## 1 Introduction  
Since [PERSON] et al. first detected the presence of _Asaia_ spp. in fruit-flavored bottled water in 2002, it has become recognized as a common bacterial spoilage in the beverage industry. It is difficult to determine the origin of _Asaia_ spp. contamination in soft drinks. However, flowers and fruits from Asia have been suggested as the source [1; 2; 3; 4]. _Asaia_ spp. have also been isolated from grapes grown in South Australian vineyards and from insects native to tropical climates [5; 6]. These bacteria exhibit unique adaptive abilities [7]. In the soft drinks environment, _Asaia_ spp. are able to grow at pH 3.45, in the presence of sorbate, benzoate, and dimethyldicarbonate at concentrations of 1.5 mmol/L and higher [2]. The resistance of _Asaia_ spp. to common preservatives limits not only the options for preventing the spoilage of soft drinks, but also the effectiveness of sanitation procedures in the beverage industry. These bacteria exhibit polysaccharide encapsulation, as well as very rigid biofilm formation on surfaces used commonly in the beverage industry: glass, polyethylene terephthalate, and polypropylene in the presence of sucrose [1; 8; 9]. Its removal may require additional forcing media (e.g., hot sodium hydroxide and detergent solutions), and in the case of difficult to access areas (e.g., pipe bends, branches, connections, valves) procedures based on mechanical treatment [2]. Microorganisms in biofilms can have up to 1000-times greater resistance to antimicrobial agents, such as disinfectants and sanitizers, than planktonic cells [10; 11]. For this reason, novel biofilm control strategies use both conventional disinfectants (such as peracetic acid or quaternary ammonium compounds) and more novel approaches for reducing microbial adhesion abilities and increasing their sensitivity to antimicrobial agents. For example, substances with biocidal and/or antiadhesive properties--such as organosilanes or nanostructured silver multilayers--may be coated on the internal surfaces of industrial installations [12; 13; 14]. Various plant extracts and juices with antimicrobial properties can be used as soft drink additives [1; 15; 16; 17]. Natural detergents can increase the permeability of microbial cell membranes, so enhancing their susceptibility to disinfection. One group of natural detergents are saponins--classified as triterpen or steroid glycosides. Saponins show a wide range of important properties, and are used in medicine as well as in the beverage and cosme industries. They are non-toxic and environmentally friendly. Their amphipathic properties enable them to penetrate cellular membranes [18]. The beverage industry commonly uses extracts from _Quillaja saponaria_, mainly as a foaming agent and stabilizer in soft drinks or emulsion-based products. Saponins are stable in a wide range of environmental conditions (pH, ionic strength, temperature). This fact makes _Q. saponaria_ saponins suitable for a wide range of applications in food products. According to the Codex Alimentarius Commission, _Q. saponaria_ extracts (QEs) may be used as a foaming agent in soft drinks at doses of up to 200 mg/kg [19]. In the European Union, QEs appear on labels as E999, classified as a foaming agent for use in water-based, flavored, and non-alcoholic drinks (dose 200 mg/L calculated as anhydrous extract) [20; 21]. Saponins in general show significant antifungal activity. Recent research on _Quillaja_ saponins conducted in Poland found that saponin treatment leads to increased cell membrane permeability in different yeast strains [22; 23]. The antibacterial activity of saponins is usually weak; however, such activity may occur in the case of Gram-negative bacteria. In Gram-negative bacteria, the outer membranes of the cell walls are covered in lipopolysaccharidesaccharides. _Q. saponaria_ extracts interact with the lipid part of cell membrane and increase the permeability of the bacterial cells.