Walnut oil with high quality and nut flavor as well as preparation method and application of walnut oil

Abstract

The invention discloses a preparation method of walnut oil with high quality and nut flavor, and belongs to the field of edible oil processing. The walnut oil with high quality and nut flavor is obtained by baking the hulled walnut kernels for aroma enhancement and then extracting by using a low-water extraction method. The walnut oil extraction time is greatly shortened, and the energy consumption is reduced; the oxidation stability and micronutrient content of the obtained walnut oil are remarkably improved, and the walnut oil is high in quality and has a nut flavor.

Description

Technical Field

[0001] The invention belongs to the technical field of oils and fats, and particularly relates to high-quality walnut oil with nut flavor, a preparation method and application thereof. Background Art

[0002] Walnut is one of the four most popular nuts and is the woody oil with the highest annual output in my country (the annual output will reach 5.93 million tons in 2022). Walnut kernels contain 60% to 75% oil, and walnut oil is rich in essential fatty acids (linoleic acid, linolenic acid) that are beneficial to the human body, as well as micronutrients such as phytosterols, tocopherols, and phenolic compounds. In addition, the unique nutty flavor of walnut oil is also widely loved by consumers.

[0003] As a typical high-oil oil, walnuts are often used in the industry to extract oil by screw pressing and pre-pressing-leaching. According to the temperature of the pressing chamber, it can be further divided into cold pressing and hot pressing. The Maillard reaction, lipid oxidation, and amino acid degradation in hot pressing give walnut oil a toasted nutty flavor, but at the same time it will cause protein denaturation and the generation of harmful substances. Low-temperature cold pressing allows better retention of bioactive ingredients, but its poor flavor and sensory quality lead to low consumer acceptance. Due to the high oil content of walnuts, the walnut kernels cannot be efficiently squeezed between the barrel wall of the screw press during production, resulting in "slippery bore" and "piling" in production, and the oil yield is low. The cake after pressing is further extracted with a solvent to obtain the residual oil, but it needs to be refined to remove wax, free fatty acids, pigments and other substances. The high temperature during the refining process causes the quality of walnut oil to decline and the content of flavor substances to decline.

[0004] In recent years, consumers have paid more and more attention to the quality and flavor of edible oils. How to obtain high-quality and flavorful walnut oil at the same time will help to expand the oil market. Without considering the variety and source of oil, the quality of oil mainly depends on the extraction method. The water substitution method uses water as a solvent and uses the density difference and immiscible characteristics of water and oil to extract oil from crushed oil. This method has simple process, low equipment requirements, high quality of the obtained oil (can retain bioactive ingredients such as tocopherol) and no need for refining, but usually requires a large amount of water (solid-liquid ratio>1:5, w / v) and will produce emulsions that affect the oil yield. The low-water water substitution method is similar to the water substitution method (solid-liquid ratio>1:5, w / v), but only less than 20% (solid-liquid ratio<5:1, w / v) of water is added during the extraction to achieve efficient separation of oil, greatly reducing the use of water and avoiding the formation of emulsions. The generation of flavor substances is affected by heat treatment during the extraction process (usually baking the oil in pretreatment). The purpose of roasting is not only to enhance the flavor, but also to improve the quality of the oil. However, too high a temperature will lead to a decrease in the quality of the oil. Combining roasting with low water substitution can theoretically produce high-quality walnut oil with a nutty flavor after roasting. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In order to solve the problems of poor quality and poor oxidative stability of walnut oil and difficulty in simultaneously meeting high quality and flavor, the present invention uses walnut kernels with skin as raw materials, constructs a baking process combined with a low water replacement method to prepare walnut oil. The walnut oil prepared by the method has high oil quality, and the oxidative stability, trace nutrient content and walnut oil flavor substance content are significantly increased.

[0007] The low water-water replacement method is similar to the water replacement method (solid-liquid ratio>1:5, w / v), but only less than 20% (solid-liquid ratio<5:1, w / v) of water needs to be added during the extraction to achieve efficient separation of oils and fats. Moderate baking can not only change the composition and content of trace nutrients, but also improve the flavor and oxidative stability of the oils and fats. Excessive baking will reduce the quality of the oils and fats and produce harmful substances. Therefore, combining baking with the low water-water replacement method can produce high-quality walnut oil with a nutty flavor.

[0008] The present invention overcomes the deficiencies in the prior art and aims to provide a method for preparing walnut oil with high quality and nutty flavor. The method has low cost, simple process, and is suitable for large-scale production. The basic physical and chemical indicators of the acid value and peroxide value of the obtained walnut oil are significantly better than the walnut oil index requirements in the national standard, the quality is better than commercially available walnut oil, and the walnut oil has a nutty flavor after baking.

[0009] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0010] Therefore, the object of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing walnut oil with high quality and nut flavor.

[0011] In order to solve the above technical problems, the present invention provides the following technical solutions: comprising:

[0012] The shelled walnut kernels with seed coat are roasted, and then ground into walnut paste after cooling; water is added to the walnut paste, and stirred to obtain an oil-water mixture, and the mixture is centrifuged to obtain an upper layer of clear oil and a lower layer of oil residue, and the upper layer of clear oil is taken out to obtain walnut oil;

[0013] The baking includes one or more of infrared baking, oven baking and microwave baking, and the baking temperature of the infrared baking is 120-140° C. and the time is 10-40 min;

[0014] The added amount of water is 10% to 20% of the dry weight of the walnut kernel.

[0015] As a preferred solution of the method for preparing the high-quality walnut oil with nut flavor described in the present invention, the oil content of the walnut kernel is 62% to 75%.

[0016] As a preferred embodiment of the method for preparing the high-quality walnut oil with nutty flavor described in the present invention, the infrared baking and oven baking are performed at a temperature of 120 to 140° C. and for a time of 10 to 40 minutes.

[0017] As a preferred embodiment of the method for preparing high-quality walnut oil with nutty flavor described in the present invention, the microwave baking has a power of 600-700 W and a time of 2.5-4.5 min.

[0018] As a preferred embodiment of the method for preparing high-quality walnut oil with nutty flavor described in the present invention, the particle size of the walnut paste is 100 to 300 μm.

[0019] As a preferred solution of the method for preparing the high-quality walnut oil with nutty flavor described in the present invention, the amount of water added is 15% of the dry weight of the walnut kernel.

[0020] As a preferred embodiment of the method for preparing high-quality walnut oil with nut flavor described in the present invention, the stirring is performed at a speed of 100 to 300 r / min for a time of 1 to 5 min.

[0021] As a preferred embodiment of the method for preparing high-quality walnut oil with nut flavor described in the present invention, the centrifugation has a rotation speed of 5000-12000 r / min and a time of 5-15 min.

[0022] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a walnut oil with high quality and nut flavor.

[0023] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a walnut oil with high quality and nut flavor for use in the fields of functional food, food preparation and cosmetics.

[0024] Beneficial effects of the present invention:

[0025] (1) The present invention adopts a low-water-water replacement method to extract walnut oil in a short time and efficiently, and the obtained oil does not need to be refined, which meets the relevant quality requirements of walnut oil in the national standard "GB / T 22327-2019 Walnut Oil".

[0026] (2) The present invention uses infrared, oven, and microwave baking to treat walnut kernels, while maintaining the quality of the oil, increasing the content of volatile compounds and improving the nutty flavor of the walnut oil.

[0027] (3) The present invention solves the problems of poor quality, poor oxidative stability and difficulty in simultaneously meeting high quality and flavor requirements of traditional walnut oil. The walnut oil prepared by baking treatment combined with a low water replacement method is of high quality and has a nutty flavor. In addition, the walnut oil has low oleic acid value and peroxide value, high oxidative stability, significantly increased micronutrient content, and increased oil flavor substance content. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0029] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0030] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0031] The raw materials used in the present invention are all commercially available unless otherwise specified.

[0032] The edible oil prepared in the embodiment of the present invention was tested for performance as follows:

[0033] Acid value: The acid value of oils and fats is determined according to GB 5009.229-2016.

[0034] Peroxide value: refer to GB 5009.227-2023 to measure the peroxide value of oils and fats.

[0035] Fatty acid composition: The fatty acid composition of oils and fats was determined according to GB 5009.168-2016.

[0036] Oxidation stability: Refer to GB / T 21121-2007 to test the oxidation stability index (OSI) of oils and fats. Accurately add 3g of oil sample (accurate to 0.001g) into a glass test tube and use a Rancimat oil oxidation stability instrument to measure. The test temperature is 120℃ and the air flow rate is 20L / h. The experimental results are expressed in h as the OSI value of the oil sample.

[0037] Tocopherol content: refer to GB 26635-2011 to determine the tocopherol content in oils and fats.

[0038] Sterol content: refer to GB / T 25223-2010 to determine the sterol content in oils and fats.

[0039] Polyphenol content: refer to LS / T 6119-2017 to determine the polyphenol content in oils and fats.

[0040] Flavor substances: Volatile components in walnut oil were determined by headspace solid phase microextraction-gas chromatography-mass spectrometry. Weigh 3.0g of walnut oil and add 40μL of 54.6μg / mL 1,2-dichlorobenzene in a 20mL vial. After incubation at 60℃ for 5min, StableFlex styrene / carboxyl / polydimethylsiloxane fiber (DVB / CAR / PDMS) was used for adsorption for 30min, followed by 5min of GC-MS inlet analysis at 250℃, using EI ion source mode, fixed electron energy 70eV, and scanning range 33-550m / z to analyze volatile compounds. The heating program was: 45℃ for 2min, increased to 180℃ at 3℃ / min, and then increased to 240℃ at 10℃ / min and maintained for 5min. The helium flow rate was 1.898mL / min.

[0041] Example 1

[0042] This embodiment provides a method for preparing walnut oil with high quality and nutty flavor. This embodiment combines infrared baking and aroma enhancement with a low water replacement method to prepare walnut oil with high quality and nutty flavor in a short time and with high efficiency. Specifically, the method is as follows:

[0043] (1) Oil preparation: cracked walnut kernels with seed coat are infrared-baked at 130°C for 30 min, cooled to room temperature and set aside;

[0044] (2) Oil treatment: using a colloid mill to grind the cooled walnut kernels into walnut paste with a particle size of 200 μm;

[0045] (3) Oil-water mixing: add 15% water to the walnut paste and stir at 200 r / min for 1 min to obtain an oil-water mixture.

[0046] (4) Oil separation: The oil-water mixture is centrifuged at 10,000 r / min for 10 min to obtain two phases, namely, the upper clear oil and the lower residue. Walnut oil is obtained after extraction.

[0047] Example 2

[0048] The difference between this embodiment and embodiment 1 is that the baking time is adjusted to 10 minutes, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0049] Example 3

[0050] The difference between this embodiment and embodiment 1 is that the baking time is adjusted to 20 minutes, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0051] Example 4

[0052] The difference between this embodiment and embodiment 1 is that the baking time is adjusted to 40 minutes, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0053] Comparative Example 1

[0054] Commercially available "Moore's Farm" walnut oil.

[0055] The performance of the walnut oil prepared in the above embodiment was tested, and the comparison results with those in Example 1 are shown in Table 1.

[0056] Table 1

[0057]

[0058]

[0059] As can be seen from the above table, the walnut oil prepared by the infrared baking treatment combined with the low water replacement method using the skinned walnut kernel as raw material in the present invention is of high oil quality, and the oxidative stability, trace nutrient content, and walnut oil flavor substance content are significantly increased compared with the commercially available walnut oil. Among them, the oxidative stability, trace nutrient content, and flavor substance content of the walnut oil obtained after baking for 30 minutes in Example 1 are significantly higher than those in Example 2 (baking for 10 minutes) and Example 3 (20 minutes). Although the content of trace nutrients in Example 4 (40 minutes) is higher than that in Example 1, due to the little difference in its oxidative stability, in order to consider the production cost, the present invention selects Example 1 as the optimal condition. In summary, the preferred baking time of the present invention is 30 minutes.

[0060] Example 5

[0061] The difference between this embodiment and embodiment 1 is that the baking procedure is adjusted to oven baking at 130° C. for 10 min, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0062] Example 6

[0063] The difference between this embodiment and embodiment 1 is that the baking procedure is adjusted to oven baking at 130° C. for 20 minutes, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0064] Example 7

[0065] The difference between this embodiment and embodiment 1 is that the baking procedure is adjusted to oven baking at 130° C. for 30 minutes, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0066] The performance of the walnut oil prepared in the above embodiment was tested, and the comparison results with those in Example 1 are shown in Table 1.

[0067] Table 2

[0068]

[0069]

[0070] As can be seen from the above table, adjusting the baking method of walnut kernels has a significant effect on the performance of walnut oil. This is because compared with oven baking, infrared baking can quickly and evenly heat walnut kernels, promote the release of micronutrients, and the generation of Maillard reaction, so that the quality and flavor of walnut oil are excellent. Although oven baking can also improve the quality and flavor as time increases, the effect is worse than infrared baking treatment at the same temperature and time. In summary, the preferred infrared of the present invention is that the baking temperature is 130°C and the time is 30min.

[0071] Example 8

[0072] The difference between this embodiment and embodiment 1 is that the baking procedure is adjusted to microwave baking at 700 W for 2.5 min, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0073] Example 9

[0074] The difference between this embodiment and embodiment 1 is that the baking procedure is adjusted to microwave baking at 700 W for 3.5 min, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0075] Example 10

[0076] The difference between this embodiment and embodiment 1 is that the baking procedure is adjusted to microwave baking at 700 W for 4.5 min, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0077] The performance of the walnut oil prepared in the above embodiment was tested, and the comparison results with those in Example 1 are shown in Table 2.

[0078] Table 3

[0079] Example 1 Example 7 Example 8 Example 9 Acid value (mgKOH / g) 0.28 0.31 0.25 0.23 Peroxide value (g / 100g) 0.02 0.02 0.02 0.02 Oxidation stability (h) 2.20 2.01 1.93 2.11 Tocopherol content (mg / kg) 815.71 648.78 786.63 912.81 Sterol content (mg / kg) 1206.93 1209.40 1197.17 1189.84 Polyphenol content (mgGAE / kg) 9.58 6.56 9.10 11.32 Volatile compound content (μg / kg) 3081.13 2107.19 2881.23 5748.30 Unsaturated fatty acids (%) 90.58 90.91 91.01 91.08 Polyunsaturated fatty acids (%) 66.52 66.26 67.27 67.96

[0080] As can be seen from the above table, the effect of adjusting the baking method of walnut kernels on the performance of walnut oil is significant, which is due to the different energy inputs of infrared baking (Example 1) and microwave baking (Examples 7, 8, and 9). According to the changing trend of the content of volatile compounds, it is found that the energy input of Example 9 is greater than that of Example 1. As time increases, microwave baking helps to increase the tocopherol content and polyphenol content in walnut oil, especially the volatile compound content increases significantly, but the sterol content and oxidative stability of walnut oil decrease. In summary, the preferred infrared of the present invention, wherein the baking temperature is 130° C. and the time is 30 min.

[0081] Embodiment 11

[0082] The difference between this embodiment and embodiment 1 is that the amount of water added is adjusted to 10% of the dry weight of the walnut kernels, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0083] Example 12

[0084] The difference between this embodiment and embodiment 1 is that the amount of water added is adjusted to 20% of the dry weight of the walnut kernel, and the rest of the preparation process is the same as that of embodiment 1 to obtain walnut oil.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 1 is that the amount of water added is adjusted to 5% of the dry weight of the walnut kernel, and the rest of the preparation process is the same as that of Example 1 to obtain walnut oil.

[0087] Comparative Example 3

[0088] The difference between this comparative example and Example 1 is that the amount of water added is adjusted to 30% of the dry weight of the walnut kernels, and the rest of the preparation process is the same as that of Example 1 to obtain walnut oil.

[0089] The performance of the walnut oil prepared in the above embodiment was tested, and the comparison results with those in Example 1 are shown in Table 1.

[0090] Table 4

[0091] Example 1 Embodiment 11 Example 12 Comparative Example 2 Comparative Example 3 Acid value (mgKOH / g) 0.28 0.24 0.26 0.20 0.21 Peroxide value (g / 100g) 0.02 0.01 0.01 0.01 0.01 Oxidation stability (h) 2.20 2.05 2.07 2.00 2.00 Tocopherol content (mg / kg) 815.71 695.38 777.86 750.13 750.21 Sterol content (mg / kg) 1206.93 1090.62 1090.30 999.32 800.20 Polyphenol content (mgGAE / kg) 9.58 5.87 5.31 4.23 4.98 Volatile compound content (μg / kg) 3081.13 3014.73 2936.62 2896.01 2985.11 Unsaturated fatty acids (%) 90.58 90.49 90.50 90.12 90.82 Polyunsaturated fatty acids (%) 66.52 66.44 66.27 65.23 64.81 Oil yield (%) 82.95 74.02 65.94 70.02 34.28

[0092] It can be seen from the above table that the amount of water added during the extraction process not only affects the quality and flavor of walnut oil, but also affects the yield of walnut oil.

[0093] Comparative Example 4

[0094] The difference between this comparative example and Example 1 is that the walnut kernels are not roasted, and the rest of the preparation process is the same as that of Example 1 to obtain walnut oil.

[0095] Comparative Example 5

[0096] The difference between this comparative example and Example 1 is that the walnut kernels are subjected to boiling water peeling treatment, and the rest of the preparation process is the same as that of Example 1 to obtain walnut oil.

[0097] Comparative Example 6

[0098] The difference between this comparative example and Example 1 is that the baking temperature is adjusted to 150° C., and the rest of the preparation process is the same as that of Example 1 to obtain walnut oil.

[0099] The color of walnut oil rises significantly and it has a distinct burnt smell.

[0100] The performance of the walnut oil obtained in the above comparative example was tested, and the comparison results with those of Example 1 are shown in Table 1.

[0101] Table 4

[0102] Example 1 Comparative Example 4 Comparative Example 5 Acid value (mgKOH / g) 0.28 0.26 0.21 Peroxide value (g / 100g) 0.02 0.01 0.01 Oxidation stability (h) 2.20 2.06 1.63 Tocopherol content (mg / kg) 815.71 736.62 573.51 Sterol content (mg / kg) 1206.93 1109.55 861.66 Polyphenol content (mgGAE / kg) 9.58 5.38 5.84 Volatile compound content (μg / kg) 3081.13 1400.55 2485.77 Unsaturated fatty acids (%) 90.58 90.49 90.42 Polyunsaturated fatty acids (%) 66.52 66.35 63.18

[0103] As can be seen from the above table, the infrared baking treatment in Example 1 can not only ensure the physical and chemical indicators of walnut oil, but also improve the content of micronutrients and volatile compounds in walnut oil, so as to achieve the simultaneous preparation of high-quality and nutty walnut oil. Compared with Comparative Example 4 (unbaked), infrared baking helps to increase the content of tocopherol, sterol, polyphenols, the oxidative stability of walnut oil, and increase the content of unsaturated fatty acids. Walnut oil prepared under the same conditions by boiling water peeled walnut kernels (Comparative Example 5) has a significantly reduced oxidative stability, and the content of micronutrients is also lower than that of unpeeled walnuts (Example 1).

[0104] In summary, in order to solve the problems of poor quality and poor oxidative stability of walnut oil and difficulty in simultaneously meeting high quality and flavor, the present invention uses walnut kernels with skin as raw materials, constructs a baking process combined with a low water replacement method to prepare walnut oil. The walnut oil prepared by the method has high oil quality, and the oxidative stability, trace nutrient content, and walnut oil flavor substance content are significantly increased.

[0105] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing walnut oil with high quality and nutty flavor, characterized in that: include, The shelled walnut kernels with seed coat are roasted, and then ground into walnut paste after cooling; water is added to the walnut paste, and stirred to obtain an oil-water mixture, and the mixture is centrifuged to obtain an upper layer of clear oil and a lower layer of oil residue, and the upper layer of clear oil is taken out to obtain walnut oil; The baking includes one or more of infrared baking, oven baking and microwave baking, and the baking temperature of the infrared baking is 120-140° C. and the time is 10-40 min; The added amount of water is 10% to 20% of the dry weight of the walnut kernel.

2. The method for preparing walnut oil with high quality and nutty flavor as claimed in claim 1, characterized in that: The oil content of the walnut kernel is 62% to 75%.

3. The method for preparing walnut oil with high quality and nutty flavor as claimed in claim 2, characterized in that: The oven is baked, wherein the baking temperature is 120-140° C. and the time is 10-30 minutes;.

4. The method for preparing walnut oil with high quality and nutty flavor as claimed in claim 3, characterized in that: The microwave baking has a power of 600-700W and a time of 2.5-4.5min.

5. The method for preparing walnut oil with high quality and nutty flavor as claimed in claim 1, characterized in that: The particle size of the walnut paste is 100 to 300 μm.

6. The method for preparing walnut oil with high quality and nutty flavor as claimed in claim 1, characterized in that: The amount of water added is 15% of the dry weight of the walnut kernel.

7. The method for preparing walnut oil with high quality and nutty flavor as claimed in claim 1, characterized in that: The stirring is carried out at a speed of 100 to 300 r / min and a time of 1 to 5 min.

8. The method for preparing walnut oil with high quality and nutty flavor as claimed in claim 1, characterized in that: The centrifugation has a rotation speed of 5000 to 12000 r / min and a time of 5 to 15 min.

9. Walnut oil with high quality and nutty flavor prepared by the method according to any one of claims 1 to 8.

10. Use of the high-quality walnut oil with nutty flavor prepared by the method according to any one of claims 1 to 8 in the fields of functional food, food preparation and cosmetics.

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