Crispy-outside and crisp-inside reconstituted walnuts and preparation method thereof

Abstract

The invention provides reconstituted walnuts with crispy outside and crispy inside and a preparation method of the reconstituted walnuts. The method comprises the following steps: 1, removing seed coats of walnut kernels, performing three-stage crushing-grading, and respectively preparing compact particles (enzymolysis treatment) with the thickness of 0.3-0.8 mm on the outer layer, porous particles (hot air puffing) with the thickness of 2.5-3 mm on the inner layer and buffer particles with the thickness of 1-1.5 mm on the transition layer; 2, corresponding three-layer slurry is prepared, the outer layer is high in viscosity, the inner layer is low in viscosity, and the transition layer is in gradient connection; 3, quick-freezing for 6 hours at-35 DEG C after three-section type injection molding; 4, performing segmented freeze-drying until the water content is less than 3%; and 5, after low-temperature standing, temperature returning, nitrogen filling and packaging. Through three-stage particle graded modification and a three-layer slurry gradient adaptation technology, a structure system with the outer layer being ultra-fine and dense, the transition layer being medium in buffering and the inner layer being coarse-grained and porous is constructed, differential design of the particle size, the water content and the surface structure is utilized, the slurry viscosity and the auxiliary material proportion are combined, and the effects that the outer portion is crisp, the inner portion is crisp, and the taste is naturally transited in a gradient mode are achieved; the problems that traditional reconstituted walnuts are single in taste and unclear in layering are solved from the structure source.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a reconstituted walnut with a crispy exterior and a crunchy interior, and its preparation method. Background Technology

[0002] Walnuts, as a nutritious nut, are rich in active ingredients such as polyphenols and unsaturated fatty acids, making them highly sought after in the snack food industry. However, the walnut deep processing industry currently suffers from significant shortcomings. Most products remain at the primary processing stage, with a deep processing rate of less than 10%. Product forms are limited and have low added value, failing to meet consumers' demands for diverse and high-quality foods. To enhance product appeal, the industry is gradually attempting to develop multi-layered reconstituted walnut products, enriching the eating experience through different layers of texture and flavor combinations. However, existing technologies still face numerous bottlenecks.

[0003] In terms of structural forming, existing multi-layer reconstituted walnuts mostly adopt a simple layer-by-layer injection molding process, lacking precise design for the particle characteristics and slurry compatibility of each layer. The outer layer is prone to problems such as coarse particles and loose structure, while the inner layer, due to the difficulty in rapid moisture migration, results in either being too hard and gritty after drying or sticky when not fully dried. Furthermore, the lack of an effective buffering and connecting structure between layers makes it easy for delamination or abrupt changes in taste to occur, failing to achieve a smooth gradient of taste. At the same time, the slurry is prone to air bubbles and uneven dispersion during the injection molding process, further affecting the structural stability and appearance quality of the product.

[0004] In terms of process control, traditional processing often employs freeze-drying at a single temperature or vacuum level, without differentiated control based on the dehydration characteristics of the multi-layered structure. High-temperature processing or improper freeze-drying parameters not only destroy the heat-sensitive nutrients in walnuts, leading to a significant loss of active substances such as walnut polyphenols and unsaturated fatty acids, but also cause structural imbalances in the product, resulting in an overly dry and brittle outer layer and a dense, non-crisp inner layer. Furthermore, existing processes lack sufficient control over the product's shelf life, making the finished product prone to absorbing moisture and softening, and making it difficult to maintain a crisp texture for an extended period.

[0005] In summary, existing reconstituted walnut products have significant shortcomings in terms of structural design, process control, and formula optimization, resulting in unclear product taste layers, low retention of nutrients, and poor structural stability. There is an urgent need for a technical solution that can address these issues in a coordinated manner to promote the upgrading and development of the walnut deep processing industry. Summary of the Invention

[0006] The technical problem to be solved: The purpose of this invention is to provide a reconstituted walnut with a crispy exterior and a crunchy interior. Through three-level particle grading modification and three-layer slurry gradient adaptation technology, a structural system is constructed with an ultra-fine outer layer, a medium buffer transition layer, and a coarse-particle porous inner layer. By utilizing the differentiated design of particle size, moisture content, and surface structure, combined with slurry viscosity and auxiliary material ratio, the effect of a crispy exterior and a crunchy interior with a natural transition in taste gradient is achieved. This solves the problem of the single taste and unclear layering of traditional reconstituted walnuts from the root of the structural issue.

[0007] Technical solution: A method for preparing reconstituted walnuts that are crispy on the outside and crunchy on the inside, comprising the following steps: (1) After removing the seed coat from the walnut kernels, use a three-stage crushing and grading process: Preparation of dense outer layer particles: 25-35% of walnut kernels are ultra-finely pulverized to obtain particles with a particle size of 0.3-0.8 mm. They are then dried with hot air at 30-40℃ to a moisture content of 6-8% to obtain dried walnut kernel particles. Subsequently, cellulase solution is added, and the mixture is gently stirred at 40℃ for 10-12 min. After rinsing with water, the mixture is drained. Preparation of porous inner layer particles: 45-55% of walnut kernels are crushed to a particle size of 2.5-3 mm and fed into a hot air puffing machine for processing until 1-3 μm micropores are formed on the particle surface; then, using deionized water as a medium, the particles are centrifuged and sprayed until the moisture content of the particles increases to 12-14%; Preparation of transition layer buffer particles: Crush 15-25% of walnut kernels to a particle size of 1-1.5 mm, air dry at room temperature, and adjust the moisture content to 9-11%; (2) Preparation of three-layer slurry: Outer layer high-viscosity barrier slurry: Add 12-18 kg of outer layer dense particles, 7-9 kg of freeze-dried strawberry powder, 2 kg of xanthan gum, and 0.8-1.1 kg of trehalose to 30 kg of deionized water, and stir for 20 min at 60℃ and 450-550 r / min until the slurry is uniform and free of particles. Cool down to 25℃ for later use. Xanthan gum should be pre-dissolved in 50℃ warm water for 30 min in advance. Inner layer low-viscosity guiding slurry: Add 23-27 kg of inner layer porous particles, 9-11 kg of freeze-dried apple powder, 0.5 kg of guar gum, and 0.3 kg of monoglyceride to 20 kg of deionized water, and stir for 15 min at 50℃ and 800-900 r / min until the micropores have fully absorbed the liquid. Cool to 25℃ for later use; the guar gum should be pre-dissolved in 50℃ warm water for 30 min in advance. Gradient transition layer slurry: Add 8-12 kg of transition layer buffer particles, 5 kg of mixed fruit and vegetable powder, 1 kg of xanthan gum, 0.15-0.25 kg of guar gum, and 0.3-0.4 kg of konjac glucomannan to 15 kg of deionized water, and stir at 55℃ and 600 r / min for 18-20 min to form a gel network structure. Cool to 25℃ for later use. Xanthan gum and guar gum should be pre-dissolved in 50℃ warm water for 30 min in advance. (3) Three-section automatic injection molding machine is used for injection molding: Step 1: Inject 1.4-1.6g of high-viscosity barrier slurry into the outer layer, let it stand for 2 minutes to allow the slurry to spread evenly and form a 2-3mm thick surface layer; Step 2: Inject 0.4-0.6g of low-viscosity guiding slurry into the inner layer, and gently vibrate to ensure tight bonding with the outer layer, forming a 0.5-1mm buffer layer; Step 3: Inject 2.8-3.2g of low-viscosity guiding slurry into the inner layer to avoid air bubbles from entering; Step 4: Place the sample in a -35℃ quick-freezing chamber and quick-freeze for 6 hours until the center temperature of the sample is ≤-25℃ to ensure that each layer of slurry is completely frozen; (4) The pre-frozen sample is sent to a freeze dryer for segmented dehydration until the moisture content is <3%; (5) Transfer to -5℃~0℃ and let stand for 4 hours to complete structural stabilization; then let it naturally warm to room temperature in a clean environment of 25℃ and relative humidity ≤60%, and then fill with nitrogen for packaging.

[0008] Furthermore, in step (1), the amount of cellulase solution added is 0.1-0.15% of the mass of the dried walnut kernels, the enzyme activity of the cellulase solution is 8000U / g-12000U / g, and the mass concentration of the solution is 5-8%.

[0009] Furthermore, the processing conditions in the hot air puffing machine in step (1) are: temperature 45-55℃, wind speed 1.3-1.6m / s, and time 7-10min.

[0010] Furthermore, in step (2), the freeze-dried strawberry powder is 500 mesh and the freeze-dried apple powder is 100 mesh.

[0011] Furthermore, in step (2), the mixed fruit and vegetable powder is strawberry powder and apple powder in a mass ratio of 1:1.

[0012] Furthermore, the vibration frequency of the slight vibration in step (3) is 50Hz, and the mold temperature is maintained at 5-8℃ during the vibration process.

[0013] Furthermore, the segmented dehydration in step (4) specifically involves: First stage (preheating and differentiation period): Vacuum degree set to 65-75 Pa, temperature raised to 18-22℃, maintained for 2-3 hours, outer layer dehydration rate controlled at 0.3-0.4% / h during this stage; The second stage (drying enhancement period): the vacuum degree is reduced to 35-45 Pa, the temperature is raised to 28-32℃ and maintained for 2-3 hours. During this stage, the dehydration rate of the inner layer is increased to 1.0-1.2% / h. The third stage (deep dehydration period): the vacuum degree is maintained at 35-45 Pa, the temperature is raised to 38-42℃ and maintained for 2-3 hours. During this stage, the dehydration rate of the transition layer is stable at 0.7-0.8% / h. Fourth stage (equilibrium and shaping period): maintain vacuum at 35-45 Pa, raise temperature to 48-52℃, and maintain for 30-35 hours.

[0014] The above-mentioned preparation method produces reconstituted walnuts that are crispy on the outside and tender on the inside.

[0015] Furthermore, the reconstituted walnut has a three-layer structure, with the outer layer having a hardness of 1500-1800 g / cm². 2 The inner layer hardness is 2500-3000 g / cm. 2 The hardness of the transition layer is 1800-2500 g / cm. 2 . Beneficial effects

[0016] 1. This invention constructs a structural system with an outer ultra-fine and dense layer, a transitional layer with medium buffer, and an inner coarse and porous layer by using three-level particle grading modification and three-layer slurry gradient adaptation technology. By utilizing the differentiated design of particle size, moisture content, and surface structure, combined with slurry viscosity and auxiliary material ratio, it achieves the effect of crispy outside and crispy inside with a natural transition of taste gradient, solving the problem of monotonous taste and unclear layering of traditional reconstituted walnuts from the structural root. 2. This invention utilizes an inner layer particle hot air expansion treatment technology to form a high-density microporous structure on the particle surface, expanding the moisture evaporation channels. Simultaneously, it is combined with a low-viscosity guiding slurry to accelerate the inner layer moisture migration rate during freeze-drying. The outer layer uses ultrafine particles and a high-viscosity barrier slurry to slow down moisture evaporation. Combined with the buffering effect of the transition layer gel network, it achieves a matching effect of dehydration rates between the inner and outer layers, avoiding the imbalance problem of the outer layer becoming too dry and brittle or the inner layer becoming too dry and sticky. 3. This invention uses cellulase to gently treat the outer layer of particles, degrading some of the fibrous components on the particle surface to form a smooth surface structure. At the same time, it works synergistically with the binding and anti-crystallization effects of trehalose to achieve a delicate and smooth outer layer with a dense structure that is not easily broken, thus improving the smooth experience of reconstituted walnuts in the mouth. 4. This invention utilizes a segmented gradient freeze-drying process to dynamically adjust vacuum and temperature parameters based on the dehydration characteristics of the three-layer structure. This establishes dehydration differences during the preheating differentiation period, amplifies the rate differences during the drying enhancement period, and stabilizes the product structure during the balancing and shaping period. This achieves the dual effect of preserving the porous and crispy structure and heat-sensitive nutrients, ensuring the crispy texture of the inner layer while reducing the oxidative loss of walnut polyphenols and unsaturated fatty acids. 5. This invention achieves a transition layer hardness between the outer and inner layers through the synergistic effect of particle size, slurry viscosity, and functional additives. At the same time, it utilizes the gel network formed by konjac glucomannan to block water migration, thus achieving a tight interlayer bond and a smooth taste without abrupt changes, avoiding the problems of separation between the inner and outer layers or a discontinuous taste. 6. This invention utilizes differentiated addition technology of colloids such as xanthan gum and guar gum. The outer layer has a high proportion of xanthan gum to improve the stability and adhesion of the slurry, while the inner layer has a low proportion of guar gum to ensure particle dispersion. Combined with vibration treatment technology after injection molding, this invention achieves uniform molding of each layer of slurry, resulting in a dense and non-porous structure, thereby improving the product's shape stability and the consistency of its crispness when chewed.

[0017] 7. This invention utilizes low-temperature static setting and gradient temperature recovery technology to promote molecular arrangement stability and slowly release internal structural stress through a low-temperature environment after freeze-drying. Combined with nitrogen-filled packaging to block oxygen and moisture, this results in long-term product structural stability, extended shelf life with crisp texture, and avoids the problems of traditional freeze-dried foods being prone to moisture absorption and deterioration in taste.

[0018] 8. This invention avoids the damage to the nutritional components of walnuts caused by high-temperature processing through the synergistic effect of physical structure optimization and mild process. At the same time, it improves the uniformity of nutrient dispersion by modifying the particles and adapting them to the slurry, thereby maximizing the retention of active ingredients such as walnut polyphenols and unsaturated fatty acids, so that the product has both excellent taste and rich nutritional value. Attached Figure Description

[0019] Figure 1 Comparative images of walnuts prepared in Example 1, Comparative Example 4, and Comparative Example 12 after being stored at room temperature for 3 months. Detailed Implementation

[0020] This invention proposes a reconstituted walnut with a crisp outer layer and a crunchy inner layer, and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following will provide a more detailed description of the invention with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0021] Example 1 A method for preparing a reconstituted walnut with a crispy exterior and crunchy interior includes the following steps: (1) After removing the seed coat from the walnut kernels, use a three-stage crushing and grading process: Preparation of dense outer granules: 30% of walnut kernels were ultra-finely pulverized to obtain particles with a diameter of 0.3-0.8 mm. The particles were then dried with hot air at 35°C until the moisture content was 7.3%, resulting in dried walnut kernel particles. Subsequently, 0.12% (by weight of the dried walnut kernel particles) of a 6% cellulase solution (enzyme activity of 10000 U / g) was added. The mixture was gently stirred at 40°C for 11 min, rinsed with water until neutral, and then drained. Preparation of porous inner layer particles: 50% of walnut kernels were crushed to a particle size of 2.5-3 mm and fed into a hot air puffing machine for processing at a temperature of 50℃, a wind speed of 1.5 m / s, and a time of 8 min, until 1-3 μm micropores were formed on the particle surface; then, using deionized water as a medium, the particles were centrifuged and sprayed until the moisture content of the particles increased to 13%; Preparation of transition layer buffer particles: 20% of walnut kernels were crushed to a particle size of 1-1.5 mm, air-dried at room temperature, and the moisture content was adjusted to 10%; (2) Preparation of three-layer slurry: Outer layer high-viscosity barrier slurry: Add 15kg of outer layer dense particles, 8kg of freeze-dried strawberry powder (500 mesh), 2kg of xanthan gum, and 1.0kg of trehalose to 30kg of deionized water, stir for 20min at 60℃ and 500r / min, and cool to 25℃ for later use. Xanthan gum is pre-dissolved in 50℃ warm water for 30min in advance. Inner layer low-viscosity guiding slurry: Add 25kg of inner layer porous particles, 10kg of freeze-dried apple powder (100 mesh), 0.5kg of guar gum, and 0.3kg of monoglyceride to 20kg of deionized water, stir for 15min at 50℃ and 850r / min, and cool to 25℃ for later use; Guar gum is pre-dissolved in 50℃ warm water for 30min in advance. Gradient transition layer slurry: 10 kg of transition layer buffer particles, 2.5 kg of freeze-dried strawberry powder, 2.5 kg of freeze-dried apple powder, 1 kg of xanthan gum, 0.2 kg of guar gum, and 0.35 kg of konjac glucomannan were added to 15 kg of deionized water and stirred at 55℃ and 600 r / min for 19 min to form a gel network structure. The mixture was then cooled to 25℃ for later use. Xanthan gum and guar gum were pre-dissolved in 50℃ warm water for 30 min beforehand. (3) Three-section automatic injection molding machine is used for injection molding: Step 1: Inject 1.5g of high-viscosity barrier slurry into the outer layer, let it stand for 2 minutes to allow the slurry to spread evenly and form a 2.5mm thick surface layer; Step 2: Inject 0.5g of gradient bonding slurry into the transition layer, and gently vibrate at a frequency of 50Hz. During the vibration process, the mold temperature is maintained at 6℃ to form a 0.8mm buffer layer. Step 3: Inject 3g of low-viscosity guiding slurry into the inner layer; Step 4: Place the sample in a -35℃ quick-freezing chamber and quick-freeze for 6 hours until the center temperature of the sample is ≤-25℃ to ensure that each layer of slurry is completely frozen; (4) The pre-frozen sample is sent to a freeze dryer for segmented dehydration: First stage: Set the vacuum level to 70 Pa, raise the temperature to 20°C, and maintain for 2.5 hours; Second stage: Reduce the vacuum to 40 Pa, raise the temperature to 30 °C, and maintain for 2.5 h; Third stage: Maintain vacuum at 40 Pa, raise temperature to 40 °C, and maintain for 2.5 h; Fourth stage: Maintain vacuum at 40 Pa, raise temperature to 50℃, maintain for 32 hours, until moisture content reaches 2.5%; (5) Transfer to -3℃ and let stand for 4 hours; then allow to naturally warm to room temperature in a clean environment of 25℃ and 55% relative humidity, and package with nitrogen-filled aluminum foil composite film (nitrogen purity 99.95%, residual oxygen rate 0.8%).

[0022] Example 2 The difference between this embodiment and Embodiment 1 is that: (1) The outer layer particles account for 25%, the inner layer particles account for 55%, and the transition layer particles account for 20%; (4) The first stage lasts for 2 hours, the second stage lasts for 2 hours, the third stage lasts for 2 hours, and the fourth stage lasts for 30 hours. Example 3

[0023] The difference between this embodiment and Embodiment 1 is that: (2) The stirring speed of the outer layer slurry is 450 r / min, and the stirring speed of the inner layer slurry is 800 r / min. Example 4

[0024] The difference between this embodiment and Embodiment 1 is that: (1) The inner layer of particles was puffed at 45℃, with a wind speed of 1.3m / s and a processing time of 7min. The moisture content was 12%. The amount of cellulase solution added was 0.1%, the concentration was 5%, and the enzyme activity was 8000U / g. (4) The temperature of the first stage is 18℃, the temperature of the second stage is 28℃, and the temperature of the third stage is 38℃. Example 5

[0025] The difference between this embodiment and Embodiment 1 is that: (1) Cellulase solution addition amount 0.15%, concentration 8%, enzyme activity 12000U / g, stirring for 12min; transition layer particle moisture content 11%; (2) The amount of trehalose used in the outer layer is 0.8 kg, and the amount of konjac glucomannan used in the transition layer is 0.4 kg. Example 6

[0026] The difference between this embodiment and Embodiment 1 is that: (2) Outer layer granules 12kg, freeze-dried strawberry powder 7kg; inner layer granules 23kg, freeze-dried apple powder 9kg; transition layer granules 8kg; (3) The amount of grout injected into the outer layer is 1.2g (to form a 2mm surface layer), the amount of grout injected into the transition layer is 0.4g (to form a 0.5mm buffer layer), and the amount of grout injected into the inner layer is 2.5g. Example 7

[0027] The difference between this embodiment and Embodiment 1 is that: (1) The outer layer drying temperature is 40℃ and the moisture content is 8%; the inner layer particle size is 3.0mm, the puffing temperature is 55℃, the wind speed is 1.6m / s, and the processing time is 10min; (4) The vacuum degree of the first stage is 75 Pa, the vacuum degree of the second stage is 45 Pa, and the temperature of the fourth stage is 52℃ and maintained for 35 h. Example 8

[0028] The difference between this embodiment and Embodiment 1 is that: (3) The temperature of the vibrating mold is maintained at 8℃, and the quick-freezing time is 7h; (5) Low temperature static temperature 0℃, warming environment relative humidity 60%, nitrogen filling packaging nitrogen purity 99.9% and residual oxygen rate 1.0%. Example 9

[0029] The difference between this embodiment and Embodiment 1 is that: (2) 9 kg of outer layer strawberry powder, 11 kg of inner layer apple powder, and 12 kg of transition layer granules; (3) The amount of grout injected into the outer layer is 1.8g (to form a 3mm surface layer), the amount of grout injected into the transition layer is 0.6g (to form a 1mm buffer layer), and the amount of grout injected into the inner layer is 3.5g. Comparative Example 1

[0030] The difference between this comparative example and Example 1 is as follows: (1) The outer layer particles account for 20%, the inner layer particles account for 60%, and the transition layer particles account for 20% (the outer layer has a low proportion); (3) The amount of slurry injected into the outer layer is 1.0g (to form a 1.5mm surface layer). Comparative Example 2

[0031] The difference between this comparative example and Example 1 is as follows: (1) The outer layer particles have a particle size of 1.0-1.2 mm, and the inner layer particles have a particle size of 3.5-4.0 mm; the outer layer is dried at 45℃ with a moisture content of 5%; (2) Freeze-dried strawberry powder 300 mesh, freeze-dried apple powder 150 mesh. Comparative Example 3

[0032] The difference between this comparative example and Example 1 is as follows: (1) The transition layer is eliminated, with the outer layer particles accounting for 40% and the inner layer particles accounting for 60%; (3) The injection molding process involves only two steps: injecting 2.0g of the outer layer slurry and then injecting 4.0g of the inner layer slurry. Comparative Example 4

[0033] The difference between this comparative example and Example 1 is as follows: (1) The inner layer of particles is expanded at a temperature of 60℃, the wind speed is 2.0m / s, and the processing time is 12min; (2) The stirring speed of the inner layer slurry is 1000 r / min. Comparative Example 5

[0034] The difference between this comparative example and Example 1 is as follows: (1) The outer particles are not treated with cellulase; (2) No trehalose is added to the outer layer of the slurry. Comparative Example 6

[0035] The difference between this comparative example and Example 1 is as follows: (1) Add 0.2% cellulase solution at a concentration of 10% and stir for 15 minutes; (2) The amount of xanthan gum used in the outer layer is 3 kg. Comparative Example 7

[0036] The difference between this comparative example and Example 1 is as follows: (2) No xanthan gum was added to the slurry of the outer layer and the transition layer; (3) No vibration treatment is performed after injection molding. Comparative Example 8

[0037] The difference between this comparative example and Example 1 is as follows: (3) The injection sequence is reversed: first inject 3g of inner layer slurry, then inject 0.5g of transition layer slurry, and finally inject 1.5g of outer layer slurry; (4) The temperature of the first stage of freeze drying is 30℃. Comparative Example 9

[0038] The difference between this comparative example and Example 1 is as follows: (3) Quick-freezing temperature -25℃, quick-freezing time 4h; (4) The vacuum level in the first stage is 80 Pa. Comparative Example 10

[0039] The difference between this comparative example and Example 1 is as follows: (4) Eliminate segmented dehydration and maintain freeze drying at 30℃ and 50Pa vacuum for 40h throughout the process; (5) After freeze-drying, the freeze-dried food is brought to room temperature directly without being allowed to stand at low temperature. Comparative Example 11

[0040] The difference between this comparative example and Example 1 is as follows: No konjac glucomannan is added to the transition layer; (5) Low temperature standing temperature 5℃, warming environment relative humidity 70%. Comparative Example 12

[0041] The difference between this comparative example and Example 1 is as follows: (1) The inner layer particles were not subjected to hot air expansion treatment.

[0042] Performance testing: Inner layer porous particle micropore density (pores / cm) 2 The cross-section of the sample was observed using a scanning electron microscope (SEM) at 500x magnification. Three different fields of view were selected, and the number of micropores with a diameter of 1-3 μm in each field of view was counted. The average value per unit area was calculated. Hardness (g / cm) 2 The TA.XTPlus texture analyzer was used, with a P / 50 cylindrical probe, a test speed of 1 mm / s, a compression distance of 5 mm, and a trigger force of 5 g. The central areas of the outer layer, inner layer, and transition layer were selected as test points. Each sample was tested 5 times, and the average value was taken. Walnut polyphenols (mg / 100g): The Folin-phenol colorimetric method was used. The sample was extracted with 70% ethanol by ultrasonication for 30 min (power 200W, temperature 40℃). After centrifugation, the supernatant was collected. After reacting with Folin reagent and sodium carbonate solution, the absorbance was measured at a wavelength of 765nm. A standard curve was plotted with gallic acid as the standard, and the content was calculated. Unsaturated fatty acids (g / 100g): Gas chromatography (GB5009.168-2016) was used. The sample was methylated with potassium hydroxide-methanol solution. The HP-88 capillary column (100m×0.25mm×0.2μm) was used with a programmed column temperature (initial 100℃, hold for 1 min, increase to 240℃ at 10℃ / min, hold for 20 min). Flame ionization detector (FID) was used for detection, and external standard method was used for quantification. Sensory evaluation: A panel of 10 trained professional evaluators conducted blind evaluations according to a unified scoring standard. The evaluation focused on the uniformity and gloss of the color, the crispness of the crunch when chewing, the smoothness of the texture without any grainy feeling in the mouth, the flavor integration of the walnut and fruit and vegetable flavors, and the lack of stickiness of the texture without any stickiness in the mouth after chewing. The average score of the 10 evaluators was taken as the final result. The results are shown in Table 1 below: Table 1 Physical Indicators Inner porous particle micropore density (pieces / cm 2 ​ <![CDATA[Outer hardness (g / cm 2 )]]> <![CDATA[Inner layer hardness (g / cm 2 )]]> <![CDATA[Hardness of the transition layer (g / cm 2 )]]> Example 1 <![CDATA[1.2×10 5 ]]> 1685 2723 2187 Example 2 <![CDATA[1.1×10 5 ]]> 1724 2815 2232 Example 3 <![CDATA[1.2×10 5 ]]> 1631 2688 2056 Example 4 <![CDATA[0.9×10 5 ]]> 1706 2564 2083 Example 5 <![CDATA[1.3×10 5 ]]> 1753 2709 2128 Example 6 <![CDATA[1.2×10 5 ]]> 1617 2652 2014 Example 7 <![CDATA[1.4×10 5 ]]> 1738 2861 2325 Example 8 <![CDATA[1.2×10 5 ]]> 1642 2735 2139 Example 9 <![CDATA[1.2×10 5 ]]> 1679 2794 2267 Comparative Example 1 <![CDATA[1.2×10 5 ]]> 1863 2927 2415 Comparative Example 2 <![CDATA[1.0×10 5 ]]> 1926 3154 2538 Comparative Example 3 <![CDATA[1.2×10 5 ]]> 1729 2836 - Comparative Example 4 <![CDATA[0.7×10 5 ]]> 1668 2429 2027 Comparative Example 5 <![CDATA[1.2×10 5 ]]> 2034 2768 2219 Comparative Example 6 <![CDATA[1.3×10 5 ]]> 1428 2715 1863 Comparative Example 7 <![CDATA[1.2×10 5 ]]> 1519 2663 1964 Comparative Example 8 <![CDATA[1.2×10 5 ]]> 2725 1618 2117 Comparative Example 9 <![CDATA[1.1×10 5 ]]> 1697 2513 2019 Comparative Example 10 <![CDATA[1.0×10 5 ]]> 1815 2318 2067 Comparative Example 11 <![CDATA[1.2×10 5 ]]> 1769 2614 2213 Comparative Example 12 <![CDATA[0.3×10 5 ]]> 1665 3208 2256 As shown in Table 1, the micropore density of the inner layer porous particles in Examples 1-9 was maintained at 0.9 × 10⁻⁶. 5 -1.4×10 5 pcs / cm 2 The outer layer hardness is 1617-1753 g / cm. 2 The inner layer hardness is 2564-2861 g / cm. 2 The hardness of the transition layer is 2014-2325 g / cm. 2 The material exhibits a gradient distribution of "moderate hardness in the outer layer, higher hardness in the inner layer, and hardness in the transition layer between the two," which aligns with the design objective of this invention for a "crispy on the outside and tender on the inside" structure. Specifically, the micropore density of Example 1 is 1.2 × 10⁻⁶. 5 pcs / cm 2 The hardness of the three layers is 1685 g / cm. 2 2723g / cm 2 2187g / cm 2 The gradient transition is smooth. In contrast, the inner layer hardness of Comparative Examples 2 and 12 exceeds 3150 g / cm². 2 Too hard and uncomfortable to chew; comparative examples 6 and 7 have an outer layer hardness of less than 1520 g / cm. 2 The sample was too soft and lacked crispness; in Comparative Example 8, due to the reversed injection molding order, the outer layer hardness was 2725 g / cm³. 2 ) is much higher than the inner layer (1618g / cm) 2 The texture of the sample was reversed; in Comparative Example 3, the transition layer was removed, and a gradient transition in hardness could not be achieved.

[0043] Table 2 Nutritional Indicators Walnut polyphenols (mg / 100g) Unsaturated fatty acids (g / 100g) Example 1 186 62.5 Example 2 178 61.8 Example 3 183 63.2 Example 4 172 60.5 Example 5 192 64.1 Example 6 175 61.2 Example 7 180 62.3 Example 8 188 63.5 Example 9 181 62.8 Comparative Example 1 165 59.8 Comparative Example 2 158 58.2 Comparative Example 3 170 60.1 Comparative Example 4 142 56.7 Comparative Example 5 153 57.5 Comparative Example 6 160 58.8 Comparative Example 7 155 57.9 Comparative Example 8 162 59.3 Comparative Example 9 157 58.5 Comparative Example 10 148 57.1 Comparative Example 11 163 59.6 Comparative Example 12 171 60.8 As shown in Table 2, the walnut polyphenol content of Examples 1-9 was 172-192 mg / 100g, and the unsaturated fatty acid content was 60.5-64.1 g / 100g. Both nutritional indicators remained at a high level. Among them, the walnut polyphenol (192 mg / 100g) and unsaturated fatty acid (64.1 g / 100g) content of Example 5 were the highest. The two indicators of Example 1 were 186 mg / 100g and 62.5 g / 100g, respectively, showing a balanced performance. Comparative Example 4 had the lowest content of walnut polyphenols (142mg / 100g) and unsaturated fatty acids (56.7g / 100g) due to the excessively high inner layer puffing temperature (60℃). Comparative Example 10 had only 148mg / 100g and 57.1g / 100g for the two indicators, respectively, due to the lack of a segmented freeze-drying process. The remaining comparative examples all had a 5%-15% decrease in nutrient retention rate due to deviations in raw material processing, formulation, or process parameters. It can be seen that the method of the present invention has a good protective effect on heat-sensitive nutrients.

[0044] Table 3 Sensory Evaluation Appearance and color (2 points) Crispyness (3 points) Fineness (2 points) Flavor integration (2 points) No sticky feeling on teeth (1 point) Total score (10 points) Example 1 1.9 2.8 1.8 1.9 1 9.3 Example 2 1.8 2.7 1.7 1.8 1 8.9 Example 3 1.9 2.8 1.8 1.8 1 9.1 Example 4 1.7 2.5 1.7 1.7 0.9 8.6 Example 5 1.9 2.8 1.8 1.9 1 9 Example 6 1.8 2.7 1.7 1.8 0.9 8.8 Example 7 1.8 2.6 1.6 1.7 0.9 8.4 Example 8 1.9 2.8 1.8 1.9 1 9.2 Example 9 1.8 2.7 1.7 1.8 0.9 8.9 Comparative Example 1 1.6 2 1.3 1.5 0.5 6.4 Comparative Example 2 1.5 1.8 1 1.4 0.4 5.7 Comparative Example 3 1.6 2.1 1.2 1.2 0.3 5.1 Comparative Example 4 1.4 1.7 1.3 1.1 0.6 6.1 Comparative Example 5 1.5 1.9 1.1 1.4 0.6 6.7 Comparative Example 6 1.5 1.6 1.2 1.5 0.4 5.8 Comparative Example 7 1.4 1.7 1.1 1.3 0.4 5.9 Comparative Example 8 1.5 1.2 1.3 1.4 0.3 4.4 Comparative Example 9 1.5 1.8 1.2 1.4 0.5 6.2 Comparative Example 10 1.4 1.6 1.1 1.3 0.4 5.4 Comparative Example 11 1.6 1.9 1.3 1.5 0.6 6.5 Comparative Example 12 1.6 1.5 1.3 1.6 0.4 4.7 As shown in Table 3, the sensory scores of Examples 1-9 all ranged from 8.4 to 9.3, demonstrating excellent overall performance: Appearance and color scores were 1.7-1.9, indicating uniform and glossy color; crispness scores were 2.5-2.8, indicating a noticeable crispness during chewing; delicacy scores were 1.6-1.8, indicating no rough or grainy texture in the mouth; flavor integration scores were 1.7-1.9, indicating a harmonious blend of walnut and fruit / vegetable flavors; and the absence of stickiness scores were 0.9-1.0, indicating minimal oral residue. Example 1 ranked first with a score of 9.3, demonstrating balanced and outstanding scores across all sub-categories. The sensory scores of the comparative examples were only 4.4-6.7 points, significantly lower than those of the examples: Comparative example 8 had a crispness score of only 1.2 points due to the reversed texture; Comparative example 3 had a flavor integration score of only 1.2 points due to the lack of a transition layer; Comparative example 12 had a crispness score of only 1.5 points due to the lack of puffing treatment in the inner layer. Most of the comparative examples had problems such as insufficient delicacy and obvious stickiness. It can be seen that the "crispy on the outside and crispy on the inside" texture is the most reasonable and popular.

[0045] The walnuts prepared in Example 1, Comparative Example 4, and Comparative Example 12 were stored at room temperature for 3 months, then photographed. The results are as follows. Figure 1 As shown.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A process for preparing an extracrispy, intracrispy reconstituted walnut, characterized in that: The method comprises the following steps: (1) After removing the kernel shell, three-stage crushing and grading are performed: Preparation of outer dense particles: 25-35% of the walnut kernels are ultra-finely crushed to obtain particles with a particle size of 0.3-0.8 mm, and hot air drying is performed at 30-40 ℃ until the water content is 6-8%, to obtain dried walnut kernel particles; then, a cellulase solution is added, and gentle stirring is performed at 40 ℃ for 10-12 min, and then the particles are washed with clean water and drained; Preparation of inner porous particles: 45-55% of the walnut kernels are crushed to a particle size of 2.5-3 mm, and then fed into a hot air puffing machine, and then centrifugal spraying is performed in deionized water until the water content of the particles is increased to 12-14%; Preparation of transition layer buffer particles: 15-25% of the walnut kernels are crushed to a particle size of 1-1.5 mm, and then air-dried at room temperature, and the water content is adjusted to 9-11%; (2) Preparation of three-layer slurry: Outer high-viscosity barrier slurry: 12-18 kg of outer dense particles, 7-9 kg of freeze-dried strawberry powder, 2 kg of xanthan gum, and 0.8-1.1 kg of trehalose are added to 30 kg of deionized water, and stirring is performed at 60 ℃ and 450-550 r / min for 20 min until the slurry is uniform and free of particles, and then cooled to 25 ℃ for standby; Inner low-viscosity flow guide slurry: 23-27 kg of inner porous particles, 9-11 kg of freeze-dried apple powder, 0.5 kg of guar gum, and 0.3 kg of monoglyceride are added to 20 kg of deionized water, and stirring is performed at 50 ℃ and 800-900 r / min for 15 min, and then cooled to 25 ℃ for standby; Transition layer gradient connection slurry: 8-12 kg of transition layer buffer particles, 5 kg of mixed fruit and vegetable powder, 1 kg of xanthan gum, 0.15-0.25 kg of guar gum, and 0.3-0.4 kg of konjac glucomannan are added to 15 kg of deionized water, and stirring is performed at 55 ℃ and 600 r / min for 18-20 min, and then cooled to 25 ℃ for standby; (3) Injection molding is performed using a three-stage automatic injection molding machine: First step: inject the outer high-viscosity barrier slurry, and stand for 2 min to evenly spread the slurry, to form a 2-3 mm thick surface layer; Second step: inject the inner low-viscosity flow guide slurry, and slightly shake to form a 0.5-1 mm buffer layer; Third step: inject the inner low-viscosity flow guide slurry to avoid air bubbles; Fourth step: send to a-35 ℃ quick-freezing library, and quick-freeze for 6 h until the center temperature of the sample is ≤-25 ℃; (4) The pre-frozen sample is sent to a freeze dryer for staged dehydration until the water content is <3%; (5) Transfer to-5 ℃-0 ℃ and stand for 4 h, and then naturally warm to room temperature in a clean environment at 25 ℃ and a relative humidity of ≤60%, and then nitrogen-packing is performed to obtain the product.

2. A process for the preparation of an outer crisp and inner crunchy reconstituted walnut according to claim 1, characterized in that: In step (1), the cellulase solution is added in an amount of 0.1-0.15% of the mass of the dried walnut kernel particles, and the enzyme activity of the cellulase solution is 8000 U / g-12000 U / g, and the solution mass concentration is 5-8%.

3. A process for preparing an outer crisp and inner crunchy reconstituted walnut according to claim 1, characterized in that: In step (1), the hot air puffing machine is operated at a temperature of 45-55 ℃, a wind speed of 1.3-1.6 m / s, and a time of 7-10 min.

4. The method of making an extracrispy, intracrispy reconstituted walnut of claim 1, wherein: In step (2), the freeze-dried strawberry powder is 500 mesh, and the freeze-dried apple powder is 100 mesh.

5. The method of making an extracrispy intracrispy reconstituted walnut of claim 1, wherein: The mixing of the fruit and vegetable powder in step (2) is strawberry powder and apple powder at a mass ratio of 1:

1.

6. A process for preparing an outer crisp and inner crunchy reconstituted walnut according to claim 1, characterized by: The frequency of the slight vibration in step (3) is 50 Hz, and the temperature of the mold is maintained at 5-8 ℃ during the vibration.

7. A process for preparing an outer- crunchy and inner- crispy reconstituted walnut according to claim 1, characterized in that: The stepwise dehydration in step (4) is as follows: First stage: the vacuum degree is set to 65-75 Pa, the temperature is raised to 18-22 ℃, and maintained for 2-3 h; Second stage: the vacuum degree is reduced to 35-45 Pa, the temperature is raised to 28-32 ℃, and maintained for 2-3 h; Third stage: the vacuum degree is maintained at 35-45 Pa, the temperature is raised to 38-42 ℃, and maintained for 2-3 h; Fourth stage: the vacuum degree is maintained at 35-45 Pa, the temperature is raised to 48-52 ℃, and maintained for 30-35 h.

8. The outer-crispy and inner-fragile reconstituted walnut prepared by the preparation method according to any one of claims 1-7.

9. The extruded and puffed restructured walnut kernel of claim 8, wherein: The reconstituted walnut has a three-layer structure, the outer layer has a hardness of 1500-1800 g / cm 2 , the inner layer has a hardness of 2500-3000 g / cm 2 , and the transition layer has a hardness of 1800-2500 g / cm 2 .

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