Abstract

I. I. Nkafamiya, B. A. Aliyu, A. J. Manji, and U.U. Modibbo

The deterioration of Adansonia digitata and Prosopsis africana oils on storage for 140 days was evaluated using chemical and physical parameters. The chemical parameters evaluated included peroxide value (PV), iodine value (IV), percentage free fatty acids (%FFA), and saponification value (SV). The physical parameters used involved the measurement of infrared (IR) spectroscopy and refractive index (RI). The metallic ions present in the A. digitata and P. africana oil have been analysed using atomic absorption spectroscopy (AAS). The metallic ions found to be present included calcium (Ca), iron (Fe), zinc (Zn), phosphorus (P), potassium (K) and sodium (Na) with potassium occurred in relatively high amount in A. digitata oil (280 �?� 1.34 mg/100 g). Systematic variations in these parameters with storage time were observed. These include initial increase followed by decrease in peroxide value, iodine value and increase in free fatty acids, saponification value and refractive index. These changes have been interpreted to be due to some structural changes in the triglyceride leading to the formation of new chemical properties or products over the period of storage. The IR spectra also have given an indication of the rancid state of the oils, due to bands observed at 3470 – 3490, 1745 – 1740, 970 and 870-890 cm-1 for hydroperoxides, ester C = O stretching (indicating possible formation/presence of aldehyde, ketones and acids), trans-isomer, peroxides, respectively, which are products of oxidative rancidity.