Abstract
Launea taraxacifolia and Crassocephalum rubens are among many wild, underutilized and under cultivated vegetables in Nigeria that are at risk of extinction. Total flavonoid contents (TFC), total phenolic contents (TPC), and antioxidant activities of different concentrations (1-5 mg ml -1 ) were evaluated; using in vitro assays to assess the scavenging properties of 2, 2-diphenyl-1-picryl hydrazyl (DPPHRSP), nitric oxide (NORSP) and hydroxyl (OHRSP). Phenolic profiles of the alcoholic extracts were characterized using high-performance liquid chromatography techniques. The results revealed higher TFC (mg/100g RE) in aqueous (6.06± 0.02-78.79±0.01) than alcohol extracts (with methanol 0.93±0.01—12.73±0.04, and with ethanol -0.85±0.01-- 7.70±0.03). In a similar trend, OHRSP (%) was higher in aqueous extracts (40.83±0.10--91.74±0.19) than alcoholic extracts (with methanol -11.67±0.3-- 30.83±0.06; and with ethanol -14.42±0.06- 40.27±0.05). TPC (mg/100g GAE) which was higher in alcoholic extracts (with methanol -21.48±0.01--133.20±0.16 and with ethanol -9.45±0.01--59.73±0.02) than aqueous extracts (14.83±0.01--52.64±0.03) was in agreement with the trend observed for NORSP (28.24±0.05-151.76±0.08 for methanolic extracts, 21.99±0.13--49.93±0.04 for ethanolic extracts and 38.47±0.11--86.15±0.05 for aqueous extracts). DPPHRSP was also higher in alcoholic extracts (methanolic -22.81±0.01-48.41±0.05 and ethanolic-- 14.53±0.01-62.68±0.07) than aqueous extracts (13.66±0.13--42.86±0.03). TFC, TPC and antioxidant activities showed concentration dependent increase and strong positive correlation with TFC (r= 0.926 – 0.997and r= 0.432 – 1.000) and TPC (r= 0.825 – 0.999 and r= 0.473 - 0.994) for L. taraxacifolia and C. rubens respectively. Caffeic acid, chlorogenic acid, ellagic acid, quercetin and kaempferol were identified as major phenolic components in the extracts. The vegetables have high antioxidant potential for promoting good health; which could be attributed to the identified phytochemicals in them.
Highlights
The antioxidant activity of fruits and vegetables is generally positively correlated with their content of polyphenols (Wang & Lin, 2000; Koffi, Sea, Dodehe, & Soro, 2010)
The percentage inhibition was plotted against the corresponding sample concentration (1-5 mg mL−1) and IC50 calculated from the graph equation
The results of this study clearly indicate that aqueous and alcoholic extracts of L. taraxacifolia and C. rubens possess significant in vitro antioxidant capacities
Summary
The antioxidant activity of fruits and vegetables is generally positively correlated with their content of polyphenols (Wang & Lin, 2000; Koffi, Sea, Dodehe, & Soro, 2010). The most effective antioxidants seem to be flavonoids and phenolic compounds of many plant raw materials, in fruits, vegetables, herbs and seeds as many studies have suggested (Kim, Tsao, Yang, & Cui, 2006; Adom & Liu, 2002). The leaf is used as a vegetable in some parts of South-Western Nigeria in West Africa where it is called efo yanrin and research has established its high nutritional and medicinal values (Adebisi, 2004) It is mostly collected from the wild and only cultivated to a limited extent for home use and for local markets; whereas, it is known only as a weed in many parts of Nigeria. The present study was aimed at investigating phenolic composition and antioxidant activities of the different concentrations of aqueous and alcoholic extracts of the leaves of the above mentioned vegetables
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