Promising challenges on bioactivity of heat-treated Lacticaseibacillus rhamnosus MIUG BL38 paraprobiotics

Nowadays, paraprobiotics are considered a promising evolution of probiotics, due to their capacity to preserve or sometimes to enhance the functional properties of their counterpart probiotic viable cells. The present study investigates the production of heat-treated paraprobiotics derived from the selected probiotic Lacticaseibacillus rhamnosus MIUG BL38 strain. The paraprobiotics obtained after treatments at 82°C for 5 min exhibited higher ABTS free radical scavenging activity (15.34 ± 1.34%) compared to the untreated cells (10.62 ± 3.18%). SEM analysis confirmed that L. rhamnosus MIUG BL38 cellular morphology was largely preserved at 74°C treatment, while the temperature increase led to enhanced cell wall alterations. FT-IR results indicated the presence of specific functional groups of lipids, proteins, or carbohydrates, suggesting that structural modifications of these molecules may appear as a consequence of the cells exposure to increased temperature of 82°C. Although the heat-treated paraprobiotics were characterized by changes within the cell wall molecules, their cell surface proteins (CSPs) maintained antimicrobial activity against potentially pathogenic E. coli and P. aeruginosa strains, highlighting that this property was preserved from the L. rhamnosus MIUG BL 38 strain. Further, the molecular modelling investigations focused on the SpaC pilus model of L. rhamnosus GG revealed that the thermal treatment at 82°C resulted in vWFA domain loosening and important rearrangements of the arm-like structure, therefore suggesting the potential interference with mucin proteins recognition and binding. The obtained results revealed the suitability of the L. rhamnosus MIUG BL 38 strain to be used for obtaining paraprobiotics through heat-treatment, with promising properties.