There is very little data on the sugar content of tree sap in Central Europe. In order to fill this gap we measured sugar content in the spring sap of 55 trees from 8 species (six native and two introduced). Sugar content was measured chromatographically using an HPLC Dionex Ultimate 3000 system and CAD detection. The proportion of sugar was highly genus-specific: maples contained sucrose, birches a mix of glucose, fructose and sucrose and hornbeams glucose and fructose. Acer saccharinum had the sweetest sap (4.0%), followed by A. platanoides (3.2%), A. pseudoplatanus (3.2%), A. negundo (2.9%) and A. campestre (2.8%). Birches were slightly less sweet (Betula pendula 2.5% and B. pubescens 2.6%). Carpinus betulus sap contained only 0.9% sugar. The reported values for birches are higher than those reported in other European studies and the values for maples are similar to those for sugar maples in North America. As southeastern Poland has many large populations of maples and birches, a small-scale sugar syrup industry could become an additional source of income for forest owners.
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.
Analizowano soki drzewne ośmiu gatunków drzew z Podkarpacia: brzozy zwisłej (brodawkowatej)-Betula pendula Ehrh., brzozy omszonej-Betula pubescens Ehrh., grabu pospolitego-Carpinus betulus L., klonu zwyczajnego-Acer platanoides L,. klonu jawora-Acer pseudoplatanus L., klonu polnego-Acer campestre L., klonu jesionolistnego-Acer negundo L. i klonu srebrzystego-Acer saccharinum L. Określono zawartość anionów nieorganicznych: chlorków, azotanów(V), siarczanów(VI) oraz fosforanów(V), a także składników mineralnych: miedzi, cynku, wapnia, magnezu, sodu i potasu. Największą średnią zawartość chlorków (32,68 mg•l-1) i siarczanów (21,8 mg•l-1) oznaczono w sokach grabowych, a magnezu (18,96 mg•l-1) i wapnia (30,52 mg•l-1) w sokach z klonu polnego. W sokach z klonu jesionolistnego stwierdzono największą średnią zawartość fosforanów (114,53 mg•l-1), miedzi (1,45 mg•l-1) i azotanów (25,99 mg•l-1), a w soku z brzozy zwisłej-cynku (1,85 mg•l-1) i sodu (0,59 mg•l-1). Soki z klonu zwyczajnego odznaczały się z kolei największą średnią zawartością potasu (82,15 mg•l-1). Otrzymane wyniki zestawiono z obowiązującymi w Polsce normami żywieniowymi. Wskazują one, że soki drzewne mogą być wartościowym źródłem składników mineralnych, szczególnie miedzi i cynku, w mniejszym stopniu wapnia, magnezu i fosforu. Jednocześnie stwierdzono znikome zagrożenie ze strony składników potencjalnie niekorzystnych dla ludzkiego zdrowia, tzn. anionów nieorganicznych: azotanów(V) i siarczanów(VI) oraz sodu.
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