Supercritical extraction (SFE) and subcritical fluid extraction (SUBE) technology

SFE technology is different from traditional solvent extraction methods and has the advantages of high safety, good selectivity, fast extraction speed, and no solvent residue. SFE uses a fluid exceeding the critical temperature and pressure as an extractant. The temperature is relatively high. CO2 is mostly used as a solvent for the extraction of non-polar or weakly polar substances such as lipids, but the polarity of the solvent can also be adjusted by adding appropriate co-solvents; SUBE uses a solvent below the critical temperature and pressure as an extractant. Based on the principle that similar organic matter dissolves in the same, the target product in the raw material is transferred to the liquid extractant through the molecular diffusion process during the soaking process, and then the extractant and the target product are separated by reduced pressure evaporation. The temperature is relatively low, and the solvent is usually propane, butane, dimethyl ether or water. Therefore, the choice between the two can be made according to the polarity and thermal sensitivity of the target product to be extracted. Using ethanol to modify subcritical water to extract curcumin can increase the solubility of curcumin and effectively prevent its thermal degradation; similarly, adding polar co-solvents during supercritical CO2 extraction can extract and separate polar substances such as flavonoids and amino acids. Lefebvre et al. selectively separated rosmarinic acid, carnosic acid and chlorophyll from rosemary leaves by controlling SFE parameters; when SFE is used in combination with SUBE, the extraction efficiency can be further improved. For example, when Kamchonemenukool et al. successively used supercritical CO2 extraction and subcritical liquefied dimethyl ether extraction to extract γ-oryzanol from rice bran cake, since CO2 removed other non-polar compounds during the first extraction, γ-oryzanol was easily dissolved by liquefied dimethyl ether during the second extraction, and the extracted γ-oryzanol content was much higher than that of the traditional method and other methods combined, reaching 8128.51 mg/100 g.