Lycopene fortified milk skin yoghurt and method for preparing the same

Abstract

The application relates to the field of dairy product processing and discloses a lycopene fortified milk skin yoghurt and a preparation method thereof. The yoghurt is made of main line logistics, lycopene functional meso-compound emulsion and lactic acid bacteria starter, wherein the main line logistics is skimmed or low-fat cow milk, the meso-compound emulsion contains sodium hexametaphosphate, and lycopene is embedded in a structure constructed by soybean phospholipid and separated whey protein powder. During preparation, the independently pretreated main line material is uniformly mixed with the meso-compound emulsion, the starter is injected on line, and then the yoghurt is filled, fermented and cooled in the packaging container, and the stability of lycopene is improved through meso-embedding. The fouling problem of the heat exchange pipeline is solved by using sodium hexametaphosphate and a dynamic heat treatment process. And through the density difference of components and the in-situ fermentation process, a fat-rich milk skin layer with a continuous phase characteristic is formed on the top of the yoghurt, and good industrialized continuous production feasibility is achieved.

Description

Technical Field

[0001] This invention relates to the field of dairy processing technology, specifically to a lycopene-fortified milk skin yogurt and its preparation method. Background Technology

[0002] Yogurt holds an important position in the dairy market due to its rich nutritional value and unique fermented flavor. Among them, yogurt with a dense milk skin structure on top has a differentiated sensory experience due to its rich textural layers. Meanwhile, lycopene, a natural carotenoid with strong antioxidant activity, is an important research direction for enhancing the nutritional and health value of dairy products by incorporating it into the dairy product matrix for functional fortification.

[0003] However, there are complex technical obstacles to the effective application of lycopene in the industrial continuous production of yogurt with a milk skin. Lycopene is a highly unsaturated hydrocarbon with low solubility in aqueous systems and is prone to oxidative degradation under conventional processing and storage conditions, resulting in discoloration and loss of activity. To improve its dispersibility in the milk matrix, a composite carrier containing lipids and whey proteins is often introduced. However, during the industrial high-temperature sterilization stage, free calcium ions in the milk matrix can induce unintended thermal gelation and cross-linking of denatured and unfolded protein molecules. This cross-linking can easily evolve into severe scaling on the pipe walls of heat exchange equipment, leading to abnormal pressure drop in the pipeline and even production interruption. In addition, traditional yogurt processing systems usually rely on high-pressure homogenization to maintain the long-term homogeneity and stability of the system. This strong shearing action disrupts the natural distribution of the lipid phase and restricts the spontaneous directional migration of lipid components to the system surface, making it difficult to form a milk skin structure with continuous phase characteristics and high mechanical strength on the top of the final fermented product.

[0004] Therefore, existing formulations and conventional processing techniques cannot simultaneously meet the multiple requirements of protecting functional components, preventing scaling in continuous production equipment, and constructing specific physical layered structures. The industry urgently needs to develop a novel material matrix architecture and fermentation process to achieve stable formation of a fat-rich, continuous milk skin layer on top of yogurt, while ensuring the chemical stability of lycopene and the feasibility of industrial-scale production. Summary of the Invention

[0005] The technical problem solved by this invention is that lycopene has low solubility in aqueous systems and is relatively easy to undergo oxidative degradation, which limits its application in dairy products. In addition, in industrial-scale production, when a composite mesoscopic carrier rich in fat-soluble substances is introduced into a protein-containing fluid, unintended thermal gelation of proteins can easily occur during the heat treatment stage, which often causes scaling and a sudden drop in pressure in the heat exchange equipment pipelines.

[0006] Meanwhile, conventional yogurt processing technology cannot form a skin structure with continuous phase characteristics and high mechanical strength on the top of the yogurt.

[0007] To address the above problems, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a lycopene-fortified milk skin yogurt, which adopts the following technical solution:

[0009] A lycopene-fortified milk skin yogurt is made from raw materials including main ingredients, lycopene functional mesoscopic complex emulsion, and lactic acid bacteria starter.

[0010] The main logistics stream is skimmed or low-fat milk. The lycopene functional mesoscopic complex emulsion contains sodium hexametaphosphate, and lycopene is embedded in a mesoscopic complex structure constructed from soybean lecithin and whey protein isolate.

[0011] The lycopene-fortified milk skin yogurt has a continuous phase milk skin layer on top.

[0012] By adopting the above technical solution, using skim or low-fat milk as the main feedstock and introducing a lycopene emulsion containing sodium hexametaphosphate and a specific mesoscopic complex structure, the system stability can be significantly improved, the tendency for pipe scaling can be alleviated, and the formation of a continuous milk skin structure at the top can be facilitated. Its specific underlying mechanism is as follows:

[0013] At the microstructural level, lycopene is typically a highly unsaturated hydrocarbon. After dissolving it within the free fat of a high-fat system, soybean lecithin provides amphiphilic molecules, while whey protein powder unfolds and adsorbs at the interface, together forming a composite interfacial layer. Ascorbate palmitate preferentially undergoes oxidation at the water-oil interface, thus to some extent blocking the free radical chain oxidation pathway of internal lycopene by dissolved oxygen in the aqueous phase, achieving chemical stability of lycopene.

[0014] Regarding the system's resistance to thermal gelation, sodium hexametaphosphate was introduced into the system before adding isolated whey protein powder for heat treatment.

[0015] Milk and whey protein systems contain a large amount of free calcium ions. High-temperature treatment induces the unfolding of protein peptide chains, exposing hydrophobic groups and negatively charged regions. At this time, free calcium ions act as electrostatic bridging agents, promoting rapid macroscopic cross-linking of the unfolded protein molecules. Sodium hexametaphosphate undergoes the following complexation reaction with calcium ions in the system: Na6P6O18 + Ca2+ → Na4CaP6O18 + 2Na+.

[0016] This reaction significantly reduced the concentration of free calcium in the liquid phase, weakening the calcium ion-induced protein thermal gelation pathway and fundamentally alleviating protein scaling and sudden pressure drop on the walls of industrial heat exchange pipes. Regarding the phase reorganization and the formation of the top continuous phase milk skin, due to the low system density of the lycopene functional mesoscopic complex emulsion, in a essentially static fermentation environment, as the system pH gradually decreased due to the acid production by lactic acid bacteria, the steric hindrance effect of casein micelles weakened.

[0017] Low-density lipid mesoscopic carriers carry lycopene to the top of the system via Stokes-oriented migration. The lipid droplets that migrate to the top undergo covalent and non-covalent cross-linking with the gradually decalcified and aggregated protein network, solidifying at the air-water interface to form a continuous milk skin layer rich in lipids and lycopene, while the lower layer forms a homogeneous set-type yogurt body.

[0018] Preferably, the lycopene-fortified milk skin yogurt is made from raw materials comprising the following parts by weight: 810-8650 parts of main material;

[0019] Lycopene functional mesoscopic complex emulsion 100-1300 parts; lactic acid bacteria starter 0.1-2.5 parts.

[0020] By adopting the above technical solution, a macroscopic ratio of the main emulsion to the lipid-containing side emulsion was determined. This mass range ensures that the system has sufficient defatted matrix to provide the underlying gel network, while the proportion of the side emulsion provides enough lipid phase and coloring components to form a complete top milk skin layer. This often reduces the probability of the milk skin cracking due to excessive thinness or the bottom layer clearing due to excessive lipids.

[0021] Preferably, the lycopene functional mesoscopic complex emulsion is made from the following components in parts by weight: 100.0 to 1200.0 parts of light cream;

[0022] Sodium hexametaphosphate 0.2–3.5 parts; lycopene oleoresin 0.010–0.110 parts, calculated based on the mass of pure lycopene;

[0023] Soybean lecithin 1.0–16.0 parts;

[0024] Ascorbyl palmitate 0.1–2.0 parts;

[0025] 3.0 to 42.0 parts of whey protein isolate.

[0026] By adopting the above technical solution, the proportion of the core components of the mesoscopic composite emulsion was defined.

[0027] A specific mass ratio of sodium hexametaphosphate to whey protein isolate helps to maintain sufficient protein monomers at the interface to cover the oil droplet surface while complexing free calcium.

[0028] The ratio of soybean phospholipids to whey protein achieves a competitive adsorption balance between small molecule emulsifiers and large molecule polymers at the interface, thereby moderately reducing interfacial tension and providing sufficient steric hindrance.

[0029] Preferably, the fat content of the light cream is 30.0% to 35.0% by mass;

[0030] The fat content of the main stream is less than or equal to 1.5%. By adopting the above technical solution, the density difference between the two streams after mixing is amplified by creating a difference in fat content between the main stream and the side stream of cream.

[0031] High-fat cream forms the hydrophobic core of the mesoscopic carrier, while the ultra-low-fat main stream provides a continuous phase with low viscosity resistance. This physically accelerates the migration rate of lipid droplets to the top during the initial stage of static fermentation, enabling the target component to be enriched to the top more fully before the system pH reaches the isoelectric point and network solidification occurs.

[0032] Secondly, the present invention provides a method for preparing lycopene-fortified milk skin yogurt, which adopts the following technical solution: a method for preparing lycopene-fortified milk skin yogurt, including main material processing, high-temperature heat treatment and sterilization of skim or low-fat milk, and cooling for later use.

[0033] To prepare a lycopene functional mesoscopic complex emulsion, light cream and sodium hexametaphosphate were mixed and stirred. Lycopene oleoresin, soybean lecithin, and ascorbate palmitate were added. After emulsification and high-pressure homogenization, whey protein isolate powder was added, and the mixture was heated and subjected to isothermal heat treatment before cooling. Subsequently, the main stream material was combined with the lycopene functional mesoscopic complex emulsion and mixed thoroughly. A quantitative amount of lactic acid bacteria starter culture was injected, and the mixture was dispensed into packaging containers and sealed.

[0034] Finally, the packaging container is placed in a constant temperature environment for static fermentation. After reaching the target endpoint pH value, it is transferred to a cold storage for cooling and further maturation.

[0035] By adopting the above technical solution, the use of dual-line independent pretreatment combined with aseptic fusion and in-situ static fermentation process can facilitate the formation of a specific physical structure of the final product while taking into account the feasibility of continuous industrial production.

[0036] Its technological mechanism mainly involves two aspects: isolating heat-sensitive parameters and in-situ fermentation molding.

[0037] During the material pretreatment stage, the main skim milk is rich in casein, while the side emulsions are rich in isolated whey protein and fat-soluble lycopene. If combined with heat treatment, the strong heat load of the main line would trigger intense disulfide bond exchange and hydrophobic aggregation between casein and whey protein, increasing the risk of early gelation. By employing independent sterilization in two lines, the main line meets sterilization requirements, while the side line controls the heat load to only moderately denature and develop interfacial proteins, avoiding rheological collapse.

[0038] During the fermentation stage, a method is adopted in which physical filling is completed first, followed by acid-producing fermentation.

[0039] As the micro-fermentation and acid production process progresses inside the container, lipid droplets rise and protein aggregates simultaneously. This process eliminates the need for subsequent dispensing and stirring operations that disrupt the gel network, thus completely preserving the solidified, high-fat milk skin layer at the top.

[0040] Preferably, in the main logistics processing, the specific conditions for high-temperature heat treatment and sterilization are to keep at 82-88 degrees Celsius for 15-20 minutes, and then cool to 40-45 degrees Celsius for later use.

[0041] By adopting the above technical solution, the heat load range enables the endogenous whey protein in the main stream to undergo sufficient denaturation and attach to the surface of casein micelles, which to a certain extent increases the water retention of the gel network after fermentation and reduces the risk of bottom water separation. At the same time, the cooling endpoint temperature matches the suitable fermentation temperature of the subsequent fermentation strains.

[0042] Preferably, the specific method for preparing the lycopene functional mesoscopic complex emulsion is as follows: place light cream in a mixing tank, add sodium hexametaphosphate at 20-30 degrees Celsius and stir;

[0043] The temperature was raised to 55–65 degrees Celsius, and lycopene oleoresin, soybean lecithin, and ascorbate palmitate were added sequentially and emulsified by constant temperature stirring; then, single-stage homogenization was carried out at 55–65 degrees Celsius and 3.0–5.0 MPa.

[0044] After homogenization, pump the mixture into a sterilization tank with a circulation loop, add whey protein isolate and stir until homogeneous, heat to 82-88 degrees Celsius and maintain the temperature for 15-20 minutes; finally cool to 40-45 degrees Celsius.

[0045] By adopting the above technical solution, the processing sequence of each material was rationally arranged.

[0046] During the emulsification and homogenization stages, a preliminary oil-water interface is established using small-molecule emulsifiers; after homogenization is completed, large-molecule isolated whey protein powder is introduced for heat treatment.

[0047] This delayed addition of feed avoids mechanical denaturation of whey protein during the previous shearing and cavitation effects, which helps the subsequent heat treatment induce the protein to form a secondary membrane structure on the intact lipid droplet surface.

[0048] Preferably, in the heat treatment stage, the circulation loop consists of a sterilization tank with a stirring device and an external tubular heat exchanger.

[0049] The material is continuously circulated between the sterilization tank and the tubular heat exchanger, heated to the target temperature at a heating rate of 1.5 to 2.5 degrees Celsius per minute, and the material is kept flowing in the circulation loop during the constant temperature maintenance period.

[0050] By adopting the above technical solution, dynamic anti-fouling heat exchange conditions were constructed.

[0051] Generally, isolated whey protein is prone to local concentration polarization and adhesion to the tube wall in the critical temperature range of thermal denaturation. By combining a specific heating rate with flow shear force, the fluid at the endothermic interface can be kept in a certain turbulent state.

[0052] When the fluid shear force is greater than the initial non-covalent bonding force between microscopic protein aggregates, it can promote the unfolding whey protein to preferentially attach to the surface of mesoscopic lipid droplets with high specific surface area, rather than the metal wall of the pipeline. This effectively overcomes the engineering obstacle of heat exchanger pressure drop deterioration in production.

[0053] Preferably, in the mixing and filling steps, the main stream material cooled to the same temperature and the lycopene functional mesoscopic complex emulsion are simultaneously pumped into an online dynamic mixer and mixed evenly. Then, lactic acid bacteria fermentation agent is aseptically injected online at the outlet pipe, and after being mixed evenly through a static mixing tube, it is filled.

[0054] By adopting the above technical solution, the homogeneity fluctuations and secondary contamination risks associated with traditional batch mixing are reduced. Isothermal mixing avoids thermal shock between materials;

[0055] The online dynamic and static series mixing process evenly disperses trace amounts of starter culture into the substrate liquid within a very short time scale, which better ensures the consistency of the fermentation start point inside each independent packaging container.

[0056] Preferably, the static fermentation conditions are fermentation at a temperature of 40 to 45 degrees Celsius, during which the system is kept static, and the endpoint is reached when the pH value of the system naturally drops to 4.5 to 4.7.

[0057] The post-cooking conditions are to allow the food to cool at a temperature of 2–6 degrees Celsius for 12–24 hours.

[0058] By employing the above technical solution, boundary conditions for phase transition and structural fixation in yogurt were established. During fermentation, the yogurt was kept in a static state, providing a gravitational field as the primary microscopic driving force for lipid uplift.

[0059] When the pH drops to the range of 4.5 to 4.7, the protein completes the construction of a three-dimensional network through isoelectric point precipitation. At this point, convective mass transfer basically stops, and the thickness of the milk skin and the underlying gel are fixed.

[0060] The subsequent low-temperature, long-term ripening process causes the milk fat core to crystallize and shrink, further enhancing the surface penetration and yield strength of the top milk skin.

[0061] This invention provides a lycopene-fortified milk skin yogurt and its preparation method. It has the following beneficial effects:

[0062] 1. This invention physically encapsulates lycopene by constructing a mesoscopic structure of soybean phospholipids and isolated whey protein, and synergistically introduces ascorbate palmitate to block the oxidation pathway of internal lycopene by dissolved oxygen in the aqueous phase. This significantly improves the solubility and chemical stability of lycopene in the aqueous system of dairy products, and overcomes the application obstacle of its easy oxidative degradation during processing and storage.

[0063] 2. In this invention, sodium hexametaphosphate is added before heat treatment of the side-line emulsion containing isolated whey protein. By complexing the free calcium ions in the system, the calcium ion-induced thermal gelation of the protein is weakened. At the same time, the dynamic heating process with a circulation loop intervenes in protein adhesion with fluid shear force, thereby effectively alleviating the protein scaling phenomenon on the heat exchange pipe wall in industrial scale-up production and reducing the risk of abnormal pressure drop in equipment during continuous production.

[0064] 3. This invention uses a very low-fat main stream emulsion mixed with a high-fat side stream mesoscopic emulsion to increase the local density difference within the mixed system. Combined with a process of physical filling followed by static fermentation, it promotes the directional enrichment of lipid mesoscopic carriers carrying lycopene at the top of the system before the isoelectric point of the protein three-dimensional network solidifies. In this process, it crosslinks with the aggregated protein network, successfully constructing a high-fat milk skin layer with continuous phase characteristics and high mechanical strength on the top of the yogurt. Attached Figure Description

[0065] Figure 1 The figures show the mesoscopic particle size distribution test results of each experimental group in this invention at different treatment stages; wherein, Figure 1 (a) is a comparison chart of particle size distribution curves. Figure 1 (b) is a comparison chart of characteristic particle size parameters (D10, D50, D90, D[4,3]);

[0066] Figure 2This is a diagram illustrating the evolution of the physicochemical properties of the side-stream fluid during the heat treatment stage of this invention; wherein, Figure 2 (a) is a comparison diagram of the evolution of free calcium concentration during the side-stream fluid heat treatment stage. Figure 2 (b) is a comparison diagram of the apparent viscosity evolution during the heat treatment stage of the side-stream fluid;

[0067] Figure 3 These are isothermal rheological evolution diagrams of the fluids in each experimental group of this invention at different recombination temperatures; wherein, Figure 3 (a) is a graph showing the evolution of the rheological modulus of Example 1 over time under recombination conditions at 42°C. Figure 3 (b) is a graph showing the evolution of the rheological modulus of Comparative Example 4 under recombination conditions at 85℃ over time;

[0068] Figure 4 The figures show the test results of each experimental group of this invention during the operation and cleaning stages of industrial heat treatment heat exchange equipment; wherein, Figure 4 (a) is a comparison diagram of the evolution of pipeline pressure drop in industrial heat treatment processes. Figure 4 (b) is a comparison chart of the concentration of soluble eluted proteins in the CIP cleaning solution;

[0069] Figure 5 This is a comparison chart of the relative retention rates of lycopene in the yogurt products of each experimental group during the shelf life of the present invention.

[0070] Figure 6 These are characterization test diagrams of the texture and mechanical strength of the continuous phase (milk skin) at the top of the yogurt products in each experimental group of this invention; wherein, Figure 6 (a) is a displacement-force response curve during the texture analyzer puncture test. Figure 6 (b) is a comparison of the top yield force and surface penetration work values. Detailed Implementation

[0071] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0072] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0073] Raw milk is industrial standard crude milk, with a fat content of 3.5% to 4.2% and a non-fat milk solids content of ≥8.5%.

[0074] The main feedstock used in this invention is skimmed or low-fat milk obtained from raw milk through centrifugation and fat standardization, with a fat mass fraction not exceeding 1.5%.

[0075] The light cream used is a milk fat concentrate obtained by centrifugation of raw milk, with a fat mass fraction of 30.0% to 35.0%.

[0076] Before feeding, the fat, protein and nonfat milk solids content of both the main feed and the cream were determined using a milk composition analyzer. In the same embodiment, the main feed and the cream were from the same standardized batch.

[0077] The CAS number of lycopene, the active ingredient in lycopene oleoresin, is 502-65-8. The mass fraction of lycopene in this oleoresin is 5% to 10%, and the matrix carrier oil is soybean oil.

[0078] Before use, the actual mass fraction of lycopene in each batch of lycopene oleoresin was determined by high performance liquid chromatography. The actual mass of the feed was calculated as "target pure lycopene mass ÷ measured mass fraction of lycopene in lycopene oleoresin".

[0079] The CAS number of soybean phospholipids is 8002-43-5, in which the mass fraction of phosphatidylcholine is ≥60%.

[0080] The total protein content of the whey protein isolate powder is ≥90%, of which β-lactoglobulin accounts for 50% to 65% of the total protein. The CAS number of ascorbate palmitate is 137-66-6, and it is a food additive grade.

[0081] Sodium hexametaphosphate has the CAS number 10124-56-8, an average degree of polymerization ranging from 10 to 20, and is classified as a food additive.

[0082] The direct-inoculation lactic acid bacteria starter is a commercially available freeze-dried bacterial powder, composed of Lactobacillus bulgaricus and Streptococcus thermophilus.

[0083] The masses listed in the following preparation examples and embodiments are the actual feed masses. No additional water, emulsion or volume adjustment is added during the preparation process. The total batch mass is based on the sum of the actual feed masses of each raw material, and is not based on integer batches of 1000.0 kg or 10000.0 kg as the volume adjustment target.

[0084] Preparation Example 1:

[0085] This preparation example provides a method for preparing a lycopene-functional mesoscopic complex emulsion, comprising the following steps:

[0086] Take 150.0 kg of light cream with a fat content of 32.0% and place it in a mixing container. Control the system temperature at 25℃, add 0.4 kg of sodium hexametaphosphate, and stir at 40 r / min for 12 minutes.

[0087] Heat the system in the mixing tank to 60°C, and add lycopene oleoresin (calculated based on the measured mass fraction of lycopene in the oleoresin and containing 0.012 kg of pure lycopene), 1.8 kg of soybean lecithin, and 0.2 kg of ascorbate palmitate in sequence. Increase the stirring speed to 150 r / min and stir at a constant temperature for 25 minutes.

[0088] The mixed material is fed into a high-pressure homogenizer, and the single-stage homogenization valve is opened. The homogenization process is carried out once under the conditions of homogenization temperature of 60℃ and homogenization pressure of 4.0MPa.

[0089] The homogenized material is pumped into a sterilization tank equipped with a stirring device, which forms a circulation loop with an external tubular heat exchanger. 3.0 kg of separated whey protein powder is added and stirred evenly. The circulation pump is turned on to make the material circulate continuously between the sterilization tank and the tubular heat exchanger. The material is heated to 82°C at a heating rate of 1.5°C / min and kept at this temperature for 15 minutes. During the temperature holding period, the material is kept flowing in the above circulation loop.

[0090] After the isothermal period, the material was rapidly cooled to 42°C using a heat exchanger to obtain a lycopene functional mesoscopic complex emulsion.

[0091] Preparation Example 2:

[0092] This preparation example provides a method for preparing a lycopene-functional mesoscopic complex emulsion, comprising the following steps:

[0093] Take 100.0 kg of light cream with a fat content of 30.0% and place it in a mixing container. Control the system temperature at 20℃, add 0.2 kg of sodium hexametaphosphate, and stir at 30 r / min for 10 minutes.

[0094] Heat the system in the mixing tank to 55°C, and add lycopene oleoresin (calculated based on the measured mass fraction of lycopene in the oleoresin and containing 0.010 kg of pure lycopene), 1.0 kg of soybean lecithin, and 0.1 kg of ascorbate palmitate in sequence. Increase the stirring speed to 100 r / min and stir at a constant temperature for 20 minutes.

[0095] The mixed material is fed into a high-pressure homogenizer, and the single-stage homogenization valve is opened. The homogenization process is carried out once under the conditions of homogenization temperature of 55℃ and homogenization pressure of 3.0MPa.

[0096] The homogenized material is pumped into a sterilization tank equipped with a stirring device, which forms a circulation loop with an external tubular heat exchanger. 6.0 kg of separated whey protein powder is added and stirred evenly. The circulation pump is turned on to make the material continuously circulate between the sterilization tank and the tubular heat exchanger. The material is heated to 88°C at a heating rate of 2.5°C / min and kept at this temperature for 20 minutes. During the constant temperature period, the material is kept flowing in the above circulation loop.

[0097] After the constant temperature period, the material was rapidly cooled to 40°C using a heat exchanger to obtain a lycopene functional mesoscopic complex emulsion.

[0098] Preparation Example 3:

[0099] This preparation example provides a method for preparing a lycopene-functional mesoscopic complex emulsion, comprising the following steps:

[0100] Take 180.0 kg of light cream with a fat content of 35.0% and place it in a mixing container. Control the system temperature at 30℃, add 0.6 kg of sodium hexametaphosphate, and stir at 50 r / min for 15 minutes.

[0101] Heat the system in the mixing tank to 65°C, and add lycopene oleoresin (calculated based on the measured mass fraction of lycopene in the oleoresin and containing 0.015 kg of pure lycopene), 2.5 kg of soybean lecithin, and 0.3 kg of ascorbate palmitate in sequence. Increase the stirring speed to 200 r / min and stir at a constant temperature for 30 minutes.

[0102] The mixed material is fed into a high-pressure homogenizer, and the single-stage homogenization valve is opened. The homogenization process is carried out once under the conditions of homogenization temperature of 65℃ and homogenization pressure of 5.0MPa.

[0103] The homogenized material is pumped into a sterilization tank equipped with a stirring device, which forms a circulation loop with an external tubular heat exchanger. 42.0 kg of separated whey protein powder is added and stirred evenly. The circulation pump is turned on to make the material continuously circulate between the sterilization tank and the tubular heat exchanger. The material is heated to 86°C at a heating rate of 2.2°C / min and held at this temperature for 16 minutes. During the holding period, the material is kept flowing in the above circulation loop.

[0104] After the constant temperature period, the material was rapidly cooled to 45°C using a heat exchanger to obtain a lycopene functional mesoscopic complex emulsion.

[0105] Preparation Example 4:

[0106] This preparation example provides a method for preparing a lycopene-functional mesoscopic complex emulsion, comprising the following steps:

[0107] Take 1200.0 kg of light cream with a fat content of 30.0% and place it in a mixing container. Control the system temperature at 28℃, add 3.5 kg of sodium hexametaphosphate, and stir at 45 r / min for 10 minutes.

[0108] Heat the system in the mixing tank to 62°C, and add lycopene oleoresin (calculated based on the measured mass fraction of lycopene in the oleoresin and containing 0.110 kg of pure lycopene), 16.0 kg of soybean lecithin, and 2.0 kg of ascorbate palmitate in sequence. Increase the stirring speed to 180 r / min and stir at a constant temperature for 25 minutes.

[0109] The mixed material is fed into a high-pressure homogenizer, and the single-stage homogenization valve is opened. The homogenization process is carried out once under the conditions of homogenization temperature of 62℃ and homogenization pressure of 4.5MPa.

[0110] The homogenized material is pumped into a sterilization tank equipped with a stirring device, which forms a circulation loop with an external tubular heat exchanger. 4.5 kg of separated whey protein powder is added and stirred evenly. The circulation pump is turned on to make the material continuously circulate between the sterilization tank and the tubular heat exchanger. The material is heated to 85°C at a heating rate of 2.0°C / min and kept at this temperature for 18 minutes. During the temperature holding period, the material is kept flowing in the above circulation loop.

[0111] After the constant temperature period, the material was rapidly cooled to 43°C using a heat exchanger to obtain a lycopene functional mesoscopic complex emulsion.

[0112] Example 1:

[0113] This embodiment provides a method for preparing lycopene-fortified yogurt with a milk skin, including the following steps:

[0114] Take 835.0 kg of main feedstock (skimmed or low-fat milk with a fat mass fraction ≤1.5%, the main feedstock used in the same embodiment comes from the same standardized batch, and the fat mass fraction is confirmed to meet the above requirements by a milk component analyzer before feeding), send it into a plate heat exchanger, keep it at 85°C for 18 minutes to complete independent high-temperature heat treatment and sterilization, and then quickly cool it to 42°C for use.

[0115] The above-mentioned main stream at 42°C and the lycopene functional mesoscopic complex emulsion at 42°C obtained in Preparation Example 1 were simultaneously pumped into a sterile online dynamic mixer and combined and mixed evenly according to the preset flow rate.

[0116] At the mixer outlet pipe, 0.3 kg of direct-inoculation lactic acid bacteria starter is aseptically injected online in a quantitative manner. After being mixed evenly through the static mixing tube, it is immediately distributed into individual yogurt packaging containers through the filling line and sealed.

[0117] The packaging container is placed in a constant temperature fermentation chamber and allowed to ferment statically at 42°C. During fermentation, the packaging container is not stirred, turned, or mechanically vibrated. The fermentation endpoint is determined when the pH value of the fermentation system naturally drops to 4.6.

[0118] The product fermented to the end is transferred to a cold storage and left to cool at 4°C for 18 hours to obtain the lycopene-fortified milk skin yogurt product.

[0119] Example 2:

[0120] This embodiment provides a method for preparing lycopene-fortified yogurt with a milk skin, including the following steps:

[0121] Take 880.0 kg of main line logistics (skimmed or low-fat milk with a fat mass fraction of ≤1.5%), send it into a plate heat exchanger, keep it at 82℃ for 15 minutes to complete independent high-temperature heat treatment and sterilization, and then quickly cool it to 40℃ for use.

[0122] The above-mentioned main stream at 40°C and the lycopene functional mesoscopic complex emulsion at 40°C obtained in Preparation Example 2 were simultaneously pumped into a sterile online dynamic mixer and combined and mixed evenly according to the preset flow rate.

[0123] At the mixer outlet pipe, 0.1 kg of direct-inoculation lactic acid bacteria starter is aseptically injected online in a quantitative manner. After being mixed evenly through the static mixing tube, it is immediately distributed into individual yogurt packaging containers through the filling line and sealed.

[0124] The packaging container was placed in a constant temperature fermentation chamber and allowed to undergo absolute static fermentation at 40°C. The fermentation endpoint was determined when the pH value of the fermentation system naturally dropped to 4.7.

[0125] The product fermented to the end is transferred to a cold storage and left to cool at 6°C for 12 hours to obtain the lycopene-fortified milk skin yogurt product.

[0126] Example 3:

[0127] This embodiment provides a method for preparing lycopene-fortified yogurt with a milk skin, including the following steps:

[0128] Take 810.0 kg of main line logistics (skimmed or low-fat milk with a fat mass fraction of ≤1.5%), send it into a plate heat exchanger, keep it at 88℃ for 20 minutes to complete independent high-temperature heat treatment and sterilization, and then quickly cool it to 45℃ for use.

[0129] The above-mentioned main stream at 45°C and the lycopene functional mesoscopic complex emulsion at 45°C obtained in Preparation Example 3 were simultaneously pumped into a sterile online dynamic mixer and combined and mixed evenly according to the preset flow rate.

[0130] At the mixer outlet pipe, 0.5 kg of direct-inoculation lactic acid bacteria starter is aseptically injected online in a quantitative manner. After being mixed evenly through the static mixing tube, it is immediately distributed into individual yogurt packaging containers through the filling line and sealed.

[0131] The packaging container is placed in a constant temperature fermentation chamber and allowed to undergo absolute static fermentation at 45°C. The fermentation endpoint is determined when the pH value of the fermentation system naturally drops to 4.5.

[0132] The product fermented to the end is transferred to a cold storage and left to cool at 2°C for 24 hours to obtain the lycopene-fortified milk skin yogurt product.

[0133] Example 4:

[0134] This embodiment provides a method for preparing lycopene-fortified yogurt with a milk skin, including the following steps:

[0135] Take 8650.0 kg of main pipeline (skimmed or low-fat milk with a fat mass fraction of ≤1.5%), send it into a plate heat exchanger, keep it at 86℃ for 16 minutes to complete independent high-temperature heat treatment and sterilization, and then quickly cool it to 43℃ for use.

[0136] The above-mentioned main stream at 43°C and the lycopene functional mesoscopic complex emulsion at 43°C obtained in Preparation Example 4 were simultaneously pumped into a sterile online dynamic mixer and combined and mixed evenly according to the preset flow rate.

[0137] At the mixer outlet pipe, 2.5 kg of direct-inoculation lactic acid bacteria starter is aseptically injected online in a quantitative manner. After being mixed evenly through the static mixing tube, it is immediately distributed into individual yogurt packaging containers through the continuous filling line and sealed.

[0138] The packaging container was placed in a constant temperature fermentation chamber and allowed to undergo absolute static fermentation at 43°C. The fermentation endpoint was determined when the pH value of the fermentation system naturally dropped to 4.55.

[0139] The product fermented to the end is transferred to a cold storage and left to cool at 5°C for 20 hours to obtain the lycopene-fortified milk skin yogurt product.

[0140] Examples 1-4 are used to verify the applicability of the present invention under different formulation scales and combinations of process parameters. The amount of starter culture added in each example is adjusted according to the total amount of material, fermentation temperature, and target endpoint pH. The fermentation process ends when the system reaches the specified endpoint pH, not when the fermentation time is fixed. Examples 1-4 are not used to evaluate the independent effect of a single parameter.

[0141] Comparative Example 1:

[0142] Compared with Example 1, the difference is that the main stream and side stream are not separated. Instead, the same amount of main stream, light cream, lycopene oleoresin, sodium hexametaphosphate, soybean lecithin, ascorbyl palmitate and whey protein isolate powder as in Example 1 are pre-mixed to obtain a mixture with the same total feed mass and raw material composition as in Example 1.

[0143] The mixture was then subjected to high-pressure homogenization at 20.0 MPa, and then subjected to overall heat treatment at the temperature and time specified in Example 1. After cooling to 42°C, it was inoculated, filled, and fermented, with the rest being the same.

[0144] Comparative Example 2:

[0145] Compared with Example 1, the difference is that sodium hexametaphosphate is not added in the preparation of the side stream, and 0.4 kg of the same main stream as in Example 1 is used to make up the total feed mass, while the rest are the same.

[0146] Comparative Example 3:

[0147] Compared with Example 1, the difference is that whey protein isolate powder is not added in the preparation of the side stream, and the total feed mass is made up with 4.5 kg of the same main stream as in Example 1, while the rest are the same.

[0148] Comparative Example 4:

[0149] Compared with Example 1, the difference is that the side stream material that has completed heat denaturation and the main stream material that has completed sterilization are directly merged at a high temperature of 85°C and then cooled to 42°C as a whole, instead of being cold-reconstituted at 42°C. All other aspects are the same.

[0150] Unless otherwise specified, each test shall be performed using at least three independently prepared batches of samples, and each independent batch shall be technically replicated according to the corresponding test method.

[0151] The data listed in the table represent representative measurement results or arithmetic mean results for each experimental group. For Table 6, the data are explicitly stated as the arithmetic mean of five parallel samples. Instrument repeat scans are only used to evaluate the measurement stability of the same sample and do not replace independent batch repeats.

[0152] Examples 1-4 employ different formulation scales and combinations of process parameters to verify the applicability of the technical solution of the present invention under different conditions, and do not constitute single-factor gradient experiments. Comparative Examples 1-4 are used to evaluate the effects of global high-pressure homogenization, sodium hexametaphosphate, whey protein isolation, and recombination temperature and time sequence on product structure and processing performance.

[0153] The differences in data between Examples 1 to 4 are not simply attributed to a single process parameter.

[0154] Test Example 1: Verification of Mesoscopic Particle Size Distribution and Evolution of Sidestream Streams

[0155] The test subjects included the side stream material after the high-pressure homogenization process in Example 1, the side stream material after the 85°C heat denaturation process in Example 1, the material after global high-pressure homogenization in Comparative Example 1, and the fluid after high-temperature recombination in Comparative Example 4.

[0156] Turn on the laser particle size analyzer and preheat for 30 minutes to stabilize the laser. Set the continuous phase to pure water and the refractive index to 1.33.

[0157] The dispersed phase was set as a milk fat and protein complex, the refractive index was set to 1.46, and the absorbance was set to 0.001.

[0158] Take liquid samples from each of the above stages respectively. To avoid the influence of multiple scattering on the test accuracy, slowly drop the samples into a dispersant containing a whey diluent with a continuous phase ionic composition and pH similar to the corresponding sample. Control the light-blocking degree of the system to be stable between 10% and 15%.

[0159] During the test, only low-speed circulating dispersion was activated, and the ultrasonic function was not used to avoid ultrasonic treatment damaging the fat-protein complex particles or weak flocculation structure. The whey dilution was prepared by filtering the clear aqueous phase obtained by centrifuging the corresponding sample at 10000×g for 30 minutes at 4°C through a 0.45μm filter membrane.

[0160] Start the measurement program, scan each sample independently 3 times, the system automatically records the light scattering signal of different particle size channels, and uses the Mie scattering theory model to fit and calculate, extracting the data of volume average diameter D[4,3], median diameter D50 and boundary diameters D10 and D90, and clean the pipeline after the test is completed.

[0161] For samples with D10 below 0.30 μm in the laser particle size analysis results, another sample from the same batch was used for cross-validation using a dynamic light scattering instrument.

[0162] The dynamic light scattering test temperature was 25℃. Each sample was measured independently three times. The dynamic light scattering results were compared with the laser particle size test results to reduce the measurement deviation caused by the optical parameter settings in the submicron particle size range.

[0163] Table 1. Mesoscopic particle size distribution test data of different treatment stages in each experimental group.

[0164]

[0165] Based on the data in Table 1 and Figure 1 According to the test results, the median diameter D50 of the homogenized side-line material in Example 1 was 4.82 mm. The volume average diameter D[4,3] is 5.15. .

[0166] Under specific low-pressure homogenization parameters, combined with the interfacial emulsification properties of soybean phospholipids, the characteristic particle size of fat globules in the side-line system remains at the mesoscale without excessive fragmentation.

[0167] After undergoing a heat denaturation process at 85℃, the D50 and D[4,3] of the side-stream material increased slightly to 5.31. and 5.68 The particle size distribution curve exhibits a single-peak structure with slight broadening.

[0168] The above evolution indicates that, at this stage, due to the significant reduction of free calcium ion concentration in the aqueous phase by sodium hexametaphosphate beforehand, the whey protein undergoes molecular chain extension during thermal denaturation and adsorbs or binds to the interface of soybean phospholipid-modified fat globules through hydrophobic interactions. At the same time, thiol-disulfide bond exchange and non-covalent association occur between whey protein molecules at the interface, thereby forming a protein network at the fat globule interface, but without triggering homogeneous aggregation phenomena that lead to scaling or macroscopic gelation.

[0169] Comparative Example 1, after conventional global high-pressure homogenization, had a D50 that decreased to approximately 0.65. .

[0170] High-pressure shearing forces caused irreversible miniaturization of fat globules.

[0171] According to the Stokes settling or buoyancy relation, under the condition that the density difference between the dispersed phase and the continuous phase and the viscosity of the continuous phase are approximately constant, the buoyancy velocity of the particles is approximately proportional to the square of the particle radius.

[0172] Therefore, when the fat globules containing lycopene are reduced from the micrometer scale to the submicrometer scale, their upward migration rate in the gravitational field during fermentation decreases significantly, making it difficult to achieve sufficient top enrichment within a limited fermentation time.

[0173] It cannot accumulate at the top, thus losing the physical basis for constructing a continuous and dense milky skin phase.

[0174] After the fluid in Comparative Example 4 underwent recombination of the main stream and side stream at high temperature, its particle size distribution shifted significantly, with D50 surging to 42.15. The D90 reached 88.06. .

[0175] Under high temperature conditions, free calcium ions in the main skim milk re-enter the heat-denatured protein dispersion system and promote ion bridging and aggregation between protein particles.

[0176] Under sustained high temperature, the system further develops from finite micro-flocculation to disordered large-scale aggregation or macro-thermal condensation.

[0177] The irregular aggregation of large amounts of protein and fat complexes results in the loss of uniform distribution and controlled self-assembly, leading to a coarse final product with whey separation.

[0178] The above data verify the necessity of the separation and temporal phase transition mechanisms in this scheme for regulating the evolution of microstructures.

[0179] Test Example 2:

[0180] System free calcium ion concentration tracking and thermorheological verification

[0181] The test subjects were the side stream fluid in the initial stage of the preparation process in Example 1 and the same side stream fluid in Comparative Example 2 without the addition of sodium hexametaphosphate.

[0182] The calcium ion selective composite electrode, calibrated with a standard solution, was immersed in a side-stream fluid stirred at a constant temperature of 25°C. The data acquisition cycle was set to 30 seconds, and the potential signal of the system was continuously acquired and converted into free calcium ion concentration. The monitoring time covered 15 minutes before and after the addition of sodium hexametaphosphate.

[0183] At the end of the heating process (60℃, 85℃, and 85℃), 5.0 mL of sample was taken and immediately placed in an ice-water bath and cooled to 25.0±0.5℃ within 2 minutes.

[0184] After the sample cooled, it was equilibrated for 3 minutes under sealed conditions, and then the concentration of free calcium ions was measured using the same calibrated calcium ion selective composite electrode.

[0185] All samples were measured at 25℃ to eliminate the influence of measurement temperature on electrode response and calcium salt balance.

[0186] After the ingredients were mixed, each group of side-line fluid samples were extracted and transferred to a rotational rheometer equipped with a coaxial cylindrical measurement system.

[0187] The rheometer was set to steady-state shear mode with a constant shear rate of 50. .

[0188] Start the temperature control program to heat the fluid from 25°C to 85°C at a rate of 2.0°C / min, and then maintain the temperature at 85°C for 18 minutes.

[0189] The rheological measurement unit uses a sealed anti-evaporation hood. The measuring cup is sealed immediately after the sample is loaded to reduce the impact of moisture evaporation during the 85℃ heating and isothermal process on the apparent viscosity test results.

[0190] The system synchronously records the apparent viscosity and temperature data during the heating and isothermal processes.

[0191] Table 2. Test data of free calcium concentration and apparent viscosity at different treatment stages for each experimental group.

[0192]

[0193] Based on the data in Table 2 and Figure 2 The test results showed that in the system of Example 1, after the addition of polyphosphate, the free calcium concentration increased from 4.26%. Decrease by ~0.13 And maintain this low concentration range in subsequent processes.

[0194] In Comparative Example 2, since this excipient was not added, the free calcium concentration in the system remained consistently at 3.8%. above.

[0195] Polyphosphates chelate metal ions through their spatial structure, thereby reducing the content of free calcium ions in the aqueous system.

[0196] In thermorheological tests, the apparent viscosity of Example 1 decreased during the mid-temperature rise (from 22.4%). Dropped to 16.5 This conforms to the fluid viscosity-decrease law of thermal motion as temperature increases; upon reaching 85℃ and maintaining that temperature, the viscosity slowly increases to 26.7. .

[0197] At high temperatures, the internal structure of isolated whey protein unfolds, exposing hydrophobic residues. Since the concentration of free calcium ions in the system has been significantly reduced, the extent to which calcium ions participate in the formation of ion bridges is limited, and the protein molecules do not undergo large-scale homogeneous aggregation.

[0198] The apparent viscosity of the fluid in Comparative Example 2 increased to 285.4 when heated to 85°C. It reached 1456.2 at the end of the isothermal period. .

[0199] The high concentration of free calcium ions retained in the system promotes the aggregation of unfolded whey protein polypeptide chains through electrostatic interactions and ion bridging, forming a high-viscosity protein network structure and exhibiting a significant tendency for macroscopic gelation.

[0200] The aforementioned differences in rheological behavior indicate that pre-exclusion of free calcium ions in the aqueous phase affects the polymerization state of the whey protein system during the thermal denaturation stage, limits the formation of the macroscopic gel phase, and maintains the rheological properties of the fluid in the heat exchange equipment.

[0201] Test Example 3: Isothermal Rheological and Flocculation Kinetics Tests during the Aseptic Cold Reconstitution Stage

[0202] The test subjects were the main stream and side stream samples prepared for aseptic recombination at 42°C in Example 1, and the main stream and side stream samples prepared for recombination at 85°C in Comparative Example 4.

[0203] Turn on the rotational rheometer and configure the coaxial cylinder test module. Pre-set and stabilize the temperature of the system measurement unit to 42°C (for Example 1 group) and 85°C (for Example 4 group).

[0204] Using a dual-channel micro-injection pump, the two streams at corresponding temperatures were simultaneously injected into the rheometer measuring cup according to the main stream to side stream mass ratio specified in Example 1 and Comparative Example 4.

[0205] Startup system apply 15 The mixture was continuously mixed at a low shear rate for 8 seconds, after which the shearing action was immediately stopped, and the static monitoring phase began.

[0206] Before the formal time-scan test, oscillatory strain scans were performed at 42℃ and 85℃ respectively, with an oscillation frequency of 1.0Hz and a strain range of 0.01% to 10%, confirming that the 0.5% oscillatory strain was located within the linear viscoelastic region of each sample.

[0207] The 85℃ test uses a sealed anti-evaporation cover to avoid the impact of moisture evaporation on the energy storage modulus and loss modulus during the test.

[0208] Start the time-scan test program, set the oscillation strain to a constant 0.5%, and the oscillation frequency to a constant 1.0Hz.

[0209] The system continuously records data for 30 minutes under constant temperature conditions, extracting the evolution data of energy storage modulus and loss modulus over time.

[0210] Table 3. Isothermal rheological test data of fluids in each experimental group at different recombination temperatures.

[0211]

[0212] Based on the data in Table 3 and Figure 3 According to the test results, after the system in Example 1 was recombined at 42°C, the storage modulus G' gradually increased from 0.38 Pa to 3.44 Pa. This reflects that after the abundant natural free calcium ions in the main stream were backfilled into the side stream system, they electrostatically combined with the negatively charged area on the surface of the heat-denatured whey protein, which promoted local mesoscopic microflocculation.

[0213] Throughout the 30-minute monitoring period, the loss modulus G'', representing the fluid viscosity characteristics, was consistently higher than the storage modulus G', representing the elastic characteristics, while the loss tangent (tanδ) decreased from 8.53 to 2.30 but remained greater than 1.

[0214] The above rheological characteristics indicate that, under mild conditions of 42°C, calcium ion-induced protein bridging is limited, and the system can form a certain degree of micro-flocculation, but no macroscopic gel network is formed throughout the entire system. The system as a whole does not undergo phase transition and maintains the macroscopic flowability required for continuous pumping in industrial filling lines.

[0215] When the system of Comparative Example 4 was mixed and recombined at 85℃, G' surged to 38.6 Pa within the first 5 minutes, and a modulus crossover phenomenon of G' being greater than G'' appeared. The tanδ decreased to ~0.50, indicating that the system rapidly changed from a viscous response to an elastic response between 1 and 5 minutes, and obvious gelation behavior was observed.

[0216] At the end of the monitoring period, G' further increased to 281.5 Pa.

[0217] Calcium ion backfilling is performed under high temperature conditions. The synergistic effect between molecular thermal motion and highly reactive free calcium causes the unfolded whey protein to rapidly construct a three-dimensional macroscopic gel network through dense disulfide bonds and salt bridges.

[0218] Because this global disordered coagulation occurs before the pipeline transportation and fermentation initiation stages, it disrupts the prerequisite for the spatial migration of composite particles according to the law of gravity and buoyancy, leading to eventual phase separation and equipment blockage.

[0219] The test results support the ability of time-sequential temperature control to affect the aggregation degree of protein-fat complex particles and the macroscopic rheological state of the system.

[0220] Test Example 4: Pressure Drop Monitoring and Anti-scaling Effect Evaluation of Industrial Heat Exchange Equipment

[0221] The test subjects were the tubular heat exchanger system fluids and heat exchange equipment during the side-line heat treatment process in Examples 1, 2, 3, 4 and Comparative Example 2.

[0222] In the circulating heating loop formed by the side-stream material sterilization tank and the external tubular heat exchanger, industrial-grade online pressure transmitters are installed at the inlet and outlet of the tubular heat exchanger, respectively.

[0223] When the side-stream fluid reaches the target thermal denaturation temperature (e.g., 82℃~88℃) and enters the isothermal holding section, the system begins to record pressure data, extracts the inlet and outlet pressure readings at the 5th minute, 10th minute, 15th minute, and the end of the isothermal holding period, and calculates the difference to obtain the pipeline pressure drop data.

[0224] After material processing is complete, empty the pipeline of any residual material and start the standard in-situ cleaning (CIP) procedure for the heat exchange equipment. Inject an equal volume of 1.5% sodium hydroxide alkaline cleaning solution into the pipeline, set the cleaning temperature to 75°C, and circulate the system for 15 minutes.

[0225] Samples of the first alkaline cleaning solution from each experimental group were collected and centrifuged at 4000 r / min for 10 minutes to remove insoluble impurities.

[0226] Extract the supernatant, adjust its pH to 7.0 ± 0.2 with hydrochloric acid solution, and then dilute appropriately. Prepare a protein standard curve using a blank matrix identical to that of the neutralized CIP washing buffer, and set up a blank control and a spiked recovery control.

[0227] Subsequently, BCA protein concentration assay reagent was added, and after a colorimetric reaction occurred in a water bath, the absorbance value at 562 nm was measured using a UV-Vis spectrophotometer. The concentration of soluble eluted protein per unit volume of washing solution was calculated by referring to the standard curve.

[0228] Table 4. Evolution of pipeline pressure drop and CIP soluble protein concentration test data during industrial heat treatment process.

[0229]

[0230] Based on the data in Table 4 and Figure 4 According to the test results, after entering the high-temperature constant temperature maintenance stage, the pressure drop values ​​at the inlet and outlet of the heat exchanger in Examples 1 to 4 remained in the low range of 11.52 kPa to 16.29 kPa over time.

[0231] In Example 2, the isothermal holding time was 15 minutes, and the pressure drop at the 15th minute was the isothermal endpoint pressure drop.

[0232] In the CIP cleaning process of the corresponding equipment, the concentration of soluble protein in the alkaline eluent after neutralization matrix correction was in the range of 38.64 mg / L to 62.41 mg / L. This data is used to characterize the level of residual protein on the equipment surface that can be eluted by alkaline solution under the same cleaning procedure.

[0233] The above parameters indicate that the hydrodynamic resistance inside the system pipeline is under normal pumping load conditions, and only a very small amount of fluid residual boundary layer is attached to the inner wall of the heat exchange metal. High-concentration isolated whey protein did not deposit on the pipe wall during the thermal denaturation stage.

[0234] The pressure drop of the equipment in Comparative Example 2 showed a non-linear and rapid increase with the extension of heating time, climbing from 15.43 kPa at the 5th minute to 198.74 kPa at the end of the isothermal period.

[0235] The concentration of soluble protein eluted by its CIP cleaning solution reached 1856.32 mg / L, which is orders of magnitude different from that of the example group, indicating that more protein deposits can be eluted by alkaline solution under the same cleaning conditions.

[0236] Sideline material that was not pretreated with sodium hexametaphosphate retained a high concentration of natural free calcium ions.

[0237] Driven by thermal energy, the whey protein molecular chains unfold, exposing reactive groups that interact with free calcium ions at the metal interface, resulting in strong ion bridging and disulfide bond exchange network expansion, forming an irreversible thermogel layer with extremely strong adhesion.

[0238] Increased gel layer thickness leads to reduced pipe diameter, obstructing fluid channels and causing a surge in pressure drop. This test, from the perspectives of macroscopic fluid dynamics and equipment maintenance indicators, demonstrates that pre-establishing a low free calcium environment is beneficial for ensuring the continuity of thermal denaturation processing of high-protein side-line materials.

[0239] Test Example 5: Verification of the relative retention rate of lycopene and its antioxidant barrier efficacy during storage

[0240] The test subjects were the yogurt products prepared in Examples 1, 2, 3, and 4, as well as the yogurt products prepared by global homogenization in Comparative Example 1 and without the addition of whey protein isolate in Comparative Example 3.

[0241] Each group of yogurt products was stored in a 4℃ constant temperature and light-proof incubator, and samples were taken on day 0, day 14 and day 28 of storage.

[0242] Each time a sample was taken, a complete single cup of yogurt (including the top skin layer and the bottom gel layer) was homogenized to assess the total retention of lycopene in the system. All sampling and extraction processes were performed under light-protected conditions.

[0243] Accurately weigh 5.0g of homogenized yogurt sample and place it in a centrifuge tube. Add 15.0mL of a mixed extraction solvent prepared by mixing hexane, acetone and ethanol in a volume ratio of 2:1:1.

[0244] Extract by vortexing for 10 minutes in an ice bath, followed by centrifugation at 5000 rpm for 8 minutes to promote phase separation. Collect the upper hexane extract and repeat the extraction twice on the residue.

[0245] The hexane extracts were combined and concentrated to dryness under vacuum and in the dark. The solution was then brought to a final volume of 2.0 mL with chromatographically pure dichloromethane. The solution was then subjected to a 0.22... The solution was filtered through an organic microporous membrane and used as the test solution.

[0246] The analysis was performed using a high-performance liquid chromatograph equipped with a UV-Vis detector.

[0247] The chromatographic column used was a C18 reversed-phase column (250mm × 4.6mm, 5). The column temperature is set to 30℃.

[0248] The mobile phase was configured as an isocratic elution system of methanol:acetonitrile:dichloromethane = 50:40:10, and the flow rate was set to 1.0 mL / min. The detection wavelength was set to 472 nm.

[0249] The lycopene content was quantitatively determined using the external standard method. The lycopene content measured on day 0 of each experimental group was defined as 100.0%. The relative retention rate of lycopene during storage was calculated for each storage time point relative to the content on day 0 of the group.

[0250] The relative retention rate is used to evaluate the stability of lycopene during storage, and not to evaluate the initial loss that has already occurred in each experimental group during processing.

[0251] Table 5. Test data on the relative retention rate of lycopene in yogurt products of each experimental group during shelf life.

[0252]

[0253] Based on the data in Table 5 and Figure 5 According to the test results, after the yogurt samples of Examples 1 to 4 were stored at 4°C for 28 days, the lycopene retention rate remained between 86.1% and 89.5%.

[0254] The degradation rate is slow during this period.

[0255] This result reflects that isolated whey protein self-assembles into a network structure around mesoscopic fat globules containing lycopene through hydrophobic interactions, and combines with ascorbate palmitate distributed in the fat phase to construct a sterically hindered antioxidant barrier.

[0256] During the fermentation and acidification process, the surface charge of this protein-fat interface phase gradually decreases, the hydrophobic interaction and electrostatic shielding between proteins and the interaction with the casein network are enhanced, and after being enriched at the top, they synergistically solidify to form a macroscopic milk skin structure, thereby reducing the contact between lycopene and pro-oxidative factors in the aqueous phase and ambient oxygen.

[0257] The retention rate of Comparative Example 1 decreased to 41.7% after 28 days.

[0258] Global high-pressure homogenization miniaturizes fat globules containing lycopene to the submicron level. With the total dispersed phase volume remaining approximately constant, the total interfacial area of ​​spherical particles is approximately inversely proportional to the characteristic radius of the particles; therefore, reducing the fat globule size leads to a significant increase in the total oil-water interfacial area.

[0259] Lycopene is dispersed and directly exposed to the large water-oil interface, which increases the probability of its reaction with dissolved oxygen in the aqueous phase, triggering significant oxidative degradation.

[0260] Comparative Example 3 showed a retention rate of 46.5% after 28 days. Since no whey protein isolate was added to the system, the surface tension of the mesoscopic fat globule interface was maintained solely by soybean lecithin, and a dense polymer network could not be formed in situ.

[0261] Lycopene lacks external physical barriers, and the system fails to solidify at the isoelectric point to form a continuous and dense top phase layer, thus losing the structural protection brought about by phase recombination, leading to the continuous degradation of the active substance in an acidic environment.

[0262] Data indicate that the synergistic mechanism of microscopic interface polymer network construction and macroscopic phase separation has an intervention effect on maintaining the chemical stability of long-chain polyene molecules.

[0263] Test Example 6: Texture and Mechanical Strength Characterization of the Top Continuous Phase (Milk Skin)

[0264] The test subjects were the yogurt products prepared in Examples 1, 2, 3, and 4, as well as the yogurt products prepared by global high-pressure homogenization in Comparative Example 1, without the addition of whey protein isolate in Comparative Example 3, and by high-temperature recombination in Comparative Example 4.

[0265] Samples of the original plastic fermentation cups with complete fermentation were taken from each group. The products first completed the initial cooling procedure after fermentation as specified in each example or comparative example, and then were uniformly transferred to a 4°C environment to stand and equilibrate for 24 hours before the texture test was conducted.

[0266] Turn on the texture analyzer, install the 12.7mm diameter polycarbonate cylindrical flat-bottom probe, and perform weight calibration and height zeroing on the probe.

[0267] Carefully peel off the top film from the unopened yogurt sample and place it in the center of the testing platform, keeping the surface structure of the sample intact.

[0268] All experimental groups used plastic fermentation cups of the same material, with the same inner diameter and effective volume. The filling quality of each cup was kept consistent to reduce the impact of differences in container cross-sectional area, sample height and cooling rate on the formation of top milk skin and puncture test results.

[0269] Configure the penetration test program in the system software.

[0270] The test parameters were set as follows: pre-test speed 2.0 mm / s, test speed 1.0 mm / s, post-test speed 2.0 mm / s, trigger force 0.02 N, and target penetration depth 15.0 mm.

[0271] The test program is started, and the probe moves downward to contact the sample surface and continues to penetrate the internal gel phase.

[0272] The system records the relationship between probe displacement and resistance at a sampling rate of 200 points / sec.

[0273] Five parallel samples were taken from each group for testing. The arithmetic mean of the five parallel samples was calculated and listed in Table 6.

[0274] The first peak force that appears when the probe pierces the surface is extracted from the displacement-force curve as the top yield force, and the surface penetration work is calculated by integrating the force-displacement curve within the first 4.0 mm of probe penetration.

[0275] Table 6. Test data of top yield strength and surface penetration work for the quality and texture characterization of yogurt in each experimental group.

[0276]

[0277] Based on the data in Table 6 and Figure 6 The test results showed that the yogurt samples in Examples 1 to 4 all exhibited a prominent surface puncture peak force in the initial stage of probe penetration (at a displacement of about 2.5 mm), with the corresponding top yield force ranging from 0.46 N to 0.63 N and the surface penetration energy ranging from 0.95 mJ to 1.42 mJ.

[0278] After the probe breaks through this mechanical peak, the resistance drops rapidly and then rises steadily with a low slope as the depth increases (representing the characteristics of the internal matrix gel).

[0279] The peak response characteristics of the puncture texture curve indicate that there is a macroscopic continuous phase with high density and structural rigidity at the top of the sample.

[0280] This is because during the process, the side fat globules are maintained at a specific mesoscopic scale and migrate to the top of the system according to the Stokes buoyancy law under the influence of density difference.

[0281] Meanwhile, the surface charge of denatured whey proteins distributed at the fat globule interface decreases during fermentation and acidification, and interfacial solidification and phase reorganization occur through protein intermolecular association and interaction with the casein network.

[0282] The displacement-force curve of Comparative Example 1 did not show a sudden peak on the surface, and the yield strength was only 0.08 N.

[0283] Global high-pressure homogenization significantly reduces the size of fat globules, resulting in a significant decrease in their gravitational upward velocity, making it difficult to achieve sufficient top migration and enrichment within the specified fermentation time.

[0284] The fatty phase is uniformly dispersed in the internal casein network, failing to achieve spatially oriented enrichment, and thus cannot be separated into an independent dense phase at the top.

[0285] The yield strength of Comparative Example 3 decreased to 0.14 N.

[0286] Even if fat globules can float to the surface after the separation of whey protein is missing, the interface is mainly stabilized by small molecule interfacial active components such as soybean phospholipids, and there is a lack of interfacial protein layer that can form a three-dimensional network on the surface of fat globules.

[0287] The surface fatty phase failed to form a solidified structure with sufficient mechanical strength through intermolecular protein association and synergistic effect with the casein network during the pH decrease process.

[0288] The yield strength of Comparative Example 4 was 0.11 N, and its puncture inner layer curve showed irregular stress fluctuations. High-temperature recombination caused disordered thermal gelation involving free calcium to occur in the system before filling, and the large-volume fat-protein flocs lost their migration freedom in the viscous matrix.

[0289] The flocs are randomly distributed or settled under the influence of gravity, which hinders the formation of the continuous phase at the top, resulting in a loose surface structure and overall deterioration of texture.

[0290] The test data above confirms the effectiveness of this scheme in controlling the macroscopic three-dimensional spatial distribution of products by combining the principles of fluid mechanics and interface physicochemistry.

[0291] In summary, this invention creatively separates the milk flow into a main stream and side streams and controls the heat treatment sequence separately. Combined with the free calcium regulation of sodium hexametaphosphate and the interfacial assembly of separated whey proteins, it successfully overcomes the scaling problem of high-concentration active ingredients during heat treatment and achieves the directional and targeted migration of mesoscopic fat globules during fermentation. Finally, it produces a compound yogurt rich in lycopene and with a dense milk skin structure, which significantly improves the shelf stability of active substances and the macroscopic texture of the product.

[0292] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A lycopene-fortified yogurt with a milk skin, characterized in that, Made from raw materials containing the following components: main stream material, lycopene functional mesoscopic complex emulsion, and lactic acid bacteria starter; The main logistics line is skim or low-fat milk; The lycopene functional mesoscopic complex emulsion contains sodium hexametaphosphate, and lycopene is embedded in a mesoscopic complex structure constructed from soybean lecithin and whey protein isolate. The lycopene-fortified milk skin yogurt has a continuous phase milk skin layer on top.

2. The lycopene-fortified milk skin yogurt according to claim 1, characterized in that, Made from the following ingredients in parts by weight: Main logistics volume: 810-8650 items; Lycopene functional mesoscopic complex emulsion, 100-1300 parts; 0.1 to 2.5 parts of lactic acid bacteria starter.

3. The lycopene-fortified milk skin yogurt according to claim 1, characterized in that, The lycopene functional mesoscopic complex emulsion is made from the following components in parts by weight: 100.0 to 1200.0 parts of heavy cream; Sodium hexametaphosphate 0.2–3.5 parts; Lycopene oleoresin 0.010–0.110 parts, calculated based on the mass of pure lycopene contained therein; soybean lecithin 1.0–16.0 parts; Ascorbyl palmitate 0.1–2.0 parts; 3.0 to 42.0 parts of whey protein isolate.

4. The lycopene-fortified milk skin yogurt according to claim 3, characterized in that, The fat content of the light cream is 30.0% to 35.0% by mass; The fat content of the skim or low-fat milk is ≤1.5%.

5. A method for preparing lycopene-fortified milk skin yogurt, comprising the lycopene-fortified milk skin yogurt according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Main line logistics processing: high temperature heat treatment and sterilization of skim or low fat milk, and then cooling it for use as the main line logistics. (2) Preparation of lycopene functional mesoscopic complex emulsion: light cream and sodium hexametaphosphate were mixed and stirred, then lycopene oleoresin, soybean lecithin and ascorbate palmitate were added. After emulsification and high pressure homogenization, whey protein powder was added and heated and constant temperature heat treatment was carried out. After cooling, it was used as lycopene functional mesoscopic complex emulsion for later use. (3) Mixing and filling: Combine the main material obtained in step (1) with the lycopene functional mesoscopic complex emulsion obtained in step (2) and mix them evenly. Quantitatively inject lactic acid bacteria fermentation agent into the mixture, distribute it into packaging containers and seal them. (4) Fermentation and post-ripening: The packaging container is placed in a constant temperature environment for static fermentation. When the fermentation system reaches the target endpoint pH value, it is transferred to a cold storage for cooling and post-ripening to obtain the final product.

6. The method for preparing lycopene-fortified milk skin yogurt according to claim 5, characterized in that, In step (1), the specific conditions for the high-temperature heat treatment and sterilization treatment are: keep warm at 82-88℃ for 15-20 minutes, and then cool to 40-45℃ for later use.

7. The method for preparing lycopene-fortified milk skin yogurt according to claim 5, characterized in that, The specific implementation method of step (2) is as follows: S21. Place the light cream in the ingredient container, control the system temperature at 20-30℃, add sodium hexametaphosphate and stir for 10-15 minutes. S22. Heat to 55-65°C, add the lycopene oleoresin, soybean lecithin and ascorbate palmitate in sequence, and stir at a constant temperature for 20-30 minutes to emulsify. S23. The material is fed into a high-pressure homogenizer and subjected to single-stage homogenization at a homogenization temperature of 55-65℃ and a homogenization pressure of 3.0-5.0MPa. S24. Pump the homogenized material into a sterilization tank with a circulation loop, add the separated whey protein powder and stir evenly, heat to 82-88℃ and maintain the temperature for 15-20 minutes. S25. After the constant temperature is completed, cool the material to 40-45℃ for later use.

8. The method for preparing lycopene-fortified milk skin yogurt according to claim 7, characterized in that, In step S24, the circulation loop consists of a sterilization tank with a stirring device and an external tubular heat exchanger; The material is continuously circulated between the sterilization tank and the tubular heat exchanger, heated to the target temperature at a heating rate of 1.5 to 2.5 °C / min, and the material is kept flowing in the circulation loop during the constant temperature period.

9. The method for preparing lycopene-fortified milk skin yogurt according to claim 5, characterized in that, In step (3), the specific conditions for mixing and filling are as follows: the main stream material cooled to the same temperature and the lycopene functional mesoscopic complex emulsion are simultaneously pumped into an online dynamic mixer and mixed evenly. Subsequently, lactic acid bacteria starter is aseptically injected online at the outlet pipe, and after being mixed evenly through a static mixing tube, it is filled.

10. A method for preparing lycopene-fortified milk skin yogurt according to claim 5, characterized in that, In step (4), the conditions for static fermentation are: fermentation is carried out at a temperature of 40-45°C, and the fermentation is kept static during the fermentation period. When the pH value of the fermentation system naturally drops to 4.5-4.7, the fermentation endpoint is reached. The conditions for cooling and ripening are: standing and cooling at 2-6°C for 12-24 hours.

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