Selection of promising strains of probiotics for foods: Proposal for a possible flow-chart with a special focus on the dark side of probiotics

The use of foods as vehicles for probiotics is a great challenge, as the microorganisms should possess the technological robustness, i.e., the ability to survive throughout the production and within the storage, without affecting the sensorial properties of foods. An increasing trend in food industry is the selection of autochthonous and wild strains with promising probiotic traits, as they possess an intrinsic technological robustness for a given raw material or product. Thus, this paper will report on the lab approach to select promising probiotic strains, with a special focus on: a) the classical probiotic traits (survival under simulated gastro-intestinal conditions, antagonistic activity towards foodborne and intestinal pathogens, adhesion to cell lines simulating the mucosa of the gut); b) some new screening and rapid procedures (auto-aggregation, co-aggregation with pathogens, hydrophobicity and determination of the Minimal Inhibitory Concentration of some antibiotics through the E-test) and innovative traits (competitive adhesion to the mucosa with pathogens); In addition, the chapter proposes two-case studies on what is the technological robustness of a probiotic, with a focus on the vegetables (table olives) and meat. As a final step, the chapter will focus on the QPS status (Qualified Presumption of Safety) and on the dark-side of probiotics, following the most recent guidelines of EFSA (European Food Safety Authority). The starting point of this last section will be the evidence that in some situations the probiotics could be a challenge for human health, as shown by some episodes of infections in the Northern Europe. Thus, the chapter will propose a report on the antibiotic resistance and translocation of probiotics in order to propose some additional traits to select promising strains intended for foods.