# Influence of Ozone on the Biochemical Composition of Birch Sap
## 1 Introduction  
Birch sap is a forest resource with a deep tradition of use in northern and eastern Europe, where it is obtained from the silver birch (_Betula pendula_ [PERSON]) and the curly birch (_Betula pubescens_ [PERSON]) [1], as well as in North America, where it is obtained from the white birch (_Betula pupyifera_ [PERSON]), sweet birch (_Betula lenta_ [PERSON]), and yellow birch (_Betula allephanitis_ [PERSON]) [2]. Birch sap consists mainly of water and a solution of sugars, which contains various amounts of amino and organic acids, peptides, vitamins, and phenolic substances [3; 4; 5; 6; 7]. Birch sap is traditionally used as a fresh refresh drink when fresh [8], or as a fermented drink all year round [9]. It is also used in traditional medicine in many countries [10; 11]. Birch sap has been known as a valuable remedy for anemia, kidney, stomach, and liver disease, arthritis, gallstones, skin diseases, gout, rheumatism and colds, infectious diseases, and intestinal parasites, as well as weakened immune systems [8; 12; 13]. It has also been used for hair and skincare [14]. Currently, birch sap is becoming increasingly popular as a natural probiotic that is developed by fermentation [8]. Recently, the traditional consumption of sap and its products is declining, and more and more industrially produced sap products are being used. Traditionally, sap is used fresh or fermented and consumed as kvass [1], because at the right temperature, the carbohydrates in the sap become a source of nutrients for fermenting microorganisms [15; 16]. Industrially obtained sap must be processed before the start of fermentation, because fermentation causes changes in color and odor, as well as the chemical composition of the sap [3; 15]. With the increase in popularity of a healthy lifestyle, there is an increasing demand for less processed products, made while retaining as many of the original properties as possible. Up to now, the main method for preserving birch sap has been pasteurization, which reduces the health properties of the drink. Thermal treatment is still a standard sap preservation technology that can cause changes in the vitamins and other valuable nutrients, as well as a loss of original raw material quality [17; 18]. Thermal technologies are also energy-intensive [19; 20]. These methods are based on the indirect transfer of heat to the product using a heating medium obtained by burning fossil fuels [21]. The high energy demand causes greenhouse gas emissions, which can have a significant impact on the environment. Rising energy demand and increased global competition call for continuous improvements in technology [22]. In order for fresh sap to retain its original properties for as long as possible and to prevent fermentation, it must be processed immediately. However, this is not always possible, or it might not be economically viable to transport the product for processing in small quantities, so ways need to be found to slow down the growth of micro-organisms in sap stored under field conditions. In order to keep the product fresh and of good quality for as long as possible, alternative ways of keeping the products must be sought. Many alternative processing methods can be used to preserve the properties of fresh birch sap apart from pasteurization: microfiltration, treatment with ultrasound, UV radiation, magnetic fields, high pressure, and various combinations of these methods. These new innovative methods inactivate the majority of microorganisms without the use of high temperatures which allows for preserving the original structure and properties of the product [3; 9; 15; 23; 24]. One such method could be the use of ozone gas. In the field of food processing, interest in ozone has grown rapidly in recent decades as consumer interest in nonthermal processing methods has increased [25; 26].