Low-temperature fermented milk and preparation method thereof

Abstract

The invention relates to the field of food, in particular to low-temperature fermented milk and a preparation method thereof.The preparation method of the low-temperature fermented milk comprises the steps that after raw milk is fermented, cooling is conducted firstly, then heat shock is conducted, cooling is conducted till the temperature is 10-25 DEG C, then the temperature is increased to 62-68 DEG C, and heat shock treatment is conducted for 30-300 s. According to the invention, through specific process conditions, i.e., a mode of first cooling and then heat shock after fermentation, a self-protection mechanism of lactic acid bacteria is stimulated, the lactic acid bacteria are induced to enter a low metabolic activity state, and the metabolic activity and nutritional requirements of the lactic acid bacteria in the state are reduced, so that the survival rate of thalli under external stimulation is improved, and the production cost is reduced. Meanwhile, reproduction and acid production in the storage period are inhibited, so that the shelf life of a low-temperature product under different leavening agents and different fermented milk systems can be prolonged to 60 days or above, the acidity of the product can still be kept unchanged within 14 days even under the condition of 30 DEG C, and the viable count is 1 * 10 < 6 > cfu / g or above.

Description

Technical Field

[0001] The invention relates to the field of food, and in particular to low-temperature fermented milk and a preparation method thereof. Background Art

[0002] Low-temperature fermented milk products are popular among consumers for their unique flavor and rich nutritional ingredients. Compared with milk, yogurt fermented by microorganisms not only retains the nutrients of milk, but also has a thicker texture. The lactic acid produced after fermentation can also improve intestinal function and promote gastrointestinal motility. Therefore, from the perspective of nutrition and health, fermented milk is a snack product that is both healthy and delicious.

[0003] Because low-temperature fermented dairy products contain active lactic acid bacteria, their shelf life is usually within 28-30 days, which is generally shorter than room temperature sterilized fermented milk, the latter of which can often have a shelf life of more than 45-60 days. There are three main factors that limit the shelf life of low-temperature fermented dairy products: (1) Biosafety issues: The sterilization intensity during the production and manufacturing of low-temperature fermented milk is not sufficient to kill the spores in the raw milk. During storage, the spores are prone to germinate into vegetative bodies due to environmental changes, causing product bloating and damage, resulting in microbial contamination of the product; (2) Lactic acid bacteria activity issues: During low-temperature storage, lactic acid bacteria will gradually lose their activity and die. During the storage period, the number of live lactic acid bacteria in low-temperature fermented milk will continue to decrease. When the storage period exceeds the shelf life, the number of live lactic acid bacteria will drop to 1×10 ^6 cfu / g, which is lower than the national standard requirement; (3) Product sensory decline: Since low-temperature fermented milk contains live bacteria, the long-shelf-life low-temperature yogurt fermentation bacteria continuously produce acid, which causes the yogurt to taste sour. It also causes precipitation and whey precipitation in the product, resulting in a decline in yogurt sensory indicators and a significant decline in consumer acceptance.

[0004] At present, in order to solve this problem, specific weak post-acid bacteria are often used, or preservatives (such as lactobacillus Nisin, potassium sorbate, polylysine, etc.) are used to inhibit the activity of fermentation bacteria. However, the above methods have a narrow scope of application and cannot meet the needs of enterprises for diversified products. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a low-temperature fermented milk and a preparation method thereof. The low-temperature fermented milk does not rely on the addition of special ingredients such as preservatives, nor does it rely on the use of weak post-acid fermentation agents. The shelf life can be extended to 60 days at 4°C, and the acidity can be preserved for 14 days at 30°C without changing. The number of viable bacteria is above 1×10^6 cfu / g.

[0006] On the one hand, the present invention provides a method for preparing low-temperature fermented milk, comprising the steps of chilling the raw milk and then heat shocking it after fermentation, wherein the raw milk is chilled to a temperature of 10-25°C and then heated to 62-68°C for heat shock treatment for 30-300s.

[0007] The present invention starts with the metabolic mechanism of lactic acid bacteria, activates the self-protection mechanism of lactic acid bacteria through the specific conditions of first cooling and then heating, and induces lactic acid bacteria to enter a state of low metabolic activity. The metabolic activity and nutritional requirements of lactic acid bacteria in this state are reduced, thereby improving the survival rate of the bacteria under external stimuli, while inhibiting their reproduction and acid production during the storage period, thereby achieving the shelf life of low-temperature products under different starters and different fermented milk systems Extended to 60 days.

[0008] In a specific embodiment of the present invention, the specific value of the heat shock treatment time in the range of 30-300 s is slightly different according to the characteristics of different strains and the differences in fermentation systems.

[0009] In a preferred embodiment of the present invention, the heat shock treatment temperature is 66-67° C. and the time is 80-100 s.

[0010] According to the method for preparing low-temperature fermented milk provided by the present invention, the temperature is raised from the chilling temperature to the heat shock treatment temperature, and the heating time is controlled within 1 minute.

[0011] Preferably, the heating method of the heat shock treatment is heating by heat transfer from a heating plate.

[0012] According to the preparation method of low-temperature fermented milk provided by the present invention, the raw milk comprises, by mass percentage, 80%-99% raw milk, 0-3.4% protein powder, 0-8% sweetener, 0-3.3% stabilizer, 0-5% fruit particles and 0-0.6% edible flavor.

[0013] There is no restriction on the specific selection of each raw material, and it can be a component allowed to be added to the commonly used food in the art. In some specific embodiments of the present invention, the raw milk is raw cow's milk or reconstituted milk; the protein powder is one or more of whey protein powder, casein powder, concentrated milk protein powder, skim milk powder or whole milk powder; the sweetener is one or more of sucrose, erythritol, xylitol, maltitol, allulose, sucralose, fructose syrup, monk fruit sweet, and steviol glycoside; the stabilizer is one or more of pectin, starch, and soybean polysaccharide; the fruit particles are one or more of strawberry, yellow peach, pineapple, pineapple, and blueberry jam.

[0014] According to the method for preparing low-temperature fermented milk provided by the present invention, the raw milk is centrifuged and sterilized before mixing the raw milk. This step is to further remove spores in the raw milk and avoid the risk of spore germination after extending the shelf life.

[0015] In some specific embodiments of the present invention, the temperature of centrifugal sterilization is 50° C. and the centrifugal speed is 4000 r / min.

[0016] In a specific embodiment of the present invention, the method for preparing the low-temperature fermented milk comprises: after mixing to obtain the raw milk, homogenizing, sterilizing, inoculating and fermenting in sequence; after fermentation, first chilling and then heat shocking, and then chilling and filling.

[0017] Wherein, the sterilization conditions are temperature 85-95°C and time 150-600 seconds.

[0018] The inoculated bacteria are one or more of thermophilic streptococci, bulgaricus lactobacillus, plantarum lactobacillus, helveticus lactococcus lactis subsp. cremoris, diacetyl lactococcus lactis subsp. and rhamnosus lactobacillus, and the inoculation amount is 50U-180U / ton.

[0019] The fermentation conditions are 30-45°C for 4-12 hours, with pH = 4.3-5.2 at the end of the fermentation being the criterion. In a specific embodiment, the specific fermentation temperature is adjusted according to the fermentation strain.

[0020] On the other hand, the present invention also provides a low-temperature fermented milk prepared by the above preparation method, which can be stored at 4°C for more than 60 days, and the number of viable bacteria in the product is not less than 1×10 6 cfu / g.

[0021] The low-temperature fermented milk of the present invention is a series of fermented milk products stored at low temperatures, specifically low-temperature yogurt, low-temperature fermented cheese, low-temperature sour cream and the like.

[0022] The present invention provides a low-temperature fermented milk and a preparation method thereof. The self-protection mechanism of lactic acid bacteria is stimulated by a specific process condition, i.e., first chilling and then heat-shocking after fermentation, so as to induce the lactic acid bacteria to enter a low metabolic activity state. The metabolic activity and nutritional requirements of the lactic acid bacteria in this state are reduced, thereby improving the survival rate of the bacteria under external stimulation, and inhibiting the reproduction and acid production during the storage period. Therefore, the shelf life of the low-temperature product can be extended to more than 60 days under different starters and different fermented milk systems, and the acidity can be kept unchanged for 14 days even at 30°C, and the number of live bacteria is more than 1×10^6 cfu / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A process flow chart for preparing low-temperature fermented milk provided by an embodiment of the present invention;

[0024] Figure 2 The changes in pH, acidity and viable count of the products of Example 5 and Comparative Example 1 during the storage period;

[0025] Figure 3 The changes in pH, acidity, viable count and water holding capacity of the products of Example 5 and Comparative Example 2 during the storage period;

[0026] Figure 4 The changes in diacetyl content, lactic acid content and citric acid content of the products of Example 5 of the present invention and Comparative Example 2 during the storage period;

[0027] Figure 5 The comparison of LDH enzyme activity in the supernatant of the products of Example 5 of the present invention and Comparative Example 2 after storage at 4°C for 60 days;

[0028] Figure 6 The following are the changes in the appearance of the products of Example 5, Comparative Example 3 and Comparative Example 4 of the present invention after being placed at 4° C. for 60 days. DETAILED DESCRIPTION

[0029] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0030] Unless otherwise specified, the methods involved in the following embodiments can be implemented by conventional methods in the art.

[0031] The raw materials and equipment involved in the following examples, unless otherwise specified, can all be purchased from the market. In the following examples, unless otherwise specified, the parts of the raw materials mentioned are parts by weight.

[0032] In the following examples, the scoring method for sensory evaluation of sourness, sweetness, powdery feeling, astringency, etc. is based on the sensory descriptors for yogurt in GB / T16861-1997, using a 9-point scale, with a scoring standard of 1-2 points for faint presence, 3 points for confirmed presence but very weak, 4-5 points for moderate presence, and 6 points and above for very strong. Standardized objects are selected as references for scoring, such as the sourness reference is a citric acid aqueous solution, the sweetness is a white sugar aqueous solution, the astringency is a tannin aqueous solution, and the powdery feeling is a skimmed milk powder solution.

[0033] Use an acidity meter to test the acidity of the product.

[0034] The number of live lactic acid bacteria was tested according to the method in GB4789.35-2016.

[0035] The viscosity was measured using a Brookfield DV-2T viscometer with a rotation speed of 100 r / min, a torque of 10%-100%, and a measurement time of 30 s.

[0036] The TA method was used to determine the changes in hardness, consistency, cohesion and other indicators. The method was to use the 5kg measuring unit of the texture analyzer, select the A / BE probe, the speed was 1mm / s, the penetration depth was 30mm, and the sample was placed from low temperature conditions to room temperature for testing after warming up.

[0037] The water holding capacity test method is to take 20g of sample, place it on quantitative filter paper and place it in a funnel, let it stand at room temperature for 120 minutes, collect the filtrate and weigh it. The water holding capacity calculation formula is:

[0038] Water holding capacity (%) = 1 - (filtrate mass (g) / sample mass (g)) × 100%.

[0039] In the following examples, raw milk is sterilized by centrifugation before mixing, the temperature is 50°C, and the centrifugal speed is 4000r / min; the time from the cold temperature to the heat shock temperature is controlled within 1 minute, and the heating method is heating by heat transfer on a heating plate.

[0040] Example 1

[0041] This embodiment provides a low-temperature fermented milk, and its preparation process is as follows Figure 1 As shown, the specific steps are as follows:

[0042] 92 parts of raw milk, 6.5 parts of sucrose and 1.5 parts of starch were mixed and homogenized, sterilized at 95°C for 300s, inoculated with 150U / ton of thermophilic Streptococcus and bulgaricus mixed fermentation agent (bacterial ratio 9:1), fermented at 42°C for 6 hours, cooled to 18°C, heat-shocked at 67°C for 100s, and then cooled and filled to make a fermented milk product.

[0043] As shown in Table 1, after the fermented milk of Example 1 was placed at 4°C for 60 days, its acidity did not change significantly, its viscosity did not change significantly, its sensory sweetness and sourness did not differ significantly, its powdery feeling and astringency did not increase significantly, and its viable bacterial count was still around 1×10^ 6 Above cfu / g level.

[0044] Table 1 Product stability of Example 1 stored at 4°C

[0045]

[0046] As shown in Table 2, after the fermented milk of Example 1 was placed at 30°C for 14 days, its acidity did not change significantly, its viscosity did not change significantly, its sensory sweetness and sourness did not differ significantly, its powdery feeling and astringency did not increase significantly, and its viable bacterial count was still around 1×10^ 6 Above cfu / g level.

[0047] Table 2 Product stability of Example 1 product stored at 30°C

[0048]

[0049] Example 2

[0050] This embodiment provides a low-temperature fermented milk, and the preparation steps are as follows:

[0051] 90 parts of raw milk, 7 parts of erythritol, 0.5 parts of pectin and 2.5 parts of whey protein powder were mixed and then homogenized, sterilized at 93°C for 300s, inoculated with 120U / ton of thermophilic Streptococcus, bulgaricus and Lactobacillus rhamnosus mixed fermentation agent (bacterial ratio of 10:1:1), fermented at 42°C for 5.5 hours, cooled to 25°C, heat-shocked at 64.5°C for 75s, and then cooled and filled to make a fermented milk product.

[0052] As shown in Table 3, after the fermented milk of Example 2 was placed at 4°C for 60 days, there was no significant change in acidity, viscosity, sourness and sweetness, and the number of viable bacteria was still 1×10^ 6 Above cfu / g level.

[0053] Table 3 Product stability of Example 2 product stored at 4°C

[0054]

[0055] As shown in Table 4, after the fermented milk of Example 2 was placed at 30°C for 14 days, its acidity did not change significantly, its viscosity did not change significantly, its sensory sweetness and sourness did not differ significantly, its powdery feeling and astringency did not increase significantly, and its viable bacterial count was still around 1×10^ 6 Above cfu / g level.

[0056] Table 4 Product stability of Example 2 product stored at 30°C

[0057]

[0058] Example 3

[0059] This embodiment provides a low-temperature fermented milk, and the preparation steps are as follows:

[0060] 98 parts of raw milk and 2 parts of whey protein powder were mixed and homogenized, sterilized at 85°C for 360s, inoculated with 100U / ton of thermophilic Streptococcus, Lactobacillus bulgaricus, Lactobacillus rhamnosus and Lactobacillus plantarum mixed fermentation agent (bacterial ratio of 10:1:1:1), fermented at 41°C for 6 hours, cooled to 10°C, heat-shocked at 62°C for 300s, and finally cooled and filled to make a fermented milk product.

[0061] As shown in Table 5, after the fermented milk of Example 3 was placed at 4°C for 60 days, there was no significant change in acidity, viscosity, sourness and sweetness, and the number of viable bacteria was still 1×10^ 6 Above cfu / g level.

[0062] Table 5 Product stability of Example 3 products stored at 4°C

[0063]

[0064] As shown in Table 6, after the fermented milk of Example 3 was placed at 30°C for 14 days, its acidity did not change significantly, its viscosity did not change significantly, its sensory sweetness and sourness did not differ significantly, its powdery feeling and astringency did not increase significantly, and its viable bacterial count was still around 1×10^ 6 Above cfu / g level.

[0065] Table 6 Product stability of Example 3 product stored at 30°C

[0066]

[0067] Example 4

[0068] This embodiment provides a low-temperature fermented milk, and the preparation steps are as follows:

[0069] 92 parts of raw milk, 4 parts of maltitol, 2 parts of starch and 2 parts of strawberry jam were mixed and homogenized, sterilized at 90°C for 300s, inoculated with 50U / ton of a mixed starter of thermophilic Streptococcus, bulgaricus and Lactococcus lactis subsp. cremoris (strain ratio 5:1:3), fermented at 32°C for 10 hours, cooled to 21°C, heat-shocked at 66°C for 100s, and finally cooled and bottled to make a fermented milk product.

[0070] As shown in Table 7, after the fermented milk of Example 4 was placed at 4°C for 60 days, there was no significant change in acidity, viscosity, sourness and sweetness, and the number of viable bacteria was still 1×10^ 7 Above cfu / g level.

[0071] Table 7 Product stability of Example 4 product stored at 4°C

[0072]

[0073] As shown in Table 8, after the fermented milk of Example 4 was placed at 30°C for 14 days, its acidity did not change significantly, its viscosity did not change significantly, its sensory sweetness and sourness did not differ significantly, its powdery feeling and astringency did not increase significantly, and its viable bacterial count was still around 1×10^ 6 Above cfu / g level.

[0074] Table 8 Product stability of Example 4 product stored at 30°C

[0075]

[0076] Example 5

[0077] This embodiment provides a low-temperature fermented milk, and the preparation steps are as follows:

[0078] 93 parts of raw milk and 7 parts of sucrose are mixed and homogenized, sterilized at 95°C for 300s, inoculated with 150U / ton starter, specifically a mixed starter of thermophilic Streptococcus and Lactobacillus bulgaricus (bacterial ratio 9:1), fermented at 42°C for 6 hours, cooled to 15°C, heat-shocked at 67°C for 80s, and finally cooled and filled to make a fermented milk product.

[0079] Comparative Example 1 (no cooling before heat shock)

[0080] This comparative example provides a low-temperature fermented milk, and the preparation steps are as follows:

[0081] 93 parts of raw milk and 7 parts of sucrose are mixed and homogenized, sterilized at 95°C for 300s, inoculated with 150U / ton fermentation agent, specifically a mixed fermentation agent of thermophilic Streptococcus and Lactobacillus bulgaricus (bacterial ratio 9:1), fermented at 42°C for 6 hours, heat-shocked at 67°C for 80s after fermentation, and then cooled and bottled to make a fermented milk product.

[0082] The product of Example 5 and the product of Comparative Example 1 were placed at 4°C for 60 days, and the changes in pH, acidity and viable bacterial count were detected on the 1st, 7th, 14th, 21st, 27th, 35th, 42nd, 49th and 60th days respectively.

[0083] The results are as follows Figure 2 As shown in the figure, it can be seen that the two preparation methods have little effect on pH and acidity, but the heat shock after chilling retains a higher initial viable count. Therefore, at the end of the shelf life, the viable count of the heat shock group after chilling (Example 5) is significantly higher than that of the group without chilling before heat shock (Comparative Example 1). However, both can meet the national standard that the viable count of low-temperature dairy products during the shelf life is higher than 1×10 ^6 cfu / g requirement.

[0084] Comparative Example 2 (non-heat shock group)

[0085] This comparative example provides a low-temperature fermented milk, and the preparation steps are as follows:

[0086] 93 parts of raw milk and 7 parts of sucrose are mixed and homogenized, sterilized at 95°C for 300s, inoculated with 150U / ton starter, specifically a mixed starter of thermophilic Streptococcus and bulgaricus (strain ratio 9:1), fermented at 42°C for 6 hours, cooled to 15°C and then bottled to make a fermented milk product.

[0087] The product of Example 5 and the product of Comparative Example 2 were placed at 4°C for 60 days, and the changes in pH, acidity, viable bacterial count and water holding capacity were detected on the 1st, 7th, 14th, 21st, 27th, 35th, 42nd, 49th and 60th days respectively.

[0088] The results are as follows Figure 3As shown in the figure, it can be seen that the pH and viable count of the product after the heat shock process (Example 5) changed relatively stably during the storage period, and the viable count was still around 1×10 ^6 cfu / g or more. Relatively speaking, the acidity of the non-heat-shock group (Comparative Example 2) increased significantly after 21 days of storage, and the pH decreased significantly, which was manifested as a stronger sour taste of the product. The number of viable bacteria was less than 1×10 after 42 days. ^6 cfu / g, which no longer meets the national standard requirements. Water holding capacity reflects the texture stability of the product. Generally, when the acidity of yogurt increases, the degree of protein denaturation increases, which is manifested as a serious decrease in water holding capacity. Figure 3 As shown in the figure, the water holding capacity after heat shock is slightly lower than that of the non-heat shock group, which may be due to slight denaturation of protein caused by heat shock. However, after the product was stored for 42 days, the water holding capacity of the non-heat shock group was lower than that of the heat shock group. After 60 days of storage, the water holding capacity of the heat shock group was still around 0.8%, while that of the non-heat shock group had dropped to about 0.6%, indicating that the product protein had obviously denatured.

[0089] In addition, the changes in diacetyl content, lactic acid content and citric acid content of the product of Example 5 and the product of Comparative Example 2 were detected during storage at 4° C. for 60 days. The diacetyl content was detected by chemical colorimetry, and the lactic acid content and citric acid content were detected by liquid chromatography.

[0090] The results are as follows Figure 4 As shown, it can be seen that the diacetyl content of the heat shock group (Example 5) remains stable throughout the shelf life, indicating that the lactic acid bacteria in this group are metabolically inactive and in a dormant state; while the diacetyl content of the non-heat shock group (Comparative Example 2) increases significantly after 28 days, indicating that the metabolic activity of the strain is enhanced. Lactic acid and citric acid are the main sources of the sour taste of yogurt, and citric acid is more sour than lactic acid. From the results in the figure, it can be seen that the lactic acid and citric acid contents of the heat shock group are relatively stable during the shelf life, while the lactic acid and citric acid contents of the non-heat shock group begin to increase significantly after 28 days, indicating that the metabolic activity of the strain in the non-heat shock group is enhanced. The above results further prove that the process conditions of the present invention can achieve the stability of the flavor substance content of the product stored at 4°C for 60 days.

[0091] In addition, the microbial status of the product of Example 5 was tested after storage at 4°C for 60 days. Common pathogens in dairy products such as Escherichia coli, Bacillus, Staphylococcus aureus and Listeria monocytogenes were detected. The results showed that the above pathogens were not detected in the samples after storage for 60 days.

[0092] The yogurt cells were removed by centrifugation, and the activity of lactate dehydrogenase (LDH) in the supernatant was tested. This enzyme is an intracellular enzyme of lactic acid bacteria and is responsible for synthesizing lactic acid. If the cell membrane is ruptured, the enzyme will be released into the supernatant, causing the enzyme activity of the supernatant to increase. This indicator can be used to determine whether the heat shock process has caused damage to the cells. The results are as follows: Figure 5Compared with the non-heat shock group (Comparative Example 2), the LDH enzyme activity in the supernatant after heat shock did not increase significantly, indicating that the current heat shock conditions would not cause damage to the lactic acid bacteria cell membrane.

[0093] Comparative Example 3

[0094] This comparative example provides a low-temperature fermented milk, and the preparation steps are as follows:

[0095] 93 parts of raw milk and 7 parts of sucrose were mixed and homogenized, sterilized at 95°C for 300s, inoculated with 150U / ton starter (same as Example 5), fermented at 42°C for 6 hours, cooled to 15°C, heat-shocked at 69°C for 80s, and then cooled and bottled to make a fermented milk product.

[0096] Comparative Example 4

[0097] This comparative example provides a low-temperature fermented milk, and the preparation steps are as follows:

[0098] 93 parts of raw milk and 7 parts of sucrose were mixed and homogenized, sterilized at 95°C for 300s, inoculated with 150U / ton starter (same as Example 5), fermented at 42°C for 6 hours, cooled to 15°C, heat-shocked at 71°C for 80s, and then cooled and bottled to make a fermented milk product.

[0099] like Figure 6 As shown, the changes in product appearance of Example 5, Comparative Example 3, and Comparative Example 4 after being placed at 4°C for 60 days were compared. The results showed that there was no obvious stratification and whey precipitation in the product appearance of the 67°C group (Example 5) during the storage period, the stratification was not obvious in the 69°C group (Comparative Example 3), and more obvious stratification appeared in the 71°C group (Comparative Example 4). The above results indicate that heat shock temperature greater than or equal to 69°C will lead to stratification and whey precipitation during the shelf life of the product.

[0100] In summary, the treatment process of first chilling and then heat shocking under the specific conditions of the present invention can significantly improve the stability of low-temperature fermented milk products during storage, including sensory stability, texture stability and viable bacteria count, thereby extending the shelf life of the product.

[0101] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing low-temperature fermented milk, characterized in that: The method comprises the steps of chilling the raw milk and then heat shocking it after fermentation, wherein the raw milk is chilled to a temperature of 10-25° C., and then the temperature is raised to 62-68° C. for heat shock treatment for 30-300 seconds.

2. The method for preparing low-temperature fermented milk according to claim 1, characterized in that: The heat shock treatment temperature is 66-67° C. and the time is 80-100 s.

3. The method for preparing low-temperature fermented milk according to claim 1, characterized in that: The temperature is raised from the cooling temperature to the heat shock treatment temperature, and the heating time is controlled within 1 minute; And / or, the heating method of the heat shock treatment is heat transfer heating by a heating plate.

4. The method for preparing low-temperature fermented milk according to any one of claims 1 to 3, characterized in that: Calculated by mass percentage, the raw milk comprises: 80%-99% raw milk, 0-3.4% protein powder, 0-8% sweetener, 0-3.3% stabilizer, 0-5% fruit particles and 0-0.6% edible flavor.

5. The method for preparing low-temperature fermented milk according to claim 4, characterized in that: Before the raw milk is mixed, the raw milk is centrifuged and sterilized.

6. The method for preparing low-temperature fermented milk according to claim 5, characterized in that: The preparation method comprises: after mixing to obtain the raw milk, homogenizing, sterilizing, inoculating and fermenting are performed in sequence; after fermentation is completed, first chilling and then heat shocking, and then chilling and filling.

7. The method for preparing low-temperature fermented milk according to claim 6, characterized in that: The sterilization conditions are a temperature of 85-95°C and a time of 150-600 seconds; And / or, the inoculated bacteria are one or more of thermophilic Streptococcus, bulgaricus, Lactobacillus plantarum, Lactobacillus helveticus, Lactococcus lactis subsp. cremoris, Lactococcus lactis subsp. diacetyl, and Lactobacillus rhamnosus, and the inoculation amount is 50U-180U / ton.

8. The method for preparing low-temperature fermented milk according to claim 6, characterized in that: The fermentation conditions are 30-45° C. for 4-12 hours, with pH reaching 4.3-5.2 at the fermentation end point as the judgment standard.

9. The method for preparing low-temperature fermented milk according to claim 8, characterized in that: The specific fermentation temperature is adjusted according to the fermentation bacteria.

10. A low-temperature fermented milk, characterized in that: The product is prepared by the preparation method according to any one of claims 1 to 9, which can be placed at 4°C for more than 60 days, or at 30°C for 14 days, and the acidity of the product remains unchanged, and the number of viable bacteria is not less than 1×10 6 cfu / g.

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