Method for extracting walnut oil and co-producing double-type low-fat peptide-containing walnut milk

Abstract

The invention relates to the technical field of walnut kernel processing, in particular to a method for extracting walnut oil and co-producing double-type low-fat peptide-containing walnut milk. The invention provides a method for extracting walnut oil and co-producing double-type low-fat peptide-containing walnut milk. The method comprises the following steps: preparing deastringency walnut kernels; performing dry grinding on the obtained deastringency walnut kernels to obtain walnut sauce; mixing the obtained walnut sauce with water, and carrying out solid-liquid separation to obtain a supernatant and a precipitate; carrying out first enzymolysis on the obtained supernate, then carrying out oil phase and water phase separation, refining the oil phase to obtain walnut oil, and carrying out enzyme deactivation on the water phase to obtain first low-fat peptide-containing walnut milk; and carrying out enzymolysis on the obtained precipitate to prepare the second low-fat peptide-containing walnut milk. The preparation method provided by the invention can improve the oil yield of walnuts, and the first low-fat peptide-containing walnut milk and the second low-fat peptide-containing walnut milk which are relatively high in protein content and relatively high in stability are obtained through co-production.

Description

Technical Field

[0001] The invention relates to the technical field of walnut kernel processing, and in particular to a method for extracting walnut oil and co-producing dual-type low-fat peptide-containing walnut milk. Background Art

[0002] Walnut is a nut rich in nutrients, rich in protein, unsaturated fatty acids and multiple vitamins. The protein in walnut is a high-quality plant protein that contains a variety of essential amino acids and is suitable for all kinds of people. It is especially effective in promoting the growth and development of children and enhancing the immunity of the elderly. Compared with other animal dairy products, plant protein beverages made from walnuts are less likely to cause symptoms such as lactose intolerance and are more easily accepted by consumers. However, there are two problems in the actual processing of walnut kernel products. First, the endocarp of walnut kernels contains astringent substances, which is not easy for consumers to accept. Traditional walnut kernel processing methods, such as hot water soaking, long-term alkali treatment, high-concentration alkali treatment, baking, etc., can achieve de-astringency to a certain extent, but the operation process is complicated, time-consuming and economically costly, and easily lead to a large loss of walnut kernels. Traditional de-astringency methods often choose to remove the entire outer skin of walnut kernels, which means that a large amount of nutrients will be lost; second, the oil content in walnuts is as high as 55% to 70%, and the high oil content of walnut milk will cause a greasy taste; the content of insoluble protein (such as gluten) in walnut protein is high, resulting in poor protein solubility; high oil content and poor solubility of walnut protein lead to poor stability of walnut milk, and high-concentration stabilizers are usually required to construct high-stability walnut milk. Therefore, in the prior art, there is an urgent need for a method for extracting walnut oil with low energy consumption using walnut kernels that remove astringency and retain the walnut inner seed coat, and obtaining walnut milk with higher nutrition, stability and sensory quality.

[0003] Traditional walnut oil extraction methods mainly include solvent extraction and mechanical pressing. Although these methods can effectively remove some walnut oil, they all have some problems. The solvent extraction method has potential risks to health caused by solvent residues, as well as environmental pollution caused by improper waste liquid treatment. The mechanical pressing process uses mechanical external force to squeeze oil out of oil, and the main equipment includes a screw oil press and a hydraulic oil press. Due to the high oil content of walnut kernels (50-70% by dry weight of walnut kernels), a stable three-dimensional structure cannot be established when using screw pressing, resulting in a smooth bore problem. At the same time, mechanical pressing requires heating, and the heating process causes walnut protein denaturation. While removing walnut oil, the protein quality and utilization rate of walnuts are reduced.

[0004] Related technology provides a deep processing method for producing low-fat walnut milk, active peptides, and protein powder by comprehensively utilizing walnut kernels. The method proposes a high-value processing method for walnut protein: first, walnut oil is separated by low-temperature cold rolling to obtain walnut kernel protein, wherein the walnut kernel is soaked in 0.6% NaOH solution for 2 hours when the seed coat is removed, and then the walnut kernel is washed with a large amount of clean water; then walnut milk is prepared by micro-crushing and homogenization process, and the specific steps are adding auxiliary materials such as white sugar and sodium carboxymethyl cellulose, and obtaining walnut milk after high-pressure homogenization; then the insoluble walnut protein is enzymatically hydrolyzed, and a composite enzyme (papain and flavor enzyme 1:1) is added, the amount is 1% of the mass of the filter residue, the enzymatic hydrolysis temperature is 50°C, the enzymatic hydrolysis is 3 hours, filtered through a 3kD ultrafiltration membrane, concentrated and spray-dried, and active peptides with a molecular weight of less than 3000 are obtained; finally, the remaining protein residue is processed into walnut powder. This method realizes the full component utilization of walnut kernels, but requires multi-step processing, complex operation, long time, and large enzyme requirements, which may affect the nutritional and functional integrity of walnut protein. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is that the related art lacks a method for extracting walnut oil with low energy consumption using walnut kernels that have been de-astringent and retain the walnut inner seed coat, and obtaining walnut milk with higher stability and sensory quality, thereby providing a method for extracting walnut oil and co-producing dual-type low-fat peptide-containing walnut milk.

[0006] The present invention discloses a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0007] (1) soaking the initial walnut kernels in an alkali solution, taking them out and letting them stand, and then steaming and washing them to remove moisture from the surface of the washed walnut kernels to obtain the de-astringent walnut kernels;

[0008] (2) dry-grinding the de-astringent walnut kernels obtained in step (1) to obtain walnut paste;

[0009] (3) mixing the walnut paste obtained in step (2) with water and performing solid-liquid separation to obtain a supernatant and a precipitate;

[0010] (4) subjecting the supernatant obtained in step (3) to a first enzymatic hydrolysis and then separating the oil phase and the water phase, refining the oil phase to obtain walnut oil, and inactivating the enzyme in the water phase to obtain a first low-fat peptide-containing walnut milk;

[0011] (5) The precipitate obtained in step (3) is mixed with water, and then subjected to a second enzymatic hydrolysis and enzyme inactivation to obtain a second low-fat peptide-containing walnut milk precursor, and then the second low-fat peptide-containing walnut milk precursor is mixed with an additive to obtain a second low-fat peptide-containing walnut milk.

[0012] It is understandable that the initial walnut kernel refers to the walnut kernel without removing the walnut endocarp. In the present invention, the initial walnut kernel used is free of mildew, oily smell, insect pests, impurities, and full grains.

[0013] Preferably, in step (1), the mass ratio of walnut to alkali solution during the soaking of the initial walnut kernel in alkali solution is 1:(2-8);

[0014] Preferably, the alkali solution is selected from aqueous sodium hydroxide solution;

[0015] Preferably, the concentration of the sodium hydroxide aqueous solution is 0.3-3.0%;

[0016] Preferably, the soaking temperature is 15-35°C and the soaking time is 30s-2min;

[0017] Preferably, the standing temperature is 20-35°C; the standing time is 30s-2min;

[0018] Preferably, the water vapor temperature during the water vapor treatment process is 95-120°C and the time is 1-5min;

[0019] Preferably, the water vapor pressure is 0-0.2 MPa.

[0020] Preferably, in step (1), the cleaning process includes rinsing;

[0021] Preferably, the rinsing is performed by water rinsing;

[0022] Preferably, the water temperature in the elution is 15-35°C; the elution time is 10-50s;

[0023] Preferably, the water temperature during water immersion is 40-80° C., and the immersion time is 4-21 min.

[0024] Preferably, the process of removing the moisture on the surface of the washed walnut kernels is to use air to flush away the moisture on the surface of the washed walnut kernels;

[0025] Preferably, the air is high-pressure air;

[0026] Preferably, the pressure of the high-pressure air is 0.3-1.2 MPa;

[0027] Preferably, the time for flushing the surface moisture of the washed walnut kernels with air is 10-50s.

[0028] Preferably, in step (2), the dry grinding is anhydrous colloid grinding;

[0029] Preferably, the anhydrous colloid is ground 2-4 times;

[0030] Preferably, the temperature of the dry grinding is 50-65°C;

[0031] Preferably, the particle size Dv(90) of the walnut paste obtained by the dry grinding is less than 550 μm.

[0032] Preferably, in step (3), the walnut paste obtained in step (2) and water are mixed at a temperature of 50-65° C. and a stirring rate of 30-100 rpm;

[0033] Preferably, the mass ratio of the walnut paste obtained in step (2) to water is 1:(2-3);

[0034] Preferably, the solid-liquid separation is performed by centrifugal separation; wherein the centrifugal force is 4000-6000g;

[0035] Preferably, in step (4), the temperature of the first enzymatic hydrolysis is 55-65°C, the time is 1-4h, and the stirring speed of the first enzymatic hydrolysis is 30-100rpm;

[0036] Preferably, the enzymes for the first enzymatic hydrolysis include alkaline protease and flavor protease;

[0037] Preferably, in the first enzymatic hydrolysis, the amount of alkaline protease added is 0.4-1‰ of the initial walnut kernel mass in step (1); the amount of flavor protease added is 1-2‰ of the initial walnut kernel mass in step (1);

[0038] Preferably, the separation of the oil phase and the water phase is carried out by a centrifuge;

[0039] Preferably, the centrifuge is a disc centrifuge;

[0040] Preferably, the oil phase refining process includes degumming, deacidification and dehydration;

[0041] Preferably, the temperature of the aqueous phase enzyme inactivation is 80-90°C and the time is 20-30 minutes.

[0042] Preferably, in step (5), the mass ratio of precipitate to water is 1:(1.5-3);

[0043] Preferably, the mixing temperature of the precipitate and water is 50-65° C., and the mixing stirring rate is 30-100 rpm.

[0044] Preferably, in step (5), the enzymes for the second enzymatic hydrolysis include alkaline protease and flavor protease;

[0045] Preferably, in the second enzymatic hydrolysis, the amount of alkaline protease added is 1-2.5‰ of the initial walnut kernel mass in step (1); the amount of flavor protease added is 2-5‰ of the initial walnut kernel mass in step (1);

[0046] The second enzymatic hydrolysis time is 2-5h.

[0047] Preferably, in step (5), the additive is an auxiliary material aqueous solution; the mass ratio of the auxiliary material to water in the auxiliary material aqueous solution is 1:(30-100);

[0048] Preferably, the auxiliary materials include monoglyceride of fatty acid, sodium stearoyl lactylate, and casein;

[0049] The amount of auxiliary materials added to the second low-fat peptide-containing walnut milk is 1.5‰-15‰ of the initial walnut kernel mass;

[0050] Preferably, monoglyceride accounts for 0.5‰-5‰ of the mass of the initial walnut kernel; sodium stearoyl lactylate accounts for 0.5‰-5‰ of the mass of the initial walnut kernel; casein accounts for 0.5‰-5‰ of the mass of the initial walnut kernel;

[0051] Preferably, the preparation process of the auxiliary material aqueous solution is to mix the auxiliary material with water at 65-78°C.

[0052] Preferably, after mixing the second low-fat peptide-containing walnut milk precursor with the additive in step (5), the process further includes volume fixing, homogenization, and a second enzyme inactivation process;

[0053] The constant volume temperature is 60-80℃;

[0054] Homogenization pressure is 30-40MPa;

[0055] The second enzyme inactivation temperature is 120-125°C; the enzyme inactivation time is 20-25 minutes.

[0056] The technical solution of the present invention has the following advantages:

[0057] The present invention provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps: (1) soaking initial walnut kernels in alkaline solution, taking them out and letting them stand, then subjecting them to water vapor treatment, washing, and removing moisture from the surface of the washed walnut kernels to obtain the de-astringent walnut kernels; (2) dry-grinding the de-astringent walnut kernels obtained in step (1) to obtain walnut paste; (3) mixing the walnut paste obtained in step (2) with water and performing solid-liquid separation to obtain a supernatant and a precipitate; (4) subjecting the supernatant obtained in step (3) to a first enzymatic hydrolysis, then separating the oil phase and the water phase, refining the oil phase to obtain walnut oil, and inactivating the enzyme in the water phase to obtain a first low-fat peptide-containing walnut milk; (5) mixing the precipitate obtained in step (3) with water, then subjecting it to a second enzymatic hydrolysis, inactivating the enzyme to obtain a second low-fat peptide-containing walnut milk precursor, and then mixing the second low-fat peptide-containing walnut milk precursor with an additive to obtain a second low-fat peptide-containing walnut milk.

[0058] Step (1) of the present invention can remove the astringency of the walnut while retaining the initial walnut endocarp, and the structure of the walnut kernel after the astringency is removed is more conducive to the oil precipitation therein, and the walnut kernel after the astringency is removed does not need to be subjected to additional high-energy-consuming drying treatment, and its water content can be less than 15%. In the subsequent dry grinding, the emulsification degree is low, which is conducive to the oil precipitation and thus improves the oil yield, and avoids the destruction of the nutrition of the walnut kernel during the drying process;

[0059] Furthermore, through step (2) dry grinding and step (3) solid-liquid separation, a supernatant and a precipitate are obtained; through step (4) treating the supernatant, walnut oil and a first low-fat peptide-containing walnut milk can be obtained; through step (5) treating the precipitate, a second low-fat peptide-containing walnut milk can be obtained; because there is no interference from insoluble substances in the supernatant, demulsification can be achieved by enzymatic hydrolysis with a small dose of enzyme, so that separable walnut oil and the first low-fat peptide-containing walnut milk can be easily obtained, and the first low-fat peptide-containing walnut milk has a high protein content and high stability; because there is little residual fat in the precipitate and the viscosity is low, a second low-fat peptide-containing walnut milk with a high protein content and good stability can be prepared by enzymatic hydrolysis with a small dose of enzyme. DETAILED DESCRIPTION

[0060] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0061] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0062] The initial walnut kernels used in the embodiments of the present invention and the comparative examples are free of mildew, oily smell, insect pests, impurities, and full grains. The moisture content of the initial walnut kernels is less than 5%.

[0063] Example 1

[0064] This embodiment provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0065] (1) 1 kg of initial walnut kernels are placed in 3 kg of 0.5% sodium hydroxide solution, soaked at 25° C. for 40 seconds, taken out, and allowed to stand for 1 minute (to ensure that the alkali solution fully enters the walnut endocarp); then treated with steam at a gauge pressure of 0.1 MPa and a temperature of 120° C. for 250 seconds (short-term treatment with steam destroys the fiber structure and cell tissue of the walnut endocarp, releases astringent substances such as polyphenols, but has little effect on the walnut kernels, and the protein and fat loss in the walnut kernels is small); after the steam treatment, the walnut kernels are rinsed with water at a temperature of 25° C. for 8 minutes using a drum elution device (this process can remove phenols, quinones and dark polymer substances remaining on the surface of the walnut endocarp); after the water elution, the surface of the walnut kernels is rinsed with high-pressure air at 0.4 MPa for 30 seconds (this process reduces the moisture content of the walnut kernels and reduces the rates of enzymatic reactions and fat oxidation reactions), thereby obtaining the de-astringent walnut kernels;

[0066] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water, to obtain a walnut paste having a Dv(90) of less than 500 μm;

[0067] (3) the walnut paste prepared in step (2) was fully mixed with water under stirring at 60° C. and 50 rpm (so that the temperature of the mixture reached 60° C.), and then solid-liquid separation was performed using a horizontal centrifuge under the action of a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water was 1:2;

[0068] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil (which can be contained in a PET plastic container); the aqueous phase is deenzymed at 85° C. for 20 min to obtain the first low-fat peptide-containing walnut milk;

[0069] (5) After the precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2), 1 g of alkaline protease and 2 g of flavor protease are added, and enzymatic hydrolysis is carried out at a stirring speed of 50 rpm for 4 hours to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor at 70°C and the volume is adjusted to 3 kg. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0070] Example 2

[0071] This embodiment provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0072] (1) placing 1 kg of initial walnut kernels in 4 kg of 1% sodium hydroxide solution, soaking for 1 min at 25° C., taking out, and standing for 1 min; then treating with water vapor at a gauge pressure of 0.05 MPa and a temperature of 109° C. for 3 min; after the water vapor treatment, eluting with water at a temperature of 25° C. for 8 min through a drum eluting device; after the water eluting, rinsing the surface of the walnut kernels with 0.4 MPa high-pressure air for 20 s (this process reduces the moisture content of the walnut kernels, reduces the rates of enzymatic reactions and fat oxidation reactions), thereby obtaining the de-astringent walnut kernels;

[0073] (2) grinding the de-astringent walnut kernels obtained in step (1) with anhydrous colloid for four times without adding water to obtain walnut paste (the Dv(90) of the walnut paste is less than 350 μm);

[0074] (3) the walnut paste prepared in step (2) was fully mixed with water under stirring at 60° C. and 50 rpm (so that the temperature of the mixture reached 60° C.), and then solid-liquid separation was performed using a horizontal centrifuge under the action of a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water was 1:3;

[0075] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil (which can be contained in a PET plastic container); the aqueous phase is deenzymed at 80° C. for 30 min to obtain the first low-fat peptide-containing walnut milk;

[0076] (5) The precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm, and then 1 g of alkaline protease and 2 g of flavor protease are added. After enzymatic hydrolysis at a stirring speed of 50 rpm for 4 hours, a second low-fat peptide-containing walnut milk precursor is obtained; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, and 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor and fixed to volume at 70°C. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain the second low-fat peptide-containing walnut milk.

[0077] Example 3

[0078] This embodiment provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0079] (1) placing 1 kg of initial walnut kernels in 4 kg of 1.5% sodium hydroxide solution, soaking for 1 min at 25° C., taking out, and standing for 1 min; then treating with steam at a gauge pressure of 0 MPa and a temperature of 100° C. for 3 min; after steam treatment, rinsing with water at a temperature of 28° C. for 8 min using a drum rinsing device; after rinsing with water, washing the surface of the walnut kernels with 0.4 MPa high-pressure air for 50 s (this process reduces the moisture content of the walnut kernels, reduces the rates of enzymatic reactions and fat oxidation reactions), thereby obtaining the de-astringent walnut kernels;

[0080] (2) grinding the de-astringent walnut kernels prepared in step (1) three times with anhydrous colloid without adding water to obtain a walnut paste having a Dv(90) of less than 400 μm;

[0081] (3) the walnut paste prepared in step (2) was fully mixed with water under stirring at 60° C. and 50 rpm (so that the temperature of the mixture reached 60° C.), and then solid-liquid separation was performed using a horizontal centrifuge under the action of a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water was 1:2;

[0082] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil (which can be contained in a PET plastic container); the aqueous phase is deenzymed at 90° C. for 20 min to obtain a first low-fat peptide-containing walnut milk;

[0083] (5) The precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm, and then 1 g of alkaline protease and 2 g of flavor protease are added. After enzymatic hydrolysis at a stirring speed of 50 rpm for 4 hours, a second low-fat peptide-containing walnut milk precursor is obtained; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, and 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor and fixed to volume at 70°C. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain the second low-fat peptide-containing walnut milk.

[0084] Example 4

[0085] This embodiment provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0086] (1) placing 1 kg of initial walnut kernels in 4 kg of 2.5% sodium hydroxide solution, soaking at 25° C. for 1 min, taking out, and standing for 1 min; then treating with steam at a gauge pressure of 0 MPa and a temperature of 100° C. for 3 min; after the steam treatment, washing with water at a temperature of 35° C. for 8 min through a drum washing device; after the water washing, washing the surface of the walnut kernels with 0.4 MPa high-pressure air for 20 s, thereby obtaining the de-astringent walnut kernels;

[0087] (2) grinding the de-astringent walnut kernels prepared in step (1) four times with anhydrous colloid without adding water to obtain a walnut paste having a Dv(90) of less than 350 μm;

[0088] (3) the walnut paste prepared in step (2) was fully mixed with water under stirring at 60° C. and 50 rpm (so that the temperature of the mixture reached 60° C.), and then solid-liquid separation was performed using a horizontal centrifuge under the action of a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water was 1:3;

[0089] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil (which can be contained in a PET plastic container); the aqueous phase is deenzymed at 90° C. for 20 min to obtain a first low-fat peptide-containing walnut milk;

[0090] (5) The precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm, and then 1 g of alkaline protease and 2 g of flavor protease are added. After enzymatic hydrolysis at a stirring speed of 50 rpm for 4 hours, a second low-fat peptide-containing walnut milk precursor is obtained; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, and 1 g of casein) are weighed, and the materials are dissolved in 200 g of water at 78°C to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor and fixed to volume at 70°C. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0091] Comparative Example 1

[0092] This comparative example provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0093] (1) placing 1 kg of initial walnut kernels in 4 kg of 40% ethanol aqueous solution, extracting with 28 kHz ultrasonic wave at 50° C. for 30 min, and then eluting with water at 25° C. for 8 min through a drum elution device; after eluting with water, washing the surface of the walnut kernels with 0.4 MPa high-pressure air for 30 s to obtain the de-astringent walnut kernels;

[0094] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water to obtain walnut paste (the Dv(90) of the walnut paste is less than 500 μm);

[0095] (3) the walnut paste prepared in step (2) was fully mixed with water under stirring at 60° C. and 50 rpm (so that the temperature of the mixture reached 60° C.), and then solid-liquid separation was performed using a horizontal centrifuge under the action of a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water was 1:2;

[0096] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil (which can be contained in a PET plastic container); the aqueous phase is deenzymed at 85° C. for 20 min to obtain the first low-fat peptide-containing walnut milk;

[0097] (5) After the precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2), 1 g of alkaline protease and 2 g of flavor protease are added, and enzymatic hydrolysis is carried out at a stirring speed of 50 rpm for 4 hours to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor at 70°C and the volume is adjusted to 3 kg. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0098] Comparative Example 2

[0099] This comparative example provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0100] (1) placing 1 kg of initial walnut kernels in 4 kg of 5% NaHCO3 solution, soaking at 65°C for 60 min, then taking out, placing in 4 kg of 2% citric acid solution, soaking at 65°C for 10 min, then taking out; then washing with water at 25°C for 8 min using a drum washing device; after water washing, using 0.4 MPa high-pressure air to rinse the surface of the walnut kernel for 30 s, thereby obtaining the de-astringent walnut kernel;

[0101] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water to obtain walnut paste (the Dv(90) of the walnut paste is less than 500 μm);

[0102] (3) the walnut paste prepared in step (2) was fully mixed with water under stirring at 60° C. and 50 rpm (so that the temperature of the mixture reached 60° C.), and then solid-liquid separation was performed using a horizontal centrifuge under the action of a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water was 1:2;

[0103] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil (which can be contained in a PET plastic container); the aqueous phase is deenzymed at 85° C. for 20 min to obtain the first low-fat peptide-containing walnut milk;

[0104] (5) After the precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2), 1 g of alkaline protease and 2 g of flavor protease are added, and enzymatic hydrolysis is carried out at a stirring speed of 50 rpm for 4 hours to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor at 70°C and the volume is adjusted to 3 kg. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0105] Comparative Example 3

[0106] This comparative example provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0107] (1) placing 1 kg of initial walnut kernels in 4 kg of a solution of a 1% tannase-cellulase complex enzyme preparation, oscillating in an ultrasonic wave of 60 W at 50° C. for 15 min, and then taking out; then eluting in water at a water temperature of 50° C. for 30 s through a drum elution device; then soaking in warm water at 50° C. for 4 times, each time for 5 min (the pH value of the soaking water after the last soaking is 6.3); after the soaking is completed, placing the walnut kernels in a centrifuge, dehydrating at a speed of 200 r / min for 2 min, and finally baking at 60° C. for 10 min to obtain the de-astringent walnut kernels;

[0108] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water, to obtain a walnut paste having a Dv(90) of less than 500 μm;

[0109] (3) the walnut paste prepared in step (2) is fully mixed with water under stirring at 60° C. and 50 rpm, and then solid-liquid separation is performed using a horizontal centrifuge under a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water is 1:2;

[0110] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil (which can be contained in a PET plastic container); the aqueous phase is deenzymed at 85° C. for 20 min to obtain the first low-fat peptide-containing walnut milk;

[0111] (5) After the precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2), 1 g of alkaline protease and 2 g of flavor protease are added, and enzymatic hydrolysis is carried out at a stirring speed of 50 rpm for 4 hours to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor at 70°C and the volume is adjusted to 3 kg. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0112] Comparative Example 4

[0113] This comparative example provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0114] (1) placing 1 kg of initial walnut kernels in 3 kg of 0.5% sodium hydroxide solution, soaking at 25° C. for 1 min 40 s, and then taking out; then treating with water vapor at a gauge pressure of 0.1 MPa and a temperature of 120° C. for 250 s; after the water vapor treatment, washing with water at a water temperature of 25° C. for 8 min through a drum washing device; after the water washing, washing the surface of the walnut kernels with 0.4 MPa high-pressure air for 30 s, thereby obtaining the de-astringent walnut kernels;

[0115] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water, to obtain a walnut paste having a Dv(90) of less than 500 μm;

[0116] (3) the walnut paste prepared in step (2) is fully mixed with water under stirring at 60° C. and 50 rpm, and then solid-liquid separation is performed using a horizontal centrifuge under a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water is 1:2;

[0117] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil (which can be contained in a PET plastic container); the aqueous phase is deenzymed at 85° C. for 20 min to obtain the first low-fat peptide-containing walnut milk;

[0118] (5) After the precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2), 1 g of alkaline protease and 2 g of flavor protease are added, and enzymatic hydrolysis is carried out at a stirring speed of 50 rpm for 4 hours to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor at 70°C and the volume is adjusted to 3 kg. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0119] Comparative Example 5

[0120] This comparative example provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0121] (1) placing 1 kg of initial walnut kernels in 3 kg of 0.5% sodium hydroxide solution, soaking at 25° C. for 40 seconds, taking out, and standing for 1 minute; then treating with air at a gauge pressure of 0.1 MPa and a temperature of 120° C. for 250 seconds; after air treatment, washing with water at a water temperature of 25° C. for 8 minutes through a drum washing device; after water washing, washing the surface of the walnut kernels with 0.4 MPa high-pressure air for 30 seconds, thereby obtaining the de-astringent walnut kernels;

[0122] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water, to obtain a walnut paste having a Dv(90) of less than 500 μm;

[0123] (3) the walnut paste prepared in step (2) is fully mixed with water under stirring at 60° C. and 50 rpm, and then solid-liquid separation is performed using a horizontal centrifuge under a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water is 1:2;

[0124] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil; and the aqueous phase is deenzymed at 85° C. for 20 min to obtain a first low-fat peptide-containing walnut milk;

[0125] (5) After the precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2), 1 g of alkaline protease and 2 g of flavor protease are added, and enzymatic hydrolysis is carried out at a stirring speed of 50 rpm for 4 hours to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor at 70°C and the volume is adjusted to 3 kg. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0126] Comparative Example 6

[0127] This comparative example provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0128] (1) placing 1 kg of initial walnut kernels in 2 kg of a 3% sodium hydroxide solution, soaking at 90° C. for 6 minutes, taking out, and peeling the kernels using 0.3 MPa water; after peeling, rinsing the kernels using a drum rinsing device using water at a temperature of 25° C. for 8 minutes; after rinsing, rinsing the kernel surfaces with 0.4 MPa high-pressure air for 30 seconds to obtain the de-astringent walnut kernels;

[0129] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water, to obtain a walnut paste having a Dv(90) of less than 500 μm;

[0130] (3) the walnut paste prepared in step (2) is fully mixed with water under stirring at 60° C. and 50 rpm, and then solid-liquid separation is performed using a horizontal centrifuge under a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water is 1:2;

[0131] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil; and the aqueous phase is deenzymed at 85° C. for 20 min to obtain a first low-fat peptide-containing walnut milk;

[0132] (5) After the precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2), 1 g of alkaline protease and 2 g of flavor protease are added, and enzymatic hydrolysis is carried out at a stirring speed of 50 rpm for 4 hours to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor at 70°C and the volume is adjusted to 3 kg. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0133] Comparative Example 7

[0134] This comparative example provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0135] (1) placing 1 kg of initial walnut kernels in 2 kg of 3% sodium hydroxide solution and stirring at 30° C. for 200 seconds, taking out the kernels and peeling them with 0.3 MPa water; after peeling, washing them with 25° C. water for 8 minutes using a drum washing device; after washing with water, washing the surface of the walnut kernels with 0.4 MPa high-pressure air for 20 seconds to obtain the de-astringent walnut kernels;

[0136] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water, to obtain a walnut paste having a Dv(90) of less than 500 μm;

[0137] (3) the walnut paste prepared in step (2) is fully mixed with water under stirring at 60° C. and 50 rpm, and then solid-liquid separation is performed using a horizontal centrifuge under a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water is 1:2;

[0138] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil; and the aqueous phase is deenzymed at 85° C. for 20 min to obtain a first low-fat peptide-containing walnut milk;

[0139] (5) After the precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2), 1 g of alkaline protease and 2 g of flavor protease are added, and enzymatic hydrolysis is carried out at a stirring speed of 50 rpm for 4 hours to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor at 70°C and the volume is adjusted to 3 kg. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0140] Comparative Example 8

[0141] This comparative example provides a method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, comprising the following steps:

[0142] (1) placing 1 kg of initial walnut kernels in 3 kg of 0.5% sodium hydroxide solution, soaking at 25° C. for 40 seconds, taking out, and standing for 1 minute; then treating with water vapor at a gauge pressure of 0.1 MPa and a temperature of 120° C. for 250 seconds; after the water vapor treatment, washing with water at a water temperature of 25° C. for 8 minutes through a drum washing device; after the water washing, washing the surface of the walnut kernels with 0.4 MPa high-pressure air for 30 seconds, thereby obtaining the de-astringent walnut kernels;

[0143] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water, to obtain a walnut paste having a Dv(90) of less than 500 μm;

[0144] (3) the walnut paste prepared in step (2) was fully mixed with water at 60° C. and 50 rpm, and then 1.5 g of alkaline protease and 3 g of flavor protease were added for enzymatic hydrolysis at a stirring speed of 50 rpm for 4 h, and then solid-liquid separation was performed using a horizontal centrifuge under a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water was 1:3;

[0145] (4) using a butterfly centrifuge to separate the water phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil; the water phase is enzyme-inactivated at 85° C. for 20 min to obtain the first low-fat peptide-containing walnut milk;

[0146] (5) The precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2) to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1g monoglyceride, 1g sodium stearoyl lactylate, 1g casein) are weighed and dissolved in 78°C and 1kg water to obtain an auxiliary material solution, the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor and the volume is adjusted to 3kg at 70°C, and after being homogenized twice at 35MPa, it is sterilized at 120°C for 20min to obtain a second low-fat peptide-containing walnut milk.

[0147] Comparative Example 9

[0148] This comparative example is similar to comparative example 7, except that after the step (1) of comparative example 7 is washed with high-pressure air, the step further comprises drying at 60° C. to a moisture content equal to that of the de-astringent walnut kernels obtained in Example 1. The specific process is as follows:

[0149] (1) 1 kg of initial walnut kernels are placed in 2 kg of 3% sodium hydroxide solution and stirred at 30° C. for 200 seconds, then taken out and peeled using 0.3 MPa water; after peeling, the kernels are rinsed for 8 minutes using a drum rinsing device using water at a temperature of 25° C.; after water rinsing, the surface of the kernels is rinsed with 0.4 MPa high-pressure air for 20 seconds, and dried at 60° C. to a water content the same as that of the de-astringent walnut kernels obtained in Example 1, thereby obtaining the de-astringent walnut kernels;

[0150] (2) grinding the de-astringent walnut kernels obtained in step (1) twice with anhydrous colloid without adding water, to obtain a walnut paste having a Dv(90) of less than 500 μm;

[0151] (3) the walnut paste prepared in step (2) is fully mixed with water under stirring at 60° C. and 50 rpm, and then solid-liquid separation is performed using a horizontal centrifuge under a centrifugal force of 7000 g to obtain a supernatant and a precipitate, wherein the mass ratio of the walnut paste prepared in step (2) to water is 1:2;

[0152] (4) adding 0.5 g of alkaline protease and 1 g of flavor protease to the supernatant obtained in step (3) at 60° C., performing enzymatic hydrolysis at a stirring speed of 50 rpm for 1 h, and then using a butterfly centrifuge to separate the aqueous phase and the oil phase; wherein the oil phase is degummed, deacidified and dehydrated to obtain walnut oil (which can be contained in a PET plastic container); the aqueous phase is deenzymed at 85° C. for 20 min to obtain the first low-fat peptide-containing walnut milk;

[0153] (5) After the precipitate obtained in step (3) is fully mixed with water under stirring at 60°C and 50 rpm (the mass ratio of precipitate to water is 1:2), 1 g of alkaline protease and 2 g of flavor protease are added, and enzymatic hydrolysis is carried out at a stirring speed of 50 rpm for 4 hours to obtain a second low-fat peptide-containing walnut milk precursor; auxiliary materials (1 g of monoglyceride, 1 g of sodium stearoyl lactylate, 1 g of casein) are weighed, and the materials are dissolved in 78°C and 200 g of water to obtain an auxiliary material solution, and the auxiliary material solution is added to the second low-fat peptide-containing walnut milk precursor at 70°C and the volume is adjusted to 3 kg. After being homogenized twice at 35 MPa, it is sterilized at 120°C for 20 minutes to obtain a second low-fat peptide-containing walnut milk.

[0154] Test Case

[0155] 1. The protein yield, endocarp retention rate and moisture content of the de-astringent walnut kernels obtained in the examples and comparative examples were measured. The results are shown in Table 1.

[0156] The protein yield was determined as follows:

[0157] After the de-astringency treatment, the moisture content of the walnut kernels was dried to the same level as the raw material moisture content, and the protein content was tested by the Kjeldahl method to calculate the protein yield. The calculation formula (1) is as follows:

[0158]

[0159] Wherein: X is the protein yield of walnut kernel after drying, %; m is the protein mass in every 100g of walnut kernel after drying, g; M is the protein mass in every 100g of raw material walnut kernel, g.

[0160] The method for determining the endocarp retention rate is as follows:

[0161] The walnut endocarp retention rate was determined using imageJ software. Main steps: High-resolution images of walnut samples before and after endocarp removal were collected, and the images were binarized using ImageJ software to measure the endocarp area and calculate the endocarp retention rate.

[0162] The specific process includes the following steps:

[0163] S1 Image acquisition: Take high-resolution images of the walnut samples before and after endocarp removal to ensure uniform lighting and clear visibility of the endocarp part of the sample.

[0164] S2 Image processing: The collected images were imported into ImageJ software. The “Thresholding” tool in the software was used to binarize the image (separate the endocarp region from other regions in the image). The “AdjustThreshold” function was used to precisely adjust the threshold to accurately distinguish the endocarp region.

[0165] S3 Area measurement: Use the "Analyze Particles" tool or the "Measure" function to measure the area of ​​the endocarp in the binary image. Record the endocarp area of ​​the sample before and after endocarp removal.

[0166] S4 Calculate the endocarp retention rate:

[0167] Endocarp retention rate (%) = (endocarp area after peeling / endocarp area before peeling) × 100%

[0168] At least 20 samples were photographed and the average value was taken. The endocarp retention rate is shown in Table 1.

[0169] The moisture content of the deastringent walnut kernels was determined by taking the initial walnut kernel raw material, the deastringent walnut kernels obtained in the embodiments and the comparative examples (5 g each, referring to the method GB5009.3—2016 National Food Safety Standard Determination of Moisture in Food), drying them at 105°C to constant weight, weighing them and calculating the mass ratio of the deastringent walnut kernels after drying in the embodiments and the comparative examples to the initial walnut kernels, which was the moisture content of the deastringent walnut kernels.

[0170] Table 1

[0171]

[0172]

[0173] 2. Deastringency rate of deastringent walnut kernels

[0174] Determination of the deastringency rate of deastringent walnut kernels The Folin phenol method was used to determine the content of phenolic substances in the deastringent walnut kernels of the embodiments and comparative examples before and after the deastringent walnut kernels were tested. The average value was taken after 20 repeated tests on a single sample. The change in the content of phenolic substances before and after the deastringency of the walnut kernels was expressed as gallic acid concentration equivalent. The standard curve is y=0.0088x+0.1948, x is the gallic acid concentration (mg / g), and y is the absorbance (A). (The decolorization rate of the peeled walnut kernels is 100%); among them, the minimum deastringency rate of the deastringent walnut kernels prepared in Examples 1-4 is 89.4%; the deastringency rate of the deastringent walnut kernels obtained by removing the skin in the comparative example is higher than that of the deastringent walnut kernels in Example 1, and the deastringency rate of the deastringent walnut kernels in other comparative examples is as high as 87%.

[0175] 3. Oil yield

[0176] The oil yield is calculated using the following formula:

[0177]

[0178] The fat content in the initial walnut kernels was determined by the Soxhlet extraction method according to GB 5009.6-2016. 10 g of the sample was weighed, mixed with 20 g of quartz sand in an evaporating dish, evaporated to dryness in a boiling water bath, dried in a forced air drying oven at 100 °C for 30 min, fully ground, and then subjected to Soxhlet extraction and weighed.

[0179] The oil yield results are shown in Table 2.

[0180] Table 2

[0181] Oil yield (%) Example 1 81％ Example 2 80％ Example 3 82％ Example 4 80％ Comparative Example 1 62％ Comparative Example 2 23％ Comparative Example 3 27％ Comparative Example 4 73％ Comparative Example 5 72％ Comparative Example 6 44％ Comparative Example 7 46％ Comparative Example 8 75％ Comparative Example 9 61％

[0182] 4. Protein content, fat content, and stability test

[0183] The protein peptide content in the peptide-containing skimmed walnut milk prepared in Examples 1 to 4 and the walnut milk in Comparative Examples 1 to 9 was measured and calculated using the Kjeldahl nitrogen method in "GB 5009.5-2016 National Food Safety Standard Determination of Protein in Food";

[0184] The fat content refers to the Soxhlet extraction method of GB 5009.6-2016. Weigh 10g of sample, mix it with 20g of quartz sand in an evaporating dish, evaporate it to dryness in a boiling water bath, place it in a forced air drying oven at 100℃ for 30min, grind it thoroughly, extract it with Soxhlet, and weigh it;

[0185] The stability test is characterized by the overall stability index TSI (Turbiscan Stability Index), which is an important indicator for stability analysis of emulsions, suspensions or other dispersed systems using a Turbiscan instrument. TSI quantifies the stability of the system by evaluating the particle size changes, aggregation, sedimentation or floating phenomena that occur in the sample during the measurement. TSI test and calculation method: Sample preparation and measurement: Inject 20mL of walnut milk sample into the measuring cell with a height of 40mm and place the sample in the detection chamber. Using the Turbiscan instrument, scan the sample cell from bottom to top at intervals of 40μm. Measurements are taken every hour for 24 hours, and the test temperature is kept constant at 25°C. TSI is calculated based on the change in backscattered light intensity at each measuring point:

[0186]

[0187] ΔBS i is the backscattered light intensity change at the i-th scanning point. i is the height of the i-th layer in the sample pool. n is the total number of scanned layers in the sample pool. The larger the TSI value, the worse the stability of the sample, and the more significant the particle size change, aggregation, sedimentation or floating phenomenon.

[0188] Table 3 shows the protein content, fat content and overall stability index of the first low-fat peptide-containing walnut milk;

[0189] Table 4 shows the protein content, fat content, and overall stability index of the second low-fat peptide-containing walnut milk;

[0190] Table 3

[0191]

[0192]

[0193] Table 4

[0194]

[0195]

[0196] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for extracting walnut oil and producing dual-type low-fat peptide-containing walnut milk, characterized in that: The steps include: (1) soaking the initial walnut kernels in an alkali solution, taking them out and letting them stand, and then steaming and washing them to remove moisture from the surface of the washed walnut kernels to obtain the de-astringent walnut kernels; (2) dry-grinding the de-astringent walnut kernels obtained in step (1) to obtain walnut paste; (3) mixing the walnut paste obtained in step (2) with water and performing solid-liquid separation to obtain a supernatant and a precipitate; (4) subjecting the supernatant obtained in step (3) to a first enzymatic hydrolysis and then separating the oil phase and the water phase, refining the oil phase to obtain walnut oil, and inactivating the enzyme in the water phase to obtain a first low-fat peptide-containing walnut milk; (5) The precipitate obtained in step (3) is mixed with water, and then subjected to a second enzymatic hydrolysis and enzyme inactivation to obtain a second low-fat peptide-containing walnut milk precursor, and then the second low-fat peptide-containing walnut milk precursor is mixed with an additive to obtain a second low-fat peptide-containing walnut milk.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of walnut to alkali solution during the soaking of the initial walnut kernel in alkali solution is 1:(2-8); Preferably, the alkali solution is selected from aqueous sodium hydroxide solution; Preferably, the concentration of the sodium hydroxide aqueous solution is 0.3-3.0%; Preferably, the soaking temperature is 15-35°C and the soaking time is 30s-2min; Preferably, the standing temperature is 20-35°C; the standing time is 30s-2min; Preferably, the water vapor temperature during the water vapor treatment process is 95-120°C and the time is 1-5min; Preferably, the water vapor pressure is 0-0.2 MPa.

3. The method according to claim 1 or 2, characterized in that: In step (1), the cleaning process includes rinsing; Preferably, the rinsing is performed by water rinsing; Preferably, the water temperature in the elution is 15-35°C; the elution time is 10-50s; Preferably, the water temperature during water immersion is 40-80°C and the immersion time is 4-21 minutes; Preferably, the process of removing the moisture on the surface of the washed walnut kernels is to use air to flush away the moisture on the surface of the washed walnut kernels; Preferably, the air is high-pressure air; Preferably, the pressure of the high-pressure air is 0.3-1.2 MPa; Preferably, the time for flushing the surface moisture of the washed walnut kernels with air is 10-50s.

4. The method according to any one of claims 1 to 3, characterized in that: In step (2), the dry grinding is anhydrous colloid grinding; Preferably, the anhydrous colloid is ground 2-4 times; Preferably, the temperature of the dry grinding is 50-65°C; Preferably, the particle size Dv(90) of the walnut paste obtained by the dry grinding is less than 550 μm.

5. The method according to any one of claims 1 to 4, characterized in that: In step (3), the walnut paste obtained in step (2) and water are mixed at a temperature of 50-65° C. and a stirring rate of 30-100 rpm; Preferably, the mass ratio of the walnut paste obtained in step (2) to water is 1:(2-3); Preferably, the solid-liquid separation is carried out by centrifugal separation; wherein the centrifugal force is 4000-6000g.

6. The method according to any one of claims 1 to 5, characterized in that: In step (4), the temperature of the first enzymolysis is 55-65°C, the time is 1-4h, and the stirring speed of the first enzymolysis is 30-100rpm; Preferably, the enzymes for the first enzymatic hydrolysis include alkaline protease and flavor protease; Preferably, in the first enzymatic hydrolysis, the amount of alkaline protease added is 0.4-1‰ of the initial walnut kernel mass in step (1); the amount of flavor protease added is 1-2‰ of the initial walnut kernel mass in step (1); Preferably, the separation of the oil phase and the water phase is carried out by a centrifuge; Preferably, the centrifuge is a disc centrifuge; Preferably, the oil phase refining process includes degumming, deacidification and dehydration; Preferably, the temperature of the aqueous phase enzyme inactivation is 80-90°C and the time is 20-30 minutes.

7. The method according to any one of claims 1 to 6, characterized in that: In step (5), the mass ratio of the precipitate to water is 1:(1.5-3); Preferably, the mixing temperature of the precipitate and water is 50-65° C., and the mixing stirring rate is 30-100 rpm.

8. The preparation method according to any one of claims 1 to 7, characterized in that: In step (5), the enzymes for the second enzymatic hydrolysis include alkaline protease and flavor protease; Preferably, in the second enzymatic hydrolysis, the amount of alkaline protease added is 1-2.5‰ of the initial walnut kernel mass in step (1); the amount of flavor protease added is 2-5‰ of the initial walnut kernel mass in step (1); The second enzymatic hydrolysis time is 2-5h.

9. The method according to any one of claims 1 to 8, characterized in that: In step (5), the additive is an auxiliary material aqueous solution; the mass ratio of the auxiliary material to water in the auxiliary material aqueous solution is 1: (30-100); Preferably, the auxiliary materials include monoglyceride of fatty acid, sodium stearoyl lactylate, and casein; The amount of auxiliary materials added to the second low-fat peptide-containing walnut milk is 1.5‰-15‰ of the initial walnut kernel mass; Preferably, monoglyceride accounts for 0.5‰-5‰ of the mass of the initial walnut kernel; sodium stearoyl lactylate accounts for 0.5‰-5‰ of the mass of the initial walnut kernel; casein accounts for 0.5‰-5‰ of the mass of the initial walnut kernel; Preferably, the preparation process of the auxiliary material aqueous solution is to mix the auxiliary material with water at 65-78°C.

10. The method according to any one of claims 1 to 9, characterized in that: After the second low-fat peptide-containing walnut milk precursor is mixed with the additive in step (5), the process further includes volume fixing, homogenization, and a second enzyme inactivation process; The constant volume temperature is 60-80℃; Homogenization pressure is 30-40MPa; The second enzyme inactivation temperature is 120-125°C; the enzyme inactivation time is 20-25 minutes.

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