CN107629873B - A kind of method of low-temperature crystallization enriching fish oil EPA, DHA - Google Patents

Abstract

The invention relates to a method for enriching fish oil EPA and DHA by low-temperature crystallization, belonging to the technical field of aquatic product processing and health products. The method comprises the following steps: pretreating fish oil, adding an organic solvent and a crystallization assistant agent into the fish oil, wherein the mass ratio of the fish oil to the organic solvent to the crystallization assistant agent is 100 (200-1000) to 0.5-2, uniformly mixing, performing low-temperature crystallization, performing vacuum filtration to separate crystals and non-crystallized liquid, and removing the organic solvent and the crystallization assistant agent in the non-crystallized liquid to obtain the enriched fish oil EPA and DHA. The method for enriching the EPA and the DHA in the fish oil by low-temperature crystallization has the advantages of simple equipment, simple and convenient operation, large single treatment capacity, low cost, difficult oxidation, isomerization, aggregation and other reactions of effective components, and better maintenance of the natural activity of the EPA and the DHA.

Description

A kind of method of low-temperature crystallization enriching fish oil EPA, DHA

technical field

The invention belongs to the technical field of aquatic product processing and health care products, and relates to a method for enriching fish oil EPA and DHA by low-temperature crystallization.

Background technique

Today, China has grown into the third largest EPA and DHA oil market in the world. DHA+EPA has obtained the new resource food certification and is about to be included in the DRI, which will help further improve consumer awareness. With the increasing income, education level and health awareness of consumers in my country year by year, EPA and DHA are more sensitive to physiological functions such as preventing atherosclerosis and cardiovascular diseases, preventing and fighting cancer, improving brain function, improving memory, and promoting the intellectual development of infants and young children. With the general understanding, especially the increase of aging population in my country in recent years, it is bound to bring new market opportunities to EPA and DHA products.

EPA and DHA belong to the n-3 series of polyunsaturated fatty acids, which have important health care effects on the human body. Fish oil has been one of the hot spots of research at home and abroad for many years because it is rich in n-3 series of polyunsaturated fatty acids, especially EPA and DHA.

At present, the methods for separating and enriching polyunsaturated fatty acids in fish oil mainly include low-temperature solvent crystallization method, urea inclusion, supercritical _CO2 extraction, molecular distillation, enzyme concentration method, etc. Among them, the low-temperature crystallization method has the advantages of simple operation, low requirements for instruments and equipment, and can better maintain the natural activity of unsaturated fatty acids in a low-temperature environment, and has a better separation effect. Yuan Xiaoyan et al. dissolved the mixed fatty acid in petroleum ether at 1:3 (acid:solvent), cooled it to 5-7°C, crystallized the saturated fatty acid, and then filtered and distilled to obtain the unsaturated fatty acid, and the yield could reach 80%. It can be seen that the low temperature crystallization method has a certain enrichment effect (Yuan Xiaoyan, et al. Research on the separation of unsaturated fatty acids from linseed oil [J]. Journal of Liaoning Institute of Science and Technology, 2005, 7(4): 12-13).

So far, there are many reports on the enrichment of polyunsaturated fatty acids in fish oil. Most of the industrial production of ethyl esterified fish oil adopts the combination of urea inclusion and molecular distillation, and there has been no breakthrough for decades. The urea inclusion method has the advantages of simple equipment, mild conditions, low cost, and complete retention of the physiological activity of the active ingredients. In order to improve the yield, multiple urea inclusion methods are generally used or combined with molecular distillation technology. The separation and purification process of molecular distillation technology is relatively cumbersome, such as the need for multi-stage purification, how to realize continuous feeding, and the influence of solid feed on material degradation when heated at high temperature. Supercritical extraction technology has the characteristics of low temperature, high pressure and air isolation, and is especially suitable for the separation of heat-sensitive substances and easily oxidizable substances. It can fully protect the quality of fish oil from damage, and the product quality is good, but this method requires high equipment. , the energy consumption is large,

However, there is no report on the specific process research on the enrichment of EPA/DHA in fish oil by low temperature crystallization, and it is more difficult to find relevant condition parameters as a reference. Therefore, more enrichment methods are explored and more possibilities are sought for the future upgrade of the fish oil industry. Reform is very important.

SUMMARY OF THE INVENTION

The object of the present invention is to address the above-mentioned problems existing in the prior art, and propose a method for enriching EPA and DHA of fish oil by low-temperature crystallization, which has simple equipment, simple and convenient operation, large single treatment capacity, low cost, and the active ingredients are not easily oxidized. Isomerization, polymerization and other reactions can better maintain the natural activity of EPA and DHA.

The object of the present invention can be realized by the following technical solutions: a method for enriching fish oil EPA, DHA by low-temperature crystallization, the method comprises the steps:

The fish oil is pretreated, and then an organic solvent and a crystallizing agent are added to the fish oil. Crystallization at low temperature, vacuum filtration to separate crystals and uncrystallized liquid, and then remove organic solvent and crystallizer in uncrystallized liquid to obtain enriched fish oil EPA and DHA.

The invention enriches EPA and DHA in fish oil by a low-temperature crystallization method, which is easy to operate, has low requirements for instruments and equipment, has large single processing capacity, good separation effect, and can better maintain EPA and DHA in a low-temperature environment. Natural activity of DHA. In the low-temperature crystallization process, the addition of organic solvent increases the liquid phase ratio and the degree of freedom of crystals, making it easier to filter and separate crystals from the uncrystallized liquid in the later stage. The addition of the crystallizing agent promotes the crystallization, reduces the degree of undercooling required for the crystallization, increases the crystallization temperature, and reduces the crystallization time. The amount of organic solvent is related to the content of saturated fatty acid in the raw oil. If the amount is too small, all crystallization cannot be precipitated. If the amount is too large, it may lead to excessive dilution of the raw material oil, which may affect the particle size and distribution of the crystals, so that the particle size of the formed crystals is too small. Too small grains will adsorb more EPA and DHA, reduce the separation efficiency, and also cause waste of solvent. Therefore, the ratio of fish oil to organic solvent is limited to the above range. The crystal structure of saturated fatty acid formed by freezing is limited, and the separation of crystals and uncrystallized liquids by vacuum filtration can avoid flocculation shearing as much as possible and reduce the damage to crystals.

Preferably, the fish oil is ethyl ester type fish oil.

Preferably, the mass percentage content of EPA and DHA in the ethyl esterified fish oil is 50-70%.

Preferably, the pretreatment is to heat the fish oil at 30-50° C. for 5-30 min.

In the processing, storage and transportation of fish oil, uneven crystal nuclei are often formed, which is not conducive to the formation of crystal nuclei during low-temperature crystallization. Therefore, the uneven crystal nuclei must be destroyed before low-temperature crystallization. Heat treatment at 30～50℃ for 5～30min can completely melt the fish oil and destroy the uneven crystal nucleus.

Preferably, the organic solvent is one or more of methanol, absolute ethanol, acetone and n-hexane.

During low-temperature crystallization separation, saturated acid and monoenoic acid, dienoic acid and other low-unsaturated fatty acids in the fish oil fatty acid are required to be separated out in the form of crystals, while EPA and DHA remain in the solution, and the above-mentioned organic solvents are at a lower temperature. , still has good solubility for EPA and DHA, ensuring that EPA and DHA remain in the solution as much as possible.

Preferably, the organic solvent contains 0.8-1.2% by mass of citric acid.

The addition of a small amount of citric acid can promote the rapid crystallization and grain refinement of EPA and DHA at low temperature, and improve the crystallization efficiency.

Preferably, the organic solvent is a mixed solvent of methanol and absolute ethanol with a volume ratio of (6-12):1, and the organic solvent also contains 0.9-1.1% by mass of citric acid.

The effect of methanol in removing saturated fatty acids is that it has the best enrichment effect on EPA and DHA, followed by anhydrous ethanol, and anhydrous ethanol has a better removal effect on low-unsaturated fatty acids. , high flash point, but relatively high viscosity, low temperature required for crystallization. Comprehensive consideration, compound methanol and anhydrous ethanol are selected as solvents for low temperature crystallization.

Preferably, the crystallizing agent is one or both of diatomite and white clay.

Diatomite and clay have a huge surface area. In the present invention, a small amount of diatomite and clay are added in the low-temperature crystallization process, which can provide a larger activation surface for the nucleation of saturated fatty acids in fish oil, reduce the nucleation free energy, and make crystals form. A tightly ordered structure that accelerates subsequent crystal growth on its surface. In addition, diatomite and white clay can be removed by centrifugation in the subsequent process, which is safe and non-toxic. If the addition amount of auxiliaries is too small, the number of crystal nuclei generated is small, the crystallization rate is small, and the effect of promoting crystallization is not obvious. The ability of molecules to diffuse to the crystallization front is weakened, reducing the crystallization rate.

Preferably, the low-temperature crystallization is carried out in ultrasonic stirring, the ultrasonic power of the ultrasonic stirring is 300-500w, and the stirring rate is n=15-30r/min

Ultrasonic treatment of fish oil under supercooled conditions will form a large number of crystal nuclei due to the flocculation of ultrasonic waves, and the cavitation of ultrasonic waves will crush the formed crystal nuclei to form new crystallization centers, promote the second nucleation, and accelerate saturated fatty acids. Crystallization, shorten the crystallization induction time, change the crystal form, make the crystal particles fine and uniform, and increase the hardness. If the stirring strength is not enough, local crystal nuclei will be generated. If the stirring is too vigorous, the crystal will be torn apart, so the appropriate stirring speed should be controlled. Continuous slow stirring should be maintained during the crystallization and growth process, which is beneficial to improve the heat transfer efficiency and the growth of crystals.

Preferably, the low-temperature crystallization includes a first stage and a second stage, the first stage is cooled to -10～5°C, the temperature is kept for 3～4 hours, the second stage is cooled to -30～-50°C, and the temperature is kept at a temperature of 2.5～3.5 h.

Temperature is one of the key factors for the formation and separation of fatty acid crystals. If the temperature is too high, it is difficult to transfer heat from the mixture of solvent and fish oil to the environment, so that a good degree of subcooling cannot be formed, and the formation of crystal nuclei is limited. In addition to EPA and DHA, the uncrystallized liquid still contains a large amount of other components, resulting in a decrease in the ratio of EPA and DHA. Appropriate crystallization temperature is conducive to the formation of crystallization of saturated fatty acids. However, if the temperature is too low, EPA and DHA will migrate to the crystal nucleus, and eventually precipitate as crystals, reducing the enrichment rate of EPA and DHA, and may cause the formed crystals to be larger and difficult to filter. At the same time, the decrease in temperature will increase energy consumption. , so the present invention controls the crystallization temperature within the above range.

The process of crystallization is carried out in two steps, the growth of the nucleus and the growth of the crystal. Once the nucleus is formed, the crystal starts to grow. As long as the system is not saturated and the temperature is not supercooled, the fatty acid molecules also have high mobility to form crystals, which will continue to form until the system reaches equilibrium. The growth of crystals takes a certain amount of time, so the crystallization time is an important factor. Insufficient crystallization time, incomplete crystallization, and some saturated fatty acid components still exist in the organic solvent, reducing the proportion of EPA and DHA in the final product; while the crystallization time is too long, some EPA and DHA components may tend to crystallize, resulting in EPA and DHA. content reduction. Therefore, the present invention controls the crystallization time within the above-mentioned range.

The low-temperature crystallization process of the present invention is carried out in two stages. During the process of gradually decreasing the crystallization temperature, when the crystallization temperature is lowered to -10 to 5° C., the crystallization rate of saturated fatty acids in the fish oil increases rapidly, and when the temperature decreases again, the crystallization rate increases slowly. , until it decreased to -30～-50℃, the growth rate of crystallization rate accelerated again, indicating that the crystallization rate of saturated fatty acids in fish oil was higher at -10～5℃ and -30～-50℃. Therefore, the present invention adopts the method of segmental crystallization, firstly carries out the first stage of crystallization at -10 to 5°C, so that the saturated fatty acids that can be crystallized in this stage are fully crystallized, and then carries out the second stage at -30 to -50°C. The crystallization of the first stage reduces the pressure of the second stage crystallization, which helps to reduce the energy consumption, and the first stage crystallization can be used as the crystal nucleus of the second stage crystallization, which is conducive to the progress of the second stage crystallization. .

Preferably, the cooling rate of the first stage is 1-1.5°C/min, and the cooling rate of the second stage is 1.3-1.8°C/min.

During the separation process of crystal and crystalline liquid, the crystal form of crystal affects the separation effect, and the most stable crystal form is determined by cooling rate and crystallization temperature. Rapid cooling with a large temperature difference is likely to form inseparable glassy crystals, and the corresponding crystal form can be obtained by slowly cooling to the crystallization temperature with an appropriate cooling rate. The invention adopts a lower cooling rate in the first stage, which is helpful for the preliminary growth of the crystal formed by the crystal nucleus, and adopts a faster cooling rate in the second stage, which is conducive to the rapid formation of the crystal, thereby improving the crystallization efficiency.

Compared with the prior art, the present invention has the following beneficial effects: the present invention takes the ethyl ester type fish oil as a raw material, enriches EPA and DHA by a low-temperature crystallization method, reasonably selects an organic solvent and a crystallizing agent, and optimizes its process parameters, and separates the The fish oil with high content of EPA and DHA can be obtained by enrichment; it is easy to operate, has low requirements for equipment, large single processing capacity, good separation effect, and can better maintain the natural activity of EPA and DHA under low temperature environment. The deep processing and utilization of fish oil and the development of polyunsaturated fatty acid series health care products have important reference significance.

Detailed ways

The following are specific embodiments of the present invention to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

The method for enriching fish oil EPA and DHA in the present invention is further explained below through specific examples 1-12.

Example 1

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the steps:

The ethyl ester type fish oil is heated at 30°C for 30min, and the mass percentage content of EPA and DHA in the ethyl ester fish oil is 50%;

Add methanol and diatomaceous earth to fish oil, the mass ratio of fish oil, methanol and diatomaceous earth is 100:200:0.5, and mix well to form a mixture;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to 5°C at a rate of 1.0°C/min, kept for crystallization for 3 hours, and then cooled to -30°C at a rate of 1.3°C/min, kept for 2.5 hours for crystallization, and the ultrasonic power 300w, stirring rate n=15r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 87.53%.

Example 2

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the steps:

The ethyl ester fish oil was heated at 35°C for 25 minutes, and the mass percentage content of EPA and DHA in the ethyl ester fish oil was 55%;

Add absolute ethanol and clay to the fish oil, the mass ratio of fish oil, absolute ethanol and clay is 100:400:1, and mix to form a mixture;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to 0°C at a rate of 1.3°C/min, kept for crystallization for 3.5 hours, and then cooled to -35°C at a rate of 1.5°C/min, kept for 3 hours for crystallization, and the ultrasonic power 350w, stirring speed n=20r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 87.62%.

Example 3

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the steps:

The ethyl ester type fish oil was heated at 40°C for 20min, and the mass percentage content of EPA and DHA in the ethyl ester fish oil was 60%;

Add acetone and diatomaceous earth to fish oil, the mass ratio of fish oil, acetone and diatomaceous earth is 100:600:1.5, and mix to form a mixture;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -3 °C at a rate of 1.5 °C/min, kept for crystallization for 4 hours, and then cooled to -40 °C at a rate of 1.8 °C/min, kept for 3.5 hours for crystallization, and ultrasonicated. Power 400w, stirring speed n=25r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 88.87%.

Example 4

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the steps:

The ethyl ester fish oil was heated at 40°C for 10 min, and the mass percentage content of EPA and DHA in the ethyl ester fish oil was 70%;

Add n-hexane and clay to fish oil, the mass ratio of fish oil, n-hexane and clay is 100:800:2, and mix to form a mixture;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -5°C at a rate of 1.4°C/min, kept for crystallization for 3.5 hours, and then cooled to -45°C at a rate of 1.7°C/min, kept for 3 hours for crystallization, and ultrasonicated. Power 450w, stirring speed n=30r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 89.71%.

Example 5

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the steps:

The ethyl ester fish oil was heated at 50°C for 5 min, and the mass percentage content of EPA and DHA in the ethyl ester fish oil was 65%;

Add organic solvent and diatomaceous earth to fish oil, the mass ratio of fish oil, organic solvent and diatomaceous earth is 100:1000:2, mix well to form a mixture, the organic solvent is methanol and absolute ethanol with a volume ratio of 6:1 mixed solvent;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -10°C at a rate of 1.3°C/min, kept for 3.5 hours for crystallization, and then cooled to -50°C at a rate of 1.6°C/min, kept for 3 hours for crystallization, and ultrasonicated. Power 500w, stirring speed n=25r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 89.63%.

Example 6

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the steps:

The ethyl ester type fish oil was heated at 40°C for 20min, and the mass percentage content of EPA and DHA in the ethyl ester fish oil was 60%;

Add organic solvent and crystallizer to fish oil, the mass ratio of fish oil, organic solvent and crystallizer is 100:600:1.5, mix well to form a mixture, and the organic solvent is methanol and absolute ethanol with a volume ratio of 9:1 Mixed solvent, the crystallization aid is a mixture of diatomite and white clay with a mass ratio of 2:1;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -10°C at a rate of 1.3°C/min, kept for 3.5 hours for crystallization, and then cooled to -50°C at a rate of 1.7°C/min, kept for 3 hours for crystallization, and ultrasonicated. Power 400w, stirring speed n=20r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 89.20%.

Example 7

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the steps:

The ethyl ester type fish oil was heated at 40°C for 20min, and the mass percentage content of EPA and DHA in the ethyl ester fish oil was 60%;

Add organic solvent and crystallizer to fish oil, the mass ratio of fish oil, organic solvent and crystallizer is 100:600:1.5, mix well to form a mixture, and the organic solvent is methanol and absolute ethanol with a volume ratio of 12:1 Mixed solvent, the crystallization aid is a mixture of diatomite and white clay with a mass ratio of 1:1;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -10 °C at a rate of 1.2 °C/min, kept for 3.5 hours for crystallization, and then cooled to -50 °C at a rate of 1.6 °C/min, kept for 3 hours for crystallization, and ultrasonicated. Power 400w, stirring speed n=20r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 89.21%.

Example 8

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the following steps, and the mass percentage content of EPA and DHA in the ethyl esterified fish oil is 60%:

The ethyl ester fish oil was heated at 40°C for 20min;

Add organic solvent and crystallizer to fish oil, the mass ratio of fish oil, organic solvent and crystallizer is 100:600:1.5, mix well to form a mixture, and the organic solvent is methanol and absolute ethanol with a volume ratio of 9:1 Mixed solvent, the organic solvent contains citric acid with a mass percentage of 0.8%, and the crystallizing agent is a mixture of diatomite and white clay with a mass ratio of 2:1;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -10 °C at a rate of 1.2 °C/min, kept for 3.5 hours for crystallization, and then cooled to -50 °C at a rate of 1.6 °C/min, kept for 3 hours for crystallization, and ultrasonicated. Power 400w, stirring speed n=20r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 90.02%.

Example 9

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the following steps, and the mass percentage content of EPA and DHA in the ethyl esterified fish oil is 60%:

The ethyl ester fish oil was heated at 40°C for 20min;

Add organic solvent and crystallizer to fish oil, the mass ratio of fish oil, organic solvent and crystallizer is 100:600:1.5, mix well to form a mixture, and the organic solvent is methanol and absolute ethanol with a volume ratio of 9:1 Mixed solvent, the organic solvent contains citric acid with a mass percentage of 0.9%, and the crystallizing agent is a mixture of diatomite and white clay with a mass ratio of 2:1;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -10 °C at a rate of 1.3 °C/min, kept for crystallization for 3.5 hours, and then cooled to -50 °C at a rate of 1.8 °C/min, kept for 3 hours for crystallization, and ultrasonicated. Power 400w, stirring speed n=20r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 90.11%.

Example 10

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the following steps, and the mass percentage content of EPA and DHA in the ethyl esterified fish oil is 60%:

The ethyl ester fish oil was heated at 40°C for 20min;

Add organic solvent and crystallizer to fish oil, the mass ratio of fish oil, organic solvent and crystallizer is 100:600:1.5, mix well to form a mixture, and the organic solvent is methanol and absolute ethanol with a volume ratio of 9:1 Mixed solvent, the organic solvent contains citric acid with a mass percentage of 1.0%, and the crystallizing agent is a mixture of diatomite and white clay with a mass ratio of 2:1;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -10°C at a rate of 1.1°C/min, kept for 3.5 hours for crystallization, and then cooled to -50°C at a rate of 1.6°C/min, kept for 3 hours for crystallization, and ultrasonicated. Power 400w, stirring speed n=20r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 92.00%.

Example 11

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the following steps, and the mass percentage content of EPA and DHA in the ethyl esterified fish oil is 60%:

The ethyl ester fish oil was heated at 40°C for 20min;

Add organic solvent and crystallizer to fish oil, the mass ratio of fish oil, organic solvent and crystallizer is 100:600:1.5, mix well to form a mixture, and the organic solvent is methanol and absolute ethanol with a volume ratio of 9:1 Mixed solvent, the organic solvent contains citric acid with a mass percentage of 1.1%, and the crystallizing agent is a mixture of diatomite and white clay with a mass ratio of 2:1;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -10°C at a rate of 1.3°C/min, kept for 3.5 hours for crystallization, and then cooled to -50°C at a rate of 1.7°C/min, kept for 3 hours for crystallization, and ultrasonicated. Power 400w, stirring speed n=20r/min;

After low-temperature crystallization, vacuum filtration to separate the crystal and the uncrystallized liquid, centrifugally remove the crystallizer in the uncrystallized liquid, and molecular distillation to remove the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 91.65%.

Example 12

The method for enriching fish oil EPA and DHA by low-temperature crystallization in the present invention comprises the following steps, and the mass percentage content of EPA and DHA in the ethyl esterified fish oil is 60%:

The ethyl ester fish oil was heated at 40°C for 20min;

Add organic solvent and crystallizer to fish oil, the mass ratio of fish oil, organic solvent and crystallizer is 100:600:1.5, mix well to form a mixture, and the organic solvent is methanol and absolute ethanol with a volume ratio of 9:1 Mixed solvent, the organic solvent contains citric acid with a mass percentage of 1.2%, and the crystallizing agent is a mixture of diatomite and white clay with a mass ratio of 2:1;

The mixture was placed in a low-temperature equipment, and while ultrasonically stirred, it was first cooled to -10°C at a rate of 1.2°C/min, kept for 3.5 hours for crystallization, and then cooled to -50°C at a rate of 1.5°C/min, kept for 3 hours for crystallization, and ultrasonicated. Power 400w, stirring speed n=20r/min;

After low-temperature crystallization, vacuum filtration separates crystals and uncrystallized liquid, centrifugally removes the crystallizer in the uncrystallized liquid, and molecular distillation removes the organic solvent in the uncrystallized liquid to obtain the enriched fish oil EPA and DHA. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 91.86%.

Comparative Example 1

No crystallizing agent was added during the enrichment process, and the others were the same as in Example 10. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 83.16%.

Comparative Example 2

During the low-temperature freezing process, the temperature was lowered to -30°C at a rate of 18°C/min while ultrasonic stirring, and the temperature was kept for 5.5h for crystallization. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 83.93%.

Comparative Example 3

During the low-temperature freezing process, ultrasonic waves were not used, and others were the same as in Example 10. After testing, the total content of EPA and DHA in the enriched fish oil EPA and DHA was 86.19%.

To sum up, the present invention uses ethyl ester type fish oil as raw material, enriches EPA and DHA by low-temperature crystallization method, and rationally optimizes its technological parameters during the enrichment process; Increase the proportion of heterogeneous nucleation, reduce the degree of undercooling, and increase the crystallization temperature; and supplemented by ultrasonic stirring to increase the crystallization efficiency; the two-stage crystallization method is used in the crystallization process to reduce the energy consumption of crystallization and increase the crystallization efficiency; this method is easy to operate , The requirements for instruments and equipment are low, the single treatment capacity is large, the separation effect is good, and the natural activity of EPA and DHA can be better maintained in a low temperature environment.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention pertains can make various modifications or additions to the described specific embodiments or substitute in similar manners, but will not deviate from the spirit of the present invention or go beyond the definitions of the appended claims range.

Claims (5)

1. a method for low-temperature crystallization enrichment fish oil EPA, DHA, is characterized in that, described method comprises the steps: The fish oil is pretreated, and then an organic solvent and a crystallizing agent are added to the fish oil, and the mass ratio of the fish oil, the organic solvent and the crystallizing agent is 100: (200-1000): (0.5-2), and the mixing is carried out. Crystallization at low temperature, vacuum filtration to separate crystals and uncrystallized liquid, remove the organic solvent and crystallizer in the uncrystallized liquid, and obtain enriched fish oil EPA and DHA; Described fish oil is ethyl ester type fish oil, The pretreatment is to heat the fish oil at 30 to 50°C for 5 to 30 minutes, The organic solvent is one or more of methanol, absolute ethanol, acetone and n-hexane, and the organic solvent contains 0.8-1.2% citric acid by mass, The crystallization aid is one or both of diatomite and white clay. 2. the method for low-temperature crystallization enrichment fish oil EPA, DHA according to claim 1, is characterized in that, described organic solvent is the mixed solvent that volume ratio is (6～12): 1 methanol and dehydrated alcohol, so The organic solvent also contains 0.9-1.1% by mass of citric acid. 3. the method for low-temperature crystallization enrichment fish oil EPA, DHA according to claim 1, is characterized in that, described low-temperature crystallization is carried out in ultrasonic stirring, the ultrasonic power 300～500w of described ultrasonic stirring, stirring speed n=15 ~30r/min. 4. the method for low-temperature crystallization enrichment fish oil EPA, DHA according to claim 1, is characterized in that, described low-temperature crystallization comprises the first stage and the second stage, the first stage is cooled to-10～5 ℃, insulation crystallization 3 to 4 hours, the temperature is lowered to -30 to -50°C in the second stage, and the temperature is kept for 2.5 to 3.5 hours for crystallization. 5. the method for low-temperature crystallization enrichment fish oil EPA, DHA according to claim 4, is characterized in that, the cooling rate of described first stage is 1.0～1.5 ℃/min, and the cooling rate of described second stage is 1.3 ~1.8°C/min.