Antimicrobial Activity and Total Soluble Phenolic Content in Momordica balsamina and Momordica foetida Extracts

Introduction: Momordica balsamina (inkakha) and Momordica foetida (inshubaba) are two plants used in several countries, including Swaziland, both for food and as a traditional medicine to treat several diseases.  Increasing resistance and allergic reactions to synthetic antibiotics and preservatives validates the search for potential antimicrobial agents from these indigenous vegetables.

Purpose: In this study, antibacterial activity of M. balsamina and M. foetida extracts against different pathogenic bacteria was evaluated and its relationship with soluble phenolic content determined.

Methods: Different oven dried plant parts of the two Momordica subspecies were extracted using methanol-water (7:3 v/v). Antimicrobial activity was determined using a disc diffusion assay against Staphylococcus aureus NCTC 10652, Staphylococcus aureus NCTC 10655, Listeria monocytogenes 11944, Salmonella Typhimurium LT2 and E. coli O157:H7 Shiga toxin minus (stx) Sakai. Total soluble phenolic content was determined using a Folin-Ciocalteu reagent and calculated as Gallic acid equivalents (GAE).

Results: Momordica extracts showed antimicrobial activity against Gram positive bacteria only. M. balsamina leaf and stem extracts displayed the highest inhibitory activity with zones up to 17 mm while the M. balsamina fruit extracts did not show any activity. M. foetida leaf and fruit extracts gave inhibition zones up to 14 mm, yet M. foetida stem extracts did not show any inhibition zone. Total soluble phenolic content in M. balsamina extracts ranged from 0.043 to 0.192 mg while for M. foetida extracts the range was 0.059 to 0.272 mg. Leaf and stem extracts for both Momordica plants showed higher phenolic contents than fruits extracts. There was a weak linear relationship between antimicrobial activity and phenolic content of Momordica extracts with R² values of 0.29, 0.39 and 0.44.

Significance: These results could indicate the potential use of Momordica extracts as antimicrobial agents and also provide the basis for isolation and identification of the biologically active substances in these extracts.