Inhibitory effect of bioactive compounds derived from freeze-dried paraprobiotic of Pediococcus acidilactici against food-borne pathogens: In-vitro and food model studies

It was aimed to assess the antimicrobial potential of lyophilized/freeze-dried paraprobiotic (LP) of P. acidilactici against some food-borne pathogens under in-vitro conditions and food model, and determination of bioactive compounds that contribute to the antimicrobial activity of LP. For this purpose, minimum inhibitory concentration (MIC), inhibition zones were determined against Listeria monocytogenes, Salmonella Typhimurium and Escherichia coli O157:H7. The MIC value was 6.25 mg/mL and a 20 µL LP displayed 8.78 to 10.0 mm inhibition zones against these pathogens. In the food matrice challenge, two concentrations of LP (3% and 6%) alone or in combination with EDTA (0.02 M) were added to pathogenic bacteria spiked meatballs, and antimicrobial activity of LP was also determined during refrigerated storage. 6% LP + 0.02 M EDTA treatment provided 1.32 to 3.11 log10 CFU/g reductions in the numbers of these pathogens (P < 0.05). Furthermore, this treatment provided significant reductions on psychrotrophs, TVC, LAB, mold-yeast, and Pseudomonas spp. over the storage (P < 0.05). Regarding characterization results, LP contained contained a wide variety of bioactive compounds, including 5 organic acids (2.15 to 30.64 g/100 g), 19 free amino acids (6.97 to 699.15 mg/100 g), free fatty acids (short-, medium-, and long-chain fatty acids), 15 polyphenols (0.03 to 383.78 mg/100 g), and some volatile compounds such as pyrazines, pyranone and pyrrole derivatives. These bioactive compounds are not only involved in antimicrobial activity but also contribute to the free radical scavenging activity according to the DPPH, ABTS and FRAP assays. In conclusion, the result revealed that the LP improved the chemical and microbiological quality of foods due to containing biologically-active metabolites involved in antimicrobial and antioxidant capacity.