Abstract

The effects of roasting conditions (time-temperature) on the rate of extraction and quality of oils from two peanut (Arachis hypogea L.) cultivars (namely, kampala and ex-Dakar) were investigated. The oils were extracted at 50 ml hot-water/250 g peanut paste. High extraction rates were obtained by roasting the peanuts at 140°C for 20 min with Kampala yielding the highest oil. Above 140°C/20 min treatment, the rate of extraction decreased for both peanuts. Ex-Dakar responds faster to heat treatment than did Kampala assessed by colour. Crude fat and total carbohydrates were found to be high in Kampala and protein high in ex-Dakar. Free fatty acids (FFA) contents of both oils were below 20% and peroxide values (PV) were below rancidity level of 10 Meq/kg for both oils at 0 week. At treatment 140°C/ 20 min for both oils, ex-Dakar oil deteriorate faster than kampala assessed by FFA and PV levels after nine weeks storage under laboratory conditions. At this stage, ex-Dakar’s oil developed rancidity while kampala remained edible (PV< 10 Meq/kg). Boiling points, smoke points, refractive indices and specific gravities decreased with the heat treatments. Kampala oil was more stable after nine weeks storage, and had high smoke point good for frying operations. It also had more extractable fat compared to ex-Dakar.

Key words: Nigerian peanut, processed oil, temperature.