Effect of roasting time on selected properties of extracted groundnut seeds (Arachis hypogea L.) oil

Abstract

Effect of different roasting times on the yield and selected physicochemical properties of the oil extracted from groundnuts was investigated. Raw groundnut seeds purchased were cleaned, roasted (110-120^oC for 4, 6, 8, 10, and 12 min), dehulled and milled into paste. Unroasted groundnut seeds served as control. N-hexane was utilized for oil extraction (1000ml n-hexane per 500g peanut paste). Proximate composition of the seeds and physicochemical properties (acid value, iodine value, peroxide value, refractive index and free fatty acid value) of oil extracted were determined. Results indicated that the seeds contained 43.30% crude fat, 32.50% crude protein, 3.20% crude fiber, 2.20% ash, 4.11% moisture and 9.70% carbohydrate. The volume of oil extracted ranged from 130 to 175ml for 0 to 12 min. Data for acid value were 1.89-2.50 mgKOH/g, 0.39-0.90 meq/kg for peroxide value, 91.15-105.50mg/ KOH for iodine value, 167.60-204.70 mgKOH/g for saponification value, 0.95-1.26mgKOH/g for free fatty acid, and 1.46-1.47 for refractive index. Overall results indicated that roasting time of six (6) min at a temperature range of 100-120^oC could be chosen for optimum yield and enhanced selected physicochemical properties of groundnut oil. Besides, the method of extraction can be adopted at both rural community and urban level in Nigeria and other developing countries.

Keywords: Acid value, extraction, groundnuts, roasting time, yield