Changes in the Nutrient and Anti-Nutritional Composition in Two Varieties of Cocoyam (Var esculenta and Var. antiquorum (L) Schott) Caused by Isolated Fungi Species in Plateau State, Nigeria

Abstract

Biochemical analyses were carried out to determine the changes that occurred in two varieties of cocoyam (var. esculenta and var. antiqourum (L.) Schott (Hubbard & Render) corms and cormels inoculated with Alternaria alternate, Fusarium oxysporum, Verticilium lateritium, Botrydiplodia theobramae, Colletotricum coccoides, Phythium myriotylum, Fusarium verticillioides, Rhizopus stolonifer and Geotricum candidum. Significant increases (P<0.05) were observed in moisture, protein, crude fat, fiber and ash contents of the two varieties of the cocoyam corms and cormels inoculated with the fungi during the 14-day period of incubation, when compared with the un-inoculated corms and cormels. In the var. esculenta, A. alternata, B. theobromae, P. myriotylum, F. stolonifer, F. verticillioides, F. oxysporium, G. candidum, C. coccoides and V. lateritium increased the moisture content, protein content,crude fat content,fiber content and ash content in corms and cormels incubated for 14 days in complete darkness at 25° C ± 2 C, when compared to their controls. The nine fungi caused a significant (P<0.05) reduction in carbohydrate and in vitamin content when compared to their controls. Similarly, in the var. antiquorum, A. alternata, F. oxysporium, F. stolonifer, P. myriotylum, B. theobromae, P. myriotylum, C. coccoides, V. lateritium, G. candidum and F. verticillioides increased the moisture content, protein content, crude fat, crude fiber and ash content when compared to the controls. The nine fungi caused a significant (P<0.05) reduction in carbohydrate and in vitamin contents. Vitamin composition showed the highest rate of decrease in var. antiquorum 0.10%-0.02% than var. esculenta 0.11%-0.05% inoculated with the same fungus (V. lateritium) compared to the control and the ones observed in both healthy varieties. The result revealed the presence of anti-nutritional composition of phytates, oxalates and cyanite in mg/l00g in both varieties, even though they both differed in concentration and thus, there was no significant difference (P>0.05) between them. The composition of oxalate is a little higher in var. esculenta than var. antiquorum with (2.53% and 2.17%) respectively. Moisture, protein and crude fiber contents increased more in var. esculenta than var. antiquourum, while crude fat and ash contents increased more in var. antiquorum than var. esculenta due to the effects of the fungi. Similarly, the fungi caused a higher decrease in the carbohydrate content of var. esculenta than var. antiquorum . The results of the study showed that the presence of fungi in cocoyam causes significant changes in the nutritional and biochemical components of the corms and cormels.