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To evaluate the antioxidant potential of less valued green leafy vegetables of Bangladesh, the methanolic extracts of Alternanthera sessilis, A. philoxeroides, A. paronychioides, Glinus oppositifolius and Portulaca oleracea were subjected to assay for total phenolic content, total flavonoid content and DPPH free radicle scavenging activity. Among the studied materials, A. sessilis showed the highest phenolic and flavonoid content. However, G. oppositifolius presented the lowest phenolic content (14.53 ± 0.48 mg of GAE/g of sample) and P. oleracea exhibited minimum (7.005 ± 0.25 mg of RUE/g of sample) flavonoid content. DPPH radical scavenging activity was found to increase with increase in the concentration of each individual material. A. philoxiroides (IC50 = 6.07 ± 0.27 μg/ml) was found as the most active in DPPH radical percentage inhibition, which was followed by A. sessilis (IC50 = 7.17 ± 0.67 μg/ml). Interestingly, A. paronychioides, in spite of having good amount of total phenolic and flavonoid content, showed less DPPH scavenging activity. No linear relationship was found to exist in case of the total phenolic, flavonoid content and DPPH scavenging activity among G. oppositifolius, P. oleracea and A. paronychioides. The results from different methods may differ substantially because each complex chemical reaction generates unique values. However, all the five plants exhibited creditable antioxidant activity and thus consumption of these vegetables may play important role in combating oxidative stresses and thereby help in retaining good health. Introduction Free radicals are continuously produced in human body and they are important for the preservation of normal physiological functions (Singal and Krishenbaum 1990). Oxidative stress is a condition in which there is an accelerated production of reactive oxygen species (ROS) and reduced levels of antioxidant system resulting in cell damage leading to the pathogenesis of a variety of human diseases (Frei 1994). Though humans and other organisms have antioxidant defenses (enzymes, such as superoxide dismutase and catalase, or compounds such as ascorbic acid, tocopherols and glutathione) and repair systems that have evolved to guard them against oxidative damages, these systems are inadequate to totally defend the damage (Simic 1998, Mau et al. 2004). In present times, it is believed that the regular consumption of dietary antioxidants may reduce the risk of several serious diseases. Fruits and vegetables contain a wide variety of biologically active, non-nutritive compounds known as phytochemicals. These phytochemicals impart health benefits beyond basic nutrition. Moreover, WHO (2002) reported that 25% of herbal drugs in modern pharmacopeia are plant based and several synthetic drugs are manufactured by using chemical substances isolated from plants. In a developing country, like Bangladesh where about 80% of the people are from rural areas and dependent upon ethno botanical knowledge, the search for potential plant species and their proper validation for consumption are of great importance. Green leafy vegetables are rich sources of many nutrients and form a major category of vegetable groups that have been designated as ‘nature’s anti-aging wonders’. Diverse green leafy vegetables are consumed in different parts of Bangladesh of which some are common throughout the country and cultivated commercially (e.g. red amaranth, leaf amaranth, basella, spinach etc.). However, a number of other leafy vegetables are consumed by rural as well urban *Author for correspondence: <kishwar.botany@du.ac.bd>. 954 SHETHI AND UDDIN people which are commercially less valued in spite of their occurrence throughout the country. Ethno medicinal reports (Uddin et al. 2015) on such plants indicate their food value and accountability to commercialize those vegetables. Although ethno botanical studies have been carrying out to document existing knowledge on plants from people in different districts of Bangladesh, fewer attempts have been initiated yet to validate that knowledge through in vitro analyses. During antioxidant activity study, Djordjevic et al. 2011 placed focus on determination of plant derived polyphenols because phenolic compounds act as radical scavengers, reducing agents and chelators of metal ions. According to Frankel 1995, flavonoids a group of polyphenolic compounds with known properties, which include free radical scavenging, inhibition of hydrolytic and oxidative enzymes and antiinflammatory actions, might be considered as a part of antioxidant activity determination. The DPPH radical has been widely used to evaluate the free radicals scavenging ability of various natural products and has been accepted as a model compound for free radicals originating in lipids (Porto et al. 2000). Though several research works have been carried out on the antioxidant capacity of Alternanthera sessilis, A. philoxiroides, Glinus oppositifolius and Portulaca oleracea separately (Asok et al. 2009, Erkan 2012, Ho et al. 2012, Uddin et al. 2012, Chinmayee et al. 2013, Vasincu et al. 2014), no works have been reported on A. paronychioides so far. Besides, this is a first attempt to compare among five commercially under rated but common ethnic green vegetables from Bangladesh in regard to their potential antioxidant context. Therefore, the present work was designed to collect the above mentioned five samples from the study area and subjected to determine amount of total phenolic and flavonoid content and DPPH free radical scavenging activity. Materials and Methods Five trivialized species of leafy vegetables which are available throughout the country and occasionally sold in street markets of Dhaka city were selected for the biochemical analyses in order to determine their potential antioxidant activity. The species for the present study include Helencha (Alternanthera philoxeroides (Mart.) Griseb.), Sechi (A. sessilis (L.) R.Br. ex DC.), Putishak (A. paronychioides A. St. Hil), Gima (Glinus oppositifolius (L.) Aug. DC.) and Nuinna (Portulaca oleracea L.) (Fig. 1). All the materials were collected form Abdullahpur, Keranigonj, Dhaka and authenticated by the taxonomists of Dhaka University Salar Khan Herbarium, Department of Botany, University of Dhaka. Except rotary evaporation which was conducted in Center for Advanced Research in Sciences (CARS), University of Dhaka all the experiments were carried out in the Plant Physiology, Nutrition and Plant Biochemistry Laboratory, Department of Botany, University of Dhaka. Edible portion i.e. leaves were used for the experimental study (fresh weight 500 g for each material) and cleaned properly with distilled water, dried in room temperature (around 25o C) under shed for 3 days and oven dried at 50o C for 3 days before powdered in a grinder machine. The scientific names, local names, English names, family names, parts used and voucher specimen numbers are presented in Table 1. Powdered plant materials were kept in air tight container in dark and cool place. About 25 g of powdered sample from each plant material was extracted with 300 ml of 99% methanol in an orbital shaker at 180 rpm for 48 hrs at 25o C. The extracts were filtered using Rotilabo®round filters, type 601A (125 mm) and concentrated in a rotary evaporator at around 40o C. Per cent recovery of the concentrated extracts of 5 plant materials was calculated as follows and shown in Table 2. ANTIOXIDANT POTENTIAL OF FIVE COMMERCIALLY LESS VALUED LEAFY VEGETABLES 955

Antioxidant potential of five commercially less valued leafy vegetables from Bangladesh