Physical properties of seeds of African walnut (Plukenetia conophorum Muell Arg.) From South eastern Nigeria, and the effect of boiling on the proximate qualities

Abstract

A study of the physical and proximate traits of seeds of African walnut (Plukenetia conophorum) from four locations (states) in south-eastern Nigeria was carried out in 2011. The locations considered were Enugu, Anambra, Abia and Rivers. Results of statistical analysis showed remarkable variation (p < 0.05) in all the seed physical traits across the sampled locations. Accessions from Anambra were outstanding in seed weight, seed circumference and seed diameter. However, the Enugu accession was the best in terms of seed edible proportion, followed by that of Abia, while seeds obtained from Anambra had the least percentage edible proportion. The accession from Rivers had the least seed weight, kernel weight, seed circumference and seed radius. Correlation coefficients among the physical traits indicated that seed weight had significant statistical linkage with all the other physical traits except seed coat thickness. Seed coat thickness, just like the seed edible proportion had poor statistical linkage with most of the seed physical traits; whereas kernel weight recorded a high significant positive relationship (r = 0.913**) with seed weight. Kernel weight, seed volume, seed circumference and seed diameter showed more or less similar pattern of relationship. Principal Components Analysis (PCA) results identified five physical traits including seed weight, kernel weight, seed volume, seed circumference and seed diameter as the most discriminatory traits among the accessions. Location significantly (p < 0.05) influenced only moisture, fat and ash content of the seeds. Fat concentration of the Anambra and Abia accessions were higher than those of the other two accessions. Boiling lowered the moisture content of seeds and significantly (p < 0.05) increased the fibre content. Location × processing interaction had no remarkable effect on the proximate attributes of the seeds. Correlation analysis linked high fat content with large kernel diameter. Thus, seeds with large kernels could be selected for fat content and those with small size could give higher percentage edible proportion. Seeds of African walnut in the sampled zone have adequate nutritional content to qualify as a protein-rich oilseed and have shown enough variability to warrant selection for further improvement.

Keywords: Physical and proximate traits, African walnut, boiling treatment, southeast Nigeria.