Purpose: In this study, Psoraleae semen was evaluated in in vitroand in sausage for its application as a natural antimicrobial agent in food and pharmaceutical fields.
Methods: Antibacterial effects of 69 therapeutic herbal plants extracts were investigated on 9 bacterial strains through a disc diffusion assay. Among them, the antimicrobial activity of Psoraleae semen was further evaluated using MIC (minimal inhibition concentration) and biofilm formation assays. The effect of Psoraleae semen extract on bacterial cell membranes was determined by measuring the leakage of 280 nm-absorbing materials and observing the bacterial cell through scanning electron microscope (SEM) in the presence of the extract. Finally, the antimicrobial activity of Psoraleae semenwas confirmed in sausages.
Results: Disc diffusion assay determined that the extract displayed no antimicrobial effect on Gram-negative bacteria, but significant effect on Gram-positive bacteria. The MICs of Psoraleae semen extract were determined as 8 µg/mL for Streptococcus mutans, and 16 µg/mL for Enterococcus sp. and Staphylococcus aureus. Furthermore, biofilm formation was inhibited at 8-16 µg/mL of the extract. Measurement of 280 nm-absorbing materials leakage and SEM images revealed that cell membranes of Gram-positive bacteria were damaged by the exposure to the extract during bacterial growth. The growth of Listeria monocytogenes in sausage was hindered during storage in the presence of the extract at 4°C for 10 days.
Significance: These results showed that Psoraleae semenextract could be applied for the growth control of Gram-positive bacteria as a natural antimicrobial agent in food and pharmaceutical industries.