Preparation method and application of biological source selenium viable bacteria type fermented milk

Abstract

The invention discloses a preparation method and application of biological source selenium viable bacteria type fermented milk, and belongs to the technical field of fermented milk preparation, the preparation method comprises the following steps: S1, preparing a fermented milk base by taking SeNPs and casei paracasei SCFF20 as leavening agents; and S2, preparing the viable bacterium type fermented milk by using the fermented milk base in the step S1. According to the preparation method and the application of the biological source selenium viable bacteria type fermented milk, the fermentation activity of the casei paracasei SCFF20 can be promoted and the fermentation process can be accelerated by adding SeNPs, so that the fermentation end point can be reached more quickly, the a * value of the fermented milk can be remarkably increased by adding the SeNPs, meanwhile, the casei paracasei SCFF20 can also effectively convert sodium selenite in the fermented milk to generate SeNPs, and the selenium viable bacteria type fermented milk has the advantages that the quality of the fermented milk is improved. The a * value of the fermented milk is increased, and the SeNPs and the lactobacillus paracasei SCFF20 have a synergistic effect in the fermentation process.

Description

Technical Field

[0001] The present invention relates to the technical field of fermented milk preparation, and particularly to a preparation method and application of a bio - sourced selenium live - bacteria type fermented milk. Background Art

[0002] In selenium - deficient areas, the selenium ingested from food is difficult to meet the needs of normal human physiological metabolism. The various physiological effects of lactic acid bacteria, as well as their advantages such as safety and high - efficiency selenium supplementation, make it a research hotspot for the biosynthesis of SeNPs. At present, many studies use methods such as converting inorganic selenium into organic selenium by microorganisms, selenium - enriched fermentation of lactic acid bacteria, or adding other selenium - rich substances during the production process to prepare selenium - rich fermented dairy products.

[0003] Selenium - enriched fermentation of lactic acid bacteria can further expand the performance of lactic acid bacteria, and also contribute to the development of new functional foods and dietary selenium supplements. While retaining the nutritional value of milk itself, it also has the unique flavor, health - promoting probiotic effects, and selenium - rich characteristics of fermented products. In addition, live - bacteria type fermented milk beverages have gradually received wide attention due to their water - replenishing and portability. Their unique health - promoting probiotic and selenium - rich characteristics make the research and development of live - bacteria type fermented milk show great potential among selenium - rich products.

[0004] Based on this, the present invention uses the selenium - rich strain Lactobacillus paracasei SCFF20 to ferment and prepare selenium - rich active fermented milk, and explores the effects of different selenium - addition methods on the color difference, elemental selenium content, total selenium content, and volatile flavor components of selenium - rich fermented milk. The aim is to develop a selenium - rich live - bacteria fermented milk beverage to provide a safer selenium - supplement product for selenium - deficient people. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method and application of a bio - sourced selenium live - bacteria type fermented milk to solve the problems in the background art.

[0006] To achieve the above - mentioned purpose, in the first aspect, the present invention provides a preparation method of a bio - sourced selenium live - bacteria type fermented milk, including the following steps:

[0007] S1. Using SeNPs and Lactobacillus paracasei SCFF20 as starters to prepare a fermented milk base;

[0008] S2. Using the fermented milk base of S1 to prepare a live - bacteria type fermented milk.

[0009] Preferably, in S1, the preparation of the fermented milk base includes:

[0010] S11. Adding 2% white granulated sugar to fresh milk and sterilizing at 85°C for 20 min;

[0011] S12. Inoculating the starter, setting the fermentation temperature at 42°C, and fermenting for 12 h;

[0012] S13. After fermentation, it is placed in a refrigerator at 4°C for 12 hours of cold ripening.

[0013] Preferably, in S1, the inoculation amount of Lactobacillus paracasei SCFF20 is 10 8 CFU / mL.

[0014] Preferably, in S2, the preparation of the live bacteria fermented milk includes:

[0015] S21. Sodium tripolyphosphate and granulated sugar are successively added to sterile water at 60°C, and sterilized at 85°C for 20 minutes;

[0016] S22. After the sterilization in S21 is completed, it is cooled to room temperature, and the fermented milk base is added, and then stirred and homogenized to obtain.

[0017] Preferably, in S21, the addition amount of sodium tripolyphosphate is 0.3% of the mass of the sterile water, and the addition amount of granulated sugar is 10% of the mass of the sterile water.

[0018] Preferably, in S22, the addition amount of the fermented milk base is 50% of the mass of the sterile water in step S21.

[0019] In the second aspect, the present invention provides a biogenic selenium live bacteria fermented milk prepared by the above preparation method.

[0020] In the third aspect, the present invention provides an application of the above biogenic selenium live bacteria fermented milk in the preparation of selenium supplement products.

[0021] In the fourth aspect, the present invention provides an application of the starter in the above preparation method in the preparation of biogenic selenium live bacteria fermented milk.

[0022] Therefore, the preparation method and application of a biogenic selenium live bacteria fermented milk of the present invention have the following beneficial effects:

[0023] (1) The addition of SeNPs can promote the fermentation activity of Lactobacillus paracasei SCFF20, and can reach the fermentation end point faster;

[0024] (2) The addition of SeNPs can significantly increase the a* value of the fermented milk. At the same time, Lactobacillus paracasei SCFF20 can also effectively transform sodium selenite in the fermented milk to produce SeNPs, increasing the a* value of the fermented milk;

[0025] (3) Through the determination of the total selenium content of the fermented milk, it is found that Lactobacillus paracasei SCFF20 has the ability to reduce most of the Na2SeO3 to organic selenium and elemental selenium in the fermented milk;

[0026] (4) The diversity of flavor substances produced by the SeNPs particles + Lactobacillus paracasei SCFF20 group is superior to that of commercially available Lactobacillus paracasei, mainly reflected in some acids, ketones, and aldehydes, such as 2,3-dihydroxypropionic acid, 3-hydroxy-2-butanone, and furfural, etc., bringing buttery fragrance, milk fat aroma, cinnamon oil aroma, almond flavor, as well as woody and bread flavors to fermented milk.

[0027] The technical solution of the present invention will be further described in detail below through the accompanying drawings and examples. Brief Description of the Drawings

[0028] In order to more clearly illustrate the technical solution of the embodiments of the present invention, the accompanying drawings required for the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor.

[0029] Figure 1 It is a process flow chart for preparing a fermented milk base;

[0030] Figure 2 It is a process flow chart for preparing live bacteria type fermented milk;

[0031] Figure 3 It is the analysis of dynamic physicochemical indexes of SF, BF, XF, and YF groups of fermented milk, where A is pH, B is titratable acidity, C is viscosity, and D is total number of colonies;

[0032] Figure 4 It is the comparison of the content of elemental selenium Se(0) in SF, BF, XF, and YF groups of fermented milk;

[0033] Figure 5 It is the comparison of the total selenium concentration in SF, BF, XF, and YF groups of fermented milk;

[0034] Figure 6 It is the principal component analysis of volatile flavor components in SF, BF, XF, YF, and NR groups of fermented milk. Detailed Embodiments

[0035] The technical solution of the present invention will be further described below through the accompanying drawings and examples.

[0036] In order to make the purpose, technical solution, and advantages of the present application clearer, more thorough, and more complete, the technical solution of the present invention will be clearly and completely described below through the accompanying drawings and examples. The following detailed descriptions are all descriptions of embodiments, aiming to provide further detailed descriptions of the present invention. Unless otherwise specified, all technical terms adopted by the present invention have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs.

[0037] The instrument and equipment, reagent materials used in the examples are obtained through commercial channels unless otherwise specified.

[0038] Example 1

[0039] A preparation method of biogenic selenium live bacteria fermented milk specifically includes the following steps:

[0040] S1. Preparation of fermented milk base, the process is as Figure 1 shown.

[0041] Add 2% white granulated sugar to fresh milk, sterilize at 85 °C for 20 min and then cool, and then inoculate with a starter culture (10 8 CFU / mL). A total of 4 groups of starter cultures are set, namely: commercially available Lactobacillus paracasei group (SF), Lactobacillus paracasei SCFF20 group (BF), SeNPs (the amount of SeNPs obtained by reducing 120 μg / mL sodium selenite with a sufficient number of SCFF20) + Lactobacillus paracasei SCFF20 group (XF), sodium selenite + Lactobacillus paracasei SCFF20 group (YF).

[0042] Preparation method of SeNPs

[0043] Set the fermentation temperature at 42 °C, sample and measure the indicators every 3 h, that is, draw fermentation samples at 0, 3, 6, 9 and 12 h after inoculation until the pH reaches 4.6 - 4.7, and measure its acidity, pH, viable count and viscosity. Finally, place the fermented milk (pH = 4.6 - 4.7) in a 4 °C refrigerator for 12 h of after-ripening. Lactobacillus paracasei SCFF20 is a publicly available strain.

[0044] The addition methods of the four kinds of starter cultures are shown in Table 1:

[0045] Table 1 Addition methods of four groups of starter cultures

[0046]

[0047]

[0048] S2. Preparation of live bacteria lactic acid bacteria fermented milk, the process is as Figure 2 shown.

[0049] Prepare sterile water at 60 °C, add 0.3% sodium tripolyphosphate and 10% white granulated sugar in sequence, stir evenly, sterilize at 85 °C for 20 min, cool to room temperature and then add the ripened fermented milk base (50%), stir and homogenize to obtain the final product.

[0050] Test Example 1

[0051] Measure the pH value, titratable acidity, viscosity and total colony count of the fermented milk every 3 h after inoculating the fermentation starter culture.

[0052] Accurately pipette 10 mL of the fermented milk base and measure the pH value using a calibrated pH meter.

[0053] Use a pipette to aspirate 25 mL of the fermented milk base, homogenize it by pipetting up and down, and then place the sample on the rheometer platform for viscosity analysis. The test conditions are as follows: the shear rate is set to 20 s -1 , the operating temperature is set to 20 °C, and the operating time is set to 10 s.

[0054] Take 15 mL of the fermented milk base for the determination of titratable acidity, dilute and spread the fermented milk base, and then perform colony counting (CFU / mL).

[0055] Method for determining titratable acidity: Refer to the phenolphthalein indicator method in "GB 5009.239—2016 National Food Safety Standard Determination of Food Acidity" for determination.

[0056] Method for colony counting:

[0057] (1) Dilute the sample: Take 6 test tubes containing sterile normal saline, number them sequentially as 10 -1 , 10 -2 , ……, 10 -6 , and perform serial dilution. Method for diluting the bacterial solution: Before diluting the sample each time, first shake the sample well. Then use a 1 mL sterile pipette to aspirate and blow the sample in the sample to be diluted several times, and then accurately transfer 1 mL of the sample to the test tube of 10 -1 . Take another 1 mL sterile pipette, in the same way, first aspirate and blow the sample in the test tube of 10 -1 several times, and accurately transfer 1 mL of the bacterial solution to the test tube of 10 -2 , and so on until dilution to 10 -6 .

[0058] (2) Add the bacterial solution and pour the culture medium: Pipette 1 mL of the bacterial solution from each of the tubes of 10 -4 , 10 -5 and 10 -6 and add it to the surface of the corresponding numbered petri dish. Randomly add about 20 mL of the culture medium at about 50 °C to the petri dishes with the bacterial solution and shake well.

[0059] (3) Incubate: Incubate in a 37 °C incubator for 36 - 48 h and then count.

[0060] (4) Calculate the number of colonies: Select the petri dishes with the number of colonies between 30 - 300 CFU and no spreading colony growth to count the total number of colonies. If there is only one dilution factor with the number of colonies in the appropriate counting range, calculate the average of the number of colonies on the two petri dishes, and then multiply the average by the corresponding dilution factor as the result of the total number of colonies per g (or mL) of the sample.

[0061] When the number of colony - forming units on two consecutive dilution plates is within the appropriate counting range, calculate according to the following formula:

[0062]

[0063] Where N is the number of colonies in the sample; C is the sum of the number of colonies on the plates (plates with the number of colonies within the appropriate range); n 1， is the number of plates of the first dilution (low dilution multiple); n2 is the number of plates of the second dilution (high dilution multiple); d is the dilution factor (first dilution).

[0064] The results of the dynamic physicochemical indexes of the four groups of fermented milk, SF, BF, XF, and YF, are as Figure 3 shown. Among them, A is the change in pH value, B is the change in titratable acidity, C is the change in viscosity, Figure 3 and D in it is

[0065] The results show that after 12 h of fermentation, the pH values of the four groups of fermented milk, SF, BF, XF, and YF, are all close to the mature stage. During the whole fermentation period, the pH values of the four groups of samples generally show a downward trend. Among them, the downward trend of the pH value of the XF group far exceeds that of the other three groups of fermented milk, and the titratable acidity and viscosity of the XF group are also higher than those of the other fermented milk.

[0066] Fermented dairy products may continue to acidify during the post - ripening storage process. From Figure 3 A, it can also be seen that the pH values of the four groups of fermented milk are still decreasing during the post - ripening stage. However, due to the influence of low temperature during storage, the change in acidity value is not significant.

[0067] pH and titratable acidity are highly correlated with viscosity. From Figure 3 C, it can be seen that after 9 h of fermentation, the viscosity of the four groups of fermented milk gradually increases. It may be that the decrease in pH and the increase in titratable acidity cause the pH of the fermented milk to approach the isoelectric point of casein, resulting in a coagulation phenomenon.

[0068] The results of the analysis of the total number of colonies in fermented milk show that each group of fermented milk maintains the viable count at 10 8 CFU / mL at the end of its fermentation. Due to the consumption of sugar source and the inhibitory effect of increased acidity, the SF group grows rapidly within 0 - 11 h and then slowly. The BF group and the XF group grow rapidly from 0 - 9 h and tend to be stable from 9 - 12 h. The viable count of the YF group may start to decrease after 9 h of fermentation due to the effect of sodium selenite.

[0069] In summary, as the fermentation time extended, the pH of fermented milk showed a downward trend, while the titratable acidity, viscosity, and viable cell count generally showed upward trends. The lactic acid fermentation ability of Lactobacillus paracasei SCFF20 was superior to that of commercially available Lactobacillus paracasei. The addition of SeNPs could promote the fermentation activity of Lactobacillus paracasei SCFF20, enabling it to reach the fermentation end point first, while the addition of sodium selenite would inhibit the growth of Lactobacillus paracasei and reduce the viable cell count of fermented milk.

[0070] Test Example 2

[0071] Determination of Color Difference of Fermented Milk

[0072] Set the mode type to TTRAB - total transmission, select an observation area of 0.375 mm for the calibration of the color difference meter. After calibration, pipette 25 mL of fermented milk into a 40 - mm large - surface light - transmitting quartz cuvette, and use a pipette gun to blow and mix evenly. Use fresh milk as the blank standard sample and fermented milk as the test sample to measure and record the L*, b*, a*, and △E* values of the color difference. The results are shown in Table 2:

[0073] Table 2 L*, a*, b*, and △E* Values of Color Difference of Fermented Milk

[0074] L* a* b* ΔΕ* SF group 1.13±0.01a 0.23±0c 1.5±0.02a 1.89±0.02a BF group 0.82±0.01b 0.24±0.01c 1.42±0b 1.66±0.01b XF group 0.57±0.01d 1.3±0.02a 1.26±0.01d 1.9±0.02a YF group 0.61±0.01c 1.19±0.01b 1.33±0.01c 1.89±0.01a

[0075] It was found that there were significant differences in the color parameters L* and b* values between the SF group and the BF group, XF group, and YF group fermented with Lactobacillus paracasei SCFF20. This difference was because each strain of bacteria could make the fermented milk produce unique colors, textures, and flavors. In the color difference system, L* represents the lightness and darkness values from 100 to 0, representing white to black, the a* value ranges from negative (green) to positive (red), and the b* value ranges from negative (blue) to positive (yellow). It was also obtained from Table 2 that different selenium - addition methods would also significantly change the L*, a*, and b* values of fermented milk. The a* value of the fermented milk in the XF group after adding SeNPs was the highest (1.30 ± 0.02 a), followed by the YF group (1.19 ± 0.01 b). This proved that Lactobacillus paracasei SCFF20 could also effectively convert sodium selenite in fermented milk to produce SeNPs, bringing red nanoparticles to the fermented milk and increasing the color parameter a* value. Also, since the b* value of the selenium - rich fermented milk was also positive, it indicated that the color of the selenium - rich milk was red or slightly brown.

[0076] Test Example 3

[0077] Determination of Elemental Selenium Content in Fermented Milk

[0078] Determination method of elemental selenium content: Use black powdered elemental selenium powder Se(0) as the standard of elemental selenium to draw the selenium content standard curve. After the strain is cultured with selenium enrichment, collect the bacterial culture and Se(0) by centrifuging at 8000 rpm for 10 min. Then wash it twice with 0.9% sodium chloride solution, and resuspend the red elemental selenium in the precipitate in 15 mL of sodium sulfide (1 M), and shake evenly. Subsequently, centrifuge to remove the bacterial precipitate, and measure the absorbance of the resulting reddish-brown solution with an ultraviolet spectrophotometer at a wavelength of OD500 nm for the supernatant.

[0079] The elemental selenium Se(0) content of four groups of fermented milk is as Figure 4 shown. The Se(0) content of the XF group was 4.05 ± 0.01a (mg), which was significantly higher than that of other groups (P < 0.05). The YF group was also significantly higher than the SF group and BF group without added selenium (P < 0.05). In addition, the difference in Se(0) content between the YF group and the XF group was 0.95 mg, indicating that Lactobacillus paracasei SCFF20 can effectively convert sodium selenite into safe elemental selenium in fermented milk, but the conversion ability of this strain in fresh cow's milk is lower than that in MRS medium, probably because the nutrients available for microorganisms in fresh cow's milk are insufficient, or the fermentation time of fermented milk is shorter, so microorganisms have not been able to metabolize and convert all sodium selenite into Se(0).

[0080] Test Example 4

[0081] Determination of total selenium content in fermented milk

[0082] Determination method of total selenium content: Use a crucible reaction vessel containing 2 mL of concentrated HNO3 and 1 mL of 30% (v / v) H2O2 to perform acid digestion on the obtained fermented milk. After cooling, dilute the resulting solution to a final volume of 100 mL with ultrapure water, and quantitatively analyze the total selenium content of the fermented milk using inductively coupled plasma (ICP-OES).

[0083] The total selenium content in each group of selenium-enriched fermented milk was determined using an inductively coupled plasma optical emission spectrometer ICP-OES. As Figure 5 shown, the selenium content in the diluted XF group was 0.49 ± 0.00b (mg / L), and the content in the YF group was 0.50 ± 0.01a (mg / L). It can be calculated that the conversion rate of Lactobacillus paracasei SCFF20 to convert sodium selenite into organic selenium was 97.35%. And the selenium content in both the SF and BF groups was < 0.02 mg / L.

[0084] In GB1903.21-2016 Food Nutrition Fortifier Selenium-enriched Yeast, it is required that the organic selenium content of the strain ≥ 97%. Therefore, Lactobacillus paracasei SCFF20 meets the relevant regulations of this food nutrition fortifier. In addition, it can be calculated that the total selenium content of the two groups of selenium-enriched fermented milk is between 49 and 50 μg / L. According to the regulations of GB14880-2012 Food Nutrition Fortifier Use Standard for milk-containing beverages: the content of the nutrition fortifier selenium should be in the range of 50-200 μg / kg. The selenium-enriched fermented milk of the present invention basically meets the requirements.

[0085] Test Example Five

[0086] Determination of Volatile Flavor Substances in Fermented Milk

[0087] The volatile flavor substances of selenium-enriched active fermented milk were determined using an electronic nose. 10 mL of fermented milk was pipetted into a headspace vial, sealed with plastic wrap, and manually injected. The measurement was repeated 3 times in parallel and the average value was taken. Measurement parameters: sensor cleaning time 120 s, data zeroing time 10 s, data acquisition time 60 s; flow rate 0.5 L / min. The types of sensitive substances of the electronic nose sensors are shown in Table 3:

[0088] Table 3 Types of Sensitive Substances of Electronic Nose Sensors

[0089]

[0090]

[0091] The electronic nose flavor analysis of fermented milk is as Figure 6 shown. It can be seen that the contribution rate of PC1 is 97.35%, the contribution rate of PC2 is 2.22%, and the total contribution rate reaches 99.57% (> 85%), indicating that PC1 and PC2 meet the requirements for reflecting the characteristics of the sample, and the flavor of fermented milk is mainly determined by PC1. The higher the aggregation state of the data points of the same sample, the better the repeatability and stability of the same group. The distances between different groups are scattered and there is no overlap, indicating that there are differences in the flavor composition between different groups. It can be seen that the PCA diagrams of the 5 groups of fermented milk, namely SF, BF, XF, YF, and NR, do not show overlap or proximity, indicating that the volatile flavor substances they produce are significantly different.

[0092] The volatile flavor substances of selenium-enriched fermented milk were also determined by GC-MS. 10 mL of fermented milk sample was placed in a 25 mL headspace vial, with methyl heptanoate as the internal standard substance (concentration 1% v / v), preheated at 50 °C for 10 min. The 50 / 30 μm DVB / CAR / PDMS solid-phase microextraction needle was inserted into the headspace vial, and solid-phase adsorption was carried out at 50 °C for 30 min, and desorption was carried out at the injection port at 250 °C for 5 min.

[0093] GC-MS parameters: High-purity helium (>99.99%) was used as the carrier gas with a constant flow rate of 1.0 mL / min. The initial temperature was maintained at 35°C for 5 min, then increased to 140°C at a rate of 5°C / min and held for 5 min, and further increased to 250°C at a rate of 10°C / min and then held at this temperature for 3 min. The MS conditions were as follows: electron ionization energy of 70 eV, ion source temperature of 280°C, and a full-scan mode with a scanning range of 40 - 400 m / z.

[0094] The results are shown in Table 4:

[0095] Table 4 Comparison of Volatile Flavor Compounds in Fermented Milk

[0096]

[0097]

[0098] The results showed that there were significant differences in the flavor compounds of fermented milk among different fermentation groups. A total of 16 volatile flavor compounds were detected in the 5 groups of fermented milk samples. Among them, there were 12 in the SF group, 13 in the BF group, 14 in the XF group, 14 in the YF group, and 6 in the NR group (fresh cow's milk).

[0099] It can be found that the flavor compounds in fermented milk were significantly more than those in fresh cow's milk, including esters, alcohols, aldehydes, etc.

[0100] The aroma thresholds of ester compounds are generally very low, so they have a greater impact on the flavor of fermented milk. The typical fruity aroma in fermented milk is contributed by ester compounds. Among them, ethyl hexanoate has a sweet, fruity, and cellar aroma, and ethyl acetate has a fresh and fruity aroma. In addition, esters can also dilute the bitterness brought by fatty acids and amines. Among the generated alcohol compounds, isoamyl alcohol gives fermented milk unique flavor characteristics such as fusel oil and whisky flavor, which may come from amino acid metabolism, methyl ketone reduction, lactose metabolism, and linoleic acid degradation. Aldehyde compounds are the products of oil oxidation, and slight oxidation helps the formation of flavor. For example, furfural detected in the XF group and YF group can provide cinnamon oil aroma, almond flavor, as well as woody and bread flavors. In addition, the diversity of flavor compounds produced by Lactobacillus paracasei SCFF20 is also better than that of commercially available Lactobacillus paracasei, mainly reflected in some acids, ketones, and aldehydes. Acid compounds are mainly the products of the catabolism of sugars and amino acids by lactic acid bacteria, giving yogurt its unique flavor.

[0101] According to the results, only Lactobacillus paracasei SCFF20 can produce 2,3-dihydroxypropionic acid, with the contents being 2869.35 ng / kg in the BF group, 5239.56 ng / kg in the XF group, and 4926.82 ng / kg in the YF group, which are the main components of the flavor substances in fermented milk. Ketone substances are mainly produced by the thermal degradation and oxidation of unsaturated fatty acids or microbial metabolism, and can endow yogurt with a unique flavor. 3-Hydroxy-2-butanone has a buttery fragrance, a milky fat aroma, and a slightly sweet taste.

[0102] 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 preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a biological selenium active bacteria type fermented milk, characterized in that: The steps include: S1, using SeNPs and Lactobacillus paracasei SCFF20 as starter to prepare fermented milk base; S2. Prepare live bacteria type fermented milk using the fermented milk base of S1.

2. The method for preparing a biological source selenium live bacteria type fermented milk according to claim 1, characterized in that: In S1, the preparation of the fermented milk base includes: S11, add 2% white sugar to fresh milk, sterilize at 85℃ for 20min; S12, adding fermentation agent, setting the fermentation temperature to 42°C, and fermenting for 12 hours; S13. After fermentation, place in a refrigerator at 4°C and ripen for 12 hours.

3. The method for preparing a biological source selenium live bacteria type fermented milk according to claim 1, characterized in that: In S1, the inoculation amount of Lactobacillus paracasei SCFF20 was 10 8 CFU / mL.

4. The method for preparing a biological source selenium live bacteria type fermented milk according to claim 1, characterized in that: In S2, the preparation of live bacteria type fermented milk includes: S21, add sodium tripolyphosphate and white sugar to 60℃ sterile water, sterilize at 85℃ for 20min; After the sterilization in S22 and S21 is completed, cool to room temperature, add fermented milk base, and stir to obtain the product.

5. The method for preparing a biological source selenium live bacteria type fermented milk according to claim 4, characterized in that: In S21, the amount of sodium tripolyphosphate added is 0.3% of the mass of sterile water, and the amount of white sugar added is 10% of the mass of sterile water.

6. The method for preparing a biological selenium live bacteria type fermented milk according to claim 4, characterized in that: In step S22, the amount of fermented milk base added is 50% of the mass of the sterile water in step S21.

7. A biological selenium active bacteria type fermented milk prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the biological selenium live bacteria fermented milk as claimed in claim 7 in the preparation of selenium supplement products.

9. Use of the starter in the preparation method according to any one of claims 1 to 6 in the preparation of biological selenium live bacteria type fermented milk.

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