Polyunsaturated fatty acid bacterial powder with reduced spontaneous combustion risk, preparation method and application thereof

Abstract

The present invention provides a polyunsaturated fatty acid bacterial powder that reduces the risk of spontaneous combustion, as well as its preparation method and application. The preparation method comprises the following steps: wet-mixing a DHA fermentation broth with Nannochloropsis algae, followed by drying to obtain the polyunsaturated fatty acid bacterial powder; the polyunsaturated fatty acid bacterial powder has a particle size of no less than 200 microns and is rich in the polyunsaturated fatty acids DHA and EPA. This invention utilizes a specific preparation method to reduce the risk of spontaneous combustion of the resulting polyunsaturated fatty acid bacterial powder. Dry-mixing does not require the addition of minerals such as silicates, does not affect the palatability of the powder when used as animal feed, and is economical.

Description

Technical Field

[0001] The present invention relates to the technical field of feed additives, and more particularly to a polyunsaturated fatty acid bacterial powder capable of reducing the risk of spontaneous combustion, and a preparation method and application thereof. Background Art

[0002] Polyunsaturated fatty acid powders, especially those containing four or more double bonds like ARA / EPA / DPA / DHA, are susceptible to oxidation under the influence of light, air, temperature, and moisture, producing oxides and peroxides. If the heat generated during oxidation cannot be dissipated promptly, it can cause spontaneous combustion, ultimately leading to accidental explosions and fires. While this phenomenon can be mitigated by using smaller packaging or improving storage conditions, these solutions would undoubtedly increase costs for economically sensitive industries such as animal nutrition, hindering product adoption.

[0003] To improve this problem, the prior art CN110087481A proposes mixing with silicates, such as in sepiolite (magnesium silicate), to effectively maintain a safe environment. However, the risk of spontaneous combustion is reduced only by dry mixing silicates, and the silicate addition ratio is as high as 10-50%. If used as feed, it may affect palatability, reduce feed intake, and even lead to mineral poisoning in severe cases. Summary of the Invention

[0004] The first purpose of the present invention is to provide a method for preparing polyunsaturated fatty acid bacterial powder. The bacterial powder obtained by the preparation method has a high ignition point and a low risk of spontaneous combustion. At the same time, the economic cost is low and the palatability when used as animal feed is not affected.

[0005] The preparation method of the polyunsaturated fatty acid bacterial powder comprises the following steps: wet-mixing DHA fermentation liquid and Nannochloropsis algae powder and then drying to obtain the polyunsaturated fatty acid bacterial powder; the particle size of the polyunsaturated fatty acid bacterial powder is not less than 200 microns.

[0006] The present invention unexpectedly discovered that the polyunsaturated fatty acid bacterial powder obtained using the above method has a low risk of spontaneous combustion and low economic cost, and is suitable for industrial production, especially in the field of animal nutrition preparations. In the present invention, Nannochloropsis algae powder refers to dried Nannochloropsis algae powder.

[0007] In a preferred embodiment of the present invention, the drying is fluidized drying. In the solution of the present invention, the polyunsaturated fatty acid bacterial powder obtained by fluidized drying has a lower risk of spontaneous combustion.

[0008] In a specific embodiment of the present invention, the DHA fermentation broth contains Schizochytrium, the most common DHA-producing microorganism in the field. The total oil content of the broth is between 35-60%, and the DHA content in the broth is between 20-35%. Due to the high DHA content of Schizochytrium, it is very prone to spontaneous combustion in improper solvent atmospheres and storage methods.

[0009] In a specific embodiment of the present invention, Nannochloropsis is an autotrophic algae with low production cost. It is also a common oil-containing algae in the field. It can produce oils rich in chlorophyll, EPA and other polyunsaturated fatty acids. After fermentation, the total oil content of Nannochloropsis can reach 25-42%, of which the EPA content can reach 3-10%.

[0010] In a preferred embodiment of the present invention, the ratio of the weight of Schizochytrium to the weight of Nannochloropsis in the DHA fermentation broth is 2:5-1:10.

[0011] The Nannochloropsis algae is dried Nannochloropsis algae powder. In the present invention, Nannochloropsis algae and Nannochloropsis algae powder can be used interchangeably.

[0012] In a preferred embodiment of the present invention, the preparation method of the polyunsaturated fatty acid bacterial powder specifically comprises the following steps: adding DHA fermentation liquid to Nannochloropsis algae powder and wet mixing, granulating and fluidizing drying, and sieving to obtain polyunsaturated fatty acid bacterial powder; the particle size of the polyunsaturated fatty acid bacterial powder is not less than 200 microns.

[0013] As can be seen from the background technology, bacterial powder containing polyunsaturated fatty acid oil is prone to spontaneous combustion. One reason is the characteristics of polyunsaturated fatty acid oil itself, and the other is the oil overflow caused by the drying process of the bacterial powder. The oil content in Nannochloropsis is actually not low. However, the present invention found that adding Nannochloropsis powder to the granulation of Schizochytrium can overcome the problems caused by the storage of pure Schizochytrium algae powder, which is an unexpected discovery.

[0014] Direct granulation of Schizochytrium fermentation broth as the starting material has lower economic costs than first spray drying or vacuum drying and concentrating to obtain dry cells / mud and then granulating, making it more suitable for the animal nutrition industry. However, due to the low solids content of the fermentation broth, even centrifugal concentration of the fermentation broth itself cannot directly produce dry granules of suitable particle size. The addition of Nannochloropsis powder can achieve direct granulation of Schizochytrium fermentation broth, optimize the particle size of the mixture, and reduce surface oil. At the same time, the applicant discovered that the composition of the oil in Nannochloropsis is very different from that of algae such as Schizochytrium. Its oil composition is glycerides, phospholipids, and glycolipids. This difference is also one of the reasons why the risk of spontaneous combustion of Nannochloropsis and Schizochytrium is reduced after granulation. More importantly, the EPA contained in Nannochloropsis itself has important physiological functions in the field of animal nutrition. When it forms a certain ratio with the DHA in Schizochytrium, it has more prominent effects on maintaining animal health, etc. This is also the advantage of the present invention compared with the prior art solution of adding silicate.

[0015] The moisture content of the polyunsaturated fatty acid bacterial powder obtained using the above preparation method is preferably less than 5%, and the surface oil content is preferably less than 5%. It is further preferred that the surface oil content is less than 2%. It has a very low risk of spontaneous combustion. At the same time, this method has low preparation cost and high industrial economic value, and is very suitable for preparing polyunsaturated fatty acid bacterial powder for animal nutrition.

[0016] That is, another object of the present invention is to provide the polyunsaturated fatty acid bacterial powder obtained by the above-mentioned preparation method.

[0017] Based on the ratio of Schizochytrium to Nannochloropsis and the content of characteristic polyunsaturated fatty acids, the weight ratio of DHA:EPA in the bacterial powder prepared by the present invention is 3:1-3:10.

[0018] Another object of the present invention is to provide the above preparation method or the use of the polyunsaturated fatty acid powder obtained by the above preparation method in the preparation of animal nutrition.

[0019] The present invention utilizes a specific preparation method (wet-mixing a DHA fermentation broth with Nannochloropsis algae followed by drying to produce a polyunsaturated fatty acid bacterial powder with a particle size of no less than 200 microns) to reduce the risk of spontaneous combustion of the resulting polyunsaturated fatty acid bacterial powder. This method eliminates the need for dry-mixing with minerals such as silicates, does not affect the palatability of the powder when used as animal feed, and does not cause problems such as animal mineral poisoning. Furthermore, the powder is enriched with an appropriate ratio of DHA and EPA. Compared to existing technologies, the preparation method provided by the present invention also offers lower energy consumption and is more suitable for industrial production. DETAILED DESCRIPTION

[0020] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0021] The method for detecting polyunsaturated fatty acids is the commonly used gas phase method, and the method for detecting the auto-ignition coefficient is specifically as follows:

[0022] Place the sample into a dedicated sample container (stainless steel mesh with a 100mm side, open at the top, and placed inside a stainless steel mesh container cage). Fill to the brim and tap the container several times to refill. Cover the container with the stainless steel mesh container cage and hang it in the center of the oven. Raise the oven temperature to 140°C and maintain it for 24 hours, continuously recording the sample and oven temperatures. If spontaneous combustion occurs or if the sample temperature exceeds the oven temperature by 60°C, it is a self-heating substance and poses a risk of spontaneous combustion.

[0023] Example 1

[0024] 1) The DHA fermentation broth was centrifuged and concentrated to a concentration of 23.54%, a total bacterial oil content of 55%, and a DHA content of 29.75%;

[0025] 2) 1000 g of the concentrated DHA fermentation broth was added to 2236 g of Nannochloropsis powder (30.9% total oil, 4.7% EPA content, the same as in the subsequent examples (except Example 3) and the comparative example) and wet mixed to a ratio of 1:10 by dry weight of Schizochytrium:Nanochloropsis. The mixture was granulated with a 20-mesh 900-μm swing granulator and then fluidized dried to obtain a bacterial powder product with a 20-mesh sieving rate of 100%.

[0026] After testing, the particle size d90 of the above product is 472 microns, the DHA content is 2.8%, DHA:EPA (weight ratio) = 2:3, moisture is 3.4%, surface oil is 0.95%, and the highest temperature reached in the self-heating test is 161°C, which does not pose a risk of spontaneous combustion.

[0027] Example 2

[0028] 1) The DHA fermentation broth was concentrated by centrifugation to a concentration of 23.54%, a total bacterial oil content of 55%, and a DHA content of 29.75%;

[0029] 2) 1000 g of the concentrated DHA fermentation broth was added to 587 g of Nannochloropsis algae powder by wet mixing, with the dry weight ratio of Schizochytrium to Nannochloropsis algae being approximately 2:5. The mixture was granulated with a 20-mesh 900 μm swing granulator and then fluidized-dried to obtain a bacterial powder product with a 20-mesh sieving rate of 100%.

[0030] After testing, the particle size d90 of the above product is 372 microns, the DHA content is 8.5%, the DHA:EPA ratio is 2.5:1, the moisture content is 5.4%, the surface oil is 1.2%, and the highest temperature reached in the self-heating test is 180°C, which does not pose a risk of spontaneous combustion.

[0031] Example 3

[0032] 1) The DHA fermentation broth was concentrated by centrifugation to a concentration of 23.54%, a total bacterial oil content of 55%, and a DHA content of 29.75%;

[0033] 2) 1000 g of the concentrated DHA fermentation broth was added to 587 g of Nannochloropsis algae powder (40.9% total oil, 9.6% EPA content) by wet mixing, with a Schizochytrium:Nannochloropsis algae cell dry weight ratio of approximately 2:5. The mixture was granulated with a 20-mesh 900 μm swing granulator and then fluidized-dried to obtain a bacterial powder product with a 20-mesh sieving rate of 100%.

[0034] After testing, the particle size d90 of the above product is 380 microns, the DHA content is 8.5%, the DHA:EPA ratio is 1.25:1, the moisture content is 5.2%, the surface oil is 1.3%, and the highest temperature reached in the self-heating test is 184°C, which does not pose a risk of spontaneous combustion.

[0035] Example 4

[0036] 1) The DHA fermentation broth was centrifuged and concentrated to a concentration of 23.54%, a total bacterial oil content of 55%, and a DHA content of 29.75%;

[0037] 2) 1000 g of the concentrated DHA fermentation broth was added to 352 g of Nannochloropsis algae powder. The dry weight ratio of Schizochytrium:Nanochloropsis algae was approximately 2:3, making direct granulation impossible. Therefore, vacuum dehydration was performed to a concentration of 70%, followed by 20-mesh 900 μm swing granulation and fluidized drying to obtain a bacterial powder product with a 20-mesh sieving rate of 100%.

[0038] After testing, the particle size d90 of the above product is 306 microns, the DHA content is 11.2%, the DHA:EPA ratio is 4.2:1, the moisture content is 4.4%, the surface oil is 3.2%, and the highest temperature reached in the self-heating experiment is 200°C (critical), which has a certain risk of spontaneous combustion. At the same time, the energy consumption of vacuum dehydration is relatively high.

[0039] Comparative Example 1

[0040] 1) The DHA fermentation broth was centrifuged and concentrated to a concentration of 23.54%, a total bacterial oil content of 55%, and a DHA content of 29.75%;

[0041] 2) The concentrated DHA fermentation broth was centrifugally spray-dried at an air inlet temperature of 200° C. and an air outlet temperature of 85° C., and filtered through a 20-mesh vibrating sieve to obtain a bacterial powder product.

[0042] After testing, the particle size d90 of the above product is 92 microns, the moisture content is 2.3%, the surface oil content is 7.73%, and the maximum temperature reached in the self-heating test is >200°C, which poses a risk of spontaneous combustion.

[0043] Comparative Example 2

[0044] 1) The DHA fermentation broth was concentrated by centrifugation to a concentration of 23.54%, a total bacterial oil of 55%, and a DHA content of 29.75%.

[0045] 2) Steam-heating the roller drying equipment to a roller surface temperature of about 140° C., evenly spreading the concentrated DHA fermentation liquid on the roller surface, and then grinding it after drying to obtain a bacterial powder product with a 20-mesh sieving rate of 100%.

[0046] After testing, the particle size d90 of the above product is 351 microns, the moisture content is 4.7%, the surface oil content is 23.24%, and the maximum temperature reached in the self-heating test is >200°C, which poses a risk of spontaneous combustion.

[0047] Comparative Examples 1 and 2 reflect the problems caused by directly spray-drying the Schizochytrium fermentation broth, and attempts to change the drying method still failed to improve the problem.

[0048] Comparative Example 3

[0049] 1) The DHA fermentation broth was centrifuged and concentrated to a concentration of 23.54%, a total oil content of 55%, and a DHA content of 29.75%;

[0050] 2) The concentrated DHA fermentation broth was centrifugally spray-dried at an air inlet temperature of 200° C. and an air outlet temperature of 85° C., and filtered through a 20-mesh vibrating sieve to obtain a bacterial powder product.

[0051] 3) The bacterial powder obtained in step 2 was mixed with 587 g of Nannochloropsis powder and mixed in a double cone mixer.

[0052] After testing, the particle size d90 of the above product is 98 microns, the moisture content is 3.2%, the surface oil content is 8.01%, and the maximum temperature reached in the self-heating test is >200°C, which poses a risk of spontaneous combustion.

[0053] Comparative Example 4

[0054] 1) Another batch of DHA fermentation broth was centrifuged and concentrated to a concentration of 25.10%, 45% total oil, and 15.35% DHA content;

[0055] 2) The concentrated DHA fermentation broth was centrifugally spray-dried at an air inlet temperature of 200° C. and an air outlet temperature of 85° C., and filtered through a 20-mesh vibrating sieve to obtain a bacterial powder product.

[0056] After testing, the particle size d90 of the above product is 92 microns, the moisture content is 2.5%, the surface oil content is 6.53%, and the maximum temperature reached in the self-heating test is >200°C, which poses a risk of spontaneous combustion.

[0057] The results of Comparative Examples 3-4 show that the risk of spontaneous combustion can be avoided not only by reducing the content of long-chain polyunsaturated fatty acids and the total oil content.

[0058] Comparative Example 5

[0059] 1) The DHA fermentation broth was concentrated and vacuum dried, with a total oil content of 55% and a DHA content of 29.75%;

[0060] 2) The DHA dried bacterial cell blocks were crushed to obtain a bacterial powder product with a 20-mesh sieving rate of 100%.

[0061] After testing, the particle size d90 of the above product is 453 microns, the moisture content is 3.3%, the surface oil content is 7.28%, and the maximum temperature reached in the self-heating test is >200°C, which poses a risk of spontaneous combustion.

[0062] Comparative Example 6

[0063] 1) 1000 g of DHA fermentation broth was concentrated and vacuum dehydrated to a concentration of 70.2%, a total bacterial oil content of 55%, and a DHA content of 29.75%;

[0064] 2) The dehydrated DHA solids were granulated with a 20-mesh 900 μm swing granulation and then fluidized dried to obtain a bacterial powder product with a 20-mesh sieving rate of 100%. The product was then mixed with 587 g of similarly granulated Nannochloropsis algae particles in a double-cone mixer.

[0065] After testing, the particle size D90 of the above product is 405 microns, the moisture content is 3.8%, the surface oil content is 3.4%, and the maximum temperature reached in the self-heating test is 190°C, which means there is no risk of spontaneous combustion.

[0066] From Comparative Example 5, it can be seen that if a cake-like product is obtained by vacuum drying and then crushed, the surface oil content will be high. Comparative Example 6 shows that if the existing technology is used to vacuum dehydrate the entire fermentation liquid and then granulate it, and then mix it with the similarly granulated Nannochloropsis powder, the risk of spontaneous combustion can be avoided. However, the granulation conditions of the fermentation liquid and the dry Nannochloropsis powder are different, resulting in a difference in their particle size. The uniformity of the wet mixing (DHA, CV: 4.5%) is higher than that of the dry mixing (DHA, CV: 10.3%), which can make the nutritional cost distribution of the two algae more uniform. More importantly, in this comparative example, the two are granulated separately and go through two steps. At the same time, the process time and energy consumption cost burden of vacuum dehydration are much greater than those of the method described in the present invention. In the method of the present invention, the fermentation liquid only undergoes a simple centrifugation treatment to allow the subsequent granulation process to proceed smoothly.

[0067] Comparative Example 7

[0068] 1) The DHA fermentation broth was centrifuged and concentrated to a concentration of 23.54%, a total oil content of 55%, and a DHA content of 29.75%;

[0069] 2) 1000 g of the concentrated DHA fermentation broth was added to 587 g of dinoflagellate powder (42% total dinoflagellate oil, 11.3% DHA content) and wet-mixed. The mixture was granulated with a 20-mesh 900 μm swing granulator and then fluidized-dried to obtain a bacterial powder product with a 20-mesh sieving rate of 100%.

[0070] After testing, the particle size d90 of the above product is 385 microns, the moisture content is 5.1%, the surface oil content is 1.02%, and the maximum temperature reached in the self-heating test is >200°C, which poses a risk of spontaneous combustion.

[0071] The results of Example 3 and Comparative Example 7 show that when the overall total oil and main PUFA contents are similar, Nannochloropsis can play an important role in reducing the risk of bacterial powder spontaneous combustion.

[0072] Finally, the method of the present invention is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing polyunsaturated fatty acid bacterial powder, characterized in that: The steps include: The DHA fermentation liquid and the Nannochloropsis algae powder are wet-mixed and then dried to obtain polyunsaturated fatty acid powder; the particle size of the polyunsaturated fatty acid powder is not less than 200 microns; the weight ratio of the Schizochytrium fungus body in the DHA fermentation liquid to the Nannochloropsis algae is 2:5-1:10; and the drying is fluidized bed drying.

2. The preparation method according to claim 1, characterized in that The DHA content of the bacterial cells in the DHA fermentation liquid is 20-35%.

3. The preparation method according to claim 1 or 2, characterized in that The EPA content in the Nannochloropsis algae is 3-10%.

4. The preparation method according to claim 1 or 2, characterized in that The specific steps include: The DHA fermentation liquid is added to the Nannochloropsis algae powder and wet-mixed, granulated, fluidized-dried, and sieved to obtain the product.

5. The polyunsaturated fatty acid bacterial powder obtained by the preparation method according to any one of claims 1 to 4.

6. The polyunsaturated fatty acid bacterial powder according to claim 5, characterized in that The water content of the polyunsaturated fatty acid bacterial powder is less than 5%, and the surface oil content is less than 5%.

7. The polyunsaturated fatty acid bacterial powder according to claim 5 or 6, characterized in that The ratio of DHA to EPA in the polyunsaturated fatty acid bacterial powder is 3:1-3:

10.

8. Use of the preparation method according to any one of claims 1 to 4 or the polyunsaturated fatty acid bacterial powder according to any one of claims 5 to 7 in the preparation of an animal nutritional agent.