Abstract
The search for new antimicrobial compounds is ongoing. Its importance cannot be overemphasized in an era of emerging resistant pathogenic organisms. This study therefore investigated the phytochemical composition and antioxidant and antimicrobial activities of different citrus juice concentrates. Fruit juices of Citrus tangerine (tangerine), Citrus paradisi (grape), Citrus limon (lemon), and Citrus aurantifolia (lime) were evaluated. Antimicrobial activities against five bacterial and three fungal strains were evaluated. The results revealed the presence of alkaloids, flavonoids, steroids, terpenoids, saponins, cardiac glycosides, and reducing sugars in all the juice concentrates. DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging capacities varied with tangerine and grape juices having better scavenging capacities than lemon and lime juices. Grape juice was observed to have a significantly higher (P<0.05) ferric-reducing antioxidant potential (FRAP) value (364.2±10.25μmol/L Fe(II)/g of the extract) than the reference antioxidant, ascorbic acid (312.88±5.61μmol/L). Antimicrobial studies revealed differential antimicrobial activities against different microbial strains. Zones of inhibition ranging from 4 to 26mm were observed for the antibacterial tests with 0-24mm for antifungal test. Minimum inhibitory concentrations (MIC) and minimum bacteriostatic concentrations (MBC) for concentrates against bacterial strains ranged from 12.5 to 200μg/mL. Lemon and lime juice concentrates had lower MIC and MBC values with orange and tangerine having the highest values. Minimum fungicidal concentrations ranged from 50 to 200μg/mL. The results of this study suggest that these juice concentrates may have beneficial antimicrobial roles that can be exploited in controlling unwanted microbial growth.
Highlights
Normal physiological processes in vivo result in the production of free radicals
The phytochemical composition of the citrus juice concentrates revealed the presence of alkaloids, flavonoids, steroids, terpenoids, saponins, cardiac glycosides, and reducing sugars
The results revealed that the juice concentrates are not as effective as diphenyl-1-picryl-hydrazyl radical (DPPH) radical scavengers when compared to ascorbic acid
Summary
Normal physiological processes in vivo result in the production of free radicals. Oxidative stress results when there is an insufficient capacity of the biological system to neutralize excess free radicals that have been produced. The results from this study showed increase in the radical scavenging activities of all extracts as the concentration increased from 0.5 to 1.0 mg/mL (Table 2). The standard antioxidant, ascorbic acid had significantly higher (P < 0.05) percentage inhibitions of the DPPH radical than all the juice concentrates at both concentrations studied (40.10 ± 0.02% and 70.20 ± 0.20% at concentrations of 0.5 and 1.0 mg/mL of extract).
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