Sorrel (Hibiscus sabdariffa) Seed Oil Extraction Optimization and Quality Characterization

Aims: This study was aimed at separating seed oil from sorrel (Hibiscus sabdariffa) oilseeds using application of solvent extraction method. The process was optimized using response surface methodology and the quality of the seed oil was determined.

Methodology: Optimization of oil extraction from the oilseeds using response surface methodology was carried out. The effects of three independent factors (extraction time, solvent volume and sample weight) and their respective interactions on the response, oil yield, were investigated. A total of 17 experimental runs were generated using Box-Behnken design. The extracted seed oil was characterized to determine its quality.

Results: A quadratic polynomial was obtained to predict the oil yield and the ANOVA test showed the developed 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, 22g, solvent volume, 157 ml and time, 2 h. The optimized condition was validated with the actual oil yield of 17.85%, which was well within the range predicted. The seed oil analysis showed the physical state of the oil to be liquid/yellow-greenish in colour, specific gravity 0.886 ± 0.026, viscosity (at 40ºC) 15.40 cP, p-anisidine value 6.31, Totox number 16.31, %FFA 0.40 ± 0.01, acid value 0.80 ± 0.01 mg KOH.g oil-1, saponification value 197.75 ± 0.05 mg KOH.g oil-1, iodine value 97.77 ± 0.02 g I2.100 g oil-1, peroxide value 5.00 ± 0.01 meq O2.kg oil-1 and cetane number 51.90 ± 0.1. The fatty acid profile of the oil revealed that it is highly unsaturated (76.45%) with linoleic acid the highest (44.39%).

Conclusion: The physicochemical analysis of the sorrel seed oil indicated it is edible and could serve as feedstock for many industrial applications.