No abstract

Lacticaseibacillus rhamnosus GG, or LGG, is one of the most studied probiotic bacterium worldwide. The health benefit properties of LGG are mainly ensured by SpaCBA pili, which are polymeric proteins located at the cell surface. These pili confer the ability to interact with the surrounding environment and notably to adhere to intestinal cells mainly through interactions with mucin glycoproteins. For an expected probiotic effect, cell viability is an essential parameter. Nevertheless, the stability and the integrity of the pili is of paramount importance, from the conservation process of bacteria to the subsequent gastrointestinal digestion. One way to preserve bacterial viability is to encapsulate them within a matrix made of milk proteins where bacteria-matrix interactions occur and play an essential role. In the present study, nanoDSF and MST analyses revealed the remarkable thermal and detergent stability, respectively, of purified native SpaCBA pili and of the corresponding recombinant pilins. Crosslinking experiments have shown that SpaC can directly interact with β-lactoglobulin, the most abundant whey protein in the matrix with a dissociation constant (Kd) around 100 µM. The preservation of SpaCBA pili on protected LGG after spray drying was evidenced. Finally, the improved survival rate of protected LGG by resisting to simulated human digestion was shown compared to unprotected LGG. This study demonstrated that LGG encapsulation in a relevant matrix is mandatory to preserve bacteria viability and functionality after spray drying and to guarantee its preservation during the subsequent human digestion.