# Valorization Potential of Oilseed Cakes by Subcritical Water Extraction
## 4 Discussion
### Mineral Contents  
Adequate mineral intake is essential for normal functioning of body systems (cardiovascular, urogenital, nerve, bone) and all organs. Macro- and microelements have structural and regulatory functions, and are involved in growth, healing, fluid balance, energy production, utilization of other nutrients and vitamins and biochemical processes--components of enzyme systems [25]. Potassium is necessary for the normal functioning of all cells. It regulates the heartbeat, ensures the proper functioning of muscles and electrical transmission, and it is vital for protein synthesis and carbohydrate metabolism. Regarding K, there is no specific recommended daily intake (RDA) for healthy adults, although the Institute of Medicine (IOM) sets an adequate intake of 0.4 g per day [24]. Sodium, together with K, regulates water balance and blood and tissue acidity. This element is also important in heart activity and certain metabolic functions [26]. The RDA of Na for healthy adults is less than 2.3 g per day [27]; elevated intakes have been associated with increased blood pressure and adverse effects on other target organs, blood vessels, heart, kidneys, and brain [27]. Ca has a structural role in the bones and teeth and it is involved in blood clotting, muscle contraction, nerve impulse transmission, heart function and fluid balance within cells [28]. The RDA for Ca for maintaining these functions is about 1 g per day [26]. P is an essential structural component of cell membranes and nucleic acids. This element is also involved in cell signalisation through phosphorylation processes, bone mineralization, energy production and acidity regulation [29]. The RDA of P for healthy male adults is 0.7 g per day [26]. Owing to the important functions of these minerals in human health, subcritical water extracts of oilseed cakes were investigated as possible sources of these minerals.  
Depending on the treatment conditions, the mineral content in extracts varied, especially for Ca and Na (Table 2). In most of the cases, extraction in a carbon dioxide atmosphere or with a HClmodifier released more minerals into the aqueous phase, indicating their better release from matrix constituents. Extractability of minerals from all oilseed cakes, nevertheless, was also quite satisfactory with pure water. Average mineral contents (Table 2) allow the comparison of the samples as mineral sources. Flax seed cake extracts were the richest in Na and Ca, whereas hemp seed cake extract had the greatest P (4.27 \(\pm\) 0.02 mg/100 g dry extract) and Na (50.08 \(\pm\) 0.11 mg/100 g dry extract) contents. Hemp and flax seed cake extracts showed comparable contents of K and Ca, whereas pumpkin seed cake extracts showed to be the poorest source of Na. [PERSON] et al. [30] determined much higher contents of K, Na and Ca in lyophilized aqueous extracts of copra and sesame cakes in comparison to all analysed samples. Analyzed extracts also had much lower contents of minerals in comparison to extracts of brown seaweed _Sacorhizas polyschides_, obtained by subcritical water under similar conditions [31]. [PERSON] et al. [32] compared mineral release from greater celandine (_Chelidonium majus_ L) into water by infusion and microwave heating at 45 and 60 \({}^{\circ}\)C and concluded that only 9.54% of Ca, 15.14% of K, 70.38% of Na and 9.57% of P is released from the plant with microwave heating at 60 \({}^{\circ}\)C. For certain elements (K and P), significantly improved release was facilitated in a simple infusion with hot water (53.8% for K and 56.64% for P). Owing to the lack of information about minerals extractability by subcritical water, it can only be assumed that for more efficient mineral release, more severe matrix degradation is required.