Method for improving flavor of peanut oil through germination pretreatment

Abstract

The invention discloses a method for improving the flavor of peanut oil by utilizing germination pretreatment. The method specifically comprises the following steps: step 1, cleaning raw materials; step 2, soaking and imbibing the peanuts until the moisture content of the peanuts is 30-50%; 3, peanut germination pretreatment: during germination, peanuts are in a critical infiltration state and are uniformly placed in a tray, the interval between every two adjacent peanuts is about 1-2 cm, the tray is placed in a constant-temperature and constant-humidity incubator, and culture is performed for 6-48 h under the conditions that the temperature is 25-30 DEG C and the humidity is 60-100%; step 4, drying the peanuts: drying the germinated peanuts until the moisture content is 5-15%; step five, baking the peanuts: baking the peanuts to produce fragrance; and step 6, squeezing and extracting oil: physically squeezing the baked peanuts by using a spiral or hydraulic squeezer, filtering to remove impurities, and taking clear grease on the upper layer to obtain the strong-fragrance peanut oil. On the basis of not changing a peanut oil production process, compared with peanut oil prepared by a traditional process, the prepared peanut oil is fuller in flavor and richer in fragrance, and meanwhile, the high oil yield is still kept.

Description

Technical Field

[0001] The invention belongs to the technical field of peanut oil processing and flavor enhancement, and particularly relates to a method for improving the flavor of peanut oil by utilizing germination pretreatment. Background Art

[0002] Peanut oil is a very popular flavor oil for consumers. It is often used in cooking, hot pot, cold dishes, etc. to increase consumers' flavor sensory experience. Good and rich flavor is one of the key qualities that determine consumers to buy peanut oil. Peanut oil processing companies have been committed to developing methods to enhance the flavor of peanut oil.

[0003] High-temperature frying of peanut seeds is a key process for the formation of peanut oil flavor, which mainly forms the characteristic flavor of peanut oil through Maillard reaction, lipid oxidation reaction, caramelization reaction, etc. The Maillard reaction is mainly a non-enzymatic browning reaction between the amino groups provided by peptides and amino acids in peanuts and the carbonyl groups provided by reducing sugars, which produces key flavor substances of peanut oil such as pyrazine, pyrrole, pyridine, furan, thiazole and other heterocyclics. In addition, the thermal degradation reaction of macromolecules such as proteins and polysaccharides in peanuts during high-temperature frying can also release a small amount of flavor precursors such as amino acids and oligosaccharides, which can participate in the Maillard reaction to form the aroma substances of peanut oil. However, the thermal degradation of these macromolecules in peanuts only occurs under high temperature conditions (>160℃), and the efficiency of forming small molecular flavor precursors through thermal degradation is extremely low. Most macromolecules such as proteins and polysaccharides do not participate in the formation of peanut oil flavor.

[0004] Before the high-temperature frying of seeds to produce fragrance, the addition of exogenous biological enzymes can efficiently degrade the macromolecular substances in peanuts under mild conditions, release more small molecular flavor precursor substances in advance, and effectively improve the formation efficiency of flavor substances during the frying of seeds, thereby improving the flavor of peanut oil. For example, CN200810110396.X uses exogenous composite protease to enzymolyze peanuts, and then mixes the enzymolyzate with refined peanut oil for thermal reaction to prepare fragrant peanut oil. CN202010826254.4 uses a variety of exogenous enzymes (protease, amylase, composite saccharifying enzyme, polygalacturonase, etc.) to enzymolyze germination peanut powder, and then adds peanut oil to mix and heat to produce fragrance, and the overall flavor intensity of the resulting oil is improved. However, exogenous enzymes are expensive, and the enzymolysis process involves seed crushing, the addition of enzymolyzate and the removal of water. The new peanut oil preparation process requires that the existing process equipment and production line must first be greatly modified. These factors greatly limit the application and promotion of exogenous enzymes in oil production. In addition, the flavor characteristics of peanut oil prepared by using exogenous enzyme enzymatic hydrolysis-thermal reaction to produce aroma are significantly different from those of peanut oil prepared by traditional processes. For example, the caramel flavor is too strong and there is a sauce flavor that traditional peanut oil does not have. Consumers are not familiar with its flavor characteristics, which affects its market acceptance.

[0005] During the germination process of plant seeds, morphological changes and physiological metabolic changes will occur, which are mainly reflected in the activation of endogenous enzymes. At the same time, it is also accompanied by complex biochemical metabolism, which causes significant changes in the main components of the seeds, such as the decomposition and conversion of substances such as protein, starch, cellulose, and fat into free amino acids, soluble sugars, dietary fiber, fatty acids, vitamins or other active substances. Existing studies have found that the nutritional value of oils can be improved by using the action of endogenous enzymes through germination treatment technology. For example, in Chinese patent CN202010729804.0, peanut seeds are germination treated, and the content of dietary fiber, total sugar, glucose, pectin, total phenols, total flavonoids, phenolic acid and other substances is significantly increased. At the same time, the cold-pressed peanut oil prepared using germinated peanuts as raw materials has a significantly increased resveratrol content, and germination improves the nutritional and application value of peanut oil. Chinese patent CN202010827376.5 crushes a small amount of sprouted peanut seeds, mixes the peanut powder with refined peanut oil for thermal reaction, and can prepare a light-colored, low-residual-oil oil with a specific peanut oil flavor. However, the flavor characteristics of the oil prepared by this method are significantly different from those of traditional peanut oil, which affects consumer acceptance. Existing research and technology have not clarified whether peanut sprout pretreatment has a flavor-enhancing effect on the flavor of peanut oil and the specific sprouting conditions required for flavor enhancement.

[0006] It is necessary to develop a new flavoring method that does not require large-scale changes to the existing physical pressing peanut oil production process production line and equipment, while significantly improving the characteristic flavor of peanut oil. Compared with the flavoring effect of exogenous enzymes, the application of natural endogenous enzymes in peanut oil flavoring is more economical and feasible, can be combined with the existing pressing process, and is suitable for rapid promotion and application in peanut oil companies. Summary of the invention

[0007] In order to overcome the shortcomings and bottlenecks of the existing peanut oil flavoring technology, avoid adding expensive exogenous enzymes, and ensure a high oil extraction rate without large-scale changes in the existing physical pressing peanut oil production process, the present invention utilizes germination pretreatment under specific conditions to increase the activity of endogenous enzymes in peanut seeds, promotes the release of flavor precursors in peanuts, and fries the germinated peanuts and then physically presses them to obtain a strong-flavor pressed peanut oil with significantly improved flavor intensity, high consumer acceptance, and good industrial application prospects.

[0008] The present invention is a method for improving the flavor of peanut oil by using germination pretreatment, which uses germination pretreatment of peanut seeds under specific conditions to activate endogenous enzymes of peanuts, promote the enzymatic release of small molecular flavor precursors in peanuts, and obtain rich-flavor peanut oil by traditional processes such as frying seeds, physical pressing, and filtering. The peanut oil obtained by this method has the characteristic flavor of traditional pressed peanut oil and has a stronger aroma and better flavor quality. The specific steps are as follows:

[0009] (1) Step 1: Raw material cleaning: Select fresh peanuts with full grains, no damage, no pests or diseases as raw materials, and remove impurities in the raw materials;

[0010] (2) Step 2: Peanuts are soaked and swollen: After washing the peanuts with purified water, the peanuts are soaked in water for 2-12 hours and then the water is drained. After soaking, the water content of the peanuts is 30-50%;

[0011] (3) Step 3, peanut germination pretreatment: When germinating, the peanuts are in a critical infiltration state and are evenly placed in a tray, with each peanut about 1-2 cm apart. The tray is placed in a constant temperature and humidity incubator and cultured for 6-48 hours at a temperature of 25-30° C. and a humidity of 60-100%;

[0012] (4) Step 4, peanut drying: drying the sprouted peanuts in an oven at 25-50° C., or freeze-drying at a temperature ≤-50° C.;

[0013] (5) Step 5: Peanut roasting: hot air roasting or microwave roasting of the peanuts to produce aroma;

[0014] (6) Step 6: Pressing and oil extraction: Use a screw press or a hydraulic press to physically press the roasted peanuts, centrifuge or filter by sedimentation to remove impurities, and take the upper layer of clear oil to obtain the fragrant peanut oil.

[0015] (7) Preferably, the amount of pure water required to soak the peanuts is ≥3:1 for water (mL): peanuts (g). (8) Preferably, in order to avoid a significant increase in the acid value of the peanut oil, ensure a high oil yield, and significantly improve the flavor intensity of the peanut oil, the optimal conditions for germination are 25°C, humidity ≥90%, and no light for 6-36 hours. (9) Preferably, the germination peanuts are dried to a moisture content of 5-15% before roasting, which is conducive to the preparation of peanut oil with a strong and harmonious flavor.

[0016] (10) Preferably, the peanut roasting conditions are: hot air roasting at 140-200° C. for 20-60 min, or microwave at 540-900 W for 5-15 min.

[0017] (10) Peanut germination can be carried out in the absence of light or in the presence of light.

[0018] Compared with the prior art, the present invention has the following beneficial effects: without changing the existing physical peanut oil pressing process on a large scale, the present invention utilizes the germination pretreatment of peanut raw materials under specific conditions to improve the activity of endogenous enzymes in peanuts, promotes the release of flavor precursors in peanuts and the formation of aroma when frying seeds, and the peanut oil prepared by the method has a fuller and richer flavor than the peanut oil prepared by the traditional process, while still maintaining a high oil yield. The peanut oil flavoring method provided by the present invention is simple and safe, does not require the addition of additional raw materials other than peanuts, meets national standards, and has better flavoring effect, economic cost and application prospects than the existing exogenous enzyme flavoring method. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a process flow chart of the present invention;

[0020] Figure 2 is a heat map of the volatile matter concentration of the peanut oil prepared in each example;

[0021] Figure 3 The sensory profile of peanut oil prepared in each embodiment;

[0022] Figure 4 The differences in the endogenous enzyme activities of peanuts in various examples are shown in the figure: (a) α-amylase, (b) lipase, (c) acid protease, and (d) neutral protease;

[0023] Figure 5 The effect of germination on the content of peanut flavor precursors in various examples, (a) soluble sugar, (b) free amino acids. DETAILED DESCRIPTION

[0024] The present invention is described in more detail below in conjunction with specific embodiments. The specific parameters in the embodiments are only used to illustrate the present invention and are not used to limit the scope. Those skilled in the art can appropriately modify the parameters of the present invention.

[0025] Example 1

[0026] Soak 1kg of fresh peanuts in 3L of pure water at 28℃ for 12h, then place the swollen peanuts evenly in a germination tray (30cm×23cm) with 1cm between the peanut seeds, and incubate them in a constant temperature box with a temperature of 25℃, a humidity of 95%, and no light for 12h. Freeze-dry the germinating peanuts at -56℃ for 12h until the moisture content is about 6.5%. Microwave 1kg of dried peanuts at 540W for 8min. The microwaved peanuts (1kg) are hydraulically pressed at 60MPa, and the obtained peanut crude oil is centrifuged at 5000rpm for 15min to remove impurities, and a clarified fragrant peanut oil is obtained.

[0027] Example 2

[0028] Soak 1kg of fresh peanuts in 3L of pure water at 28℃ for 12h, then place the swollen peanuts evenly in a germination tray (30cm×23cm) with 1cm between the peanut seeds, and incubate them in a constant temperature box with a temperature of 25℃, a humidity of 95%, and no light for 24h. Freeze-dry the germinating peanuts at -56℃ for 12h until the moisture content is about 6.5%. Microwave 500g of dried peanuts at 540W for 8min. Microwaved peanuts (1kg) are hydraulically pressed at 60MPa, and the obtained peanut crude oil is centrifuged at 5000rpm for 15min to remove impurities, and a clarified fragrant peanut oil is obtained.

[0029] Example 3

[0030] After soaking 1kg of fresh peanuts in 3L of pure water at 28℃ for 12h, the swollen peanuts were evenly placed in a germination tray (30cm×23cm) with a 1cm interval between the peanut kernels, and cultivated in a constant temperature box with a temperature of 25℃, a humidity of 95%, and no light for 36h. The germinating peanuts were freeze-dried at -56℃ for 12h until the moisture content was about 6.5%. 500g of the dried peanuts were microwaved at 540W for 8min. The microwaved peanuts (1kg) were hydraulically pressed at 60MPa, and the obtained peanut crude oil was centrifuged at 5000rpm for 15min to remove impurities to obtain clarified fragrant peanut oil.

[0031] Example 4

[0032] After soaking 1kg of fresh peanuts in 3L of pure water at 28℃ for 12h, the swollen peanuts are evenly placed in a germination tray (30cm×23cm) with a 1cm interval between the peanut kernels, and incubated in a constant temperature box with a temperature of 25℃, a humidity of 95%, and no light for 48h. The germinating peanuts are freeze-dried at -56℃ for 12h to a moisture content of about 6.5%. 500g of dried peanuts are microwaved at 540W for 8min. The microwaved peanuts (1kg) are hydraulically pressed at 60MPa, and the obtained peanut crude oil is centrifuged at 5000rpm for 15min to remove impurities to obtain clarified fragrant peanut oil.

[0033] Comparative Example 1

[0034] After 1 kg of fresh peanuts were soaked in 3 L of pure water at 28 ° C for 12 hours, the soaked peanuts were directly freeze-dried at -56 ° C for 12 hours without germination pretreatment until the moisture content was about 6.5%. 1 kg of dried peanuts were microwaved at 540 W for 8 minutes. The microwaved peanuts (1 kg) were hydraulically pressed at 60 MPa, and the obtained peanut crude oil was centrifuged at 5000 rpm for 15 minutes to remove impurities, and the fragrant peanut oil was obtained.

[0035] Comparative Example 2

[0036] 100g of peanut meal, add 500g of pure water, heat to 50℃, adjust pH to 5.0 with hydrochloric acid, add 8000U / g of cellulase and 9000U / g of pectinase, hydrolyze for 2h; then adjust pH to 10.0 with sodium hydroxide, add 8000U / g of alkaline protease and 400U / g of flavor protease, and continue hydrolysis for 3h. After the enzymolysis is completed, adjust pH to 7.0, and inactivate the enzyme in a water bath at 90℃ for 10min. After centrifugation at 4000rpm for 10min to remove the precipitate, freeze-dry the supernatant at -56℃ to obtain peanut meal enzymolysate. Take 50g of freeze-dried enzymolysate and dissolve it in 100g of water, add 50g of refined peanut oil in a high-pressure thermal reactor, heat to 160℃, and react for 1h to obtain the flavor base. The flavor base was cooled to room temperature and then mixed with refined peanut oil at a ratio of 1:5 (w:w) for extraction, stirred at 25°C for 6 hours, and dehydrated with anhydrous sodium sulfate. The precipitate was removed by centrifugation at 5000 rpm for 10 minutes to obtain the upper layer of flavored peanut oil.

[0037] Comparative Example 3

[0038] After soaking 1kg of fresh peanuts in 3L of pure water at 28℃ for 12h, the swollen peanuts were evenly placed in a germination tray (30cm×23cm) with a 1cm interval between the peanut kernels, and cultivated in a constant temperature box with a temperature of 25℃, a humidity of 95%, and no light for 60h. The germinating peanuts were freeze-dried at -56℃ for 12h until the moisture content was about 6.5%. 500g of the dried peanuts were microwaved at 540W for 8min. The microwaved peanuts (1kg) were hydraulically pressed at 60MPa, and the obtained peanut crude oil was centrifuged at 5000rpm for 15min to remove impurities to obtain clarified fragrant peanut oil.

[0039] The volatile flavor composition and sensory quality of the peanut oil prepared in the embodiments and comparative examples are as follows: Figure 2 and 3 Compared with comparative example 1 (no germination), with the increase of germination pretreatment time, the content of pyrazine, pyrrole, pyridine and phenol volatile compounds in peanut oil gradually increased, and the content of ketones gradually decreased ( Figure 2 At the same time, germination pretreatment increased the sensory intensity of the nutty, roasted peanut, caramel, buttery, and burnt flavors of peanut oil ( Figure 3 ). At 48h of germination, the characteristic aroma of peanut oil, including nut flavor, roasted peanut flavor, caramel flavor, and butter flavor, is the strongest, and the overall flavor is harmonious. However, at 60h of germination, due to the substantial increase in phenolic volatile flavor substances in peanut oil (Comparative Example 3) ( Figure 2), which significantly increased the intensity of the smoky flavor of the peanut oil and made it the dominant flavor. The smoky flavor caused significant sensory inhibition on the nutty flavor, roasted peanut flavor, caramel flavor and butter flavor. Therefore, the flavor quality of the peanut oil obtained after germination for 60 hours was reduced and the overall flavor harmony was poor.

[0040] As the germination pretreatment time increased, the activities of endogenous enzymes in peanuts, including α-amylase, lipase, acid and neutral proteases, gradually increased ( Figure 4 ), while the content of macromolecular substances such as protein, oil and total sugar in peanuts gradually decreased (Table 1), and the macromolecular substances were degraded to form more soluble sugars and free amino acids ( Figure 5 ) and other small molecule flavor precursors. When the germination pretreatment time is ≤48h, the loss of oil (crude fat) in peanuts is less than 2% of the dry weight of peanuts. When the germination pretreatment time is ≥60h, the oil loss in peanuts exceeds 5% of the dry weight of peanuts, and the yield of peanut oil is significantly reduced.

[0041] The above results indicate that the germination pretreatment under specific conditions of the present invention (e.g., germination temperature of 28°C, time of 12-48h) can significantly improve the flavor quality of peanut oil, making the flavor of peanut oil richer, fuller, and more harmonious than that of peanut oil prepared by traditional processes, while still maintaining a relatively high oil yield.

[0042] Compared with the peanut oil prepared by the traditional non-germination process (Comparative Example 1), the peanut oil prepared by the exogenous enzyme method (Comparative Example 2) has stronger butter, caramel and burnt flavors, but weaker increases in the intensity of the nut flavor and roasted peanut flavor, and the sauce flavor exhibited by Comparative Example 2 is not possessed by the traditional peanut oil. The flavor profile of the peanut oil flavored by the exogenous enzyme in Comparative Example 2 deviates greatly from that of the peanut oil prepared by the traditional process, and consumers are less familiar with and accept it.

[0043] The method of significantly improving the flavor of peanut oil by using germination pretreatment under specific conditions (such as Examples 1, 2, 3, and 4) of the present invention is more natural, richer, and more harmonious than the flavor of peanut oil prepared by the exogenous enzyme flavoring method. The process for improving the flavor of peanut oil of the present invention is simple and safe, does not require the addition of additional raw materials other than peanuts, meets the requirements of national standards for peanut oil, is economical and easy to implement, can meet market demand, and has good prospects for industrial application.

[0044] Table 1 Comparison of total sugar, crude fat and crude protein content of peanuts obtained by different pretreatment methods

[0045]

Claims

1. A method for improving the flavor of peanut oil by using germination pretreatment, characterized in that: The method comprises the following steps: (1) Step 1: Raw material cleaning: remove impurities from the raw materials; (2) Step 2: Peanut soaking and swelling: Wash the peanuts with pure water, soak them in water for 2-12 hours and then drain the water. The moisture content of the peanuts after soaking is 30-50%; (3) Step 3: Peanut germination pretreatment: When germinating, the peanuts are in a critical infiltration state and are evenly placed in a tray, with each peanut about 1-2 cm apart. The tray is placed in a constant temperature and humidity incubator and cultured for 6-48 h at a temperature of 25-30°C and a humidity of 60-100%; (4) Step 4: Peanut drying: Dry the peanuts after germination to a moisture content of 5-15%; (5) Step 5: Peanut roasting: roasting the peanuts to produce fragrance; (6) Step 6: Physical pressing and oil extraction: Use a press to physically press the roasted peanuts, filter to remove impurities, and take the clear oil on the top to obtain the fragrant peanut oil.

2. The method according to claim 1, characterized in that: The weight ratio of the pure water added in step 2 to the peanuts is water: peanuts ≥ 3:

1.

3. The method according to claim 1, characterized in that: In step three, the germination conditions of peanuts are 25°C, humidity ≥90%, and no light for 6-36 hours.

4. The method according to claim 1, characterized in that: The drying method in step 4 is to oven dry the sprouted peanuts at 25-50°C, or freeze dry them at a temperature ≤-50°C.

5. The method according to claim 1, characterized in that: The peanut roasting conditions in step 5 are: hot air roasting at 140-200°C for 20-60 min, or microwave at 540-900 W for 5-15 min.

6. The method according to claim 1, characterized in that: Step six is ​​to physically press the roasted peanuts using a screw press or a hydraulic press, and centrifugally filter or sediment filter to remove impurities.

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