A method for preparing walnut oil and walnut protein powder

Abstract

The present invention relates to a method for preparing walnut oil and walnut protein powder, comprising the following steps: Step 1, pressing the peeled walnut kernels with a hydraulic oil press to obtain cold-pressed walnut oil and walnut cakes; Step 2, adding alcohol to the walnut cakes, soaking and then pressing, repeating 1-3 times to obtain an oil-alcohol mixture and defatted walnut cakes; Step 3, drying the defatted walnut cakes at a low temperature under vacuum and pulverizing them to obtain walnut protein powder; allowing the oil-alcohol mixture to stand or centrifuging it to separate the alcohol and the oil into layers, removing the alcohol layer to obtain alcohol-assisted pressed walnut oil; The present invention obtains two kinds of walnut oil: cold-pressed walnut oil and alcohol-assisted pressed walnut oil; Since the walnut skins are removed and the pressing and residual oil removal processes are carried out at low temperature or normal temperature without using non-environmentally friendly solvents, the obtained walnut protein powder is white in color and its commerciality is greatly improved, and it can be used for developing low-fat and high-protein healthy foods.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and vegetable protein processing, and particularly relates to a method for preparing walnut oil and walnut protein powder. Background Art

[0002] Walnut kernels contain 65 - 70% lipids and 15% protein. Walnut oil is favored in markets such as for mothers and infants because it is rich in polyunsaturated fatty acids and has potential in improving intelligence. Walnut protein is a good source of arginine and contains abundant protease and antioxidant enzymes, having great application prospects in the fields of special medical care and intelligence improvement. Currently, the main products of walnut processing are walnut nuts and walnut milk. With the increase in walnut production in China, the deep processing of walnuts is increasing and becoming more urgent. Extracting oil and preparing protein from walnut kernels is an important and effective direction.

[0003] Currently, for this direction, mainly walnut oil and cake are obtained through pressing, and the residual oil in the walnut cake is extracted by the subcritical extraction process. In order to maximize the walnut oil yield during pressing, on the one hand, the moisture content of the walnut kernels needs to be dried to less than 3%, and on the other hand, heating is carried out during pressing, which can reach above 75 °C. This has an adverse effect on walnut oil (lipid oxidation) and walnut protein (denaturation and loss of activity). In addition, a large amount of phenolic substances contained in the walnut shell will be oxidized during the processing, which will also greatly affect the appearance and commercial value of the walnut protein product, resulting in the walnut cake meal being only used in the feed industry with low value output, becoming an urgent problem in the industry. In order to improve the appearance of the walnut cake meal, currently, mainly after pressing the walnut kernels, part of the walnut shell is removed by air separation. However, the improvement degree of the appearance of the walnut cake meal is not large. Finally, the pressed walnut cake is subjected to subcritical extraction, and the organic solvents used are alkanes, which are somewhat toxic. On the one hand, it is not environmentally friendly, and on the other hand, there will be a residue problem in the product, restricting the high-value utilization of the walnut cake after oil extraction.

[0004] The walnut oil and walnut cake prepared by the cold pressing process can solve some problems caused by heating in the above process. However, after pressing, the residual oil rate in the walnut cake is relatively high, usually above 20%, which greatly reduces the output of walnut oil. Moreover, after these walnut cakes with high oil residues are prepared into walnut protein powder, it is not conducive to the healthy pursuit of fat control. And due to the imperfect intestinal function of infants, it cannot be applied to high-value infant foods. Therefore, how to improve the appearance of the walnut protein product is an important issue for increasing the value output of walnut kernels. Summary of the Invention

[0005] The object of the present invention is to overcome the defects in the prior art, and provides a method for preparing walnut oil and walnut protein powder. The method is simple and easy to operate, realizes the efficient extraction of walnut oil, does not use environmentally unfriendly alkane organic solvents, and does not heat during the pressing process and the residual oil removal process, greatly improving the quality of the walnut protein product.

[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] A method for preparing walnut oil and walnut protein powder, comprising the following steps:

[0008] Step 1: Press the de-skinned walnut kernels with a hydraulic oil press to obtain cold-pressed walnut oil and walnut cakes;

[0009] Step 2: Add alcohol to the walnut cakes, soak and then press, repeat 1 - 3 times (it can be 1 time, 2 times or 3 times) to obtain an oil-alcohol mixture and defatted walnut cakes;

[0010] Step 3: Volatilize and dry the defatted walnut cakes at low temperature under vacuum and then pulverize them to obtain walnut protein powder. In the process of removing residual oil from the walnut cakes in the present invention, by using the fluid property of alcohol, the alcohol fluid penetrates into the walnut cakes, increasing the fluid content in the walnut cakes, improving the fluidity of the oil, and enabling the oil and alcohol to be pressed out together during the pressing process to form an oil-alcohol mixture, thus realizing the defatting of the walnut cakes.

[0011] As a further technical solution, the preparation of the de-skinned walnut kernels includes: soaking the walnut kernels in water, using a high-pressure water gun to wash off the walnut skins, and drying them at low temperature to obtain de-skinned walnut kernels.

[0012] As a further technical solution, the temperature of the low-temperature drying ≤ 50°C (it can be selected as 50°C, 48°C, 46°C, 44°C, 42°C, 40°C, etc.), and the moisture content of the de-skinned walnut kernels after low-temperature drying ≤ 7%. Compared with the traditional pressing process, in the present invention, it is only necessary to reduce the moisture content to below 7%, without the need to reduce the moisture content to below 3%, and the present invention performs hydraulic pressing at normal temperature, maintaining the quality of the walnut oil and walnut protein.

[0013] As a further technical solution, the pressing in Step 1 adopts a cold pressing process.

[0014] As a further technical solution, in Step 2, the volume concentration of the alcohol ≥ 95% (it can be selected as 95%, 96%, 97%, 98%, 99%, 100%, etc.).

[0015] As a further technical solution, the amount of alcohol added per kilogram of walnut cake ≥ 0.3 L (0.3 L, 0.35 L, 0.4 L, 0.45 L, 0.5 L, 0.55 L, 0.6 L, 0.65 L, 0.7 L, 0.75 L, 0.8 L, 0.85 L, 0.9 L, 0.95 L, 1.0 L, 1.05 L, 1.1 L, 1.2 L, 1.3 L, 1.4 L, 1.5 L, 1.6 L, 1.7 L, 1.8 L, 1.9 L, 2.0 L, 2.1 L, 2.2 L, 2.3 L, 2.4 L, 2.5 L, 2.6 L, 2.7 L, 2.8 L, 2.9 L, 3.0 L, 3.1 L, 3.2 L, etc. can be selected), preferably ≥ 0.5 L.

[0016] As a further technical solution, in step 2, the number of repetitions is 2 times.

[0017] As a further technical solution, in step 2, the soaking time is ≥ 2 h (2 h, 2.5 h, 3 h, 4.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h, 12 h, etc. can be selected).

[0018] As a further technical solution, in step 2, the pressing is carried out by hydraulic pressing (cold pressing), and the pressure of the hydraulic pressing ≥ 50 MPa (50 MPa, 55 MPa, 60 MPa, 65 MPa, 70 MPa, etc. can be selected).

[0019] As a further technical solution, it also includes: the oil-alcohol mixture obtained after several times of soaking and pressing is respectively allowed to stand or centrifuged, or combined and then allowed to stand or centrifuged to separate the alcohol and the oil into layers, and the alcohol layer is removed to obtain alcohol-assisted pressed walnut oil. Since the low-temperature or normal-temperature (i.e., room temperature) alcohol is used in the present invention, compared with the use of hot alcohol (hot alcohol is usually greater than 50 °C, and oil is soluble in hot alcohol and insoluble in low-temperature or normal-temperature alcohol), the phenomenon of mutual dissolution of oil and alcohol does not occur throughout the process. Therefore, only standing or centrifuging is required for layer separation, which simplifies the operation steps.

[0020] As a further technical solution, in step 3, the temperature of the low-temperature vacuum evaporation is ≤ 50 °C (50 °C, 48 °C, 46 °C, 44 °C, 42 °C, 40 °C, etc. can be selected).

[0021] As a further technical solution, the oil content rate of the walnut protein powder is less than 3%.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1), Taking shelled walnut kernels as raw materials, after cold pressing to extract walnut oil, the cold-pressed walnut cake is then subjected to alcohol soaking and pressing to recover the residual oil in the walnut cake, obtaining walnut protein powder with low oil content, no harmful solvent residues, and no thermal denaturation, greatly improving the quality of the walnut protein powder.

[0024] 2), In the process of recovering the residual oil in the walnut cake, this invention breaks through the limitations of traditional techniques such as the leaching method (similar solubility principle) and the aqueous method (using the water-in-oil structure to promote oil dissolution principle), selects environmentally friendly alcohol, and utilizes the fluid properties of alcohol to make the alcohol fluid penetrate into the walnut cake, increasing the fluid content in the walnut cake, improving the fluidity of the oil in the walnut cake, and then pressing out the alcohol and oil together during the pressing process to form an oil-alcohol mixture (at low or normal temperature, the solubility of oil in alcohol is very low and no water-in-oil structure will be formed). Then, through static settling or centrifugation of this mixture, the alcohol can be separated from the walnut oil, realizing the extraction and recovery of the walnut oil in the walnut cake. Compared with the leaching method and the aqueous method, it has simple operation, does not use non-environmentally friendly alkane solvents, and does not require any heat treatment during pressing and residual oil removal, avoiding the problem of the poor quality of walnut protein powder caused by alkane solvents and heating.

[0025] 3), The equipment used in this invention includes a walnut shelling machine, a hydraulic oil press, a centrifuge or a separating tank, and a vacuum drying equipment. These equipments are all mature in industrial production and have large production capacity. Therefore, this invention does not involve equipment that affects production, laying a solid foundation for the industrial production of walnut oil and walnut protein powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is an intuitive comparison diagram of cold-pressed walnut oil and alcohol-assisted pressed walnut oil;

[0027] Among them, a: cold-pressed walnut oil (Example 1); b: alcohol-assisted pressed walnut oil (Example 1).

[0028] Figure 2 It is a color comparison diagram of the walnut protein powder prepared in Example 1 and Comparative Example 1;

[0029] Among them, a: Comparative Example 1; b: Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0030] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0031] In addition, it should be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or apparatus comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or apparatus.

[0032] Unless otherwise specified, the raw materials used are commercially available raw materials.

[0033] Example 1

[0034] A method for preparing walnut oil and walnut protein powder, comprising the following steps:

[0035] S1. Soak walnut kernels in water for 30 min, wash off the walnut skins with a high-pressure water gun, and dry them in a blast dryer at 50 °C for 6 h to make the moisture content less than 7%, obtaining de-skinned walnut kernels;

[0036] S2. Adopt the cold pressing process, press the de-skinned walnut kernels at a hydraulic pressure of 60 MPa to obtain cold-pressed walnut oil and walnut cake A;

[0037] S3. According to the mass-volume ratio of walnut cake A to alcohol of 1 kg: 0.5 L, add 99% alcohol to the walnut cake, soak for 2 h, and press with a hydraulic press at a pressure of 60 MPa to obtain walnut cake B and oil-alcohol mixture A;

[0038] S4. According to the mass-volume ratio of walnut cake B to alcohol of 1 kg: 0.5 L, add 99% alcohol to walnut cake B, soak for 2 h, and press with a hydraulic press at a pressure of 60 MPa to obtain walnut cake C and oil-alcohol mixture B;

[0039] S5. Combine oil-alcohol mixture A and oil-alcohol mixture B, then let it stand or centrifuge to separate the oil and alcohol by stratification, and remove the alcohol layer to obtain alcohol-assisted pressed walnut oil;

[0040] Vacuum dry and pulverize the walnut cake C at 50 °C to obtain a walnut protein powder product.

[0041] The lipid content of the walnut protein powder product was measured by the chloroform-methanol method. The results showed that its residual oil rate was 2.82%.

[0042] Compare the colors of the cold-pressed walnut oil and alcohol-assisted pressed walnut oil obtained in Example 1. It was found that: the alcohol-assisted pressed walnut oil was slightly darker in color than the cold-pressed walnut oil, but still showed transparency (see Figure 1 ).

[0043] Examples 1-3: Influence of alcohol soaking time on residual oil removal

[0044] I. Test method

[0045] Example 2: The same as Example 1, except that in S3 and S4, the soaking time in alcohol is 4 h for both.

[0046] Example 3: The same as Example 1, except that in S3 and S4, the soaking time in alcohol is 6 h for both.

[0047] II. Index analysis and results

[0048] The lipid contents of the walnut protein powder products prepared in Examples 2 - 3 were measured by the chloroform - methanol method. The results showed that the residual oil rate of the walnut protein powder product in Example 2 was 2.57%, and the residual oil rate of the walnut protein powder product in Example 3 was 1.45%. Through the comparison of Examples 1 - 3, it can be seen that as the soaking time prolongs, the residual oil rate decreases.

[0049] Example 4

[0050] A method for preparing walnut oil and walnut protein powder, comprising the following steps:

[0051] S1. Soak the walnut kernels, wash off the walnut skins with a high - pressure water gun, dry, and cold - press. The drying conditions and cold - pressing conditions are the same as those in Example 1 to obtain walnut cake A and cold - pressed walnut oil;

[0052] S2. Add 95% alcohol to the walnut cake A according to the mass - volume ratio of walnut cake A to alcohol of 1 kg:0.5 L, soak for 12 h, and press with a hydraulic press at a pressure of 60 MPa to obtain walnut cake B and oil - alcohol mixture A;

[0053] S3. Add 99% alcohol to the walnut cake B according to the mass - volume ratio of walnut cake B to alcohol of 1 kg:0.5 L, soak for 12 h, and press with a hydraulic press at a pressure of 60 MPa to obtain walnut cake C and oil - alcohol mixture B;

[0054] S4. Combine the oil - alcohol mixture A and the oil - alcohol mixture B, then let it stand or centrifuge to separate the oil and alcohol into layers, and remove the alcohol layer to obtain alcohol - assisted pressed walnut oil;

[0055] Vacuum - dry and crush the walnut cake C at 50 °C to obtain a walnut protein powder product.

[0056] The lipid content of the prepared walnut protein powder product was measured by the chloroform - methanol method. The results showed that the lipid content was 0.32%.

[0057] Examples 1, 5 - 6: Influence of the ratio of sunflower seed cake to alcohol on residual oil removal

[0058] I. Test method

[0059] Example 5: Identical to Example 1, except that in S3 and S4, the mass-to-volume ratio of cold-pressed walnut cake to 99% alcohol is 1 kg: 3 L;

[0060] Example 6: Identical to Example 1, except that in S3 and S4, the mass-to-volume ratio of cold-pressed walnut cake to 99% alcohol is 1 kg: 0.3 L.

[0061] The lipid contents of the walnut protein powder products prepared in Examples 5 and 6 were measured using the chloroform-methanol method. The results showed that the residual oil rate of Example 5 was 2.94%; the residual oil rate of Example 6 was 4.73%; Therefore, from the comparison of Example 1 and Examples 5-6, it can be seen that the amount of alcohol used (the ratio of alcohol to walnut cake) has a certain effect on residual oil removal, but the effect is not obvious. In the present invention, as long as the amount of alcohol used per kilogram of cold-pressed walnut cake is greater than or equal to 0.5 L, it can ensure that the oil content in the walnut protein powder is less than 3%.

[0062] Comparative Example 1

[0063] A method for preparing cold-pressed walnut oil and walnut cake, comprising the following steps:

[0064] S1. Press the walnut kernels (without removing the skin) at 60 MPa (cold pressing process) to obtain walnut cake A and walnut oil A;

[0065] S2. After manually breaking walnut cake A, press it at 60 MPa (cold pressing process) to obtain walnut cake B and walnut oil B;

[0066] S3. After manually breaking walnut cake B, press it at 60 MPa (cold pressing process) to obtain walnut cake C and walnut oil C;

[0067] The lipid content of the prepared walnut cake C was measured using the chloroform-methanol method. The results showed that its residual oil rate was 16.4%, which was much higher than that of Examples 1-5 of the present invention. After grinding walnut cake C into walnut protein powder and comparing its color with the walnut protein powder of Example 1, it was found that its color was significantly darker than that of Example 1 (see Figure 2 ).

[0068] Comparative Example 2

[0069] A method for preparing walnut oil and walnut protein powder, comprising the following steps:

[0070] Identical to Example 1, except that in S3, the volume concentration of alcohol is 75%; at this alcohol concentration, during the pressing process, the walnut cake material was extruded, causing blockage of the pressing oil path.

[0071] Comparative Example 3

[0072] A method for preparing walnut oil and walnut protein powder, comprising the following steps:

[0073] Same as Example 1, except that in S3 and S4, the soaking time is 1 h for both.

[0074] The lipid content of the prepared walnut protein powder product was measured by the chloroform - methanol method. The results showed that its residual oil rate was 4.68%, higher than that of Examples 1 - 5.

[0075] Comparative Example 4

[0076] A method for preparing walnut oil and walnut protein powder, comprising the following steps:

[0077] Same as Example 1, except that in S3 and S4, the pressing pressure is 40 MPa for both.

[0078] The lipid content of the prepared walnut protein powder was measured by the chloroform - methanol method. The results showed that its residual oil rate was 8.4%, much higher than that of Examples 1 - 5.

[0079] Comparative Example 5

[0080] A method for preparing walnut oil and walnut protein powder, comprising the following steps:

[0081] Same as Example 1, except that in S3 and S4, suction filtration is used instead of pressing.

[0082] The lipid content of the prepared walnut protein powder was measured by the chloroform - methanol method. The results showed that its residual oil rate was 19.2%, much higher than that of Examples 1 - 5.

[0083] The above - described embodiments are only the preferred embodiments of the present invention, rather than an exhaustive list of all feasible embodiments of the present invention. For those of ordinary skill in the art, any obvious changes made without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing walnut oil and walnut protein powder with a residual oil content as low as 1.45%, characterized in that, It includes the following steps: S1. Soak the walnut kernels in water for 30 min, rinse off the walnut skins with a high-pressure water gun, and dry them in a blast dryer at 50 °C for 6 h to make the moisture content less than 7%, obtaining peeled walnut kernels; S2. Adopt the cold pressing process, press the peeled walnut kernels under 60 MPa hydraulic pressure to obtain cold-pressed walnut oil and walnut cake A; S3. According to the mass-volume ratio of walnut cake A to alcohol of 1 kg: 0.5 L, add 99% alcohol to the walnut cake, soak for 6 h, and press with a hydraulic press under a pressure of 60 MPa to obtain walnut cake B and oil-alcohol mixture A; S4. According to the mass-volume ratio of walnut cake B to alcohol of 1 kg: 0.5 L, add 99% alcohol to walnut cake B, soak for 6 h, and press with a hydraulic press under a pressure of 60 MPa to obtain walnut cake C and oil-alcohol mixture B; S5. Combine oil-alcohol mixture A and oil-alcohol mixture B, then let it stand or centrifuge to separate the oil and alcohol by stratification, and remove the alcohol layer to obtain alcohol-assisted pressed walnut oil; Vacuum dry and crush the walnut cake C at 50 °C to obtain a walnut protein powder product.

Images