Lactose-free fermented milk and a preparation process

Abstract

The application belongs to the technical field of fermented milk and specifically relates to zero-lactose fermented milk and a preparation process. The preparation process comprises the following steps: (1) weighing the following raw materials: raw cow milk, white granulated sugar, sodium glutamate and a fermentation agent; the fermentation agent comprises Streptococcus salivarius subsp. thermophilus, Lactococcus lactis, Lactococcus lactis subsp. lactis and Bifidobacterium animalis lactis; (2) preheating the raw cow milk and the white granulated sugar and uniformly mixing them; homogenizing, sterilizing and obtaining sterilized materials; (3) cooling the sterilized materials, adding Lactococcus lactis subsp. lactis, Bifidobacterium animalis lactis, Streptococcus salivarius subsp. thermophilus and Lactococcus lactis, simultaneously adding sodium glutamate, uniformly stirring, performing fermentation, performing filling after the fermentation is completed, and performing cold storage to obtain zero-lactose fermented milk. The fermented milk of the application can simultaneously achieve the effects of zero-lactose characteristics, GABA functional enhancement and low sodium glutamate residue, and provides a safe, nutritious and high-quality product.

Description

Technical Field

[0001] This invention belongs to the field of fermented milk technology, specifically relating to a lactose-free fermented milk and its preparation process. Background Technology

[0002] With the increasing health awareness and upgrading of consumption patterns among the population, fermented dairy products that combine nutritional suitability and functional activity have become a core direction for food industry research and development and market competition. Zero-lactose fermented milk, through lactase-directed hydrolysis technology, fundamentally solves the problem of lactose intolerance prevalent in East Asian populations, significantly expanding the consumer base for fermented milk. For example, Chinese patent CN107136214B discloses a zero-lactose fermented milk and its preparation method, using *Lactococcus lactis* subsp. *lactococcus* 4.01SWEET purchased from the Soyuzisnab Group to degrade lactose, resulting in a fermented milk with a refreshing taste and delicate texture; the lactose content of the obtained fermented milk meets the internationally stipulated lactose-free standard.

[0003] Current production of functional fermented milk rich in gamma-aminobutyric acid (GABA) largely relies on the exogenous addition of monosodium glutamate (MSG) as a biosynthetic precursor, utilizing the lactic acid bacteria's own glutamate decarboxylase to catalyze the decarboxylation of the substrate to generate GABA. While this process ensures GABA yield, it suffers from insufficient substrate conversion efficiency, resulting in high levels of MSG residue in the product. Long-term excessive intake may increase the body's sodium load and metabolic burden. Furthermore, existing quality evaluation systems for lactose-free fermented milk are mostly limited to basic nutritional indicators such as lactose, protein, and fat. The precise control of the stability of the functional active substance GABA content and the potential risk factor—residual MSG—is not yet perfect, making it difficult to meet consumers' demands for safe, nutritious, and efficient functional fermented milk.

[0004] Therefore, developing a fermented milk preparation technology that can simultaneously achieve zero lactose, GABA functional enhancement, and low sodium glutamate residue has become a key requirement for the high-quality development of the functional fermented milk industry. Summary of the Invention

[0005] The purpose of this invention is to provide a lactose-free fermented milk and its preparation process, which can simultaneously achieve lactose-free characteristics, GABA functional enhancement, and low sodium glutamate residue.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A process for preparing lactose-free fermented milk includes the following steps: (1) Weigh the following raw materials: raw milk, white sugar, monosodium glutamate, and starter culture; the starter culture contains Streptococcus salivarius subsp. thermophilus, Lactococcus lactis, Lactococcus lactis subsp. lactis, and Bifidobacterium animalis subsp. lactis. (2) Preheat raw milk and white sugar, mix them evenly, homogenize and sterilize to obtain sterilized material; (3) Cool the sterilized material, add Lactococcus lactis subsp. lactis, Bifidobacterium animalis subsp. lactis, Streptococcus salivarius thermophilus subsp. lactococcus, and sodium glutamate, stir evenly, and ferment; after fermentation, fill and refrigerate to obtain lactose-free fermented milk.

[0007] This invention uses a combination of commercially available Lactococcus lactis subsp. lactis, Streptococcus salivarius subsp. thermophilus, Lactococcus fatii, and Bifidobacterium animalis subsp. lactis. This specific bacterial combination has a highly efficient lactose metabolism capacity, and can completely decompose and utilize the lactose in raw milk without the need for exogenous lactase during fermentation. The synergistic effect of this bacterial combination is significant, meeting the national requirements for zero-lactose fermented milk.

[0008] Preferably, the raw materials are prepared according to the following proportions: 92-95 parts by weight of raw milk, 3-7 parts by weight of white sugar, 0.1-0.4 parts by weight of sodium glutamate, and 0.01-0.03 parts by weight of starter culture.

[0009] Preferably, the ratio of live bacteria of Streptococcus salivarius subsp. thermophilus, Lactococcus lactis, Lactococcus lactis subsp. lactis, and Bifidobacterium animalis subsp. lactis is (0.6-0.8):(0.4-0.5):1:(0.1-0.3).

[0010] Preferably, the sterilization material is cooled to 40-45°C.

[0011] Preferably, the fermentation conditions are anaerobic fermentation at 40-45℃ for 35-38 hours.

[0012] Preferably, the total viable count of *Streptococcus thermophilus*, *Lactococcus fabri*, *Lactococcus lactis*, and *Bifidobacterium animalis* in the starter culture is (2-4) × 10⁻⁶. 10 CFU / g.

[0013] The existing strain *Lactococcus lactis* subsp. *lactococcus* AIBIS4.01SWEET can achieve low lactose in fermented milk, but it cannot simultaneously control GABA content and monosodium glutamate residue. This invention, through specific fermentation conditions, achieves a synergistic effect with three strains, ensuring zero lactose while increasing GABA production and reducing monosodium glutamate residue, significantly improving the product's functionality and safety.

[0014] The lactose-free fermented milk is prepared using the aforementioned process.

[0015] The content of γ-aminobutyric acid in lactose-free fermented milk is 1.92-1.98 mg / kg.

[0016] The sodium glutamate content in lactose-free fermented milk is 0.25-0.47 mg / kg.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention uses commercially available Lactococcus lactis subsp. lactis, Streptococcus salivarius subsp. thermophilus, Lactococcus fat subsp. lactis, and Bifidobacterium animalis subsp. lactis for compounding. This specific strain combination has a highly efficient lactose metabolism capacity. During the fermentation process, lactose in raw milk can be completely decomposed and utilized without the need for the addition of exogenous lactase. The synergistic effect of this strain combination is significant and meets the national requirements for zero-lactose fermented milk.

[0018] 2. The specific fermentation conditions of this invention can fully leverage the synergistic effect between strains, ensuring zero lactose while increasing GABA production and reducing monosodium glutamate residue, thus significantly improving the functionality and safety of the product. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] All raw materials used in the following embodiments of the present invention are commercially available products: Streptococcus salivarius subsp. thermophilus, Xinyang Mufan Biotechnology Co., Ltd., Product No.: MF-013465.

[0021] The strain number of *Lactococcus lactis* is CICC 23198; the strain number of *Lactococcus lactis* subsp. *lactococcus* is CICC20209; and the strain number of *Bifidobacterium animalis* subsp. *lactococcus* is CICC 21710. All of these strains were obtained from the China Industrial Microbial Culture Collection Center.

[0022] Raw milk contains 3.2% protein, 3.6% fat, and 4.7% lactose.

[0023] Example 1

[0024] This embodiment provides a lactose-free fermented milk, the preparation process of which includes the following steps: (1) Prepared according to the following raw material ratio: 93.8 parts by weight of raw milk, 5 parts by weight of white sugar, 0.2 parts by weight of monosodium glutamate, and 0.02 parts by weight of starter culture; the starter culture contains *Streptococcus thermophilus* subsp. *salicylate*, *Lactococcus fatii*, *Lactococcus lactis* subsp. *lactococcus*, and *Bifidobacterium animalis* subsp. *lactococcus*, and the total viable count of *Streptococcus thermophilus* subsp. *salicylate*, *Lactococcus fatii*, *Lactococcus lactis* subsp. *lactococcus*, and *Bifidobacterium animalis* subsp. *lactococcus* in the starter culture is 3 × 10⁻⁶. 10The CFU / g ratio of viable Streptococcus thermophilus subsp., Lactococcus fatense, Lactococcus lactis subsp. lactis, and Bifidobacterium animalis subsp. lactis was 0.7:0.4:1:0.2. (2) Preheat raw milk and white sugar to 60°C and mix them evenly; homogenize them at 70°C and 18MPa, and sterilize them at 110°C for 300s to obtain sterilized material; (3) Cool the sterilized material to 42°C, add Lactococcus lactis subsp. lactis, Bifidobacterium animalis subsp. lactis, Streptococcus salivarius thermophilus subsp. lactococcus, and sodium glutamate, stir evenly, and ferment. The fermentation conditions are anaerobic fermentation at 42°C for 36 hours. After fermentation, fill and refrigerate to obtain lactose-free fermented milk.

[0025] Example 2

[0026] This embodiment provides a lactose-free fermented milk, the preparation process of which includes the following steps: (1) Prepared according to the following raw material ratio: 94.2 parts by weight of raw milk, 5.5 parts by weight of white sugar, 0.23 parts by weight of monosodium glutamate, and 0.022 parts by weight of starter culture; the starter culture contains *Streptococcus thermophilus* subsp. *salicylate*, *Lactococcus fatii*, *Lactococcus lactis* subsp. *lactococcus*, and *Bifidobacterium animalis* subsp. *lactococcus*, and the total viable count of *Streptococcus thermophilus* subsp. *salicylate*, *Lactococcus fatii*, *Lactococcus lactis* subsp. *lactococcus*, and *Bifidobacterium animalis* subsp. *lactococcus* in the starter culture is 3 × 10⁻⁶. 10 The CFU / g ratio of viable Streptococcus thermophilus subsp., Lactococcus faecium, Lactococcus lactis subsp. lactis, and Bifidobacterium animalis subsp. lactis was 0.6:0.5:1:0.3. (2) Preheat raw milk and white sugar to 60°C and mix them evenly; homogenize them at 70°C and 18MPa, and sterilize them at 110°C for 300s to obtain sterilized material; (3) Cool the sterilized material to 42°C, add Lactococcus lactis subsp. lactis, Bifidobacterium animalis subsp. lactis, Streptococcus salivarius thermophilus subsp. lactococcus, and sodium glutamate, stir evenly, and ferment. The fermentation conditions are anaerobic fermentation at 40°C for 35 hours. After fermentation, fill and refrigerate to obtain lactose-free fermented milk.

[0027] Example 3

[0028] This embodiment provides a lactose-free fermented milk, the preparation process of which includes the following steps: (1) Prepared according to the following raw material ratio: 94.1 parts by weight of raw milk, 5.5 parts by weight of white sugar, 0.28 parts by weight of monosodium glutamate, and 0.026 parts by weight of starter culture; the starter culture contains *Streptococcus thermophilus* subsp. *salicylate*, *Lactococcus fatii*, *Lactococcus lactis* subsp. *lactococcus*, and *Bifidobacterium animalis* subsp. *lactococcus*, and the total viable count of *Streptococcus thermophilus* subsp. *salicylate*, *Lactococcus fatii*, *Lactococcus lactis* subsp. *lactococcus*, and *Bifidobacterium animalis* subsp. *lactococcus* in the starter culture is 3 × 10⁻⁶. 10 The CFU / g ratio of viable Streptococcus thermophilus subsp., Lactococcus faecium, Lactococcus lactis subsp. lactis, and Bifidobacterium animalis subsp. lactis was 0.8:0.45:1:0.1. (2) Preheat raw milk and white sugar to 60°C and mix them evenly; homogenize them at 70°C and 18MPa, and sterilize them at 110°C for 300s to obtain sterilized material; (3) Cool the sterilized material to 42°C, add Lactococcus lactis subsp. lactis, Bifidobacterium animalis subsp. lactis, Streptococcus salivarius thermophilus subsp. lactococcus, and sodium glutamate, stir evenly, and ferment. The fermentation conditions are anaerobic fermentation at 45°C for 38 hours. After fermentation, fill and refrigerate to obtain lactose-free fermented milk.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that the fermentation conditions are anaerobic fermentation at 42℃ for 30 hours.

[0030] Comparative Example 2 The difference between this comparative example and Example 1 is that the fermentation conditions are anaerobic fermentation at 42℃ for 45 hours.

[0031] Comparative Example 3 The difference between this comparative example and Example 1 is that Lactococcus lactis subsp. milkis is replaced with Lactococcus lactis subsp. milkis 4.01SWEET, which is purchased from Soyuzsnab Group and is used in a zero-lactose fermented milk and its preparation method disclosed in Chinese Patent CN107136214B.

[0032] Comparative Example 4 The difference between this comparative example and Example 1 is that the starter culture contains *Streptococcus salivarius* subsp. *thermophilus*, *Lactococcus fabri*, and *Lactococcus lactis* subsp. *lactococcus*, and the total viable count of these bacteria in the starter culture is 3 × 10⁻⁶. 10 The CFU / g ratio of viable Streptococcus thermophilus subsp., Lactococcus faecium, and Lactococcus lactis subsp. lactis was 0.7:0.4:1.

[0033] Comparative Example 5 The difference between this comparative example and Example 1 is that the ratio of live bacteria of Streptococcus salivarius subsp. thermophilus, Lactococcus lactis, Lactococcus lactis subsp. lactis, and Bifidobacterium animalis subsp. lactis is 0.5:1:1:0.5.

[0034] Comparative Example 6 The difference between this comparative example and Example 1 is that the starter culture contains *Streptococcus salivarius* subsp. *thermophilus*, *Lactococcus lactis*, *Lactococcus lactis* subsp. *lactophoresis*, and *Bifidobacterium animalis* subsp. *lactophoresis*, and the total viable count of these bacteria in the starter culture is 3 × 10⁻⁶. 10 The CFU / g ratio of viable Streptococcus thermophilus subsp., Lactococcus faecium, Lactococcus lactis subsp. lactis, and Bifidobacterium animalis subsp. lactis was 1:1.2:0.5:0.5.

[0035] Comparative Example 7 The difference between this comparative example and Example 1 is that the starter culture contains *Streptococcus thermophilus* subsp. *salivarius*, *Lactococcus lactis*, and *Bifidobacterium animalis* subsp. *lactobacter*, and the total viable count of these bacteria in the starter culture is 3 × 10⁻⁶. 10 The CFU / g ratio of live Streptococcus thermophilus subsp., Lactococcus lactis and Bifidobacterium animalis subsp. lactis was 1:1:1.

[0036] Performance testing 1. The nutritional components of zero-lactose fermented milk were tested according to the following methods: Method 1 (Kjeldahl method) of the National Food Safety Standard for Determination of Protein in Food; Method 3 (Alkaline hydrolysis method) of the National Food Safety Standard for Determination of Fat in Food; Method 3 (Alkaline hydrolysis method) of the National Food Safety Standard for Determination of Fat in Food; and Method 1 of GB5009.8-2023. The test results are shown in Table 1.

[0037] 2. Determine the γ-aminobutyric acid content according to "QB / T4587-2013 γ-aminobutyric acid".

[0038] 3. Refer to GB5009.124-2016, "National Food Safety Standard: Determination of Amino Acids in Food". The content of glutamic acid is determined, and then the content of monosodium glutamate is obtained.

[0039] The test results are shown in Table 1.

[0040] Table 1 Performance Test Results

[0041] As shown in Table 1, Examples 1-3 adopted specific strain combinations and fermentation processes, which resulted in complete lactose degradation, efficient conversion of GABA, and extremely low sodium glutamate residue, achieving optimal synergistic effect among the three objectives.

[0042] Comparative Example 1 had too short a fermentation time, and the strain failed to fully complete lactose metabolism and monosodium glutamate conversion, resulting in high lactose residue, insufficient GABA production, and a significant increase in monosodium glutamate residue.

[0043] In Comparative Example 2, the fermentation time was too long. Although lactose was completely broken down, the GABA content decreased. This may be because some GABA was further metabolized or degraded, while monosodium glutamate was almost depleted, reflecting the loss of functional components due to over-fermentation.

[0044] Comparative Example 3 used a single strain from patent CN107136214B to replace Lactococcus lactis subsp. lactis, which resulted in a significant decrease in lactose degradation capacity and a substantial increase in lactose residue. At the same time, the GABA conversion efficiency decreased and the monosodium glutamate residue increased, indicating that this strain could not work synergistically with other strains to complete efficient sugar removal and conversion.

[0045] Comparative Example 4 showed a significant decrease in lactose degradation capacity, reduced GABA production, and increased sodium glutamate residues in Bifidobacterium animalis subsp. lactose, indicating that Bifidobacterium animalis subsp. lactose plays an irreplaceable synergistic role in promoting lactose decomposition and GABA synthesis.

[0046] An imbalance in the ratio of strains 5 and 6 in the comparison ratio can lead to the disruption of metabolic synergy among the bacterial communities, a decrease in lactose degradation efficiency, an obstruction of GABA conversion, and a significant increase in monosodium glutamate residues.

[0047] Comparative Example 7 showed the absence of *Lactococcus lactis* subsp. *lactococcus*. Although lactose degradation was still somewhat effective without this strain, GABA production capacity decreased significantly and monosodium glutamate residue increased substantially, indicating that *Lactococcus lactis* subsp. *lactococcus* plays a key role in the GABA synthesis pathway.

[0048] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for preparing lactose-free fermented milk, characterized in that, Includes the following steps: (1) Weigh the following raw materials: raw milk, white sugar, monosodium glutamate, and starter culture; the starter culture contains Streptococcus salivarius subsp. thermophilus, Lactococcus lactis, Lactococcus lactis subsp. lactis, and Bifidobacterium animalis subsp. lactis. (2) Preheat raw milk and white sugar, mix them evenly, homogenize and sterilize to obtain sterilized material; (3) Cool the sterilized material, add Lactococcus lactis subsp. lactis, Bifidobacterium animalis subsp. lactis, Streptococcus salivarius thermophilus subsp. lactococcus, and sodium glutamate, stir evenly, ferment, and after fermentation, fill and refrigerate to obtain lactose-free fermented milk.

2. The preparation process of lactose-free fermented milk according to claim 1, characterized in that, Prepare according to the following raw material ratio: 92-95 parts by weight of raw milk, 3-7 parts by weight of white sugar, 0.1-0.4 parts by weight of monosodium glutamate, and 0.01-0.03 parts by weight of starter culture.

3. The preparation process of lactose-free fermented milk according to claim 1, characterized in that, The ratio of viable bacteria of Streptococcus salivarius subsp. thermophilus, Lactococcus lactis, Lactococcus lactis subsp. lactis, and Bifidobacterium animalis subsp. lactis was (0.6-0.8): (0.4-0.5): 1: (0.1-0.3).

4. The preparation process of lactose-free fermented milk according to claim 1, characterized in that, Cool the sterilized material to 40-45℃.

5. The preparation process of lactose-free fermented milk according to claim 1, characterized in that, The temperature for anaerobic fermentation is 40-45℃.

6. The preparation process of lactose-free fermented milk according to claim 1, characterized in that, The anaerobic fermentation time is 35-38 hours.

7. The preparation process of lactose-free fermented milk according to claim 1, characterized in that, Preheat the raw milk and white sugar to 55-60℃ and mix well.

8. A lactose-free fermented milk prepared by any one of claims 1-7.

9. The lactose-free fermented milk according to claim 8, characterized in that, The content of γ-aminobutyric acid in lactose-free fermented milk is 1.92-1.98 mg / kg.

10. The lactose-free fermented milk according to claim 8, characterized in that, The sodium glutamate content in lactose-free fermented milk is 0.25-0.47 mg / kg.

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