Corn embryos, which are generally used for oil extraction, are by-products that are isolated during the processing of starch by corn, while high-oil corns are used for processing oil, including the separation of embryos and the oil extraction of embryos.

(I) Separation of corn embryos

The separation of corn embryos mainly includes dry dehullation and embryo extraction and wet milling. The raw materials are directly peeled and exfoliated to prepare powder without water treatment, which is called dry exfoliation and embryo extraction. General grain moisture content of about 18% can be used, but the loss of processing is large; wet grinding embryo extraction method, is the grain after soaking treatment after peeling extract embryo powder. Wet grinding method has high embryo extraction rate and oil yield, and its production process flow is:

(1) Soaking

The cleaned seeds are first soaked with sulfur dioxide solution (0.15% to 0.2%, pH 3.5, temperature 50-55°C) and soaked for 40-60 hours. The reductive and acidic dispersal of the sulfur dioxide solution destroys the protein network structure in the grain, so that the embryo, skin, and starch in the grain are dispersed. The soaking barrel is generally a stainless steel barrel having a diameter of 5 to 6 meters and a height of 12 to 15 meters.

(2) Separation of crushing and embryos

After soaking, the corn kernels have softened, loosened between the various tissue components, broken by a mill or a crusher, and then the embryos are floated on the surface of the water through the embryo separation tank to separate the embryos. The use of embryo separation tank is a traditional process in China, but the highest separation rate is only 85%, and the separation efficiency is low. At present, foreign and China's larger processing plants use cyclones for separation, and the embryo separation rate can reach more than 95%.

(B) Maize embryo oil

Corn embryos, like other oils, also need to be cleaned, rolled, steamed, pressed, and squeezed. The leaching method (extraction method) is an advanced oil extraction method in modern times, and has a high oil yield, and the use effect of the pancake is also good. However, because corn embryos are mostly separated from starch factories or other corn processing plants, and there are not many raw materials for corn embryos, the majority of corn embryo oils are squeezed by pressing methods, unless a certain amount of corn embryos can be concentrated to establish a certain scale. Leaching corn oil plant. The process of corn embryo oil extraction is:

Maize embryo → pretreatment (screening, magnetic separation) → heat treatment → embryo rolling → steaming → pressing → oil

1. Pretreatment

Maize embryos used for oil extraction should have a certain degree of freshness; the shorter the storage time, the more fresh the better the oil yield and the quality of the oil; on the contrary, if the storage time is too long, the oil yield will be reduced and the oil will be affected. The quality of the product may even be mildewed and there is the potential for contamination. The resulting corn oil can also cause harm to humans. Therefore, corn embryos should not be stored for too long, and it is best to start new embryos. If new embryos cannot be pressed, corn embryos can be dried or fried to prevent deterioration.

Maize embryos that enter the oil mill have dry and wet-separated corn embryos. Dry corn embryos are poorly separated and contain many starch and corn bran. The biggest impurity factor affecting the oil rate is starch, which will be gelatinized during the steaming process of corn embryos, reducing the area of ​​oil flowing out of the oil during the pressing process and blocking the oil path. Therefore, the screening method should be used as far as possible before pressing oil. Remove these debris. Wet-processed corn embryos have high purity and high oil yield. Maize embryos should also undergo magnetic separation before entering the press to remove magnetic metal debris to protect the oil extraction equipment.

2. Rolling the embryo

Before the corn is crushed and decoctioned, the corn generally undergoes a process of moistening the skin to increase the moisture content of the corn embryo. Before the embryo is rolled, the softening treatment must be performed to adjust the temperature and moisture of the corn embryo and reduce its toughness. It can be softened by a hot air dryer, dried to moisture below 10%, and then subjected to the embryo rolling process.

The purpose of rolling the embryos is to break the germs, destroy the cell walls of the germ, and denature the proteins to facilitate oil extraction. The general small oil mill uses the φ200370 type of rolling mill, the rolling distance should be adjusted properly, and the rolled embryo thickness should not exceed 0.5 mm, preferably 0.3-0.4 mm. When feeding the embryos, the feed should be even and not too much. The corn embryo should be pressed thin and not broken, without exposing the oil.

3. Heat treatment

Heat treatment is steaming. This is the most important part of the corn embryo oil pretreatment stage. Its effect is good or bad, directly affecting the oil quality and oil extraction effect. In the process of steaming and frying, the protein can be fully denatured and solidified by heating, and at the same time, the viscosity of the oil is reduced, and the oil droplets are further accumulated, which facilitates the outflow of oil from the cells, and also helps to improve the quality of the oil and provide favorable conditions for oil extraction. .

The effect of steaming and frying is affected by various factors such as moisture, temperature, heating time, and heating speed, among which the main factor is the mastery of moisture and temperature. Dry embryos or embryos. When water content is below 12%, steaming is required to add water. In the initial stage of steaming, the temperature must rise quickly and evenly, and the temperature does not have to rise too high. The whole process of steaming and frying takes 40 to 50 minutes, and the water content drops to 3% to 4%. The temperature of the steamed material is expected to reach 100°C before entering the press.

4. Pressing

Presses are divided into two types, batch type and continuous type, and now use screw presses to squeeze out oil. To obtain a high oil yield, it must be guaranteed that the pressure is above 69 MPa. The main technical parameters of the commonly used 95 screw presses are:

Processing capacity 500 to 700 kg/hour

Spindle speed 26-28 rpm

Pressing diameter 96.5 ~ 102 mm

Internal pressure time 35 to 38 seconds

Motor power 7.5 kW

Machine weight 850 kg

When the 95-type screw press is driven, it is necessary to feed less material. After the temperature rises in the crucible, it is gradually added to prevent clogging. When feeding normally, pay attention to cake, oil, slag and load conditions. Cake cake should be solid, the thickness of 1 ~ 1.3 mm is good, if found that the cake coke or smoke phenomenon, indicating that the water is too low; if the oil is less, the oil bubble more, large or "cake thin" Phenomenon, indicating that the water is too high. Regardless of whether the water is high or low, it is necessary to pay attention to the timely adjustment of steaming, so that the moisture in the embryo meets the requirements of oil extraction. When it is found that the oil is not flowing, it is likely that the oil line is blocked. Most of the reasons are caused by too much corn flour contained in the corn embryos. In this case, some oil residue or cake crumbs will be added, and the stock in the squeezing mash will be added. Top out to clear the oil road. Dry-separated corn embryos have an oil yield of no more than 20% and gross oil yields account for only 1% to 2% of corn kernels. Wet-processed corn embryo oil yield can reach 40% to 45%, and wool oil accounts for 3% to 3.5% of corn kernels. After the crude oil is precipitated, it can be used as a raw material to leave the factory. However, it is not suitable for human consumption and needs further refining.

(III) Refining of corn oil

The purpose of refining corn oil is to obtain corn oil that meets the requirements. When corn germ oil is used as edible oil, it must go through such processes as sedimentation, filtration, hydration degumming, deodorization, and sometimes further refining, such as alkali refining, decolorization, and dewaxing. The general corn oil refining process is:

Corn oil → precipitation → hydration degumming → alkali refining → water washing → dehydration decolorization → filtration → deodorization → refining corn oil

Precipitation

The principle of sedimentation is based on the difference in the specific gravity of oil and various impurities. After the crude oil is allowed to stand for a certain period of time, the specific gravity of the water and mechanical impurities is greater than that of the oil and sinks at the bottom of the oil; a small amount of suspended impurities and phospholipids, proteins, and starch pastes float on the surface of the oil. The factors influencing the precipitation effect are mainly temperature and time, high temperature and long time, good precipitation effect, low temperature and short precipitation time. Summer temperatures are high. After 3 days, the sedimentation basically meets the requirements. In winter, when the environment is maintained above 0°C, the sedimentation time should not be less than 7 days. In spring and autumn, the temperature can be properly controlled according to the temperature conditions.

2. Hydration degumming

Hydration is the heating of water to separate the phospholipids, proteins, and mucus from the oil. Phospholipids swell after swelling and increase in size, and bind to proteins, mucus, and other impurities to form colloids, which increase in specific gravity and precipitate at the bottom of the oil.

The oil is first heated to 75-80°C, and then the salt is added with 5%-10% salt water. The concentration of salt water is 5%. Add water while stirring constantly. During the hydration process, the colloid expands in volume and dissolves in water, which precipitates at the bottom of the oil. The water and oil containing the colloid are then separated to achieve the purpose of hydration degumming.

3. Alkali

Corn oil contains a large amount of free fatty acids. The role of alkali refining is to make alkali liquor act on corn germ oil to neutralize the free fatty acids in corn germ oil, generate flocculent soap, and absorb the impurities in oils and fats, thereby playing the role of deacidification, impurity removal and decolorization. Role, to further increase the value of corn germ oil.

The effect of deacidification with caustic soda (sodium hydroxide) is good, and at the same time, the color of the oil can be improved, but the disadvantage is that a small amount of saponification occurs. Alkali refining with sodium carbonate can prevent the saponification of neutral oils, but the resultant grease has poor color. Small-sized oil plants generally use open-type reaction tanks, and the lye is added to the oil by spraying. The steps for caustic refining are:

(1) The acid value and free fatty acid of the corn germ oil to be treated are measured to determine the amount of alkali added.

(2) Weigh the corn germ oil to be causticized and pour into the reaction tank. The heating is slowly performed so that the bubbles disappear, and the preconditioned lye is quickly and uniformly added to the oil, and the mixture is stirred to be thoroughly mixed and saponified. This is a neutralization step.

(3) When a soap particle is found to be in a separated state, it is rapidly heated to rapidly raise the temperature of the oil, stirred while raising the temperature, and the temperature is raised to 50 to 60° C. in a short time, and heating and stirring are then stopped. When it is found that the soapy foot is not easy to sink, add clean water and salt water at the same temperature or lower temperature as the oil. When adding water, the stirring speed should be slowed down. After stirring was stopped, the oil was precipitated again for 24 hours.

4. Dehydration

Corn germ oil is orange-yellow and can be removed by general refining and alkali refining. However, for the high-quality corn germ oil, it needs to undergo decolorization process. The decolorization process not only adsorbs pigment but also removes a small amount of colloidal substances such as soapslips from the oil. At the same time, decolorization is also the removal process of trace amounts of water, so the decolorization is performed under vacuum.

The commonly used decoloring method is an adsorption method, and the adsorbents include bleaching powder, acid clay, diatomaceous earth and activated carbon. The commonly used adsorbents (bleaching agents) are white clay and activated carbon, and the combined use of white clay and activated carbon is better than using clay or activated carbon alone. The process of decolorization is to pour the corn germ oil into the decolorization tank and add the adsorbent when the oil temperature rises to 70-80°C. Stir while adding the adsorbent. The temperature was then raised to 110-120C and the decoloring time was 10-20 minutes. Samples are taken during the decolorization process until the color is considered acceptable and heating can be stopped. The amount of adsorbent is generally 3% to 5% of the weight of the oil.

5. Filter dewaxing

Maize embryo oil contains a small amount of wax, which affects the transparency of the oil, so after decolorization, it needs to be dewaxed. The decolorized corn germ oil is first cooled to allow the wax to crystallize and then filtered through a filter press to remove the wax and decolorizing agent.

6. Deodorization

After degumming, alkaline refining, decolorization and dewaxing of corn germ oil, most of the free fatty acids, phospholipids, proteins, mucilages, pigments, etc. are removed, the appearance is yellow and transparent, but it still retains a peculiar smell of corn germ oil, and The “soap smell” brought about in the process of alkali refining and the “soil smell” caused by the decoloring agent in the decoloring process. Therefore, vacuum deodorization must be performed so that the product meets the flavor requirements.

The deodorizing operation step is: the oil is injected into the deodorizing pot, and the oil intake volume is about 2/3 of the pot volume. The oil is heated with a steam pipe and direct steam is introduced into the pot to turn the oil layer and remove the air. When the oil temperature rises to 150°C, it begins to enter the deodorization process. After that, the direct steam was opened, the turning was increased, the temperature rose to 180°C, and the degree of vacuum reached 0.093 MPa. The entire deodorization process is generally 7-8 hours. After cooling, the direct steam is turned off. When the oil temperature drops to 80° C., it is turned off. When the oil temperature drops to 70°C, it can be filtered. The filtered oil is the finished product. After the above-mentioned processing of several comprehensive processes, the quality of corn embryo oil has been significantly improved, and the value of commodities has suddenly risen.

7. Product standard

(1) Sensory index

The appearance of orange yellow, clear and transparent, with a unique smell of corn germ oil, no odor.

(2) Physical and chemical indicators

Color (Luo Weiming) Red ≤3.5, Yellow 3.0

Acid price ≤ 1.0 mg/g

Impurity ≤0.1%

Moisture and volatiles ≤0.1%

Soap content≤0.03%

Heating test (280°C) No precipitate, no deeper oil

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