Time-related variability of the mineral content in birch tree sap

Minerals are among the most important substances promoting the beneficial effect of tree sap on a human body. However, the composition of tree saps is characterised by high intra- and interspecies variability and it is also known to vary in time even when collected from trees of the same species. The aim of this work was to evaluate the time-related variability of the mineral content in birch tree sap, to prove dependencies between the mineral composition and basic physical parameters of tree saps, and to refer the results obtained in our study to the Polish nutritional standards. Based on the results, it can be concluded that there is no point in time when birch sap invariably achieves superior nutritive values. This is proven by the fact that two of the three tested birch trees had a higher content of minerals at the beginning of sap collection, while the remaining one produced better sap at the end of the experiment. The differences in the mineral composition of tree saps observed during the two-week study raise doubt about the nutritional benefits of their content. For example, one liter of sap collected during two weeks from the three tested birches supplied from 8.49 to 26.34%, 0.9 to 2.80% and 9.17 to 20.23% of the adequate intake of potassium defined in the Nutritional standards for the Polish population (2013). For zinc, the recommended dietary allowance value based on the Nutritional standards for the Polish population (2013) was covered by one liter of sap in the following ranges: from 0 to 2.11%, from 0.85 to 21.50% and from 7.34 to 15.63%. Moreover, it is impossible to estimate the nutritional value of tree saps, understood as the mineral content, from the physical parameters of birch saps. The values of the examined parameters did not correspond reliably to the mineral content. Nonetheless, electrolytic conductivity may reflect more faithfully the nutritional benefits. The higher the EC in the saps from two out of the three birch trees tested, the higher the expected concentration of minerals important for humans, i.e. calcium, zinc and potassium.