Antioxidant properties of extracts from indigenous vegetables consumed in Kenya and Malawi

Abstract

Excessive production of free radicals than the human body antioxidant system effectively terminate or retard can negatively impacts on health by causing several oxidative stress related diseases including cancer, hypertension, heart diseases and diabetes. Synthetic antioxidant to supplements to the body antioxidant system has been observed not to be safe. Plant antioxidant sources such as fruits, mushrooms, tea and exotic vegetables as possible natural antioxidant sources have been extensively studied. However, there is limited knowledge on antioxidant properties of indigenous vegetables of Africa. This study qualitatively and quantitatively determined the antioxidant phytochemicals and evaluated the in vitro antioxidant properties of extracts from Ipomoea batatas, Amaranthus spinosus, Manihot esculenta, Urtica ferox, Solanum psedocapsicum, Corchorus olitorius and Cleome gynandra consumed in Kenya and Malawi. The levels of antioxidant phytochemicals and properties were estimated spectophotometrically while energy dispenser X-ray fluorescence (EDXF) analytical method was used to de-t.erm.ine the antioxidant trace elements in the i extracts. The hot water extracts of S. psedocapsicum had the highest(8.31±0.2 g/lOOg) dry extract yield among the extracts. Ethanol extracts had significantly (t-test, p<0.05) higher quantities of total phenol, carotenoids and lycopene while hot water extracts had high , . . quantities of ascorbic acid but no significant difference in flavonoid content was observed between the two extracts. The hot water extracts of M esculenta had the highest ascorbic acid (2.59±0.06 mg/g) and flavonoids (156'.43±0.02 mg/g) while the highest total phenol (475.88±0.02 mg/g) and lycopene (0. 13±0.02 mg/g) were detected in the ethanol extracts of I batatas and C. gynandria, respectively. Highest carotenoids (0.78±0.02 mg/g) content among both extracts was found inethanol extracts of B. oleracea. The abundant trace elements in the vegetable extracts W0f{: Iron, Copper, Manganese, Zinc and Potassium with high quantities of Iron (560.17±O.6· mg/g) in extracts of S. psedocapsicum, Copper (81.81±07 mg/g) and Zinc (66.58±03 mg/g) in C. gynandria, Manganese (72.32± 07) in C. olitorus and Potassium (50.98±0.3) in I batatas. This study also revealed concentration-dependent ability and species-specific antioxidant properties among the extracts. Based on EC 50 values, the hot water extracts were more effective than ethanolic extracts in almost all antioxidant properties assayed. Among the hot water extracts, 1 batatas, M esculenta, A. spinosus, S. pseudocapsicum, Colitorius, gynandra and U ferox were more effective in scavenging DPPH radicals with EC50 values (mg/ml) of 0.59, 0.69, 0.71, 0.72, 0.75, 0.79 and 0.82, respectively while extracts of B .oleracea, S. pseudocapsicum, M esculenta and C. olitorius were more effective in scavenging hydroxyl radicals with EC50 values of 0.56, 0.64, 0.64 and 0.67, respectively. The extracts of M esculanta and S. pseudocapsicum were more effective in scavenging superoxide anion radicals with EC50 values (mg/ml) of 0.91 and 1.34; respectively while olitorius and M esculenta extracts were more effective in reducing ability with EC50 values (mg/ml) of 0.59 and 1.39, respectively. Among the ethanolic extracts, A. spinosus, 1 batatas and M esculenta were more effective in scavenging DPPH radicals with EC50 values (mg/ml) of 0.56, 0.58 and 0.70, respectively while B. oleracea, S. pseudocapsicum and C. olitorius extracts were more effective in scavenging hydroxyl radicals with EC50 values (mg/ml) of 0.73, 0.83 and 0.84, respectively. The extracts of C. gynandra were more effective in scavenging superoxide anion radicals with EC50 value of 11.04 with extracts of A. spinosus being more effectlve in reducing ability w:th EC50 value of 0.99. The hot water extracts of M esculenta were the most potent extracts as they contained most phytochemicals determined and were more effective in reducing power and scavenging most radicals assayed. These findings revealed that these vegetables contain high quantities of antioxidant phytochemical and mineral elements. They were also shown to be more effective in reducing power and scavenging DPPH, hydroxyl, superoxide anion radicals with individual vegetable species showing variations irrtheir capacities towards them. They should therefore be utilized as easily accessible, rich natural antioxidant sources and thus their consumption should be highly encouraged for health benefit notably the antioxidant effect.