Preparation method of composite microgel and application thereof in low-salt meat paste product

Abstract

The application discloses a preparation method of composite microgel and application of the composite microgel in low-salt minced meat products, and belongs to the technical field of food processing. The composite microgel is prepared by adopting phase separation method and taking soybean protein isolate and sodium alginate as raw materials. The application of the composite microgel in the low-salt minced meat products is that the composite microgel is added into the minced meat and then processed into a shape. The composite microgel has the advantages of narrow particle size distribution and precisely controllable particle size. By using the composite microgel as a filler, the problem of quality reduction of the low-salt minced meat products can be solved, and the application of the composite microgel in food is widened.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, specifically relating to a method for preparing composite microgels and their application in low-salt minced meat products. Background Technology

[0002] Unhealthy diet is one of the main risk factors for the high incidence of chronic diseases among Chinese residents. The "Healthy China Action (2019-2030)" proposes a rational diet action, emphasizing the encouragement of reducing oil, salt, and sugar intake throughout society. According to the World Health Organization, the average daily salt intake per person is 9-12g, twice the maximum recommended intake for adults, which brings significant health risks such as hypertension, cardiovascular disease, and weakened immunity. Minced meat products are a major category of meat products, generally containing more than 3% salt, making them one of the main sources of excessive salt intake for consumers. Myofibrillar protein is a salt-soluble protein and a core component of minced meat. During meat processing, salt can increase the content of salt-soluble proteins, forming a dense three-dimensional network structure, which helps to obtain meat products with good gelling properties, reduces water loss during heating, and improves the cohesiveness of meat products. In actual production, directly reducing the addition of sodium chloride will destroy the gel network structure of meat products, reduce gelling properties such as water retention and texture, and thus reduce sensory acceptance. Therefore, there is an urgent need to develop a strategy that can maintain the sensory, water-holding and textural properties of meat products under low-salt conditions.

[0003] Protein-based fillers (such as micronized proteins and protein microgels) have a filling effect; adding them to gels can improve the gel's textural properties. The filling effect is influenced by various factors, including the modulus of the filler and matrix, the amount of filler added, and the particle size of the filler. Commercial products of micronized whey protein are also mentioned. Widely used in the dairy industry. Unlike micronized proteins, protein microgels are mainly composed of water (85-95 wt%). Their water-swelling properties and loose structure give them a wider modulus range (0.1-10 kPa) and rheological properties between proteins and protein gels, giving them stronger and richer physicochemical properties and the potential to improve the texture of low-sodium minced meat products.

[0004] Common methods for preparing food-grade microgels include top-down and bottom-up approaches. The top-down method involves inducing a protein solution to form a hydrogel, followed by high-speed shearing to prepare microgel particles. The bottom-up method applies shearing during the gel network formation stage, reducing gel size by adjusting gel formation conditions to obtain microgel particles. Microgels are typically prepared using natural biomacromolecules such as proteins and polysaccharides as raw materials. When proteins and polysaccharides have the same charge, their repulsive interactions and differences in solvent affinity lead to phase separation. In the continuous polysaccharide phase, protein droplets are dispersed and subsequently thermally gelled to form uniformly sized and narrowly distributed microgels. Further research is needed to explore how to apply microgel technology to meat products to address the negative impact of salt reduction on meat texture and taste. Summary of the Invention

[0005] To address the quality and taste degradation issues of low-salt minced meat products in existing technologies, the inventors have provided a method for improving the quality of low-salt minced meat products using composite microgels. The technical solution is as follows:

[0006] A composite microgel is prepared by phase separation method using soy protein isolate (SPI) and sodium alginate (SA) as raw materials.

[0007] Furthermore, the composite microgel has a particle size range of 19.03±0.35μm to 45.27±0.31μm and a swelling ratio of 31.65±0.10g / g to 45.06±0.49g / g.

[0008] A method for preparing a composite microgel, comprising the following steps:

[0009] (1) Solution preparation: Disperse SPI powder in deionized water to prepare an SPI dispersion with a mass percentage of 15-20%; disperse SA powder in deionized water to prepare an SA solution with a mass percentage of 2-6%; and adjust the pH of the prepared solution to 6.8-7.2 using 1.0M and 0.1M sodium hydroxide solutions, and refrigerate overnight at 2-8℃.

[0010] (2) Preparation of composite microgels: Mix SPI and SA solutions and dilute with deionized water to a final SPI concentration of 2-6% and a final SA concentration of 0.6-1.5% in the mixed system. All final concentrations are mass percentages. Heat the SPI and SA mixed solution in a water bath at 70-100℃ for 10-20 min, and then immediately cool it to room temperature with ice water. After refrigerating overnight, centrifuge at 8000-12000g for 20-40 min to remove excess free polysaccharides and proteins to obtain crude SPI / SA composite microgels. Repeat the centrifugation and washing steps 2-4 times. The collected precipitate is the SPI / SA composite microgel, which can be directly used to prepare low-salt minced meat products. Alternatively, the SPI / SA composite microgel can be freeze-dried for 36-60 h to prepare microgel powder for storage.

[0011] The application of a composite microgel in low-salt minced meat products involves adding auxiliary materials to the minced meat, stirring and mixing it, then adding 5-20% by weight of SPI / SA composite microgel, refrigerating at 2-8℃ for 8-16 hours, and boiling the meatballs in boiling water for 5-10 minutes to form a meat gel; cooling yields the low-salt minced meat product.

[0012] Furthermore, the auxiliary materials, based on the total amount of raw meat, include 25-35% water and 1.5-2% salt, all by weight percentage.

[0013] The advantages of the above technical solution, which differs from existing technologies, are as follows:

[0014] (1) The modulus and particle size of the composite microgels prepared by this method can be controlled by adjusting the concentrations of SPI and SA and the heating temperature. The network structure of the composite microgel system is maintained by hydrogen bonds, disulfide bonds, electrostatic interactions and hydrophobic interactions.

[0015] (2) After adding the composite microgel to the low-salt minced meat, all indicators of the low-salt pork gel, such as whiteness, texture characteristics, sensory evaluation, water holding capacity and cooking loss rate, were improved. Moreover, after the amount of composite microgel added reached 15%, all indicators of the low-salt pork gel were better than those of the high-salt group.

[0016] (3) The composite microgel can convert free water in the low-salt pork system into immobilized water, reduce the proportion of free water, and increase the content of non-flowing water; and the composite microgel is hydrophilic and can combine with free water in the system, reduce the migration rate of free water, thereby improving the water retention performance of the low-salt pork gel. Attached Figure Description

[0017] Figure 1 The mechanism for preparing SPI / SA composite microgels using the phase separation technique described in the specific implementation method is explained.

[0018] Figure 2 The effect of different SPI and SA concentrations on the particle size distribution of SPI / SA composite microgels is described in the specific implementation method.

[0019] Figure 3 The ζ-potential is the SPI / SA composite microgel described in the specific embodiment.

[0020] Figure 4 The microstructure of the SPI / SA composite microgel described in the specific embodiment is characterized by laser confocal microscopy.

[0021] Figure 5 The swelling rate of the SPI / SA composite microgel is determined by the different SPI and SA concentrations described in the specific implementation method.

[0022] Figure 6 The effect of different heating temperatures on the microgel particle size distribution is described in the specific implementation method.

[0023] Figure 7 The effect of different heating temperatures on the swelling rate of microgels is described in the specific implementation method.

[0024] Figure 8 The effect of different heating temperatures on the centrifugation loss rate of microgels, as described in the specific implementation method.

[0025] Figure 9 The effect of the amount of microgel added as described in the specific embodiment on the water-holding capacity (a) and cooking loss rate (b) of low-salt pork gel.

[0026] Figure 10 The effect of the amount of microgel added as described in the specific embodiment on the gel strength of low-salt pork gel.

[0027] Figure 11 The effect of the amount of microgel added as described in the specific embodiments on the sensory evaluation of low-salt pork gel. Detailed Implementation

[0028] To explain in detail the technical content, structural features, objectives, and effects of the technical solution, the following description is provided in conjunction with specific embodiments and accompanying drawings.

[0029] Example 1

[0030] 1. Preparation of composite microgels

[0031] 1.1 Solution Preparation

[0032] Prepare a 16% (w / w) SPI dispersion by dispersing SPI powder in deionized water. Prepare a 4% (w / w) SA solution by dispersing SA powder in deionized water. Adjust all prepared solutions to pH 7 using 1.0M and 0.1M sodium hydroxide solutions, then refrigerate at 4°C until the next day for use.

[0033] 1.2 Preparation of Mixed Solutions and Microgels

[0034] The SPI and SA solutions were mixed and diluted with deionized water to achieve final SPI concentrations of 2%, 4%, or 6% (w / w) and SA concentrations of 0.3%, 0.6%, 0.9%, 1.2%, or 1.5% (w / w). The SPI and SA mixture was heated in a 90°C water bath for 15 min, followed immediately by cooling to room temperature with ice water. After refrigeration overnight, the mixture was centrifuged at 10,000 g for 30 min to remove excess free polysaccharides and proteins, yielding the SPI / SA composite microgel. This washing step was repeated three times. The collected precipitate, the SPI / SA composite microgel, was freeze-dried for 48 h, and the resulting powder was stored in a desiccated petri dish.

[0035] 2. Characterization of composite microgels

[0036] 2.1 Particle size determination

[0037] The particle size distribution of the composite microgels was measured using a Massizer 3000 laser particle size analyzer. The sample was diluted to 0.1% (w / w). The refractive index of the sample was 1.50, and that of water was 1.33. The sample was added until the opacity was 10%, and the stirring speed in the sample cell was set to 2500 rpm. Each sample was tested in triplicate.

[0038] 2.2 Measurement of ζ potential

[0039] The zeta potential of the composite microgel suspension was determined using a Zetasizer Nano Series particle size analyzer with a detector angle of 90°, a temperature of 25°C, a temperature equilibration period of 2 min, a sample loading volume of 1 mL, and charge measurements were performed three times, with the average value calculated.

[0040] 2.3 CLSM Scan

[0041] Nile blue (0.1% w / v, isopropanol) and 5-aminofluorescein (0.1% w / v, DMSO) were prepared. The samples were thoroughly mixed with equal portions of Nile blue and 5-aminofluorescein solutions. The microstructure of the stained composite microgels was observed using a confocal laser scanning microscope (CLSM). Images of the composite microgels were scanned using a 60× magnification lens. The excitation wavelengths for 5-aminofluorescein and Nile blue were 488 nm and 633 nm, respectively.

[0042] 2.4 Swelling Properties

[0043] Weigh 0.5 g of the composite microgel at room temperature and immerse it in 6 mL of PBS (pH = 2.0, 7.4, or 11.0) solution for 30 min. The swelling ratio (SR) is calculated using the following formula:

[0044] SR(g / g)=(M2-M1) / M1

[0045] In the formula, M1 and M2 are the weight values ​​of the composite microgel before and after swelling, respectively.

[0046] 3 Results and Discussion

[0047] 3.1 Discussion on the mechanism of composite microgel formation

[0048] The formation process of SPI / SA composite microgels is as follows: Figure 1 As shown, both SPI and SA in the mixed system carry a negative charge at pH 7, thus electrostatic repulsion dominates in the mixed solution. The strongly negatively charged SA provides electrostatic repulsion and steric hindrance in the mixed solution. Furthermore, protein denaturation and unfolding under heating conditions enhance the thermodynamic incompatibility and repulsion between the protein and polysaccharide, resulting in phase separation in the mixed system. With increasing polysaccharide concentration, SA, due to its steric hindrance effect, occupies more space, continuously compressing SPI. When SA reaches a certain concentration, it forms a continuous phase, promoting the formation of SPI-enriched regions, allowing SPI to disperse as a dispersed phase within the continuous SA phase. When the protein concentration in the SPI-enriched regions reaches the critical gelation point under the continuous compression of SA, the protein aggregates and gels to form microgels. At pH 7, although the protein carries a negative charge, positively charged residues remain on its surface. Therefore, after the SPI aggregates gel, SA is stably adsorbed onto their surface by electrostatic attraction, forming a core-shell composite microgel with SPI as the core and SA as the shell.

[0049] 3.2 Particle Size Analysis

[0050] The particle size distribution of SPI / SA composite microgels prepared with different SPI and SA concentrations was characterized, and the results are as follows: Figure 2 As shown, except for the sample with an SA concentration of 0.3%, all other samples exhibited a narrow particle size distribution and a single peak. This indicates that the prepared SPI / SA composite microgel has a uniform particle size.

[0051] With decreasing SPI concentration and increasing SA concentration, the particle size of the SPI / SA composite microgel gradually decreased from 44.2 ± 0.31 μm to 19.4 ± 0.35 μm (except for 0.3% SA). This indicates that the particle size of the SPI / SA composite microgel can be controlled by adjusting the concentrations of SPI and SA. This is because the growth of the composite microgel size is related to the competition between gelation and the growth of protein-rich domains in the mixed system, as the final particle size of the composite microgel depends on the cessation of protein-rich domain growth caused by their gelation. At low protein and polysaccharide concentrations, the concentration of protein-rich regions increases due to the enhanced electrostatic repulsion and steric hindrance of polysaccharides, thereby increasing the opportunity for aggregation and binding between protein molecules, which accelerates the protein gelation process. Furthermore, the viscosity of the mixed system increases with increasing polysaccharide concentration, which slows down the growth rate of protein-rich regions. On the other hand, due to the extremely low interfacial tension of the water-in-water system, the tendency for aggregation between water-in-water droplets is also very low. This can help control the microgel size distribution to some extent and prevent rapid random aggregation. However, when the SA concentration is 0.3%, the particle size distribution exhibits a multi-peak state. This is because the SA concentration is too low, resulting in low electrostatic repulsion and steric hindrance in the mixed system. This leads to the concentration of the protein-rich region not reaching the critical gelation concentration, hindering the completion of the gelation process and the formation of SPI / SA composite microgels. Only unstable and loose protein aggregates are formed, so its particle size distribution is unstable.

[0052] 3.3 Potential Analysis

[0053] The zeta potential of microgels can reflect the electrostatic interactions between the protein-polysaccharide mixture. For example... Figure 3 The zeta potential of the SPI / SA composite microgel was demonstrated.

[0054] The negative potential values ​​of all samples indicate that both the SPI and SPI / SA composite microgel systems are negatively charged. At all SPI concentrations, the absolute potential value of the system showed the same trend with increasing SA concentration. When the SPI concentration was 2%, the absolute potential value was 19.29 mV. After adding SA, the absolute potential value of the mixed system increased significantly, and further increased with increasing SA concentration, reaching a maximum of 69.1 mV when the SA concentration reached 1.5%. This indicates that SA can provide a negative charge, significantly enhancing the electrostatic repulsion in the mixed system. This is because SA itself is an anionic polysaccharide with a strong negative charge; therefore, adding SA to the SPI solution enhances the electrostatic repulsion in the system. However, at the same polysaccharide concentration, the absolute potential value of the system decreased with increasing protein concentration. This is because as the SPI concentration increases, the proportion of SA in the mixed system decreases, thus reducing the absolute potential value. The study shows that at high absolute potential values, i.e., with stronger electrostatic repulsion, proteins are more easily dispersed, and the system exhibits higher stability.

[0055] 3.4CLSM

[0056] After staining the SPI / SA composite microgel sample, the aggregation of SPI was observed, and its CLSM image is shown below. Figure 4 As shown, at the same SA concentration, the size of SPI aggregates increases with the increase of SPI concentration, and the aggregate distribution density also becomes denser. This is because the more protein content in the system, the closer the distance between protein molecules, making it easier for them to aggregate and cross-link after heating, resulting in clumping.

[0057] At all SPI concentrations (2%, 4%, or 6%), the size of the SPI aggregates decreased and their distribution became more uniform with increasing SA concentration, indicating that the formed SPI-enriched regions had smaller volumes and higher protein concentrations. The volume reduction is because the higher SA concentration in the system increases electrostatic repulsion and steric hindrance in the mixture, thus subjecting the SPI to greater compressive forces. This results in more compact protein aggregates, leading to smaller SPI aggregates and higher protein concentrations within the regions.

[0058] 3.5 Swelling properties

[0059] The swelling properties of composite microgels are crucial for their application in the food industry. The swelling ratio of SPI / SA composite microgels is as follows: Figure 5As shown, the swelling ratio of the composite microgel decreases with increasing SPI concentration, reaching its minimum at a SPI concentration of 6%. This is because as the SPI concentration increases, proteins are more likely to aggregate and cross-link, leading to gelation. Gelation inhibits phase separation, resulting in larger SPI aggregates and a looser three-dimensional gel network, making it easier for water molecules to escape, thus decreasing the swelling ratio. At all SPI concentrations (2%, 4%, or 6%), the swelling ratio of the composite microgel shows the same trend with increasing SA concentration. The swelling ratio initially increases and then decreases with increasing SA concentration, reaching its highest value at a SA concentration of 1.2%. This is because as the SA concentration increases, phase separation in the system is enhanced, resulting in a denser and more uniform dispersion of the SPI phase, and a denser three-dimensional network formed after gelation, thus increasing the swelling ratio. However, at a SA concentration of 1.5%, the overly dense structure of the SPI / SA microgel hinders water penetration, leading to a decrease in the swelling ratio. Therefore, the swelling ratio reaches its maximum value of 41.03 g / g when the SA concentration is 1.2% and the SPI concentration is 2%.

[0060] Example 2

[0061] 1. Preparation of composite microgels

[0062] 1.1 Solution Preparation

[0063] The method is the same as 1.1 in Example 1.

[0064] 1.2 Preparation of Mixed Solutions and Microgels

[0065] The SPI and SA solutions were mixed and diluted with deionized water to a final SPI concentration of 2% (w / w) and a final SA concentration of 1.2% (w / w). The SPI and SA mixture was heated in a water bath for 15 min at temperatures of 60°C, 70°C, 80°C, 90°C, or 100°C. Other procedures were the same as in section 1.2 of Example 1. The untreated control group was designated NT.

[0066] 2. Characterization of composite microgels

[0067] 2.1 Particle size determination

[0068] The method is the same as 2.1 in Example 1.

[0069] 2.2 Potential Measurement

[0070] The method is the same as 2.2 in Example 1.

[0071] 2.3 Swelling performance test

[0072] The method is the same as 2.4 in Example 1.

[0073] 2.4 Centrifugal Loss Rate Test

[0074] Weigh a certain amount of microgel at room temperature and place it in a centrifuge tube, then record the weight. Centrifuge at 1000g for 10 minutes at 4℃, then invert the tube to allow excess water to drain, and record the weight after centrifugation. The formula for calculating the centrifugation loss rate is as follows:

[0075] Centrifugation loss rate (%) = (M1-M2) / (M1-M0) × 100%

[0076] In the formula: M0 is the weight of the centrifuge tube in g; M1 is the weight of the composite gel and centrifuge tube before centrifugation in g; M2 is the weight of the composite gel and centrifuge tube after centrifugation in g.

[0077] 3 Results and Discussion

[0078] 3.1 Particle size and potential analysis

[0079] The degree of protein aggregation and gelation is closely related to heating temperature. For example... Figure 6 The effect of heating temperature on the particle size distribution of the composite microgels was demonstrated. Table 1 shows the effect of heating temperature on the average particle size and potential value of the composite microgels. Except for the untreated sample, all other samples showed a single-peak distribution. When the heating temperature increased from 60℃ to 100℃, the particle size of the SPI / SA composite microgel gradually increased from 10.5±0.69μm to 24.9±1.04μm. The particle size distribution of the untreated polymer showed a multi-peak state. This is because the structure of SPI cannot be fully expanded under the condition of no heating treatment. The formation of the polymer mainly relies on the electrostatic interaction between SPI and SA to form electrostatic complexes. Its network structure is relatively loose and cannot achieve the uniformity of the composite microgel. Moreover, judging from the particle size distribution, the particle size of the formed complexes shows a large peak in the 100-1000μm range, so the particle size is relatively large.

[0080] The electrostatic repulsion in the mixed system can be characterized by electrostatic potential. The electrostatic potentials of the composite microgel particle suspensions treated at different temperatures were tested, and the results are shown in the figure. The sample without temperature treatment had the lowest absolute potential value. This is because this group of samples did not form core-shell structured composite microgel particles, but rather formed large-sized and structurally unstable aggregates, resulting in weaker electrostatic repulsion and thus the smallest absolute potential value. After temperature treatment, the higher the heating temperature, the lower the absolute potential value of the resulting composite microgel particle suspension. Higher heating temperatures also resulted in larger particle sizes of the formed composite microgel particles. Larger particle sizes lead to a lower polysaccharide concentration in the mixed system at the same biopolymer concentration, thus resulting in a lower absolute potential value for the mixed system.

[0081] Table 1. Effects of different heating temperatures on the average particle size and potential of microgels

[0082]

[0083] Note: Different letters in the same line indicate significant differences (p<0.05).

[0084] 3.2 Swelling properties

[0085] Due to the hydrophilicity of proteins and polysaccharides, composite microgels exhibit high swelling properties. These swelling properties are crucial for their application in the food industry. Figure 7 The swelling properties of the composite microgels treated at different temperatures in aqueous solutions at different pH values ​​(pH = 2.0, 7.4, or 11.0) were demonstrated. At pH = 2.0, 7.4, or 11.0, the swelling ratio of the composite microgels initially increased and then decreased with increasing heating temperature, reaching its highest value at 80℃. At lower temperatures, the phase separation time was longer, resulting in higher and denser concentrations of the formed SPI aggregates. However, if the temperature was too low, protein unfolding was incomplete, hydrophobic interactions were weaker, the resulting gel network structure was weaker, and water-holding capacity was poor, leading to a lower swelling ratio. Composite microgels obtained at higher temperatures exhibited stronger gel network strength, which could improve their swelling ratio. However, when the heating temperature exceeded 80℃, the structure of the composite microgels became too dense, making it difficult for water to fully penetrate, thus reducing the swelling ratio.

[0086] However, although the swelling rates of the composite microgels treated at the same temperature showed the same trend in different pH environments, there were still differences. In neutral and alkaline environments, there was no significant difference in the swelling rate of the composite microgels, while in acidic environments, the swelling rate decreased significantly (P<0.05). This is because the composite microgels have a core-shell structure with SPI as the core and SA as the shell. In acidic environments, the SA on the shell gels and shrinks, which hinders the absorption of water molecules, thus leading to a decrease in the swelling rate.

[0087] 3.3 Centrifugal loss rate

[0088] Water retention capacity is an important indicator for evaluating the properties of microgels. The water retention performance of the SPI / SA composite microgel was characterized by the centrifugal loss rate, and the results are as follows: Figure 8As shown, the centrifugal loss rate of the untreated sample was relatively high, reaching 8.61%. This is because the electrostatic complex has a loose structure and low gel strength, leading to gel structure rupture under high-speed centrifugation and resulting in a high centrifugal loss rate. With increasing heating temperature, the centrifugal loss rate of the SPI / SA composite microgel decreased. At a heating temperature of 80℃, the centrifugal loss rate was approximately 0.07%, close to 0%. This is because after heating, the SPI / SA composite microgel formed a robust gel network structure, with a tighter bond between it and water molecules, thus significantly reducing the centrifugal loss rate. Furthermore, the higher the temperature, the better the network structure and the lower the centrifugal loss rate. At 80℃, the centrifugal loss rate was not significantly different from that at 90℃ and 100℃, indicating that the SPI / SA composite microgel had already formed a robust three-dimensional network structure at a treatment temperature of 80℃. When microgel particles are filled into food, the high gel strength ensures that the structure of the microgel particles themselves is not damaged, and the strong water retention capacity allows for the fixation of more water in the food matrix, improving the texture and water-holding capacity of the food.

[0089] Example 3

[0090] 1 Experimental Methods

[0091] 1.1 Preparation of low-salt minced meat

[0092] Excess fat, tendons, and connective tissue were removed from the raw pork tenderloin. The meat was cut into small pieces and ground into mince using a meat grinder. Addition ingredients were added to the mince and mixed thoroughly. Different proportions of composite microgels were added in groups. The mixture was refrigerated at 4°C for 12 hours. After forming meatballs, they were boiled in boiling water for 7 minutes to form pork gel. After cooling, the mixture was refrigerated at 4°C for further characterization.

[0093] The auxiliary materials, based on the total amount of raw meat, consist of 30% water and 1.75% salt. The amount of compound microgel added is divided into 5 groups: no compound microgel added, 5% compound microgel added, 10% compound microgel added, 15% compound microgel added, and 20% compound microgel added, named CG-0%, CG-5%, CG-10%, CG-15%, and CG-20%, respectively.

[0094] 1.2 Whiteness Measurement

[0095] Cut a 1cm thick slice of pork gel and immediately measure its center using a colorimeter. After calibration with a standard plate, measure the L value using a fully automated colorimeter. * value, a * value and b * Whiteness value. The whiteness value is expressed by the following formula:

[0096]

[0097] 1.3 Water Holding Capacity Measurement

[0098] Weigh a certain amount of pork gel at room temperature, wipe off the surface moisture, and weigh it. Centrifuge at 1000g for 10 minutes at 4℃, then wipe off the surface moisture with absorbent paper and record the mass after centrifugation. Calculate the water-holding capacity of the sample using the following formula:

[0099] Water holding capacity (%) = (M2 / M1) × 100%

[0100] In the formula: M1 is the mass of the sample before centrifugation (g); M2 is the mass of the sample after centrifugation (g).

[0101] 1.4 Determination of cooking loss

[0102] Weigh a certain amount of raw minced pork at room temperature, squeeze it into balls, and record the weight before steaming. Steam in boiling water for 7 minutes, then remove and wipe off the surface moisture with absorbent paper. Record the weight after steaming. The steaming loss rate is expressed by the following formula:

[0103] Cooking loss rate (%) = (W1-W2) / W2 × 100%

[0104] In the formula: W1 is the weight of the raw minced meat before steaming / g; W2 is the weight of the pork meatballs after steaming / g.

[0105] 1.5 Analysis of Texture Properties

[0106] The textural properties of cubic pork gels with dimensions of 2 cm (length, width, and height) were determined using a texture analyzer (probe model P36). The initial and subsequent testing speeds were both 5 mm / s, while the speed during testing was set to 1 mm / s. The compression set was 50%. The hardness, elasticity, cohesiveness, adhesiveness, and chewiness values ​​for different treatment groups were recorded.

[0107] 1.6 Determination of gel strength

[0108] The gel strength of pork gel was determined using a P / 5S spherical plunger structural analyzer. The test speed was mm / s, the compression distance was 10 mm, and the trigger force was 5 g.

[0109] 1.7 Sensory Evaluation

[0110] Five factors were used as sensory evaluation indicators for low-salt pork meatballs: elasticity, texture, color, flavor, and hardness (see Table 2).

[0111] Table 2 Sensory Evaluation Criteria (Maximum Score: 25 points)

[0112]

[0113] 2 Results Analysis

[0114] 2.1 Color Analysis

[0115] In meat and meat products, color is one of the most critical parameters related to quality for consumers, directly impacting their acceptance of the product. Table 3 shows the effect of different amounts of added composite microgels on the color of low-salt minced meat gel. Compared to the high-salt group (CK), reducing the amount of salt decreased both the brightness and whiteness values ​​of the pork gel. This is because lower salt content reduces the content of salt-soluble proteins, resulting in a looser three-dimensional gel network structure with more and larger pores, and an uneven gel surface, thus reducing the brightness and whiteness values.

[0116] After adding the composite microgel, the whiteness and brightness values ​​of the low-salt pork gel gradually increased with the increase of the amount of composite microgel added, reaching their maximum values ​​of 72.18 and 73.97 respectively when the addition amount was 20%. Notably, when the addition amount of composite microgel reached 15%, the whiteness and brightness values ​​exceeded those of the high-salt group. This is because the composite microgel can fix the free water present in the low-salt pork mince system, increasing the water content of the low-salt pork gel. Furthermore, after absorbing water, the composite microgel forms smooth, spherical particles that fill the low-salt mince, enhancing the smoothness of the low-salt pork gel. The light reflection intensity increases with the increase of the amount of composite microgel added. Therefore, the whiteness and brightness values ​​of the gel increase with the increase of the amount of composite microgel added.

[0117] Table 3. Effects of different amounts of composite microgel added on the color of low-salt minced meat gel.

[0118]

[0119] Note: Different letters in the same column indicate significant differences (P<0.05).

[0120] 2.2 Cooking loss and water holding capacity

[0121] The water-holding capacity and cooking loss rate of meat products are closely related to their quality and taste. For example... Figure 9 As shown in (a) and 9(b), the cooking loss rate and water holding capacity of pork gel are negatively correlated. The cooking loss rate of low-salt pork gel with added composite microgel is reduced, while the water holding capacity is increased. Compared with the high-salt group, the cooking loss rate of low-salt pork gel increased from 5.67% to 7.73%, and the water holding capacity decreased from 93.13% to 88.45%. However, with the increase of the amount of composite microgel added, the cooking loss rate of low-salt pork gel decreased from 7.74% to 4.2%, and the water holding capacity increased from 88.45% to 96.24%. When the amount of composite microgel added reached 15%, the cooking loss rate and water holding capacity of low-salt pork gel with added composite microgel were 4.71% and 94.77%, respectively, both of which were better than those of the high-salt group.

[0122] 2.3 Texture Characteristics Analysis

[0123] Texture parameters in meat products can indirectly reflect the integrity of the three-dimensional gel network structure. Table 4 shows the effects of different amounts of composite microgels on the hardness, adhesiveness, chewiness, elasticity, and cohesion of low-salt pork gel. As shown in Table 4, compared to the high-salt group, the hardness of the low-salt pork gel decreased from 1951.96 g to 1474.85 g, adhesiveness from 1075.29 N to 929.27 N, chewiness from 1460.31 mJ to 869.72 mJ, elasticity from 0.92 mm to 0.84 mm, and cohesion from 0.68 to 0.61. This indicates that the reduction in salt concentration disrupts the integrity of the gel network, resulting in a looser three-dimensional gel network structure. After adding SPI / SA composite microgels, the hardness, adhesiveness, chewiness, elasticity, and cohesion of the low-salt pork gel all increased, and the higher the amount of SPI / SA composite microgels added, the higher the texture parameter values. It is noteworthy that when the addition amount reaches 15%, all textural parameters of CG-15% are superior to those of CK. This indicates that the SPI / SA composite microgel can improve the resistance to large deformations of low-salt pork gel, i.e., improve the macroscopic integrity of the composite material. This phenomenon occurs because the hydrophilicity of the SPI / SA composite microgel stabilizes the flowing water on the filler surface, reducing the migration rate of free water in the low-salt pork gel. The higher the addition amount of SPI / SA composite microgel, the larger its usable surface area, and therefore the stronger its ability to retain free water. This is consistent with the results regarding water retention capacity and cooking loss rate.

[0124] Table 4. Effects of different amounts of composite microgels on the textural properties of low-salt pork gels.

[0125]

[0126] Note: Different letters in the same column indicate significant differences (P<0.05).

[0127] 2.4 Gel strength analysis

[0128] Gel strength largely represents the ability of proteins to aggregate during heat-induced gelation. For example... Figure 10 As shown, the gel strength of the low-salt group was significantly lower than that of the high-salt group. This is because the reduced salt concentration in the system decreases the content of soluble proteins, weakening the interactions between proteins after heating, resulting in a less dense gel structure and thus reduced gel strength. The addition of the composite microgel significantly enhanced the gel strength of the low-salt pork gel (P<0.05), reaching its maximum at an addition level of 20%. This is because the composite microgel provides rigid filling for the myofibrillar protein gel matrix, thereby enhancing the gel strength of the low-salt pork gel. When the addition level of the composite microgel was 15% or higher, the gel strength of the low-salt pork gel exceeded that of the high-salt group.

[0129] 2.5 Sensory Evaluation Analysis

[0130] The effect of the amount of composite microgel added on the sensory evaluation of low-salt pork gel, including elasticity, texture, color, flavor, and firmness, is as follows: Figure 11 As shown, compared to the high-salt group, the sensory scores of the low-salt group without the addition of composite microgels all decreased. However, after adding composite microgels, sensory acceptance increased. The color score increased with the increase of the amount of composite microgels added, because the addition of composite microgels enhanced light diffraction. The scores for elasticity, firmness, and texture also significantly improved, because the filling of composite microgels enhanced the network strength of the low-salt pork gel, improved its water retention, and thus increased the sensory scores. The improvement in flavor may be because the composite microgels improved the gelation properties of the low-salt pork gel, making it taste better.

[0131] In summary, the particle size of the composite microgel can be precisely controlled by changing the concentrations of SPI and SA, or by adjusting the heating temperature. Higher temperatures result in more elastic composite microgels and a stronger gel network structure. The swelling ratio of the composite microgel reaches its maximum at a SPI concentration of 2%, an SA concentration of 1.2%, and a heating temperature of 80℃. The composite microgel can improve the sensory evaluation, textural properties, and gel strength of low-salt pork gel. When the composite microgel addition reaches 15%, all indicators of the low-salt pork gel are optimal and superior to those of the high-salt group.

[0132] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection of the present invention. Therefore, any changes and modifications made to the embodiments described herein based on the innovative concept of the present invention, or equivalent structural or procedural transformations made using the content of the present invention's specification and drawings, directly or indirectly applying the above technical solutions to other related technical fields, are all included within the scope of patent protection of the present invention.

Claims

1. A composite microgel, characterized in that: The composite microgel is prepared using soy protein isolate and sodium alginate as raw materials via a phase separation method; the preparation method steps are as follows: Solution preparation: Disperse soy protein isolate powder in deionized water to prepare a soy protein isolate dispersion with a mass percentage of 15-20%; disperse sodium alginate powder in deionized water to prepare a sodium alginate solution with a mass percentage of 2-6%; adjust the pH of the prepared solution to 6.8-7.2 using 1.0M and 0.1M sodium hydroxide solutions, and refrigerate overnight at 2-8℃. Preparation of composite microgels: Soy protein isolate and sodium alginate solution are mixed and diluted with deionized water to a final concentration of 2-6% for soy protein isolate and 0.6-1.5% for sodium alginate, all of which are mass percentages. The soy protein isolate and sodium alginate solution is heated in a water bath at 70-100℃ for 10-20 min, and then immediately cooled to room temperature with ice water. After refrigerating overnight, it is centrifuged at 8000-12000g for 20-40 min to remove excess free polysaccharides and proteins, obtaining crude soy protein isolate / sodium alginate composite microgel. The centrifugation and washing steps are repeated 2-4 times. The collected precipitate is the soy protein isolate / sodium alginate composite microgel, which can be directly used to prepare low-salt minced meat products. Alternatively, the soy protein isolate / sodium alginate composite microgel can be freeze-dried for 36-60 h to prepare microgel powder for storage.

2. The composite microgel according to claim 1, characterized in that: The particle size range of the composite microgel is 19.4±0.35 µm to 44.2±0.31 µm.

3. The composite microgel according to claim 1, characterized in that: The maximum swelling ratio of the composite microgel is 41.03 g / g.

4. The application of the composite microgel as described in any one of claims 1-3 in low-salt minced meat products, characterized in that: The application method involves adding auxiliary materials to the minced meat and stirring until well mixed. Then, 5-20% by weight of soy protein isolate / sodium alginate composite microgel is added. The mixture is refrigerated at 2-8℃ for 8-16 hours. After the meatballs are formed, they are boiled in boiling water for 5-10 minutes to form a gel. After cooling, a low-salt minced meat product is obtained.

5. The application of the composite microgel according to claim 4 in low-salt minced meat products, characterized in that: The auxiliary materials mentioned are based on the total amount of raw meat, with water accounting for 25-35% and salt for 1.5-2%, all by weight percentage.

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