Method for synchronously preparing cyperus esculentus oil and cyperus esculentus protein isolate

Abstract

The invention discloses a method for synchronously preparing cyperus esculentus oil and cyperus esculentus protein isolate, and belongs to the technical field of comprehensive processing of agricultural products. The method for synchronously preparing the cyperus esculentus oil and the cyperus esculentus protein isolate comprises the following steps: (1) mixing cyperus esculentus powder and water, adjusting the pH value to 7.0-9.0, stirring, centrifuging, and removing solid residues to obtain clear liquid, namely cyperus esculentus liquid; (2) freezing the cyperus esculentus milk at-30 to-5 DEG C for 6-14 hours, and taking out the frozen cyperus esculentus milk; heating and stirring at 30-60 DEG C for 0.5-2 hours, and centrifuging to obtain cyperus esculentus oil and a water phase; and (3) adjusting the temperature of the water phase to 30-70 DEG C, adjusting the pH value to 4.5-6.5, stirring for 0.5-2 hours, centrifuging, and taking the precipitate, namely the cyperus esculentus protein isolate. According to the method, no organic solvent or enzyme preparation is introduced, and the extraction rate of the cyperus esculentus oil is high; and the cyperus esculentus protein isolate is high in purity, good in acid stability and suitable for products such as acidic milk beverages and the like.

Description

Technical Field

[0001] The invention relates to a method for synchronously preparing cyperus oleifera oil and cyperus oleifera protein isolate, and belongs to the technical field of comprehensive processing of agricultural products. Background Art

[0002] Tiger nut (Cyperus esculentus L.) is known as the "underground walnut". Its main nutrients are fat (22.14% to 44.92%), protein (3.28% to 8.45%), starch (23.21% to 48.12%), fiber (8.26% to 15.47%), as well as minerals, phytosterols, organic acids, alkaloids, saponins, phenols and other active substances. Tiger nut is rich in unsaturated fatty acids (oleic acid 67.70% to 74.60%), and its fatty acid composition is similar to olive oil, with high nutritional value. Essential amino acids account for about 46% of tiger nut protein, and it has good functional properties and is regarded as a high-quality protein source. The rich nutrients and bioactive substances give tiger nut a high nutritional value. Tiger nut has become a promising production resource for food, oil, and bioactive substances, which can meet the growing dietary needs of humans.

[0003] The ideas for comprehensive utilization of cyperus oleifera are generally as follows:

[0004] (1) Extracting cyperus oleifera oil by pressing or solvent extraction, and then extracting protein, starch and other components from cyperus oleifera meal as raw material, but the disadvantages of these two methods are also obvious. The oil extraction rate of the pressing method is low, only about 50%. The solvent extraction method can extract cyperus oleifera oil to the maximum extent; for example: CN107307175A discloses a method for comprehensive utilization of cyperus oleifera meal, which is a method for extracting cyperus oleifera protein isolate by extracting cyperus oleifera meal with an organic solvent, and the protein content thereof can reach 91% or more, but this method is prone to cause organic solvent residues and does not conform to green processing.

[0005] (2) The prior art involves the use of enzyme preparations to extract cyperus oleiferus oil by aqueous media. For example, CN110200123A discloses a method for preparing cyperus oleiferus protein isolate by enzymatic method, which is a method for extracting protein isolate by using cyperus oleiferus meal. The raw material is defatted cyperus oleiferus meal, and the amount of enzyme added in this technology is relatively large (3% to 5%), which has the problems of high production cost and complicated process; CN102311867A discloses a method for extracting cyperus oleiferus oil by aqueous enzyme method-freeze-thaw coupling technology, which is to first crush the cyperus oleifera, then soak it in water, use alkaline protease and cellulase for enzymolysis, and then freeze it to -30°C for 30 minutes, thaw it at room temperature, and then centrifuge it again to obtain cyperus oleifera oil. This method has the problems of long enzymolysis time (6h) and high enzyme addition amount (2.5%), and the problem of protein being hydrolyzed; CN102234335A discloses a production process for continuously extracting starch, oil and sugar from cyperus oleifera, which is to first crush the cyperus oleifera, then add water for pulping, and adjust the slurry to pH 4.5 The protein mixture is obtained by centrifugation and dried to be used as feed. The upper emulsion is enzymatically hydrolyzed to obtain cyperus oleiferus oil. This method has the problems of low protein purity (feed grade) and low oil yield (70%). CN117844566A discloses a method for simultaneously preparing cyperus oleiferus starch sugar and cyperus oleiferus oil, which comprises first crushing cyperus oleiferus, washing with water, and centrifuging to obtain a residue phase, an oil phase, and an emulsion, and then freezing the emulsion (-20°C, 12h) to demulsify the cyperus oleiferus oil, and liquefying and saccharifying the residue phase to obtain cyperus oleiferus starch sugar. The oil extraction rate of this method is 89.40%, but the utilization of the protein part is not involved. CN108504442A discloses a method for enzymatic extraction of cyperus oleiferus oil and CN107099375A discloses a method for preparing cyperus oleiferus oil and cyperus oleiferus fraction, both of which utilize enzyme preparations to hydrolyze proteins and cell walls to release oil.

[0006] All of the above methods require the use of solvents or enzyme preparations to prepare cyperus oleifera oil and cyperus oleifera protein isolate, which is costly or has residual organic solvents.

[0007] At present, there are also documents that mention the use of solvent-free methods for extraction, for example: CN109879975A discloses a method for rapid separation of cyperus oleifera components; specifically, preparing cyperus oleifera coarse powder; preparing cyperus oleifera coarse pulp; preparing cyperus oleifera husk residue and cyperus oleifera peeled pulp; preparing peeled thin pulp; preparing cyperus oleifera husk residue powder; preparing dietary fiber and defibered pulp; centrifugally dehydrating and drying the dietary fiber to obtain cyperus oleifera dietary fiber; adjusting the pH value of the defibered pulp; preparing cyperus oleifera starch; adjusting the pH value of the light brown sugar solution to make water for beating the next batch of cyperus oleifera coarse powder; separating the oil layer and the water layer; preparing cyperus oleifera oil; preparing light brown paste; preparing cyperus oleifera crude protein powder; preparing cyperus oleifera sugar; but it can only obtain 16.85 kg of cyperus oleifera oil and 4.55 kg of cyperus oleifera crude protein powder from 100 kg of cyperus oleifera; the extraction rate is very low, and the protein content is not mentioned.

[0008] In addition, the conventional extraction process of cyperus oleifera protein is alkali dissolution and acid precipitation, and the acid precipitation pH is basically 4.5; for example: literature (Wang Lin, Zhou Guowei, Yu Zhichao, et al. Effect of pH offset treatment on the structure and emulsification properties of cyperus oleifera protein [J]. Food Science, 2020, 41(22):8. DOI:10.7506 / spkx1002-6630-20191014-113.), CN110200123A (A method for preparing cyperus oleifera protein isolate powder by enzymatic method), etc.; there is no mention of how to adjust the acid precipitation pH to further increase the protein content of the product.

[0009] In addition, conventional plant proteins are generally derived from oilseeds or grains. For example, soybean and wheat, soybean protein is mainly composed of globulin (about 90%) and albumin (about 10%); wheat protein is mainly composed of alcohol-soluble protein (about 45%), gluten (about 40%), albumin (about 5%) and globulin (about 10%). The protein of serrata oleifera is quite different from conventional plant proteins. Its protein composition is mainly albumin (82% to 92%), and the content of globulin, alcohol-soluble protein and gluten is 3% to 7.5%. The sedimentation rate of albumin at pH 4.5 is low, so the existing process cannot be fully used for protein extraction. Summary of the invention

[0010] [Technical issues]

[0011] Conventional methods of extracting cyperus oleifera oil and cyperus oleifera protein using enzyme preparations and organic solvents have problems of solvent residue and high cost.

[0012] The solvent-free method for extracting cyperus oleifera oil and cyperus oleifera protein has the problems of low extraction rate and low purity;

[0013] There is a difference between jatropha protein and general plant protein.

[0014] [Technical solution]

[0015] In order to solve the above problems, the present invention provides a method for simultaneously preparing cyperus oleifera oil and cyperus oleifera protein isolate, which does not require organic solvent extraction and has a high extraction rate of cyperus oleifera oil, which can reach more than 90%; and the prepared cyperus oleifera protein isolate has high purity and good acid stability, and is suitable for products such as acidic milk beverages.

[0016] The first object of the present invention is to provide a method for synchronously preparing cyperus oleifera oil and cyperus oleifera protein isolate, comprising the steps of:

[0017] (1) mixing cyperus oleifera powder and water, adjusting the pH to 7.0-9.0, stirring, centrifuging, removing the solid residue, and the clear liquid is cyperus oleifera slurry;

[0018] (2) freezing the cyperus oleifera slurry at -30 to -5°C for 6 to 14 hours, taking it out; heating and stirring it at 30 to 60°C for 0.5 to 2 hours, and centrifuging it to obtain cyperus oleifera oil and an aqueous phase;

[0019] (3) The temperature of the aqueous phase is adjusted to 30-70°C, the pH is adjusted to 4.5-6.5, and after stirring for 0.5-2 hours, centrifugation is performed to obtain the precipitate, which is the cyperus oleifera protein isolate.

[0020] In one embodiment of the present invention, the cyperus juncea powder in step (1) is obtained by dry-crushing cyperus juncea; the particle size of the cyperus juncea powder is 100-150 meshes.

[0021] In one embodiment of the present invention, the mass ratio of cyperus oleifera flour to water in step (1) is 1:6-8, more preferably 1:7.

[0022] In one embodiment of the present invention, the solution used to adjust the pH in step (1) is a NaOH aqueous solution with a concentration of 1.5 to 2.5 mol / L.

[0023] In one embodiment of the present invention, the pH is adjusted to 8.0 in step (1).

[0024] In one embodiment of the present invention, the stirring in step (1) is carried out at 20-30° C. (room temperature) and 100-200 rpm for 0.5-2 h.

[0025] In one embodiment of the present invention, the centrifugation in step (1) is performed at 1000-5000 g for 10-20 min, more preferably at 3000 g for 15 min.

[0026] In one embodiment of the present invention, the solid residue in step (1) can be further washed with water and centrifuged again, and the process is repeated 1 to 3 times, with the amount of water added each time being 4 to 6 times the mass of the raw materials. The resulting clear liquids are combined to obtain the cyperus oleifera slurry.

[0027] In one embodiment of the present invention, the freezing in step (2) is performed at -18°C for 8 hours.

[0028] In one embodiment of the present invention, the heating and stirring in step (2) is performed in a water bath; the heating and stirring is performed at 40° C. and 100-200 rpm for 1 hour.

[0029] In one embodiment of the present invention, the centrifugation in step (2) is performed at 3000-12000 g for 15-30 min; more preferably, at 10000 g for 20 min.

[0030] In one embodiment of the present invention, the temperature adjustment in step (3) is performed using a water bath.

[0031] In one embodiment of the present invention, the pH is adjusted in step (3) by using an aqueous solution of HCl at a concentration of 1.5 to 2.5 mol / L.

[0032] In one embodiment of the present invention, the stirring in step (3) is carried out at 60° C. and 100 to 200 rpm for 0.5 to 2 h.

[0033] In one embodiment of the present invention, the centrifugation in step (3) is performed at 3000-6000 g for 15-30 min; more preferably, at 5000 g for 20 min.

[0034] The second object of the present invention is the cyperus oleifera protein isolate prepared by the method of the present invention.

[0035] The third object of the present invention is to provide a method for extracting more cyperus oleifera oil and cyperus oleifera protein isolate with higher protein content from cyperus oleifera, which adopts the method for simultaneously preparing cyperus oleifera oil and cyperus oleifera protein isolate described in the present invention.

[0036] The fourth object of the present invention is to provide a method for increasing the protein content in cyperus oleifera protein isolate, which adopts the method for simultaneously preparing cyperus oleifera oil and cyperus oleifera protein isolate described in the present invention.

[0037] The fifth object of the present invention is to provide a method for increasing the proportion of albumin in cyperus oleifera protein isolate, which adopts the method for simultaneously preparing cyperus oleifera oil and cyperus oleifera protein isolate described in the present invention.

[0038] The sixth object of the present invention is to provide a method for improving the acid stability of cyperus juncea protein isolate, which adopts the method for simultaneously preparing cyperus juncea oil and cyperus juncea protein isolate described in the present invention.

[0039] The seventh objective of the present invention is the application of the cyperus oleifera protein isolate described in the present invention in the food field.

[0040] In one embodiment of the present invention, the food is an acidic milk beverage.

[0041] [Beneficial Effects]

[0042] (1) The present invention makes comprehensive use of Cyperus oleifera. Compared with the prior art, the present invention does not require the introduction of organic solvents and enzyme preparations, is more environmentally friendly and safe, and achieves high-value utilization of Cyperus oleifera.

[0043] (2) The method of the present invention can effectively extract cyperus oleifera oil and cyperus oleifera protein isolate; the final cyperus oleifera oil extraction rate is as high as 92.56%±0.21%; the cyperus oleifera protein isolate has high purity, the protein content can reach 91.83%±0.06%, the acid stability is 93.37%±1.05%, and the protein extraction rate is 65.65%±0.12%. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the effect of extraction pH on protein extraction rate in Example 2.

[0045] Figure 2 The figure shows the effect of freezing time on the extraction rate of jatropha oil in Example 3.

[0046] Figure 3 The figure shows the effect of demulsification temperature on the extraction rate of jatropha oil in Example 3.

[0047] Figure 4 This is the effect of centrifugal pH on the protein content in cyperus oleifera protein in Example 4.

[0048] Figure 5 This is the effect of centrifugal pH on the protein composition of cyperus oleifera protein in Example 4.

[0049] Figure 6 This is the effect of centrifugal pH on the acid stability of cyperus oleifera protein in Example 4.

[0050] Figure 7 This is the effect of sedimentation temperature on the extraction rate of cyperus oleifera protein isolate in Example 5. DETAILED DESCRIPTION

[0051] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0052] Test method:

[0053] 1. Test of basic ingredients of cyperus oleifera:

[0054] The protein content was determined according to the Kjeldahl method in GB5009.5-2016, and the protein conversion factor was 6.25;

[0055] The fat content is determined by Soxhlet extraction method in GB5009.6-2016;

[0056] The moisture content is determined by the direct drying method in GB5009.3-2016;

[0057] Data processing: The experiments were repeated three times, and Origin was used to analyze and plot the data. The results were expressed as “mean ± standard deviation”.

[0058] 2. Calculation of extraction rate:

[0059]

[0060] 3. Determination and calculation of albumin ratio in cyperus oleifera protein isolate:

[0061] SDS-PAGE gel electrophoresis was used to identify the protein composition of the cyperus oleifera protein isolate. The concentrations of the separation gel and the concentration gel were 16.5% and 4%, respectively, the anode buffer was a Tris-HCl buffer (containing 2.42% Tris) at pH 8.9, and the cathode buffer was a buffer system containing 1.2% Tris, 1.79% Tricine, and 0.1% SDS.

[0062] 1.5 mg of protein sample was added to 1 mL of prepared sample solution (containing 20% ​​(v / v) pH 6.8 Tris-HCl, 24% (w / v) glycerol, 8% (w / v) SDS, 0.02% (w / v) Coomassie Brilliant Blue G-250), and then 2% (v / v) β-mercaptoethanol was added.

[0063] Before electrophoresis, the protein solution treated above was boiled in boiling water for 4 min, cooled, and 10 μL was injected into each electrophoresis lane. Electrophoresis was performed at 30 V voltage to the separation gel (~2 h), and then electrophoresis was performed at a constant voltage of 100 V to the end, fixed, stained with Coomassie Brilliant Blue G-250, decolorized with 30% acetic acid until the background was transparent, and scanned with a gel imager.

[0064] The calculation formula of albumin ratio is as follows:

[0065]

[0066] 4. Test of acid stability of cyperus oleifera protein isolate:

[0067] Take 10 g of cyperus oleifera protein isolate, add deionized water to prepare a solution with a concentration of 2% (w / v), stir evenly, adjust the pH to 4.0 with 1 mol / L HCl solution, and continue stirring for 30 minutes.

[0068] Take 50g of the solution and centrifuge it at 3000g for 20min, pour off the supernatant, take the precipitate and dry it at 105℃ for 2h, then weigh it.

[0069] The calculation formula of acid stability of cyperus oleifera protein isolate is as follows:

[0070]

[0071] The raw materials used in the examples are:

[0072] The basic components of the cyperus oleifera raw material are shown in Table 1:

[0073] Table 1 Basic ingredients of Cyperus oleifera raw materials

[0074]

[0075] From Table 1, we can see that the fat content of cyperus oleiferus is relatively high, reaching 24.25%±1.23%, which is close to oilseeds such as soybeans and linseeds; the protein content of cyperus oleiferus is 6.57%±0.05%, which is close to grains such as wheat, corn, and barley. The nutritional value of cyperus oleiferus oil is relatively high, with unsaturated fatty acids accounting for more than 80%, mainly oleic acid; the essential amino acids of cyperus oleiferus protein account for about 46%, which is a high-quality protein source. Therefore, the development of cyperus oleiferus oil and protein products is of great significance.

[0076] Cyperus chinensis powder: Cyperus chinensis is dry-crushed to obtain Cyperus chinensis powder with a particle size of 120 meshes.

[0077] The solutions involved in the embodiments and comparative examples that do not mention the solvent all use water as the solvent, the % involved that does not specify the meaning is the mass percentage; the temperature that does not specify the meaning refers to the room temperature, which is 20-30° C.; w / v is g / mL.

[0078] Example 1

[0079] A method for simultaneously preparing cyperus oleifera oil and cyperus oleifera protein isolate comprises the following steps:

[0080] (1) Cyperus oleifera powder and water were mixed in a mass ratio of 1:7, the pH was adjusted to 8.0 with a 2 mol / L NaOH solution, the mixture was stirred at room temperature and 150 rpm for 1 hour, and the mixture was centrifuged at 3000 g for 15 minutes to remove the solid residue; the solid residue was washed with water (the amount of water added was 5 times the mass of the raw material) and centrifuged again, and the mixture was repeated twice, and the resulting clear liquid was combined to obtain Cyperus oleifera slurry;

[0081] (2) freezing the cyperus oleifera slurry at -18°C for 8 hours, taking it out, heating and stirring it in a water bath at 40°C and 150 rpm for 1 hour, and centrifuging it at 10,000 g for 20 minutes to obtain cyperus oleifera oil and an aqueous phase;

[0082] (3) The aqueous phase was placed in a water bath at 60°C, and the pH was adjusted to 5.8 with a 2 mol / L HCl solution. After stirring at 150 rpm for 1 hour, the mixture was centrifuged at 5000 g for 20 minutes to obtain the precipitate, which was the cyperus oleifera protein isolate.

[0083] The obtained cyperus oleifera oil and cyperus oleifera protein isolate were subjected to performance tests, and the test results were as follows:

[0084] The extraction rate of cyperus oleifera oil was 92.56% ± 0.21%;

[0085] The protein content of the cyperus oleifera protein isolate was 91.83%±0.06%, the acid stability was 93.37%±1.05%, and the protein extraction rate was 65.65%±0.12%.

[0086] Example 2 Effect of extraction pH on protein extraction rate

[0087] Cyperus oleifera powder and water were mixed in a mass ratio of 1:7, and then divided into 5 equal parts, and the pH was adjusted to 7.0, 7.5, 8.0, 8.5 and 9.0 respectively with 2 mol / L NaOH solution, and stirred at room temperature and 150 rpm for 1 h;

[0088] After stirring, the suspensions with different pH values ​​were centrifuged at 3000 g for 15 min, the solid residues were washed with water and centrifuged again, and this process was repeated twice. The amount of water added was 5 times the mass of the raw materials. The resulting clear liquids were combined to obtain cyperus oleifera slurries with different extraction pH values, and their protein contents were determined.

[0089] The results are as follows:

[0090] Effect of extraction pH on protein extraction rate Figure 1 .

[0091] from Figure 1 It can be seen that when the pH is 7.0, 7.5, 8.0, 8.5 and 9.0, the protein dissolution amount is 61.25% ± 0.25%, 70.22% ± 0.31%, 78.36% ± 0.17%, 79.01% ± 0.26% and 79.13% ± 0.11% respectively; it can be seen that when the pH is 7.0, the protein dissolution rate is the lowest; when the pH increases to 8.0, the increase is small as the pH increases. Therefore, the optimal pH is 8.0.

[0092] Example 3 Effect of Freezing Time and Demulsification Temperature on Oil Extraction Rate

[0093] (1) Cyperus oleifera powder and water were mixed in a mass ratio of 1:7, the pH was adjusted to 8.0 with a 2 mol / L NaOH solution, the mixture was stirred at room temperature and 150 rpm for 1 hour, and the mixture was centrifuged at 3000 g for 15 minutes to remove the solid residue; the solid residue was washed with water (the amount of water added was 5 times the mass of the raw material) and centrifuged again, and the mixture was repeated twice, and the resulting clear liquid was combined to obtain Cyperus oleifera slurry;

[0094] (2) Divide the cyperus oleifera slurry into 10 equal portions;

[0095] Six of the slurries were frozen at -18 °C for 0, 6, 8, 10, 12, and 14 h, respectively, and then taken out and heated and stirred in a water bath at 40 °C and 150 rpm for 1 h;

[0096] The other 4 portions of slurry were frozen at -18 °C for 8 h, taken out, and heated and stirred in a water bath at 30, 40, 50, and 60 °C and 150 rpm for 1 h, respectively;

[0097] Ten portions of the slurry were centrifuged at 10,000 g for 20 min to obtain cyperus juncea oil and an aqueous phase. The cyperus juncea oil was weighed and its extraction rate was calculated.

[0098] Effects of freezing time and demulsification temperature on the extraction rate of jatropha oil Figure 2 and Figure 3 .

[0099] from Figure 2 It can be seen that when the cyperus oleifera slurry is directly centrifuged without freezing, its demulsification rate is low and the extraction rate of cyperus oleifera oil is only 30.32%±0.11%; when the freezing time is 6, 8, 10, 12 and 14h, the extraction rates of cyperus oleifera oil are 85.03%±0.16%, 92.56%±0.21%, 92.32%±0.18%, 92.03%±0.26% and 92.98%±0.15%, respectively; it can be seen that freezing can peel off the lipids tightly bound to the protein from the protein, but when the freezing time reaches 8h and the freezing time is further extended, the increase in the oil extraction rate is negligible.

[0100] from Figure 3It can be seen that when the frozen cyperus oleifera slurry is heated to demulsify, the extraction rates of cyperus oleifera oil are 86.59%±0.35%, 92.56%±0.21%, 88.61%±0.16% and 80.33%±0.22% when the demulsification temperatures are 30, 40, 50 and 60°C; it can be seen that 40°C is the optimal demulsification temperature, at which the puncture rate of the protein-lipid interface membrane is the highest and the oil droplet aggregation speed is the fastest; when the demulsification temperature continues to rise, it will cause protein aggregation and sedimentation, increase the lipid content in the precipitate, and thus affect the extraction rate of cyperus oleifera oil.

[0101] Example 4 Effect of centrifugal pH on protein content, protein composition and acid stability of cyperus oleifera protein

[0102] (1) Cyperus oleifera powder and water were mixed in a mass ratio of 1:7, the pH was adjusted to 8.0 with a 2 mol / L NaOH solution, the mixture was stirred at room temperature and 150 rpm for 1 hour, and the mixture was centrifuged at 3000 g for 15 minutes to remove the solid residue; the solid residue was washed with water (the amount of water added was 5 times the mass of the raw material) and centrifuged again, and the mixture was repeated twice, and the resulting clear liquid was combined to obtain Cyperus oleifera slurry;

[0103] (2) freezing the cyperus oleifera slurry at -18°C for 8 hours, taking it out, heating and stirring it in a water bath at 40°C and 150 rpm for 1 hour, and centrifuging it at 10,000 g for 20 minutes to obtain cyperus oleifera oil and an aqueous phase;

[0104] (3) The aqueous phase was divided into 10 equal parts, and the pH was adjusted to 4.5, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2 and 6.5 respectively using 2 mol / L HCl solution, and stirred in a water bath at 60°C and 150 rpm for 1 h;

[0105] Ten portions of the slurry were centrifuged at 5000 g for 20 min and the protein content of the precipitate was determined.

[0106] Effect of centrifugal pH on protein content in cyperus oleifera protein Figure 4 .

[0107] from Figure 4It can be seen that when the pH of the aqueous phase was adjusted to 4.5, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2 and 6.5, respectively, the protein contents in cyperus oleiferus protein were 78.33% ± 0.10%, 79.05% ± 0.08%, 81.67% ± 0.05%, 86.56% ± 0.08%, 89.12% ± 0.11%, 90.41% ± 0.07%, 91.83% ± 0.06%, 87.15% ± 0.10%, 85.63% ± 0.09% and 80.26% ± 0.12%, respectively; it can be seen that when the aqueous phase was adjusted to pH 4.5-6.5 for precipitation, it was found that the protein content of cyperus oleiferus protein showed a trend of first increasing and then decreasing. The protein content reached the maximum at pH 5.8, which was 91.83%±0.06%, much higher than 78.33%±0.10% at pH 4.5.

[0108] Effect of centrifugal pH on protein composition of cyperus oleifera protein Figure 5 .

[0109] from Figure 5 It can be seen that when the pH of the aqueous phase was adjusted to 4.5, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2 and 6.5, respectively, the proportion of albumin in serrata protein was 43.39% ± 0.41%, 50.21% ± 0.59%, 59.32% ± 0.46%, 67.57% ± 0.35%, 75.25% ± 0.53%, 79.62% ± 0.61%, 83.06% ± 0.37%, 78.08% ± 0.55%, 73.16% ± 0.29% and 69.25% ± 0.35%, respectively, and the rest was globulin, alcohol-soluble protein and glutenin, etc.; It can be seen that the composition of the protein precipitated at different pH is different. At 5.8, the proportion of albumin in jatropha protein was the highest, reaching 89.06%±0.37%.

[0110] Effect of centrifugal pH on the stability of cyperus oleifera protein acid Figure 6 .

[0111] from Figure 6It can be seen that when the pH of the aqueous phase was adjusted to 4.5, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2 and 6.5, the acid stability of the obtained serrata protein was 32.17% ± 0.76%, 43.81% ± 0.85%, 59.62% ± 1.37%, 71.05% ± 1.21%, 82.65% ± 0.53%, 89.21% ± 0.65%, 93.37% ± 1.05%, 85.25% ± 0.89%, 80.33% ± 0.71% and 73.26% ± 1.22%, respectively; it can be seen that due to the different protein compositions of the serrata protein obtained by precipitation at different pH values, its acid stability was different. When the albumin ratio was the highest (pH 5.8) Its acid stability is the best, reaching 93.37%±1.05%.

[0112] Example 5 Effect of Sedimentation Temperature on Extraction Yield of Cyperus oleifera Protein Isolate

[0113] (1) Cyperus oleifera powder and water were mixed in a mass ratio of 1:7, the pH was adjusted to 8.0 with a 2 mol / L NaOH solution, the mixture was stirred at room temperature and 150 rpm for 1 hour, and the mixture was centrifuged at 3000 g for 15 minutes to remove the solid residue; the solid residue was washed with water (the amount of water added was 5 times the mass of the raw material) and centrifuged again, and the mixture was repeated twice, and the resulting clear liquid was combined to obtain Cyperus oleifera slurry;

[0114] (2) freezing the cyperus oleifera slurry at -18°C for 8 hours, taking it out, heating and stirring it in a water bath at 40°C and 150 rpm for 1 hour, and centrifuging it at 10,000 g for 20 minutes to obtain cyperus oleifera oil and an aqueous phase;

[0115] (3) The aqueous phase was placed in a water bath and the pH was adjusted to 5.8 using a 2 mol / L HCl solution; the aqueous phase was divided into five equal portions and stirred at 30, 40, 50, 60 and 70°C, 150 rpm for 1 h, and then centrifuged at 5000 g for 20 min. The precipitate was obtained, which was the cyperus oleifera protein isolate. The precipitate was weighed and its protein content was determined to calculate the protein extraction rate.

[0116] Effect of sedimentation temperature on the extraction rate of cyperus oleifera protein isolate Figure 7 .

[0117] from Figure 7It can be seen that when the temperature is 30, 40, 50, 60 and 70 ℃, the extraction rate of cyperus oleiferus protein isolate is 36.61% ± 0.25%, 48.51% ± 0.23%, 58.32% ± 0.16%, 65.65% ± 0.12% and 56.52% ± 0.26% respectively; it can be seen that proper heating is conducive to accelerating the aggregation and collision between cyperus oleiferus protein particles, and then to sedimentation; however, too high a temperature is easy to cause protein denaturation, which is not conducive to the aggregation and sedimentation of protein. The optimal sedimentation temperature of cyperus oleiferus protein is 60 ℃.

[0118] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for synchronously preparing cyperus oleifera oil and cyperus oleifera protein isolate, characterized in that: The steps include: (1) mixing cyperus oleifera powder and water, adjusting the pH to 7.0-9.0, stirring, centrifuging, removing the solid residue, and the clear liquid is cyperus oleifera slurry; (2) freezing the cyperus oleifera slurry at -30 to -5°C for 6 to 14 hours, taking it out; heating and stirring it at 30 to 60°C for 0.5 to 2 hours, and centrifuging it to obtain cyperus oleifera oil and an aqueous phase; (3) The temperature of the aqueous phase is adjusted to 30-70°C, the pH is adjusted to 4.5-6.5, and after stirring for 0.5-2 hours, the mixture is centrifuged to obtain the precipitate, which is the cyperus oleifera protein isolate.

2. The method according to claim 1, characterized in that The freezing in step (2) is performed at -18°C for 8 hours.

3. The method according to claim 1 or 2, characterized in that: The heating and stirring was carried out at 40°C and 100-200 rpm for 1 h.

4. The method according to any one of claims 1 to 3, characterized in that: The stirring in step (3) is carried out at 60° C. and 100 to 200 rpm for 0.5 to 2 h.

5. The cyperus oleifera protein isolate prepared by the method according to any one of claims 1 to 4.

6. A method for extracting more cyperus juncea oil and cyperus juncea protein isolate with higher protein content from cyperus juncea, characterized in that: The method according to any one of claims 1 to 4 is adopted.

7. A method for increasing the protein content in cyperus oleifera protein isolate, characterized in that: The method according to any one of claims 1 to 4 is adopted.

8. A method for increasing the proportion of albumin in cyperus oleifera protein isolate, characterized in that: The method according to any one of claims 1 to 4 is adopted.

9. A method for improving the acid stability of cyperus oleifera protein isolate, characterized in that: The method according to any one of claims 1 to 4 is adopted.

10. Application of the cyperus oleifera protein isolate according to claim 5 in the field of food; Furthermore, the food is an acidic milk beverage.

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