Читать книгу X-Ray Fluorescence in Biological Sciences - Группа авторов - Страница 35

Vegetal foodstuffs are one of the principal sources of essential, major, and trace elements for human beings and for this reason a significant number of studies and scientific contributions have been made utilizing multi‐elemental analysis of foodstuff (i.e. cabbage, spinach, seaweed, tomatoes, mushrooms, and mulberries) for both nutritional and safety purposes [45, 46]. In addition to the total elemental content determined by conventional XRF systems, in some studies, the benefits of using μ‐EDXRF have also been discussed. For instance, the use of this technique allows studying the micronutrient distribution within the different parts of the rice grain which is of interest in view of the large consumption of this cereal worldwide [47]. Due to the high consumption of the species in many cultures, elemental composition of this type of sample has also been a topic of research [48]. In this regard, it is interesting to highlight the use of WDXRF systems for a reliable determination of light elements such as magnesium, sulfur and chlorine which are elements of interest for nutritional purposes, but are difficult to determine with conventional absorption and emission atomic spectroscopic techniques [6].

The regular consumption of coffee, tea, and medicinal herbs may contribute to the daily dietary requirements of several elements. For instance, tea is an important source of manganese and the large amount of potassium in comparison with sodium could be beneficial for hypertensive patients. Different configurations of XRF systems have been used to get information about multi‐elemental composition of coffee grains [49], teas and medicinal herbs [50, 51] as well as their infusions [24]. In the latter case, TXRF systems which allow the analysis of both solid (by means of a previous suspension or digestion preparation) and liquid samples such as infusions could be of interest.

Some other applications in the field of vegetable food analysis include for instance the study of specific elements or groups of elements that can be potentially toxic if consumed by humans. Within this category, Gupta and co‐workers studied the presence of heavy metals in cauliflower grown in contaminated and uncontaminated soils [52]. An interesting finding of this study was that similar elemental concentrations in the edible flower part were found irrespective of the soil type. A similar study was also performed about the determination of arsenic in onion plants growing in contaminated substrates using TXRF [53].

Finally, XRF instrumentation has also been widely employed as a fast and cost‐effective technique in agronomic studies with the aim of studying elemental composition of edible vegetal crops using different growing conditions. Due to the multi‐elemental capability of EDXRF systems, it was possible, for instance, to study the effect of different fertilization types and farming regimes on the nutritional mineral content of different vegetal foodstuffs (i.e. wheat, lentil, sunflower, chickpea, tomato plants) [54–56]. Similarly, the effect of irrigation with reclaimed wastewaters on different types of crops was also studied through the multi‐elemental analysis of the vegetation tissues [10]. Moreover, in this contribution, μ‐EDXRF analysis were also carried out in transversal and longitudinal carrot sections. Carrots were grown in experimental plots irrigated with fresh water and reclaimed wastewaters and it was demonstrated that the water used for irrigation purposes affects the concentration but not the spatial distribution of these elements within the vegetal tissue (see Figure 2.5). The benefits of obtaining information about the location and distribution of elements within the vegetal tissues of edible plants through μ‐EDXRF analysis have also been highlighted in some studies dealing with the addition of supplements (i.e. Zn, Fe) to the studied crops [57, 58].

Figure 2.5 Phosphorus 2D‐mappings of transversal and longitudinal sections of Dacuscarota (carrot) irrigated with fresh and treated wastewaters. EDXRF conditions: scan resolution of 770 × 770 pixel, step size of 25 μm and a dwell time of 0.76 ms/pixel.