Antimicrobial efficacy of pummelo (Citrus maxima (Burm.) Merr.) extracts on spoilage and pathogenic microorganisms in raw chicken meat

The antimicrobial activity of crude ethanolic extracts of pericarp, mesocarp and segment membrane of Citrus maxima (Burm.) Merr. fruit was evaluated against four selected pathogenic bacteria, Escherichia coli, Salmonella typhimurium, Staphylococcus aureus and Listeria monocytogenes after a prelimianry phytochemical and antioxidant activity tests was carried out of the sample extracts. The inhibitory effect was measured by means of total plate count (CFU/g) and by in-vitro antibacterial assay using the cup cylinder method. Preliminary phytochemical Test revealed the presence of phenols (CE/100 ml), tannins (CE/100 ml), flavonoid (GAE/100 ml) and saponin (CE/100 ml) in which the order was as follows pericarp segment membrane mesocarp. The strongest antioxidant activity was obtained by the pericarp extract (29.64% LP). The differences in the measured amount of phytochemicals and antioxidant activity among the three sample extracts were found to be significant. The inhibition test showed tht treating the raw chicken neck with pericarp, mesocarp, and segment membrane extracts using 100% concentration and 1:1 w/v ratio, significantly achieved 1.63, 1.77 and 1.36 log CFU/g reductions, respectively, after 3 days of storage at 4 deg C. The log CFU/g reduction of the control was measured at 0.48. The in vitro antimicrobial activity showed that Salmonella typhimurium was inhibited significantly by increasing concentrations of extracts as compared to other test organisms. The growth of Staphylococcus aureus and Listeria monocytogenes were moderately suppressed by the extracts significantly at increasing concentrations while Escherichia coli was resistant to all the extracts. The contrasting reaction of the gram negative test organisms against the pummelo extract was investigated further. Both of the gram negative test organisms exhibited negative exoenzyme activity. The ability of E. coli to resist the inhibitory effect of the phytochemicals in the extract may be morphological in nature that is to say its rough corrugated cell water and thick periplasmic space as opposed to the smooth curved cell wall and very thin periplasmic space of Salmonella typhimurium. The zone of inhibition produced by the standard antibiotic Kanamycin sulfate (1000 ppm), was 30-60% greater than the sample extracts. The pericarp extract displayed the highest significant antimicrobial effect with eman zone of inhibition of 17.10 mm, 9.90 mm and 15.25 mm for Salmonella typhimurium, Staphylococcus aureus and Listeria monocytogenes, respectively. The phytochemical content and antioxidant activity were found to be significantly correlated to the in vitro antimicrobial activity against all the test organisms except for Salmonella typhimurium. Although results showed fair inhibitory effect, these data provide evidence that Citrus maxima (Burm.) Merr. can be a potential source of natural antimicrobial and antioxidant agents.