Introduction

The human immune system protects us from microscopic organisms in the environment. These microbes could be threatening to the host because of their ability to cause unpleasant pathological conditions. The immune system protects various mechanisms to eliminate toxic foreign microorganisms. The mechanisms are usually required to distinctly differentiate between the structural features of the host organism and the foreign microorganism to be eliminated.¹

The Marula fruit is an underused edible fruit belonging to the Anacardiaceae family. Marula (Sclerocarya birrea, A, Rich) grows naturally in many parts of sub-Saharan Africa, especially the open woodlands. The fruit has been an essential component of many rural cultures in African communities such as in South Africa and Madagascar. Two major species that make up the Sclerocarya genus are birrea and gillettii. Marula is made up of health-beneficial vitamins, minerals, and other beneficial components such as phenolic compounds and ascorbic acid. These have been found to exert antimicrobial, antioxidant, anticonvulsant and even astringent effects and benefits. The high composition of polyphenols and antioxidant effects accounts for a lot of these properties.²

The marula tree

The Marula tree varies in size from a medium to a large sized tree. It can grow from between nine to eighteen meters long and as much as 120 cm wide. The tree usually flourishes in geographical areas with altitudes from sea level up to 1800 m. The required rainfall ranges from 200 mm to 1500 mm. The marula tree parts and extracts are an economic product and are well known for their social, economic, cosmetic, dietary and pharmacological effects. The female tree produces edible fruits that look like small mangoes and the fruit pulp is a delicacy in many cultures. The kernel of the seeds is the source of its edible oil. The various parts of the S.birrea tree like the leaves, the bark, the roots, and the seed kernel have been shown to have numerous medicinal benefits for centuries in many local populations in Africa.³

Use of marula in traditional medicine

The Marula parts, including the fruits, bark, and oil are used for many purposes by indigenous populations, which may include its cosmetic, traditional medicinal, and food purposes. Marula fruits can be eaten freshly, roasted, juiced, processed into a jam or even fermented into alcoholic beverages such as beer, liquor or wine. The fruit has a bitter and acidic taste, however, they have a pleasant taste when they ripen. The nuts are also edible and highly nutritious for both humans and animals In many parts of Africa, the bark of their tree stems as well as their leaves and roots are popularly used for their medicinal effects.

Some conditions where they have found use include diarrhoea, dysentery, fevers, bodily pain, and even infertility. The Ministry of Agriculture in Namibia approves and promotes the use of Marula as a medicinal plant. These nuts can be consumed with vegetables or as snacks, they can be crushed and added as a component in the baking of breads. The nuts provide oil for cosmetic purposes as well as dietary consumption.⁴

Nutritional compositions of marula

The Marula contains a high concentration of Vitamin C. This can be up to 2,100 mg per every 100 g in an average raw fruit. The vitamin C content is believed to be many times higher than that in many citrus fruits, especially in ripe marula fruits.

Also, the juice extracts of Marula have been found to contain up to 56 mg/ 100 ml of pyrogallol equivalent of phenols as well as 382 mg/ 100 ml equivalent of vitamin C. Some comparative studies show that the Marula fruit has higher antioxidant activity than fruits such as orange or pomegranate juice, however, more studies need to be carried out with various analytical methods to obtain conclusive evidence on the antioxidant activity of the Marula fruit in comparison with other fruits. Juice extraction involves multiple processes, including washing the fruits, boiling and steaming, then peeling, juicing and sieving. This is then followed by pasteurization and storage.

Additionally, the marula juice contains a large concentration of polyphenols which may range between 226 and 414 mg per every 100 ml of tannic acid, this may vary slightly from tree to tree due to methods of extraction.

The Marula also has a variation in its mineral composition depending on the geographical origin where it is sourced from as well as soil, climate, and time between harvesting and use. However, magnesium, potassium, calcium, iron, and phosphorus are abundantly present in the Marula juice. The following are also found in the juice in lower concentrations: manganese, lead, copper, zinc, cobalt, and sodium. Marula is also rich in other phenolic bioactive compounds like epicatechin, catechin, quercetin, myricetin, and proanthocyanidins.^4,5

Effects of marula on immune health

Free radicals in the human body have been identified as causes of cell damage and loss of structure and function of many healthy cells. They have been implicated in the pathogenesis of many diseases. Free radicals are not stable and they possess an unpaired electron, which tends to be very active and requires other unpaired electrons to find their stability. It consequently produces even more free radicals and a chain reaction that may be harmful to the host body leading to oxidative damage. Free radicals are sometimes formed from the very reactive oxygen and may bond and form harmful ‘free radicals’, which not only lead to cell damage and malfunctions leading to cardiovascular disorders, cancer, or cataracts but may also lead to premature ageing of cells.

Antioxidants such as those found in Marula have been found to help mop up these unwanted free radicals from the body and eliminate them. This singular activity helps to reverse oxidative damage, which would have manifested as different debilitating and degenerating diseases and boosts the physiological immune functions of the body.

Antioxidants are known to prevent diseases that are caused by free radicals and even delay chronic health problems. The DNA-damaging effect of free radicals occurs due to the replication of damaged cells from damaged parent cells leading to conditions like cancer, rheumatoid arthritis, ocular, cardiovascular, and neurological disease among others. However, studies show that consumption of an antioxidant-rich diet significantly reduces the prevalence of these conditions.⁶

Summary

The article discusses the immune-enhancing benefits of the Marula. It is a significantly underused edible fruit and is native to sub-Saharan Africa. Its benefits have been known and explored for many centuries among local communities in Africa.

The marula tree is a medium to large-sized tree with cosmetic, economic and pharmacological benefits as well as being used as a dietary component in many indigenous populations. Marula and its many parts such as oil and juice extracts, and bark among others are consumed in different ways. This may be raw, boiled, roasted, juiced or even processed into jam or fermented into alcoholic beverages. The medicinal uses have been known to vary, from its use in diarrhoea, and fevers to its use in certain cancers and cardiovascular diseases.

The Marula juice is high in many antioxidants including vitamin C and many phenolic compounds, which are higher in comparison with many other citrus fruits. The Marula is highly beneficial for immune health because of its antioxidant properties and its ability to scavenge and eliminate many free radicals thereby preventing oxidative damage of the cells which in turn would have caused loss of cellular structure and function of human cells. Oxidative damage may result in many life-threatening diseases such as cancers, neurological diseases, and cardiovascular diseases among many others, thereby enhancing bodily immune functions.