X-Ray Fluorescence in Biological Sciences. Группа авторов

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СКАЧАТЬ 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. Thirteen elements were found in the concentration range from 0.2 ppm to 1.56%. The K concentration in grains is higher than in pulp (~1.5 and 1%, respectively) and significantly lower in cascarilla (0.07%). A typical Ca concentration is 0.15% in grains, 0.5% in pulp and 0.06% in cascarilla. Elements other than Zn and Fe show no significant changes in concentrations. The Zn content is generally higher in pulp (60–70 ppm) than in grains and cascarilla. Fe concentrations vary from 50 to 92 ppm (in the text for some reason up to 1300 ppm) in various grain samples, while Cu concentrations range are from 15 to 20 ppm. It is obtained that the As content is in the range of concentrations between 0.2 to 10 ppm and Pb is about 1 ppm. In some pulp samples, extremely high (~180 ppm) concentrations of Pb were found, but these coffee trees were treated with insecticides for experimental purposes. Concentrations of As and Pb, elements which are of interest were close to their minimum detection limits in some samples, and therefore the results obtained for these elements should be taken with caution. For these cases, the authors pre‐tested two methods of concentration: chemical decomposition followed by precipitation and low temperature ashing. The first method gives particularly good results for all non‐volatile elements such as Fe, Ni, Cu, Zn, Cd, Hg, and Pb. On the other hand, low temperature ashing can be effectively used for both high Z metals and volatile elements, among which As is the most important in coffee analysis.

Table 3.2 Concentrations of elements in some coffee products (ppm).

СКАЧАТЬ

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Element	Sample
Grain 1	Grain 2	Grain 3	Pulp	Cascarilla
K	15 645	15 304	14 700	10 370	725
Ca	1482	1372	1514	5390	621
Ti	—	—	1.2	11	—
Mn	38	36	22	30	11
Fe	54	54	92	45	70
Ni	0.3	0.5	—	0.3	0.6
Cu	18	17	18	27	22
Zn	5.8	5.9	10	57	6
As	—