16 August 2019
The generous tree
Discover Croton megalocarpus – the multipurpose tree in Africa.
Biofuels, cosmetics, fertilisers and livestock feed are just some of the valuable commercial products produced from the nuts of the African tree Croton megalocarpus. But there may be more uses to uncover.
Treasure tree and a useful weed
Growing up to 36m in height, African C. megalocarpus trees are very tall weeds. But despite the trees invading the landscapes of Eastern and Central Africa, this species is a very useful weed. The trees provide shade for a variety of crops, such as coffee, and its bark is often used for traditional medicinal purposes. Bees that forage on the light-yellow flowers produce a dark-ambered and strongly flavoured honey. However, it’s the nuts, plentiful in number, that are of high commercial interest.
Each tree can yield between 25 and 40kg of nuts per year, which are harvested sustainably by smallholder farmers and sold to local industries to generate valuable income. The nuts are oblong in shape and are comprised of approximately 30 per cent oil and 50 per cent protein. Although the oil is not used within the food industry, the composition has been compared with that of sunflower and rapeseed meaning that it could, with research, be substituted for these less sustainable sources in the future.
Biofuels and by-products
Extracted by mechanically squeezing the nuts, the oil is used within cosmetics or as a sustainably-sourced biodiesel. There are many by-products resulting from the oil extraction process. Due to the high protein content of the nuts, seedcakes are used to supplement livestock feeds, while a steam-smoke distillate of the seed kernel is used as a botanical insecticide and repellent.
But these uses are of low value. I’m therefore interested in the additional by-products from the Croton oil extraction process that could support income generation for East Africa. My preliminary research has already shown that husks of the C. megalocarpus nuts contain trans-ozic acid, a chemical which has been reported in wild sunflower and may provide the sunflower with resistance to insects. I’ve also found that the seedcake contains magnoflorine, a chemical proposed to inhibit anxiety.
I’ve been involved in developing a network of scientists in Kenya and the UK to identify potential new uses and optimise their safety. Through this network we’re carrying out analyses to understand the chemistry of C. megalocarpus nuts, identifying useful and toxic chemicals. We’ll be working to determine if the nuts offer beneficial chemical compounds that could have pesticidal, antifungal, antimicrobial, antimalarial and even anticancer effects. It’s hoped that this work will grow small industries in East Africa and increase the income of farmers.