Chemical composition and the effect of processing on oxalate content of cocoyam Xanthosoma sagittifolium and Colocasia esculenta cormels

The chemical composition as well as the effect of processing on the cormels of two Xanthosoma sagittifolium species and Colocasia esculenta cormels were evaluated. A 3×3 factorial experimental design with cocoyam varieties [Xanthosoma (white-flesh), Xanthosoma (red-flesh) and Colocasia] and cormel section (distal, middle and apical) was performed to determine the chemical composition of the cormels. Oxalate contents of the various cormels were also evaluated and the effect of processing assessed using standard analytical methods. The mean values of the proximate composition of the three cocoyam species evaluated were; crude protein 2.98–5.50 g/100 g, total fat 0.28–0.97 g/100 g, ash 1.56–2.98 g/100 g, starch 12.2–36.0 g/100 g and crude fibre 1.11–3.00 g/100 g. The results showed that the different sections of the cocoyam cormels studied were significantly different (P⩽0.05) in chemical composition. The apical section of all the species had high protein content while the distal section had high levels of ash, fibre and minerals. Potassium was the most abundant mineral (763–1451 μg/100 g) with appreciable amounts noted for zinc (17–51.1 μg/100 g), magnesium (46.7–85.0 μg/100 g) and phosphorus (41.6–63.1 μg/100 g). Oxalate compositions of the fresh samples were in the range of 254–381 μg/100 g for the X. sagittifolium (red-flesh), 302–323 μg/100 g for the X. sagittifolium (white-flesh) and 328–460 μg/100 g for the Colocasia esculenta. No significant differences (P⩽0.05) were found between the oven-dried and solar-dried samples. However, drum drying reduced the oxalate levels by approximately 50% to average levels ranging from 99.9 to 191 μg/100 g.