Effect of heat processing on the proximate composition and energy values of selected Nigerian staple foods from oil-producing areas of the Niger Delta

Proximate composition and energy values of four raw and heat processed staple foods (yams, cassava, cocoyam and maize) from oil-producing (Eleme, Ogoni, Okrika, and Nembe) areas of Rivers and Bayelsa States and Abakaliki (a non-oil producing area in Ebonyi State, Nigeria) as control were investigated. In raw yam tubers, moisture was high in all the locations and ranged from 61.96 ± 0.02% in Abakaliki to 63.77±0.25% in Ogoni. Crude protein ranged from 1.39±0.13% in Okrika to 1.71±0.06% in Abakaliki while ash was highest (2.57±0.12%) in Okrika followed by 2.33±0.01% in Eleme and was lowest (0.97±0.06%) in Abakaliki. Crude fat was low in all the locations and ranged from 0.10±0.00% in Okrika to 0.17±0.01% in Nembe while total carbohydrate was high in all the locations ranging from 33.32±0.42% in Ogoni to 35.21±0.13% in Abakaliki. The calorific value (kcal/100 g sample) in all the locations was low. It was highest (149.08) in yams from Abakaliki followed by Eleme (142.55) and lowest in Ogoni (140.09). Similar trends in values of the constituents were obtained in raw cassava, cocoyam and maize from different oil-producing and control locations investigated. In each of these locations, heat processing generally increased moisture content of all the samples (yam, cassava products, cocoyam and maize), but decreased dry matter, crude protein, ash, crude fat, total carbohydrate and calorific value. With the exception of moisture and ash, other nutrients were significantly (p<0.05) higher in the control area of Abakaliki than values obtained in similar samples from oil producing areas of the Niger Delta investigated.