Acacia, commonly known as wattle, belongs to the family Fabaceae. The seeds were eaten either green and cooked, or dried and milled to a flour for a type of bush bread. Acacia victoriae, the elegant wattle, is the most common of the edible species and is considered the food industry standard. Acacia murrayana and A. victoriae have been studied as candidates for commercial production.
Composition
The seeds of four Acacia species were rich in protein (23-27%) and dietary fibre (33-41%). Fat content was relatively high in A. cowleana (19.3%), A. sophorae (14.8%) and A. retinodes (16.4%), with oleic acid the predominant fatty acid. The seeds contained high amounts of essential amino acids, among them histidine, lysine, valine, isoleucine and leucine. Methionine is the limiting amino acid in all four of these species. Because of its low glycemic index, acacia seed flour is suitable for diabetic foods. Acacia seed is also a source of minerals such as potassium, sodium and iron. All four species had low moisture content, below 9%, and similar ash contents of 3.4-3.9%. Seeds of Acacia colei contain about 23% crude protein, 57% carbohydrate and 8% fat, and over half of the carbohydrate is dietary fibre. The amino acid profile of acacia seed flour shows tryptophan, methionine and cysteine as limiting amino acids, so it is not a complete food and should supplement rather than replace existing diets. Laboratory rats fared well on diets with up to 25% acacia flour, but in long-term trials with 40% acacia flour as the only protein source, amino acid imbalance caused health problems.
Roasting and Aroma
Roasting mainly serves to develop a unique nutty flavour and aroma that depends on the species and roasting conditions. It also reduces anti-nutrients and protease inhibitors, particularly trypsin inhibitors. Many species require pre-treatment of the seeds by parching at high temperatures, soaking or cracking with seed grinders. Earlier studies found that a unique aroma and flavour was perceived in five species after roasting. Roasting may also form new compounds or release bound ones, such as phenolic compounds, and the aroma and flavour compounds may form or be released during roasting. After roasting, no protein band was visible in the four wattle seed species apart from two faint bands in A. coriacea at 55 kDa.
Traditional Food Use
The seeds of some 50 other Australian Acacia species have also been used as seasonal foods by Aboriginal people. The seeds of Acacia victoriae are used in breads and ground as meal, and have also been used as fodder.
Acacia victoriae
Acacia victoriae is commonly known as elegant wattle, bramble wattle, prickly wattle, gundabluey, gundabluie or bardi bush, and is a shrub-like tree native to Australia. It reaches a height of about 5-6 metres and has a life-span of about 10-15 years. Its flowers are yellowish and strongly scented. The seeds are held in pale-coloured pods of 8 cm. Flowering begins in August and continues into late December, depending on the region. The tree has a large root system that can extend to 20 m, and it survives drought fairly well but not severe drought. It grows in arid and semiarid areas, generally in alkaline soils. It is used as a windbreak, helps to stabilise soil, and has been used for site rehabilitation.
Cultivation
Wattleseed Acacia are perennial woody crops of varying age and size, with some reaching 4 m tall and 5 m across. Their large size and multiple stems hinder harvesting, which has led to several ways of collecting pods: finger stripping, butt shaking of the tree, and whole biomass harvesting. In A. victoriae, trees do not begin flowering until 2-4 years old. The large number of Acacia species has been seen as an advantage for developing wattleseed as a commercial crop. Trees can be arranged in alley or phase layouts in plantations, and Acacia have also served as windbreaks and groundcover in areas of high salinity. Preparation can involve deep ripping of the soil so that water can soak in. Water stress can induce flowering and raise seed production when enough nutrients are available. How long the trees live depends on spacing, climate and species.
