Modulation of Surface Hydrophobicity of Lactic Acid Bacteria by Ohmic Heating

Probiotics are defined as live microorganisms capable of conferring health benefits to the host. Among them, lactic acid bacteria are widely recognized as one of the main representatives of this group. However, these microorganisms are highly sensitive to common factors in the human gastrointestinal tract, such as pH fluctuations, enzymatic activity, and temperature variation. In this context, research has focused on strategies to enhance the survival rate of these microorganisms. Encapsulation has emerged as a promising approach to improve their viability; however, due to the distinct characteristics of bacterial membranes, the application of this technique remains complex. Alternatives such as Ohmic Heating, an emerging technology, may have the potential to modulate membrane structure through the application of an electric current to the sample, thereby improving its functional properties. The aim of this study was to evaluate the influence of Ohmic Heating on the surface hydrophobicity of the cell wall of lactic acid bacteria and to analyze their behavior post-treatment. Electric field intensities of 5, 10, and 15 V·cm⁻¹ were applied to cell suspensions containing one of the five bacterial strains used: L. innocua, L. rhamnosus, L. lactis, L. acidophilus, and L. gasseri. Colony counts were performed before and after the treatments, and surface hydrophobicity was quantified using two solvents: hexane and toluene. Results indicated that the electric field caused significant alterations in membrane structure. All samples treated at 5 V·cm⁻¹ exhibited an increase in colony counts, which may be associated with the tendency of cells to aggregate following membrane electroporation, forming clusters similar to biofilms. In contrast, treatments at 10 V·cm⁻¹ and 15 V·cm⁻¹ resulted in stable colony counts, suggesting that higher voltages induce more severe electroporation, potentially leading to cellular death or stagnation. Regarding surface hydrophobicity, a reduction was observed with increasing electric field intensity. However, compared to the control samples, L. gasseri and L. acidophilus demonstrated a significant increase in surface hydrophobicity, when assessed with hexane and toluene respectively, even under more intense treatments (10 and 15 V·cm⁻¹). This indicates a strain-specific alteration in membrane composition that enhances cell aggregation tendencies following electroporation. In conclusion, when applied as a pre-treatment for probiotic encapsulation, the increased tendency for biofilm formation and the consequent enhancement in surface hydrophobicity can be highly beneficial. These effects may substantially improve probiotic resistance during gastrointestinal transit, thereby enhancing their efficacy in producing health-promoting compounds.