Cell effect of CFS
Several substances can be produced by the LAB used in this study, especially organic acids (mainly lactic and acetic), hydrogen peroxide, diacetyl, fatty acids, and different bacteriocins[15], with variations according to the medium used for growth and the individual potential of the strains. This study evaluated the production of CFS in MRS broth, with manganese in its composition. This production method can result in the absence of hydrogen peroxide, catalyzed in oxygen and water[16], thus removing a substance with high antimicrobial activity.
Through the results, it can be seen that high concentrations of the CFS were cytotoxic in HT-29 cells. According to Chen et al.[17], the pH of CFS results in reduced cell viability. In addition, CFS can present high concentrations of nitric oxide when produced in MRS broth, a highly cytotoxic compound at high concentrations. With the reduction in the concentration of L. plantarum 6.2 and L. plantarum 7.1 CFS, there was no change in cell viability.
When exposed to L. fermentum 5.2 CFS, there was cell proliferation at concentrations ≤ 10 mg/mL. Although widely studied as antimicrobial compounds, the compounds generated by LAB, mainly fatty acids, can cause the proliferation of several cell types. Blottiere et al. and Balaban et al. [18,19] demonstrated that short-chain fatty acids resulted in a proliferation of intestinal cellsin vitro and in vivo , in addition to acting on breast tumor cells, due to their use as metabolic substrates and in the production of growth factors.