Low-calorie nut and preparation method thereof

Abstract

The invention relates to the technical field of food, in particular to a low-calorie nut and a preparation method thereof. The preparation method of the low-calorie nuts comprises the following steps: step 1, pretreatment: shelling or peeling the nuts for later use; step 2, preparing a spraying liquid: mixing a plant extract, table salt, an acidulant, a sweetening agent and water to prepare the spraying liquid; 3, the pretreated nuts are baked and cooled, baked nuts are obtained, then the spraying liquid is sprayed, and a crude product is obtained; and step 4, drying the crude product to obtain the low-calorie nuts. According to the invention, the low-calorie nuts are used as raw materials to prepare the low-calorie nuts; meanwhile, spraying liquid containing plant extracts is prepared, the taste and the nutritional effect of the nuts are adjusted, and the effects of resisting oxidation and helping digestion are improved in an auxiliary mode.

Description

Technical Field

[0001] The invention relates to the technical field of food, and in particular to low-calorie nuts and a preparation method thereof. Background Art

[0002] Nuts are the essence of plants; they are rich in vegetable oils, which lubricate the intestines. After consumption, they can help promote bowel movements and can effectively prevent and treat constipation; they contain many unsaturated fatty acids, which can help brain cell metabolism and promote intellectual growth and development. Appropriate intake of nuts can help the brain develop fully and improve intelligence, which is very helpful; they are rich in fat, and fat is high in calories. After consumption, it can help people restore physical strength and provide sufficient energy; they also contain many rich trace elements, such as zinc, selenium, manganese, and calcium. The intake of these trace elements has a good promoting and absorption effect on enzymes and coenzymes in the body, and these trace elements can effectively regulate, help and improve normal metabolism in the body.

[0003] Currently, there are many processing methods and varieties of nuts on the market, and the quality is uneven. In addition, as people pursue low-fat and healthy diets, it is a technical problem that needs to be solved to provide a low-calorie nut that is beneficial to human health. Summary of the invention

[0004] The present invention aims at the above-mentioned technical problems and proposes a technical solution of the present invention, which includes a low-calorie nut and a preparation method.

[0005] The present invention provides a method for preparing low-calorie nuts, comprising the following steps:

[0006] Step 1: Pre-processing: Shell or peel the nuts and set aside;

[0007] Step 2: Prepare a spray liquid: mix the plant extract, salt, acidulant, sweetener and water to prepare a spray liquid;

[0008] Step 3: roasting the pretreated nuts, cooling them to obtain roasted nuts, and then spraying the spraying liquid to obtain a crude product;

[0009] Step 4: Drying the crude product to obtain the low-calorie nuts.

[0010] Preferably, in order to obtain a low-calorie nut product, the present invention uses low-calorie nuts as raw materials, which include at least one of almonds, pecans, cashews, hazelnuts, pistachios, almonds or chestnuts.

[0011] Preferably, the acidulant comprises at least one of citric acid and DL-malic acid.

[0012] Preferably, the sweetener comprises at least one of mogroside, xylitol and erythritol.

[0013] Preferably, the present invention uses a spray liquid to add active ingredients to enhance the health effects of nut products, for example, giving nut products the effect of assisting the human body in resisting aging; at the same time, the spray liquid contains plant active ingredients that are both medicinal and edible, which increases the nutritional content, taste and food tonic effect of the nuts.

[0014] Preferably, in the spray liquid, the raw material composition is 0.1-5 parts of plant extract, 2-4 parts of salt, 0.005-0.1 parts of acidulant, 0.1-3 parts of sweetener and 20-40 parts of water in parts by mass.

[0015] Preferably, the mass of the spraying liquid is 0.1-5% of the mass of the roasted nuts.

[0016] Preferably, in step 4, the drying is performed until the moisture content is lower than 5.2 wt%.

[0017] Preferably, the plant extract is obtained by crushing mulberry, radish seed, polygonatum, kelp and lophatherum odoratum in sequence, enzymolysis with pectinase and cellulase, enzymolysis with ficin and bromelain, extraction with a composite extractant, filtering, ultrafiltration, concentration and drying the aqueous phase after extraction. The plant extract of the present invention contains rich active ingredients and nutrients, which can significantly assist in improving the effect of human body in resisting body aging, and increase the nutritional content, taste and food supplement effect of nuts.

[0018] The present invention also provides a plant extract, and the preparation method of the plant extract comprises:

[0019] Step A: According to weight parts, 1-2.2 parts of mulberry, 0.5-1.5 parts of radish seeds, 1.2-2 parts of polygonatum, 1.5-2.5 parts of kelp and 1.2-2.4 parts of lophatherum gracile are mixed and crushed to obtain a powder mixture;

[0020] Step B: adding 10-30 times the weight of water to the powder mixture, mixing to obtain a material; adding 600-1200 U / g of pectinase and 600-1200 U / g of cellulase to the material, performing enzymolysis at 35-52° C. for 2-4 hours, inactivating the enzymes, and obtaining an enzymolyzate 1;

[0021] Step C: adding 800-1300 U / g of ficin and 800-1350 U / g of bromelain to the hydrolysate 1, performing enzymolysis at 37-55° C. for 2.2-6 hours, inactivating the enzymes, and obtaining the hydrolysate 2;

[0022] Step D: The enzymatic hydrolysate 2 is concentrated to obtain a concentrate 1, which is then shaken with a composite extractant at a mass ratio of 1:20-60, extracted at 30-38° C. for 3-7 hours, and the organic phase after extraction is poured out to obtain an extracted aqueous phase;

[0023] Step E: filtering the extracted aqueous phase, ultrafiltering, concentrating the ultrafiltrate, and freeze-drying to obtain the plant extract;

[0024] The composite extractant is composed of an organic phase and an aqueous phase in a mass ratio of 1:2-5, the organic phase is composed of cyclopentane and ethyl acetate in a mass ratio of 2-4:1, and the aqueous phase is water.

[0025] Preferably, the ultrafiltration uses an ultrafiltration membrane with a cut-off molecular weight lower than 1.5 KDa.

[0026] Preferably, the plant extract prepared by the above preparation method is used as the plant extract in the spray liquid.

[0027] On the other hand, the present invention also provides low-calorie nuts prepared by the preparation method.

[0028] Beneficial effects of the present invention:

[0029] The invention adopts low-calorie nuts as raw materials to prepare low-calorie nuts; at the same time, a spray liquid containing plant extracts is prepared to adjust the taste and nutritional effect of the nuts and to assist in improving the oxidation resistance and digestion-aiding effect.

[0030] The plant extract prepared by the invention has excellent effects of removing free radicals and assisting in promoting digestion.

[0031] The free radical scavenging ratio of the plant extract prepared by the present invention after being diluted to 1.5% reaches 75.6%, which can effectively enhance the resistance of nuts to oxidation and increase the anti-aging effect of the human body.

[0032] The simulated digestion test of the plant extract prepared by the present invention showed that compared with the blank group, the plant extract increased the release of flavonoids by 65.4 mg / 100 g, and the proportion of flavonoids released increased by 21.53% compared with the blank group, which can effectively enhance the effect of nuts in assisting digestion.

[0033] The invention adopts mulberry, radish seed, polygonatum, kelp and bamboo leaf for extraction to prepare an extract with antioxidant and digestion-aiding effects; the extract prepared by combining kelp and bamboo leaf has better effect than the extract prepared by using only one of them.

[0034] The present invention adopts ficin and bromelain for composite enzymolysis, which can enhance the digestion-assisting and free radical-scavenging effects of the extract; the combination of the two enhances the active species and content in the extract, thereby increasing the efficacy of the extract.

[0035] The present invention uses a composite extractant to extract a liquid feed to prepare a plant extract, which can greatly improve the efficacy of the extract; in the extract, an organic phase obtained from cyclopentane and ethyl acetate is used to remove impurities such as oiliness in the liquid feed, thereby increasing the concentration and purity of the active ingredients in the extract in the aqueous phase, thereby increasing the efficacy of the extract to a certain extent. In particular, the extract prepared by the extractant obtained by the mass ratio of cyclopentane to ethyl acetate is better.

[0036] The nuts prepared by the present invention are low in calories, good in taste, have certain effects of resisting oxidation and assisting in promoting digestion, and have good experience and application prospects. DETAILED DESCRIPTION

[0037] The present invention will be described below in conjunction with specific embodiments, and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific embodiments are used to illustrate the present invention, rather than to limit the present invention.

[0038] 1. Preparation of plant extracts

[0039] 1. Extract 1

[0040] The preparation steps are specifically as follows: Step A: According to weight parts, 1.5 parts of mulberry, 1.2 parts of radish seeds, 1.5 parts of polygonatum, 1.8 parts of kelp and 2.1 parts of lophatherum gracile are mixed and crushed to less than 50 meshes to obtain a powder mixture;

[0041] Step B: adding 22 times the weight of water to the powder mixture, mixing to obtain a material; adding 1000U / g of pectinase and 900U / g of cellulase to the material, stirring at 45°C and 60rpm for enzymolysis for 3.2 hours, inactivating the enzyme, and obtaining an enzymolyzate 1;

[0042] Step C: adding 1200 U / g of ficin and 1200 U / g of bromelain to the hydrolysate 1, stirring at 47° C. and 60 rpm for 4.5 hours, inactivating the enzymes, and obtaining the hydrolysate 2;

[0043] Step D: The hydrolysate 2 is concentrated to 7.5% of the mass of the hydrolysate 2 at 60° C. and 0.003 MPa to obtain a concentrate 1, which is then mixed with a composite extractant at a mass ratio of 1:35, extracted at 35° C. for 5.2 hours, and the organic phase after extraction is poured out to obtain an extracted aqueous phase;

[0044] Step E: filtering the extracted aqueous phase using a 0.5 micron pore size filter membrane, and ultrafiltering the filtrate using an ultrafiltration membrane with a molecular weight cutoff of 1.2 KDa. After the ultrafiltrate is concentrated at 60° C. and 0.003 MPa for a period of time, the organic phase of the composite extractant cannot be detected, and the concentration is continued until the mass of the concentrate is 10.3% of the mass of the ultrafiltrate, and the concentration is stopped. The concentrate is freeze-dried at -40° C. to a water content of 3.16%, thereby obtaining the plant extract;

[0045] The composite extractant is composed of an organic phase and an aqueous phase in a mass ratio of 1:3.5, the organic phase is composed of cyclopentane and ethyl acetate in a mass ratio of 3.2:1, and the aqueous phase is water.

[0046] 2. Extract 2

[0047] The preparation steps are specifically as follows: Step A: According to weight parts, 2 parts of mulberry, 0.8 parts of radish seeds, 1.8 parts of polygonatum, 2.1 parts of kelp and 1.9 parts of lophatherum gracile are mixed and crushed to less than 50 meshes to obtain a powder mixture;

[0048] Step B: adding 25 times the weight of water to the powder mixture, mixing to obtain a material; adding 950 U / g of pectinase and 900 U / g of cellulase to the material, stirring at 42° C. and 60 rpm for enzymolysis for 4 hours, inactivating the enzymes, and obtaining an enzymolyzate 1;

[0049] Step C: adding 1150 U / g of ficin and 1250 U / g of bromelain to the hydrolysate 1, performing enzymolysis at 48° C. and 60 rpm for 5.2 hours, inactivating the enzymes, and obtaining the hydrolysate 2;

[0050] Step D: The hydrolysate 2 is concentrated to 7.4% of the mass of the hydrolysate 2 at 60° C. and 0.003 MPa to obtain a concentrate 1, which is then mixed with a composite extractant at a mass ratio of 1:32, extracted at 32° C. for 55 hours, and the organic phase after extraction is poured out to obtain an extracted aqueous phase;

[0051] Step E: filtering the extracted aqueous phase using a 0.5 micron pore size filter membrane, and ultrafiltering the filtrate using an ultrafiltration membrane with a molecular weight cutoff of 1.2 KDa. After the ultrafiltrate is concentrated at 60° C. and 0.003 MPa for a period of time, the organic phase of the composite extractant cannot be detected, and the concentration is continued until the mass of the concentrate is 10.7% of the mass of the ultrafiltrate. The concentrate is freeze-dried at -40° C. to a water content of 3.19%, thereby obtaining the plant extract;

[0052] The composite extractant is composed of an organic phase and an aqueous phase in a mass ratio of 1:4, the organic phase is composed of cyclopentane and ethyl acetate in a mass ratio of 2:1, and the aqueous phase is water.

[0053] 3. Extract 3

[0054] Step A is: according to weight parts, 1.5 parts of mulberry, 1.2 parts of radish seeds, 1.5 parts of polygonatum and 3.9 parts of lophatherum gracile are mixed and crushed to less than 50 meshes to obtain a powder mixture; the rest are the same as extract 1.

[0055] 4. Extract 4

[0056] Step A is: according to weight parts, 1.5 parts of mulberry, 1.2 parts of radish seeds, 1.5 parts of polygonatum and 3.9 parts of kelp are mixed and crushed to less than 50 meshes to obtain a powder mixture; the rest are the same as extract 1.

[0057] 5. Extract 5

[0058] Step C is as follows: adding 2400 U / g bromelain of the hydrolysate 1 to the hydrolysate 1, stirring at 47° C. and 60 rpm for 4.5 hours, inactivating the enzyme, and obtaining the hydrolysate 2; the rest is the same as the extract 1.

[0059] 6. Extract 6

[0060] Step C is as follows: adding 2400 U / g of ficin to the hydrolysate 1, performing enzymolysis at 47° C. and 60 rpm with stirring for 4.5 hours, inactivating the enzyme, and obtaining the hydrolysate 2; the rest is the same as that of the extract 1.

[0061] 7. Extract 7

[0062] The preparation steps are specifically as follows: Step A: According to weight parts, 1.5 parts of mulberry, 1.2 parts of radish seeds, 1.5 parts of polygonatum, 1.8 parts of kelp and 2.1 parts of lophatherum gracile are mixed and crushed to less than 50 meshes to obtain a powder mixture;

[0063] Step B: adding 22 times the weight of water to the powder mixture, mixing to obtain a material; adding 1000U / g of pectinase and 900U / g of cellulase to the material, stirring at 45°C and 60rpm for enzymolysis for 3.2 hours, inactivating the enzyme, and obtaining an enzymolyzate 1;

[0064] Step C: adding 1200 U / g of ficin and 1200 U / g of bromelain to the hydrolysate 1, stirring at 47° C. and 60 rpm for 4.5 hours, inactivating the enzymes, and obtaining the hydrolysate 2;

[0065] Step D: The hydrolysate 2 is filtered through a 0.5 micron pore size filter membrane, and the filtrate is ultrafiltered through an ultrafiltration membrane with a molecular weight cutoff of 1.2 KDa. The ultrafiltrate is concentrated at 60° C. and 0.003 MPa to 10.3% of the mass of the hydrolysate 2, and the concentration is stopped. The concentrate is freeze-dried at -40° C. to a water content of 3.16% to obtain the plant extract.

[0066] 8. Extract 8

[0067] The composite extractant is composed of an organic phase and an aqueous phase in a mass ratio of 1:3.5, the organic phase is cyclopentane, and the aqueous phase is water; the rest is the same as Extract 1.

[0068] 9. Extract 9

[0069] The composite extractant is composed of an organic phase and an aqueous phase in a mass ratio of 1:3.5, the organic phase is ethyl acetate, and the aqueous phase is water; the rest is the same as Extract 1.

[0070] 10. Extract 10

[0071] The composite extractant is composed of an organic phase and an aqueous phase in a mass ratio of 1:3.5, the organic phase is composed of cyclopentane and ethyl acetate in a mass ratio of 1:1, and the aqueous phase is water; the rest is the same as Extract 1.

[0072] 11. Extract 11

[0073] The composite extractant is composed of an organic phase and an aqueous phase in a mass ratio of 1:3.5, the organic phase is composed of cyclopentane and ethyl acetate in a mass ratio of 7:1, and the aqueous phase is water; the rest is the same as Extract 1.

[0074] 12. Extract 12

[0075] The composite extractant is composed of an organic phase and an aqueous phase in a mass ratio of 1:3.5, the organic phase is composed of chloroform and ethyl acetate in a mass ratio of 3.2:1, and the aqueous phase is water; the rest is the same as Extract 1.

[0076] 2. Extract performance test

[0077] 1. Free radical scavenging effect test

[0078] The extract was diluted with 40% ethanol aqueous solution to a mass concentration of 1.5 wt % to obtain a sample to test the free radical scavenging effect.

[0079] Weigh DPPH and dilute it with 75% ethanol aqueous solution to prepare 2.5×10 -4 4mL DPPH solution and 1mL 75% ethanol aqueous solution were mixed and kept away from light for half an hour. The absorbance was measured at 515nm and recorded as A0. 4mL 75% ethanol and 1mL sample were mixed and kept away from light for half an hour. The absorbance was measured at 515nm and recorded as A1. 4mL DPPH solution and 1mL sample were mixed and kept away from light for half an hour. The absorbance was measured at 515nm and recorded as A2. Calculate the scavenging rate of different samples for DPPH free radicals = 100% × [1-(A2-A1) / A0]. The test results are shown in Table 1.

[0080] Table 1: Free radical scavenging effect test

[0081] test Free radical scavenging rate% test Free radical scavenging rate% Extract 1 75.6 Extract 7 50.7 Extract 2 74.9 Extract 8 66.5 Extract 3 73.1 Extract 9 68.3 Extract 4 71.8 Extract 10 73.1 Extract 5 69.3 Extract 11 71.2 Extract 6 71.4 Extract 12 67.8

[0082] 2. Digestive effect test

[0083] The digestive effect of the extract was verified by the flavonoid release in the digestive juice.

[0084] Sample treatment: 1. Experimental group treatment method: 20 grams of flour, 200 grams of water and 4.5 grams of extract (the above extracts 1-13), mix, boil in a boiling water bath for 20 minutes, and add water to a total of 224.5 grams; adjust the pH to 2.0 with hydrochloric acid, add 3mL of simulated gastric juice (0.2g of pepsin and 5 ml of 0.01 mol / L hydrochloric acid), seal, protect from light, and shake in a 37°C water bath for 2 hours. Then take the treated liquid, centrifuge at 5°C and 15000rpm for 20 minutes, take the supernatant, add acetone to 80wt% to remove impurities, filter, and obtain the experimental group test sample. 2. Blank group treatment method: Use an equal amount of physiological saline to replace the extract in the experiment, and the rest is the same as the experimental group treatment method to obtain a blank group test sample.

[0085] The test process is as follows: take 1g of the test sample and mix it with an equal volume of 80% ethanol aqueous solution, let it stand at 50℃ for 2 hours; centrifuge at 5000rpm for 12min. Take 10mL of the centrifugal supernatant, add 0.7mL of 5% sodium nitrite aqueous solution, mix it, let it stand for 10min; add 0.7mL of 10% aluminum nitrate aqueous solution, mix it, let it stand for 10min; add 5mL of 4wt% sodium hydroxide aqueous solution, and use 80% ethanol aqueous solution to make the volume 25mL, let it stand at room temperature for 20min. Take 6mL of the static liquid and pour it into a centrifuge tube, centrifuge it at 5000rpm for 5min, take the supernatant and measure the absorbance at 510nm, convert it into the flavonoid release in the simulated digestive fluid (mg / 100g), and then calculate the increase in flavonoid release and the rate of improvement of different groups compared with the blank group. The specific results are shown in Table 2.

[0086] Table 2: Flavonoids release in simulated digestive fluid and the increase and ratio of flavonoids release compared with the blank group

[0087]

[0088]

[0089] It can be seen from the test results in Table 1-2 that the plant extract prepared by the present invention has excellent effects of scavenging free radicals and assisting in promoting digestion.

[0090] The free radical scavenging ratio of the plant extract prepared by the present invention after being diluted to 1.5% reaches 75.6%, which can effectively enhance the resistance of nuts to oxidation and increase the anti-aging effect of the human body.

[0091] The simulated digestion test of the plant extract prepared by the present invention showed that compared with the blank group, the plant extract increased the release of flavonoids by 65.4 mg / 100 g, and the proportion of flavonoids released increased by 21.53% compared with the blank group, which can effectively enhance the effect of nuts in assisting digestion.

[0092] The present invention uses mulberry, radish seed, polygonatum, kelp and bamboo leaf for extraction to prepare an extract with antioxidant and digestive effects; tests on extracts 1, 3-4 show that extract 1 prepared by combining kelp and bamboo leaf has better effects than extracts 3-4 prepared by using only one of them.

[0093] Through the test results of extracts 1, 5-6, it can be obtained that the present invention uses ficin and bromelain for composite enzymatic hydrolysis, which can enhance the extract's digestion-aiding and free radical-scavenging effects; the possible reason is that the combination of the two increases the active species and content in the extract, thereby increasing the efficacy of the extract.

[0094] The present invention uses a composite extractant to extract a liquid feed to prepare a plant extract, which can greatly improve the efficacy of the extract; in the extract, an organic phase obtained from cyclopentane and ethyl acetate is used to remove impurities such as oiliness in the liquid feed, thereby increasing the concentration and purity of the active ingredients in the extract in the aqueous phase, thereby increasing the efficacy of the extract to a certain extent. In particular, the extract prepared by the extractant obtained by the mass ratio of cyclopentane and ethyl acetate is better. The above content can be obtained in combination with the test results of extracts 1, 7-12.

[0095] 3. Preparation of nuts

[0096] 1. Almond nuts, which are prepared as follows:

[0097] Step 1: Pretreatment: Shell the almonds and set aside;

[0098] Step 2: Prepare a spray liquid: Mix 0.15 parts of plant extract (the extract 1 above), 3.2 parts of salt, 0.08 parts of citric acid (acidifier), 0.7 parts of xylitol (sweetener) and 35 parts of water to prepare a spray liquid.

[0099] Step 3: roasting the pretreated nuts at 175° C. for 20 minutes, cooling to obtain roasted nuts, and then spraying 1.1% of the spray liquid by weight of the roasted nuts to obtain a crude product;

[0100] Step 4: Dry the crude product at 65°C to a moisture content of 2.79 wt% to obtain almond nuts.

[0101] 2. Pistachio nuts, prepared as follows:

[0102] Step 1: Pre-processing: Shell the pistachios and set aside;

[0103] Step 2: Prepare a spray liquid: Mix 0.18 parts of plant extract (the extract 2 above), 3.3 parts of salt, 0.02 parts of acidulant citric acid, 0.4 parts of sweetener xylitol and 35.3 parts of water to prepare a spray liquid.

[0104] Step 3: roasting the pretreated nuts at 172° C. for 30 minutes, cooling to obtain roasted nuts, and then spraying 1.7% of the mass of the roasted nuts with a spraying liquid to obtain a crude product;

[0105] Step 4: Dry the crude product at 65° C. to a moisture content of 2.04 wt %, to obtain pistachio nuts.

[0106] 3. Pecan nuts, prepared as follows:

[0107] Step 1: Pre-processing: Shell the pistachios and set aside;

[0108] Step 2: Prepare a spray liquid: Mix 0.15 parts of plant extract (the extract 1 above), 3.05 parts of salt, 0.03 parts of citric acid (acidifier), 0.3 parts of xylitol (sweetener) and 28.5 parts of water to prepare a spray liquid.

[0109] Step 3: roasting the pretreated nuts at 178° C. for 25 minutes, cooling to obtain roasted nuts, and then spraying 1.2% of the mass of the roasted nuts with a spraying liquid to obtain a crude product;

[0110] Step 4: Dry the crude product at 67° C. to a moisture content of 2.13 wt %, to obtain pecan nuts.

[0111] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing low-calorie nuts, characterized in that: The steps include: Step 1: Pre-processing: Shell or peel the nuts and set aside; Step 2: Prepare a spray liquid: mix the plant extract, salt, acidulant, sweetener and water to prepare a spray liquid; Step 3: roasting the pretreated nuts, cooling them to obtain roasted nuts, and then spraying the spraying liquid to obtain a crude product; Step 4: Drying the crude product to obtain the low-calorie nuts.

2. The preparation method according to claim 1, characterized in that: The nuts include at least one of almonds, pecans, cashews, hazelnuts, pistachios, and almonds.

3. The preparation method according to claim 1, characterized in that: The acidulant includes at least one of citric acid and DL-malic acid.

4. The preparation method according to claim 1, characterized in that: The sweetener includes at least one of mogroside, xylitol and erythritol.

5. The preparation method according to claim 1, characterized in that: In the spraying liquid, the raw material composition is 0.1-5 parts of plant extract, 2-4 parts of salt, 0.005-0.1 parts of acidulant, 0.1-3 parts of sweetener and 20-40 parts of water in parts by mass.

6. The preparation method according to claim 1, characterized in that: The mass of the spraying liquid is 0.1-5% of the mass of the roasted nuts.

7. The preparation method according to claim 1, characterized in that: In step 4, drying is performed until the water content is lower than 5.2 wt %.

8. The preparation method according to claim 1, characterized in that: The plant extract is obtained by crushing mulberry, radish seed, polygonatum, kelp and loblolly leaf in sequence, enzymolyzing with pectinase and cellulase, enzymolyzing with ficin and bromelain, extracting with a composite extractant, filtering, ultrafiltering, concentrating and drying the extracted water phase.

9. Low-calorie nuts prepared according to the preparation method according to any one of claims 1 to 8.

10. A plant extract, characterized in that The preparation method thereof comprises the following steps: Step A: According to weight parts, 1-2.2 parts of mulberry, 0.5-1.5 parts of radish seeds, 1.2-2 parts of polygonatum, 1.5-2.5 parts of kelp and 1.2-2.4 parts of lophatherum gracile are mixed and crushed to obtain a powder mixture; Step B: adding 10-30 times the weight of water to the powder mixture, mixing to obtain a material; adding 600-1200 U / g of pectinase and 600-1200 U / g of cellulase to the material, performing enzymolysis at 35-52° C. for 2-4 hours, inactivating the enzymes, and obtaining an enzymolyzate 1; Step C: adding 800-1300 U / g of ficin and 800-1350 U / g of bromelain to the hydrolysate 1, performing enzymolysis at 37-55° C. for 2.2-6 hours, inactivating the enzymes, and obtaining the hydrolysate 2; Step D: The enzymatic hydrolysate 2 is concentrated to obtain a concentrate 1, which is then shaken with a composite extractant at a mass ratio of 1:20-60, extracted at 30-38° C. for 3-7 hours, and the organic phase after extraction is poured out to obtain an extracted aqueous phase; Step E: filtering the extracted aqueous phase, ultrafiltering, concentrating the ultrafiltrate, and freeze-drying to obtain the plant extract; The composite extractant is composed of an organic phase and an aqueous phase in a mass ratio of 1:2-5, the organic phase is composed of cyclopentane and ethyl acetate in a mass ratio of 2-4:1, and the aqueous phase is water.

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