Preparation method of high-quality virgin peanut oil

Abstract

This invention discloses a method for preparing high-quality virgin peanut oil, comprising the following steps: Step 1, crushing peanut skins and then ultrasonicating them to obtain ultrasonic material; Step 2, adding 10-50 times the weight of peanut kernels to the ultrasonic material and mixing evenly, then microwaved at 400-700W for 1-4 minutes; Step 3, pressing the microwaved material to obtain crude peanut oil; Step 4, processing the crude peanut oil to obtain virgin peanut oil. This invention has the beneficial effects of enriching proanthocyanidins in peanut skins, increasing the solubility of proanthocyanidins in peanut oil, improving the stability of the oil, and being suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of edible oils. More specifically, this invention relates to a method for preparing high-quality virgin peanut oil. Background Technology

[0002] Driven by market demand for high-quality oils, oil processing enterprises have begun to transform and upgrade, focusing on developing edible oils with high nutritional value, such as sunflower oil with alpha-vitamin E, rice bran oil with oryzanol, and corn oil with phytosterols. Peanut oil is the world's fourth largest edible oil, with consumption showing a generally slow growth trend, with an average annual compound growth rate of 1.61% (2010-2016). As a major consumer and producer of peanut oil, China accounts for about 53% of global consumption, with consumption expected to reach 6.19 million tons in 2019. Among these, high-quality peanut oils with nutritional fortification functions, such as high-oleic peanut oil, are increasingly popular with consumers.

[0003] Peanut skin, also known as peanut pericarp, is the red (or black) seed coat covering the peanut seed. Studies have found that peanut skin is rich in polyphenols, possessing high nutritional and utilization value. Its antioxidant capacity is more than 50 times that of the peanut kernel. The key substance responsible for its antioxidant effect is proanthocyanidins, which comprise approximately 14-17% of the peanut skin. Proanthocyanidins have been proven to have beneficial effects such as cancer prevention and cardiovascular disease control, making it a safe and non-toxic new type of natural antioxidant. Currently, the utilization rate of peanut skin is low, with most being discarded, resulting in resource waste and environmental pollution.

[0004] Proanthocyanidins are readily soluble in water and also in organic solvents such as methanol, ethanol, and acetone. However, they are poorly soluble in oils and fats, which limits their application in oils and oil-based foods. Therefore, increasing their solubility in oils and fats is an urgent problem for the industry to solve. Summary of the Invention

[0005] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0006] Another objective of this invention is to provide a method for preparing high-quality virgin peanut oil, which innovatively combines the extraction and enrichment of proanthocyanidins from peanut skins with peanut oil extraction technology to prepare a high-quality virgin peanut oil rich in proanthocyanidins suitable for industrial production.

[0007] To achieve these objectives and other advantages according to the present invention, a method for preparing high-quality virgin peanut oil is provided, comprising the following steps:

[0008] Step 1: Crush the peanut skins and then sonicate them to obtain ultrasonic material;

[0009] Step 2: Add peanut kernels in an amount of 10-50 times the weight of peanut skins to the ultrasonic material, mix well, and microwave at 400-700W power for 1-4 minutes.

[0010] Step 3: Microwave the material and press it to obtain crude peanut oil;

[0011] Step 4: Process the crude peanut oil to obtain virgin peanut oil.

[0012] Preferably, in step one, the peanut skin is crushed to 40-80 mesh.

[0013] Preferably, after the peanut skin is crushed in step one, it is ultrasonicated at 500W power for 10-90 minutes.

[0014] Preferably, in step two, 0.3-0.8% by weight of lipase is added to the microwave material before pressing, and the mixture is mixed evenly before pressing.

[0015] Preferably, the pressing in step three is as follows: after preheating at a preheating temperature of 70-80℃ and a preheating time of 25-35min, the pressing pressure is adjusted to 35-41MPa and the pressing temperature is 50-65℃ for pressing.

[0016] Preferably, the peanut crude oil treatment in step four specifically involves decolorizing the peanut crude oil, adjusting the rotation speed to 4000 rpm, centrifuging for 10 minutes, and then filtering.

[0017] The present invention has at least the following beneficial effects:

[0018] First, this invention uses peanut skin and peanut kernel to be pressed simultaneously. Before pressing, the proanthocyanidins in the peanut skin are enriched by ultrasonic and microwave-assisted methods, and the solubility of proanthocyanidins in peanut oil is increased. This can enrich the proanthocyanidins in the peanut oil and prepare high-quality virgin peanut oil with a proanthocyanidin content of 796.8 mg / kg.

[0019] Secondly, based on ultrasound and microwave, this invention increases the solubility of proanthocyanidins in peanut oil through microwave-assisted enzymatic esterification treatment, thereby enriching proanthocyanidins in peanut oil and preparing high-quality virgin peanut oil with a proanthocyanidin content as high as 853.8 mg / kg.

[0020] Third, this invention uses a low-temperature pressing process with a temperature not exceeding 65℃, which is simple to operate, time-saving, and low-cost. Furthermore, by optimizing key processing parameters, the stability of the oil is improved, the nutritional components of peanut oil are preserved to the greatest extent, and no harmful substances such as trans fatty acids and trichloropropanol esters are generated, making it suitable for industrial production.

[0021] Fourth, this invention uses peanut skins to natively enrich proanthocyanidins, realizing the high-value utilization of peanut skins, avoiding resource waste and environmental pollution, and the various indicators of peanut oil also meet the national standards for edible vegetable oils, with good nutritional fortification function and good application value and market prospects.

[0022] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0023] Figure 1 A schematic diagram showing the effect of the mesh size of peanut skin on the proanthocyanidin content in virgin peanut oil;

[0024] Figure 2 This is a schematic diagram illustrating the effect of ultrasound time on the proanthocyanidin content in virgin peanut oil.

[0025] Figure 3 A schematic diagram illustrating the effect of the peanut skin to peanut kernel mass ratio on the proanthocyanidin content in virgin peanut oil;

[0026] Figure 4 This is a schematic diagram showing the effect of microwave power on the proanthocyanidin content in virgin peanut oil.

[0027] Figure 5 This is a schematic diagram illustrating the effect of microwave time on the proanthocyanidin content in virgin peanut oil.

[0028] Figure 6 This is a schematic diagram illustrating the effect of lipase addition on the proanthocyanidin content in virgin peanut oil. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, so that those skilled in the art can implement it based on the description.

[0030] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0031] The reagents and instruments used in this invention are as follows:

[0032] Peanut skins: Provided by Jinsheng Grain and Oil Co., Ltd.

[0033] Peanuts: Harvested in October 2018 from peanut raw material bases in Xinjiang. Peanut kernels are obtained by removing the peanut skin from peanut kernels.

[0034] All other reagents were of chromatographic grade.

[0035] Centrifuge: LXJ-IIB type, Shanghai Anting Scientific Instrument Factory;

[0036] Ultra-high performance liquid chromatograph: ACQUITY H Class, Waters;

[0037] Vortex oscillator: Vortex-Genie 2, Scientific Industries;

[0038] Microwave oven: MG720KG3-NA1, Guangdong Midea Microwave Appliances Manufacturing Co., Ltd.

[0039] <Example 1>

[0040] The preparation method of high-quality virgin peanut oil includes the following steps:

[0041] Step 1: Grind the dried peanut skins to 40 mesh and then sonicate them at 500W for 20 minutes to obtain ultrasonic material;

[0042] Step 2: Add peanut kernels in an amount 40 times the weight of peanut skins to the ultrasonic feed, mix, and microwave at 700W for 3 minutes to obtain microwave feed;

[0043] Step 3: Add 0.8% of the lipase by mass to the microwave feed, mix well, and then press to obtain crude peanut oil. The pressing process is as follows: after preheating at a preheating temperature of 80℃ and a preheating time of 30 minutes, adjust the pressing pressure to 41MPa, the pressing temperature to 65℃, and the pressing time to 2 hours.

[0044] Step 4: After decolorizing the crude peanut oil, adjust the speed to 4000 rpm, centrifuge for 10 minutes, and then filter to obtain virgin peanut oil.

[0045] <Example 2>

[0046] The preparation method for high-quality virgin peanut oil is the same as in Example 1, except that the peanut skin is crushed to 50 mesh.

[0047] <Example 3>

[0048] The preparation method for high-quality virgin peanut oil is the same as in Example 1, except that the peanut skin is pulverized to 60 mesh.

[0049] <Example 4>

[0050] The preparation method for high-quality virgin peanut oil is the same as in Example 1, except that the peanut skin is crushed to 80 mesh.

[0051] <Example 5>

[0052] The preparation method of high-quality virgin peanut oil is the same as in Example 3, except that ultrasound is performed for 10 minutes in step one.

[0053] <Example 6>

[0054] The preparation method of high-quality virgin peanut oil is the same as in Example 3, except that ultrasound is performed for 30 minutes in step one.

[0055] <Example 7>

[0056] The preparation method of high-quality virgin peanut oil is the same as in Example 3, except that ultrasound is performed for 60 minutes in step one.

[0057] <Example 8>

[0058] The preparation method of high-quality virgin peanut oil is the same as in Example 3, except that ultrasound is performed for 90 minutes in step one.

[0059] <Example 9>

[0060] The preparation method of high-quality virgin peanut oil is the same as in Example 6, except that the mass ratio of peanut skin to peanut kernel in step two is 1:10.

[0061] <Example 10>

[0062] The preparation method of high-quality virgin peanut oil is the same as in Example 6, except that the mass ratio of peanut skin to peanut kernel in step two is 1:20.

[0063] <Example 11>

[0064] The preparation method of high-quality virgin peanut oil is the same as in Example 6, except that the mass ratio of peanut skin to peanut kernel in step two is 1:30.

[0065] <Example 12>

[0066] The preparation method of high-quality virgin peanut oil is the same as in Example 6, except that the mass ratio of peanut skin to peanut kernel in step two is 1:50.

[0067] <Example 13>

[0068] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the microwave power in step two is 400W.

[0069] <Example 14>

[0070] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the microwave power in step two is 500W.

[0071] <Example 15>

[0072] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the microwave power in step two is 600W.

[0073] <Example 16>

[0074] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the microwave time in step two is 1 minute.

[0075] <Example 17>

[0076] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the microwave time in step two is 2 minutes.

[0077] <Example 18>

[0078] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the microwave time in step two is 4 minutes.

[0079] <Example 19>

[0080] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the amount of lipase added in step three is 0.3%.

[0081] <Example 20>

[0082] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the amount of lipase added in step three is 0.4%.

[0083] <Example 21>

[0084] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the amount of lipase added in step three is 0.5%.

[0085] <Example 22>

[0086] The preparation method of high-quality virgin peanut oil is the same as in Example 9, except that the amount of lipase added in step three is 0.6%.

[0087] <Example 23>

[0088] The preparation method of high-quality virgin peanut oil is the same as in Example 22, except that the pressing is specifically as follows: after preheating at a preheating temperature of 70°C and a preheating time of 35 min, the pressing pressure is adjusted to 35 MPa and the pressing temperature is 65°C for pressing.

[0089] <Example 24>

[0090] The preparation method of high-quality virgin peanut oil is the same as in Example 22, except that the pressing is specifically as follows: after preheating at a preheating temperature of 80°C and a preheating time of 25 min, the pressing pressure is adjusted to 41 MPa and the pressing temperature is 50°C for pressing.

[0091] <Example 25>

[0092] The preparation method of high-quality virgin peanut oil is the same as in Example 22, except that lipase is not added to the microwave feed in step three, and the oil is directly pressed.

[0093] <Comparative Example 1>

[0094] The method for preparing peanut oil includes the following steps:

[0095] Step 1: Crush the dried peanut skins to 60 mesh, add 10 times the weight of peanut kernels, mix well, and press to obtain crude peanut oil. The pressing process is as follows: after preheating at a preheating temperature of 80℃ for 30 minutes, adjust the pressing pressure to 41MPa, the pressing temperature to 65℃, and the pressing time to 2 hours.

[0096] Step 2: After decolorizing the crude peanut oil, adjust the speed to 4000 rpm, centrifuge for 10 minutes, and then filter to obtain virgin peanut oil.

[0097] Research Experiment

[0098] 1. Quality evaluation of virgin peanut oil

[0099] The virgin peanut oils prepared in Examples 1-25 were all subjected to quality testing. The test results showed that the quality of the virgin peanut oils prepared in Examples 1-25 all met the national standards for edible vegetable oils. Partial test results for Examples 3, 6, 9, and 22 are summarized in Table 1.

[0100] Table 1 Quality Indicators of Virgin Peanut Oil

[0101]

[0102] 2. Experiment on the determination of proanthocyanidin content in virgin peanut oil

[0103] The proanthocyanidin content in the virgin peanut oil prepared in Examples 1-25 and Comparative Example 1 was determined, and the results are shown in the table below:

[0104] Table 2 shows the proanthocyanidin content in Examples 1-25 and Comparative Example 1.

[0105]

[0106] As shown in Comparative Example 1, by adding a certain proportion of peanut skin to peanut kernels during pressing, peanut oil containing proanthocyanidins can be obtained without adding any single proanthocyanidin product. However, the proanthocyanidin content in the obtained peanut oil is relatively low, only 524.4 mg / kg. As shown in Example 25, ultrasonic treatment of the crushed peanut skin before pressing promotes the conversion of bound proanthocyanidins into free proanthocyanidins. After further mixing with peanut kernels and then short-term microwave treatment, the release of proanthocyanidins is further promoted, and the free proanthocyanidins combine with the oil in the peanut kernels to form a stable state. This promotes enrichment and enhances the solubility of proanthocyanidins in peanut oil. Therefore, the proanthocyanidin content in the obtained peanut oil is increased to 796.8 mg / kg, which is much higher than that in Comparative Example 1. As shown in Example 22, in addition to ultrasonic and microwave treatments, the addition of lipase can further increase the proanthocyanidin content in the obtained peanut oil to 853.8 mg / kg.

[0107] further, Figure 1 This diagram illustrates the effect of peanut skin grinding mesh size on the proanthocyanidin content in virgin peanut oil. Corresponding to the data in Examples 1-4 in the table above, analysis shows that the proanthocyanidin content in peanut oil gradually increases with the increase in peanut skin grinding mesh size, and the increasing trend gradually slows down. The highest proanthocyanidin content in peanut oil is 732.1 mg / kg when the peanut skin grinding mesh size is 80 mesh. However, as the grinding mesh size increases, energy consumption also increases. Considering both the proanthocyanidin content and energy consumption in peanut oil, 60 mesh is considered the most suitable peanut skin grinding mesh size.

[0108] Figure 2 This is a schematic diagram showing the effect of ultrasonic time on the proanthocyanidin content in virgin peanut oil. From left to right, the data correspond to those in Examples 5-8 in the table above. The analysis shows that the proanthocyanidin content in peanut oil first increases with the increase of ultrasonic time in peanut skin, reaching 725.3 mg / kg at 30 min. After 30 min, the content does not change much with the continued increase of ultrasonic time.

[0109] Figure 3 This diagram illustrates the effect of the peanut skin to peanut kernel mass ratio on the proanthocyanidin content in virgin peanut oil. From left to right, these correspond to Examples 9-11, 6, and 12 in the table above. It can be seen that the proanthocyanidin content in peanut oil decreases with the increase of peanut kernel content. When the ratio is less than 1:40, the proanthocyanidin content decreases sharply. When the peanut skin / kernel ratio is 1:10, the proanthocyanidin content in peanut oil is 823.5 mg / kg.

[0110] Figure 4This is a schematic diagram showing the effect of microwave power on the proanthocyanidin content in virgin peanut oil. From left to right, it corresponds to Examples 13-15 and Example 9 in the table above. It can be seen that the proanthocyanidin content in peanut oil increases slowly with the increase of microwave power. When the microwave power is 700W, the proanthocyanidin content in peanut oil is 827.12mg / kg.

[0111] Figure 5 This diagram illustrates the effect of microwave time on the proanthocyanidin content in virgin peanut oil. From left to right, these correspond to Examples 16-17, 9, and 18 in the table above. It shows that the proanthocyanidin content in peanut oil increases slowly with increasing microwave time. When the microwave time is 4 minutes, the proanthocyanidin content in the peanut oil is 836.4 mg / kg.

[0112] Figure 6 This diagram illustrates the effect of lipase addition on the proanthocyanidin content in virgin peanut oil. From left to right, it corresponds to Examples 19-22 and Example 9 in the table above. As can be seen, the proanthocyanidin content in peanut oil increases slowly at first and then decreases with the increase of lipase addition. When the lipase addition is 0.6%, the proanthocyanidin content in peanut oil is 853.8 mg / kg.

[0113] 3. Induction time determination

[0114] The peanut oils prepared in Example 22 and Comparative Example 1 were tested using a 743 Rancimat oxidative stability tester. The procedure was as follows: 3.0 g of each peanut oil sample was placed in the Rancimat oxidative stability tester. The heating temperature was set to 120°C, and the air flow rate was 20 L / h to accelerate the oxidation of the oil, generating volatile organic acids. These volatile organic acids were then introduced into the conductivity chamber. The deionized water in the conductivity chamber dissolved the volatile organic acids, causing ionization and a change in the conductivity of the deionized water. Simultaneously, the computer recorded the induction time for accelerated oxidation of the oil. All data were averaged from three measurements. The results are shown in Table 3 below.

[0115] Table 3. Induction Time Measurement

[0116] Group Induction time Example 22 6.5 Comparative Example 1 4.6

[0117] As shown in the table above, the induction time of the virgin peanut oil prepared in Example 22 is 1.4 times that of the peanut oil prepared in Comparative Example 1, which means that the oil stability of the virgin peanut oil prepared in Example 22 is better than that of Comparative Example 1.

[0118] 4. Hazardous substance detection

[0119] 4.1 Detection of trans fatty acids (gas chromatography)

[0120] Weigh 200 mg of the virgin peanut oil prepared in Examples 1-25 into 10 mL centrifuge tubes, add 2 mL of C11:0 internal standard solution, add 0.1 mL of 2 mol / L potassium hydroxide methanol solution, vortex mix for 30 s, centrifuge at 4000 rpm for 10 min, take 20 μL of the supernatant and dilute to 1 mL volumetric flask for analysis.

[0121] The analysis was performed using a Shimadzu GC-2010 gas chromatograph with an SLB-IL111 column (200m × 0.25mm × 0.20μm). The chromatographic conditions were as follows: injection port temperature: 200℃; injection volume: 1μL; split ratio: 80:1. The initial column temperature was 70℃, held for 5 min, then increased to 175℃ at a rate of 15℃ / min, held for 22 min, and then increased to 185℃ at a rate of 3℃ / min, held for 35 min.

[0122] Detector: Flame Ionization Detector (FID); Detector temperature: 250℃; Wake flow rate: 30.0 mL / min; Hydrogen flow rate: 40 mL / min; Air flow rate: 400 mL / min.

[0123] Results: No trans fatty acids were detected in the virgin peanut oils prepared in Examples 1-25.

[0124] 4.2 Detection of trichloropropanol esters (GC-MS detection)

[0125] Weigh approximately 0.1 g of the virgin peanut oil prepared in Examples 1-25 into stoppered test tubes. Dissolve the oil in 0.5 mL of mixed solvent A (methyl tert-butyl ether: ethyl acetate = 8:2, volume ratio) to release free 3-MCPD. Simultaneously, add 12 μL (40 ng / mL) of internal standard solution (based on free 3-MCPD-d5) and 1.0 mL of NaOCH3 solution. Sonicate the solution at 45 °C for 15 min. Then, add 3.0 mL of n-hexane for defatting and 3.0 mL of mixed solvent B (glacial acetic acid: 20% sodium chloride solution = 1:30, volume ratio) to neutralize excess sodium methoxide. Vortex thoroughly and let stand at room temperature for 8 minutes. Remove the organic layer after significant separation. Then, add 3.0 mL of n-hexane as the extractant and mix thoroughly. The aqueous phase is used for the derivatization reaction. Add 250 μL of phenylboronic acid solution as the derivatizing agent to the above aqueous phase. Vortex thoroughly and derivatize at 80 °C for 20 min. When the reaction system cools to room temperature, add 1.0 mL of n-hexane and mix thoroughly. After separation, transfer the supernatant to a test tube containing approximately 1.5 g of anhydrous sodium sulfate. Repeat the extraction step once more. After vortex separation, accurately measure 1 μL of the supernatant for GC-MS analysis.

[0126] GC conditions: Column start temperature: 80℃; Temperature program: Preheat for 1 min, increase to 190℃ at a rate of 10℃ / min, then increase to 300℃ at a rate of 40℃ / min and hold for 5 min; Injector temperature: 280℃; DB-5MS capillary column (30m×0.25mm×0.25μm); Carrier gas: High-purity helium, flow rate 3.0mL / min; Injection volume: 1μL; Injection method: Splitless injection. MS conditions: Filament current: 100μA; Electron multiplier: +250V; Transfer line temperature: 250℃; Trap temperature: 230℃; Manifold temperature: 50℃; Electron impact ion source (EI); Mass spectrometry acquisition time: 3.00-29.75min; Solvent delay: 5min; Scan rate: 0.65s / s; Scan mass number range: m / z 90-300.

[0127] Results: Trichloropropanol esters were not detected in the virgin peanut oils prepared in Examples 1-24.

[0128] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing high-quality virgin peanut oil, characterized in that, Includes the following steps: Step 1: Crush the peanut skins and then sonicate them to obtain ultrasonic material; Step 2: Add peanut kernels in an amount of 10-50 times the weight of peanut skins to the ultrasonic material, mix well, and microwave at 400-700 W power for 1-4 minutes. Step 3: Microwave the material and press it to obtain crude peanut oil; Step 4: Process the crude peanut oil to obtain virgin peanut oil; In step one, the peanut skins are crushed to 40-80 mesh; After the peanut skins are crushed in step one, they are ultrasonicated at 500 W for 10-90 min. In step two, before pressing the microwave material, add 0.3-0.8% of its mass of lipase to the microwave material, mix well, and then press. The pressing in step three is as follows: after preheating at a preheating temperature of 70-80 ℃ and a preheating time of 25-35 min, the pressing pressure is adjusted to 35-41 MPa and the pressing temperature is 50-65 ℃ for pressing. In step four, the peanut crude oil treatment specifically involves decolorizing the peanut crude oil, adjusting the rotation speed to 4000 rpm, centrifuging for 10 minutes, and then filtering.

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