Tea seed oil is derived from the seeds of the Camellia oleifera plant. It possesses a distinctive aroma, is easy to store, and is quickly absorbed by the human body, with high nutritional value. This oil contains various fatty acids, including oleic acid, linoleic acid, palmitic acid, stearic acid, and myristic acid.
Several methods exist for extracting tea seed oil. Since tea seed oil is heat-sensitive and cannot withstand high temperatures, traditional hot pressing significantly alters its color. Solvent extraction, on the other hand, leaves residual solvents, resulting in poor product stability and potential health risks.
Different extraction methods yield different results for tea seed oil. Hot pressing destroys nutrients in the oil, making the final product difficult to store, causing significant nutritional losses, reducing oil yield, and negatively affecting color. Solvent extraction produces an unstable product with residual solvents, which is detrimental to health.
Supercritical fluid extraction technology is characterized by low energy consumption, high efficiency, and no pollution. It is simple to operate and easy to control, and is therefore widely applied in numerous fields such as food, medicine, chemicals, and biochemistry. This extraction method preserves both nutrients and active ingredients without damaging tea seed oil due to high temperatures, making it a green and efficient process. It is commonly used in food and grain processing and is particularly suitable for extracting functional components from plants. For instance, it can be used to extract oils such as walnut oil, grapeseed oil, sea buckthorn oil, and pumpkin seed oil, as well as substances such as lecithin, flavors, and pigments.
Experiments showed that several key factors influence the extraction yield of tea seed oil: extraction pressure, extraction temperature, extraction time, and CO₂ flow rate.
Effect of Pressure on Extraction Yield
The extraction yield increases with rising pressure. Higher pressure increases the density of CO₂, thereby enhancing its capacity to dissolve tea seed oil. The optimal extraction pressure was determined to be 35 MPa.
Effect of Temperature on Extraction Yield
Temperature exerts a complex influence on the solubility of supercritical CO₂. Under constant pressure, increasing temperature accelerates molecular motion, strengthens molecular interactions, reduces fluid viscosity, and improves solubility. However, it also decreases fluid density, which reduces the fluid's capacity to carry tea seed oil. These two opposing effects collectively determine the optimal extraction temperature. For tea seed oil, the optimal extraction temperature is 50°C.
Effect of CO₂ Flow Rate on Extraction Yield
During dynamic extraction, a higher CO₂ flow rate results in a higher extractant-to-material ratio, which promotes the diffusion and solubility of the extract. As shown in Figure 3, the extraction yield increases with the increase in CO₂ flow rate; however, when the flow rate exceeds 20 kg/h, the extraction yield decreases slightly. This may be attributed to the excessively high flow rate, which shortens the residence time of CO₂ in the material, leading to insufficient contact between CO₂ and the material and thus reduced solubility. Experimental results indicate that the optimal CO₂ flow rate is 20 kg/h.
Effect of Extraction Time on Extraction Yield
The total extraction yield gradually increases with the extension of extraction time. From both technical and economic perspectives, prolonging the extraction time increases energy consumption. Therefore, the appropriate extraction time is 150 minutes.
When extracting tea seed oil using supercritical CO₂, the optimal process conditions (with raw material particle size of 40 mesh) are as follows: pressure of 35 MPa, temperature of 50°C, CO₂ flow rate of 20 kg/h, and extraction time of 150 minutes. Under these conditions, the extraction yield can reach 33.5%. In contrast, the conventional solvent extraction method takes 6 hours and achieves an extraction yield of only 30.3%. The supercritical method not only requires less time but also extracts more tea seed oil from the raw material, resulting in higher raw material utilization. Thus, it is a new technology with broad development prospects.
When extracting tea seed oil using supercritical CO₂, the operating temperature is low, which prevents the destruction of heat-sensitive components in the oil and allows the oil to retain its natural aroma. Food-grade CO₂ was used in the experiment, so the resulting product contains no solvent residues and is a natural green food.