Macadamia nuts contain over 75% of their weight as oil, the remainder is: 9.0% protein, 9.3% carbohydrates, 1.5% moisture, 1.6% mineral matter and 2.0% fiber. Macadamia kernels contain vitamin A1, B1, B2, niacin and essential elements such as calcium, iron, phosphorus, magnesium and potassium. The oil is a triglyceride and contains primarily monounsaturated fats up to 80–84%. Macadamia oil contains the highest percentage of monounsaturates when compared to both olive and canola oils. Macadamia integrifolia is an Australian tree with holly-like leaves that grows well in a moist organic soil and can withstand temperatures as low as −4.4 °C. Seedlings bear in 5–7 years. The fruit is borne in a case enclosing an extremely hard spherical nut. The kernel is whitish, sweet and eaten raw or roasted. The flowers are white to cream and the leaves are in whorls of three. Propagation is by seed, grafting or air layering. It is grown commercially. Common names of the trees are the Australian nut or the Queensland nut. Species are “smooth shelled macadamia” called Macadamia integrifolia and “rough shelled macadamia” called Macadamia tetraphylla. Macadamia ternifolia is also the name used for M. integrifolia. Macadamia integrifolia is native to Australia where it grows in rain forests and close to streams. Macadamia tetraphylla is native to Southeastern Queensland and Northeastern New South Wales. The oil content ranges from 65% to 75% and sugar content ranges from 6% to 8%. These factors result in variable colors and texture when the nuts are roasted under the same conditions. Macadamia oil is liquid at room temperature. The refined oil is clear, lightly amber-colored with a slightly nutty smell. It has a specific gravity of 900–920 and a flash point of over 300 °C . Oil accumulation does not commence until the nuts are fully grown and the shell hardens. It accumulates rapidly in the kernel during late summer when the reducing sugar content decreases. The composition of mature, roasted and salted macadamia nuts is shown. As with many oil seeds, the protein is low in methionine. Fresh kernels contain up to 4.6% sugar, mostly non-reducing sugar. The oil consists of mainly unsaturated fatty acids and is similar in both species, although the proportion of unsaturated to saturated fatty acids appears to be slightly higher in M. integrifolia. The fatty acid composition and the absence of cholesterol may lead to the promotion of macadamias as a high-energy health food. The major volatile components in roasted macadamia kernels are apparently similar to those found in other roasted nuts, although little detailed information is available.
Uses in food
Macadamia oil can be used for frying due to its high heat capacity along with other properties useful as an edible oil:
It contains up to 85% monounsaturated fats
It has an unrefrigerated shelf life of one to two years
