Extraction, properties and utilization potentials of African walnut (Tetracarpidium Conophorum) as an alternative to conventional vegetable oils

Abstract

The extraction, physical and sensory properties, proximate composition, chemical properties, mineral and fatty acid composition of African walnut (Tetracarpidium conophorum-Mull. Arg) nuts and oil extracted using soxhlet extractor was evaluated in this work using standard analytical procedures. Physical properties of African walnut oil showed that the oil was liquid at room temperature (25°C), pale yellow colouration, odourless and tasteless. The proximate composition results showed the percentage (%) moisture, crude fibre, ash, crude protein, lipids and carbohydrate contents of the nut was 2.36, 1.6, 1.42, 14.5, 59.4 and 26.9 while the calorific values were 523.8 Kcal/100 g respectively. Chemical characteristics of the nut oil indicated the Specific gravity (SG) 0.94, Refractive index (PI) 1.445, Acid Value (AV) as 0.92 mg KOH g-1, Free Fatty Acids (FFA) as 0.56 %, Peroxide Values (PV) as 1.02 meg O2 kg-1, Saponification Value (SV) as 170.1 mg KOH g-1, Unsaponification Value as 4.1 g/ Kg-1, Iodine Values (IV) as 91.3 (mg of 1g-1 of oil ) Wijis. These results suggest that the African walnut examined may be nutritionally potent and also viable source of oil judging by its oil yield value. The data also showed that the oil is edible, a semi-drying inferring from the low AV and low FFA contents. Industrially, the results revealed the nut oil have great potentials in soap manufacturing industries because of the high SV. The main fatty acids identified by gas chromatography were palmtic (1.53 %), linoleic (13.05 %), linolenic (80.59 %), stearic (4.41 %) and eicosenoic (0.42 %) acids. The mineral contents of walnut were established by using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). African walnut was highly rich in minerals such as K (3450.3 mg/kg), P (3021.7 mg/kg), Mg (1076.9 mg/kg), Ca (1008.5 mg/kg) with low amounts of B (52.5 mg/kg), Mn (38.7 mg/kg), Na (36.6 mg/kg), Fe (29.8 mg/kg), Zn (20.2 mg/kg), Se (13.6 mg/kg) and trace amounts of Cr (7.9 mg/kg), Ni (1.8 mg/kg) and Li (0.56 mg/kg). The results obtained for African walnut oil are compared with values reported for other conventional vegetable oils available commercially and discussed in terms of potential uses of the oil.