Several pressing methods of camellia seeds
According to the production needs of different grades of tea seed oil, the industrial extraction and preparation methods of tea seed oil mainly include the more mature mechanical pressing method, solvent extraction method and supercritical fluid extraction method. The production of camellia oil in my country generally adopts mechanical pressing method and solvent extraction method.
1. Mechanical pressing
Mechanical pressing is the basic way to extract camellia oil. Tea seed pressing has gone through several stages such as soil pressing (mainly wedge pressing), hydraulic oil pressing and screw pressing. According to the different temperature of tea seeds in the pressing chamber during the pressing process, usually the first two are called low temperature pressing process, and the latter one is called hot pressing process.
1) Low temperature pressing
In rural areas of tea seed production areas, camellia oil is often extracted by hydraulic oil pressing process. The hair tea oil obtained by this process has few impurities and light color. There are two types of hydraulic oil presses, vertical and horizontal. In actual production, most of the horizontal hydraulic oil presses are used.
The process flow of the commonly used tea seed low temperature pressing method:
Camellia seed → low temperature storage → cleaning and grading → magnetic separation and shelling → rolling → cold pressing → oil residue separation → tea seed oil → low temperature crystallization and crystallization→ low temperature filtration
↓ ↓
Tea seed cake→Extraction finished cold-pressed oil
The key process quality control points of the low temperature cold pressing method are low temperature storage, cleaning and grading, 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 after-ripening of Camellia oleifera seeds; in the cleaning and grading process, the classification process is carried out according to the different particle sizes, and then the raw materials with relatively uniform particles are threshed to ensure that the Shelling efficiency; in the cold pressing process, a special cold pressing machine is used, and the pressing temperature is 70~80°C. The special cold pressing machine can avoid the darkening of the color of tea seed oil and the loss of effective components caused by high temperature; In the oil residue separation process, the separation time and retention time should be well controlled, and the crude oil does not need to pass through the sedimentation tank during filtration.
2) Hot pressing
The hot pressing method mainly uses a screw press for dynamic pressing. When the oil is pressed in the pressing chamber, the temperature is high, which affects both the oil and the pressed cake. For example, the camellia oil has many impurities and dark color, which reduces the refining rate of the tea oil. Therefore, the process of screw oil extraction requires peeling of tea seeds.
The key process quality control points of the hot pressing method are peeling, steaming and frying, and pressing. In the shelling process, the roasted tea seeds (with a moisture content of 12% and 14%) are put into a tea seed sheller to break the shells, and then subjected to wind sorting and kernel shell separation; in the steaming and frying process, The moisture and temperature of the tea seed kernels should be adjusted to control the moisture of the tea seeds to be about 3%, and the pressing temperature to reach 110~120°C; release.
The advantages of the mechanical pressing method are simple and flexible process, strong adaptability, low cost, low investment, no solvent residue in the pressed oil, but its oil yield is not high. The content of reducing sugar, total sugar and starch is high. Maillard reaction is easy to occur when oil is produced by pressing method, which deepens the color of oil and increases the amount of activated clay in the process of decolorization. In addition, because the raw materials of the mechanical pressing method need steaming or baking heat treatment, the protein will be denatured, and the comprehensive utilization value of the cake after oil extraction will decrease, and the residual oil rate in the residue is high, which still needs to be leached by solvent.
2. Solvent extraction
Solvent extraction method is an oil production method that emerged after the 1970s. The solvent leaching method is a method of extracting the oil from the preform or pre-pressed cake by using the characteristics of certain organic solvents (such as n-hexane, petroleum ether, anhydrous ethanol) to dissolve the oil. There are three basic processes: pre-press leaching, direct leaching and secondary leaching.
Process flow of solvent extraction and oil extraction:
Oil → billet making (or billet pre-pressing) → solvent leaching → mixed oil separation → crude oil refining
↓
Finished meal←Meal desolvation
Meng Wei et al. compared the extraction effects of several different solvents on tea seed oil. The research results show that, with petroleum ether as the extraction solvent, at a solid-liquid ratio of 1:10 and an extraction temperature of 50 °C, the extraction is performed twice for 3 hours each time. , the extraction rate of tea seed oil is more than 93%, and the obtained tea seed oil is 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 for laboratory research; but it is easy to cause inconvenience in the process of solvent recovery. The decomposition of saturated fatty acids makes the saponification value of the obtained crude oil on the high side, and there are solvent residues in the product, which are extremely flammable, and require higher operational safety. Recently, there were news reports that the camellia oil benzopyrene produced by a company exceeded the standard. The company said that the excess benzopyrene is mainly due to the leaching oil, and the excess benzene content is mainly because farmers repeatedly roasted, steamed and fried the tea seeds in order to increase the oil yield when pressing the tea oil, resulting in the occurrence of scorching. , This charred tea cake is prone to produce benzopyrene, and there is a phenomenon of high temperature chemical reaction between benzene substances and solvent oil during the extraction process, which further increases the content of benzopyrene in tea oil. Therefore, when extracting camellia oil by solvent extraction, attention should be paid to the temperature control of the tea seeds roasting, steaming and frying process to prevent overheating and safety problems.
