A fermentation and enzymatic ripening process for edible butter

Abstract

This application belongs to the field of food ripening technology, specifically relating to a fermentation and enzymatic ripening process for edible butter. This application first discloses a fermentation and enzymatic ripening process for edible butter, which involves adding citric acid and yeast extract to fresh butter, and then using *Lactococcus lactis* and *Leuconostoc mesenteroides* for co-fermentation and enzymatic hydrolysis, supplemented by washing and settling steps, to form a unique fermentation and enzymatic ripening process. This fermentation and enzymatic ripening process can effectively increase the content of flavor substances such as diacetyl, acetoin, caprylic acid, δ-decanoic acid, 2-nonanone, and decanoic acid in ripened edible butter, thereby enhancing the sensory flavor of the ripened edible butter. Unexpectedly, the shelf life of the resulting ripened edible butter is also extended, specifically manifested in extremely low initial acid value and peroxide value, and minimal change in acid value and peroxide value after storage under accelerated aging conditions.

Description

Technical Field

[0001] This invention belongs to the field of food ripening technology, specifically relating to a fermentation and enzymatic ripening process for edible butter. Background Technology

[0002] Butter ripening is a traditional process that improves the flavor and texture of butter by controlling the fermentation process. Originating in Europe, this process has a history spanning hundreds of years. Modern butter ripening technology, while retaining the essence of this tradition, incorporates advanced technologies from microbiology, food chemistry, and engineering to form a systematic production process.

[0003] The core of the maturation process lies in utilizing specific microbial communities to biotransform milk fat, producing a rich array of flavor compounds. These microorganisms mainly include lactic acid bacteria, yeasts, and molds, which, through complex metabolic pathways, convert fatty acids in milk fat into ketones, aldehydes, and alcohols, compounds with distinctive flavors. Butter treated with different maturation processes exhibits significant differences in fatty acid composition, directly impacting the flavor characteristics of the final product.

[0004] The butter ripening process can be divided into five main stages: raw milk treatment, starter culture preparation, fermentation ripening, butter making, and post-ripening treatment.

[0005] Raw milk processing is the foundation of the maturation process. Fresh milk first undergoes rigorous quality inspection to ensure it is free of antibiotic residues and pathogenic bacteria contamination. It then undergoes standardized processing to adjust the fat content to an appropriate level. Pasteurization is the key step in this stage, typically held at 72-85°C for 15-30 seconds to kill harmful microorganisms while preserving the activity of beneficial bacteria.

[0006] The preparation of starter cultures requires careful selection and cultivation of specific microbial strains. Traditional butter ripening often uses natural starter cultures, while modern industrial production tends to use standardized commercial starter cultures. These starter cultures typically contain a variety of lactic acid bacteria, such as Lactococcus lactis and Streptococcus thermophilus, which can metabolize lactic acid and secrete various enzymes to break down milk proteins, laying the foundation for the formation of subsequent flavor compounds.

[0007] Fermentation and maturation are the core of the entire process. During this stage, the milk fat inoculated with the starter culture ferments under strictly controlled environmental conditions. The temperature is typically maintained at 20-25℃, the pH value is controlled between 4.5 and 5.0, and the fermentation time varies from several hours to several days depending on product requirements. During this process, microorganisms produce abundant flavor precursors through metabolic pathways such as glycolysis, protein hydrolysis, and fat breakdown.

[0008] In the buttermaking stage, the fermented milk fat is separated into butter using physical methods. Traditional churning techniques have been replaced by modern continuous buttermaking machines. This process requires precise control of churning speed and time to ensure the formation of butter particles and the complete removal of whey.

[0009] Post-ripening is a crucial step in ensuring the stability of butter's flavor. Freshly made butter needs to be stored at low temperatures for an appropriate period to allow flavor compounds to fully develop and reach a balanced state. This process typically takes 1-2 weeks, during which the physicochemical properties and microbiological status of the butter need to be monitored regularly.

[0010] Currently, the microorganisms used in butter fermentation mainly include lactic acid bacteria and yeast. In some cases, compound starter cultures (such as kefir grains) or probiotic strains are also introduced. These microorganisms regulate the acidity, flavor compound production, fat structure, and probiotic activity of butter through metabolic activities. However, their application effects are affected by the characteristics of the strains, fermentation conditions, and product requirements, and each has its own advantages and disadvantages.

[0011] Lactic acid bacteria are the core microorganisms in butter fermentation. Their main functions are to break down lactose to produce lactic acid, lower the pH of the system, inhibit the growth of spoilage microorganisms, and generate flavor compounds (such as diacetyl and acetoin) and texture-improving metabolites through secondary metabolism. Based on their growth temperature and metabolic characteristics, lactic acid bacteria used for butter fermentation can be divided into two main categories: mesophilic lactic acid bacteria and thermophilic lactic acid bacteria. The application scenarios and effects of different types of strains vary significantly.

[0012] Mesophilic lactic acid bacteria are the mainstream choice for low-temperature fermented butter (fermentation temperature 20-30℃). Common strains include two subspecies of Lactococcus lactis (cremoris and lactis), Leuconostoc mesenteroides, and Leuconostoc cremoris. Among them, *Lactococcus lactis* subsp. cremoris produces mild acid, slowly lowering the pH value and preventing the butter from becoming coarse due to a sudden increase in acidity. It also produces a small amount of diacetyl (giving butter a light cream flavor), making it suitable for making smooth, refreshing sweet cream butter. *Lactococcus lactis* subsp. lactis and its biovar *Lactococcus lactis* biovar. diacetylactis have stronger acid-producing capabilities and can utilize citric acid to metabolize large amounts of diacetyl (a key substance in the characteristic flavor of butter) and acetoin (3-hydroxybutanone). These are the core strains for fermented butter (such as European-style fermented butter), giving the product a rich "fermented butter aroma." *Leuconostoc mesenteroides* possesses both acid-producing and polysaccharide-producing abilities. Its metabolically produced extracellular polysaccharides (EPS) increase the viscosity of butter, reduce fat particle loss during churning, improve butter yield, and alleviate hardening of butter during low-temperature storage.

[0013] Thermophilic lactic acid bacteria are mainly used in high-temperature fermentation processes (fermentation temperature 35-45℃). Common strains include *Lactobacillus delbrueckii* subsp. bulgaricus and *Streptococcus thermophilus*. The core advantage of these strains is their rapid acid production, capable of lowering the pH of cream to 4.5-4.8 within 12-16 hours, significantly shortening the fermentation cycle and making them suitable for continuous industrial production. While *Streptococcus thermophilus* has relatively limited proteolytic activity, it effectively utilizes lactose to produce acid during fermentation, generating important flavor compounds such as diacetyl and acetaldehyde. These compounds impart a refreshing "yogurt aroma" or "creamy aroma" to the product, complementing the flavor produced by *Lactobacillus delbrueckii*, thus improving the monotony of a single lactic acid flavor and enhancing the overall flavor profile of the product. Furthermore, *Streptococcus thermophilus* and *Lactobacillus bulgaricus* are often used in a 1:1 ratio, exhibiting a typical symbiotic relationship. The formic acid and carbon dioxide produced by *Streptococcus thermophilus* metabolism stimulate the growth of *Lactobacillus bulgaricus*, while *Lactobacillus bulgaricus*, through its strong proteolytic activity, breaks down casein to produce small peptides and free amino acids, providing *Streptococcus thermophilus* with essential nitrogen. This synergistic effect stabilizes the acid production rate and fermentation process, significantly reducing the risk of fermentation failure.

[0014] Although yeast does not play a dominant role in butter fermentation, it enriches flavor and improves the stability of the microbial community through metabolic activity, making it an important component of the "complex fermentation system." The yeasts used in butter fermentation are mostly acid-resistant and cold-resistant strains, primarily including *Debaryomyces hansenii*, *Kluyveromyces marxianus*, and *Saccharomyces cerevisiae*, with *Debaryomyces hansenii* being the most common.

[0015] Kefir grains are a natural, complex starter culture consisting of a symbiotic community of lactic acid bacteria, yeast, and acetic acid bacteria. Their structure consists of gel-like particles (primarily composed of glucan) encapsulating various microorganisms, including lactic acid bacteria (such as *Lactobacillus kefiri* and *Lactobacillus acidophilus*), yeasts (such as *Hansenula polymorpha* and *Kluyveromyces lactis*), and acetic acid bacteria (such as *Acetobacter spp.*).

[0016] In butter fermentation, kefir grains do not require separate strain isolation; direct inoculation can achieve "one-step compound fermentation." Its advantages lie in the stable microbial community and abundant metabolites, which can simultaneously generate lactic acid, acetic acid, ethanol, diacetyl, and polysaccharides, giving butter a multi-layered flavor of "acidity, aroma, and mellowness." Furthermore, the product has natural probiotic activity.

[0017] Studies have shown that butter fermented with kefir grains can have a lactic acid bacteria count of up to 10. 7 CFU / g (far exceeding the minimum requirement of 10 for probiotic foods) 6 (CFU / g), yeast count approximately 10 3 -10 4 With a CFU / g content, and during a 90-day refrigerated period, the activity of lactic acid bacteria decreased by only 0.5-1 orders of magnitude, demonstrating superior probiotic stability compared to butter inoculated with probiotic strains alone. Furthermore, the small amount of acetic acid (approximately 0.1-0.3%) produced by the acetic acid bacteria in the kefir grains further inhibits the growth of spoilage bacteria, while simultaneously forming a synergistic antibacterial effect with lactic acid, extending the shelf life of the butter. For consumers, kefir fermented butter not only boasts a unique flavor but also regulates gut microbiota through probiotics, making it suitable for promotion as a "functional dairy product."

[0018] To meet consumer demand for "functional foods," researchers have recently begun introducing probiotic strains into butter fermentation. Through single or combined inoculation, these strains combine traditional flavors with health benefits. Probiotic strains used in butter fermentation must meet three main conditions: acid resistance, bile salt resistance, and low-temperature storage resistance. Common strains include *Lactobacillus rhamnosus* GG strain, *Lactobacillus paracasei* 431 strain, *Lactobacillus acidophilus* LA-5 strain, and *Bifidobacterium bifidum* ATCC 29521 strain.

[0019] The application of different microorganisms in butter fermentation is essentially a balance between "functional requirements" and "processing costs." For companies pursuing traditional flavor and low-cost production, mesophilic lactic acid bacteria (such as a combination of Lactococcus lactis and Leuconostoc mesenteroides) are the optimal choice. For shorter fermentation cycles and continuous industrial production, thermophilic lactic acid bacteria (such as a combination of Lactobacillus bulgaricus and Streptococcus thermophilus) are more advantageous. For brands positioning themselves as "high-end functional products," while kefir grains or probiotic strains are more expensive, they can enhance product value through unique flavors and health benefits. In the future, with advancements in microbial screening technologies (such as CRISPR-Cas9 gene editing) and fermentation processes (such as precise temperature control and vacuum fermentation), it is expected that new microbial fermentation systems with "high flavor, high stability, and low cost" can be developed, driving the upgrade of butter from a "traditional dairy product" to a "multifunctional health food."

[0020] The content of citric acid in raw milk is very low. Flavor compounds such as diacetyl are mainly produced by the metabolism of citric acid by *Lactococcus lactis* subsp. *lactocercinus*, *Leuconostoc mesenteroides* subsp. *milk fat*, and *Leuconostoc mesenteroides* subsp. *glucan*. Citric acid metabolism is closely related to lactose glycolysis. Citric acid is first broken down into oxaloacetate, which is directly converted to α-acetolactate, and then undergoes oxidative decarboxylation to produce diacetyl and acetoin. Oxaloacetate can also undergo decarboxylation to produce pyruvate, an intermediate product of glycolysis, ultimately yielding diacetyl and acetoin. In addition, citric acid metabolism can also produce other flavor compounds, such as propionic acid and acetic acid.

[0021] Casein is one of the important precursors for flavor compounds. The protease hydrolysis system of lactic acid bacteria can degrade casein in dairy products into amino acids, which can be converted into flavor compounds. In particular, branched-chain amino acids, aromatic amino acids, and sulfur-containing amino acids are the main sources of flavor compounds.

[0022] Yeast extract, as a natural, safe, and versatile food ingredient, plays an indispensable role in the modern food industry. It is far more than a simple byproduct of brewer's yeast; rather, it is a concentrated extract of umami substances and nutrients obtained through sophisticated biotechnology, widely used in various foods to enhance flavor, improve texture, and strengthen nutrition.

[0023] Yeast extract is recognized globally as a safe food ingredient with a clear regulatory status. In China, it is more accurately classified as a "food ingredient" rather than a "food additive." It is categorized under "other foods," meets relevant food safety requirements, and does not need to be labeled as an additive.

[0024] In the European Union, yeast extract is considered a food product and is permitted for use in various food products as needed. In the United States, the Food and Drug Administration (FDA) classifies compliant yeast extract as a "Generally Recognized As Safe" (GRAS) substance, providing strong safety assurance for its widespread use in food. It is worth noting that yeast extract is naturally rich in glutamic acid, a key component in producing "umami" flavor. However, this naturally occurring glutamic acid differs from monosodium glutamate (MSG), used as a food additive, in its metabolic pathway and regulatory classification. Major global food safety regulatory agencies, including the World Health Organization (WHO) and the European Food Safety Authority (EFSA), have confirmed that this naturally occurring glutamic acid is safe and does not pose adverse effects on the vast majority of the population. Therefore, on food labels, it only needs to be labeled as "yeast extract."

[0025] Yeast extract, with its unique flavor-enhancing and nutritional fortification properties, has permeated all aspects of the food industry. Its primary and core use is as a flavor enhancer and seasoning. The rich, full-bodied umami it provides effectively elevates the overall flavor profile of a product, making it more mellow and harmonious. In soy sauce, oyster sauce, chicken bouillon, sauces, compound seasoning powders, instant noodle seasoning packets, puffed foods, and meat products, yeast extract is a key ingredient in creating a rich "base flavor." It helps reduce the amount of salt (sodium) used, meeting the health requirements of "sodium reduction" while maintaining a satisfying taste.

[0026] Secondly, yeast extract is an excellent nutritional fortifier. It is rich in high-quality protein, various B vitamins (such as B1, B2, niacin, and folic acid), minerals (such as zinc and selenium), and dietary fiber (such as beta-glucan). Therefore, it is often added to nutritional beverages, health foods, infant formula, and special medical foods to supplement protein and vitamins and enhance the nutritional value of the products.

[0027] In addition, yeast extract also has certain processing aid functions. In the production of some fermented foods (such as bread, yogurt, and cheese), it can be used as a fermentation promoter. Its rich amino acids, small peptides, and vitamins can provide high-quality nitrogen sources and growth factors for fermenting microorganisms such as lactic acid bacteria and yeast, accelerating the fermentation process, stabilizing product quality, and helping to form unique flavor compounds. Summary of the Invention

[0028] The applicant focuses on the research of edible butter and has designed a fermentation and enzymatic ripening process for edible butter. This process effectively increases the content of flavor compounds such as diacetyl, acetoin, caprylic acid, δ-decanoic acid, 2-nonanone, and decanoic acid in ripened butter, thereby enhancing its sensory flavor. Surprisingly, the shelf life of the resulting ripened edible butter is also extended. Specifically, the initial acid value and peroxide value of the butter are extremely low, and after accelerated aging storage, the changes in acid value and peroxide value are minimal, effectively improving the stability of the butter and extending its shelf life.

[0029] This application first discloses a fermentation and enzymatic hydrolysis maturation process for edible butter, the specific steps of which are as follows:

[0030] Step 1: Raw material pretreatment

[0031] Select fresh cream, add citric acid and yeast extract, mix well, sterilize, and then cool the cream to room temperature;

[0032] Step 2: Vaccination

[0033] Lactococcus lactis and Leuconostoc mesenteroides were inoculated into the cream obtained in step 1, and the mixture was stirred until homogeneous.

[0034] Step 3: Fermentation

[0035] Fermentation is carried out at room temperature in a micro-aerobic environment.

[0036] Step 4: Formation of cream granules and washing

[0037] After step 3 is completed, stir, then pour sterile cold water into the tank, soak, let stand and separate into layers, drain the lower layer of washing water containing buttermilk, and repeat the water washing operation.

[0038] Step 5: Post-ripening and flavor optimization

[0039] Cool the fermented butter obtained in step 4 to 4-6℃ and let it stand.

[0040] Step 6: Shaping and Storage

[0041] Apply pressure to remove the moisture from the intermediate product obtained in step 5, and press it into standard blocks. Then, vacuum package it using a food-grade composite film. The packaged matured butter is immediately transferred to a 0-4℃ cold storage.

[0042] As described in the steps above:

[0043] The fresh cream selected in step 1 has a fat content of ≥35%; the sterilization conditions are 72℃ for 15 seconds; the room temperature is 22-24℃; the amount of citric acid added is 0.02% w / w; and the amount of yeast extract added is 0.08% w / w.

[0044] The inoculation amount of Lactococcus lactis in step 2 is 10. 6 cfu / g, the inoculation ratio of Lactococcus lactis and Leuconostoc mesenteroides is 2:1-2:3;

[0045] The oxygen content in the micro-aerobic environment mentioned in step 3 is <5%; the fermentation refers to continuous fermentation for 12 hours.

[0046] The specific steps for forming and washing the cream granules described in step 4 are as follows:

[0047] After step 3, start the agitator inside the fermentation tank and agitate at 150-200 rpm for 15-20 minutes to form uniform butter granules with a diameter of 5-10 mm. Then, slowly pour sterile cold water at 3-5°C (approximately 1.5 times the weight of the butter granules) into the tank, soak for 5 minutes, and allow it to stand and separate into layers. Drain the lower layer containing buttermilk wash water. Repeat the washing process 3 times.

[0048] This step is used to remove residual buttermilk, lactose, and some metabolites, extending the product's shelf life and improving flavor purity.

[0049] The "resting" mentioned in step 5 refers to letting it stand for 48 hours.

[0050] The pressurization pressure mentioned in step 6 is 0.1-0.5 MPa.

[0051] The beneficial effects of this invention are:

[0052] This application discloses a fermentation and enzymatic hydrolysis maturation process for edible butter. By adding citric acid and yeast extract to fresh cream, and then co-fermenting and enzymatically hydrolyzing with *Lactococcus lactis* and *Leuconostoc mesenteroides*, supplemented by washing and settling steps, a unique fermentation and enzymatic hydrolysis maturation process is formed. This process can effectively increase the content of flavor compounds such as diacetyl, acetoin, caprylic acid, δ-decanoic acid, 2-nonanone, and decanoic acid in the matured edible butter, thereby enhancing its sensory flavor. Surprisingly, the shelf life of the resulting matured edible butter is also extended. Specifically, the initial acid value and peroxide value of the matured edible butter are extremely low, and after storage under accelerated aging conditions, the changes in acid value and peroxide value are minimal. Detailed Implementation

[0053] The present invention will be further described in detail below through embodiments. These embodiments are illustrative of the invention, but do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0054] Example 1: Preparation of Cured Edible Butter

[0055] Step 1: Raw material pretreatment

[0056] Select fresh cream with a fat content of ≥35%, add 0.02% w / w citric acid and 0.08% w / w yeast extract, mix well, pasteurize at 72℃ for 15 seconds, and then cool the cream to 22-24℃.

[0057] Step 2: Vaccination

[0058] In the cream obtained in step 1, add 10 6 CFU / g was inoculated into Lactococcus lactis subsp. lactis and Leuconostoc mesenteroides, respectively, and mixed thoroughly.

[0059] Step 3: Fermentation

[0060] At 22-24℃, nitrogen gas is injected into the fermenter to make the oxygen content <5%, and fermentation continues for 12 hours.

[0061] Step 4: Formation of cream granules and washing

[0062] After step 3, start the agitator inside the fermentation tank and agitate at 150-200 rpm for 15-20 minutes to form uniform butter granules with a diameter of 5-10 mm. Then, slowly pour sterile cold water at 3-5°C (approximately 1.5 times the weight of the butter granules) into the tank, soak for 5 minutes, and allow it to stand and separate into layers. Drain the lower layer containing buttermilk wash water. Repeat the washing process 3 times.

[0063] This step is used to remove residual buttermilk, lactose, and some metabolites, extending the product's shelf life and improving flavor purity.

[0064] Step 5: Post-ripening and flavor optimization

[0065] Cool the fermented butter obtained in step 4 to 4-6℃ and let it stand for 48 hours.

[0066] Step 6: Shaping and Storage

[0067] Under a pressure of 0.1-0.5 MPa, the moisture in the intermediate product obtained in step 5 is removed and pressed into standard blocks. Then, it is vacuum-packed using a food-grade composite film. The packaged matured butter is immediately transferred to a cold storage at 0-4℃.

[0068] Example 2: Preparation of cured butter with modified process parameters

[0069] To investigate the effects of citric acid, yeast extract, and the inoculum amounts of *Lactococcus lactis* and *Leuconostoc mesenteroides* on the flavor of the resulting matured butter, the following process parameters were set:

[0070] Table 1. Process parameters for Examples 1 and 2 (processes 1-5)

[0071] .

[0072] Example 3: Property testing of butter obtained from processes 1-5 in Examples 1 and 2.

[0073] The dry matter content of the samples was determined by the drying method, the fat content by the Geb method, the protein content by the Kjeldahl method, and the ash content by the ignition method. The data are shown in the table below:

[0074] Table 2 Chemical composition of butter obtained from processes 1-5 in Examples 1 and 2 (n=3, )

[0075] .

[0076] In GB 19646-2024, "cream" and "butter" are synonyms, both referring to animal butter as we commonly understand it.

[0077] According to the National Standard of the People's Republic of China GB 19646-2024 "National Food Safety Standard for Light Cream, Butter and Anhydrous Butter" (which was published on September 6, 2024 and officially implemented on September 6, 2025, replacing the current GB19646-2010), the fat limit requirement for animal butter is ≥80.0%.

[0078] As shown in Table 2, the butter produced in Example 1 and under processes 1-5 fully meets the requirements of current national standards in terms of its core physicochemical indicators (fat, protein, and ash).

[0079] Example 4: Detection and results of flavor compound content in butter obtained from processes 1-5 in Examples 1 and 2.

[0080] The flavor compound content of the butter obtained in Examples 1 and 2 (processes 1-5) was determined using the following method:

[0081] 1. Sample pretreatment

[0082] 2g of butter sample was placed in a 20mL screw-capped empty vial with a silicone / PTFE liner and equilibrated at 40℃ for 10min, during which time pulsed oscillation was performed at 500rpm for 5 seconds. Each sample was performed in triplicate. The analysis was conducted using a 75μm divinylbenzene / carbon molecular sieve / polydimethylsiloxane (DVB / CAR / PDMS) fiber tip. The solid-phase microextraction (SPME) fiber tip was exposed to the sample headspace region to a depth of 1.2cm for 20min. The fiber tip was then retracted and injected into the gas chromatography (GC) injector, and desorbed at 250℃ for 2min.

[0083] 2. Gas Chromatography Conditions

[0084] The gas chromatograph was equipped with an Agilent DB-5 capillary column (60 m long, 0.25 mm inner diameter, 0.25 μm film thickness) and a multi-functional injection port with a Merlin Microseal. The column oven was initially set to 35 °C, then ramped to 230 °C at a rate of 6.5 °C / min, and further ramped to 320 °C at a rate of 15 °C / min. The total gas chromatography run time was 41.5 min. Helium was used as the carrier gas, and a constant pressure of 23 psi was maintained.

[0085] 3. Mass spectrometry conditions

[0086] The detector used was a Shimadzu TQ8030 triple quadrupole mass spectrometer (MSD) operated in single quadrupole mode. The ion source temperature was set to 220℃, the interface temperature to 280℃, the mass spectrometry mode was electron ionization (electron energy -70eV), and the mass scan range was 35-250 amu.

[0087] 4. Data processing and compound identification

[0088] Data files were processed using Target View software. Compound identification was based on the matching degree between mass spectra and mass spectra in the NIST 2011 database. The linear retention index (LRI) was calculated using the method proposed by van Den Dool and Kratz (1963), and an internal database was built in Target View based on this to assist in compound identification.

[0089] To ensure optimal performance of the gas chromatography-mass spectrometry (GC-MS) instrument, it is automatically calibrated before analysis. In addition, at the beginning and end of sample group analysis, a set of external standards is analyzed, and their abundance is compared with known amounts to ensure that solid-phase microextraction (SPME) extraction and mass spectrometry detection are operating normally within specified ranges.

[0090] Table 3. Detection results of flavor compounds in butter obtained from processes 1-5 in Examples 1 and 2.

[0091] .

[0092] As shown in the table above, in the ripening process of Example 1, the addition of citric acid and yeast extract, as well as the inoculation ratio of Lactococcus lactis and Leuconostoc mesenteroides, constitute the core elements of flavor regulation. Through comparative analysis of processes 1-5 in Examples 1 and 2, the specific effects of each factor on the formation of flavor compounds and their possible mechanisms can be clearly revealed.

[0093] The effects of citric acid are mainly reflected in the increase of diacetyl, acetoin, short-chain fatty acids, and lactones. Comparing Example 1 (containing 0.02% citric acid) and Process 1 (without citric acid), both had the same yeast extract content and a 1:1 ratio of yeast strains. Data showed that the addition of citric acid increased diacetyl from 1.7 mg / kg to 1.8 mg / kg, acetoin from 3.9 mg / kg to 4.2 mg / kg, and δ-decanoic acid from 10 mg / kg to a significant increase of 16 mg / kg. Among short-chain fatty acids, butyric acid, hexanoic acid, caprylic acid, and decanoic acid increased from 32490, 13530, 253, and 256 mg / kg to 33110, 14370, 272, and 270 mg / kg, respectively. Branched aldehydes 2-methylpropionaldehyde and 2-methylbutyraldehyde also increased from 0.062 and 0.043 mg / kg to 0.094 and 0.072 mg / kg, respectively. This result indicates that citric acid, as a direct substrate for citric acid metabolism in Lactococcus lactis, is cleaved to produce oxaloacetic acid, which is further converted into α-acetolactate, and then oxidatively decarboxylated to produce diacetyl and acetoin. Meanwhile, the pH and redox potential changes caused by citric acid metabolism may activate lipase and protease activity, promote the breakdown of milk fat into short-chain fatty acids, and provide a suitable environment for the synthesis of δ-decanoic acid lactone. In addition, its metabolic intermediates may also participate in amino acid conversion pathways, indirectly promoting the generation of branched-chain aldehydes.

[0094] The effects of yeast extract are more extensive, enhancing almost all flavor compounds. Comparing Example 1 (containing 0.08% yeast extract) and Process 2 (without yeast extract), both had the same citric acid content and a 1:1 microbial ratio. Data showed that the addition of yeast extract increased diacetyl from 1.5 mg / kg to 1.8 mg / kg, acetoin from 2.9 mg / kg to 4.2 mg / kg, butyric acid, hexanoic acid, caprylic acid, and decanoic acid from 32320, 13650, 258, and 254 mg / kg to 33110, 14370, 272, and 270 mg / kg, respectively, δ-decanolide from 12 mg / kg to 16 mg / kg, and 2-methylpropionaldehyde and 2-methylbutyraldehyde from 0.073 and 0.065 mg / kg to 0.094 and 0.072 mg / kg, respectively. This phenomenon can be attributed to the fact that yeast extract is rich in amino acids, small peptides, B vitamins, and minerals, providing high-quality nitrogen sources and growth factors for *Lactococcus lactis* and *Leuconostoc mesenteroides*. Branched-chain amino acids are direct precursors to branched-chain aldehydes such as 2-methylpropionaldehyde; vitamins and cofactors enhance the activity of key enzymes in citric acid metabolism, promoting the accumulation of diacetyl and acetoin; simultaneously, yeast extract indirectly increases the expression of lipases and esterases by promoting cell growth and overall metabolism, thereby increasing the production of short-chain fatty acids and lactones.

[0095] The inoculation ratio of Lactococcus lactis to Leuconostoc mesenteroides plays a decisive role in shaping the flavor profile. The changes in flavor compounds under different ratios reflect the synergistic and competitive relationship between the metabolism of the two strains. Comparing process 3 (2:1), Example 1 (1:1), process 4 (2:3), and process 5 (1:2), all four groups added citric acid and yeast extract.

[0096] Data shows:

[0097] Diacetyl remained at a high level of 1.8 mg / kg in the range of 2:1 to 2:3, but decreased to 1.5 mg / kg at 1:2, indicating that an excessively high proportion of Leuconostoc can inhibit the citric acid metabolism of Lactococcus lactis.

[0098] Ethiopogonin was highest at 1:1 and 2:3 (4.2 mg / kg), 3.7 mg / kg at 2:1, and 3.6 mg / kg at 1:2, indicating that a moderate Leuconostoc ratio (1:1 to 2:3) is conducive to acetopogonin accumulation.

[0099] Short-chain fatty acids (butyric acid, hexanoic acid, caprylic acid, and capric acid) all reached their peak values ​​at a 2:3 ratio (33550, 14540, 280, and 287 mg / kg, respectively), while they decreased significantly at a 1:2 ratio (31400, 13830, 252, and 241 mg / kg, respectively). This indicates that the lipolytic activity of Leuconostoc mesenteroides is maximized at an appropriate ratio, but over-inoculation can lead to metabolic imbalance.

[0100] δ-decanolide also showed the highest concentration (18 mg / kg) at a 2:3 ratio, 16 mg / kg at 1:1, 13 mg / kg at 2:1, and 14 mg / kg at 1:2, indicating that increasing the proportion of Leuconostoc can promote lactone synthesis, but a balance needs to be maintained.

[0101] 2-Methylpropionaldehyde and 2-methylbutyraldehyde were higher at 1:1 and 2:3 (0.094 / 0.072 mg / kg and 0.092 / 0.071 mg / kg, respectively), followed by 2:1, and lowest at 1:2 (0.083 / 0.054 mg / kg, respectively). This indicates that the proteolytic activity of Leuconostoc provides sufficient precursors for branched aldehydes, but an imbalance in the ratio will inhibit their conversion.

[0102] Based on microbial metabolic mechanism analysis: *Lactococcus lactis*, as a mesophilic lactic acid bacterium, mainly produces acetaldehyde through glycolysis and generates diacetyl and acetoin through citric acid metabolism, but its lipolysis ability is relatively weak. *Leuconostoc mesenteroides*, on the other hand, exhibits significant proteolytic and lipolytic activities, breaking down casein to release branched-chain amino acids and milk fat to generate short-chain fatty acids, and may participate in lactone synthesis. At a balanced ratio (e.g., 2:1 to 2:3), the two strains complement each other metabolically: *Lactococcus lactis* ensures the intensity of basic creamy flavor compounds, while *Leuconostoc mesenteroides* contributes to the complexity of nutty and creamy aromas. Together, they optimize the total amount and diversity of flavor compounds. When the proportion of *Leuconostoc mesenteroides* is too high (1:2), its rapid acid production leads to an excessive decrease in pH, inhibiting the activity of *Lactococcus lactis*. Simultaneously, excessive lipolysis may cause an imbalance of fatty acids, ultimately reducing the content of most flavor compounds.

[0103] In summary, the addition of citric acid and yeast extract is the foundation for obtaining a rich flavor, while the ratio of Lactococcus lactis to Leuconostoc mesenteroides determines the specific composition of the flavor.

[0104] Example 5: Flavor evaluation of the butter obtained from processes 1-5 in Examples 1 and 2.

[0105] 5.1 Sample Preparation

[0106] The butter samples obtained from processes 1-5 in Examples 1 and 2 were first placed at 5°C for 48 hours to mature, and then frozen and stored at -80°C until analysis.

[0107] 5.2 Recruitment and Screening of Evaluators

[0108] We are recruiting 15 trained sensory evaluators aged 23-40 (with professional sensory evaluation experience). Evaluators must participate in all aspects of the experiment, be in good health, be willing to participate, and regularly consume butter.

[0109] 5.3 Experimental Environment and Procedure

[0110] Experimental environment: Sensory acceptance tests were conducted in an evaluation room that met international standards (International Organization for Standardization, 1988). The evaluation room was equipped with fluorescent lights and had separate evaluation cubicles to avoid interference between evaluators.

[0111] Sample presentation: To evaluate different butter samples, sensory pleasure descriptions were provided to the evaluators (see Table 5, Flavor Evaluation Scoring Criteria), and each sample was presented in duplicate.

[0112] Sample pretreatment and coding: The butter samples were placed in a 5°C refrigerated environment overnight the day before the analysis; during the analysis, they were presented to the evaluators in a single-blind manner at room temperature (about 21°C) and coded with a randomly generated 3-digit number. The butter was then immediately distributed to the evaluators.

[0113] Cleaning: To avoid the flavor of the previous sample interfering with the evaluation of the next sample, deionized water is provided to the evaluators, and they are instructed to clean their mouths between tasting different samples.

[0114] 5.4 Sensory Analysis

[0115] Each evaluator was required to rate the butter sample on a 10cm linear scale according to their own preference: 0 points on the left side of the scale represented "extremely dislike" and 10 points on the right side represented "extremely like". After rating, the distance (in cm) from the left side of the scale to the evaluator's marked position was measured, and this distance was used as the final score. To avoid primacy and residual effects, the presentation order of all test samples was randomized, and each sample was presented in duplicate.

[0116] Table 5 Flavor Evaluation Scoring Criteria

[0117] .

[0118] Table 6. Flavor evaluation results of butter samples obtained from processes 1-5 in Examples 1 and 2.

[0119] .

[0120] As shown in the table above, in the ripening process of Example 1, the addition of citric acid and yeast extract, as well as the inoculation ratio of Lactococcus lactis and Leuconostoc mesenteroides, significantly affected the sensory quality of the butter. A comparative analysis of sensory scores from processes 1-5 in Examples 1 and 2 clearly reveals the specific effects of each factor on consumer-perceived attributes and their possible mechanisms.

[0121] The impact of citric acid is mainly reflected in the richness of aroma and flavor. Comparing Example 1 (containing 0.02% citric acid) and Process 1 (without citric acid), both had the same yeast extract content and a 1:1 strain ratio. Data shows that the addition of citric acid increased overall acceptability from 6.1 to 6.8, aroma preference from 5.5 to 6.6, and flavor preference significantly from 5.5 to 6.8; diacetyl aroma increased from 4.2 to 6.3, and diacetyl flavor from 3.0 to 3.9; fatty / animalistic aroma increased from 1.8 to 2.4, and fatty / animalistic flavor increased from 3.8 to 5.1; persistence increased from 1.8 to 3.0. This result indicates that citric acid directly enhances the perceived intensity of buttery flavor by providing substrates for the synthesis of diacetyl and acetoin. At the same time, the microenvironmental changes caused by its metabolism may promote the generation of more complex flavor compounds, making the overall flavor profile richer and fuller, and the aftertaste more lingering.

[0122] The effects of yeast extract are more comprehensive, improving almost all sensory properties. Comparing Example 1 (containing 0.08% yeast extract) and Process 2 (without yeast extract), both had the same citric acid content and a 1:1 ratio of yeast strains. Data shows that the addition of yeast extract increased overall acceptability from 5.3 to 6.8, appearance preference from 5.6 to 6.5, aroma preference from 5.3 to 6.6, flavor preference significantly from 4.8 to 6.8, and texture preference from 5.4 to 6.8. Diacetyl aroma increased from 3.7 to 6.3, and diacetyl flavor from 2.9 to 3.9; nutty aroma from 3.2 to 3.9, and nutty flavor from 2.2 to 4.0; malty aroma from 3.2 to 4.4, and malty flavor from 3.5 to 4.6; acidity aroma from 3.8 to 5.1; fat / animal flavor from 3.6 to 5.1; melting in the mouth from 4.2 to 5.9; and persistence from 1.6 to 3.0. This phenomenon can be attributed to the abundant amino acids and small peptides provided by yeast extract. These not only directly convert into flavor compounds (such as branched-chain amino acids generating malty and nutty flavors), but also act as a nitrogen source to promote the overall metabolic activity of the strain, resulting in a more complex and harmonious flavor profile. Simultaneously, yeast extract may improve the texture and melting sensation of butter by influencing the formation of extracellular polysaccharides, making the product's mouthfeel more delicate and smooth.

[0123] The inoculation ratio of *Lactococcus lactis* to *Leuconostoc mesenteroides* showed a clear and regular variation in its effect on sensory quality, reflecting the difference in the sensory contribution of the metabolites of the two strains. Comparing process 3 (2:1), Example 1 (1:1), process 4 (2:3), and process 5 (1:2), all four groups included the addition of citric acid and yeast extract. Data showed:

[0124] Overall acceptability was 6.8 points in both Example 1 and Process 4, 6.6 points in Process 3, and dropped to 5.5 points in Process 5, indicating that the 1:1 and 2:3 ratios were most favored by the sensory evaluators.

[0125] Flavor preference score was highest in Example 1 (6.8 points), followed by Process 4 (6.6 points), Process 3 (6.3 points), and dropped to 5.4 points in Process 5.

[0126] The diacetyl aroma score was highest in Example 1 (6.3 points), significantly higher than the 5.4 points in Process 4 and the 4.6 points in Process 3, while the score in Process 5 was only 4.1 points, indicating that a 1:1 ratio is most conducive to the perception of diacetyl aroma.

[0127] The nutty flavor score was highest in Example 1 (4.0 points), 3.8 points in Process 4, 3.2 points in Process 3, and decreased to 2.8 points in Process 5;

[0128] The malt flavor score was highest in Example 1 (4.6 points), followed by Process 4 (4.4 points), Process 3 (4.1 points), and decreased to 3.5 points in Process 5.

[0129] The acidity and aroma scores were highest in Example 1 (5.1 points), followed by Process 4 (4.5 points), Process 3 (4.3 points), and Process 5 (3.8 points).

[0130] The fat / animal flavor score was highest in Example 1 (5.1 points), followed by Process 4 (4.9 points), Process 3 (4.6 points), and Process 5 (4.4 points).

[0131] The durability score in Example 1 reached 3.0, which was significantly higher than the scores of 2.5 in Process 4, 2.0 in Process 3, and 1.9 in Process 5.

[0132] This pattern indicates that at a 1:1 balanced ratio, the metabolites of the two strains create the best synergistic effect, with diacetyl aroma and flavor reaching their peak, and complex flavors such as nuts, malt, and fats also at a high level. The overall flavor is both rich and harmonious, with the best aftertaste persistence. At a 2:3 ratio, the appropriate increase in Leuconostoc mesenteroides brings stronger lipolysis and proteolysis activity, which enhances the flavors of nuts and malts, but slightly reduces the diacetyl aroma. When the ratio is further increased to 1:2, the excessive dominance of Leuconostoc mesenteroides leads to excessive acidity, a significant decrease in diacetyl aroma, and an disruption of the flavor balance, resulting in a comprehensive decline in sensory scores.

[0133] Based on comprehensive sensory data, the 1:1 ratio performed best in overall acceptability, flavor preference, key aroma intensity and persistence, making it the optimal ratio for the best eating experience; the 2:3 ratio performed well in complex flavors and can be used as a supplementary option.

[0134] Example 6 Storage Stability Testing

[0135] Accelerated aging test: The finished butter was stored at 37°C for 7 days, and the acid value and peroxide value were tested.

[0136] Acid value: This measures the content of free fatty acids; exceeding the standard indicates that the fat has decomposed and deteriorated.

[0137] Peroxide value: reflects the degree of fat oxidation; exceeding the standard will result in a rancid smell.

[0138] The obtained data is as follows:

[0139] Table 7. Accelerated aging test data of butter obtained from processes 1-5 in Examples 1 and 2.

[0140] .

[0141] As shown in the table above, in the aging process of Example 1, the addition of citric acid and yeast extract, as well as the inoculation ratio of Lactococcus lactis and Leuconostoc mesenteroides, significantly affected the storage stability of butter. By comparing the changes in acid value and peroxide value in processes 1-5 of Examples 1 and 2 under accelerated aging conditions (stored at 37°C for 7 days), the inhibitory effects of various factors on fat hydrolysis and oxidation, and their possible mechanisms, can be revealed.

[0142] Acid value analysis (reflecting the degree of fat hydrolysis):

[0143] The addition of citric acid has a positive impact on acid value stability. Comparing Example 1 (containing 0.02% citric acid) and Process 1 (without citric acid), both had the same yeast extract content and a 1:1 strain ratio. Data showed that the addition of citric acid reduced the initial acid value from 1.23 mg / g to 1.03 mg / g, and after aging, the value decreased from 2.65 mg / g to 2.01 mg / g, a change from 1.42 mg / g to 0.98 mg / g. This result indicates that the moderate pH decrease caused by citric acid may inhibit the activity of some lipases, reducing the formation of free fatty acids; simultaneously, citric acid may indirectly affect the conformation and activity of lipases by chelating metal ions, thereby reducing the rate of lipolysis.

[0144] The addition of yeast extract also improves acid value stability. Comparing Example 1 (containing 0.08% yeast extract) and Process 2 (without yeast extract), both had the same citric acid content and a 1:1 bacterial strain ratio. Data showed that the addition of yeast extract reduced the initial acid value from 1.35 mg / g to 1.03 mg / g, and after aging, the value decreased from 2.86 mg / g to 2.01 mg / g, a change from 1.51 mg / g to 0.98 mg / g. This may be related to the fact that yeast extract promotes cell growth and enhances metabolic activity; more active metabolism may consume some free fatty acids or produce metabolites with lipase inhibitory effects. Furthermore, certain peptides in yeast extract may protect the lipid globule membrane structure, reducing the contact between fat and lipase.

[0145] The inoculation ratio of Lactococcus lactis to Leuconostoc mesenteroides had the most significant impact on acid value stability.

[0146] Comparing Process 3 (2:1), Example 1 (1:1), Process 4 (2:3), and Process 5 (1:2):

[0147] Initial acid value: lowest in Example 1 (1.03 mg / g), 1.10 mg / g in Process 4, 1.10 mg / g in Process 3, and increased to 1.27 mg / g in Process 5;

[0148] Values ​​after aging: Example 1 had the lowest value (2.01 mg / g), Process 4 had 2.10 mg / g, Process 3 had 2.35 mg / g, and Process 5 increased to 2.68 mg / g;

[0149] Variation values: lowest in Example 1 (0.98 mg / g), 1.00 mg / g in Process 4, 1.25 mg / g in Process 3, and increased to 1.41 mg / g in Process 5.

[0150] This pattern suggests that fat hydrolysis in butter is maximally inhibited at a 1:1 ratio. The possible mechanism is that at this ratio, the two bacterial strains achieve an optimal metabolic balance, neither excessively producing acid to inhibit each other's activity nor causing metabolic imbalance due to the dominance of one strain. *Lactococcus lactis* maintains moderate citric acid metabolism and acid production, while *Leuconostoc mesenteroides* provides moderate proteolytic activity. Their synergy may produce peptides or organic acids with lipase-inhibiting activity while maintaining the integrity of the fat globule membrane. When the proportion of *Leuconostoc mesenteroides* is too high (1:2), its strong lipolytic activity becomes dominant, resulting in higher initial free fatty acid levels that continue to be produced during storage. When the proportion of *Lactococcus lactis* is too high (2:1), the lack of *Leuconostoc mesenteroides* may result in a deficiency of regulatory factors for lipase activity, and the stability is slightly inferior to the 1:1 ratio.

[0151] Peroxide value analysis (reflecting the degree of lipid oxidation):

[0152] The addition of citric acid significantly improves the stability of peroxide value. Comparing Example 1 and Process 1, the addition of citric acid reduced the initial peroxide value from 0.085 g / 100g to 0.068 g / 100g, and the value after aging decreased from 0.219 g / 100g to 0.169 g / 100g, with the change value decreasing from 0.134 g / 100g to 0.101 g / 100g. Citric acid may inhibit the chain reaction of lipid oxidation catalyzed by metal ions (such as iron and copper) by chelating them, while its metabolites may have direct antioxidant activity and be able to scavenge some free radicals.

[0153] The addition of yeast extract significantly improved peroxide value stability. Comparing Example 1 and Process 2, the addition of yeast extract reduced the initial peroxide value from 0.105 g / 100g to 0.068 g / 100g, and the value after aging decreased from 0.251 g / 100g to 0.169 g / 100g, with the change value decreasing from 0.146 g / 100g to 0.101 g / 100g. Some of the amino acids and small peptides abundant in yeast extract possess free radical scavenging capabilities (such as methionine and cysteine ​​among sulfur-containing amino acids), potentially directly participating in antioxidant defense. Simultaneously, the enhanced metabolic activity may consume dissolved oxygen in the system, indirectly slowing down the oxidation process. Furthermore, certain yeast extract components may exert their effects by activating endogenous antioxidant enzyme systems or providing reducing substances.

[0154] The inoculation ratio of Lactococcus lactis to Leuconostoc mesenteroides also had a significant effect on peroxide value stability:

[0155] Initial peroxide value: lowest in Example 1 (0.068 g / 100g), 0.072 g / 100g in Process 4, 0.081 g / 100g in Process 3, and increased to 0.092 g / 100g in Process 5;

[0156] Values ​​after aging: Example 1 had the lowest value (0.169 g / 100g), Process 4 had 0.186 g / 100g, Process 3 had 0.206 g / 100g, and Process 5 increased to 0.233 g / 100g;

[0157] Variation values: lowest in Example 1 (0.101 g / 100g), 0.114 g / 100g in Process 4, 0.125 g / 100g in Process 3, and increased to 0.141 g / 100g in Process 5.

[0158] A 1:1 ratio showed optimal performance in inhibiting lipid oxidation. The possible mechanisms are: microbial metabolism at this ratio may have produced antioxidant metabolites (such as certain peptides, phenolic substances, or reducing compounds); simultaneously, a balanced microbial community structure may have optimized the microstructure of butter (such as the morphology and arrangement of fat crystals), reducing oxygen permeability or the contact area between oxygen and unsaturated fatty acids; furthermore, an appropriate microbial ratio may have maintained a stable redox potential in the system, preventing both excessive reduction leading to undesirable flavor and excessive oxidation leading to quality deterioration. When the ratio is unbalanced, the production of pro-oxidative substances (such as certain free radical intermediates or peroxides) may increase, or the antioxidant defense system may be inadequate, leading to decreased oxidative stability.

[0159] Based on the combined acid value and peroxide value data, Example 1 (1:1 microbial ratio) showed the best performance in terms of initial value, post-aging detection value, and change value, making it the optimal ratio for achieving the best storage stability. Processes 4 (2:3) and 3 (2:1) also exhibited good stability, while processes 1 (lacking citric acid), 2 (lacking yeast extract), and 5 (1:2) showed significantly decreased stability, further confirming the synergistic effect of citric acid, yeast extract, and appropriate microbial ratios on extending the shelf life of butter.

[0160] Based on the flavor compound data in Table 3, the sensory evaluation data in Table 6, and the storage stability data in Table 7, a ratio of *Lactococcus lactis* to *Leuconostoc mesenteroides* ranging from 1:1 to 2:3 yields both excellent flavor quality and storage stability. The 1:1 ratio shows the best performance in both sensory evaluation and storage stability, exhibiting the highest diacetyl aroma and persistence, and the smallest changes in acid value and peroxide value. The 2:3 ratio shows the highest content of short-chain fatty acids and lactones in its flavor compounds, and also demonstrates excellent storage stability. Therefore, the optimal process parameters are: citric acid 0.02% w / w, yeast extract 0.08% w / w, and *Lactococcus lactis* inoculum amount 1.0 × 10⁻⁶. 6 cfu / g, Leuconostoc mesentery inoculum 1.0×10 6 With a cfu / g ratio (i.e., a 1:1 ratio), a matured butter product with excellent flavor quality and storage stability can be obtained.

[0161] The foregoing description and embodiments illustrate the basic principles, main features, and advantages of this invention patent application. Those skilled in the art should understand that this invention patent application is not limited to the above embodiments; the embodiments and descriptions in the specification are merely optimal technical solutions. Various changes and modifications can be made to this invention patent application without departing from its spirit and scope, all of which fall within the scope of the claims. The scope of protection of this invention patent application is defined by the appended claims and their equivalents.

Claims

1. A fermentation and enzymatic hydrolysis maturation process for edible butter, the specific steps of which are as follows: Step 1: Raw material pretreatment Select fresh cream, add citric acid and yeast extract, mix well, sterilize, and then cool the cream to room temperature; Step 2: Vaccination Lactococcus lactis and Leuconostoc mesenteroides were inoculated into the cream obtained in step 1, and the mixture was stirred until homogeneous. Step 3: Fermentation Fermentation is carried out at room temperature in a micro-aerobic environment; Step 4: Formation of cream granules and washing After step 3 is completed, stir, then pour sterile cold water into the tank, soak and let stand to separate the layers, drain the lower layer of washing water containing buttermilk, and repeat the water washing operation. Step 5: Post-ripening and flavor optimization Cool the fermented butter obtained in step 4 to 4-6℃ and let it stand. Step 6: Shaping and Storage Apply pressure to remove the moisture from the intermediate product obtained in step 5, and press it into standard blocks. Then, vacuum package it using a food-grade composite film. The packaged matured butter is immediately transferred to a 0-4℃ cold storage.

2. The curing process as described in claim 1, characterized in that, The fresh cream selected in step 1 has a fat content of ≥35%; the sterilization conditions are 72℃ for 15 seconds; the room temperature is 22-24℃; the amount of citric acid added is 0.02% w / w; and the amount of yeast extract added is 0.08% w / w.

3. The curing process as described in claim 1, characterized in that, In step 2, the inoculation amount of Lactococcus lactis is 10. 6 cfu / g.

4. The curing process as described in claim 3, characterized in that, In step 2, the inoculation ratio of Lactococcus lactis to Leuconostoc mesenteroides is 2:1-2:

3.

5. The curing process as described in claim 1, characterized in that, The oxygen content in the micro-aerobic environment in step 3 is <5%; the fermentation refers to continuous fermentation for 12 hours.

6. The curing process as described in claim 1, characterized in that, The specific steps of step 4 are as follows: After step 3 is completed, start the built-in agitator in the fermentation tank and stir at 150-200 rpm for 15-20 minutes to form uniform butter granules with a particle size of 5-10 mm. Then, slowly pour sterile cold water at 3-5°C into the tank, with the water volume being about 1.5 times the mass of the butter granules. After soaking for 5 minutes, let it stand and separate into layers. Drain the lower layer of washing water containing buttermilk and repeat the washing process 3 times.

7. The curing process as described in claim 1, characterized in that, The "resting" step in step 5 refers to letting the object stand for 48 hours.

8. The curing process as described in claim 1, characterized in that, The pressurization pressure in step 6 is 0.1-0.5 MPa.