Antimicrobial activity of cell free superntant of Lactobacillus plantarum IMC 509 against common food spoilage microbes

Objectives: This study aimed to evaluate the in vitro anti-spoilage property of Lactobacillus plantarum IMC 509 cell-free supernatant as potential natural food preservative. Methods: L. plantarum IMC 509 (1011CFU/g) lyophilized powder was cultured in MRS broth. To eliminate cells, centrifugation and 0.2μm filter membranes were used. CTR-supernatant was without treatment; in OA-supernatant pepsin, catalase, proteinase K were added to test the organic acids effects. HO-supernatant was treated with proteinase K and with neutralized pH to monitor the H2O2 effects. In BLS-supernatant catalase was added and pH neutralized to check bacteriocin-like-substance. Several Gram positive and Gram negative bacteria strains and one yeast were selected for the well diffusion test. Mueller-Hinton agars were inoculated with tested microbes and loaded with four supernatants. Plates were incubated and inhibition zones were checked and measured. Results: The pH values of CTR and OA were lower than HO and BLS. The diameters of inhibition zone demonstrated that all tested strains were sensitive to both CTR and OA samples, while not to the HO and BLS samples, with the exception of Klebsiella pneumoniae which was sensitive to all four supernatants. Conclusions: The results showed the lower pH value, the higher inhibition effects toward tested strains, demonstrating the antimicrobial properties of L. plantarum IMC 509 supernatants. The organic acids produced by the strain were the major active antimicrobial substances. Further studies are needed to evaluate its ability to extend food shelf-life by directly applying on food matrices.