A blueberry jam suitable for industrial continuous coating of sandwich cookies and its preparation method

Abstract

This invention belongs to the field of food processing and discloses a blueberry jam suitable for industrial continuous coating of sandwich cookies and its preparation method. By weight, it comprises the following ingredients: 55-65 parts blueberry puree, 25-35 parts white sugar, 5-15 parts high-fructose corn syrup, 0.3-0.8 parts high-ester pectin with an esterification degree ≥65%, and 0.1-0.5 parts citric acid. The jam does not contain modified starch. Its physicochemical properties include: water activity a. w 0.50~0.60, soluble solids 80~90 °Brix. This invention is the first to determine the specific rheological parameter thresholds at a coating temperature of 50 °C. The shear thinning characteristics of the jam are perfectly matched with the production process, making it compatible with existing industrial continuous coating production lines for sandwich cookies, thus solving the problem of the disconnect between existing technical formulas and industrial production. At the same time, the jam has a good taste, strong temperature adaptability, and stable quality during storage.

Description

Technical Field

[0001] This invention belongs to the field of food processing, specifically relating to the processing technology of jam for filling baked goods, and more specifically to a blueberry jam for sandwich cookies adapted for industrial continuous coating and its preparation method. Background Technology

[0002] Sandwich cookies, with their combination of crispy crust and creamy filling, have secured a stable share of the snack food market. As the core component of sandwich cookies, jam's taste, storage stability, and processing adaptability directly determine the final quality and production efficiency of the product.

[0003] Sandwich cookies are a typical multi-component food system. High-oil cookie dough typically has a fat content of 20%~35%, a moisture content of ≤4%, and a water activity (α) of 100%. w The a value is only 0.18~0.30, which belongs to the category of strongly hydrophobic low a. w The dry phase; while jam is a hydrophilic, high-moisture wet phase, the difference between the two is... w Gradient is the core factor driving moisture migration between layers. During storage, moisture continuously migrates from the jam to the crust, causing the crust to become damp and soft, losing its crisp texture and severely limiting the product's shelf life.

[0004] Currently, research and development in the industry regarding jams for sandwich cookies focuses on inhibiting moisture migration and extending product shelf life, with the mainstream technical approach being extreme moisture reduction. w Route: By using ultra-high content white sugar, polyols (sorbitol / glycerol), and adding modified starch, etc., the jam a w Reduced to 0.30~0.45, compared to cookie dough a w The difference is controlled within 0.15 to slow down moisture migration, which is also the mainstream solution for industrial products on the market. However, this jam may have a sticky and greasy texture, and these studies have not been designed for continuous industrial coating, making it difficult to simultaneously achieve the characteristics of "maintaining shape at room temperature and easy flow when coated at heat". Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a low-moisture blueberry jam specifically designed for industrially continuous coating of sandwich cookies. This jam ensures product stability over a 12-month shelf life while solving the problems of stickiness, easy hardening at low temperatures, and poor industrial adaptability of existing technologies, thus achieving a synergistic improvement in taste, low-temperature stability, processing performance, and storage quality.

[0006] Another objective of this invention is to provide a method for preparing low-moisture blueberry jam specifically for sandwich cookies that is adapted for industrial continuous coating. This method is simple and controllable, and the core processes are all common jam production processes. No special equipment is required, and the difficulty of industrial scale-up is low. It can accurately control the physicochemical and rheological properties of the product and ensure batch stability.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A blueberry jam specifically designed for industrial continuous coating of sandwich cookies, comprising, by weight, the following ingredients: 55-65 parts blueberry puree, 25-35 parts white sugar, 5-15 parts high-fructose corn syrup, 0.3-0.8 parts high-ester pectin with an esterification degree ≥65%, and 0.1-0.5 parts citric acid; the jam does not contain modified starch; the core physicochemical indicator is: water activity a. w 0.50~0.60, soluble solids 80~90 °Brix.

[0009] Preferably, the core physicochemical index is: water activity a. w 0.52~0.59, soluble solids 84~90 °Brix, pH 3.0~3.5.

[0010] Preferably, the core rheological parameters are divided into:

[0011] 1. Room temperature shape retention index: Yield stress ≥15Pa at 25℃;

[0012] 2. Industrial coating compatibility index: At an actual production coating temperature of 50℃, 10 s -1 At shear rates, the apparent viscosity is 15000~35000 mPa・s, the yield stress is 5~30 Pa, and the flow behavior index n is 0.33~0.42, exhibiting typical pseudoplastic fluid characteristics.

[0013] Preferably, by weight, the raw materials also contain food-grade excipients, which are at least one of the following: 0-0.5 parts of edible colloid, 0-3 parts of humectant, 0-0.3 parts of edible flavoring, and 0-0.1 parts of preservative.

[0014] Preferably, the edible colloid is at least one of carrageenan, xanthan gum, and sodium alginate; the humectant is at least one of glycerin and sorbitol; and the preservative is at least one of potassium sorbate and natamycin.

[0015] The method for preparing the blueberry jam includes the following steps:

[0016] (1) Dry material premixing: Mix white sugar and high ester pectin evenly to obtain a mixture;

[0017] (2) Ingredient mixing: Heat the blueberry puree to 45~50℃, add the mixture from step (1) and fructose syrup while stirring, and continue stirring until the materials are completely dissolved and the system is uniform and free of particles;

[0018] (3) Concentration and acid adjustment: Heat the mixture from step (2) to 90~100℃, stir and concentrate until the soluble solids reach 78~85 °Brix, add citric acid aqueous solution to adjust the pH of the system to 3.0~3.5, continue to concentrate until the soluble solids and water activity meet the standards, and then stop heating;

[0019] (4) Homogenization and degassing: The concentrated jam is homogenized under a pressure of 15~25 MPa and degassed under vacuum for 5~10 minutes to ensure that the system is uniform and delicate; thus, blueberry jam suitable for industrial continuous coating of sandwich cookies is obtained.

[0020] Preferably, the blueberry pulp has a soluble solids content of 8-12 °Brix and a pH of 3.3-3.8.

[0021] Preferably, the concentration and acid adjustment involves heating the mixture from step (2) to 95-100°C, stirring and concentrating it until the soluble solids reach 82-88 °Brix, adding citric acid aqueous solution to adjust the pH of the system to 3.0-3.2, and continuing to concentrate until both indicators meet the standards.

[0022] Preferably, the jam obtained in step (4) is further filled and sealed: the jam is filled with hot water when it is cooled to 85~90℃, and after sealing, it is sterilized in a water bath at 85±5℃ for 10~15 minutes and then cooled to room temperature.

[0023] The industrial continuous coating process for sandwich cookies requires the jam to simultaneously possess the characteristics of "maintaining shape at room temperature and easy flow when coated at hot temperature". This invention, through synergistic optimization of formula and process, precisely controls the rheological parameters of the jam within the optimal range: high yield stress at room temperature (25℃) ensures shape retention without collapse or overflow; at coating temperature (50℃), it exhibits typical pseudoplastic fluid characteristics, and the viscosity is significantly reduced under high shear, enabling uniform spreading, thus fundamentally solving the technical problem of industrial continuous coating.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1. Improves jam texture and solves the problems of excessive sweetness and stickiness in high-sugar systems: This invention uses high-ester pectin with an esterification degree of ≥65% as the core gelling agent, which does not contain any modified starch, thus avoiding the problems of pasty texture, stickiness, and poor mouthfeel caused by modified starch. Through the complex sugar system of white sugar and fructose syrup and the precise sweet-sour ratio of 3.0~3.2, the excessive sweetness caused by high sugar is greatly alleviated. At the same time, the gel network of high-ester pectin can achieve the encapsulation and rapid release of flavor substances, resulting in jam with a harmonious sweet and sour taste, rich fruit aroma, and smooth texture.

[0026] 2. Solving the problem of low-temperature hardening and adapting to all consumption scenarios: This invention completely solves the problem of low-temperature hardening of jam through four core methods: ① Completely free of modified starch, eliminating starch retrogradation at low temperatures; ② A single high-ester pectin gel system, avoiding the synergistic failure of multiple colloids and network shrinkage at low temperatures; ③ No large amount of polyols added, avoiding polyol crystallization at low temperatures; ④ A complex sugar system inhibits the crystallization of granulated sugar at low temperatures. Experimental verification shows that the hardness change rate of the jam of this invention is <20% at room temperature (25℃) and low temperature (4℃), with no hardening or water separation at low temperatures, perfectly adapting to all consumption scenarios such as low-temperature distribution and refrigerated storage in winter.

[0027] 3. Precise quantification of rheological parameters, perfectly adapted to industrial continuous coating production: This invention focuses on the actual production needs of industrial continuous coating of cookies and has for the first time determined the exclusive rheological parameters at a coating temperature of 50℃. The shear thinning characteristics of jam are perfectly matched with the production process and can be adapted to existing industrial continuous coating production lines for sandwich cookies, solving the problem of the disconnect between existing technical formulas and industrial production.

[0028] 4. Achieving a synergistic balance between shelf life and taste: This invention achieves an optimal a value of 0.52~0.59. w Interval design, no need to limit reduction of a w This effectively slows down moisture migration, and the cake can be stored at 25℃. w The increase is controlled within 0.15, which can ensure the crisp texture of the biscuit during the 12-month shelf life at room temperature, while the retention rate of characteristic flavor substances of jam is ≥85%.

[0029] 5. Simple and controllable process with low difficulty in industrial scale-up: The preparation process of this invention does not require special production equipment. The core processes are all common processes in jam production. The concentration endpoint is controlled by two indicators: soluble solids and water activity, so as to achieve precise quantification of product quality. The process parameters have a high tolerance for error and are easy to scale up for industrial production. There is no need to modify the existing production line, so it has great industrial application value. Attached Figure Description

[0030] Figure 1 The moisture relaxation time (T2) is shown for different jam samples.

[0031] Figure 2 Diameter of different jam samples flowing at 25℃ for 5 seconds.

[0032] Figure 3 Pseudocolor image of moisture distribution in cookie jam sandwich cookies after 50 days of storage. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0034] High-ester pectin was purchased from Guangzhou Shimeijia Biotechnology Co., Ltd.; F42 fructose syrup was purchased from Yilong Biotechnology Co., Ltd.; butter was purchased from Fonterra Trading (Shanghai) Co., Ltd.; glycerin and sorbitol solution were purchased from Zhengzhou Kangben Biotechnology Co., Ltd.; and other excipients such as citric acid, potassium sorbate, xanthan gum, carrageenan, and sodium alginate were purchased from Henan Ganchun Food Co., Ltd.

[0035] Table 1. Recipe Table for Low-Moisture Blueberry Jam for Sandwich Cookies (Example)

[0036]

[0037] Example 1

[0038] This embodiment provides a low-moisture blueberry jam specifically for sandwich cookies suitable for industrial continuous coating. The formula is as follows (based on 1000g of finished product, corresponding to the following mass parts): 600g blueberry puree, 300g white sugar, 80g F42 fructose syrup, 5g high-ester pectin, 3g citric acid, 0.5g potassium sorbate, 1.5g blueberry flavoring, and water added to 1000g. It does not contain modified starch or other edible colloids.

[0039] The preparation method includes the following steps: (1) Preparation of raw pulp: Fresh blueberries are washed, pulped and then passed through a 60-mesh sieve to obtain blueberry raw pulp with soluble solids of 10.2°Brix and pH 3.5, which is set aside for later use; (2) Premixing of dry materials: White sugar and high-ester pectin are manually mixed 3 times to obtain a uniform pectin-sugar mixture; (3) Mixing of ingredients: Blueberry raw pulp is poured into an electric heating jacketed kettle, heated to 48°C, and pectin-sugar mixture and fructose syrup are slowly added while stirring at 300r / min. Stirring is continued for 20min until the materials are completely dissolved and the system is uniform with no visible particles; (4) Concentration and acid adjustment: Heating is turned on and the mixture is heated to 98°C. The mixture is concentrated under normal pressure and the stirring speed is controlled at 300r / min. Soluble solids and water activity are monitored every 5min. When the soluble solids reach 85°Brix, 50% of the raw materials are added. The pH of the system was adjusted to 3.1 by citric acid aqueous solution, and the concentration was continued until the soluble solids were 87 °Brix and 0.552, and the heating was stopped; (5) Homogenization and degassing: The concentrated jam was sent to a high-pressure homogenizer and homogenized once at a pressure of 20 MPa. Then it was transferred to a vacuum degassing tank and degassed for 8 minutes at -0.08 MPa to remove air bubbles in the system; (6) Filling and sealing: When the jam was cooled to 88 °C, it was aseptically filled and sealed. After sealing, it was placed in an 85 °C water bath for sterilization for 15 minutes. Then it was cooled to room temperature in stages by water baths at 60 °C, 40 °C and 25 °C to obtain the finished jam.

[0040] Example 2

[0041] This embodiment provides a low-moisture blueberry jam specifically for sandwich cookies suitable for industrial continuous coating. The formula is as follows (based on 1000g of finished product, corresponding to the following mass parts): 650g blueberry puree, 250g white sugar, 85g F42 fructose syrup, 4g high-ester pectin, 2.5g citric acid, 10g glycerin, 0.5g xanthan gum, 0.3g potassium sorbate, 1.2g blueberry flavoring, and water added to 1000g. It does not contain modified starch.

[0042] The preparation method includes the following steps: (1) Preparation of raw pulp: Fresh blueberries are washed, pulped and passed through a 60-mesh sieve to obtain blueberry raw pulp with soluble solids of 9.8 °Brix and pH 3.6, which is then set aside; (2) Dry material premixing: White sugar, high-ester pectin and xanthan gum are mixed evenly in proportion to obtain dry material mixture; (3) Ingredient mixing: Blueberry raw pulp is poured into an electric heating jacketed kettle, heated to 50°C, and the dry material mixture, fructose syrup and glycerol are slowly added under stirring at 300r / min. The mixture is stirred for 25min until the materials are completely dissolved and the system is uniform with no visible particles; (4) Concentration and acid adjustment: Heating is turned on and the mixture is heated to 95°C. The mixture is concentrated under normal pressure and the stirring speed is controlled at 250r / min. The soluble solids and water activity are monitored every 5min. When the soluble solids reach 83 °Brix, 50% citric acid aqueous solution is added to adjust the pH of the system. Continue concentrating to 3.2, until soluble solids reach 85 ° Brix, a w 0.586, stop heating; (5) Homogenization and degassing: send the concentrated jam into a high-pressure homogenizer and homogenize it once at a pressure of 15MPa. Then transfer it to a vacuum degassing tank and degas it for 10 minutes at -0.08MPa to remove air bubbles from the system; (6) Filling and sealing: when the jam is cooled to 85℃, perform aseptic hot filling. After sealing, place it in an 85℃ water bath for sterilization for 15 minutes. Then cool it to room temperature in stages through water baths at 60℃, 40℃ and 25℃ to obtain the finished jam.

[0043] The difference between this embodiment and Example 1 is that the basic ingredient ratios were adjusted: the amount of blueberry puree added was increased from 600g to 650g, the amount of white sugar was reduced from 300g to 250g, and the amount of fructose syrup was adjusted from 80g to 85g; the amount of high-ester pectin added was reduced from 5g to 4g, and 0.5g of xanthan gum was added as an auxiliary stabilizer and 10g of glycerin as a humectant; the pH was adjusted to 3.2.

[0044] Example 3

[0045] This embodiment provides a low-moisture blueberry jam suitable for industrial continuous coating of sandwich cookies. The formula is as follows (based on 1000g of finished product, corresponding to the following mass parts): 550g blueberry puree, 350g white sugar, 90g F42 fructose syrup, 7g high-ester pectin, 4g citric acid, 0.3g carrageenan, 0.2g sodium alginate, 0.5g potassium sorbate, 2g blueberry flavoring, and water added to 1000g. It does not contain modified starch.

[0046] The preparation method includes the following steps: (1) Preparation of raw pulp: Fresh blueberries are washed, pulped and passed through a 60-mesh sieve to obtain blueberry raw pulp with soluble solids of 10.5 °Brix and pH 3.4, which is then set aside; (2) Premixing of dry materials: White sugar, high-ester pectin, carrageenan and sodium alginate are mixed evenly in proportion to obtain dry material mixture; (3) Mixing of ingredients: Blueberry raw pulp is poured into an electric heating jacketed kettle, heated to 45°C, and the dry material mixture and fructose syrup are slowly added while stirring at 350r / min. Stirring is continued for 25min until the materials are completely dissolved and the system is uniform with no visible particles; (4) Concentration and acid adjustment: Heating is turned on and the mixture is heated to 100°C. The mixture is concentrated under normal pressure and the stirring speed is controlled at 350r / min. Soluble solids and water activity are monitored every 5min. When the soluble solids reach 86 °Brix, 50% of the raw materials are added. The pH of the system was adjusted to 3.0 using an aqueous citric acid solution, and then further concentrated to 89 °Brix, a w 0.524, stop heating; (5) Homogenization and degassing: send the concentrated jam into a high-pressure homogenizer and homogenize it once at a pressure of 25MPa. Then transfer it to a vacuum degassing tank and degas it for 5 minutes at -0.08MPa to remove air bubbles from the system; (6) Filling and sealing: when the jam is cooled to 90℃, perform aseptic hot filling. After sealing, place it in an 85℃ water bath for sterilization for 15 minutes. Then cool it to room temperature in stages through water baths at 60℃, 40℃ and 25℃ to obtain the finished jam.

[0047] The difference between this embodiment and Embodiment 1 is that:

[0048] The basic ingredient ratios were adjusted: the amount of blueberry puree added was reduced from 600g to 550g, the amount of white sugar was increased from 300g to 350g, and the amount of fructose syrup was adjusted from 80g to 90g; the amount of high-ester pectin added was increased from 5g to 7g, and 0.3g of carrageenan and 0.2g of sodium alginate were added as auxiliary stabilizers; the pH was adjusted to 3.0.

[0049] Comparative Example 1

[0050] This comparative example provides a jam for sandwich cookies, with the following formula (based on 1000g of finished product, corresponding to the following mass parts): 200g white sugar, 354g F42 fructose syrup, 150g 70% sorbitol liquid, 50g hydroxypropyl distarch phosphate, 80g edible glycerin, 4g carrageenan, 1g xanthan gum, 3g potassium citrate, 3g potassium dihydrogen phosphate, 3g citric acid, 50g dried blueberries, 2g blueberry flavoring, and water to 1000g.

[0051] The preparation method was exactly the same as that in Example 1 of CN103005244A. The finished jam a w 0.407, soluble solids 82 °Brix.

[0052] The difference between this comparative example and Example 1 is that:

[0053] The core gelling systems are completely different. In this comparative example, 50g of hydroxypropyl distarch phosphate (modified starch) and a mixture of carrageenan and xanthan gum were used as the thickening gelling matrix, without the addition of high-ester pectin. Example 1 used high-ester pectin as the single gelling matrix and contained no modified starch. The sugar systems are also completely different. In this comparative example, a composite system of 354g fructose syrup, 150g sorbitol solution, and 80g glycerol was used for extreme sugar reduction. w Example 1 uses only a basic sugar system of granulated sugar and fructose syrup, without the addition of large amounts of polyols; the physicochemical properties of the finished product are completely different. This comparative example of jam a... w The value is 0.407, which is much lower than 0.552 in Example 1, and exceeds the protection limit of this invention. w The preparation methods are completely different. This comparative example uses a process of first gelatinizing starch and then concentrating it, which is completely different from the dry material premixing and dual-index controlled concentration endpoint process of Example 1.

[0054] Comparative Example 2

[0055] This comparative example provides a blueberry jam with the same formula as Example 1, only the concentration endpoint is adjusted. The finished jam a w 0.621, soluble solids 78 °Brix, contains no modified starch.

[0056] The difference between this comparative example and Example 1 is that the remaining steps of the preparation method are the same as in Example 1, except that the concentration endpoint in step (4) is adjusted to 78 °Brix for soluble solids. w 0.621, stop heating. The water activity of the finished jam is 0.621, which exceeds the upper limit of the 0.52~0.59 range protected by this invention. The rest of the formula and preparation method are completely consistent with Example 1.

[0057] The experimental methods for verifying the beneficial effects and innovativeness of this invention are as follows:

[0058] (1) Determination of moisture content, water activity and soluble solids

[0059] Moisture content: Determined by direct drying method according to GB 5009.3-2016 "National Food Safety Standard - Determination of Moisture in Food". Water activity: Directly measured using a water activity meter at a constant temperature of 25℃, with each sample measured in triplicate. Soluble solids: Measured using a handheld saccharimeter at 25℃, expressed as °Brix.

[0060] (2) Measurement of color and appearance

[0061] Take different a w The samples were photographed under constant illumination and the color difference was measured. L* represents luminance, a* represents red-green intensity, and b* represents yellow-blue intensity. Each sample was measured three times, and the average value was taken.

[0062] (3) Rheological property determination

[0063] A 40 mm diameter aluminum parallel plate was selected as the probe, with a gap of 1 mm. After loading the sample, excess sample was wiped off the edges of the fixture. A heat insulation plate was added during the temperature variation test, and the test was started after standing for 5 minutes.

[0064] Steady-state shear test: At 25 °C, shear rates (γ̇) were applied to the samples from 0.1 to 100 s. -1 A series of ascending scans were performed to record the variations in apparent viscosity (η) and shear stress (τ) as a function of γ̇. The flow curves were fitted using the Herschel Bulkley model.

[0065]

[0066] In the formula: Shear stress (Pa); K is the yield stress (Pa); K is the consistency coefficient (Pa·s) n ); n is the flow behavior exponent (dimensionless). When n < 1, the fluid exhibits pseudoplasticity (shear thinning).

[0067] (4) pH value measurement

[0068] The procedure was performed in accordance with the national standard GB 5009.237-2016 "Determination of pH Value in Food". The steps were as follows: Take 10g of the jam sample to be tested, add 90mL of carbon dioxide-free ultrapure water, stir well, and let stand for 30 minutes. Measure the pH value of the sample supernatant using a precision pH meter calibrated with a standard buffer solution. Perform three parallel tests for each sample, and calculate the average value and standard deviation.

[0069] (5) Sensory evaluation form

[0070] Ten trained evaluators were organized to conduct sensory scoring (out of 10) on indicators such as color, smell, taste, and interlayer harmony. The specific scoring criteria are shown in the table below.

[0071] Table 2 Sensory Evaluation Criteria for Jam

[0072]

[0073] Table 3 Basic physicochemical properties of different jam samples

[0074]

[0075] Table 4. Rheological properties and coating compatibility of different jam samples

[0076]

[0077] Table 5. Results of color difference tests for different jam samples.

[0078]

[0079] Table 6 Sensory evaluation results of different jam samples

[0080]

[0081] Table 7. Changes in the hardness of sandwich cookies during storage at 25℃

[0082]

[0083] Analysis of beneficial effects:

[0084] 1. Table 3 shows the water activity (a) of Examples 1-3. w The pH value is 0.524-0.586, the soluble solids content is 85.1-89.4 °Brix, the pH value is 3.02-3.18, and the yield stress at 25℃ is 18.2-96.4 Pa, all of which meet the range set by this invention (a). w 0.50-0.60, solids 84-90 °Brix, pH 3.0-3.5, yield stress ≥15 Pa). Comparative Example 1a w Extremely low (0.407), excessively high yield stress (128.3 Pa); Comparative Example 2a w The excessively high (0.621) and excessively low (12.3 Pa) yield stresses are due to insufficient concentration. These differences provide a physicochemical basis for subsequent distinctions in rheological, sensory, and storage properties.

[0085] 2. Table 4 shows that at 50℃ (actual coating temperature) and a shear rate of 10 s⁻¹, the apparent viscosity of Examples 1-3 ranged from 16800 to 32700 mPa·s, the yield stress from 6.2 to 28.4 Pa, and the flow behavior index n from 0.335 to 0.381, all falling within the optimization window. The coating suitability evaluation for all examples was "excellent" (uniform spreading, no overflow, or only slight stringing). Comparative Example 1 had excessively high viscosity (48900 mPa·s) and yield stress (36.7 Pa), and an excessively low n value (0.287), resulting in "uneven spreading and easy material breakage." Comparative Example 2 had excessively low viscosity (8200 mPa·s) and yield stress (3.1 Pa), and an excessively high n value (0.465), resulting in "sandwich overflow and poor shape retention." The results indicate that the rheological parameters determined in this invention at 50℃ are key technical characteristics for industrial continuous coating.

[0086] 3. Examples 1-3 scored ≥9.0 in all five dimensions—color, texture, stickiness, palatability, and flavor—with a total score of 9.30-9.44, significantly better than Comparative Example 1 (6.82 points) and Comparative Example 2 (7.64 points). The main defects of Comparative Example 1 were its extremely low stickiness (4.5 points) and palatability (5.2 points), directly attributed to the pasty texture of the modified starch; Comparative Example 2 scored only 5.0 points in texture, due to its fluid, amorphous structure caused by excessively low yield stress. Table 6 confirms that the formula and process of this patent can significantly improve the oral freshness and overall acceptability of the jam.

[0087] 4. After 50 days of storage, the hardness of the cakes in Examples 1-3 decreased by 6.8%-10.3%, showing a gradual and linear decline, indicating that moisture migration was effectively suppressed. Comparative Example 1 showed a decrease of only 4.1%, exhibiting the most stable storage but at the cost of sensory quality (Table 7); Comparative Example 2 showed a decrease as high as 72.2%, with the hardness dropping to 425.7 g after 28 days, rendering it commercially worthless. These results demonstrate that the a... w The range (0.50-0.60) achieves a synergistic balance between ensuring a 12-month shelf life and maintaining excellent taste.

[0088] 5. Figure 1 This is a distribution of water relaxation time (T2) in jam samples measured by low-field nuclear magnetic resonance. T2 reflects the mobility of water molecules: the smaller the T2 value, the tighter the water binding; the larger the T2 value, the higher the free water content. The main T2 peaks in Examples 1-3 are located in the 10-100 ms range, indicating that the water mainly exists in the form of weakly bound water, with a low proportion of free water. Comparative Example 1... (The sentence is incomplete and ends abruptly.) w In Comparative Example 2, very little free water was observed, and the T2 peak shifted to the left; a significant free water peak (>100 ms) was observed in Comparative Example 2, indicating a high risk of water migration. This result is consistent with that in Table 3a. w The data are consistent with the storage stability in Table 7.

[0089] 6. Figure 2 The spreading diameter of each jam sample was measured after 5g of sample was extruded onto a horizontal glass plate at 25°C under constant pressure (syringe inner diameter 5mm, rate 0.5mL / s) and allowed to stand for 5s. The spreading diameter showed a significant negative correlation with the yield stress at 25°C in Table 3. The spreading diameter of Examples 1-3 was 4-5cm, and the shape was well maintained. Comparative Example 1 experienced extrusion difficulties due to excessively high yield stress (128.3 Pa), while Comparative Example 2 suffered from severe flow due to excessively low yield stress (12.3 Pa). This test directly verifies the necessity of the "yield stress ≥15 Pa at 25°C" set in this invention for maintaining shape at room temperature.

[0090] 7. Figure 3 This is a pseudo-color image of moisture distribution obtained by low-field nuclear magnetic resonance imaging (MRI) after sandwich cookies were stored at 25°C for 50 days. Blue represents low-moisture areas, and red represents high-moisture areas. The cookie portions (edges) of Examples 1-3 remained blue, indicating no significant moisture penetration; the cookie in Comparative Example 1 was dark blue, showing extremely slow moisture migration but poor sensory quality; the cookie edge in Comparative Example 2 showed a distinct red area, indicating a large amount of free water from the jam migrated to the cookie, causing it to soften. This result is consistent with the hardness reduction data in Table 6, further confirming the invention. w The effectiveness of the range (0.50-0.60) in inhibiting water migration.

[0091] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A blueberry jam specifically for sandwich cookies adapted for industrial continuous coating, characterized in that, By weight, the jam comprises the following ingredients: 55-65 parts blueberry puree, 25-35 parts white sugar, 5-15 parts high-fructose corn syrup, 0.3-0.8 parts high-ester pectin with an esterification degree ≥65%, and 0.1-0.5 parts citric acid; the jam does not contain modified starch; the physicochemical indicators are: water activity a w 0.50~0.60, soluble solids 80~90 °Brix.

2. The blueberry jam according to claim 1, characterized in that, The core physicochemical index is: water activity a. w 0.52~0.59, soluble solids 84~90 °Brix, pH 3.0~3.

5.

3. The blueberry jam according to claim 1, characterized in that, The core rheological parameters are divided into: Shape retention index at room temperature: yield stress ≥15Pa at 25 ℃; Industrial coating compatibility index: At an actual production coating temperature of 50℃, 10 s -1 At shear rates, the apparent viscosity is 15000~35000 mPa・s, the yield stress is 5~30 Pa, and the flow behavior index n is 0.33~0.42, exhibiting typical pseudoplastic fluid characteristics.

4. The blueberry jam according to claim 1, 2, or 3, characterized in that, The raw materials also contain food-grade excipients by weight, which are at least one of the following: 0-0.5 parts of edible colloid, 0-3 parts of humectant, 0-0.3 parts of edible flavoring, and 0-0.1 parts of preservative.

5. The blueberry jam according to claim 4, characterized in that, The edible colloid is at least one of carrageenan, xanthan gum, and sodium alginate; the humectant is at least one of glycerin and sorbitol; and the preservative is at least one of potassium sorbate and natamycin.

6. The method for preparing blueberry jam according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Dry material premixing: Mix white sugar and high ester pectin evenly to obtain a mixture; (2) Ingredient mixing: Heat the blueberry puree to 45~50℃, add the mixture from step (1) and fructose syrup while stirring, and continue stirring until the materials are completely dissolved and the system is uniform and free of particles; (3) Concentration and acid adjustment: Heat the mixture from step (2) to 90~100 ℃, stir and concentrate until the soluble solids reach 78~85 °Brix, add citric acid aqueous solution to adjust the pH of the system to 3.0~3.5, continue to concentrate until the soluble solids and water activity meet the standards, and then stop heating; (4) Homogenization and degassing: The concentrated jam is homogenized under a pressure of 15~25 MPa and degassed under vacuum for 5~10 min to ensure that the system is uniform and delicate; thus, blueberry jam suitable for industrial continuous coating of sandwich cookies is obtained.

7. The preparation method according to claim 6, characterized in that, The blueberry pulp has a soluble solids content of 8-12°Brix and a pH of 3.3-3.

8.

8. The preparation method according to claim 6 or 7, characterized in that, The concentration and acid adjustment: The mixture from step (2) is heated to 95~100℃ and stirred and concentrated until the soluble solids reach 82~88 °Brix. Citric acid aqueous solution is added to adjust the pH of the system to 3.0~3.2, and the concentration is continued until the two indicators meet the standards.

9. The preparation method according to claim 6 or 7, characterized in that, The jam obtained in step (4) is then filled and sealed: the jam is filled with hot water when it is cooled to 85~90 ℃, and after sealing, it is sterilized in a water bath at 85±5℃ for 10~15 min, and then cooled to room temperature.

Images