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Extracts from wattle seeds (Acacia victoriae) were found to have strong emulsifying capacities. These findings should provide a foundation for better marketing of bushfood products and expanding their areas of application.

Who is the report targeted at?
This report is primarily targeted at primary producers and processors of bushfoods. The information is also valuable to the hospitality and food processing industries which use native spices and flavours in their products. Furthermore, information on the emulsifying properties of wattle seed extracts has commercial potential and is especially targeted at food ingredient manufacturers who might be interested in commercialising the products. Finally, the information should also be of interest to the general consumers of bushfood products.

Background
The Australian bushfood industry has grown substantially since its establishment in the early 1980s. One of the main driving forces for the growth of the industry has been the appeal of its nativeness and a distinctively Australian flavour. While this image should be carefully preserved, it is believed that a sustainable growth strategy would require the industry to make significant inroads into the mainstream food markets by exploring alternative uses and markets for bushfoods beyond their traditional area of application - mainly as flavourings.

Many Australian bushfoods are known to possess functional properties such as antimicrobial, antioxidant and emulsifying properties. These properties have broad areas of application with significant commercial values. Most commercial antimicrobials, antioxidants and emulsifiers are synthetic compounds and as consumers are becoming increasingly sceptical about artificial food additives, natural substitutes are keenly sought after by the food industry. This presents a unique opportunity for value-adding and market expansion for the bushfood industry. However, knowledge in this area is rudimentary and obtained mainly through experience rather than through systematic, scientific investigation. This lack of systematic, commercially applicable knowledge is preventing the industry from realising these opportunities; research and development to bridge this knowledge gap would be extremely beneficial to the industry.

Aims and objectives
The overall aim of this project is to contribute to the development of the industry by enhancing our understanding of the functional properties of bushfoods. Specifically, the objectives of the project are:
 

• to generate reliable data on the antimicrobial and antioxidant properties of bushfoods to enhance their consumer appeal;
• to expand the application of bushfoods to areas including antimicrobials, antioxidants and emulsifiers for food applications to augment their current uses as flavouring agents; and
• to develop antimicrobial, antioxidant and emulsifying agents for use as natural substitutes for their synthetic counterparts.

Methodology
Bushfood samples were provided by growers and processors located in East Gippsland, Victoria and Northern Rivers and Sydney, New South Wales. The samples were extracted with three solvents (hexane, water and methanol) with polarity varying from apolar to strongly polar. The extracts were sterilised by cold sterilisation techniques using sterile membrane filters with 0.45 and 0.22 ?m pore size. The extracts were tested for activity against 29 common foodborne human pathogens and food spoilage bacteria, yeasts and moulds using the disc diffusion method.

Methanol extracts of the samples were tested for total phenolic content using the Folin- Ciocalteu procedure and for antioxidant activity using two methods: ?-carotene bleaching and the DPPH free radical scavenging. Based on the initial results, five plants with relatively high antioxidant activities were selected for further analysis by the TEAC method and by high performance liquid chromatography (HPLC) to identify the active fractions.

Wattle seeds (Acacia victoriae) were ground and extracted sequentially with water, 70% ethanol and dilute alkaline solutions. The proteins in the extracts were isolated and analysed by a number of techniques including SDS-PAGE and capillary electrophoresis (CE) for molecular size and other properties. Aqueous extracts of wattle seeds were used to prepare food emulsions with varying proportions of fat, and the emulsions were tested for stability under varying conditions of processing and storage (pH, salt and temperature, etc.). The average particle size and distribution of the emulsions were analysed by small angle laser light scattering techniques.

Results and key findings
This project has generated a wealth of original data and made a number of significant findings that are relevant to the bushfood industry, the scientific community and the general consumers of bushfood products.

Many native plant food products were found to possess antimicrobial activity, several of which have relatively strong activities against a number of important foodborne human pathogens, food spoilage bacteria and yeasts. Mountain Pepper (Tasmannia lanceolata) berries and leaves were found to have the strongest antimicrobial activity, while eucalyptus oil is effective against the broadest spectrum of pathogens. All the other native plant products tested, with the exception of Warrigal greens, also had some degree of activity against some of the microorganisms, by either inhibiting or slowing down their growth. Thus, the findings of this study are able confirm the anecdotal evidence gathered by the industry in this respect, and the information can be used by the bushfood industry to promote their products.

Interestingly, some extracts, such as pepper berry and leaves, had strong activity against human pathogens and spoilage bacteria but had no activity against lactic acid bacteria. This information may prove very useful as lactic acid bacteria are beneficial microorganisms in a number of food products including cheese, yoghurt, and many fermented meat and vegetable products such as salami and sauerkraut. The selective antimicrobial activities of these extracts mean that, when used in these products, they can inhibit the pathogenic and spoilage bacteria while not affecting the normal fermentation process. All the native plant food products tested in this study were, however, ineffective against all the spoilage moulds studied.

All the native plants products tested were found to possess some antioxidant activity, however the activities varied considerably between plants. The activity, as determined by the ?- carotene bleaching method, was highest in forest berry, followed by lemon aspen, Davidson plums and mountain pepper. The native plants also possess free radical scavenging activities, which also varied markedly among the plants. Native mint was found to have the greatest free radical scavenging activity, followed by lemon iron bark, quandong, forest berry, lemon myrtle and aniseed myrtle.

Most of the antioxidant activities were found in the methanol extract while little activity was found in the hexane extract. This suggested that the antioxidants were likely to be polar compounds.

Wattle seed extracts have strong emulsifying powers. Even at very low protein concentrations (0.17-1.12%), stable oil-in-water emulsions can be formed with lasting stability. For the purpose of comparison, milk, which is an emulsion stabilised primarily by milk proteins, contains more than 3% protein.

The stability of the wattle seed emulsions was affected by pH, with the emulsions being more stable at acidic than at neutral or alkaline pH values. It’s worthwhile to note that many emulsion type food products, such as mayonnaise and salad dressings, are acidic, and wattle seed extracts could be used in these products. The emulsions are very heat stable and can withstand processing at temperatures as high as 115°C for 30 min.

Implications/Recommendations
Overall, wattle seed extracts appear to have a great potential as emulsifiers and stabilisers for the food industry, especially at low pH levels.

In conclusion, this project has confirmed some of the anecdotal evidence regarding the functional properties of Australian bushfoods. The relatively strong antimicrobial and antioxidant properties of some of the native plant products mean that they might be used in foods beyond their original purpose of being a flavouring agent. Wattle seed extracts could be a promising natural emulsifying agent applicable to a variety of food products.

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