Combination of thermal pretreatment and alcohol‐assisted aqueous processing for rapeseed oil extraction

BACKGROUND The alcohol‐assisted aqueous extraction processing (AAEP) of oil has many advantages such as no need for demulsification and relative low cost compared with enzymatic aqueous extraction processing (EAEP). Three kinds of thermal pretreatments including dry‐heating, wet‐heating and soak‐heating followed by the AAEP of rapeseed oil were investigated. RESULTS Both soak‐heating and wet‐heating had a higher contribution rate to oil yield than dry‐heating due to the enhancement of heat transfer rate owing to the high moisture content in the rapeseed cells. However, oil from soak‐heated rapeseeds showed a much lower level on peroxide value (0.41 mmol kg−1) than that of wet‐heated rapeseeds (5.23 mmol kg−1). In addition, transmission electron microscopy images illustrated that promoting effects of soak‐heating and wet‐heating on oil release were attributed to the coalescence of oil bodies. A relative low concentration of alcohol solution as an extraction medium, the highest oil recovery of 92.77% was achieved when ground rapeseeds (mean particle size: 21.23 µm) were treated with 45% (v/v) alcohol for 2 h at 70 °C and pH 9.0. Both the acid value and the peroxide value are lower than the commercial oil produced by extrusion and hexane extraction. Furthermore, the oil produced from AAEP also had higher content of tocopherols and lower content of trans‐fatty acids than the commercial oil. CONCLUSION AAEP of oil from soak‐heated rapeseeds is a promising alternative to conventional oil extraction methods. © 2019 Society of Chemical Industry