimates of this factor, presented in the last section of this chapter, have shown its significance.

      There is no denying the fact that tea is the most popular drink in the world, along with water, and therefore it can be recognized as an important part of a healthy diet. However, it can be seen from this literature review that tea consumption may also lead to oral consumption of various trace elements, as tea plants have the genetic potential to absorb non‐essential trace elements. The content of trace elements in all the analyzed tea samples discussed in this section as well as in the overview Karak et al. [30], was within safe limits for human consumption. The results demonstrated that tea still provides a significant share of human needs for trace elements. However, as of the present day, the adverse effects of tea on human health associated with individual trace elements have not been clarified.

3.5 Examples of Practical Applications of XRF for Coffee Research

      Coffee processing begins with green coffee grains undergoing a thermal procedure (roasting). As a result, fried coffee grains are produced. The composition of green coffee grains depends on several factors such as variety, origin, climate, soil quality, treatment on fields, and collection and storage procedures. During the roasting process, the beans undergo physical changes and go through several chemical reactions that alter, generate, and decompose the coffee aroma. It is noted that the chemical composition of fried coffee beans plays an important role in determining the quality of the coffee drink [81]. The quality of beans depends on the species, geographical origin, content of defective beans, and other substances added (accidentally or intentionally), i.e. coffee husks and stems, corn, barley, chicory, wheat middlings, brown sugar, soybean, rye, etc. [25].

Orlic et al. [82] published one of the first papers on the use of XRF to research of samples of coffee. Let's review their results. The authors used the X‐ray spectrometer PW 1010/30 from Philips with X‐ray tube with Mo‐anode, and two modes of a fluorescence excitation: direct and secondary excitation mode (Zr, Mo, and Ag pure foils). Coffee grains were air dried at 85 °C for 24 hours, then ground in an agate mortar manually or mechanically. Coffee powder was placed in Teflon holders or pressed into tablets. The results of analysis of some coffee products (grains, pulp and cascarilla) are shown in Table 3.2.

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