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 ± 10.25 μmol/L Fe(II)/g of the extract) than the reference antioxidant, ascorbic acid (312.88 ± 5.61 μmol/L). Antimicrobial studies revealed differential antimicrobial activities against different microbial strains. Zones of inhibition ranging from 4 to 26 mm were observed for the antibacterial tests with 0–24 mm for antifungal test. Minimum inhibitory concentrations (MIC) and minimum bacteriostatic concentrations (MBC) for concentrates against bacterial strains ranged from 12.5 to 200 μg/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 200 μg/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.

Background Citrus sinensis is one of the most abundant citrus species consumed. Orange peels are a waste by-product of the fruit and may potentially contain useful phytonutrients with biological relevance. Methods Fresh and dry peels of sweet orange were subjected to Soxhlet extraction and then concentrated using a rotary evaporator. Total phenolic, flavonoid and tannin content were determined using standard methods. Antimicrobial activities against five (5) bacterial strains (Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, Escherichia coli and Salmonella typhimurium) and three (3) fungal strains (Candida albicans, Aspergillus niger and Penicillium notatum) was carried out by observing the zone of inhibition using disc diffusion method. Results The total phenolic, flavonoid and tannin content was higher in the fresh peel extract compared to the dry peel extract. Antimicrobial activities revealed that the fresh peel extract had better antibacterial activities against all bacterial strains and one fungal strain studied compared to the dry peel extract. Growth of Aspergillus niger and Penicillium notatum were however better inhibited by the dry peel extract than the fresh peel extract. Conclusion This study investigated the phenolic content and antimicrobial activities of fresh and dry Citrus sinensis peel extracts. The results from the study conclude that the fresh Citrus sinensis peel extract contains more phenolics and possesses better antimicrobial activities against the studied microbial strains compared to the dry peel extract. The findings in this study suggest that drying plant parts before extraction for phytonutrients may lead to loss of active components.

Vernonia amygdalina and Ocimum gratissimum occupy prominent positions in the diets of several Nigerian ethnic groups. This study therefore compared the phenolic content and some antioxidative activities of the ethanolic leaf extracts of these two plants. Ethanolic extracts of freshly plucked leaves were obtained using standard procedures. The phenolic content and antioxidant capacity of the vegetables were quantified in vitro. The results show that O. gratissimum contains higher amounts of total phenolics (168.5 ± 5.50 and 97.0 ± 0.01 mg gallic acid equivalents/g extract respectively) and flavonoids (126.7 ± 1.00 and 65.4 ± 4.42 mg quercetin equivalents/g extract respectively) than V. amygdalina. A dose-dependent increase in flavonol content was observed for both extracts with higher contents obtained in the O. gratissimum extract. O. gratissimum also has higher DPPH radical scavenging activity (IC 50 values of 105.7 and 111.8 µg/ml respectively) and ferric reducing antioxidant potential (FRAP) (110.0 ± 0.02 and 85.0 ± 0.01 mg Fe 2+ /g extract). O. gratissimum also had higher reducing power than V. amygdalina at the concentrations studied. Standard ascorbic acid however had higher antioxidant activity values for the DPPH, FRAP and reducing power assays. Both plant extracts reasonably inhibit lipid peroxidation at 31.4 ± 0.15% for V. amygdalina and 42.8 ± 1.00% for O. gratissimum. The results further substantiate the medicinal value of these vegetables. Consumption of these vegetables is encouraged to help militate against deleterious effects of reactive species.

Spondias mombin and Polyathia longifolia leaves are popular choices in traditional herbal medicine practice. P. longifolia leaf extracts have not enjoyed profound investigation as more attention is paid to its stem bark and roots. The present study, therefore, evaluates the phytochemical constituents, the phenolic content and the antioxidant activity of the methanol leaf extract of P. longifolia and draws comparisons with Spondias mombin leaf extracts. Results from the phytochemical screening test on S. mombin extract revealed the presence of alkaloids, reducing sugars, cardiac glycosides, flavonoids, tannins, saponins, steroids and terpenoids. P. longifolia extract contained alkaloids, flavonoids, tannins and reducing sugars. The S. mombin extract had significantly higher total phenol content, while the total flavoniod and proanthocyanidin content were significantly higher in the P. longifolia extract. The S. mombin extract had better antioxidant activities as evidenced by the lower IC 50 values for DPPH radical scavenging, a higher FRAP value and a higher inhibition of lipid peroxidation in vitro. The results suggest that the extracts of S. mombin and P. longifolia leaves possess moderate antioxidant activities, which may be of nutraceutical and pharmaceutical importance.