Abstract
Nut collection expeditions of Plukenetia conophora L. were made to 10 locations in southwestern Nigeria. Seeds extracted were cooked or not and were assayed for phytochemical and mineral contents. Data obtained were statistically analyzed. Omuwo-Oke accession had highest phenol and tannin whereas Ijan had highest phytate; alkaloids and glycosides were higher in Ara accession than others. Accession obtained from Aramoko gave highest iron concentration while the lowest was in Ogotun accession. The concentrations of K, Mg and Na were higher in Ogotun accession while the lowest was found in Alafe, Agbado and Aba-Oyo, respectively. Alafe accession had highest concentration of phosphorus but lower concentration was obtained in Ogotun. Zinc was highest in collection from Aramoko while Abgado accession had the lowest. Phenol, phytate, alkaloids and glycosides were higher in boiled nuts than fresh nuts but tannin was higher in fresh nuts. K, Mg, Zn and Na were higher in fresh nuts than boiled nuts. Higher concentration of Fe and P were recorded in boiled nuts. Genotype x traits biplot analysis revealed that cooked nuts from Agbado, Alafe, and Aramoko had higher values for glycosides. Alkaloid was more pronounced in fresh nut from Ara. Fresh nuts from Aba-Oyo and Agbado gave higher values for phytate. Tannin was highest in fresh nuts from Omuo-Oke and boiled nuts from Igbara-Odo while phenol was higher in boiled nut from Omuo-Oke. Biplot analysis for minerals revealed higher concentration of Zn, NFE, Na and P in boiled nuts from Aramoko, Omuo- Oke, Igbara-Odo, Ogotun and Ijan. Mg was highest in fresh nuts from Ara and Igbara-Odo. Tannin and alkaloids had negative significant relationship (r = –0.581*) but the relationship between glycosides and alkaloids was positive and significant (r = 0.520*). Zn had significant relationships with Mg and P (r = 0.590* and –0.551*, respectively). Similarly, Na had positive relationships with K and Mg (r = 0.599** and 0.491*, respectively). Mg and K had an r-value of 0.502*. Inter-correlative responses between the phytochemicals and minerals revealed that only glycosides had significant relationships with K, Mg and Zn (which were negative) as well as with P (which was positive). Data obtained suggested sufficient genetic diversity in nuts of Plukenetia sourced from southwestern Nigeria, indicating posibility for selection. Besides, cooking had signifcant (in some cases, positive) effect on the phytochemicals and minerals assayed.
 Key words: African walnut, accessions, phytochemical, minerals, processing
Highlights
African walnut (Plukenetia conophora L.) is a perennial climbing species belonging to the family Euphorbiaceae (Amaeze et al, 2011)
The result corresponded with the work of Enujiugha (2003) and Sibbeth (1994) that walnut is a good source of potassium and many other micronutrients, which implies that for human consumption, African walnuts could be recommended as a good source of minerals needed for body metabolism and proper functioning of cells
Boiled nuts were higher in iron and phosphorus contents but the concentration of magnesium and zinc was higher in fresh nut; processing did not statistically influence potassium and sodium contents of the nuts
Summary
African walnut (Plukenetia conophora L.) is a perennial climbing species belonging to the family Euphorbiaceae (Amaeze et al, 2011). P. conophora is commonly referred to as African walnut because of its West African origin. It is known as ‘Ekporo’ by Efik and Ibibios of Cross River and Akwa Ibom, as ‘Ukpa’ in Igbo, ‘Awusa’ or ‘Asala’ in Yoruba, ‘Okwe’ in Edo and ‘Gwandi bairi’ in Hausa (Akpuaka and Nwankwor, 2000). Plukenetia conophora is better appreciated for its seeds, which are extensively consumed by people inhabiting the Southern region of Nigeria where the species is common (Akpuaka and Nwankwor, 2000). The immature fruits are usually green in colour but turn dark brown as they mature (Oluwole and Okusanya, 1993). The fruit (7 cm across) are light green to brown when ripe while the seeds are round dark brown at maturity.
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