Common purslane is a member of the Portulacaceae family, which consists of more than 120 species of often succulent herbs and shrubs. It is an annual plant, which grows in many areas of the world, including Mediterranean countries, Africa, and Asia. Common purslane has a long history of use for human food, animal feed, and medicinal purposes (Liu et al., 2000; Salisbury, 1961). However, interest in cultivating common purslane as a food crop has been stimulated since its identification as a rich source of bioprotective nutrients: fatty acid ω3, antioxidants, vitamins, and essential amino acids (Miller et al., 1984; Simopoulos and Salem, 1986; Simopoulos et al., 1992), glutathione, and alpha-tocopherol (Liu et al., 2000; Palaniswamy et al., 2001, 2002; Simopoulos, 1991, 2001; Simopoulos et al., 1992), together with the catecholamines, as noradrenaline and dopamine (Chen et al., 2003).
Recent studies have shown that the consumption of these substances helps reduce the incidence of coronary heart disease; they also have anticarcinogenic (Chen et al., 2003; Palaniswamy et al., 2000; Simopoulos, 1991, 2001), analgesic and antiinflammatory (Chan et al., 2000; Simopoulos 1999a, 1999b; Simopoulos et al., 1992), diuretic, antiascorbic and antipyretic (Chan et al., 2000; Simopoulos et al., 1995), bronchodilatory (Malek et al., 2004), and neuropharmacologic properties (Radhakrishnan et al., 2001).
Common purslane has been listed as a “commercially cultivated vegetable of the world” (Kays and Dias, 1995). Some varieties such as Golden Gerber, Garden (The Netherlands), and Golden (England) are grown as such; however, in many parts of the world, it is regarded as a weed (Mitich, 1997; Whitson, 2001). Common purslane is now cultivated only on a small scale in France and Holland. In the U.S., common purslane is a minor crop because of its use in ethnic cooking and its reported health benefits. However, this species is now receiving attention for cultivation by the U.S. Department of Agriculture as part of their effort to modify the “Western” diet with the increased intake of fresh fruits and vegetables. Indeed, several internal reports of the University of Florida and the University of California describe common purslane as a succulent herb with good nutritional and health properties, whereas in recent years, scientists at the University of Connecticut have investigated several factors that might affect the nutritional content of the same plant, common purslane (Palaniswamy et al., 2000, 2001, 2002, 2004). However, very little is known about culture systems, substrates, and irrigation systems suitable for its production as a commercial food crop. It is therefore important to carry out studies to determine the most suitable techniques for growing this species, which should be directed at its production and presentation as a ready-to-eat or ready-to-cook small leafy vegetable.
Among hydroponic methods used to produce baby-leaf vegetables, the “floating system” is the easiest and cheapest (Gonnella et al., 2003). This system shortens the cultivation cycle compared with soil-based culture and is very interesting for growers because of the low installation and manpower costs; weeds are avoided and harvesting is straightforward. Plants can be grown at high densities and the resulting products (leaf vegetables) are clean and ready to be packed. In a comparison of the yields of common purslane obtained in earth and in a floating system, Graifenberg et al. (2003) found similar values but that the growth cycle was considerably shorter in the floating system. It is therefore worth looking at this technique in greater depth. Our own experiments led to the rejection of growing common purslane in soil to obtain a baby-leaf plant resulting from the rapid formation of mucilage in leaves and stem and the difficulty of harvesting (unpublished data).
On the other hand, in floating systems, important parameters such as the nitrates that tend to accumulate in some species, for example, rocket (Eruca vesicaria) (Elia et al., 2001; Santamaria and Elia, 1997), can be controlled.
Although different substrates and mixtures are commercially available for use in floating systems (Carrasco et al., 2000, 2003), it is not clear which is the best for obtaining high-quality common purslane plants (adequate for consumption as baby-leaf and also with high fatty acid contents). Given that one of the main reasons for growing this species is its high fatty acid content, it would seem essential to take into account the effect of different substrates on this parameter.
There are, then, two objectives in this study: 1) to determine the most suitable substrate for a floating system designed to grow common purslane for retail as a baby-leaf vegetable and 2) to assess the possible influence of the substrate used on the fatty acid content.
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