Nutritional diversity in accessions of African walnut (<i>Plukenetia conophora L.</i>) sourced from southwestern Nigeria as influenced by collection center and processing

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