Optimization, Kinetic Degradation and Quality Characterization of Oil Extracted from Nigeria Hibiscus sabdariffa Oilseeds

Abstract

This work focused on optimization of oil extraction from Sorrel oilseeds using Response Surface Methodology (RSM), it also to investigate the physicochemical properties and kinetics of degradation of the oil during heating. Based on Box-Behnken design, 17 experimental runs were conducted to investigate the effects of extraction time, solvent volume sample weight and their reciprocal interactions on the oil yield. A quadratic polynomial was obtained to predict the oil yield and the ANOVA test showed the model to be significant (p < 0.05). A statistical model predicted the maximum seed oil yield to be 18.25% at the optimal condition of sample weight: 22 g, solvent volume: 157 ml and time: 2 h. The optimized condition was validated with the actual oil yield of 17.85%, which was within the range predicted. The physicochemical properties oil extracted showed the oil to be yellowish green liquid at room temperature, the refractive index was found to be, 1.4603; the moisture content, 0.065%; specific gravity, 0.886; viscosity, 15.40 Cp; mean molecular mass, 283.30; p anisidine value, 6.31; totox number, 16.31; FFA, 0.40; acid value, 0.80; saponification value, 197.75 (mg KOH/g oil); peroxide value, 5.00 (meq O₂/kg oil); higher heating value, 39.86 (MJ/kg) and cetane no, 51.90.  The physicochemical analysis of oil suggested the oil could have important food and industrial applications. The fatty acid profile of the oil using GC technique revealed that the oil was highly unsaturated (74.45%) with (44.39%) linoleic acid which was the highest. The kinetics data for the degradation of Sorrel oil showed that the rate of degradation of peroxide value in Sorrel (H. sabdariffa) seed oil increases as the temperature increases. However, the impact of reaction time on the rate constant k and the nature of graph obtained was linear with the optimum activation energy of the reaction was determined as 70.67 kJ/mol at 250 ^oC. The reaction was of first order with R² > 0.5, t_1/2 of 5975 s and k₁ of 0.00116 s^-1.

Keywords: Optimization, response surface methodology, Kinetics, fatty acid, physicochemical properties.