Edible oils are widely utilized in diets as a major source of fat and a heat transfer medium during frying. Improvement on nutritive value is a major concern in edible oil industry. Therefore, objectives of this work were to investigate the effects of sweet pepper (
Capsicum annuum
) and tomato fruit (
Lycopersicon esculentum
.) as additives on some physical and functional properties, nutritive values and stability of peanut (
Arachis hypogaea
) oil. Response surface methodology was employed to study effect of natural additives on peanut oil. The variables were additives ratio (5:0, 3:2, 2.5:2.5, 2:3, 0:5) of sweet pepper: tomato and incubation time (1, 1.5, 2.5, 4, 6 hrs). While the responses were oil iodine value, peroxide value, free fatty acid, saponification value, colour, viscosity, beta–carotene, vitamin E and vitamin K. The calculated means for iodine value, peroxide value, free fatty acid, saponification value, colour, viscosity, β–carotene, vitamin E and vitamin K were 105.39 ± 10.38 Wijs, 9.89 ± 2.81 mEqkg
-1, 2.4 ± 1.13%, 166.1 ± 20.53 mgKOH/g, 0.16 ± 0.2 A, 0.02 ± 0.00 Nsm
-2, 788.3 ± 69.50 µg/100g, 12.7 ± 0.87µg/100g and 7.8 ± 0.59 µg/100g, respectively. Coefficient of determination (R
2) of models for iodine value, peroxide value, free fatty acid, colour, viscosity, β-carotene and vitamin E were 0.76, 0.91, 0.76, 0.89, 0.93, 0.97 and 0.84, respectively. Functional properties of the oil including iodine value and saponification value reacted differently to treatment. Iodine value was significantly (p<0.05) influenced while non-significant (p>0.05) effect was recorded for the saponification value. The treatments significantly (p<0.05) influence peroxide value and free fatty acid of the extracted oil. Physical properties of the peanut oil measured by colour and viscosity were significantly influenced by the treatment (p<0.05). Nutritive values of the peanut oil which were beta-carotene and Vitamin E were significantly (p<0.05) influenced by the treatments but Vitamin K was not significantly influenced.
