Method for producing selenium-rich protein feed by multi-strain co-fermentation of Hami melons

Abstract

The present invention relates to the technical field of microbial fermentation, and discloses a method for producing selenium-rich protein feed by multi-strain co-fermentation of Hami melons. The Hami melons are crushed, then mixed with a carbon source and a nitrogen source, and then inoculated with a fermentation agent for fermentation; the fermented product is dried and pulverized to obtain a protein feed; the fermentation agent includes Candida utilis, Aspergillus niger, and Bacillus licheniformis; the components of the Candida utilis culture medium include yeast extract 9.56 g / L, glucose 19.86 g / L, dipotassium hydrogen phosphate 1.45 g / L, magnesium sulfate 1.12 g / L, sodium selenite 25 mg / L, L-lysine and vitamin B1. In terms of mass concentration, the ratio of sodium selenite, L-lysine and vitamin B1 is 1:(116-232):(0.06-0.12). In the present invention, multi-strain co-fermentation of Hami melons is adopted to obtain a selenium-rich protein feed.

Description

Technical Field

[0001] The present invention relates to the technical field of microbial fermentation, and particularly relates to a method for producing selenium-enriched protein feed by multi-strain co-fermentation of Hami melons. Background Art

[0002] Protein feed refers to beans, cake meals, fish meal, etc. with a natural moisture content lower than 45%, crude fiber in dry matter lower than 18%, and crude protein content in dry matter reaching or exceeding 20%. There are four major categories including plant-based and animal-based protein feeds. In China, the shortage of protein feed resources relies on imports, which affects the development of the feed industry and animal husbandry. Unconventional protein feed resources are abundant and have strong development potential. Selenium, as an important trace element, plays a crucial role in the immune system, antioxidant capacity, growth and development of animals. It helps enhance immune responses, reduce the occurrence of diseases, protect cells from oxidative damage, and also promotes reproduction and improves the quality of animal products such as meat and eggs.

[0003] Hami melons are mainly produced in the Turpan-Hami Basin (collectively referring to the Turpan Basin and Hami Basin). They have various shapes, unique flavors, thick melon flesh, and are crisp and refreshing. Hami melons are rich in nutrients and have a sugar content of up to 21% at most. The output of Hami melons in Xinjiang Uygur Autonomous Region of China is sufficient, and there is even a phenomenon that they cannot be processed in time and rot in the fields. Therefore, making full use of the surplus Hami melons is an urgent problem to be solved in Xinjiang Uygur Autonomous Region.

[0004] Using Hami melons as raw materials for producing feed can not only produce selenium-enriched protein feed but also make full use of the surplus Hami melons. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for producing selenium-enriched protein feed by multi-strain co-fermentation of Hami melons. In the present invention, multi-strain co-fermentation of Hami melons is adopted to obtain a selenium-enriched protein feed.

[0006] The present invention provides a method for producing selenium-enriched protein feed by multi-strain co-fermentation of Hami melons, including the following steps:

[0007] Crush the Hami melons, then mix them with a carbon source and a nitrogen source, then inoculate a fermentation agent and carry out fermentation; dry and crush the fermented product to obtain a protein feed;

[0008] The fermentation agent includes Candida utilis, Aspergillus niger, and Bacillus licheniformis;

[0009] The preparation method of the bacterial liquid of Candida utilis includes: culturing Candida utilis in a Candida utilis medium,

[0010] The components of the Candida utilis culture medium include 9.56 g / L of yeast extract, 19.86 g / L of glucose, 1.45 g / L of dipotassium hydrogen phosphate, 1.12 g / L of magnesium sulfate, 25 mg / L of sodium selenite, L-lysine, and vitamin B1. By mass concentration, the ratio of sodium selenite, L-lysine, and vitamin B1 is 1:(116 - 232):(0.06 - 0.12).

[0011] Furthermore, the components of the Candida utilis culture medium include 9.56 g / L of yeast extract, 19.86 g / L of glucose, 1.45 g / L of dipotassium hydrogen phosphate, 1.12 g / L of magnesium sulfate, 25 mg / L of sodium selenite, L-lysine, and vitamin B1. By mass concentration, the ratio of sodium selenite, L-lysine, and vitamin B1 is 1:232:0.12.

[0012] Furthermore, the Candida utilis is Candida utilis CICC 1769 (Beijing Yuwei Technology Co., Ltd.).

[0013] Furthermore, the Aspergillus niger is Aspergillus niger CICC 40084 (Beijing Yuwei Technology Co., Ltd.).

[0014] Furthermore, the Bacillus licheniformis is Bacillus licheniformis CICC 10095 (Beijing Yuwei Technology Co., Ltd.).

[0015] Furthermore, by volume, the ratio of the bacterial liquid of Candida utilis, the bacterial liquid of Aspergillus niger, and the bacterial liquid of Bacillus licheniformis is 1:1:1.

[0016] Furthermore, the nitrogen source includes ammonium sulfate.

[0017] Furthermore, the carbon source includes glucose.

[0018] Furthermore, by mass, the added mass of the fermenting agent is 6% of the honeydew melon.

[0019] Furthermore, by mass, the added mass of the carbon source is 5% of the honeydew melon.

[0020] Furthermore, by mass, the added mass of the nitrogen source is 2% of the honeydew melon.

[0021] Furthermore, the fermentation conditions are: the fermentation temperature is 36°C - 38°C, and the fermentation time is 24 h - 26 h.

[0022] Furthermore, the drying temperature is 50°C - 60°C.

[0023] Furthermore, those skilled in the art should understand that the purpose of crushing is to refine the protein feed, and the technicians can adjust the particle size of the crushed protein feed according to actual needs.

[0024] Furthermore, the conditions for culturing Candida utilis in the Candida utilis culture medium include: shaking culture at 30 °C for 16 h.

[0025] Furthermore, the method for preparing the Aspergillus niger bacterial solution includes: inoculating Aspergillus niger in the Aspergillus niger culture medium, and the culture conditions include: shaking culture at 35 °C for 48 h.

[0026] Furthermore, the composition of the Aspergillus niger culture medium includes: 20 g / L peptone, 10 g / L yeast extract, 20 g / L glucose, with a pH value of 6.5, and the balance is deionized water.

[0027] Furthermore, the method for preparing the Bacillus licheniformis bacterial solution includes: inoculating Bacillus licheniformis in the Bacillus licheniformis culture medium, and the culture conditions include: shaking culture at 35 °C for 36 h.

[0028] Furthermore, the composition of the Bacillus licheniformis culture medium includes: 10 g / L peptone, 3 g / L beef extract, 5 g / L sodium chloride, 15 g / L agar, with a pH value of 7, and the balance is deionized water.

[0029] The present invention also provides the application of the above method in the production of selenium-enriched protein feed by fermenting Hami melons.

[0030] The embodiments of the present invention have the following technical effects:

[0031] 1. In the present invention, Aspergillus niger can produce cellulase during growth, and cellulase can decompose some of the cellulose in the Hami melon epidermis, which will degrade the crude fiber to a certain extent, thus facilitating the further improvement of the utilization of the fermentation substrate. Cellulase can hydrolyze a large amount of cellulose in the crushed Hami melon residue into monosaccharides, providing a carbon source for the fermentation process and further improving the utilization of the fermentation substrate. Candida utilis can utilize nutrients such as monosaccharides and disaccharides during growth and convert them into proteins, increasing the protein content of the product. Bacillus licheniformis can not only improve the cell mass of Candida utilis through synergy, thus facilitating the conversion of saccharide substances into proteins, but also remove the odor of the fermentation products, thus facilitating the improvement of the quality of the final protein feed product.

[0032] 2. Selenium is one of the essential trace elements for the body and is crucial for the body. It protects the body from free radical damage, participates in heavy metal detoxification, and regulates the body's immune system. It is an important component of various proteins such as glutathione peroxidase, thioredoxin reductase, and iodothyronine deiodinase in living organisms. During the cultivation process, Candida utilis can combine inorganic selenium with macromolecules in the body through its own metabolic activities and convert it into an organic form, mainly existing in the form of selenoamino acids and selenium-containing proteins, ultimately enabling selenium to be present in protein feed.

[0033] 3. When using Candida utilis for selenium enrichment, excessive addition of sodium selenite will inhibit the growth of Candida utilis. After selenium enrichment, Candida utilis, as one of the main strains for Hami melon fermentation, has a reduced viable count. On the one hand, it is not conducive to converting proteins during Hami melon fermentation, resulting in a long fermentation cycle and low protein conversion rate. On the other hand, the selenium content in Candida utilis after selenium enrichment decreases, leading to a decrease in the selenium content in the final protein feed. Therefore, in the present invention, L-lysine and vitamin B1 are further added during the cultivation of Candida utilis. It is found that L-lysine and vitamin B1 can solve the problem of the inhibited growth of Candida utilis caused by sodium selenite. When the added mass concentration of sodium selenite in the culture medium is increased to 25 mg / L, the viable count of Candida utilis can also be increased, which is not only beneficial to the Hami melon fermentation process but also can increase the selenium content in the feed.

[0034] 4. In the present invention, Hami melon is used as the fermentation substrate. Due to its high sugar content, during the fermentation process, the change in the pH of the fermentation environment will inhibit the activity of the fermenting agent. Therefore, it is necessary to accelerate the protein conversion rate to ensure high-protein feed can be obtained in a short time, thereby avoiding the economic losses and low protein conversion rate caused by long-term fermentation. Therefore, in the present invention, it is also necessary to ensure the activity and quantity of Candida utilis in the fermentation environment, which is beneficial to rapidly increasing the protein conversion rate. Aspergillus niger and Bacillus licheniformis in the fermentation environment can promote the decomposition of Hami melon fibers into monosaccharides, which is beneficial for the rapid metabolism of Candida utilis and thus beneficial for enhancing its activity. When preparing the bacterial liquid of Candida utilis, the added L-lysine and vitamin B1 can increase the viable count of Candida utilis, thereby ensuring the viable count of Candida utilis in the initial fermentation environment and further facilitating the increase in the protein conversion rate. Specific Embodiments

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope protected by the present invention.

[0036] In a first aspect, in some embodiments of the present invention, a method for producing selenium-enriched protein feed by multi-strain co-fermentation of Hami melons is provided, including the following steps:

[0037] Crush the Hami melons, then mix them with a carbon source and a nitrogen source, then inoculate a fermentation agent and carry out fermentation; dry and crush the fermented product to obtain protein feed.

[0038] The fermentation agent includes Candida utilis, Aspergillus niger, and Bacillus licheniformis.

[0039] The preparation method of the Candida utilis bacterial solution includes: culturing Candida utilis in a Candida utilis culture medium.

[0040] The components of the Candida utilis culture medium include yeast extract 9.56 g / L, glucose 19.86 g / L, dipotassium hydrogen phosphate 1.45 g / L, magnesium sulfate 1.12 g / L, sodium selenite 25 mg / L, L-lysine, and vitamin B1. In terms of mass concentration, the ratio of sodium selenite, L-lysine, and vitamin B1 is 1:(116 - 232):(0.06 - 0.12).

[0041] In some embodiments, the components of the Candida utilis culture medium include yeast extract 9.56 g / L, glucose 19.86 g / L, dipotassium hydrogen phosphate 1.45 g / L, magnesium sulfate 1.12 g / L, sodium selenite 25 mg / L, L-lysine, and vitamin B1. In terms of mass concentration, the ratio of sodium selenite, L-lysine, and vitamin B1 is 1:232:0.12.

[0042] In some embodiments, the Candida utilis is Candida utilis CICC 1769 (Beijing Yuwei Technology Co., Ltd.).

[0043] In some embodiments, the Aspergillus niger is Aspergillus niger CICC 40084 (Beijing Yuwei Technology Co., Ltd.).

[0044] In some embodiments, the Bacillus licheniformis is Bacillus licheniformis CICC 10095 (Beijing Yuwei Technology Co., Ltd.).

[0045] In some embodiments, by volume, the ratio of the Candida utilis bacterial solution, Aspergillus niger bacterial solution, and Bacillus licheniformis bacterial solution is 1:1:1.

[0046] In some embodiments, the nitrogen source includes ammonium sulfate.

[0047] In some embodiments, the carbon source includes glucose.

[0048] In some embodiments, by mass, the added mass of the fermentation agent is 6% of the honeydew melon.

[0049] In some embodiments, by mass, the added mass of the carbon source is 5% of the honeydew melon.

[0050] In some embodiments, by mass, the added mass of the nitrogen source is 2% of the honeydew melon.

[0051] In some embodiments, the fermentation conditions are as follows: the fermentation temperature is 36°C - 38°C, and the fermentation time is 24h - 26h.

[0052] In some embodiments, the drying temperature is 50°C - 60°C.

[0053] In some embodiments, the culture conditions of Candida utilis in the Candida utilis medium include: shaking culture at 30°C for 16h.

[0054] In some embodiments, the preparation method of the Aspergillus niger bacterial solution includes: inoculating Aspergillus niger in the Aspergillus niger medium, and the culture conditions include: shaking culture at 35°C for 48h.

[0055] In some embodiments, the composition of the Aspergillus niger medium includes: 20 g / L peptone, 10 g / L yeast extract, 20 g / L glucose, pH value of 6.5, and the balance is deionized water.

[0056] In some embodiments, the preparation method of the Bacillus licheniformis bacterial solution includes: inoculating Bacillus licheniformis in the Bacillus licheniformis medium, and the culture conditions include: shaking culture at 35°C for 36h.

[0057] In some embodiments, the composition of the Bacillus licheniformis medium includes: 10 g / L peptone, 3 g / L beef extract, 5 g / L sodium chloride, 15 g / L agar, pH value of 7, and the balance is deionized water.

[0058] In a second aspect, some embodiments of the present invention also provide the application of the method in the fermentation of honeydew melons to produce selenium-enriched protein feed.

[0059] The following is a detailed description in combination with specific examples and comparative examples:

[0060] (1) Preparation of Aspergillus niger bacterial liquid: In a liquid medium, there are 20 g of peptone, 10 g of yeast extract, 20 g of glucose, 1 L of distilled water. Adjust the pH value of the medium to 6.5 and sterilize it at 121 °C for 20 min. Pick 1 - 2 loops of single colonies of the activated Aspergillus niger and inoculate them into the sterilized liquid medium. After culturing on a shaker at 35 °C and 160 r / min for 48 h, obtain the Aspergillus niger bacterial liquid, where the Aspergillus niger is Aspergillus niger CICC 40084 (Beijing Yuwei Technology Co., Ltd.).

[0061] (2) Preparation of Bacillus licheniformis bacterial liquid: In a liquid medium, there are 10 g of peptone, 3 g of beef extract, 5 g of sodium chloride, 15 g of agar, 1 L of distilled water. Adjust the pH value of the medium to 7.0 and sterilize it at 121 °C for 20 min. Pick 1 - 2 loops of single colonies of the activated Bacillus licheniformis and inoculate them into the sterilized liquid medium. After culturing on a shaker at 35 °C and 160 r / min for 36 h, obtain the Bacillus licheniformis bacterial liquid, where the Bacillus licheniformis is Bacillus licheniformis CICC 10095 (Beijing Yuwei Technology Co., Ltd.).

[0062] Example 1:

[0063] Preparation of Candida utilis bacterial liquid: In a liquid medium, there are 9.56 g of yeast extract, 19.86 g of glucose, 1.45 g of dipotassium hydrogen phosphate, 1.12 g of magnesium sulfate, 25 mg of sodium selenite, 2.9 g of L-lysine, 1.5 mg of vitamin B1, 1 L of distilled water. Adjust the pH value of the medium to 7.0 and sterilize it at 121 °C for 20 min. Pick 1 - 2 loops of single colonies of the activated Candida utilis and inoculate them into the sterilized liquid medium. After culturing on a shaker at 30 °C and 160 r / min for 16 h, obtain the Candida utilis bacterial liquid; where the Candida utilis is Candida utilis CICC 1769 (Beijing Yuwei Technology Co., Ltd.).

[0064] Weigh 500 g of the washed Hami melons and put them into a pulper. Stir appropriately during the pulping process to ensure the smoothness and uniformity of the pulping process. The pulping time is preferably about 5 minutes. Add a certain amount of carbon source according to the weight of the Hami melons. The addition amount is 5%, that is, 25 g of glucose. Add a certain amount of nitrogen source according to the weight of the Hami melons. The addition amount is 2%, that is, 10 g of ammonium sulfate. Mix the bacterial solutions of Candida utilis, Aspergillus niger, and Bacillus licheniformis according to a volume ratio of 1:1:1. Use the mixed bacterial solution as an inoculant for inoculation. The inoculation amount is 6% of the weight of the Hami melons, a total of 30 mL of bacterial solution. Place it in a sterile fermenter at 36 °C for fermentation treatment. Test the reducing sugar content after fermentation. When the reducing sugar content reaches equilibrium, that is, the fermentation ends. After the fermentation ends, dry the fermentation product at 55 °C, and then pulverize it and pass through a 20-mesh molecular sieve.

[0065] Example 2:

[0066] The preparation method is the same as that of Example 1. However, when preparing the bacterial solution of Candida utilis in Example 2, 25 mg of sodium selenite, 5.8 g of L-lysine, and 3 mg of vitamin B1 are used, and the others are the same as in Example 1.

[0067] Comparative Example 1:

[0068] The preparation method is the same as that of Example 1. However, when preparing the bacterial solution of Candida utilis in Comparative Example 1, L-lysine and vitamin B1 are not added, and the others are the same as in Example 1.

[0069] Comparative Example 2:

[0070] The preparation method is the same as that of Example 1. However, when preparing the bacterial solution of Candida utilis in Comparative Example 2, L-lysine is not added, and the others are the same as in Example 1.

[0071] Comparative Example 3:

[0072] The preparation method is the same as that of Example 1. However, when preparing the bacterial solution of Candida utilis in Comparative Example 3, vitamin B1 is not added, and the others are the same as in Example 1.

[0073] Comparative Example 4:

[0074] The preparation method is the same as that of Example 1. However, when preparing the bacterial solution of Candida utilis in Comparative Example 4, 25 mg of sodium selenite, 1.45 g of L-lysine, and 0.75 mg of vitamin B1 are used, and the others are the same as in Example 1.

[0075] Comparative Example 5:

[0076] The preparation method was the same as that of Example 1. However, in Comparative Example 5, when preparing the Candida utilis bacterial solution, 25 mg of sodium selenite, 8.7 g of L-lysine, and 4.5 g of vitamin B1 were used, and the others were the same as those in Example 1.

[0077] Comparative Example 6:

[0078] In a liquid medium, 9.56 g of yeast extract, 19.86 g of glucose, 1.45 g of potassium hydrogen phosphate, 1.12 g of magnesium sulfate, and 1 L of distilled water were used. The pH value of the medium was adjusted to 7.0 and sterilized at 121 °C for 20 min. One or two loops of activated Candida utilis single colonies were inoculated into the sterilized liquid medium. After culturing on a shaker at 30 °C and 160 r / min for 16 h, the Candida utilis bacterial solution was obtained.

[0079] The examples and comparative examples in the present invention were tested:

[0080] (1) Test method for crude protein content: Weigh about 0.5 g of the sample into a digestion tube, add 0.2 g of copper sulfate, 3 g of potassium sulfate, and 10 mL of concentrated sulfuric acid. Place the digestion tube on a graphite digestion furnace, cover it with a waste hood, and select a curve heating rate during the digestion process. The heating program is set as follows: heat at 180 °C for 30 min, heat at 320 °C for 30 min, and heat at 420 °C for 60 min. After digestion is completed, cool to room temperature and measure using a K9860 automatic Kjeldahl distiller.

[0081] (2) Test method for reducing sugar content: Take 0 mL, 0.2 mL, 0.4 mL, 0.6 mL, 0.8 mL, and 1 mL of glucose standard solution (1 mg / mL) into 25 mL test tubes respectively, accurately add 2 mL of 3,5-dinitrosalicylic acid reagent to each, heat in a boiling water bath for 2 min, cool with running water, and make up to the 15 mL scale with water. Measure the OD 540 , where the glucose concentration is y and the OD value is x, and draw a standard curve;

[0082] Take 10 g of honeydew melon homogenate, rinse it with water into a 250 mL volumetric flask, add 3 mL of potassium ferrocyanide and zinc acetate each, and make up to 250 mL; take 30 mL of the volumetric sample solution for centrifugation and take the supernatant; take 10 mL of the supernatant and make up to 100 mL in a volumetric flask; take 1 mL of the liquid of the volumetric supernatant into a 10 mL stoppered test tube, make up to 2 mL with water, then add 4 mL of 3,5-dinitrosalicylic acid and heat in a boiling water bath for 5 min, cool to room temperature, make up to volume and shake well, and measure the OD 540 , and then substitute it into the standard curve to calculate the content of reducing sugar.

[0083] (3)Method for determining the viable count of live bacteria: Take 1 g of the fermentation product, shake it well in 9 mL of sterile water, and then serially dilute it to an appropriate multiple and count using the plate counting method. The result obtained is the viable count per gram of the wet basis.

[0084] (4)Test method for the selenium content in the feed:

[0085] Accurately weigh 0.5 g (accurate to 0.001 g) of the solid sample, place it in a conical flask, add 10 mL of a nitric acid-perchloric acid mixed acid (9 + 1) and a few glass beads, cover it with a watch glass, and digest it cold overnight. The next day, heat it on a hot plate and add nitric acid in a timely manner. When the solution becomes clear, colorless and white smoke appears, continue heating until the remaining volume is about 2 mL. Do not evaporate to dryness. After cooling, add 5 mL of hydrochloric acid solution (6 mol / L), continue heating until the solution becomes clear, colorless and white smoke appears again, and then continue heating until the remaining volume is about 2 mL. Cool down. At the same time, perform a reagent blank.

[0086] Preparation of the standard curve: Measure the fluorescence intensity of 4,5-benzopiazselenol for the selenium standard series solutions in ascending order of mass. Use the mass as the abscissa and the fluorescence intensity as the ordinate to prepare the standard curve.

[0087] After adding hydrochloric acid solution (1 + 9) to the above digested sample solution and the blank solution to 5 mL, add 20 mL of the EDTA mixture, and adjust it to light red-orange (pH 1.5 - 2.0) with ammonia water solution (1 + 1) and hydrochloric acid solution (1 + 9). The following steps are carried out in a dark room: Add 3 mL of DAN reagent (1 g / L), mix well, place it in a boiling water bath and heat for 5 min. After taking it out and cooling, add 3 mL of cyclohexane, shake for 4 min. Transfer all the solution into a separating funnel. After layer separation, discard the aqueous layer. Carefully pour the cyclohexane layer from the upper mouth of the separating funnel into a covered test tube, and measure it using a fluorescence spectrophotometer. The reference conditions of the fluorescence spectrophotometer are: excitation light wavelength 376 nm, emission light wavelength 520 nm.

[0088] Results and analysis:

[0089] Table 1 Test results of the examples and comparative examples

[0090]

[0091] Before the fermentation treatment of the cantaloupe, the protein content in the cantaloupe was 5.25%. In the cantaloupe fermentation product obtained by the method of the present invention, the protein content is not less than 23%. By the method of the present invention, the protein content has increased by at least 4 times. It can be seen that the cantaloupe has been successfully prepared into protein feed by the method of the present invention. And the selenium content in the feed obtained by the present invention is not less than 0.43 mg / kg.

[0092] In the present invention, by comparing Examples 1 - 2 with Comparative Examples 1 - 5, it is found that the method of the present invention, while successfully increasing the viable count of Candida utilis, reduces the fermentation time of Hami melons and also improves the conversion rate of crude protein in the feed.

[0093] During the fermentation of Hami melons, with Hami melons as the fermentation substrate, due to the high sugar content of Hami melons, during the fermentation process, the change in the pH of the fermentation environment will inhibit the activity of the fermenting agent. Therefore, it is necessary to accelerate the conversion rate of protein to ensure obtaining protein feed in a shorter time, thereby avoiding the economic losses caused by long - term fermentation and the low protein conversion rate. For the method of improving the protein conversion rate, on the one hand, it is necessary to ensure the mutual cooperation between the fermenting agents. Aspergillus niger in the fermenting agent can produce cellulase during growth, and the cellulase can decompose some cellulose in the epidermis of Hami melons to form substances such as monosaccharides and disaccharides, which can be quickly utilized by Candida utilis. Bacillus licheniformis can not only increase the cell mass of Candida utilis through synergistic effects, and the interaction between the microbial populations promotes an increase in the viable count of Candida utilis in the fermentation environment, thus facilitating the rapid conversion of protein; on the other hand, it is necessary to ensure that there are more viable counts of Candida utilis inoculated in the fermentation environment, so that there are more basic viable counts in the fermentation environment, which is also conducive to enhancing the protein conversion process.

[0094] Therefore, further comparison between Examples 1 - 2 and Comparative Example 6 reveals that when sodium selenite is added, the viable count of Candida utilis decreases significantly. It can be seen that when using Candida utilis for selenium enrichment, excessive addition of sodium selenite will cause the growth of Candida utilis to be inhibited. Further research by comparing Examples 1 - 2 with Comparative Examples 1 - 3 shows that when L - lysine and vitamin B1 are added during the selenium enrichment process of Candida utilis, L - lysine and vitamin B1 can solve the problem of the growth inhibition of Candida utilis caused by sodium selenite. It can be seen that during the selenium enrichment process of Candida utilis, by adding L - lysine and vitamin B1, not only can the viable count of Candida utilis be increased, but also the selenium content in the feed can be increased. Therefore, further optimization shows that in the culture medium of Candida utilis, by mass concentration, the ratio of sodium selenite, L - lysine, and vitamin B1 is 1:(116 - 232):(0.06 - 0.12).

[0095] On this basis, further comparison between Examples 1 - 2 and Comparative Examples 4 - 5 found that Examples 1 - 2 were significantly superior to Comparative Examples 4 - 5, and Example 2 was the best. It may be because the addition amounts of L-lysine and vitamin B1 can affect the metabolic pathway of Candida utilis. When the addition amounts are relatively low, the protective ability against Candida utilis may be weak, so the viable cell count of Candida utilis is less than that in Examples 1 - 2; while when the addition amounts of L-lysine and vitamin B1 are higher, other metabolic pathways may be affected, resulting in a decrease in the viable cell count of Candida utilis. Therefore, it is further preferred that in the Candida utilis culture medium, by mass concentration, the ratio of sodium selenite, L-lysine and vitamin B1 is 1:232:0.12.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing selenium-enriched protein feed by multi-strain co-fermentation of Hami melons, characterized in that, It includes the following steps: Crush the cantaloupe, then mix it with a carbon source and a nitrogen source, then inoculate with a fermenting agent and ferment; dry and pulverize the fermented product to obtain a protein feed. The fermenting agent includes Candida utilis, Aspergillus niger, and Bacillus licheniformis. The preparation method of the Candida utilis bacterial liquid includes: culturing Candida utilis in a Candida utilis culture medium. The components of the Candida utilis culture medium include 9.56 g / L of yeast extract, 19.86 g / L of glucose, 1.45 g / L of dipotassium hydrogen phosphate, 1.12 g / L of magnesium sulfate, 25 mg / L of sodium selenite, L-lysine, and vitamin B1. By mass concentration, the ratio of sodium selenite, L-lysine, and vitamin B1 is 1:232:0.

12. The fermentation conditions are: the fermentation temperature is 36°C - 38°C, and the fermentation time is 24 h - 26 h.

2. The method according to claim 1, wherein By volume, the ratio of the Candida utilis bacterial liquid, the Aspergillus niger bacterial liquid, and the Bacillus licheniformis bacterial liquid is 1:1:

1.

3. The method according to claim 1, wherein The nitrogen source includes ammonium sulfate; the carbon source includes glucose.

4. The method according to claim 1, wherein By mass, the added mass of the fermenting agent is 6% of the cantaloupe.

5. The method according to claim 1, characterized in that By mass, the added mass of the carbon source is 5% of the cantaloupe.

6. The method according to claim 1, characterized in that By mass, the added mass of the nitrogen source is 2% of the cantaloupe.

7. The method according to claim 1, characterized in that The drying temperature is 50°C - 60°C.

8. The method according to claim 1, characterized in that The conditions for culturing Candida utilis in the Candida utilis culture medium include: culturing on a shaker at a temperature of 30°C for 16 h.

9. Use of the method according to any one of claims 1 - 8 in the production of selenium-enriched protein feed by fermenting cantaloupe.

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