INVESTIGATION OF ELEMENTS, SUGARS, TOTAL PHENOLICS,TOTAL FLAVONOIDS AND ANTIOXIDANT ACTIVITY OF PLECTRANTHUS EDULIS(ETHIOPIAN POTATO) TUBERS VARIETY

<strong>ABSTRACT</strong>: Plectranthus edulis is an indigenous annual tuber crop grown widely in the central, southern, western, northwestern and southwestern parts of Ethiopia. Despite its consumptions and popularity in some regions of the country, its chemical composition is not investigated in depth and there is paucity of information about the nutrition content and little is known about its starch and mineral composition in single variety. This study was aimed to analyze the selected mineral nutrients, sugars, total phenolic content,total flavonoids contentand antioxidant activities of five varieties of P.edulis samples collected from Kemba and Bonke Woreda, in Gamo Zone, SNNPR; Ethiopa. Samples were analyzed for eleven elements (Ca, Mg, Fe, Zn, Cu, Mn, Co, Cr Ni, Cd and Pb), sugars (fructose, glucose, sucrose and maltose), total phenolics and flavonoids, and antioxidant activity by Inductively Coupled Plasma-Optical Emission Spectrometry, High Performance Liquid Chromatography-Refractive Index Detector, Spectrophotometer, and DPPH assay respectively. 0.5 g of freeze-dried sample was digested using 4 mL of (69–72%) HNO3 and 4 mL of (70%) HClO4, for 2 h at variable temperature (100–1800C) with previously optimized procedures for element determination.1g of freeze-dried sample was extracted in 25 mL of 100 % methanol and 80% aq. methanol for total phenolics, total flavonoids and antioxidant activity by using ultrasonic cleaning machine at 300C for 1hr. The mean concentration range (in mg/Kg 1 ) of each metal in five P. edulis local varieties were Mg (999–1271), Ca (856–1210), Fe (248 412), Mn (34.1–46.0), Zn (17.9–35.9), Cu (17.5–42.2), Cr (0.70–11.8) and Ni (1.60–10.8). The results of the studied metals in the five samples showed the ability of P. edulis tuber to accumulate high amounts of both major and traceelements. The most abundant majorelements analyzed were Mg and Ca. The content of Fe in the P. edulis tubers was the predominant among the tested traceelements. On the other hand, Co, Cd and Pb were not detected in all the investigated P. edulis tubers varieties. The determined total phenolics content was ranged from 10.9–15.2 mg/g for 100% methanol and 14.4–23.3 mg/g for 80% aq. methanol. The total flavonoids content was ranged 3.38–5.31 mg/g for 100% methanol and 6.62–8.37 mg/g for 80% aq. methanol. The antioxidant activity of five P. edulis varieties of two solvents were ranged from 9.72–25.0 mg ascorbic acid equivalent/gramof sample dry weight.Correlations of total phenolics content and total flavonoids content with antioxidant activity were investigated and the correlation was strong and positive for both total phenolics content of 100% methanol, total x flavonoids content of 100% methanol and total flavonoids content of 80% aq. methanol, but weakly positive for total phenolics content of 80% methanol. The results showed that extraction solvents had a significant impact on the total phenolics content, total flavonoids conent and antioxidant activity, and the 80% aq. methanol extract had higher antioxidant activity compared with the 100% methanol extract. Furthermore, sugar compositions were determined and the method was characterized by linearity, precision, accuracy. The P. edulis vaieties showed the presence of glucose (15.1–21.1g/100g) and fructose (3.34–4.10 g/100g), and sucrose and maltose were not detected in all P. edulis tuber varieties.Generally the quantities of all investigated parameters were affected by varirties of P. edulis tubers and siginificantly different between some varieties.