## 1 Introduction
_Lactobacillus reuteri_ has the capability to ferment a whole range of different carbon sources and some species have been used to ferment fruit juices producing bioactive compounds of great interest such as folates and vitamin B12 [14]. Furthermore, _Lactobacillus reuteri_ has the capability to produce reuterin, a compound with potential as a food preservative, especially due to its activity against food spoilage microorganisms such as _Listeria monocytogenes_ and _Escherichia coli_. Definitively, its features and its safe status makes it a promising microorganism in the food industry [8]. Some research works show fruit juices as a good carrier for _Lactobacillus reuteri_, but their viability was strongly affected by the kind of juices. Namely, _Lactobacillus reuteri_ showed a high viability in pineapple, orange, and apple juices, while the viability was reduced in red-fruit juice [15]. In addition, thermal preservation treatments or exposure to temperatures above refrigeration also have unfavorable effects. In this sense, the viability of probiotic cells can be improved by modifying the properties of the juice after a non-thermal preservation treatment as an alternative to a conventional heat treatment. High pressures homogenization (HPH) is a non-thermal treatment, which in addition to being used for preservation purposes, also improves the physico-chemical and functional properties of fruit juices, increasing quality, stability, and phytochemical profile [16; 17]. It allows the replacement of traditional processes to better preserve sensory and nutritional characteristics, as well as to develop products with differentiated structural characteristics and functional properties [18]. The application of high and/or moderate homogenization pressures to fruit juices has proven to be less destructive for low molecular weight compounds responsible for sensory and nutritional attributes and, at the same time, sufficiently effective to inactivate the microorganisms that are responsible for spoilage [19]. Applied to strains with probiotic effect, homogenization has been shown to increase survival and improve functional properties. For example, in trials with _Lactobacillus paracasi_ A13 strains, the application of high homogenization pressures increased their hydrophobicity, which is directly related to their ability to adhere to intestinal cells and their resistance to the digestion process [20]. Moreover, HPH at 50 MPa applied to cells of _Lactobacillus paracasi_ A13 were able to modulate the murine immune system inducing a high IgA response, compared to untreated cells. In fact, modifications of the outermost cellular structures by the hyperbaric treatments play an important role in the final probiotic and immune cells interaction [21]. Finally, to ensure that _Lacobacillus_ exerts a beneficial probiotic effect on a host, it needs to survive to gastrointestinal digestion process. In vitro digestion simulation is often used to evaluate probiotic survival in the gastrointestinal tract. This technique is not only faster and less expensive than comparable methods, but also resource-efficient, with significantly lower bio-ethical constraints [22]. Based on all that has been stated, the aim of this study was to evaluate the use of lulo juice as substrate for producing a potentially probiotic beverage with _Lactobacillus reuteri_. Lulo juices at two pH levels and two pressures of HPH treatment have been considered to evaluate the effect of these variables on _Lactobacillus reuteri_ growth, physicochemical and antioxidant properties, and the resistance of microbial cells to gastrointestinal digestion in vitro.