PROCESS OPTIMISATION OF MECHANICAL OIL EXPRESSION FROM Moringa oleifera (Lam.) (MORINGA) SEEDS

Abstract

Moringa oleifera plant is a promising nutritional and economic resource for developing countries. Previous studies on moringa plant have focused largely on its medicinal and nutritional uses, with only a few on extraction of oil from its seeds; while solvent and aqueous enzymatic oil extraction methods have been reported for moringa seeds, literature is scarce on mechanical oil expression. This study was conducted to investigate and optimise mechanical oil expression from moringa seeds. Selected physical and mechanical properties of moringa seeds determined using ASABE standards were input parameters for the design and subsequent fabrication of an oil expeller. Central composite rotatable design at 4 factors and 5 levels was adopted for the experiments. Based on moisture content at harvest, preliminary tests and literature, moisture contents (8, 9, 10, 11 and 12% wet basis), heating temperature (50, 60, 70, 80 and 90oC), heating time (15, 20, 25, 30 and 35 min) and applied pressures (5, 10, 15, 20 and 25 MPa) were chosen. Oil yields were calculated as percentage of input materials; while oil quality criteria such as Free Fatty Acid (FFA), oil impurity and colour were determined using AOAC standard methods. The efficiency of oil expression was obtained in terms of yield and material output. Data analyses were done using multiple linear regression at p = 0.05. Predicted optimum conditions were validated using experimental values. Moisture content of the moringa seeds was 7.31±0.31% (wet basis). The seed length, width and thickness of 8.45±0.98, 7.82±0.92 and 6.41±1.10 mm respectively were used in determining perforation size and barrel clearance. The true and bulk densities of 971.0±0.11 and 662.0±0.03 kgm-3 respectively were useful in determining the expeller capacity and the angle of repose of 21.4±0.75o for hopper, oil and cake troughs design. The peak force, deformation and rupture energy of 67.0±5.47 N, 5.35±0.10 mm and 0.17±0.02 Nm respectively obtained were for determining energy and force requirements of the expeller. Oil yield ranged from 11.42-28.6% with the highest obtained at moisture content of 11%, temperature of 80oC, duration of 30 mins and pressure of 20 MPa. The FFA, oil impurity and colour ranged from 2.42-7.40 mg/KOH/g, 2.12-3.20% and 5.70-7.60 LU respectively and fell within acceptable limits. The expressed and material balance efficiencies were 81.7 and 93.8% respectively. Coefficients of determination (R2) for the oil yield, FFA, oil impurity and colour were 0.77, 0.94, 0.98 and 0.99 respectively. Predicted optimum oil yield of 28.2% at moisture content of 11.30%, temperature of 85.57oC, duration of 27.17 mins and pressure of 19.63 MPa was obtained. Deviations between experimental and predicted values were low and ranged from 0.01-6.20, 0.01-0.68, 0.01-0.12 and 0.01-0.12 for the oil yield, FFA, colour and oil impurity respectively. Moisture content, applied pressure, heating temperature and duration influenced the quality and quantity of oil recovery from moringa seeds using expeller. High oil expression efficiency obtained makes the expeller a potential for moringa oil expression.