Department of Forest Utilization, Institute of Forest Sciences, Warsaw University of Life Sciences-SGGW, Warsaw, Poland.
Department of Agroecology, Institute of Agricultural Sciences, Land Management and Environmental Protection, University of Rzeszów, Rzeszów, Poland.
PLoS One. 2020 Dec 29;15(12):e0244435. doi: 10.1371/journal.pone.0244435. eCollection 2020.
The aim of this study was to determine the effect of the age of trees, daily sap volume as well as the term of tapping birch sap collected in the forest environment on the content of selected minerals (zinc, copper and manganese) and heavy metals (lead, nickel, chromium and cadmium). The study was performed on material taken from two stands (aged 34 and 84 years) in a moist broadleaved forest habitat with a dominant share of silver birch (Betula pendula Roth). The research results confirmed the presence of both nutritional essential minerals and hazardous heavy metals in the birch sap. At the same time, the content of minerals and heavy metals was found to be very variable and the differences between their concentrations, recorded on the same day of collecting in several trees of the same age group, can be even several dozen times higher. Depending on the examined elements, the factors influencing their content vary. The age of the trees determines only the manganese content; daily sap volume significantly affects the content of manganese and copper, and date of collection differentiates the content of zinc, lead, nickel and cadmium. The results may be interesting in the context of developing procedures for collecting birch sap for the purpose of obtaining raw material with beneficial nutritional values and a high level of health safety. For this reason, our recommendation for guaranteeing the health safety and high nutritional value of birch sap is to combine batches of raw material taken from as many trees as possible, and at the same time to publicize the fact that collecting birch sap from just one single tree may result in a raw material that is both dangerous and has no nutritional benefits.
本研究旨在确定树木的年龄、每日树液量以及在森林环境中采集的桦树汁的采集时间对选定矿物质（锌、铜和锰）和重金属（铅、镍、铬和镉）含量的影响。该研究使用了取自两个林分（34 岁和 84 岁）的材料，这些林分位于湿润的阔叶林中，以银桦（Betula pendula Roth）为主。研究结果证实了桦树汁中既有营养必需矿物质，也有有害重金属。同时，矿物质和重金属的含量非常多变，同一天在同一年龄组的几棵树上采集的浓度之间的差异甚至可能高达几十倍。根据所研究的元素，影响其含量的因素也不同。树木的年龄仅决定了锰的含量；每日树液量显著影响锰和铜的含量，而采集日期则区分了锌、铅、镍和镉的含量。这些结果在开发桦树汁采集程序以获得具有有益营养价值和高水平健康安全性的原料方面可能具有重要意义。因此，为了保证桦树汁的健康安全性和高营养价值，我们的建议是将尽可能多的树木的原料进行混合，同时要宣传这样一个事实，即从单一的桦树上采集桦树汁可能会导致原料既危险又没有营养价值。
