## 4 Discussion
### Micronutrients  
Microelements are chemical elements that occur in very small quantities in plant and animal organisms. Their contents (copper, manganese, iron and zinc) in raw and hydrothermally processed vegetables immediately after blanching and cooking, are summarized in Table 1.  
The copper content in fresh vegetables ranged from 2.74 (kale) to 3.16 (green cauliflower) mg/kg dm, which indicates small variation in content of this element in fresh material (Table 1). In comparison with our results, most authors report either much lower [40], or much higher magnesium contents in _Brassica_ vegetables [4; 35; 37; 41].  
Both blanching and cooking led to a significant reduction of this microelement. The finding was confirmed by [PERSON] and [PERSON] [4], but only with regard to two examined Brassica vegetables (green cauliflower and broccoli), which underwent conventional cooking. In turn, [PERSON] and [PERSON] [38] observed a 12% increase of this component compared to the kale untreated hydrothermally.  
The manganese content in fresh vegetables ranged from 8.15 (ruttabaga) to 22.46 (kale) mg/kg dm, that indicates on high variation in content of this element in fresh material depending on the species (Table 1). Higher results regarding manganese content in _Brassica_ could be found in the literature [35; 36; 37]. [PERSON] and [PERSON] [36] found no statistical difference between manganese content in fresh cauliflower and water or steam boiled. This was consistent with the findings of [PERSON] and [PERSON] [37] and [PERSON] and [PERSON] [4], who only in cooked broccoli observed a significant decrease in magnesium content, by 41.3% compared to the fresh vegetable. This work showed that cooking led to significant losses of this microelement in most of the analysed vegetables; the only exception was boiled green cauliflower, in which its content increased significantly, by 16.4%.  
The human body shows a varied demand for iron, which is dependent on age, sex and physical condition. However, it should be taken into consideration that iron assimilation is approximately 5% for non-animal products. By analyzing the data in Table 1, the highest iron content in raw material was recorded in ruttabaga (250.75 mg/kg dm) and the lowest in purple cauliflower (60.23 mg/kg dm). Much higher values than given in this paper were published by [PERSON] and [PERSON], [36], [PERSON] et al. [35], [PERSON] et al. [38]. On the other hand, as reported by [PERSON] et al. [40], [PERSON] et al. [41] and [PERSON] et al. [39], its levels in kale, ruttabaga and cauliflower were significantly lower compared to our results. In turn, [PERSON] and [PERSON] [4] stated percentage reduction of magnesium depending on the applied processing, the highest for conventional cooking in water, 13.8% (_Romanesco_ cauliflower) and 38.2% (broccoli). In contrast, [PERSON] and [PERSON] [36] observed no differences in iron content between fresh cauliflower and that blanched and cooked by means of various methods.  
The zinc content of the analyzed samples varies enormously depending on the species, ranging from 18.58 (rutabaga) to 67.86 mg/kg dm (kale) (Table 1). With regard to zinc content, as was in the case of other aforementioned mineral components, the results obtained by other authors were lower [37; 39; 40] or higher [35; 36; 41], compared to our findings.  
This study showed a significant fall in zinc content due to cooking in green cauliflower and kale, compared to raw vegetables. Similar losses of 13% in kale and 23% in cauliflower were reported by [PERSON] and [PERSON] [37] and [PERSON] et al. [39]. On the other hand, [PERSON] and [PERSON] [36] found no significant changes in the content of this micronutrient due to the applied hydrothermal processes, which is congruent with our results for rutabaga and purple cauliflower.