Process of rapeseed oil pressing

1 Pretreatment of rapeseed

Pretreatment includes crushing, steaming and peeling. The purpose of rapeseed peeling is to remove the main fiber and pigment body, otherwise it will reduce the feeding value of the cake. On the other hand, the leaching process is conducive to solvent penetration (the leaching can improve the porosity of the blank). In theory, peeling (that is, removing 15 percent of the material) will increase leaching equipment capacity by 15 percent. Remove these black skins before leaching and the oil is lighter and requires less decolorization. The dry peeling of rapeseed can adopt different technologies, such as pneumatic impact, cracking between rolls or deformation cracking, and the deformation cracking effect is the best and oil loss rate is the lowest.

2 Use rapeseed to make oil

Rapeseed is first rolled to destroy the seed layer and rupture the oil cells. The steam stir-fry can rupture the remaining intact cells, improve the oil bead aggregation, increase the fluidity, and passivate the enzyme, especially the mustard enzyme. Billet in steaming in the frying pan, steaming Fried within 77 ~ 100 °C 15 ~ 20 min (depending on the rapeseed varieties). In most cases, the blanks after rolling and steaming are pre-pressed with a press machine to reduce the oil content from 42% to 16% ~ 20%. This prepress process also compresses the fine cake into a large sheet. The cake was leached with hexane solvent to extract most of the remaining oil. Leaching pulp finally in steaming offline (DT), steam spray treatment of 30 min (temperature is 100 ~ 130 °C), with removal of hexane and improve the quality of meal nutrition (by removing volatile mustard glucoside).

Protein denaturation may occur during the initial stage of steaming and dissolving. It is an effective method to passivate the mustard enzyme in rapeseed and rolled stock by microwave. Myrosinase passivation depends on the initial feed moisture content (ideal moisture content is 10%). The drawback of microwave treatment is that the sulfur content in oil increases, which is caused by the long processing time. Many rapeseed processors add an extruder after prepress and before leaching. This kind of extruder is a kind of auxiliary equipment, its benefit is enough to make the cost economical. The latest design is to combine the prepress and extrusion units into one device, which has the advantage that no additional power is required.

3 Cake processing technology

Rapeseed meal is a high quality protein source and can be used as animal feed instead of meal. Scientists in Scandinavia have developed a new method for making high-protein rapeseed meal. The key is deliberate heat treatment. In order to reduce the residual solubility in the meal as far as possible, only when the water content of rapeseed is less than 5%, can the best dissolute effect be obtained. Foreign scientists have investigated and studied the production of edible protein concentrate and protein isolate from rapeseed, but they have not put into industrial production. Danish scientists have developed a water-enzymatic process for preparing rapeseed oil. The pretreatment includes a rolling process and a heat treatment process to passivate myrosinase and other enzymes. The meal — a mixture of rapeseed powder and molasses — has been used to feed animals with a digestibility of 77.2%, a price of 92.7, and a net protein utilization rate of 71.5%.

4 Oil processing

Rapeseed oil is refined by traditional chemical neutralization. A newly designed method of total degumming has been adopted. With the total degumming process, the phospholipid metal complexes use a strong acid to decompose insoluble metal salts and phospholipids (acid type). The latter is partially neutralized so that it is converted into a hydrated compound which can then be removed from the oil. After a certain contact time, add the alkali solution and mix into the acid oil emulsion to prevent the formation of fatty acid salts. This is especially important in terms of yield. Then, the oil was degummed by the first centrifuge, so that the gel phase with the lowest oil content and the oil still containing the residual glue were obtained. Then, the oil passes through the second centrifuge to get the gel-free oil and a type of oil-rich gel phase, which is recirculated.    A new method of separation impurities by 350 centrifugal filter is developed in Xi ‘an filter qingbao filter plant. The method uses low density particles and centrifugal force. These particles form an inner layer of suspended solids through which the liquid must pass. The filtration accuracy of these particles can also be changed according to the characteristics of different oils. This adsorption is counter-current, in the operation process, the used particles can be replaced. The advantage of this method is that when oil is extracted, it is filtered through coarse filtration and water washing and then directly poured into the centrifuge. A small amount of dissolved phospholipids or emulsified water can be isolated from a large amount of oil, resulting in a clean oil. This centrifugal force exerts a force of several kilograms on the particles and the emulsion water. This method can be used to separate sulfur or phosphorus in rapeseed oil (which passivates nickel catalysts) and to separate colored ingredients or substances that affect smell.

At present, there are mainly three ways to develop and utilize rapeseed resources at home and abroad. Second, detoxification of the cake; Third, rapeseed dehulling oil, deep processing. In order to improve the utilization quality of rapeseed meal, “double low” (i.e. low erucic acid, low glucoside) quality rapeseed was successfully cultivated and popularized in China. In order to remove the content of thioside in rapeseed meal, various detoxification methods were proposed. Such as heating inactivate and detoxify the thiosidase, enzymatic hydrolysis, distillation, filtration detoxification, water leaching of thiosidase detoxification, microbial fermentation detoxification, and so on. However, these detoxification methods can only remove the sulfur glycosides and cannot solve the harm of other harmful substances to livestock.

The dehulling technology of rapeseed (also called skin) to produce oil has created certain conditions for the comprehensive development and utilization of rapeseed. The technological route of oil production is: drying – cleaning – hulling (removing the shell) – granulation – leaching. Compared with the traditional Chinese process of drying – cleaning – rolling – embryo – prepressing – leaching – oil production, the process of decanting oil production omitted the process of steaming and prepressing, which can avoid excessive protein denaturation caused by high temperature treatment in the process of steaming and prepressing, so that the water-soluble protein in the cake can be effectively preserved. At the same time, by removing the shell, the content of melanin, crude fiber, sinapine, tannin and other polyphenols was reduced, the wool oil was clear and transparent, and the quality of the cake was improved, providing quality raw materials for further processing.

Utilization and comprehensive utilization of rapeseed

Rapeseed oil from seeds is good cooking oil. Non-erucic rapeseed oil is used to make margarine and as raw vegetable oil (salad oil), shortening and flavoring oils. The main characteristic of rapeseed oil, which is composed of various fatty acids, is high in erucic acid (generally 40-55%) compared with other edible vegetable oils. Erucic acid is the long chain fatty acid of 22 carbon. By quality improved, erucic acid rapeseed oil of oleic acid and linoleic acid content increased significantly, linoleic acid is in the fat does not have, only rely on the supply of vegetable oil, easy to human digestion and absorption, and reduce serum cholesterol in the human body and glycerin three esters, softening blood vessels and prevent the formation of thrombus, have to human body fat metabolism plays a particularly important role. Rapeseed oil with high erucic acid (erucic acid content is 55-60%) is an important industrial raw material and used as lubricating oil in the casting steel industry. Generally, rapeseed oil is widely used in machinery, rubber, chemical industry, plastics, paint, textile, soap making and medicine.

The protein content of rapeseed cake after oil extraction is up to 36-38%,and its nutritive value is close to that of soybean cake, so it is a good concentrate.

Characteristics of rapeseed oil peeling and cold pressing

Its features are as follows

• High peeling rate. The rate of one peeling is over 98% to 99%
• Good peeling effect. After peeling, the proportion of half kernel and whole kernel is up to 80%, and the powder degree is less than 3%
• The preprocessing is simple. Before peeling, rapeseed does not need to be classified. Rapeseed water content of about 8% can achieve the ideal peeling effect.
• Post-processing is simple. After peeling, due to high peeling rate and low powder degree, there is almost no whole seed. It only needs to separate the two materials of kernel and skin, which is simple and easy to operate, and the necessary unpeeled and whole seed recovery and re-removal process can be omitted. The percentage of kernels after separation was less than 1%.