## 1 Introduction  
Functional foods are being used worldwide as agents targeting to prevent disease [1]. As a result, functional foods have been gaining significant attention from the food industry during the past few years [2; 3]. The international market of functional foods is rising and represents one of the most attractive areas of innovation regarding the food sector [4; 5]. In general, functional foods exert beneficial health effects and include foods that contain bioactive compounds and probioticic [1]. Probiotics are live microorganisms (mainly bacteria but also yeasts) often called \"good\" or \"helpful\" because they promote the equilibrium of intestinal microflora [6; 7]. Additionally, the consumption of probiotic food is indicated by many studies to reduce the level of serum cholesterol, to enhance the immune system and to prevent colon cancer [8]. However, probiotics should be present in adequate amounts in the food matrix in order to deliver their beneficial effects to the host [7]. Likewise, the minimum concentration of viable cells for a probiotic food product has been estimated to be approximately 10\({}^{6}\)-10\({}^{7}\) cfu/mL during the time of consumption [9]. In many studies, as well as industrial applications, the main vehicles for delivering probiotic bacteria have been demonstrated to be dairy products [10; 11; 12]. However, probiotic dairy products are often not suitable for consumption by certain groups of consumers due to increased incidence of lactose-intolerance, allergies, dyslipidemia and vegetarianism [13; 14]. As a result of increasing consumers' demand for alternative non-dairy substrates for the delivery of probiotic bacteria, academic and industrial research was triggered toward the development of innovative juice and vegetable probiotic beverages [15; 16; 17; 18; 19].  
Fruit juices and beverages market is currently demonstrating a dynamic growth worldwide [20; 21]. Functional beverages manufactured with fruit or vegetable juices with incorporated probiotic bacteria are considered as an attractive option for those who do not consume dairy products [19]. In addition, fruit juices have been reported as novel suitable carrier for the delivery of probiotic bacteria as they are rich in vitamins, minerals and antioxidant compounds providing a suitable growth substrate in parallel with a strong health appeal [15; 16]. Fermentation of fruit juice by probiotic bacteria can increase viability of the cells and in addition improve functional aspects of the produced beverage [16; 22]. As a result, a wide variety of ongoing research has recently focused on fermented juice production by the use of various probiotic strains providing outstanding results [15; 22; 23; 24]. Among many fruits, pomergnate juice is quite appreciated for its functional properties as it has potent anti-oxidative characteristics, anti-inflammatory and antimicrobial properties and has been previously employed for fermentation by probiotic lactic acid bacteria ameliorating the health benefits of the juice [25; 26; 27; 28].  
The main aim of this study was the development of a novel fermented pomergnate beverage by the application of _Lactobacillus plantarum_ ATCC 14917 [29]; a probiotic strain with good technological characteristics which was evaluated in the frame of this research. The parameters that were analyzed mainly focused on (i) concentration of residual sugars, organic acids and ethanol, (ii) volatile compounds, (iii) total phenolics content, (iv) antioxidant activity and (v) viability of the strain. To the best of our knowledge, no previous studies demonstrated the effect of pomergnate probiotic juice fermentation during cold storage (4 \({}^{\circ}\)C) for four weeks besides the 24 h of fermentation.