Optimization of Solvent Extracted Okra Seed Oil - A Response Surface Approach
A. A. Sulaiman
Department of Food Engineering, Ladoke Akintola University of Technology, Ogbomoso, Nigeria.
J. A. Adeyanju *
Department of Food Engineering, Ladoke Akintola University of Technology, Ogbomoso, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Okra (Abelmoschus esculentus) oil has a significant unsaturated fatty acid content and notable nutritional and industrial potential in food and allied industries. However, efficient extraction of the oil remains a challenge, limiting its utilisation. Therefore, this study aimed to investigate the effects of extraction parameters on the oil yield and quality attributes of oil from okra seeds. The effects of extraction temperature, extraction time, and solid-to-solvent ratio on the yield and quality attributes (acid value, free fatty acid, peroxide value, iodine value, saponification value, refractive index, and pH) of oil extracted from okra seeds were studied using RSM. Extraction temperatures, times, and solid-to-solvent ratios were 35, 45, and 55 °C; 60, 120, and 180 min; and 1:20, 1:30, and 1:40 g/mL, respectively. Data were analysed by ANOVA and regression analysis. Oil yield ranged from 10.50 to 13.00%, free fatty acid from 1.70 to 2.98 mgKOH/g, acid value from 8.03 to 12.00 mg KOH/g, peroxide value from 8.70 to 13.00 meq O₂/kg, saponification value from 182.00 to 200.80 mg KOH/g, refractive index from 1.45 to 1.47, iodine value from 15.86 to 42.82 g I₂/100 g, and pH from 2.00 to 6.60. The treatments had significant effects on all response variables at p < 0.05. The coefficients of determination (R²) for the oil yield, acid value, free fatty acid, peroxide value, iodine value, saponification value, refractive index, and pH models were 0.9273, 0.8345, 0.8331, 0.9421, 0.8457, 0.9459, 0.9374, and 0.9931, respectively. The optimum extraction temperature, time, and solid-to-solvent ratio were 36.96 °C, 100.49 min, and 21.62 g/mL, respectively. This combination gave an oil yield of 12.43%, free fatty acid of 21.48 mg KOH/g, acid value of 10.20 mg KOH/g, peroxide value of 8.70 meq O₂/kg, saponification value of 190.00 mg KOH/g, refractive index of 1.47, iodine value of 18.77 g I₂/100 g, and pH of 3.24. The extraction of okra seed oil was successfully optimised using RSM. The regression models obtained provide a basis for selecting optimum process variables for oil recovery using solvent extraction.
Keywords: Box–Behnken design, Okra seed oil, Oil yield, Physicochemical properties, Solvent extraction