Study On The Extraction Of Roselle Seed Oil By Supercritical Carbon Dioxide

Roselle seeds are the by-products in processing of roselle calyx, and supercriticalextraction is a new separation technology developing fast in recent years. In thispaper, the extraction of roselle seed oil using supercritical carbon dioxide was studied.First, through single factor experiments, we investigated the effects on the extractionyield of the pretreatment conditions of raw material and extraction parameters,including extraction temperature, pressure, CO₂flux, time, separation pressure andtemperature. Considering the factors of economy, safety, energy consumption inpractical producing process, we provided a proper range of every parameter.Moreover, based on the results of single factor experiments, the Box-Bebnkenresponse surface design was applied to optimize the process of roselle seed oilextraction. The interaction between each two parameters was analyzed. Asecond-order polynomial equation was fitted, and the optimum conditions were alsoobtained. Finally, according to the related national standards for testing edible oil, thephysicochemical properties of roselle seed oil were tested. The composition of fattyacid of the seed oil was also analyzed by GC-MS. The results as follows:（1） The optimum pretreatment conditions for extraction of roselle seed oil usingsupercritical CO₂were: the crush degree of raw material was mesh size30, theamount of influx was150g, and reach about2/3of the extraction vessel’s capacity inpractical producing process.（2） Through analyzing the results of singe experiments, the proper range of everyparameter were: extraction pressure25MPa, temperature50～60℃, CO₂flux12L/h,extraction time100min, separationⅠpressure6MPa and temperature35℃, separationⅡ temperature50℃.（3） By analyzing the data of response surface experiment, the results were: theinfluence of every parameter was pressure> time> temperature, the interactionbetween pressure and temperature had a most significant effect on the extraction yield.The coefficient of the regression model was0.9932, which meant it was accurate enough. The optimum conditions were extraction pressure28MPa, temperature50℃,time110min and the theoretical yield was22.19%. Verification result was close to thepredicated value, which revealed that the model and conditions were reasonable.（4） Compared with the results of extraction by solvent, the oil yield of extractionby supercritical CO₂was a little less. However, it took a much shorter time, and theprocess was simple and green, without any solvent left in the oil.（5） The physicochemical properties of roselle seed oil were: refractive index1.4677, specific gravity0.9058, moist and volatile matter0.05%, acid value1.215mg/g, iodine value112.6g/100g, peroxide value0.7941mmol/kg, saponificationvalue197.9mg/g, unsaponifiable matter1.32%. The values above were close to thatof rapeseed oil, the related values met the hygienic standard for edible oil，but theacid value was below that of first grade oil.（6） The composition of fatty acid was: tetradecanoic acid （1.62%）, hexadecanoicacid（33.34%）, heptadecanoic acid（1.56%）, oleic acid （19.69%）, linoleic acid（43.79%）.The total unsaturated fatty acids were63.48%and linoleic acid were the main fattyacid, which revealed the roselle seed oil was kind of functional plant oil.