Economic potential from Western Australian Acacia species: secondary plant products
David S. Seigler
Department of Plant Biology, University of Illinois, Urbana, Illinois 61801, USA; http://www.life.uiuc.edu/seigler
Widespread planting of native Western Australian trees may contribute to resolution of salinisation problems in parts of the wheatbelt and contribute to an overall increase in biodiversity. For these approaches to succeed, however, they must provide income for farmers in the area. Among the most common and most promising tree species in Western Australia are wattles, Australian species of Acacia subgenus Phyllodineae. Wattles produce a number of interesting classes of secondary compounds, some of which have potential as foods or food additives, whereas others have potential industrial applications. Water-soluble polysaccharides, known commonly as ‘gums’, are common constituents of these Acacia species. There is a significant demand for these products because of long-term shortages–a situation that appears unlikely to change in the near future. Gums are important components of food products and are often used to microencapsulate not only particles of food mixes and pharmaceuticals but also hazardous materials such as insecticides, herbicides, detergents and dyestuffs. Although gum substitutes are available, none of these gums has the desirable physical properties of gum arabic or gum acacia, now primarily derived from one African species of Acacia. Some Australian Acacia species also produce gum of excellent quality, but new methods of gum induction, harvest, extraction and purification must be perfected before they can compete in the world market. Tannins also are found in many Australian Acacia species. Mostly these compounds are used for production of leather but they have a range of other uses. In the past, Australia was a major leather producing and exporting country; the ready availability of good quality, inexpensive tannins might put this again within reach. Plants rich in tannins may not be as suitable for gum production, because the presence of tannins in gums decreases the value of the latter. However, new techniques make it possible to separate gums and tannins more efficiently.
Triglycerides and fatty acids are common components of the seeds of wattles and have a range of non- uses in food. Cultivation and harvest of the seeds can provide edible oils and protein-rich press cake for both human and domestic animal consumption. Other wattle compounds such as resins (diterpenes) probably have limited economic potential. The distribution and chemistry of saponins (triterpene or steroid glycosides) is incompletely known among wattles but some of these compounds appear to have profound biological activity. Although many compounds found in wattles are beneficial, some species contain potentially harmful substances such as cyanogenic glycosides, ß-phenylethylamine, fluoroacetate and non-protein amino acids. The presence of these compounds is not necessarily limiting, but species must be selected to avoid or at least them into account.
Why is cultivation and utilisation of wattles potentially important in the wheatbelt of W.A.? The direct value of products from cultivated wattles may produce new farm income, but large-scale cultivation of the plants may also contribute to amelioration of salinisation problems. This may be accomplished with elements of the native flora and contribute to an overall increase in biodiversity. Although products of intermediate value, such as gums and tannins, would not be expected to accomplish these goals alone, in combination with bulk products such as wood pulp and fibreboard, gums, tannins and possibly resins may improve the economic picture in W.A.