Antimicrobial activity and phytochemicals analysis of vernonia aemulans, vernonia amygdalina, lantana camara and markhamia lutea leaves as natural beer preservatives

Background: African traditional beers are both considered as food and beverages for African people and hence preserving them using the natural additive is of utmost importance. In the present study, the antimicrobial activity of aqueous and ethanol extracts of Rwandan plants Vernonia aemulans, Vernonia amygdalina, Lantana camara and Markhamia lutea leaves were tested against Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Salmonella typhimurium and Sacharomyces cerevisiae. Methodology: The antimicrobial activity was carried out by the disc diffusion method. The phytochemical screening of ethanolic extracts of these Rwandan plants was determined using standard method of analysis. Result: The results showed that the ethanol and aqueous extracts of V. aemulans, V. amygdalina, L. camara and M. lutea leaves have antibacterial activity against food spoilage bacteria and food-borne pathogens with inhibitory zone diameters ranging between 3-26 mm. All extracts analyzed did not possess antimicrobial activity against S. cerevisaie, which plays major role in African beers fermentation. The Gram-negative bacteria tested were found to be resistant only against the extracts of M. lutea leaves. The extracts of V. aemulans, V. amygdalina and L. camara possess antibacterial activities both against the Gram-positive (B. subtilis and S. aureus) and negative (E. coli and S. typhimurium) bacteria with the minimum inhibitory concentration ranging from 2-16 mg mL-1. These inhibitory properties had been attributed to the presence of tannins (9.2-99 mg g-1), flavonoids (62.4-87.4 mg g-1), saponins (39.8-65 mg g-1), phenolic compounds (22.6-42.8 mg g-1) and alkaloids (32-40.7 mg g-1) in these plants. Conclusion: The findings established that V. aemulans, V. amygdalina and L. camara leaves can be used as natural beer preservatives with considerable market opportunities in African brewing industry due to their strong antimicrobial activity imparting extended shelf-life with less harmful effects. © 2017 Francisco Abel Lemos Alves et al