Abstract
The present study focuses on the phytochemical screening, antimicrobial and antioxidant activities of the leaves extracts of Guava (Psidium guava Linn), belonging to the Myrtaceae family. The plant samples were collected from Tajura, eastern part of Tripoli in Libya. Aqueous and methanol extracts of dried and ground plant materials were prepared. Qualitative phytochemical screening of the extracts showed positive tannins, flavonoids, alkaloids, saponins, terpenes in varying proportions while alkaloids were the only exclusion in the methanolic extract. The strong positive result of flavonoids in both plant extracts motivated us to perform an individual extraction and test for flavonoids. The water, methanol crude extracts as well as flavonoids extract were effective against both Gram-positive and Gram-negative bacteria: Buscillis subtils, Staphylococcus aureus, Escherichia coli and Salmonella typhi, giving a range of 12-25 mm inhibition zone diameter. According to the minimum inhibitory concentration MIC results, flavonoids extract was the most effective against bacteria (with MICs of 2.5-5 mg/ml), followed by methanolic extracts (with MIC of 5.5-11 mg/ml). The water was found to be the least effective with MIC (12-15 mg/ml). Therefore, more investigation for antimicrobial properties of flavonoids extracts was carried out using bioautography method to specify the biologically active separated spots (against B. sub) on thin layer chromatograms from flavonoids extracts. Thin Layer-Bioautographic application showed the presence of five biologically active spots (S1-S5) with Rf values of 0.46-0.8. These results could be a preliminary orientation concerning how many possible bioactive plant components need separation and identification. Total phenols were also determined in methanolic and aqueous extracts of Psidium guajava L. in order to assess their contribution to the antioxidant activity; both extracts (aqueous and methanolic) showed reasonably high content of polyphenols, 66.21 and 64.97 mg/g, respectively. Results generally suggest that Guava leaves are not only reliable natural sources of antimicrobials but also potential sources of phenolic antioxidants and hence could be nominated for future intensive studies.