Bactericidal Effect of Fermented Milk with Cudrania Tricuspidata leaf Extract and Lactobacillus Gasseri Strains

Introduction: Cudrania tricuspidata (CT) is a traditional herb used for remedy, and it is reported as a good source of prebiotic for fermented milk. However, the antibacterial activity of the fermented milk with CT has not been studied.

Purpose: This study investigated the antibacterial activity of fermented milk with CT leaf extract and Lactobacillus gasseri strains.

Methods: Milks without (fermented milk) and with powdered CT leaf extracts (0.2% [wt/wt]; CT-fermented milk) were inoculated with Lb. gasseri strains 505, 545, 559, and 575 (ca.10⁷ CFU/ml), followed by incubation at 41°C for 40 h. Minimum bactericidal concentration (MBC) of CT-fermented milk on Listeria monocytogenes were determined by challenging L. monocytogenes strains to fermented milk and CT-fermented milk (0.32 to 10 mg/ml). To investigate the bactericidal effect of CT-fermented milk in gastrointestinal tract, 12 C57BL6/N mice were treated with a combination of 100 μl fermented milk with 100 μl L. monocytogenes and a combination of CT-fermented milk with 100 μl L. monocytogenes daily for a week. Feces were plated on CHROMagar^TMListeria on day 0, 3, 5 and 7. The mice were then euthanized, and ceca were plated on CHROMagar^TMListeria.

Results: L. monocytogenes was inhibited by CT-fermented milk with Lb. gasseri strains 505, 559, and 575. MBCs of CT-fermented milk with Lb. gasseri strains 505, 559, and 575 were 5, 0.32, and 2.5 mg/ml, respectively, while L. monocytogenes was not inhibited by fermented milk. L. monocytogenes counts in feces and ceca of the mice treated CT-fermented milk were not significantly different from those of fermented milk.

Significance: The results indicate that CT may serve as an effective prebiotic in fermented milk by Lb. gasseri, which can improve food safety of dairy products.