Summarization on vegetable oil extraction technology by aqueous medium method

Abstract: Vegetable oil is an exceedingly important and indispensable part of the modern diet. Most of the production methods of vegetable oils in traditional commercial company are the hot-pressing method and/or the solvent extraction method. The hot-pressing method is a conventional oil production method in which oilseeds are firstly treated under hyperthermal condition and then exuded by mechanical extrusion. This method has the characteristics of simple equipment and universality on the production of different oils, but its oil yield is relatively low. In addition, during the long-time hyperthermal treatment, oil may be oxidized, and then the oxidation product would degrade and generate some harmful compositions, such as trans-fatty acid and polycyclic aromatic hydrocarbons. The solvent extraction method applies hexane as extraction solvent chiefly, and has a high oil yield (>96%). But in hexane extraction, many byproducts would be dissolved out with the oil, which leads to the inferior physical-chemical characteristics of crude oil. Hence, the deep refining is needed, however, excessive refining not only causes the loss of nutrients, but also may bring new harmful substances, such as plasticizers, heavy metals and chlorine propanol esters. Furthermore, hexane has been identified as the hazardous air pollutant. Because of the toxicity and flammability of hexane and the increasing demand of food safety, the development of alternative green production process of vegetable oils is becoming extraordinarily urgent. The aqueous extraction method is recently receiving considerable attention, in which pure water is employed as main extraction medium. It is a new developed green and efficient oil extraction technology. Compared with traditional technology, this method is mild and safe due to the relatively low temperature and the complete avoidance of organic solvents. Based on the decades of our team's research work on the aqueous medium extraction technology, we have established the concept of aqueous medium method of vegetable oil extraction technology firstly in this review. The so-called aqueous medium method of vegetable oil extraction technology employs pure water as the main extraction medium, with or without the assistance of edible substances that are miscible with water like ethanol, food-grade enzyme, supersonic and microwave. The effects of these supplements were to destroy the cell wall of oil-bearing materials or prevent the formation of highly-creamed emulsion in extraction process. This method contains aqueous extraction method, aqueous enzymatic extraction method and aqueous ethanol extraction method. In this review, the technological process, technical features, development history, existing problems and promising prospects are also discussed in detail.