Bioactive compounds and antimicrobial activity of extracts from fermented African locust bean (Parkia biglobosa) against pathogenic microorganisms

Abstract

Background: The challenges of multiple antibiotic resistance by pathogenic microorganisms has necessitated the need for a continuous searching for new and effective antimicrobial bioactive compounds. Objectives: In this study, antimicrobial activity of extracts from fermented condiment from Parkia biglobosa was investigated against some pathogenic microorganisms. Materials and Methods: Gas chromatography and mass spectrometry (GC-MS) was used to identify bioactive compounds in n-hexane extract (oil). Aqueous and n-hexane extracts of locust beans were tested against clinical isolates; viz., Klebsiella spp., Aeromonas hydrophilia, Citrobacter braakii, Enterobacter aerogenes, Shigella dysenteriae, Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli, Methicillin Resistant Staphylococcus aureus (MRSA), Aspergillus spp. and Candida albicans using agar well diffusion method. Results: The study revealed the phytochemicals in oil as phenols (41.8 mg/100g), flavonoids of 19.37 mg/100g, saponins (16.7 mg/100g), alkaloids (22.9 mg/100g), steroids (6.9 mg/100g), terpenoids (10.0 mg/100g) and cardiac glycosides (3.3 mg/100g). The aqueous extract contains phenols (33.7 mg/100g), flavonoids (12.3 mg/100g), alkaloids (17.6 mg/100g), saponins (5.0 mg/100g) and cardiac glycosides (1.2 mg/100g). The bioactive compounds in the n-hexane extract were ricinoleic acid, p-cymene, octadecanoic acid, n-hexadecanoic acid and others. Oil from fermented locust bean exhibited zones of inhibition ranging from 5 mm to 14 mm against the tested isolates at 10 mg/mL, while the aqueous extract displayed inhibition zones of 4 mm to 10 mm at 10.0 mg/mL. Conclusion: The chemical constituents in locally fermented condiment (locust bean) are responsible for pronounced antimicrobial properties. Hence, the condiment can be exploited for medicinal purposes. ​Keywords: Fermented food, condiment, n-hexane, phytochemicals and antimicrobials.