Formula and preparation process of walnut powder

Abstract

The invention relates to the technical field of food processing, and discloses a formula and a preparation technology of walnut powder, and the walnut powder comprises the following components by weight: 30-40 parts of walnut kernel; 40 to 50 parts of maltodextrin; 10 to 15 parts of white granulated sugar; 0.3 to 0.5 part of sucrose fatty acid ester; 0.1 to 0.2 part of xanthan gum; 0.05 to 0.1 part of guar gum; the preparation process comprises the following steps: pretreating the raw materials; performing oxygen-controlled grinding and pulping; carrying out enzyme activity passivation; proportioning and mixing; performing high-pressure homogenization; performing sterilization; and spray drying. According to the method, a dual pretreatment scheme of oxygen-controlled grinding and enzyme activity passivation is adopted, the walnut kernels are protected by inert gas in the initial stage of grinding and crushing, then endogenous enzymes are inactivated through specific heat treatment, the generation way of rancious flavor substances is blocked from the physical and biochemical dimensions, and the inherent fresh flavor of the walnuts is reserved to the maximum extent.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, in particular to a formula of walnut powder and a preparation process thereof. Background Art

[0002] Walnuts are rich in nutrients and their unique flavor is beloved by consumers. To adapt to modern, fast-paced lifestyles, processing walnuts into ready-to-use walnut powder has become an important further processing method. This product form not only improves convenience but also opens up broader application possibilities for walnuts in dairy, baking, and solid beverages.

[0003] Existing technologies have explored the production of walnut powder. For example, some processes begin by screening and washing the walnut kernels and removing the seed coat through methods such as blanching with alkali. This, to a certain extent, reduces the astringency of the final product caused by tannins. Subsequent processing, standard pasteurization or high-temperature sterilization steps ensure the microbiological safety of the product. Furthermore, some preparation methods add a single type of thickener to provide basic suspending properties.

[0004] However, the existing technical solutions still have significant deficiencies in solving the core problem of walnut powder quality deterioration. First, the high content of polyunsaturated fatty acids in walnut kernels makes them extremely easy to oxidize. During the grinding and crushing stage, the material is fully exposed to the air, and the mechanical heat and oxygen work together to easily induce the self-oxidation reaction of fat. At the same time, the endogenous enzyme activities such as lipase and lipoxygenase contained in the walnut kernel itself have not been timely and effectively passivated in the traditional processing flow, and continue to catalyze the quality deterioration reaction, resulting in the product being prone to producing a rancid taste during storage; secondly, the texture and stability of the product are also not ideal. The stabilizer dry powder is directly added to the complex liquid system, and its hydration process is often inhibited, making it difficult to form an effective colloidal network structure, which makes the final product have a rough taste after reconstitution and is accompanied by the phenomenon of rapid sedimentation of solids; finally, these process steps are often isolated and non-systematic, and fail to consider flavor preservation, texture optimization and physical and chemical stability control as a whole, resulting in the difficulty of achieving a higher level of comprehensive product quality. For this reason, those skilled in the art propose a formula of walnut powder and its preparation process to solve the above problems. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a formula of walnut powder and a preparation process thereof, which solves the problems in the existing technology of walnut powder causing flavor deterioration due to fat oxidation and enzymatic reaction, and rough taste and poor suspension stability after brewing due to poor construction of the stabilizer system.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] A first aspect of the present invention provides walnut powder.

[0008] The walnut powder is prepared from the following raw materials in parts by weight: 30-40 parts of walnut kernels; 40-50 parts of maltodextrin; 10-15 parts of white granulated sugar; 0.3-0.5 parts of sucrose fatty acid ester; 0.1-0.2 parts of xanthan gum; and 0.05-0.1 parts of guar gum.

[0009] The mechanism of action of the components of the walnut powder is as follows:

[0010] Walnut kernels are the core ingredient that provides the product's characteristic flavor, protein, and fat. In one specific technical solution, the walnut kernels are peeled and color-protected. Removing the walnut seed coat reduces the astringent content in the final product, while color-protection treatment inhibits browning during processing.

[0011] Maltodextrin acts as an excipient and drying carrier to embed walnut oil droplets and flavor substances during the spray drying process and improve the fluidity and solubility of the final powder.

[0012] Sucrose fatty acid ester is an emulsifier. Its molecular structure has both hydrophilic and lipophilic groups, which can form an interfacial film at the oil-water interface, reduce the oil-water interfacial tension, and make the fat in the walnut stably dispersed in the aqueous phase in the form of small oil droplets.

[0013] Xanthan gum and guar gum are used as composite stabilizers. Xanthan gum is a microbial polysaccharide with a rigid molecular backbone that can form a three-dimensional network in solution, providing a high yield value and effectively suspending solid particles.

[0014] Guar gum is a galactomannan whose molecular chains interact synergistically with xanthan gum chains, enhancing the strength and stability of the three-dimensional network. The combination of the two creates a stable and synergistic colloidal network in the liquid phase, preventing the aggregation of oil droplets and the sedimentation of solids.

[0015] A second aspect of the present invention provides a process for preparing the walnut powder.

[0016] The process includes the following steps:

[0017] S1. Raw material pretreatment: peeling and color protection treatment of walnut kernels;

[0018] S2, oxygen-controlled grinding and pulping: grinding the obtained walnut kernels and water with a colloid mill under the protection of an inert gas to obtain walnut pulp;

[0019] S3, enzyme inactivation: heating the walnut puree through a plate heat exchanger or a jacketed kettle;

[0020] S4, batching and mixing: mixing the walnut pulp that has undergone enzyme inactivation treatment with maltodextrin, white sugar, sucrose fatty acid ester, xanthan gum and guar gum to obtain a liquid to be treated;

[0021] S5, high-pressure homogenization: subjecting the liquid to be treated to high-pressure homogenization through a high-pressure homogenizer;

[0022] S6. Sterilization: Sterilize the homogenized liquid through ultra-high temperature instantaneous sterilization equipment;

[0023] S7, spray drying: spray drying the sterilized liquid through a spray drying tower to obtain walnut powder.

[0024] In a specific technical solution, the steps of the above preparation process are further defined as follows:

[0025] In step S1, the specific operation of raw material pretreatment is: placing the walnut kernel in a sodium carbonate solution with a concentration of 1-2% (w / v) and treating it at 85-95°C for 1-3 minutes to soften the walnut seed coat and make it easy to remove; after peeling, placing the walnut kernel in a citric acid solution with a concentration of 0.1% (w / v) for color protection treatment to inhibit the activity of polyphenol oxidase.

[0026] In step S2, oxygen-controlled grinding and pulping are performed by continuously introducing nitrogen into the colloid mill's sealed chamber before starting the mill and throughout the grinding process. This step physically displaces oxygen from the grinding system, creating a low-oxygen environment for the polyunsaturated fatty acid-rich walnut kernels, thereby inhibiting oxidation during the crushing and shearing process.

[0027] In step S3, the specific heat treatment conditions for enzyme inactivation are: heating the walnut puree to 85-95°C and maintaining this temperature for 2-5 minutes. This step aims to use a specific temperature and time combination to irreversibly denature and inactivate endogenous enzymes such as lipase and lipoxygenase naturally present in the walnut kernel, thereby preventing them from catalyzing fat hydrolysis or oxidation during subsequent processing and product storage, which could produce unpleasant flavors.

[0028] Prior to the batching and mixing of step S4, the method also includes preparing a stabilizer activation mother solution. This step involves premixing the formulated amounts of xanthan gum and guar gum in a dry state, then adding the mixed colloidal powder to 60-70°C hot water while simultaneously applying high-speed shear and stirring until the molecular chains of the xanthan gum and guar gum are fully stretched and dissolved by the heat and mechanical energy, forming a uniform colloidal solution. Preparing the stabilizer activation mother solution ensures that the two hydrocolloids form a fully hydrated, synergistic structure before entering the complex feed liquid system, allowing them to more effectively perform their thickening and emulsification stabilization functions in the final feed liquid.

[0029] In step S5, the pressure of the high-pressure homogenizer is set to 20-25 MPa for the first homogenization stage and 5-10 MPa for the second homogenization stage. This pressure setting can break down the fat globules in the liquid into micron-sized pieces, increasing the total surface area and facilitating the formation of a strong interface film between the emulsifier and stabilizer.

[0030] In step S6, the ultrahigh temperature instantaneous sterilization equipment uses sterilization parameters of 135-140°C and a dwell time of 4-6 seconds. This step is an independent sterilization process following the enzyme inactivation step. Its purpose is to kill any microorganisms that may be present in the feed solution, achieving commercial sterility requirements and ensuring the shelf life of the product. Ultrahigh temperature instantaneous sterilization achieves sterilization while minimizing the effects of heat treatment on the color, flavor, and nutritional content of the product.

[0031] In step S7, the spray drying tower process parameters are set to: an inlet air temperature of 160-180°C and an outlet air temperature of 80-90°C. This parameter combination ensures that the water in the liquid droplets evaporates quickly to form a dry powder, while also preventing excessive Maillard reaction or caramelization of the material due to excessive temperatures or prolonged heating.

[0032] The present invention provides a formula of walnut powder and a preparation process thereof. It has the following beneficial effects:

[0033] 1. The present invention adopts a dual pretreatment scheme of oxygen-controlled grinding and enzyme inactivation. The walnut kernels are protected by inert gas in the initial stage of grinding and crushing, and then the endogenous enzymes are inactivated through specific heat treatment, which blocks the generation pathway of rancid odor substances from both physical and biochemical dimensions, retaining the inherent fresh flavor of walnuts to the maximum extent. This solves the problem that the existing technology usually relies on a single heat treatment in the subsequent sterilization process, which cannot effectively inhibit the oxidation and enzymatic reactions that occur at the moment of raw material crushing, resulting in the product being prone to odor and insufficient shelf stability.

[0034] 2. Another innovation of the present invention lies in the construction method of the stabilizer system. Xanthan gum and guar gum are first prepared into an activated mother liquor. The activated mother liquor can play a role more efficiently in the subsequent ingredients, constructing a uniform and dense emulsified network structure. The product has good suspension stability after dispensing and has a delicate and smooth taste. Compared with the mixing method of directly adding colloid dry powder into the liquid in the prior art, the present invention solves the technical problems of uneven colloid dispersion and insufficient hydration, and avoids the stratification, precipitation and rough taste that are easy to occur in the final product after dispensing.

[0035] 3. The present invention provides a set of interconnected systematic processes, from alkaline liquid peeling and acid color protection of raw materials, to oxygen control and enzyme inactivation during processing, and finally to independent high-temperature sterilization. The synergistic effect of multiple technical points comprehensively improves the overall quality of the final product, and solves the problem that traditional processes often use partial processing methods in isolation, for example, only peeling or only sterilization, ignoring the complexity and linkage of walnut powder quality deterioration, and failing to fundamentally solve the problem, resulting in defects in product color, flavor, stability and other aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the preparation process of the present invention. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] The sources and specifications of the main raw materials and reagents used in the following examples and comparative examples are as follows. Reagents not specifically specified are all commercially available products of analytical grade or higher.

[0039] Walnut kernel: food grade, complete and mold-free.

[0040] Maltodextrin: food grade, DE value 10-15; CAS number: 9050-36-6.

[0041] White sugar: food grade, main ingredient is sucrose; CAS number: 57-50-1.

[0042] Sucrose fatty acid ester: food grade, HLB value 11-15; CAS number: 37318-31-3.

[0043] Xanthan gum: food grade, 80 mesh; CAS number: 11138-66-2.

[0044] Guar gum: food grade; CAS number: 9000-30-0.

[0045] Sodium carbonate: analytical grade, anhydrous; CAS number: 497-19-8.

[0046] Citric acid: analytical grade, anhydrous; CAS number: 77-92-9.

[0047] Nitrogen: Food grade, purity ≥99.9%; CAS number: 7727-37-9.

[0048] Please see the attached Figure 1 :

[0049] Example

[0050] Example 1:

[0051] A preparation process of walnut powder, the specific steps are as follows:

[0052] 1. Raw material preparation: Weigh 30 parts of walnut kernels, 40 parts of maltodextrin, 10 parts of white sugar, 0.3 parts of sucrose fatty acid ester, 0.1 parts of xanthan gum, and 0.05 parts of guar gum.

[0053] 2. Raw Material Pretreatment: Place 30 parts of walnut kernels in a 1% (w / v) sodium carbonate aqueous solution at 85°C for 1 minute, then rinse with clean water to remove the seed coat. Immerse the peeled walnut kernels in a 0.1% (w / v) citric acid aqueous solution for 5 minutes to preserve color, then remove and drain.

[0054] 3. Oxygen-controlled grinding and pulping: Place the pretreated walnut kernels and 120 parts of drinking water (solid-to-liquid ratio 1:4) into a colloid mill. Continuously introduce nitrogen into the mill chamber before starting the equipment and throughout the grinding process. This produces walnut pulp.

[0055] 4. Enzyme inactivation: Pump the walnut pulp into the double-layer pot, heat it to 85℃, and maintain the temperature for 2 minutes. After treatment, cool the pulp to 60℃ for later use.

[0056] 5. Preparation of stabilizer mother liquor and mixing of ingredients: Dry mix 0.1 parts xanthan gum and 0.05 parts guar gum. Add the mixed colloidal powder to 60°C hot water and stir under high shear for 15 minutes to prepare the stabilizer activation mother liquor. Pump in the enzyme-activated walnut pulp into the batching tank, followed by 40 parts maltodextrin, 10 parts white sugar, and 0.3 parts sucrose fatty acid ester. Finally, pump in the prepared stabilizer activation mother liquor and stir at 60°C for 15 minutes to obtain the feed solution to be treated.

[0057] 6. High-pressure homogenization: Pump the liquid to be treated into the high-pressure homogenizer, set the first-level homogenization pressure to 20MPa and the second-level homogenization pressure to 5MPa for homogenization.

[0058] 7. Sterilization: Pass the homogenized liquid through UHT equipment and treat it at 135℃ for 4 seconds.

[0059] 8. Spray drying: Pump the sterilized liquid into the spray drying tower, set the inlet air temperature to 160℃ and the outlet air temperature to 90℃, and perform spray drying to obtain the walnut powder product.

[0060] Example 2:

[0061] A preparation process of walnut powder, the specific steps are as follows:

[0062] 1. Raw material preparation: Weigh 35 parts of walnut kernels, 45 parts of maltodextrin, 12.5 parts of white sugar, 0.4 parts of sucrose fatty acid ester, 0.15 parts of xanthan gum, and 0.075 parts of guar gum.

[0063] 2. Raw Material Pretreatment: 35 parts of walnut kernels were placed in a 1.5% (w / v) sodium carbonate aqueous solution at 90°C for 2 minutes, then rinsed with clean water to remove the seed coat. The peeled walnut kernels were immersed in a 0.1% (w / v) citric acid aqueous solution for 8 minutes to preserve color, then removed and drained.

[0064] 3. Oxygen-controlled grinding and pulping: Place the pretreated walnut kernels and 140 parts of drinking water (solid-to-liquid ratio 1:4) into a colloid mill. Continuously flow nitrogen into the mill chamber before starting the equipment and throughout the grinding process. After grinding, obtain walnut pulp.

[0065] 4. Enzyme inactivation: Pump the walnut pulp into the double-layer pot, heat it to 90℃, and maintain the temperature for 3.5 minutes. After treatment, cool the pulp to 65℃ for later use.

[0066] 5. Preparation of stabilizer mother liquor and mixing of ingredients: Dry mix 0.15 parts xanthan gum and 0.075 parts guar gum. Add the mixed colloidal powder to 65°C hot water and stir under high shear for 18 minutes to prepare the stabilizer activation mother liquor. Pump in the enzyme-activated walnut pulp into the batching tank, followed by 45 parts maltodextrin, 12.5 parts white sugar, and 0.4 parts sucrose fatty acid ester. Finally, pump in the prepared stabilizer activation mother liquor and stir at 65°C for 18 minutes to obtain the feed solution to be treated.

[0067] 6. High-pressure homogenization: Pump the liquid to be treated into the high-pressure homogenizer, set the first-level homogenization pressure to 22.5MPa and the second-level homogenization pressure to 7.5MPa for homogenization.

[0068] 7. Sterilization: Pass the homogenized liquid through UHT equipment and treat it at 137℃ for 5 seconds.

[0069] 8. Spray drying: Pump the sterilized liquid into the spray drying tower, set the inlet air temperature to 170℃ and the outlet air temperature to 85℃, and perform spray drying to obtain the walnut powder product.

[0070] Example 3:

[0071] A preparation process of walnut powder, the specific steps are as follows:

[0072] 1. Raw material preparation: Weigh 40 parts of walnut kernels, 50 parts of maltodextrin, 15 parts of white sugar, 0.5 parts of sucrose fatty acid ester, 0.2 parts of xanthan gum, and 0.1 parts of guar gum.

[0073] 2. Raw Material Pretreatment: Place 40 parts of walnut kernels in a 2% (w / v) sodium carbonate aqueous solution at 95°C for 3 minutes, then rinse with clean water to remove the seed coat. Immerse the peeled walnut kernels in a 0.1% (w / v) citric acid aqueous solution for 10 minutes to protect the color, then remove and drain.

[0074] 3. Oxygen-controlled grinding and pulping: Place the pretreated walnut kernels and 160 parts of drinking water (solid-to-liquid ratio 1:4) into a colloid mill. Continuously introduce nitrogen into the mill chamber before starting the equipment and throughout the grinding process. After grinding, obtain walnut pulp.

[0075] 4. Enzyme inactivation: Pump the walnut pulp into the double-layer pot, heat it to 95℃, and maintain the temperature for 5 minutes. After treatment, cool the pulp to 70℃ for later use.

[0076] 5. Preparation of stabilizer mother liquor and mixing of ingredients: Dry mix 0.2 parts xanthan gum and 0.1 parts guar gum. Add the mixed colloidal powder to 70°C hot water and stir under high shear for 20 minutes to prepare the stabilizer activation mother liquor. Pump the enzyme-activated walnut pulp into the batching tank, followed by 50 parts maltodextrin, 15 parts white sugar, and 0.5 parts sucrose fatty acid ester. Finally, pump in the prepared stabilizer activation mother liquor and stir at 70°C for 20 minutes to obtain the feed solution to be treated.

[0077] 6. High-pressure homogenization: Pump the liquid to be treated into the high-pressure homogenizer, set the first-level homogenization pressure to 25MPa and the second-level homogenization pressure to 10MPa for homogenization.

[0078] 7. Sterilization: Pass the homogenized liquid through UHT equipment and treat it at 140℃ for 6 seconds.

[0079] 8. Spray drying: Pump the sterilized liquid into the spray drying tower, set the inlet air temperature to 180℃ and the outlet air temperature to 80℃, and perform spray drying to obtain the walnut powder product.

[0080] Comparative Example 1: Compared to the preparation process of Example 2, the difference is that in step 3, oxygen-controlled grinding and pulping, grinding is performed under natural air conditions, and nitrogen is not introduced into the colloid mill chamber. The remaining raw material ratios, steps, and process parameters are the same as those of Example 2.

[0081] Comparative Example 2: Compared to the preparation process of Example 2, the difference is that step 4) enzyme inactivation treatment is omitted, and after the walnut pulp is prepared, step 5) ingredient mixing is directly performed. The remaining raw material ratios, steps, and process parameters are the same as those of Example 2.

[0082] Comparative Example 3: Compared to the preparation process of Example 2, the difference is that in step 5) of mixing ingredients, 0.15 parts of xanthan gum and 0.075 parts of guar gum powder were directly added to the mixing tank along with the other dry ingredients for mixing, and the preparation of the stabilizer activation mother solution was not performed. The remaining raw material ratios, steps, and process parameters were the same as those of Example 2.

[0083] Comparative Example 4: Compared with the preparation process of Example 2, the difference is that in the raw material preparation, only 0.225 parts of xanthan gum is used as the stabilizer, and guar gum is not used to ensure that the total gum content is consistent with that of Example 2. The remaining component amounts, preparation steps and process parameters are the same as those of Example 2.

[0084] Test Example 1:

[0085] 1. Test method:

[0086] This test was designed to evaluate the oxidative stability of the obtained walnut flour samples under accelerated conditions.

[0087] (1) Sample preparation and packaging: Take 50 g of each of the nuclear powder samples prepared in Examples 1-3 and Comparative Examples 1-2, place them in aluminum-plastic composite film packaging bags, evacuate them, fill them with nitrogen, and seal them.

[0088] (2) Accelerated storage: All packaged samples were placed in a constant temperature and humidity chamber at a temperature of 37°C and a relative humidity of 75% for accelerated storage. The storage period was 30 days.

[0089] (3) Index determination: Samples were collected on the 0th and 30th day of storage, and the peroxide value (POV) of each sample was determined according to the method specified in GB 5009.227-2016 "National Food Safety Standard - Determination of Peroxide Value in Food". Each sample was measured in parallel three times, and the results were averaged.

[0090] 2. Test results:

[0091] The changes in peroxide value of each sample before and after accelerated storage are recorded in Table 1.

[0092] Table 1: Changes in peroxide value (POV) of each sample before and after accelerated storage

[0093] Sample name Day 0 POV (meq / kg) Day 30 POV (meq / kg) Example 1 0.021 0.053 Example 2 0.019 0.048 Example 3 0.018 0.045 Comparative Example 1 0.023 0.287 Comparative Example 2 0.020 0.261

[0094] 3. Result analysis:

[0095] The data in Table 1 show that the peroxide values ​​(POV) of the samples of Examples 1-3 remained at a relatively low level after 30 days of accelerated storage. In contrast, the peroxide values ​​of the samples of Comparative Examples 1 and 2 increased significantly.

[0096] The sample in Comparative Example 1 was prepared without inert gas protection. The significant increase in its POV value indicates that the high-speed shearing action of the colloid mill caused the unsaturated fatty acids in the walnut kernel to come into contact with oxygen in the air, triggering an auto-oxidation chain reaction and generating a large amount of hydroperoxides. In contrast, the samples in Examples 1-3, due to the introduction of nitrogen during the grinding and pulping step, physically isolated the oxidation reaction, thereby maintaining the oxidative stability of the products.

[0097] The sample in Comparative Example 2 omitted the enzyme inactivation step, and its POV value also increased significantly. This result indicates that endogenous enzymes such as lipoxygenase present in walnut kernels, without specific heat treatment (85-95°C, 2-5 minutes) to inactivate them, will continue to catalyze fat oxidation during subsequent processing and storage. The preparation methods of Examples 1-3, however, included this enzyme inactivation step, effectively destroying the activity of endogenous enzymes and blocking the enzymatic oxidation pathway.

[0098] Comparison of the data in the Examples and Comparative Examples demonstrates that the preparation method of the present invention, through the combination of oxygen-controlled grinding and pulping with enzyme inactivation, inhibits fat oxidation through two distinct mechanisms: physical isolation and biochemical inactivation. These two steps work together to effectively control the oxidative stability of the final product, a feat not achievable by solutions employing either step alone or without any protective steps.

[0099] Test Example 2:

[0100] 1. Test method:

[0101] This test was designed to evaluate the suspension stability of the obtained walnut powder samples after rehydration.

[0102] (1) Sample rehydration: Accurately weigh 10.0 g of each walnut powder sample prepared in Examples 1-3 and Comparative Examples 3-4 and place them in 250 mL beakers. Add 150 mL of purified water at 60° C. to each beaker.

[0103] (2) Dissolution: Place the beaker on a magnetic stirrer and stir at 300 rpm for 2 minutes to completely disperse and dissolve the sample to form a rehydrated emulsion.

[0104] (3) Stand and observe: Pour the rehydrated emulsion quickly into a 150 mL stoppered measuring cylinder, stopper it and let it stand for 30 minutes.

[0105] (4) Data recording and calculation: After the standing period, record the interface scale between the upper suspension and the lower sediment in the measuring cylinder. The Suspension Index (SI) is calculated using the following formula:

[0106] SI (%) = (volume of supernatant and suspension layer / total liquid volume) × 100%;

[0107] Each sample was measured three times in parallel and the results were averaged.

[0108] 2. Test results:

[0109] The suspension index results of each sample after rehydration are recorded in Table 2.

[0110] Table 2: Suspension index (SI) of each sample after rehydration

[0111] Sample name Suspension index (SI,%) Example 1 97.2 Example 2 98.1 Example 3 97.8 Comparative Example 3 75.3 Comparative Example 4 88.6

[0112] 3. Result analysis:

[0113] The data in Table 2 show that the samples of Examples 1-3 all exhibit high suspension indexes, while the suspension indexes of Comparative Examples 3 and 4 are significantly lower.

[0114] In the sample of Comparative Example 3, xanthan gum and guar gum were directly mixed with other materials in dry powder form during preparation. In a complex system containing sugars, proteins, and electrolytes, the hydration process of the colloidal particles was inhibited, preventing the molecular chains from fully extending, making it difficult for them to form a uniform and effective network structure in the liquid phase. Consequently, after rehydration, the system had insufficient carrying capacity for solid particles, resulting in significant sedimentation and a low suspension index.

[0115] In contrast, the samples of Examples 1-3 employed a step to prepare a stabilizer activation mother liquor. In this step, xanthan gum and guar gum were fully hydrated in a pure water environment under the influence of heat and mechanical shear energy, allowing their molecular chains to fully extend and form an initial synergistic structure. When this activation mother liquor was introduced into the main feed solution, it rapidly and uniformly constructed a complete three-dimensional network structure throughout the system. This structure effectively encapsulated and suspended the walnut solid particles, maintaining a high suspension index after standing.

[0116] Comparing the results of Example 2 and Comparative Example 4, the stabilizer system of the latter only comprises xanthan gum. Although xanthan gum itself can form a certain network structure, its suspension index is still lower than that of Example 2. This shows that there is a synergistic effect at the molecular level between xanthan gum and guar gum. The galactomannan molecular chain of guar gum can interact with the rigid helical structure molecular chain of xanthan gum, further enhancing the strength and density of the three-dimensional network structure. The composite colloid system constructed by this synergistic effect has an ability to suspend solids that exceeds the level that a single colloid can achieve at equal concentrations.

[0117] Test Example 3:

[0118] 1. Test method:

[0119] The test aims to evaluate the comprehensive quality of the obtained walnut powder samples by sensory analysis method.

[0120] (1) Evaluation team: 10 personnel trained in professional sensory evaluation were selected to form the evaluation team.

[0121] (2) Sample preparation: 10.0 g of walnut powder samples prepared in Example 1-3 and Comparative Examples 1 and 3 were accurately weighed and placed in white porcelain cups of uniform size. Add 150 mL of pure water with a temperature of 60°C to each cup and stir for 2 minutes until completely dissolved. All samples were randomly coded with three digits.

[0122] (3) Evaluation process: The evaluation was carried out in a standard sensory evaluation room. The evaluators used double-blind method to evaluate the coded samples. After evaluating each sample, the evaluators rinsed their mouths with pure water to remove the aftertaste.

[0123] (4) Evaluation criteria: The samples were scored from color, aroma, taste and mouthfeel, with a maximum score of 10 for each dimension. The scoring details are as follows:

[0124] Color: uniform color, milky white, no browning or darkening phenomenon.

[0125] Aroma: whether it has the inherent and pure nutty aroma of walnut, without off-flavor, oil consumption and other odors.

[0126] Taste: whether the flavor is rich, without astringency, bitterness and other odors.

[0127] Mouthfeel: whether it is smooth and delicate, without granular and rough feeling.

[0128] 2. Test results:

[0129] The average scores of sensory evaluation of each sample are recorded in Table 3.

[0130] Table 3: Average scores of sensory evaluation of each sample

[0131] Sample name Color aroma taste Taste Total score Example 1 9.2 8.9 9.0 9.1 36.2 Example 2 9.3 9.2 9.1 9.4 37.0 Example 3 9.4 9.1 9.2 9.3 37.0 Comparative Example 1 9.1 5.3 6.8 9.0 30.2 Comparative Example 3 9.2 8.8 8.9 6.1 33.0

[0132] 3. Results analysis:

[0133] The sensory evaluation data in Table 3 shows that the samples of Example 1-3 obtained high scores in all indicators, while Comparative Examples 1 and 3 have obvious defects in specific indicators.

[0134] The aroma score of Comparative Example 1 was significantly lower than that of the sample in the Example. This is because the unsaturated fatty acids in the walnut kernels were exposed to air under the high shear and heat generation conditions of grinding, resulting in an oxidation reaction. These reactions produced small molecules of aldehydes and ketones with unpleasant flavors, i.e., a rancid smell, resulting in a low aroma score. The preparation method of the Example includes an oxygen-controlled grinding and pulping step, which physically isolates oxygen and inhibits the initiation of the oxidation reaction chain, thereby preserving the inherent aroma of the walnuts.

[0135] The taste score of Comparative Example 3 was significantly lower than that of the sample in Example 3. This is because the xanthan gum and guar gum in this comparative example were directly added in the form of dry powder. In the feed liquid rich in other solutes, a hydration layer quickly formed on the surface of the colloidal particles, hindering the penetration of internal moisture, resulting in insufficient hydration and failure of the molecular chains to fully extend. This formed tiny aggregates that were invisible to the naked eye but perceptible in the mouth, manifesting as a grainy and rough feel. In the preparation method of the example, the stabilizer pre-activation step fully hydrated the xanthan gum and guar gum in the pure water system to form a uniform colloidal mother liquor, which was then added to the main feed liquid, thereby constructing a uniform and dense three-dimensional network, giving the product a delicate and smooth mouthfeel.

[0136] The samples in Examples 1-3 also achieved high scores in color and flavor, owing to their use of a peeling treatment and subsequent color protection step. This pretreatment removed the tannin-rich seed coat and inhibited the activity of polyphenol oxidase. In summary, this technical solution, through the synergistic combination of multiple specific steps—raw material pretreatment, oxygen-controlled grinding, enzyme inactivation, and stabilizer preactivation—addressed technical issues such as product browning, off-flavor generation, and poor texture, resulting in high-quality sensory indicators across all final products.

[0137] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A walnut powder, characterized in that: The composition comprises the following components in parts by weight: Walnut kernels: 30-40 servings; Maltodextrin: 40-50 parts; White sugar: 10-15 parts; Sucrose fatty acid ester: 0.3-0.5 parts; Xanthan gum: 0.1-0.2 parts; Guar gum: 0.05-0.1 parts.

2. The walnut powder according to claim 1, characterized in that The walnut kernels are walnut kernels that have been subjected to peeling and color protection treatments.

3. A process for preparing the walnut powder according to any one of claims 1 or 2, characterized in that: The following steps are involved: S1. Raw material pretreatment: peeling and color protection treatment of walnut kernels; S2, oxygen-controlled grinding and pulping: grinding the obtained walnut kernels and water with a colloid mill under the protection of an inert gas to obtain walnut pulp; S3, enzyme inactivation: heating the walnut puree through a plate heat exchanger or a jacketed kettle; S4, batching and mixing: mixing the walnut pulp that has undergone enzyme inactivation treatment with maltodextrin, white sugar, sucrose fatty acid ester, xanthan gum and guar gum to obtain a liquid to be treated; S5, high-pressure homogenization: subjecting the liquid to be treated to high-pressure homogenization through a high-pressure homogenizer; S6. Sterilization: Sterilize the homogenized liquid through ultra-high temperature instantaneous sterilization equipment; S7, spray drying: spray drying the sterilized liquid through a spray drying tower to obtain walnut powder.

4. The preparation process of walnut powder according to claim 3, characterized in that: In S1, the raw material pretreatment step includes: treating the walnut kernels with a sodium carbonate solution having a concentration of 1-2% at 85-95° C. for 1-3 minutes to peel the walnut kernels; and performing a color protection treatment on the peeled walnut kernels with a citric acid solution having a concentration of 0.1%.

5. The process for preparing walnut powder according to claim 3, wherein: In S2, the oxygen-controlled grinding and pulping operation steps are: before starting the colloid mill and during the entire grinding process, nitrogen is continuously introduced into the closed cavity of the colloid mill.

6. The process for preparing walnut powder according to claim 3, wherein: In S3, the conditions for heating the walnut puree by using a plate heat exchanger or a jacketed kettle are: heating the walnut puree to 85-95° C. and maintaining this temperature for 2-5 minutes.

7. The process for preparing walnut powder according to claim 3, wherein: In the above S4, before the step of batching and mixing, the step of preparing a stabilizer activation mother solution is also included. The step is as follows: dry-mixing the formulated amount of xanthan gum and guar gum, adding the mixed colloid to hot water at 60-70° C., and stirring under high-speed shear conditions until a uniform colloidal solution is formed, thereby obtaining the stabilizer activation mother solution.

8. The process for preparing walnut powder according to claim 3, wherein: In S5, the pressure of the high-pressure homogenizer is set to: 20-25 MPa for the first-stage homogenization and 5-10 MPa for the second-stage homogenization.

9. The process for preparing walnut powder according to claim 3, wherein: In S6, the sterilization parameters of the ultra-high temperature instantaneous sterilization equipment are: a sterilization temperature of 135-140° C., and a residence time of the material at the sterilization temperature of 4-6 seconds.

10. The process for preparing walnut powder according to claim 3, characterized in that: In the above-mentioned S7, the process parameters of the spray drying tower are: inlet air temperature 160-180°C, outlet air temperature 80-90°C.

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