The Nutritional and Therapeutic Aspects of Australian Macadamia Nuts

1. Introduction

In order to improve health and well-being, the food industry is now very interested in launching new products. In this regard, there's a rising need for functional food items that have been fortified with long-chain fatty acids.

Tree seeds with a hard, frequently lignified shell are called nuts. Hazelnut, Brazil nut, and chestnut are examples of true nuts. They are often classified alongside other nuts like almond, cashew, and peanut. Nuts and seeds come from diverse plants, with a varied nutritional composition. They have a food supply that is intended to satisfy the requirements of the growing plant embryo, often fat or starch or polysaccharides. These foods are concentrated sources of dietary energy, protein, unsaturated fatty acids, micronutrients, and fiber (K C, 2021).

Macadamia nut trees can reach heights of 2 to 12 meters. They are indigenous to tropical rain forests in Sulawesi, Indonesia, New Caledonia, and eastern Australia. Their preferred conditions include temperatures above 10°C, 1000–2000 mm of rainfall, and rich, well-drained soils. The only naturally occurring food plants in Australia with economic significance are the two commercially significant species, Macadamia integrifolia and Macadamia tetraphylla. In 2008, the International Nut and Dried Fruit Foundation reported an annual production of around 26,000 tonnes worldwide (Ballhorn, 2011).

Around the world, people eat raw (natural) or roasted tree nuts as healthy snacks. Their high concentration of polyunsaturated fatty acids and necessary amino acids makes them very attractive (Bailey & Stein, 2020). Macadamia (Macadamia tetraphylla) nuts are creamy in texture and have a mild taste similar to butter (Moreno-Pérez, Sánchez-García et al., 2011). China's macadamia nut business has grown quickly in recent years, and 15,000 hectares of planting land are anticipated; the trees are primarily planted in the southern provinces of Yunnan and Guangxi (Hong, Groven et al., 2018; Zhong, Xiang et al., 2020). Cream-coloured macadamia kernels have an oil content of 72–78% and a moisture content of 1.5%. Browning of the kernels following roasting and the development of an unpleasant flavor as a result of oxidation and rancidity during storage are the two main flaws. It is essential to gradually dry items down to 1.5% moisture content in order to avoid browning and prolong shelf life (M. M. Wall, 2013). A nut's edible kernel is its seed, which is mainly made up of embryonic cotyledons and is protected from the environment by a fibrous husk and a hard, brown shell. Nuts are harvested following fruit falls or tree removal, then dried, roasted, and salted to a 1.5% moisture level. They are then often dry-roasted or fried in coconut oil (Gray, 2013). The subtropical Australian rainforests are home to the macadamia tree, which prefers temperatures between 25 and 35 degrees Celsius. For brief periods, it can tolerate frosts as low as -6°C, but prolonged durations or colder temperatures can harm or kill mature trees. Frost damage is especially prone to inflorescence. A minimum temperature of 20°C is needed for flowering, while prolonged exposure to temperatures higher than 35°C might result in deformed and chlorotic growth. The deep, proteoid roots and sclerophyllous leaves of the macadamia tree improve the uptake of nutrients from deficient soils. Survival conditions are not the same as ideal production conditions, though. Deep, well-drained soils with a high organic matter content, a medium cation exchange capacity, and a pH of 5.0 to 6.0 are ideal for macadamia growth (R. A. Stephenson, 2003).