THEY are enveloped in a black thick wall, they are white to creamy snack with a bitter after taste. African walnut is in season. The cooked nuts containing the edible seeds are common articles of trade in Nigeria. Most Nigerians eat African walnut just as a snack, but researchers suggest the meal and indeed the whole plant could be the panacea to several diseases.
Researchers have demonstrated how extracts of walnut reduce the risk of breast cancer; boosts fertility and cognitive skills; and stop diarrhoea, fibroids, and disease pathogens such as Candida albicans (thrush), Staphyloccocus aureus, Bacillus subtilis, Aspergillus niger and Pseudomonas aeruginosa.
Candida albicans is a fungus (a form of yeast) and a causal agent of opportunistic oral and genital infections in humans. The fungus causes candidiasis, also known as thrush, a common condition in immuno-compromised individuals such as Human Immuno-deficiency Virus (HIV)-positive patients. Candidiasis also may occur in the blood and in the genital tract.
Staphylococcus aureus, a bacterium, is the most common cause of staph infections. It can cause a range of illnesses from minor skin infections, such as pimples, boils (furuncles), and abscesses, to life-threatening diseases such as pneumonia, meningitis, and chest pain.
Pseudomonas aeruginosa is a common bacterium, which can cause disease in humans and non-human animals. It is found in soil, water, skin flora, and most man-made environments throughout the world. The symptoms of such infections are generalised inflammation and sepsis. If such colonisations occur in critical body organs such as the lungs, the urinary tract, and kidneys, the results can be fatal.
Bacillus subtilis is a bacterium commonly found in soil. B. subtilis is not a human pathogen. It may contaminate food but rarely causes food poisoning.
Aspergillus niger is a fungus, which causes a disease called black mold on certain fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food.
Nigerian researchers have shown that African walnut has a high potential as an antimicrobial medicinal plant for dug resistant strains; while their United States counterpart found that walnut consumption may provide the body with essential omega-3 fatty acids, antioxidants and phytosterols that reduce the risk of breast cancer.
Botanically called Tetracarpidium conophorum or Plukenetia conophora, African walnut belongs to the family Euphorbiaceae. In Nigeria, it is called asala or awusa in Yoruba; ukpa in Ibo; and okhue or okwe in Edo.
According to a study presented recently at the United States American Association for Cancer Research yearly meeting, mice fed the human equivalent of two ounces (56.7g) of walnuts per day
developed fewer and smaller tumours.
Associate professor of medicine at Marshall University School of Medicine, United States, Elaine Hardman, said that while her study was done with laboratory animals rather than humans, people should heed the recommendation to eat more walnuts.
Hardman said: "Walnuts are better than cookies, French fries or potato chips when you need a snack. We know that a healthy diet overall prevents all manner of chronic diseases."
Hardman and colleagues studied mice that were fed a diet that they estimated was the human equivalent of two ounces of walnuts per day.
A separate group of mice were fed a control diet. Standard testing showed that walnut consumption significantly decreased breast tumor incidence, the number of glands with a tumour and tumour size.
"These laboratory mice typically have 100 per cent tumour incidence at five months; walnut consumption delayed those tumours by at least three weeks," said Hardman.
Molecular analysis showed that increased consumption of omega-3 fatty acids contributed to the decline in tumour incidence, but other parts of the walnut contributed as well.
"With dietary interventions you see multiple mechanisms when working with the whole food," said Hardman. "It is clear that walnuts contribute to a healthy diet that can reduce breast cancer."
The Nigerian researchers led by E. O. Ajaiyeoba and D. A. Fadare of the
Department of Pharmacognosy, Faculty of Pharmacy, University of Ibadan, Oyo State, found that African walnut has a high potential as an
antimicrobial medicinal plant. They examined the antimicrobial potential of extracts and fractions of the African walnut.
The researchers in the study published in
African Journal of Biotechnology wrote: "This is therefore improving the value of the plant. It is reported to be useful in the folklore in the treatment of dysentery. This investigation therefore justifies its
ethnomedical use, having displayed activities with the human pathogenic micro-organisms that were used in this study.
"The need for development of newer antimicrobial chemotherapeutic agents is imperative. This is because there is increasing treatment failure rates of microbial infections due
to drug-resistant antibiotics. The most active fraction in the present study, the ethyl acetate fraction of the leaf methanol extract, has a
very high potential as a source for drug discovery for antimicrobial
agents. This is being investigated by our group and the results will be
presented in due course."
According to the Medicinal Plants of Nigeria- South West Nigeria Volume 1 compiled and published by Nigeria Natural Medicine Development Agency (NNMDA), Victoria Island, Lagos, walnut seeds are used in the treatment of fibroid. The leaf juice is drunk to mitigate prolonged and /or constant hiccups. Seeds are chewed to improve spermatozoa count in men. The leaf juice is used to improve fertility in women and also to regulate menstrual flow.
In southern Nigerian ethnomedicine, African walnut is used as a male fertility agent and the leaves are used for the treatment of dysentery and to improve fertility in males. The oil from the nut has found use in the formulation of wood varnish, stand oil, vulcanised oil for rubber and leather substitute. Most of the studies on the plant have been on the nutritive value of the seeds, which is a snack and delicacy.
According to The Useful Plants of Tropical West Africa by H. M. Burkill, the plant is a woody liane to over 30 metres long, of the bushy savanna. The leaves are considered a headache cure in Southern Nigeria, and have magical use to wash children to cause their mothers to conceive, the Igbo name meaning babies call babies. In Gabon, consumption of the seeds by husbands of wives already pregnant is believed to mitigate the risk of miscarriage. Nigerian material has been screened for alkaloids, a trace of which is recorded in the bark.
Previous studies had shown that African walnut prevents heart disease. They suggested eating walnuts at the end of a
meal might help cut the damage that fatty food can do to the arteries. It is thought that the nuts are rich in
compounds that reduce hardening of the arteries, and keep them flexible.
Phytochemical analysis indicates that African walnuts contain
ingredients such as omega-3 fatty acids, antioxidants and phytosterols that may all reduce the risk of the disease. Most of the studies on the plant have been on the nutritive value of the seeds, which is a snack and delicacy. Two isolectins, Agglutin I and II were characterised from the seed extract. The presence of oxalates, phytates and tannins as well as proteins, fibre, oil and carbohydrates in African walnut has been reported.
In the University of Ibadan study, clinical
strains of four human pathogenic bacteria made up of two Gram-positive
(Staphyloccocus aureus and Bacillus subtilis) and two Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli) were used for
the antibacterial assay, while for the antifungal assay, one yeast
(Candida albicans) and one mould (Aspergillus niger) were used for the study.
The micro-organisms were obtained from the laboratory stock of
the Department of Pharmaceutical Microbiology, University of Ibadan.
Preliminary phytochemical screening of the
plant parts for secondary metabolites, showed the presence of saponins,
alkaloids, tannins and anthraquinones in the plant samples.
The
concentration of these metabolites were higher in the leaves. Cardiac glycosides were not detected in leaf, stem bark, roots and kernel of
African walnut. Percentage yields of extracts were determined after
removal of solvents respectively. The extracts displayed concentration-dependent anti-bacterial and antifungal properties.
The root extract displayed
intrinsic antibacterial properties. Of the six micro-organisms used, S. aureus was most sensitive to the root and stem bark extracts. Both extracts did not show any antifungal property in the present study.
The
leaf extract exhibited the highest activities with all the
micro-organisms investigated. The leaf extract also showed anti-fungal
properties, inhibiting the growth of the A. niger, a normally resistant
mould, much more than the reference drug, tioconazole.
The kernel did
not show any activity with the micro-organisms used in this study.
The hexane, chloroform, ethyl acetate and methanol fractions of the leaf extracts displayed good anti-microbial
activities, which were concentration-dependent at the five
concentrations (100-5 mg/ml) tested.
The most
sensitive bacteria to the four fractions were P. aeruginosa. The ethyl
acetate fraction was the most active extract, while the hexane fraction
showed least activity. The fractions also inhibited the growth of the
two fungi used in the study.
The yeast, C. albicans and the mould, A. niger,
were inhibited even at a concentration of 10 mg/ml, comparable to
tioconazole (a conventional anti-fungal drug).
In the antimicrobial analyses, gentamycin was included as
reference antibacterial compound, tioconazole as the reference for
anti-fungal. Methanol was included in the experiments as a negative control and it did not display any antimicrobial activity.
