The aim of this study was to evaluate the effectiveness of cell-free supernatants (CFS) produced by selected lactic acid bacteria (LAB) strains: Lacticaseibacillus paracasei B1 and Lactiplantibacillus plantarum O24 as antioxidant and antimicrobial agents. Both CFSs showed strong antioxidant activity, but their ability to chelate iron ions not depend on the type of strain. Meanwhile, inhibition tests using the diffusion method showed that the supernatant free of L. plantarum O24 cells was the most effective in antimicrobial activity against Listeria monocytogenes, Salmonella Typhimurium, Escherichia coli, and Staphylococcus aureus. The study also determined the effect of sonication (500 W; 2.5 kHz) on cell cultures after 48 h of incubation. Analyses showed that this treatment did not alter the pH of the obtained CFS, nor did it affect the content of proteins, peptides, or the level of organic acids. However, sonication of culture fluids resulted in changes in their antioxidant properties.