Purslane


Purslane ( Portulaca oleracea L.) is a member of the Portulacaceae family, consisting of more than 120 species, which are made up of common flowering plants, succulent herb and shrubs.

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Purslane growing at Lincoln University

Use of Purslane

Purslane has been extensively reported / documented world wide to have a medicinal use and is commonly used by ethnic communities to cure aliments. There are several key reoccurring medicinal uses, for treatment of Nephrolithiasis, blood related aliments and as a muscular relaxant.There is also extensive non medicinal use of purslane as general eating herb, as in a salad. It forms part of a normal diet of green leafy vegetables.
It has been called the “vegetable for long life” in Chinese folklore (Xu, 2006).
Clearly there is un-scientific evidence that may suggest purslane has beneficial medicinal qualities and positive nutritional / dietary factors as well.
By closely scrutinising the macro and micro composition of the plant, there is compositional evidence that gives supports to some of the medicinal claims.

Vitamins and Minerals


The mineral content has been determined by several researchers. Bianco et al. (1998) reports levels of 9 , 503, 56 and 181 mg/100 g FW of Na, K, Mg and Ca , respectively. The levels of K and Mg are comparable to other green vegetables, however the Ca level is more comparable to milk than a green vegetable.
Carotenoids (vitamin A) have also been determined in purslane. Raju (2007) reports 91.03 mg of total carotenoids/100 g dry weight of leaf material. This is a moderate amount compared to the other green leafy vegetables they surveyed, which ranged from 10.32 to 449.90 mg total carotenoids/100g dry weight. Of importance nutritionally is the vitamin A activity. This was determined to be 4,508 activity units for purslane, compared to a range of 1,246 to 19,101 vitamin A activity units for other green leafy vegetables.
Ascorbic acid (vitamin C) has been determined on the fresh leaves of purslane by Sree ramulu et al. (1983), reporting levels of 46.8 mg vitamin C/100 g fresh weight, this is comparable to an orange, at 50 mg vitamin C /100 g fresh weight.

Phenolics


Phenolics include a large range and diversity of compounds in plants that are responsible for features such as colour and taste. There are certain groups of phenolic compounds found in plants that are purported to have beneficial effects with regards to human health and nutrition.

Flavonoids are commonly referred to as bioflavonoids, they are a class of plant secondary metabolites, known mostly for their antioxidant activity and other secondary effects in the body that impart positive medicinal benefits. Huang et al. (2007) identified three flavonoids in purslane, isorhamnetin, quercetin and kaempferol. More than 29 components were found, however only three were able to be confirmed by HPLC-MS and matching with reference compounds.
Using CE-ECD, Xu et al. (2006), did not detect isorhamnetin or quercetin in the leaves, stem or whole plant. Kaempferol was not clearly separated in the leaves or stem, but was able to determined in the whole plant. Apigenin was detected in the leaf, stem and whole plant, this flavonoid was not identified by Huang et al. (2007). Clearly there is variation in the type and amount of flavonoids present in purslane, with many being unidentified and there significance unknown.

Carbohydrates


Purslane has been noted to produce a viscous mucilage. Two main fractions have been identified, “cord filaments” making up 80 -90% and resin fines the remaining. Resin fines are defined as low acid sugars and include compounds such as arabinogalactan and D-xylose. Cord filaments are rich in galacturonic acid and have a high specific gravity.
With a high content of water-soluble polysaccharides purslane could be an alternative to gum Arabic, commonly used as a food stabilizer.
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Purslane Leaves

Alkaloids


Alkaloids are a large group of compounds characterised in common by having nitrogen atoms in their structure. Many alkaloids are toxic or have pharmacological properties, for example caffeine.
Xiang et al. (2005) has isolated five alkaloids from purslane, called oleraceins A, B, C, D and E. More recently Xing et al. (2008) used LC/MS/MS to screen for and identify cylo-dopa and diketopiperazine alkaloids. Five cylo-dopa and seven diketopiperazine alkaloids were identified in this study.
The presence of dopamine and noraddrenaline (catecholamines) have been determined in purslane as well. Amounts of 0.15 and 0.25% of noraddrenaline and dopamine, respectively have been determined by Zhang et al. (2002).

Lipids


Purslane is well documented to have high levels if lipid, for a green leafy plant. The major fatty is α-linolenic acid (omgea-3 fatty acid, 47.6%) (Almazan et al. 1998).
Levels of α-linolenic acid are reported to be in the range of 97-160 mg/100 g FW (Liu et al. (2000); Palaniswamy et al. (2001)). However these are five times lower than values reported by Simopoulos et al. (1992). This difference could be explained by differences in cultivar and growing conditions but obviously needs further investigation.

Antioxidant Capacity


Measurements of several different types of antioxidant capacity of purslane have been done by several researchers. Abab et al. (2006) used the ferric thiocyanate method, thiobarbituric acid method, DPPH and nitric oxide inhibitory activity assay to determine the antioxidant capacity and Lim and Quah (2007) used total phenols, DPPH, FRAP and β-carotene bleaching assay to determine antioxidant activity in purslane samples.
There is no one universally accepted measurement of antioxidant capacity used to make an objective evaluation and it is hard to compare one set of values to another. This can be seen when comparing DPPH values from the results of Abas et al. (2006), of 70.4 IC50 µg/ml to Lim & Quah (2207), of 3.41 IC50 mg/ml. A factor of x20 difference in values, this could be explained by cultivar differences and growing environment, but this is probably unlikely. Therefore it is of more relevant in this case to compare the antioxidant values obtained in context, of the respective studies.
Abas et al. (2006) studied traditional Malay vegetables and places purslane DPPH activity in the mid-range, with a lowest value recorded being 15.3 and the highest 190 IC50 µg/ml.
Lim & Quah (2007) surveyed six cultivars of purslane and found ornamental varieties gave higher total phenol and antioxidant activities compared to common Portulaca olerecea.

With the combination of many positive scientifically determined compositional factors, omega-3 oil content, high antioxidant capacity, alkaloid content, flavonoid content, carotenoids, ascorbic acid, high mineral content and presence of catecholamines, purslane would certainly appear to be the wonder plant/herb. This is in addition to the empirical evidence from across the globe and cultures using purslane to treat aliments that are similar in nature.
In conclusion, the promotion of cultivating and the production of new food or nutraceutical products from purslane would certainly warrant investigation.