Medicinal plants have bioactive compounds which are used for curing of various human diseases and also play an important role in healing of different disease. Terpenoids, flavonoids, alkaloids, tannins are some of bioactive compounds present in different parts of medicinal plants. Qualitative identification of bioactive compounds and antioxidant activity determination of crude extracts of the leaves of four different medicinal plants (Cordia africanaLam, Croton macrostachyus Hochst, Vernonia amygdalina Del. and Justicia schimperiana T.Anders.) based on peroxide value (POV) method were carried out in this study. For the phytochemical screening test, the results confirmed the presence of polyphenols, tannins, alkaloids, steroids and anthraquinons in all plants leave extracts, however flavonoids, glycosides and phlobatannins were absent. In case of peroxide value (POV) determination, the lowest value were recorded in crude extracts of Cordia africana Lam leaves (24 meq/kg ) and the highest value were observed in Justica Schimperiana leaves extracts (101 meq/kg ) in the 1st treatment. In the 4th treatment, Schimperiana T. Anders had lowest antioxidant activities [highest POV (290 meq/kg)] and C. Africana had the highest antioxidant activities [lowest POV (88meq/kg)]. The study also showed that temperature variations had its own influence on peroxide value. As the temperature of the system increased, the peroxide content of sample treated with leave extracts of plants also increased, however the degree of increment vary within different temperature range (30 to 50°C, 50 to 75°C and 75 to 100°C). In all temperatures, the peroxide production of niger seed oil containing plants leave extracts were less than oil free from extracts. The data generally indicates that the POV of plants leave extract showed antioxidant activity due to the presence of some Phytochemical (plyphenols, tannins, glycosides) present in plants leave extracts.
Key words: Medicinal plants, phytochemical, antioxidant, peroxide value (POV).
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