What is the pressing process of organic camellia oil?

According to the production needs of different grades of camellia oil, the industrial extraction and preparation methods of camellia oil mainly include mechanical pressing, solvent extraction and supercritical fluid extraction. In China, camellia oil is generally prepared by mechanical pressing and solvent extraction.

Mechanical pressing method

Mechanical pressing is the basic method to extract camellia oil. Camellia oil pressing has gone through several stages, such as soil pressing (mainly wedge pressing), hydraulic pressing and screw pressing. According to the different temperatures in the press chamber of tea seeds during pressing, the first two methods are usually called low-temperature pressing method, and the latter is called high-temperature pressing method.

Low temperature pressing method

At present, in the rural areas of tea oil producing areas, the extraction of tea oil mostly adopts hydraulic oil pressing technology. The crude camellia oil obtained by this process has few impurities and light color, which is the mainstream technology for extracting camellia oil. Hydraulic oil press has two structures: vertical and horizontal, and horizontal hydraulic oil press is the majority in actual production.

The technological process of common low-temperature pressing method for camellia oil is as follows: tea seeds → low-temperature storage → cleaning and classification → magnetic separation → hulling → rolling → cold pressing → oil residue separation → camellia oil crude oil → low-temperature crystallization and crystal growth → low-temperature filtration → tea seed cake → leaching finished product cold pressing oil.

The key process quality control points of low temperature cold pressing method are low temperature storage, cleaning classification, cold pressing and oil residue separation. In the process of low temperature storage, the temperature is controlled at 0 ~ 7℃, which is beneficial to the after-ripening of Camellia oleifera seeds. In the process of cleaning and grading, grading treatment is carried out according to different particle sizes, and then raw materials with uniform particles are threshed, which can ensure the shelling efficiency; In the cold pressing process, a special cold pressing machine is used, and the cold pressing temperature is 70-80℃. The special cold pressing machine can prevent camellia oil from blackening due to high temperature and the loss of effective components. In the process of oil residue separation, it is necessary to control the separation time and residence time, and the crude oil does not need to pass through the sedimentation tank during filtration.

High temperature pressing method

The high-temperature pressing method mainly adopts screw oil press for dynamic pressing. The instantaneous pressing temperature of oil in the press chamber is high, which has an impact on both oil and cake. For example, the crude oil of camellia oil has many impurities and dark color, which reduces the refining rate of camellia oil. Therefore, it is technically required to shell the tea seeds for spiral oil pressing.

The key process quality control points of high temperature pressing method are shelling, steaming and pressing. In the process of hulling, dried tea seeds (water content 12%- 14%) enter a tea seed sheller to break the shell, and then the air, kernel and shell are separated; In the process of steaming and frying, it is necessary to adjust the water content and temperature of tea seeds. The water content of pressed tea seeds should be controlled at about 3%, and the pressing temperature should reach110-120℃. During the pressing process, tea oil is continuously released from the press through continuous dynamic pressing.

The advantages of mechanical pressing method are simple and flexible process, strong adaptability, low cost and less investment. There is no solvent residue in the squeezed oil, but the oil yield is not high. The data shows that the oil yield is about 80%. Moreover, due to the high content of reducing sugar, total sugar and starch in Camellia oleifera seeds, Maillard reaction is easy to occur when oil is made by pressing method, which makes the color of oil deepen, thus increasing the amount of activated clay in the decoloration process. In addition, because the raw materials of mechanical pressing method need cooking or baking heat treatment, protein will be denatured, the comprehensive utilization value of the cake after oil pressing will be reduced, and the residual oil rate in the residue will be high, so it is still necessary to leach with solvent.

solvent extraction

Solvent extraction is a method of oil production that rose after 1970s. Solvent leaching is a method to extract oil from blank or pre-pressed cake by using the characteristics of some organic solvents (such as n-hexane, petroleum ether and anhydrous ethanol) to dissolve oil. There are three basic processes: preloading leaching, direct leaching and secondary leaching.

The technological process of solvent extraction and deoiling: grease → blank making (or blank prepressing) → solvent extraction → mixed oil separation → crude oil refining → finished meal/meal desolvation.

The researchers compared the extraction effects of several different solvents on camellia oil. The results showed that when petroleum ether was used as the extraction solvent, the ratio of material to liquid was 1: 10, the extraction temperature was 50℃ and the extraction time was 3h, the extraction rate of camellia oil was over 93%, and the camellia oil was light yellow.

The invention has the advantages of high oil yield (production yield can reach about 90%), complete extraction, solvent recovery, low cost, simple operation and easy laboratory research. However, in the process of solvent recovery, it is easy to cause the decomposition of unsaturated fatty acids, which makes the saponification value of crude oil high, and there are solvent residues in the product, which is easy to burn and requires high operational safety. Recently, it was reported in the news that the benzopyrene of camellia oil produced by a company exceeded the standard. The company said that the main reason for benzopyrene exceeding the standard is leaching oil, and the excessive benzene content is mainly caused by the burning phenomenon caused by repeated baking and cooking of tea seeds in order to improve the oil yield when farmers squeeze camellia oil. This kind of burnt tea cake is easy to produce benzopyrene, and benzene reacts with solvent oil at high temperature during the extraction process, which further increases the content of benzopyrene in camellia oil. Therefore, when extracting camellia oil by solvent extraction, we should pay attention to the temperature control in the process of drying and steaming tea seeds to prevent overheating from causing safety problems.

Aqueous enzymatic method

Aqueous enzymatic method is a new oil extraction method studied and utilized in recent years. It uses machinery and enzymes to degrade the cellulose skeleton of plant cell wall, so that the oil wrapped in the cell wall is released, and at the same time, other oil complexes combined with carbohydrates and protein molecules are destroyed, so that the oil is released.

Technological process of aqueous enzymatic extraction of camellia oil;

Camellia oleifera seeds → crushing → weighing → adding buffer solution → steam treatment → cooling → adding enzyme preparation → enzymolysis → enzyme inactivation → suction filtration → slagging → drying → petroleum ether extraction → suction filtration → vacuum drying → drying to constant weight → Camellia oleifera seed oil.

The researchers used different enzymes to extract camellia oil, and found that Alcalase2.0L protease was the most favorable for oil extraction. When its dosage is 0.02ml/g, the oil extraction rate is the highest. At the same time, the effects of temperature, pH value and solid-liquid ratio on oil extraction rate and protein hydrolysis degree were investigated. Response surface methodology was used to optimize and determine the optimum technological conditions of enzymatic oil extraction: temperature 55℃, pH 8, solid-liquid ratio 1:6(g/ml). Under these conditions, the oil yield reached 78.25% after enzymolysis for 4 hours, which was higher than that of ordinary pressing method.

Compared with the traditional process, the aqueous enzymatic method has the following advantages: mild conditions, high oil yield, light color and easy refining; The defatted cake has low protein denaturation and good availability. Oil and cake are easy to separate, which simplifies the process, improves the processing capacity of the equipment and reduces the production cost; By reducing energy consumption, the values of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) in wastewater are greatly reduced (about 35%~75%), which is easy to treat, conducive to energy conservation and environmental protection, and in line with the principle of sustainable development.

Supercritical carbon dioxide extraction

Supercritical fluid extraction is to contact supercritical fluid (usually CO2) with the substance to be separated, control the pressure and temperature of the system, and selectively extract one of the components. Then, through the change of temperature or pressure, the density of supercritical fluid is reduced, the extracted substance is separated, and the supercritical fluid is recovered.

The researchers put forward the method of extracting camellia oil by supercritical CO2, investigated the influence of pressure and temperature on the solubility of camellia oil in CO2, analyzed the relationship between extraction conditions and oil quality, and obtained the best technological conditions: pressure 30MPa, temperature 35 ℃, CO2 flow rate 6L/min. Fang Fang and others discussed the influence of pressure, temperature, flow rate and time of supercritical CO2 extraction on the extraction rate of camellia oil, and determined that the optimum technological conditions for supercritical CO2 extraction of camellia oil (raw material particle size is 40 mesh) are as follows: extraction pressure 35MPa, temperature 50 ℃, CO2 flow rate 20kg/h, extraction time 65438±050min, at which time the extraction rate can reach 33.5%, which is the conventional technological conditions.

Han et al. studied the optimum technological parameters of supercritical CO2 extraction of camellia oil in western Hubei and the relationship between oil yield and extraction pressure, temperature and time. The orthogonal test results showed that the extraction pressure was 35MPa, the extraction temperature was 45℃ and the extraction time was 2.5h, and the factors affecting the extraction rate were pressure, time and temperature in turn. The single factor experiment showed that the extraction rate increased with the increase of extraction pressure and temperature. The camellia oil extracted by supercritical CO2 retains the aroma of tea, with low acid value, light color, no solvent residue and no need for further refining.

The operating temperature of supercritical CO2 extraction of camellia oil is low, which will not affect the natural activity of heat-sensitive substances. The aroma of the obtained tea seed oil is closer to the natural aroma, which can save the refining process of oil, and the oil yield is above 90%. However, the requirements of process equipment are high, the price is expensive, and the operability of mass production is poor. Now it only stays in the laboratory research stage.