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 that are relatively mature in production. The production of camellia oil in my country generally adopts mechanical pressing method and solvent extraction method.
Mechanical pressing method
Mechanical pressing method is the basic way to extract camellia oil. Camellia oil pressing has gone through native pressing (mainly wedge pressing), hydraulic oil pressing and screw oil pressing. Wait for a few stages. According to the different temperatures of tea seeds in the pressing chamber during the pressing process, the first two are usually called low-temperature pressing processes, and the latter are called high-temperature pressing processes.
Low temperature pressing method
At present, hydraulic oil pressing process is often used to extract camellia oil in rural areas of Camellia oleifera producing areas. The camellia oil obtained by this process has less impurities and light color, which is the most popular method nowadays. Mainstream technology for extraction and preparation of camellia oil. Hydraulic oil presses have two structures: vertical and horizontal. In actual production, horizontal hydraulic oil presses are the most common.
The process flow of the commonly used low-temperature pressing method of camellia oil: Camellia oleifera seeds → low-temperature storage → cleaning and grading → magnetic selection and shelling → rolling → cold pressing → oil residue separation → camellia oil → low-temperature crystallization and crystal cultivation → Low-temperature filtration → Tea seed cake → Extraction of finished cold-pressed oil
The key process quality control points of the low-temperature cold-pressing method are low-temperature storage, cleaning and classification, cold pressing, and oil residue separation. In the low-temperature storage process, the temperature is controlled at 0~7°C, which is conducive to the post-ripening of Camellia oleifera seeds; in the cleaning and grading process, grading is carried out according to the different particle sizes, and then the raw materials with relatively uniform particles are threshed, which can ensure Shelling efficiency: A special cold press is used in the cold pressing process. The cold pressing temperature is 70-80°C. The special cold press can avoid the darkening of the camellia oil color and the loss of active ingredients caused by high temperatures. In the oil residue separation process , the separation time and retention time should be controlled, 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 uses a screw press for dynamic pressing. The instantaneous pressing temperature of the oil in the pressing chamber is relatively high, which affects both the oil and the pressed cake. For example, camellia oil has many impurities and a deep color, which reduces the refining rate of camellia oil. Therefore, the screw oil pressing process requires tea seeds to be shelled.
The key process quality control points of high-temperature pressing method are shelling, steaming and frying, and pressing. In the shelling process, the dried tea seeds (with a moisture content of 12%-14%) enter the tea seed shelling machine to break the shells, and then undergo wind sorting and separation of kernel shells; in the steaming and frying process, The moisture and temperature of the tea seed kernels need to be adjusted to control the moisture content of the tea seeds to be about 3% and the pressing temperature to reach 110-120°C; during the pressing process, through continuous dynamic pressing, the camellia oil will flow continuously from the press. Release it.
The advantages of mechanical pressing are simple and flexible process, strong adaptability, low cost and low investment. The pressed oil has no solvent residue, but its oil yield is not high. Data shows that the yield is about 80 %, and because the reducing sugar, total sugar, and starch content in Camellia oleifera seed kernels are high, the Maillard reaction is prone to occur when the oil is produced by pressing, which deepens the color of the oil, thus increasing the amount of activated clay used in the decolorization process. In addition, since the raw materials of the mechanical pressing method require steaming, frying or baking heat treatment, the proteins will be denatured, and the comprehensive utilization value of the cake will decrease after oil extraction. Moreover, the residual oil rate in the residue is high and still needs to be leached by solvent.
Solvent extraction method
Solvent extraction method is an oil production method that emerged after the 1970s. Solvent leaching is a method that utilizes the properties of certain organic solvents (such as n-hexane, petroleum ether, and absolute ethanol) to dissolve oil and extract oil from the billet or pre-pressed cake. The basic technology includes three methods: pre-pressing leaching, direct leaching and secondary leaching.
The technological process of solvent extraction and oil removal: oil → billet making (or billet pre-pressing) → solvent leaching → mixed oil separation → crude oil refining → finished meal ← meal desolvation
Scientific researchers compared the extraction effects of several different solvents on camellia oil. The research results showed that using petroleum ether as the extraction solvent, the material-to-liquid ratio was 1:10 and the extraction temperature was 50°C, and the extraction was performed twice, each time After 3 hours, the extraction rate of camellia oil reached more than 93%, and the obtained tea seed oil was light yellow.
The solvent extraction method has a high oil yield (the production yield can reach about 90%), the extraction is more thorough, the solvent can be recovered, the cost is reduced, the operation is simple, and it is easy to conduct laboratory research; but in The solvent recovery process can easily cause the decomposition of unsaturated fatty acids, causing the crude oil to have a high saponification value, and there are solvent residues in the product. The solvent is extremely flammable and requires high operational safety. Recently, there were news reports that the camellia oil produced by a certain company exceeded the standard of benzopyrene. The company said that benzopyrene exceeded the standard mainly in the leached oil. The excessive benzene content was mainly because when farmers pressed camellia oil, in order to increase the oil yield, they repeatedly roasted, steamed and fried the tea seeds, resulting in scorching. This kind of burnt tea cake is prone to produce benzopyrene, and during the extraction process, there is a high-temperature chemical reaction between benzene substances and solvent oil, which further increases the content of benzopyrene in camellia oil. Therefore, when using the solvent extraction method to extract camellia oil, attention should be paid to the temperature control during roasting and steaming of tea seeds to prevent safety issues caused by overheating.
Aqueous enzymatic method
Aqueous enzymatic method is a new oil extraction method that has been studied and utilized in recent years. It uses mechanical and enzymatic means to degrade the cellulose skeleton of plant cell walls. , free the oil wrapped in the cell wall, and at the same time destroy other oil complexes that are combined with molecules such as carbohydrates and proteins, thereby releasing the oil.
The technological process of extracting camellia oil by water enzymatic method:
Camellia oleifera seeds → crush → weigh → add buffer → steam treatment → cooling → add enzyme preparation → enzymatic hydrolysis → enzyme inactivation →Suction filtration→Take out the residue→Oven drying→Petroleum ether extraction→Suction filtration→Vacuum drying→Dry to constant weight→Camellia oil
Researchers used different enzymes to extract camellia oil and discovered Alcalase2.0L Protease is most beneficial to the extraction of oil. When its dosage is 0.02ml/g, the oil extraction rate reaches the highest. At the same time, the effects of temperature, pH value, solid-liquid ratio, etc. on the oil extraction rate and protein hydrolysis degree were investigated. The response surface method was used to optimize and determine the best conditions for enzymatic oil extraction: temperature 55°C, pH value 8, The solid-liquid ratio is 1:6 (g/ml). Under these conditions, enzymatic hydrolysis takes 4 hours, and the oil extraction rate reaches 78.25%, which is higher than the 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 degreased cake protein has low denaturation and good availability; the oil and cake Meal is easy to separate, simplifies the process, improves equipment processing capacity, reduces production costs; reduces energy consumption, and the biochemical oxygen demand (BOD) and chemical oxygen demand (COD) values ??in wastewater are greatly reduced (about 35%~75%). It is easy to handle, is conducive to energy saving, environmental protection, and conforms to the principle of sustainable development.
Supercritical carbon dioxide (CO2) extraction method
Supercritical fluid extraction is to contact the supercritical fluid (usually CO2) with the material to be separated in a supercritical state, and control The pressure and temperature of the system allow it to selectively extract a certain component, and then through changes in temperature or pressure, the density of the supercritical fluid is reduced, the extracted substances are separated, and the supercritical fluid is recycled.
Scientific researchers proposed a method of extracting camellia oil with supercritical CO2, examined the effects of pressure and temperature on the solubility of camellia oil in CO2, analyzed the relationship between extraction conditions and oil quality, and concluded that the best Optimal process conditions: pressure 30MPa, temperature 35°C, CO2 flow 6L/min. Fang Fang et al. discussed the impact of supercritical CO2 extraction pressure, temperature, flow, time and other factors on the extraction rate of camellia oil, and determined the optimal process conditions for supercritical CO2 extraction of camellia oil (when the raw material particle size is 40 mesh): extraction The pressure is 35MPa, the temperature is 50°C, the CO2 flow rate is 20kg/h, and the extraction time is 150min. At this time, the extraction rate can reach 33.5%. Compared with the conventional solvent extraction method (6h, 30.3%), the extraction time is shortened, the yield, and the raw materials The utilization rate has been greatly improved.
Han Weiyan et al. studied the optimal process parameters for 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 show that the extraction pressure of 35MPa, temperature of 45°C, and time of 2.5h are the optimal process parameters; the factors that affect the extraction yield are pressure, time, and temperature in order. The single factor test showed that as the extraction pressure and temperature increased, the extraction rate increased. The Western Hubei camellia oil extracted by supercritical CO2 retains the aroma of tea, has a low acid value, is relatively light in color, has no residual solvent, and does not require further refining.
Supercritical CO2 extraction of camellia oil has a low operating temperature and will not affect the natural activity of heat-sensitive substances. The aroma of the obtained tea seed oil is closer to the natural aroma, and the refining process of oil can be omitted to produce oil. The rate is above 90%. However, the process equipment requirements are high, the price is expensive, and the operability of large-scale production is poor. Now it only stays in the laboratory research stage.