Nutritive value, mineral composition, phytochemical constituents, and antioxidant properties of freshly collected Justicia secunda Vahl leaves from two locations in Oyo State, Nigeria

Abstract

Justicia secunda Vahl is an important medicinal plant in African ethnomedicine, where it is traditionally used in the management of anaemia, sickle cell disease, and inflammatory conditions. Its bioactive potential has been linked to its phytochemical composition. Because the phytochemical, nutritional, and antioxidant profiles of medicinal plants can vary with geographical location and prevailing environmental conditions, this study compared the proximate, mineral, phytochemical, and antioxidant properties of freshly collected J. secunda leaves from Iseyin and Oyo Town, Oyo State, Nigeria, designated JSVI and JSVE, respectively. The samples were authenticated, air-dried, and analysed using standard Association of Official Analytical Chemists (AOAC) methods and validated in vitro assays. Proximate analysis showed similar protein contents in JSVI (18.76 pm 0.04%) and JSVE (18.17 pm 0.04%). JSVE had higher moisture (8.91 pm 0.12%), ash (4.06 pm 0.08%), and crude fibre (19.08 pm 0.54%) contents, whereas JSVI had higher carbohydrate (51.81 pm 0.78%) and gross energy (292.81 kcal/100 g) contents. Both samples had comparable qualitative phytochemical profiles and tested positive for alkaloids, tannins, saponins, steroids, phlobatannins, flavonoids, and cardiac glycosides. Quantitatively, JSVI contained more phenolics (196.97 pm 3.03 mg/100 g), flavonoids (64.89 pm 4.68 mg/100 g), saponins (2.28 pm 0.44 mg/100 g), and cardiac glycosides (46.35 pm 3.34 mg/100 g) than JSVE, whereas JSVE had marginally more tannins. Mineral analysis showed higher potassium, sodium, iron, zinc, manganese, and copper concentrations in JSVI, while JSVE had higher magnesium and phosphorus concentrations; both samples supplied only a small fraction of the cited adult dietary reference values for most minerals. JSVI also showed greater 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity, ferric-reducing antioxidant power (FRAP), and 2,2^prime-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical-scavenging activity than JSVE, consistent with its higher phenolic and flavonoid contents. These findings indicate that geographical and environmental variation measurably influences the nutritive and phytochemical composition of J. secunda and that the Iseyin sample may possess a comparatively stronger antioxidant profile than the Oyo Town sample. Further in vivo and toxicological studies are recommended to substantiate therapeutic inferences drawn from these in vitro observations.