# Lactic Acid Bacteria Co-Encapsulated with Lactobionic Acid:
## 1 Introduction  
Currently, consumers desire high quality food products that, apart from fulfilling their nutritional demands, have the potential to improve their health and/or reduce the risk of some diseases [1]. In this context, functional foods have emerged, especially in the area of dairy products, where the greatest variety of functional food products is to be found [2,3]. These functional foods contain various bioactive compounds such as prebiotics and probiotics. The group of prebiotics is broad, and lactose derivatives such as lactobionic acid (LBA) have generated strong interest in the food field [4]. As with other prebiotics, it is resistant to digestive enzymes [5] and can be metabolised by the microflora of the gastrointestinal tract(GIT) [6; 7]. However, its use has only been approved by the Food and Drug Administration (FDA) in its salt form [8], although it is expected to be approved by other authorities in the near future. Prebiotic compounds have the ability to promote the growth of probiotic microorganisms. Probiotics are live microorganisms that, when administered in appropriate doses, have beneficial effects on consumers [9]. These bacteria have the capacity to withstand the acidic environment of the stomach and reach the lower GIT, where they can convert carbohydrates into lactic acid and other essential nutrients. In addition, they prevent the development and growth of pathogenic microorganisms [9]. The most common and widely used probiotics are lactic acid bacteria (LAB), especially bacteria belonging to the genera _Lactobacillus_ and _Bifidobacterium_[10]. Specifically, _Lactobacillus paracasei_ CBA L74 has been tested as a probiotic in in vivo studies [11] and has shown various health benefits [11; 12; 13; 14]. It has also been successfully used in the development of probiotic non-dairy matrix foods [15; 16; 17; 18; 19; 20; 21; 22; 23]. Moreover, when probiotics are combined with prebiotic compounds, symbiotic products are obtained [24; 25] and, some authors have suggested that this symbiotic combination may increase the viability of the bacteria through the GIT [25; 26]. These bioactive compounds are usually sensitive to chemical and physical factors [27]. To protect them against external agents, different strategies have been explored, such as the development of films, coatings, or encapsulation techniques. Among the matrices that can be used, alginate gels are a suitable matrix to protect and immobilise cells, as they also allow the diffusion of metabolisms through pores [28]. The choice of the coating material and the production conditions of the capsules (hardening times, crosslinking agents, and concentrations) are all factors that can influence the viability of the probiotic and must be carefully investigated [29]. Encapsulation techniques have the capacity to protect probiotic bacteria [10] and also allow other bioactive products to be subjected to different drying techniques, such as heat drying and freeze-drying, which can extend their shelf life [30]. In addition, these types of techniques can increase the survival and viability of probiotics as they pass through the acidic environment of the stomach to reach the GIT. The ultimate goal of the present work was to develop a dried symbiotic capsule, with LBA as prebiotic and _L. paracasei_ CBA L74 as probiotic, that allows a sufficient quantity of bacteria to be conveyed to the intestine for a functional effect and that has a certain stability over time. For this purpose, the ability of the probiotic to consume LBA as a single substrate source was first assessed. Then, four symbiotic capsules with different coatings were developed with sodium alginate and characterised in terms of strength. The capsule type with the best characteristics was subjected to two different drying processes (thermal drying and freeze-drying), and the ability to rehydrate in two different media (saline solution and yogurt) was tested in both. The viability over time of the encapsulated probiotic was assessed and, finally, the survival of the _L.