Assessments of Minerals, Total Phenolic, and Flavonoids contents, and Antioxidant activities of Legumes from Gondar, Ethiopia

Abstract

Legumes are one of the most widely grown crops in the world and they are a good source of minerals and trace elements, bioactive phytochemicals, and proteins, and contain low-fat contents. This study determined minerals (Fe, Cu, Zn, Mn, and Ni), total phenolic contents (TPC), total flavonoid contents (TFC), and antioxidant activities (AOA) in four legume species (chickpeas, beans, peas, and lentils) with cover, without cover, after cooked, and their cover from a commercial market in Gondar, Ethiopia. For mineral analysis, 1 g of powdered legume samples was digested with an optimum conditions of 8 mL of HNO3 and HClO4 mixture (5:3, v/v ratio) at 200 °C for 50 minutes and analyzed using Flame Atomic Absorption Spectrophotometer (FAAS). Aqueous methanol (80%) was an extraction solvent for TPC, TFC, and AOA analysis in legume samples shaking for 48 hours at 200 rpm with a 1:10 sample-to-solvent ratio. From the result, the concentrations (µg/g) of minerals in legumes with cover ranged from 67.46 to 100.79 for Fe, 8.75 to 15.60 for Cu, 27.18 to 40.70 for Zn, 2.39 to 18.78 for Mn, and 21.58 to 37.50 for Ni. Minerals like Fe, Zn, and Ni in lentils, while Cu and Mn in chickpeas were highly detected. However, Fe in beans, Cu in lentils, and Zn, Mn, and Ni in peas were less detected. Moreover, levels of metals in legumes with cover > without cover > their peels, this is due to the cumulative effects of cover and seed of legumes. Based on the overall mean concentrations of minerals in legume samples were sequenced as: Fe > Zn > Ni > Cu > Mn. The total phenolic contents (in mg GAE/g) showed 0.853 to 1.77, 0.027 to 1.86, 1.004 to 2.016, and 3.29 to 4.05 for legumes without peal, with peal, after cooked, and their peals, respectively. High phenolic content was found in legumes after being cooked next to their peels, indicating cooking of legumes before eating giving health benefits. Similarly, the total flavonoid contents (in mg QE/g) ranged from 0.27 to 0.682, 0.22 to 0.89, 0.27 to 0.92, and 1.41 to 3.49, respectively. The inhibition concentration (in mg/mL) at 50% (IC50) of legumes ranged from 1.509 to 2.055, and the IC50 value of ascorbic acid was 1.017 mg/mL. This showed IC50 values of legumes near to the standard ascorbic acid, indicating potent antioxidant activities. The one-way ANOVA test showed there was a significant difference (p <0.05) between the species and their process at a 95 % confidence interval for all analyses. Keywords: Minerals, Legumes, Total phenolic contents, total flavonoid contents, Antioxidant