This micronutrient, occurring in some enzymes, catalyses the neurotransmitter formation from amino acids and takes part in the formation of myelin in the developing brain of young children. It is also active in the fatty acid desaturation and destruction of hydrogen peroxide. Furthermore, iron is crucial for tyrosine iodination and participates in biosynthesis of prostaglandamtions, catabolism of tryptophan, detoxification and immune defence of the body [23; 24]. Zinc, being a component of many enzymes, is necessary for the proper metabolism of proteins, nucleic acids and carbohydrates. It accelerates the growth of hair and nails as well as wound healing. This mineral is crucial for the production of insulin and maintenance of acid-base balance. In addition, zinc ensures proper function of prostate and reproductive organs, positively affects growth and mental performance, and aids in the metabolism of vitamin A and bones as well as in transport of oxygen [25]. Copper, in turn, is necessary for haemoglobin synthesis and bone formation. This mineral is a component of the enzymes involved in intracellular respiration and is essential for the proper functioning of connective and nerve tissue. In addition, it soothes inflammatory reactions and prevents the occurrence of cardiovascular diseases. Copper, as a coenzyme, participates in redox processes and has also an important function in the synthesis of melanin, a pigment of skin and hair, playing also a large role in maintaining keratin structure [26; 27; 28]. Manganese is a micromineral required for the proper growth and development of the body and normal functioning of reproductive and nervous systems It helps to maintain proper bone structure, normal digestion and absorption of nutrients, and synthesis of haemoglobin. In addition, manganese is a component of many enzymes that are involved in the synthesis of proteins, nucleic acids, fatty acids and, additionally, participates in cholesterol metabolism [29]. On the other hand, environmental exposure to airborne manganese is associated with neurocognitive deficits in humans. However, the bioavailability of some of these minerals might be reduced by the presence of glucosinolates, phytates and phenolics. In most cases _Brassicas_ are not eaten immediately after being harvested; hence, storage and cooking impact upon health beneficial components [3; 30]. Vegetable processing is a multi-stage process. The first stage, pre-treatment, includes washing, cleaning, peeling, rinsing, grinding, and even soaking and storage in water. In the next stage, cooking is carried out by means of various methods, in different variants. The extent of mineral salt retention in vegetables depends on the applied cooking technique, the amount of water used, grind size of the raw material, as well as the form of mineral components (more or less soluble). During food processing minerals may be released from the complexes with organic compounds that may change their biological effects. Changes in mineral content in the product may result from their leaching (dissolution) and transition to broth [4]. To the best of our knowledge the majority of studies published to date have focused on other cultivars of _Brassicas_. Less information is available about other _Brassicas_, e.g., colored varieties of cauliflower (purple and green) or rutabaga. The aim of this study was to determine the effect of blanching and cooking in water on the content of selected macronutrients (sodium, potassium, calcium, magnesium) and micronutrients (manganese, iron, zinc and copper) in fresh _Brassicas_ vegetables (kale, rutabaga, green (Romanesco) and purple cauliflowers), and after thermal treatment.