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by Rowland Laurence
March 2006
RIRDC Publication No 05/185 RIRDC Project No UT-34A
Executive Summary
This report describes preliminary
investigations into the production of four medicinal herbs in Tasmania.
The work reflects the increased global market demand for medicinal herbs in recent years and the interest of the industry stakeholder company in this project, Botanical Resources Australia, in the opportunity to supply plant material and extracts from Australia.
A proposal for the preliminary investigation of ten extractive herb species was considered by RIRDC in 2000, after which, the number of species to be investigated was reduced to four, these being evening primrose, astralagus, bilberry and stevia. Later discussions with an overseas consultant, regarding the poor marketing prospects for evening primrose at that time, led to a decision to discontinue evening primrose investigations and to include feverfew in the project work. The four species, astragalus, bilberry, feverfew and stevia are thus the subject of this report.
The work has attempted to supply information on the suitability of these species for commercial production in south-eastern Australia by providing evidence of their ability to grow in a local, temperate climate, together with an indication of their commercial potential through plant and extract yield. Project activities involved acquisition of genotypes, plant propagation, seasonal analyses of growth and analyses of extracts, where available. In addition, the project sought to supply additional market information to that available, by seeking information on market trends in Europe.
The roots of several astragalus species, but principally Astragalus membranaceus (Fisch.) Bunge and A. mongholicus Bunge (Radix astragali, huang-ch’i in China and hwanggi inKorea), are used in traditional Chinese medicine primarily as a tonic for the treatment of respiratory tract infections and against the common cold. However, therapeutic applications also exist in immune system enhancement and treatment of cardiovascular disease, through anti-hypertensive and vaso-dilatory effects, several of which are supported by clinical pharmacological data. These pharmacological effects are associated with several polysaccharides and saponins, principally, the triterpene saponins named astragalosides I-VII and isoastragalosides I and II. Antioxidant activity has also been reported. Several species, particularly, A.
gummifer, produce an edible gum exudate, gum tragacanth, which is one of the few permitted for pharmaceutical and food use. In the current work, analyses were restricted to Astragalosides I (the accepted reference standard), II and IV.
Astragalus membranaceus was easily established in the field and grew well. Field plantings also wintered well after a first season but less well after a second, and its persistence may require further study if aged roots are preferred in Asian markets. Yield of dried roots from a fifteen month-old crop was calculated to be 1328 kg per hectare. Levels of astragalosides determined in the current study were high compared to published data, with a mean value for Astragaloside I over three sites being 0.25 per cent of dried roots.
Data presented here also suggest that levels of astragalosides may increase with plant age, which may increase the attractiveness of further agronomic study to maximize extract yields.
Feverfew (Tanacetum parthenium (L.) Schulz-Bip. (previously Pyrethrum parthenium and Chrysanthemum parthenium), a member of the plant family Asteraceae, is a perennial herb used as an ornamental plant as well as for its medicinal value. The major active ingredients are sesquiterpene lactones, of which parthenolide is in major proportion and preparations are used to prevent migraine headaches, fever and arthritis. Parthenolide is present in leaves, flowering tops and seed but levels vary greatly with genotype and morphological characteristics, and with seasonal growth. The degradation of the active ingredient in storage and the wide range of concentrations present in commercial preparations may explain why the product’s effects are sometimes questioned.
The preliminary evaluation of feverfew carried out in this project has found that the species grows and winters very well in the local temperate climate. Parthenolide yields have been found to vary considerably with genotype, season and plant management. Parthenolide contents in the top-regrowth (approx. 200mm) after trimming plants of five genotypes varied between 3.6 and 25.5 mg per kg, providing calculated parthenolide yields of between 4.9 and 32.1 kg per hectare. Parthenolide contents of dried top-growth of un-trimmed plants of one genotype reduced from 7.1 to 2.9 mg per kg between October and February.
While the market for feverfew at the time of writing this report is well supplied, these encouraging results have convinced the industry stakeholder, BRA, to maintain feverfew plantings beyond the life of the current project.
Bilberry, Vaccinium myrtillus L., is one of some 150 species of Vaccinium, some of which, such as blueberry and cranberry, are widely cultivated for their berries. Bilberry is usually wild-harvested from cool-temperate forest under-storey at the present time. Fruit extracts of bilberry and other Vaccinium species are rich in flavonoids and their extracts exhibit high antioxidant activity which, in turn, can provide inhibition of some enzymatic effects of tumour promoting compounds. Levels and the range of such antioxidants in bilberry are about three times those found in blackcurrant. Vitamins, particularly A and C, are also present.
After a slow period of establishment for bilberry, field plantings in Tasmania have flowered and produced a few fruit in their third year of growth, which timing is consistent with its growth in native habitats.
Comparative measurements at two field sites have shown that plant growth at a high altitude site in Tasmania was more than 50 per cent greater over a growing season than that at a coastal, milder location.
Additionally, when flowering commenced in the third year of the plants’ growth, flower numbers were also more than 50 per cent greater at the high altitude site. Insufficient fruit was obtained in this work to investigate extracts and further study will be needed to determine the yield potential of harvested fruit and extract in the Tasmanian environment. Indeed, the growth and yield responses of bilberry to seasonal temperature and shading regimes need to be better determined. Solutions to likely problems in mechanical fruit harvesting also remain and any development will require input over the longer term.
Stevia rebaudiana Bertoni is native to Paraguay but has a wide climatological range, having been grown successfully from tropical to cool temperate locations. The leaves contain several natural sweeteners, diterpene glycosides, named steviosides and rebaudiosides. These glycosides are heat-stable and are not digested and thence have no calorific value as food, which attribute represents a strong market driver for stevia products in developed countries, where soft drinks with high calorific value are considered to be one factor in increasing levels of obesity and related disease. The product is traded globally, with Japan and some South American countries the major markets.
Stevia grew well in the North-west Tasmanian summer but some plant loss occurred over winter months, suggesting that annual sowings may be preferable. Yields of plant dry matter, of which about fifty per cent was extractable leaf, were calculated to be 4834 kg per ha at one coastal site and 6317 kg per ha at an inland site experiencing high summer temperatures. Levels of stevioside and rebaudioside were generally consistent with published levels, particularly as some genotypes assessed were unimproved. Across ten genotypes, levels of stevioside varied between 10.2 and 2.9 per cent of leaf dry weight, and levels of rebaudioside varied between 10.6 and 0.6 per cent of leaf dry weight, with the influence also of site and season.
A current detraction to the development of stevia is the banning of the importation of stevia products by the European Union, its restriction in the USA and the possibility of its review in Japan, a major market, due to questions of safe use. While some food products containing stevioside as a dietary supplement have been marketed in Australia, imports of stevia products into Australia have recently been restricted. For these reasons, BRA has decided not to pursue the development of this species at this time.
Steady growth of markets in Europe is predicted but significant structural change is likely within the constituent countries of the expanding European Union, which will be driven by new EU directives being prepared. These directives attempt to bring tighter controls to the herbal medicine and supplement markets, to give a positive assurance of safety and enhance free trade. These issues are discussed and a commissioned report on the European market situation is provided.
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