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Rural Industries Research & Development Corporation
Summary of full report
RIRDC Publication 01/28 AGP-1A
Executive Summary
Incentives for the study
Confidence in safety is a prime consideration when choosing foods, but is often taken for granted when a food is known to have been consumed for many years without evidence of adverse effects. However, most commercial bushfoods are new products, being introduced to a highly competitive market. Potential consumers may have no previous experience of their appearance, taste and potential use, and may possibly not realise that the term "bushfood" in commercial terms does not imply opportunistic wild-harvesting of foods, which had been necessary for survival in traditional cultures. The resulting natural caution, which may limit the market for many unfamiliar bushfood products, might well be reduced by evidence supporting an image of safety, based on an apparent absence to date of reported adverse effects or harmful constituents. However, absence of such reports cannot be taken as a complete guarantee of safety, because many of the hundreds of compounds that may be present in any single plant are as yet unreported, and the degree of potential toxicity of a particular compound may vary with other factors, such as quantity consumed and personal tolerance. Therefore it is always easier to claim that a particular food may not be safe than that is it harmless.
In 1996, during the formative stages of the modern bushfood industry, a conference involving many of the principals of bushfood companies, private growers and representatives of Aboriginal communities was held in Brisbane. Information in the form of Conference Notes was provided, and the outcomes were summarised in RIRDC Research Paper 97/22: "Prospects for the Australian Native Bushfood Industry" by Graham & Hart. The paper recorded concerns which had been expressed during that meeting about inadequate information about the chemical constituents and safe use of bushfoods, and listed a number of species which at the time were seen as presenting the best commercial opportunities. The present report was commissioned in order to overcome the difficulty of obtaining scientific information about bushfoods, which might support their assumed individual safety for use, or as an alternative indicate any needs for caution due to possible adverse effects.
Traditional vs modern uses of bushfoods
In Australian traditional cultures, with food-gathering an important and time-consuming part of everyday life, seeds, fruits and other plant products of high nutritional value were especially valued. Modern clients of the bushfood industry, whose nutritional needs are more readily satisfied, tend to seek novel foods of attractive – even unique – appearance, flavour and aroma, and to use them in dishes which may contain several other ingredients. So bushfoods, as used in modern cuisine, do not always reflect traditional uses. On the other hand, foods such as cycad seeds and yams, which Aboriginal people consumed only after extensive and necessary detoxification processes, and other important foods, such as plant gums and tubers, have rarely been of interest to the commercial industry. In addition, Aboriginal uses of a large number of plant species for medicinal and other personal, but non-food, purposes cannot be taken as an indication that they may be suitable in any way for food use. Rather, medicinal use is likely to be an indication of the presence of bioactive compounds which may be undesirable in foods.
The larger bushfood producers tend to base their inventories on a few well-recognised native fruits and seeds which have a history of safe use as Aboriginal foods, or which have attractively aromatic or spicy leaves, while ignoring important Aboriginal foods from other parts of plants, such as tubers, gummy or sugary plant exudates, and associated insects.
Review of existing information
This has required continuing searches of the scientific, industry and popular literature for information on the botanical description, chemical composition, and possible toxicity of the major bushfoods, together with wide solicitation of anecdotal reports about adverse effects attributed to the collection, processing and/or consumption of bushfoods. Databases searched included Biological Abstracts, Medline, Food Science and Technology Abstracts, Agricola, Commonwealth Agricultural Bureaux abstracts, Chemical Abstracts, Current Contents and Science Citation Index. Relevant scientific papers, and articles in books and magazines, were located from these abstracts, and where possible the full text was accessed. Bushfood industry newsletters and magazines were regularly consulted. The information obtained is summarised in Section 2
The searches often extended to close relatives of bushfood species, because where information for a particular species is absent or limited, an indication of the general chemical characteristics may be indicated as a basis for further investigations, if required. In addition, chemical information for bushfoods that were not clearly defined by species in the brief, or were not originally listed in it, has been included (Section 2.3) where such a need was suggested by questions from members of the industry, or information in industry publications. A list of bushfood species mentioned in the text is given in Appendix 3. In addition, some of the many better-known plant species which should not be used as bushfood because of possible toxicity are listed in Table 2.1. It was evident that the largest bodies of chemical information were for the constituents of essential oils - the main basis of flavour and aroma in many bushfoods – and from screenings for the presence of alkaloids, cyanogens and saponins. However, in the vast majority of cases, only non-edible parts of the plants had been tested, and the results cannot be relied on as an indication of the chemistry of the parts which are actually consumed, such as fruits, seeds and nuts.
Samples and chemical tests
Bushfood samples were obtained from a number of wholesalers and producers (acknowledged in Appendix 2.1). Where possible, details of botanical identity and provenance were established and voucher samples retained, but this was not possible for wholesale samples of mixed origin. Because of the large number of species involved, even at the initial stage, a minimum of two samples of each species, from different providers, was sought for comparative purposes. This would provide a broad indication of where further analyses of any species might be required, should any reports of possible toxicity emerge at a future date. Most samples originated from Queensland, New South Wales and South Australia, where the industry is most diversified, but it proved difficult in practice to obtain samples from areas where the product ranges are smaller. Chemical constituents of plants are often arbitrarily divided into two classes according to function. Those known as primary compounds are involved in structural or transport systems and are common to large numbers of plants. Secondary compounds are also numerous, and are often peculiar to a limited numbers of plant species. These compounds include those which have defensive functions, may be involved in metabolic and other natural processes (or by-products of these processes) or have functions which are presently unknown. It is the secondary compounds which are most likely to be those with potential for toxicity to humans or other animal or insect species. It cannot be assumed that because a fruit or other bushfood is eaten avidly by birds or other herbivores that it will be equally innocuous to humans, who have somewhat different metabolic systems for dealing with various potentially bioactive constituents of foods. Relatively few of the many known alkaloids in plants have been reported to have toxic properties, while other potentially harmful compounds, including cyanogens, are present in many common foods in small quantities which do not cause adverse effects. They are only likely to be harmful if such foods are consumed in excess, or a person has a particular intolerance to a chemical component of a food. Screening analyses for the presence/absence and estimated or more exact concentration of secondary compounds including alkaloids, cyanogens, oxalates and saponins were conducted on fresh and frozen samples of the major bushfood species, the types of test being limited in a few cases by the availability of samples. Species tested included acacias, aspens, bunya nuts, myrtles, native citrus, Davidson’s plums, hibiscus, muntries, native mints and basils, Illawarra plums, quandongs, bush tomatoes, riberries, native peppers, Kakadu plums and Warrigal greens. Additional tests were conducted in the second year to determine the more important essential oil constituents of a number of commercial bushfoods used for flavouring.
Outcomes of the study
The results of analyses were generally very reassuring, and where previous studies existed, conformed well with those results. New records, for example for the presence of oxalates and saponins and cyanogens, did not exceed values recorded for widely-consumed non-bushfoods. The presence of alkaloids in the native citrus species was similar to that in commercial oranges and lemons, although still among the higher values for bushfoods as tested.
The main potential causes of adverse effects to bushfoods were found to be: ·overindulgence in unripe or very acid fruits, very strong and spicy flavourings, or bushfoods selected and processed without due care. Adverse effects can be exacerbated by other foods or beverages consumed at the same time ·mistakes in identification of source material, as in the case of some Solanum species which contain potentially toxic steroidal alkaloids ·failure to appreciate that almost all commercial bushfoods have only been cultivated for a short period, and that their chemical composition may be more variable than that of long-established crop plants ·expectation that foods prepared from native species are safe to eat if there is a recorded history of traditional use, regardless of whether Aboriginal preparation of the food had involved extensive detoxification processes. The highly variable individual human tolerance of particular constituents of foods. There is at present no reliable method of listing or investigating the cause of unusual reactions that may be attributed to particular bush foods, and any circumstances which might assist to explain or disprove the reports.
The results above are presented with the reservation that though every effort has been made to find information about the safety aspects of bushfood species, much information is unwritten or difficult to access. The previous chemical data about edible parts of native plants are extremely scattered and often lack necessary detail. In addition, the limited number of samples of each species analysed during this study was not able to represent the full range of variation of particular compounds, or classes of compound within those species. For example, the distribution of at least some potentially bioactive compounds, including the less desirable constituents of essential oils within many of the species, is well-known to be highly variable. Continuing analytical studies are already assisting producers to select the most desirable plants for commercial propagation, cultivation and sale.
The study is intended to advise members
of the industry of what is currently known about the chemistry of bushfood
species and their history of use in traditional communities, as a resource
for use for commercial purposes and requirements such as registration under
novel foods regulations, as well as to indicate areas where further research
is required.
 
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