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Macadamia is a genus of nine species of flowering plants in the family Proteaceae, with a disjunct distribution native to eastern Australia (seven species), New Caledonia (one species M. neurophylla) and Sulawesi in Indonesia (one species, M. hildebrandii).

They are small to large evergreen trees growing to 2–12 m tall. The leaves are arranged in whorls of three to six, lanceolate to obovate or elliptical in shape, 6–30 cm long and 2–13 cm broad, with an entire or spiny-serrated margin. The flowers are produced in a long, slender, simple raceme 5–30 cm long, the individual flowers 10–15 mm long, white to pink or purple, with four tepals. The fruit is a very hard, woody, globose follicle with a pointed apex, containing one or two seeds.

The genus is named after John Macadam, a colleague of botanist Ferdinand von Mueller, who first described the genus.[1] Common names include macadamia, macadamia nut, Queensland nut, bush nut, maroochi nut, queen of nuts and bauple nut; Indigenous Australian names include gyndl, jindilli, and boombera.

 

Production

The nuts are a valuable food crop. Only two of the species, Macadamia integrifolia and Macadamia tetraphylla, are of commercial importance. The remainder of the genus possess poisonous and/or inedible nuts, such as M. whelanii and M. ternifolia; the toxicity is due to the presence of cyanogenic glycosides. These glycosides can be removed by prolonged leaching, a practice used by some Indigenous Australian people for these species, as well.

The two species of edible macadamia readily hybridize, and M. tetraphylla is threatened in the wild due to this. The nut was first described by Europeans south of Brisbane in 1828 by the explorer and botanist Alan Cunningham. One of the locations where wild nut trees were originally found was at Mount Bauple near Maryborough in southeast Queensland, Australia. Locals in this area still refer to them as “bauple nuts”. The macadamia nut is the only plant food native to Australia that is produced and exported in any significant quantity.[2]

The first commercial orchard of macadamia trees was planted in the early 1880s by Charles Staff at Rous Mill, 12 km southeast of Lismore, New South Wales, consisting of M. tetraphylla.[3] Besides the development of a small boutique industry in Australia during the late 19th and early 20th centuries, macadamia was extensively planted as a commercial crop in Hawaii from the 1920s. Macadamia seeds were first imported into Hawaii in 1882 by William H. Purvis. The young manager of the Pacific Sugar Mill at Kukuihaele on the Big Island, planted seed nuts that year at Kapulena.[4]
Macadamia nut in its shell and a roasted nut

The Hawaiian-produced macadamia established the nut internationally. However, in 2006, macadamia production began to fall in Hawaii, due to lower prices from an over-supply.[5]

Outside of Hawaii and Australia, macadamia is also commercially produced in South Africa, Brazil, California, Costa Rica, Israel, Kenya, Bolivia, New Zealand, Colombia and Malawi. Australia is now the world’s largest commercial producer – accounting for roughly 40% of the approximately 100,000 tonnes of nut in shell per year produced globally.

Processing

Assessment as to whether a macadamia nut has undergone sufficient drying to ensure the moisture content is low, can be undergone by dropping the Macadamia nuts in their shell from normal hand height onto a floor surface that is relatively hard and solid, e.g. concrete or tiles. Subsequent shaking of the nut and hearing the nutmeat rattling inside indicates the nut is loose from its shell, and can thus be cracked with a higher intact-nut-yield ratio. Nuts that do not rattle have not dried sufficiently to reduce the moisture content and allow the nut to shrink away from the shell. Periodically, a nut will not rattle regardless of its moisture content due to the orientation of the kernel. To penetrate the nut’s hard protective shell, a metal vise or hammer can be used to compress the shell until it lightly fractures, then the pressure is released and the nut is repositioned to crack it along a different plane. Similarly when using a hammer, metal or wooden, a light force is to be applied when striking the shell as to be careful not to damage the inner vulnerable and edible seed [6] In Poland, a common method used is roasting of these hard nuts in an open pan.[7] This allows them to crack very easily, as seen in Polish culture during celebrations. For example, after cracking, the groom will begin to dance in a jovial manner.[8] In Malawi, the macadamia tree was first introduced in tea plantations as wind shields in the low tea fields and the tea pickers used to roast the nuts in this style as a fatty snack.

Nutritional qualities

Compared to other common edible nuts such as almonds and cashews, macadamias are high in fat and low in protein.[9] They have the highest amount of beneficial monounsaturated fats of any known nut, but also contains approximately 22% of omega-7 palmitoleic acid,[10] which has biological effects similar to saturated fat. They also contain 9% protein, 9% carbohydrate, and 2% dietary fiber, as well as calcium, phosphorus, potassium, sodium, selenium, iron, thiamine, riboflavin and niacin.[11]

Raw Macadamia kernel, per 100 grams Nutritional value per 100 g (3.5 oz)
Energy     3,080 kJ (740 kcal)
Carbohydrates     7.9 g
Fat     74.0 g
*Saturated fat: 10.0 g
*Monounsaturated fat: 60 g
*Polyunsaturated fat: 4.0 g
Protein     9.2 g
Vitamin B6     0 mg (0%)
Vitamin C     0 mg (0%)
Vitamin E     4 mg (27%)
Calcium     64 mg (6%)
Iron     2 mg (15%)
Magnesium     0 mg (0%)
Phosphorus     241 mg (34%)
Potassium     410 mg (9%)
Zinc     0 mg (0%)
Percentages are relative to US recommendations for adults.
Source: USDA Nutrient Database

Macadamias are toxic to dogs. Ingestion may result in macadamia nut toxicosis, which is marked by weakness and hind limb paralysis with the inability to stand, occurring within 12 hours of ingestion. Depending on the quantity ingested and size of the dog, symptoms may also include muscle tremors, joint pain and severe abdominal pain. In high doses of toxin, opiate medication may be required for symptom relief until the toxic effects diminish. Full recovery is usually within 24 to 48 hours.[12]

Skincare

Macadamia oil is prized for containing approximately 22% of the omega-7 palmitoleic acid,[13] which makes it a botanical alternative to mink oil, which contains approximately 17%. This relatively high content of “cushiony” palmitoleic acid plus macadamia’s high oxidative stability make it a desirable ingredient in cosmetics, especially for skincare.

Other uses

The trees are also grown as ornamental plants in subtropical regions for their glossy foliage and attractive flowers. Macadamia species are used as food plants by the larvae of some Lepidoptera species, including Batrachedra arenosella.

Macadamia nuts are often used by law enforcement to simulate crack cocaine in drug stings.[14] When chopped, the nuts resemble crack cocaine in color.[15].

Cultivation and processing

The macadamia tree is usually propagated by grafting, and does not begin to produce commercial quantities of nuts until it is 7–10 years old, but once established, may continue bearing for over 100 years. Macadamias prefer fertile, well-drained soils, a rainfall of 1,000–2,000 mm, and temperatures not falling below 10 °C (although once established, they can withstand light frosts), with an optimum temperature of 25 °C. The roots are shallow and trees can be blown down in storms; they are also susceptible to Phytophthora root disease.

Macadamia nuts are often fed to hyacinth macaws in captivity. These large parrots are one of the few animals, aside from humans, capable of cracking and shelling the nut.[16] Nuts of the “Arkin Papershell” variety crack open more readily.

Beaumont

A Macadamia integrifolia / M. tetraphylla hybrid commercial variety is widely planted in Australia and New Zealand; it was discovered by Dr. J. H. Beaumont. It has a good taste, is high in oil, but is not sweet. New leaves are reddish, flowers are bright pink, borne on long racemes. It is one of the quickest varieties to come into bearing once planted in the garden, usually carrying a useful crop by the fourth year, and improving from then on. It crops prodigiously when well pollinated. The impressive, grape-like clusters of nuts are sometimes so heavy they break the branchlet to which they are attached. In commercial orchards, it has reached 18 kg of nuts per tree by eight years old. On the downside, the nuts do not drop from the tree when ripe, and the leaves are a bit prickly when one reaches into the interior of the tree during harvest. Its shell is easier to open than that of most commercial varieties.

Maroochy

A pure M. tetraphylla variety from Australia, this tree is productive, and the small nut has a particularly good flavor. It is a good pollinator for ‘Beaumont’

 

 

 

 

 

 

 

Nelmac II

A South African M. integrifolia / M. tetraphylla hybrid cultivar, it has a sweet nut, which means it has to be cooked carefully so that the sugars do not caramelise. The sweet nut does not taste good when processed, but people who eat it uncooked relish the taste. The nut has an open micropyle (hole in the shell) which lets in mould. The crack-out percentage is high. Ten year old trees average 22 kg per tree. It is a popular variety because of its pollination of ‘Beaumont’, and the yields are almost comparable.

Renown

A M. integrifolia / M. tetraphylla hybrid, this is a rather spreading tree. On the plus side, it is high yielding (commercially, 17 kg from a 9-year-old tree has been recorded), and the nuts drop to the ground, but the nut is thick-shelled, and with not much flavor.

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