FIGURE 8.3 Tetraene alkamide levels and proportions in different parts of E. purpurea. (From Perry, N.B., et al., 1997, Planta Med., 63: 58-62. With permission.)
Wills (2000a) found that alkamide levels in E. purpurea roots significantly decreased from the preflowering stage to senescence at both of their sites.
The data from other aspects of these three studies have been combined in Figure 8.4 through Figure 8.6 and show some parallel trends. Both of the studies on cichoric acid in E. purpurea roots (Figure 8.4) showed significant differences among sites, and significant decreases at some sites as tops senesced. However, the levels of echinacoside in E. angustifolia roots did not change significantly (Berti et al., 2002). The levels of cichoric acid in E. purpurea tops (Figure 8.5) showed similar effects with significant differences between sites and significant decreases at some sites as tops senesced. One of the symptoms of senescence is browning of leaves, stems, and flower heads, which could involve enzymatic oxidation of cichoric acid (Kreis et al., 2000). There are significant correlations between cichoric acid levels in tops and roots for both the Australian and New Zealand data, suggesting some sort of translocation among plant parts.
Concentrations of alkamides in E. purpurea tops showed significant differences between sites and harvest dates for the New Zealand data (Figure 8.6). This could be ascribed to different flowering times at the various sites, with flowers known to have higher levels of alkamides than leaves or stems (Figure 8.3). However, the late season drop in alkamide levels requires a drop in flower alkamide levels that was not found by Stuart and Wills (2000a) in their senescent flowers. The Australian data therefore showed a different pattern of alkamide variation in E. purpurea tops (Figure 8.6)
Clearly, cultivation factors, both growing site and harvest stage, can have major effects on alkamide and phenolic quality indicator levels in E. purpurea and E. angustifolia, and therefore probably also in E. pallida. Medicinal herb growers need to combine these results with data on yields of plant material to enable them to select the optimum harvest time to maximize quality and economic returns.
Companies in the medicinal herb industry set their own quantitative standards for purchasing Echinacea plant material but these vary widely and are considered commercial secrets. The only published quantitative standards are proposed by U.S. Pharmacopeia (2000): for E. angustifolia roots, > 0.5% total phenolics and > 0.075% tetraene alkamides. Based on the data presented above, it should be possible to optimize cultivation and harvest to meet the following more challenging standards for high-quality Echinacea:
• E. angustifolia roots: > 1.0% echinacoside, > 0.5% tetraene alkamides
• E. purpurea roots: > 1.5% cichoric acid, > 0.2% tetraene alkamides
• E. purpurea tops: > 1.5% cichoric acid, > 0.1% tetraene alkamides
However, the levels of these quality indicator compounds in the products that reach consumers, be they encapsulated plant material or extracts, will depend on postharvest handling and processing operations.
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