The process of corn oil extraction includes the separation of embryos and the extraction of embryos.
1. Separation of embryos
The separation of corn germ mainly consists of dry desquamation and wet grinding.Dry desquamation and embryo preparation means that the raw material is directly desquamated and embryo preparation without water treatment. Generally, it can be used when the moisture content of grains is around 18%, but the processing loss is relatively large.The wet grinding method is used to prepare the embryo powder by soaking and peeling the grains. The production process is as follows
（1）Soaking: the selected seeds should be soaked with so2 solution for 40-60 hours.Immersion barrels are usually made of stainless steel with a diameter of 5-6 meters and a height of 12-15 meters.
（2）Separation of crushing and embryo: after soaking, the corn kernels have softened, and the tissue components have become loose. After grinding or crushing, the embryo separation groove is added with water to make the embryo float on the water surface and separate the embryo.Embryo separation trough is a traditional technology in China, but the highest separation rate is only 85%, and the separation efficiency is low. At present, both foreign and large processing plants in China use hydrocyclone for separation, and the embryo separation rate can reach over 95%.
2.Corn germ oil and corn oil refining process
In the process of oil pressing, it is necessary to pay attention to all the key processing steps before corn embryo being pressed and oil road dredging and wool oil recovery in the process of oil pressing, which can effectively improve the ratio of grain and oil. Hair oil produced contains a certain amount of saturated fatty acids, lipids, waxes and cholesterol, as well as non-glycerine impurities such as free fatty acids, phospholipids, pigments and a small amount of protein colloids.There is also some pigment. Therefore, in order to get refined corn oil, it must be processed by dewaxing, deacidification, decolorization and deodorization.
There are two kinds of pigments in corn wool oil: one is natural pigments, such as carotene, lutein, chlorophyll and other substances, which are easy to be adsorbed and decolorized by drift soil. The other is the pigments formed by decomposition products of organic matter, which is brown, and are not easy to be absorbed and decolorized by bleaching soil..
They are usually distributed in a positive gel state in the oil. Although some of the pigment is removed during processing, but a greater extent of recovery. The decolorization process used to produce corn oil is the cross decolorization process of the secondary decolorization effect of primary bleaching soil.To the material embryo processing is not timely, produces the oil color deeper wool oil, decolorization is more difficult, may use the predecolorization decolorization process.In addition to the original corn flavor, the decolorized corn oil also has the “soap” flavor in alkali refining and the “earth fishy” flavor in decolorization.
The production of corn oil first involves the extraction of corn germ. The extraction methods of corn germ mainly include dry method, wet method and semi-wet method.
(1) Extraction of corn germ
A.Dry embryo extraction
That is to say, the method of separating the skin, embryo and endosperm by rubbing, squeezing or impinging the grinding of corn without water regulation. The process is simple, energy consumption is low, pollution is free, but the efficiency of embryo is low and the embryo contains many endosperm.
B.Wet mention embryo
The method of soaking, crushing and degerming corn, separating the embryo and starch by hydrocyclone separator. The efficiency of the method can reach 85% ~ 95%, the water content of the embryos is up to 60%, the embryos must be dried, the dried embryos (water content is 2% ~ 4%) and the oil content is up to 44% ~ 50%.Therefore, large energy consumption, environmental pollution, large equipment investment, high production cost, long investment recovery period.
Its principle is to use the corn embryo and endosperm of the different water content, water imbibition, and after water absorption differences in flexibility, toughness, crushing strength, choose suitable machinery and equipment, corn is broken and peeling and degerming, then using the different physical properties of the embryo and endosperm, the germ flattening, the endosperm is crushed, and then through a sieve, sorting out the germ, thus realize the purpose of the embryo. The method was used to wet the corn until its water content was up to 6 % ~ 20%.This method can improve embryo efficiency by more than 85%, with low energy consumption, no pollution, less equipment investment, short payback period and low production cost, but the embryo contains a certain amount of endosperm.
(2) Preparation of corn oil
There are two methods to produce corn oil from corn germ. Second, solvent leaching method, suitable for large oil plant; Thirdly, hydrolase method is a new method developed in recent years. Currently looking for the most of the production of corn germ oil enterprises to adopt squeezing method, using the technology of corn germ oil production, its highest productivity can reach 65%, only a few large enterprises on the basis of the squeezing method and the solvent extraction method is used to produce corn germ oil, these two kinds of processing technology of corn germ oil productivity by 97%.
A、Pretreatment and press process
Generally, screw press is used. In order to ensure a higher oil yield, the pressure of the press is above 69 MPa, in addition to satisfying the above conditions. The residual oil in the crushed cake should be controlled at 6%-7% and the water content in the cake should be 3%-4%. For the sake of safety, the water content of the finished cake should be adjusted to about 12%.
The moisture content of maize germ must be controlled in an appropriate range to meet the water requirement of human-soaked billet in the post pre-pressing and leaching process. It is also conducive to non-sticking rolls during billet rolling and easy to press maize germ into uniform thin sheets, thus creating favorable conditions for reducing residual oil of billet. The suitable moisture content of billets after drying is 10% to 11%. To prevent the increase of the powder content, the thickness should be controlled between 0.35 and 0.45mm. Steaming, pre-pressing and cooling can further change the internal and external structure of embryo grain, solidify and denaturate protein, reduce the resistance of oil molecules to diffuse outward, and adjust the moisture and temperature of human soaked blank. For corn germ in pre-press leaching process, it is advisable to control the moisture requirement of human leaching billet at about 4%-6%. For solvent No. 6, the temperature of the inlet blanks is 50~55 degrees. Leaching, purification, evaporation, vapor extraction and solvent recovery are operated according to the operation rules of conventional leaching process.
C、Aqueous enzymatic production
Aqueous enzymatic solution leaching process is a process of extracting oil from plants with mixed solution of water and enzymes. It is a new technology of oil production. Oil exists in cell organs. Cell walls are composed of cellulose, hemicellulose, lignin and pectin. Oil usually binds with other macromolecules (proteins and carbohydrates) to form lipopolysaccharides, lipoproteins and other complexes. Only by destroying the cell structure and lipid complexes of oil tissue can it be removed. Grease. On the basis of mechanical breakage, oils were treated with enzymes (such as cellulase, hemicellulase, pectinase, amylase, glucanase and protease) that degraded oil tissue and lipopolysaccharide and lipoprotein complexes. These enzymes could destroy cell walls, while proteases penetrated into liposome membranes. The decomposition of lipopolysaccharides and lipoproteins by enzymes is conducive to the release of lipids from lipids and fats, thus increasing the oil yield.
The enzymatic oil extraction process can be divided into four categories: aqueous enzymatic hydrolysis water extraction process, aqueous enzymatic hydrolysis organic solvent extraction T process, oil extraction process with low-moisture enzymatic decompression and oil extraction process with low-moisture enzymatic hydrolysis solvent. It is reported that Jiangnan University has successfully developed a simple and feasible process for extracting corn oil and peanut oil by enzymatic hydrolysis, and the yield is 88%-92%. In addition, the technology of aqueous enzymatic extraction of corn oil is also reported in relevant literatures.
（3）Refining of corn oil
Crude corn oil is a deep reddish amber plant oil obtained from the extraction of corn germ. Crude corn oil contains 1-3 phospholipids, more than 1 sterol, tocopherol and other unsaponifiable substances, about 1.5 free fatty acids, about 0.05 wax, and has an unpleasant special odor. The crude corn oil has high impurity content and can not be used directly because of its turbidity at low temperature. After refining, it can be used to obtain corn refined oil or salad oil with low turbidity point, low melting point and stable storage. After further processing, it can also be used as milk powder JL for children and the elderly health food, medicine and high-grade cosmetics raw material oil, etc. .