Chemical and biological evaluation of Nigerian cottonseed meal protein quality

Abstract

Batch samples of cottonseed meals were obtained from four oilseed processors in Nigeria (Funtua (FCCC), Gusau (GuOM), Kano (KSOAP) and Combe (GOSP), and their protein quality was evaluated by chemical and biological assays. The chemical indices included nitrogen solubility, available lysine and available methionine, while the biological evaluation involved rat feeding trials. The average percentage of total meal nitrogen which was soluble in 6 N HCl ranged from 63.3 in GuOM to 80.1 in KSOAP. Average values of available lysine were 4.24, 3.76, 3.44 and 3.63 g 16 g N for KSOAP, FCCC, GuOM and GOSP, respectively, while available methionine averaged 0.61, 1.27, 1.16 and 0.79 g 16 g N for the respective meal types. The average values of protein efficiency ratio (PER) ranged from 0.66 to 1.14, net protein retention (NPR) from 2.07 to 2.56, net protein utilization (NPU) from 41.6 to 49.4 and true protein digestibility 77.9 to 84.4. Available lysine and nitrogen solubility both correlated positively and significantly with PER, NPR and NPU. The data portrayed the variability in protein quality of cottonseed meals produced under varying processing conditions and suggested a need for screening the material, especially before feeding non-ruminant animals.