Extraction of Oat Lipids and Phospholipids Using Subcritical Propane and Dimethyl Ether: Experimental Data and Modeling

Effects of subcritical solvents (propane, dimethyl ether (DME), and their 1:1 mixed solvents) and extraction temperatures (30 to 60 °C) on oat lipids and phospholipid extraction are investigated using the Patricelli kinetic model and thermodynamic analysis. The mass-transfer coefficient (k₁) of the washing stage is approximately ten times higher than the diffusion stage under different solvents and temperature conditions. Compared with the subcritical propane and mixed solvents, the maximum equilibrium yield of oat lipids and phospholipids are obtained using subcritical DME. With increased extraction temperature from 30 to 60 °C, the equilibrium yield of phospholipids increases, whereas the equilibrium yield of lipids increases to 5.30% at 40 °C and then decreases. The enthalpy and entropy changes for phospholipid extraction are higher than those for lipid extraction. The Gibbs free energy for phospholipid extraction rapidly decreases with increased extraction temperature. A loose endosperm of oat grain is observed, and the concentration of lipids in the bran layer is higher than in the endosperm. In conclusion, kinetic and thermodynamic analyses statistically prove that DME is more effective than propane and mixes solvents for extracting lipids and phospholipids from oat flakes, and that phospholipid extraction strongly depends on temperature. Practical Application: The removal of lipids and phospholipids benefits oat-product processing and storage. However, traditional industrial n-hexane extraction usually requires a high-temperature process for solute–solvent separation, which may result in low quality of the meal. Subcritical-fluid extraction is a rising technology for lipid and phospholipid extraction. The yields of lipids and phospholipids using subcritical dimethyl ether (DME) is higher than those propane and its mixed solvents. The temperature dependence of phospholipid extraction is more active than that of lipid extraction. Thus, use of subcritical DME is a promising lipid-extraction technique to obtain solvent­free oat oil and high-quality defatted oat flour with potential application in the oat-processing industry.