Abstract

Introduction. The forest environment becomes an increasingly popular place of obtaining raw materials, and one of the most promising product is birch sap. The market for bottled birch sap in Poland is monotonous, relying exclusively on pasteurized, acidified and sweetened drinks. A chance to change this situation is to develop a birch sap concentrate obtained by reverse osmosis. It has a sweet taste desired by consumers and particularly high content of minerals, unfortunately it has short shelf life. Aim. The purpose of this work was to develop an effective method of extending the shelf life of birch sap concentrate without the need for pasteurization and chemical interference in the composition. In this way, the new product will be formulated with the potential to compete effectively with synthetic dietary supplements. Material and methods. Birch sap was obtained using drilling technique and continuous collection from the trunks of birch trees (Betula pendula Roth.). The sap was concentrated using reverse osmosis apparatus of our construction, obtaining a sugar concentration, expressed by Brix refractometric extract, equal 2.6° and a dry weight of 2.557%. Microfiltration of birch sap concentrate was carried out under sterile conditions using 0.22, 0.45 and 0.8 μm filters. In the monthly storage test, the measurements were carried out every three days, the optical density parameter was determined. Results. The microfiltration of birch sap concentrate was effective only when 0.22 and 0.45 μm filters were used, no turbidity was observed in the monthly storage test. The samples filtered with a filters with pore diameter of 0.8 μm, became cloudy at analogues time of the test as the samples of non-microfiltered birch sap concentrate, but the turbidity was lowered. Conclusions. The microfiltered birch sap concentrate is characterized by extended shelf life without the addition of chemical substances and without the use of pasteurization process, as well as improved taste compared to the initial raw material without the addition of sweeteners. Thanks to the combination of reverse osmosis and microfiltration, the natural character of the sap is largely preserved. The obtained product has a chance to appear on the food market as an innovative foodstuff. Moreover, due to the high concentration of ions (e.g. zinc and manganese) the concentrate could become an interesting alternative to artificial supplements.

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