C h a p t e r
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X R F t e c h n i q u e a p p l i e d t o t h e
a g r o n o m y / f o o d i n d u s t r y
C H A P T E R 3 . X R F T E C H N I Q U E A P P L I E D T O T H E AG R O N O M Y / F O O D I N D U S T RY
meant to be consumed as food[83,84,85,86]. As the dietary impact of certain nutrients becomes clearer, via the progresses of health focused research, the need for a better understanding of the presence and localization of such elements in food products is warranted. Using some of the analytical tools described, it is then possible to pursue such endeavors.
More specifically, in this case study we will be directing our attention to cereal based products. Cereal based tissues are a very interesting research topic to the spectrometry scientific community due to their heterogeneous nature. These types of samples are very suited to being mapped and imaged with techniques such asµ-XRF due to their interesting elemental localization[87]. Moreover, they tend to be at the base of the food pyramid of most countries, and thus, make up a big portion of global population’s diet.
Perhaps the most researched cereals are rice grains due to their prevalence in most Asian countries’ diet.
The research on this topic is itself very heterogeneous combining different analytical techniques and diverse science subjects. For example, in [80], anin vivomineral distri-bution analysis of rice grains was performed in order to determine mineral distridistri-bution patterns that correlate with the progressive stages of germination via SR-XRF. This paper also features ICP-MS measurements of mineral concentrations (i.e., Ca, Mn, Fe, Zn, and K) in whole rice grains, hulls, brown rice, bran and polished rice. On another paper [88], they use both inductively coupled plasma optical emission spectrometry (ICP-OES) andµ-XRF mapping to evaluate the dynamic changes in some nutritionally important nutrient like P, Ca, K, Fe, Zn, Cu, due to accumulation of phytic acid during the rice seed development stage. Elemental analysis of this kind of samples can sometimes also be fo-cused in detecting and measuring toxic elements. Some examples of this kind of research can be seen in [89,90], where the authors provide an ICP-MS with laser ablation analysis of brown rice collected in Korea to detect the presence of both arsenic and mercury.
In this case study we will focus on wheat grains samples. Wheat is a monocot plant species, which is traditionally referred in academic context as triticum aestivum. The cereal grains of this specie are comprised of a number of highly specialized structures, as it is schematically represented in Figure3.1. Like other cereal species, wheat possess caryopses(cereal grains) as propagation units, which are single-seeded fruits where the testa(seed coat) is fused with the thinpericarp(fruit coat). Wheat grains possess atriploid endosperm(meaning three chromosome sets per nucleus) which is subdivided into aleu-rone layer(living cells) and thestarchy endosperm(dead storage tissue). They also possess highly developedembryoswhich involve the following organs: coleoptile(shoot sheath), the scutellum, theradiculaand thecoleorrhiza(root sheath). All these organs will be in-volved in germination of new grains by using the nutrients stored inendospermthe wheat ear will continuously grow.
When wheat grains go through a traditional milling process thebranis removed in order to expose to endosperm which is very rich in proteins and the major ingredient in traditional flour. This will result of the test, pericarpandaleurone layer. Even tough
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3 . 1 . S C O P E A N D O B J E C T I V E S
Figure 3.1: Structure of a wheat grain as reproduced in [91].ais a representation of the whole grain andbis a cross section view of the grain.
aleurone layerbotanically is not part of the capsule of the seed, in reality it is strongly attached to it and the removal of the branwill usually imply the removal of this layer.
Nowadays, and due to this kind of research, we know that thebranis actually composed of a lot of beneficial nutrients, with the majority being stored the aleurone layer. The awareness of this fact has pushed the food industry to start producing whole-wheat flour which is made using the complete wheat seed.
The two most notable micronutrients that whole-wheat flour is enriched with in com-parison to white flour are iron and zinc[91]. Since nutrient dietary deficiency is nowadays considered as a worldwide epidemic that affects more than two billion people according to the World Health Organization (WHO)[92] it is important to understand how impor-tant these two micronutrients are for the world’s dietary needs. In chapter 2, we have already provided an overview of how iron deficiency affects global population. Zinc defi-ciency is also a worldwide nutritional problem which is particularly impactful in infants, children, adolescents, pregnant and lactating women, for whom the requirements of this substance is higher. Zinc is intrinsically connected to the development and growth stages of the human body, and thus, its importance to these segments of the population. More-over, zinc deficiency during these stages has been connected with problems affecting the following human body systems: epidermal, central nervous, immune, skeletal, gastroin-testinal and reproductive system[93]. These physiological stages increase the normal need for zinc, but there are other segments of the population which do not meet the daily dietary recommended intakes. For example, rural diets in developing countries which consist mostly of plant-based food, or, diseases that induce excessive losses or impair utilization of zinc, also lead to zinc deficiency[94]. Furthermore, clinical diagnosis of zinc deficiency is not trivial specially in developing countries. The best known indicators are blood plasma/serum zinc concentration, dietary intake, and stunting prevalence [93].
If it is hard for developing countries to diagnosis zinc deficiency due to the lack over-whelming symptoms and the low assess to clinical staff and equipment, it is possibly
C H A P T E R 3 . X R F T E C H N I Q U E A P P L I E D T O T H E AG R O N O M Y / F O O D I N D U S T RY
harder to administer a proper medical response. The reason being that the main treat-ment for zinc deficiency are nutrient suppletreat-ments and, as it might be straightforward, their availability and assess in developing countries is scarce at best. Moreover, simi-larly to what we have seen in the last chapter with the iron supplements they might introduce unwanted elements into the consumer’s diet, specially if the quality control on pharmaceutical doesn’t enforce high standards.
An alternative natural solution to zinc deficiency is to take the already nutritious cereal based food and apply a series of techniques in order to biofortify the plants. This is specifically impactful due to the fact that multiple forms of cereals are considered staple food and already constitute the largest part of the diet in some of these countries[84]. Bio-fortification is the agronomic practice of manipulating plant species in order to enhance their nutritional value. This technique comes in different forms and through diverse methods like selective breeding, nutrient rich fertilizers or genetic manipulation. Studies find that through these kind of manipulations there is a big increase in selected micronu-trients concentrations on the crop samples[95,96,97, 98]. Furthermore, there are also studies that suggest that zinc biofortified wheat based food has a direct connection to serum zinc[99]. However, in this same study the authors claim to not have observed any increase in the population’s serum zinc when the wheat was simultaneously biofortified with other micronutrients other than zinc.
It seems clear from scientific research that biofortification can combat to a degree the zinc deficiency global nutritional problem. However, there are some issues and challenges when crops are treated with different techniques and try to enhance multiple nutrients of the crops. For example, it is important when biofortifying cereal grains or fruits that we not surpass certain elements thresholds (foe elements like Zn or Fe) in order to not dis-turb ionic balance of the plants and producing lower crop yields. There is a fine balance between biofortifying these plant species and not reach a level of toxicity detrimental to the whole crop. Another challenge is for example the widely used phosphorus fertiliza-tion methods that have been proven to decrease zinc concentrafertiliza-tions in wheat grains[100].
Phosphorus is stored in the plants in a compound that known as phytic acid that strongly binds with metallic anions. This means that not only it replaces the zinc content on the grain it actually decreases its bioavailability. Bioavailability refers to the ability of ab-sorption of the human body of a compound in a specific form. This means phytic acid is known strongly bind with micronutrients which prevents them from being absorbed by intestinal mucosa.
As it has been stated before, plant based samples provide a very interesting challenge for spectroscopy and imaging techniques. Specifically, biofortified wheat grains seem to be part of a research topic of major importance to the global population’s diet. Therefore, the application of micro-XRF and triaxial EDXRF analysis to this kind of samples can provide very important insight into element localization and element biofortification efficiency. For this purpose, in this case study, we will provide a thorough analysis of
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