Preparation method for extracting cyperus esculentus oil through water medium-freezing and unfreezing

Abstract

The invention discloses a preparation method for extracting cyperus esculentus oil through water medium-freezing and unfreezing, and relates to the technical field of food processing. Comprising the following steps: (1) removing impurities, cleaning cyperus esculentus, drying the cyperus esculentus to constant weight at 45 DEG C, crushing the cyperus esculentus, and sieving the crushed cyperus esculentus by (2) weighing 30 g of the cyperus esculentus powder in the step (1), putting the weighed cyperus esculentus powder into a conical flask, adding distilled water according to a material-liquid ratio of 1: 4-1: 7, putting the conical flask into a water bath oscillator, performing oscillation heating to 60 DEG C, taking out the conical flask, and cooling the conical flask to room temperature; (3) adjusting the pH value to 7.00-11.00, incubating for 2-6 hours in a water bath oscillator at 40-80 DEG C, centrifuging for 5 minutes at the speed of 5000r / min, and putting an upper oil layer and an emulsion layer into a 50mL plastic centrifuge tube; and (4) freezing at-5 to-25 DEG C for 8-24 hours, taking out, unfreezing in warm water at 40-80 DEG C for 10-30 minutes, centrifuging at 7000 r / min for 15 minutes, and collecting supernate. According to the invention, the cost is reduced, the oil extraction rate is improved, and the invention provides a green, efficient and economical preparation method of the cyperus esculentus oil.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to a preparation method of cyperus oleifera oil extracted by water-medium freezing and thawing. Background Art

[0002] At present, the main extraction methods of cyperus oleifera oil include pressing (hot pressing, cold pressing), organic solvent leaching, water enzyme method, water enzyme-freeze-thaw technology, ultrasonic / microwave combined water enzyme method, supercritical CO2 extraction method and subcritical fluid extraction. Among them, the pressing method usually has a low oil yield, and high temperature will lead to the loss of heat-sensitive bioactive components and the formation of harmful compounds (such as benzopyrene); although the oil extraction rate of organic solvents is high, there is potential organic solvent pollution and residue, which may cause damage to human health and the quality of edible oil. Supercritical CO2 extraction and subcritical fluid extraction are simple in process, easy to operate, and the obtained oil is of good quality, but the equipment is expensive. With the increasing attention paid to environmental pollution problems, the demand for natural edible oils is increasing. It is of great significance to research and develop safer, environmentally friendly and low-energy edible oil production technologies.

[0003] Therefore, it is necessary to provide a new technical solution to solve this technical problem, especially a preparation method of extracting cyperus oleifera oil by water-medium freezing and thawing. Summary of the invention

[0004] The purpose of the present invention is to solve the problems existing in the existing cyperus juncea oil extraction technology, and to provide a preparation method of cyperus juncea oil by water-medium-freeze-thaw extraction.

[0005] In order to achieve the above object, the present invention provides the following technical solution: A preparation method of cyperus oleifera oil by water-freeze-thaw extraction, comprising the following steps:

[0006] (1) removing impurities and washing the cyperus oleifera, drying at 45° C. to constant weight, and crushing through a 40-120 mesh sieve;

[0007] (2) Weigh 30 g of the cyperus oleifera flour prepared in step (1) into a conical flask, add distilled water at a solid-liquid ratio of 1:4-1:7, place the flask in a water bath oscillator and shake and heat to 60° C., then take the flask out and cool to room temperature;

[0008] (3) adjusting the pH to 7.00-11.00, incubating in a water bath shaker at 40-80°C for 2-6 h, centrifuging at 5000 r / min for 5 min, and taking the upper oil layer and the emulsion layer into a 50 mL plastic centrifuge tube;

[0009] (4) Freeze at -5 to -25°C for 8 to 24 hours, take out and thaw in warm water at 40 to 80°C for 10 to 30 minutes, centrifuge at 7000 r / min for 15 minutes, and collect the supernatant.

[0010] Preferably, the solid-liquid ratio in step (1) is 1:5; the pH in step (3) is 10.0, the extraction temperature of water bath oscillation is 50°C, and the incubation extraction time is 3 hours; the freezing time in step (4) is 20 hours, the freezing temperature is -20°C, the thawing temperature is 70°C, and the thawing time is 20 minutes.

[0011] Preferably, the solid-liquid ratio in step (1) is 1:4; the pH in step (3) is 10.4, the extraction temperature of water bath oscillation is 50°C, and the incubation extraction time is 2.63h; the freezing time in step (4) is 20h, the freezing temperature is -20°C, the thawing temperature is 70°C, and the thawing time is 20min.

[0012] The beneficial effects of the present invention are:

[0013] The present invention provides a green oil extraction technology, which has the characteristics of mild extraction conditions, good oil quality, high resource utilization and environmental friendliness. The present invention overcomes the technical problem of producing a large amount of emulsion in the water-based oil extraction method by freezing and thawing. The demulsification principle of freezing and thawing is that when the emulsion is frozen, the oil phase crystallizes easily. These fat crystals can penetrate the water phase and penetrate the interface membrane to cause the aggregation and merging of oil droplets, which can greatly reduce the stability of the emulsion and then break the emulsion. By combining the water-based method with the freezing and thawing technology, the oil yield is increased, so that the oil yield can reach more than 86%. At the same time, the oil flavor substances prepared by the method provided by the present invention have more types of flavor substances than the existing jatropha oil on the market, higher tocopherol content, stronger free radical scavenging ability, and better oxidative stability.

[0014] Although the invention forms more emulsions in the extraction process, centrifugation can achieve the effect of simply separating the clear oil, and the demulsification by freezing and thawing can well improve the oil extraction rate of the clear oil, and the process is relatively simple. The invention adopts a water substitution method combined with freezing and thawing to prepare cyperus juncea oil, and no enzyme preparation, organic reagent, etc. are added in the process. The method is green, natural, has a high oil extraction rate and low cost, and the obtained cyperus juncea oil is transparent and clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a graph showing the experimental results of the effect of the particle size of cyperus oleifera on the extraction rate in the preparation process of the present invention.

[0016] Figure 2 This is a graph showing the experimental results of the effect of the material-liquid ratio on the extraction rate in the preparation process of the present invention.

[0017] Figure 3 This is a graph showing the experimental results of the effect of pH on the extraction rate in the preparation process of the present invention.

[0018] Figure 4 This is a graph showing the experimental results of the effect of extraction time on extraction rate in the preparation process of the present invention.

[0019] Figure 5 This is a graph showing the experimental results of the effect of extraction temperature on the extraction rate in the preparation process of the present invention.

[0020] Figure 6 This is a graph showing the experimental results of the effect of extraction time on extraction rate in the preparation process of the present invention.

[0021] Figure 7 This is a graph showing the experimental results of the effect of freezing temperature on the extraction rate in the preparation process of the present invention.

[0022] Figure 8 This is a graph showing the experimental results of the effect of thawing temperature on the extraction rate in the preparation process of the present invention.

[0023] Fig. 9 This is a graph showing the experimental results of the effect of thawing time on the extraction rate in the preparation process of the present invention.

[0024] Fig.10 It is a data analysis diagram of the regression model in the preparation process of the present invention.

[0025] Fig.11 This is a graph showing the experimental results of the effects of the interaction of factors on the extraction rate of jatropha oil in the preparation process of the present invention.

[0026] Fig.12 The figure is a comparison chart of the oxidation stability of the cyperus juncea oil prepared by the present invention and the existing cyperus juncea oil.

[0027] Fig.13 The figure is a comparison chart of volatile compound types between the cyperus juncea oil prepared by the present invention and the existing cyperus juncea oil.

[0028] Fig.14 The figure is a comparison chart of the percentage content of volatile compounds in the cyperus juncea oil prepared by the present invention and the existing cyperus juncea oil. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with specific embodiments.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0032] 1. Preparation method of cyperus oleifera oil by water-freeze-thaw extraction

[0033] The method for extracting cyperus oleifera oil based on water substitution method of the present invention is carried out according to the following steps:

[0034] (1) Remove impurities and wash the cyperus oleifera, dry at 45°C to constant weight, and grind through a 60-mesh sieve.

[0035] (2) Weigh 30 g of the cyperus oleifera flour prepared in step (1) into a conical flask, add distilled water at a solid-liquid ratio of 1:4-1:7, place the flask in a water bath oscillator and oscillate to heat to 60° C., then take the flask out and cool to room temperature.

[0036] (3) The pH was adjusted to 7.00-11.00, and the mixture was incubated in a water bath shaker at 40-80°C for 2-6 h. The mixture was then centrifuged at 5000 rpm for 5 min, and the upper oil layer and the emulsion layer were collected and placed in a 50 mL plastic centrifuge tube.

[0037] (4) Place in a freezer at -5 to -25°C for 8 to 24 hours, take out and thaw in warm water at 40 to 80°C for 10 to 30 minutes, centrifuge at 7000 r / min for 15 minutes, and collect the clear oil. DETAILED DESCRIPTION

[0039] Example 1

[0040] (1) Remove impurities from the cyperus juncea, wash it, dry it at 45°C to constant weight, and grind it through a 60-mesh sieve.

[0041] (2) Weigh 30 g of cyperus oleifera flour into a conical flask, add distilled water at a solid-liquid ratio of 1:5, place the flask in a water bath oscillator and oscillate to heat to 60°C, then take out and cool to room temperature.

[0042] (3) The pH was adjusted to 10, and the mixture was incubated in a water bath shaker at 50°C for 3 h. The mixture was then centrifuged at 5000 rpm for 5 min, and the upper oil layer and the emulsion layer were collected and placed in a 50 mL plastic centrifuge tube.

[0043] (4) Place in a -5°C freezer for 20 h, take out and thaw in 60°C warm water for 15 min, centrifuge at 7000 r / min for 15 min, collect the clear oil, and the oil extraction rate is 73.83%.

[0044] Example 2

[0045] (1) Remove impurities from the cyperus juncea, wash it, dry it at 45°C to constant weight, and grind it through a 60-mesh sieve.

[0046] (2) Weigh 30 g of cyperus oleifera flour into a conical flask, add distilled water at a solid-liquid ratio of 1:5, place the flask in a water bath oscillator and oscillate to heat to 60°C, then take out and cool to room temperature.

[0047] (3) The pH was adjusted to 10, and the mixture was incubated in a water bath shaker at 50°C for 3 h. The mixture was then centrifuged at 5000 rpm for 5 min, and the upper oil layer and the emulsion layer were collected and placed in a 50 mL plastic centrifuge tube.

[0048] (4) Place in a -16°C freezer for 20 h, take out and thaw in 60°C warm water for 15 min, centrifuge at 7000 r / min for 15 min, collect the clear oil, and the oil extraction rate is 82.55%.

[0049] Example 3

[0050] (1) Remove impurities from the cyperus juncea, wash it, dry it at 45°C to constant weight, and grind it through a 60-mesh sieve.

[0051] (2) Weigh 30 g of cyperus oleifera flour into a conical flask, add distilled water at a solid-liquid ratio of 1:5, place the flask in a water bath oscillator and oscillate to heat to 60°C, then take out and cool to room temperature.

[0052] (3) The pH was adjusted to 10, and the mixture was incubated in a water bath shaker at 50°C for 3 h. The mixture was then centrifuged at 5000 rpm for 5 min, and the upper oil layer and the emulsion layer were collected and placed in a 50 mL plastic centrifuge tube.

[0053] (4) Place the mixture in a -20°C freezer for 20 h, take it out and thaw it in 60°C warm water for 15 min, centrifuge it at 7000 r / min for 15 min, collect the clear oil, and the oil extraction rate is 86%.

[0054] Example 4

[0055] (1) Remove impurities from the cyperus juncea, wash it, dry it at 45°C to constant weight, and grind it through a 60-mesh sieve.

[0056] (2) Weigh 30 g of cyperus oleifera flour into a conical flask, add distilled water at a solid-liquid ratio of 1:4, place in a water bath oscillator, shake and heat to 60°C, take out and cool to room temperature.

[0057] (3) The pH was adjusted to 10.4, and the mixture was incubated in a water bath shaker at 50°C for 2.63 h. The mixture was then centrifuged at 5000 rpm for 5 min, and the upper oil layer and the emulsion layer were collected and placed in a 50 mL plastic centrifuge tube.

[0058] (4) Place in a -20°C freezer for 20 h, take out and thaw in 70°C warm water for 20 min, centrifuge at 7000 r / min for 15 min, collect the clear oil, and the oil extraction rate is 86.07%.

[0059] 2. Analysis of the creativity of the reaction conditions in the process of the present invention

[0060] The invention is an innovative design for the selection of the particle size of cyperus oleifera, the solid-liquid ratio, the pH value, the incubation extraction time, the extraction temperature of the water bath oscillation, the freezing time, the freezing temperature, and the thawing time. Corresponding experiments have been conducted to screen, determine and verify. The specific screening and verification methods are as follows:

[0061] Single factor experiment

[0062] 1.1 Effect of particle size on the extraction rate of jatropha oil

[0063] The dried cyperus oleifera was crushed and sieved through 40, 60, 80, 100 and 120 mesh sieves to obtain cyperus oleifera powder. Distilled water was added at a solid-liquid ratio of 1:6 (m:V). The effect of particle size on the oil extraction rate was investigated according to the above process flow under the conditions of pH 9.0, extraction at 40°C for 1.5h, freezing at -20°C for 24h and thawing at 50°C for 15min.

[0064] 1.2 Effect of solid-liquid ratio on the extraction rate of jatropha oil

[0065] Using 60-mesh cyperus oleifera flour, distilled water was added at a solid-liquid ratio of 1:3, 1:4, 1:5, 1:6, and 1:7 (m:V). Under the conditions of pH 9.0, extraction at 40°C for 1.5h, freezing at 20°C for 24h, and thawing at 50°C for 15min, the effect of solid-liquid ratio on the oil extraction rate was investigated according to the process flow of 3.2.1.

[0066] 1.3 Effect of pH on the extraction rate of jatropha oil

[0067] Using 60-mesh cyperus oleifera flour, distilled water was added at a solid-liquid ratio of 1:5 (m:V), and the pH was adjusted to 7.0, 8.0, 9.0, 10.0, and 11.0, respectively. The extraction was performed at 40°C for 1.5 h, the freezing time was -20°C for 24 h, and the thawing time was 50°C for 15 min. According to the process flow of 3.2.1, the effect of pH on the oil extraction rate was investigated.

[0068] 1.4 Effect of extraction time on the extraction rate of jatropha oil

[0069] Using 60-mesh cyperus oleifera powder, distilled water was added at a solid-liquid ratio of 1:5 (m:V). Under the conditions of pH 10.0, extraction temperature 50℃, -20℃ freezing time 24h, and thawing at 50℃ for 15min, the extraction time was set to 2, 3, 4, 5, and 6h, respectively. According to the process flow of 3.2.1, the effect of extraction time on the oil extraction rate was investigated.

[0070] 1.5 Effect of extraction temperature on the extraction rate of jatropha oil

[0071] Using 60-mesh cyperus oleifera flour, distilled water was added at a solid-liquid ratio of 1:5 (m:V). Under the conditions of pH 10.0, extraction time 1.5h, -20℃ freezing time 24h, and thawing at 50℃ for 15min, the extraction temperatures were set to 40, 50, 60, 70, and 80℃, respectively. According to the process flow of 3.2.1, the effect of extraction temperature on the oil extraction rate was investigated.

[0072] 1.6 Effect of freezing time on the extraction rate of jatropha oil

[0073] Using 60-mesh cyperus oleifera powder, distilled water was added at a solid-liquid ratio of 1:5 (m:V). Under the conditions of pH 10.0, extraction at 50℃ for 3h, freezing temperature at -20℃, and thawing at 50℃ for 15min, the freezing time was set to 8, 12, 16, 20, and 24h, respectively. According to the process flow of 3.2.1, the effect of freezing time on the oil extraction rate was investigated.

[0074] 1.7 Effect of freezing temperature on the extraction rate of jatropha oil

[0075] Using 60-mesh cyperus oleifera flour, distilled water was added at a solid-liquid ratio of 1:5 (m:V). Under the conditions of pH 10.0, extraction at 50°C for 3h, freezing time for 20h, and thawing at 50°C for 15min, the freezing temperatures were set at -5, -7, -16, -20, and -25°C, respectively. According to the process flow of 3.2.1, the effect of freezing temperature on the oil extraction rate was investigated.

[0076] 1.8 Effect of thawing temperature on the extraction rate of jatropha oil

[0077] Using 60-mesh cyperus oleifera powder, distilled water was added at a solid-liquid ratio of 1:5 (m:V). Under the conditions of pH 10.0, extraction at 50°C for 3h, freezing time at -20°C for 20h, and thawing time of 15min, the thawing temperatures were set to 40, 50, 60, 70, and 80°C, respectively. According to the process flow of 3.2.1, the effect of thawing temperature on the oil extraction rate was investigated.

[0078] 1.9 Effect of thawing time on the extraction rate of jatropha oil

[0079] Using 60-mesh cyperus oleifera flour, distilled water was added at a solid-liquid ratio of 1:5 (m:V). Under the conditions of pH 10.0, extraction at 50°C for 3h, freezing time at -20°C for 20h, and thawing temperature of 70°C, the thawing time was set to 10, 15, 20, 25, and 30min, respectively. According to the process flow of 3.2.1, the effect of thawing time on the oil extraction rate was investigated.

[0080] 2. Single factor experimental verification and analysis

[0081] 2.1 Effect of particle size of cyperus oleifera powder on extraction rate

[0082] like Figure 1 As shown in the figure, when the particle size of cyperus oleifera powder is ≤60 mesh, the extraction rate of cyperus oleifera oil is the highest, reaching 35.41%. In the initial stage, the extraction rate gradually increases as the particle size decreases, and in the later stage, as the particle size becomes smaller and smaller, the extraction rate gradually decreases. The main reason may be that in the initial stage, due to the increase in the degree of crushing, some large particles in the oil are broken, and the oil in the particles can be released more through the water phase. When the degree of crushing reaches 60 mesh, the raw materials are fully crushed without causing proteins, starch and other substances to disperse around the oil, and the free oil in the oil cells can be released to the maximum extent; further crushing, the large particles in the oil will be more easily combined with the oil to form an emulsion if they are over-crushed, which accelerates emulsification and affects the extraction rate. Therefore, cyperus oleifera powder was selected to pass through a 60-mesh sieve for the following test.

[0083] 2.2 Effect of material-liquid ratio on extraction rate

[0084] The solid-liquid ratio has a great influence on the extraction rate. Figure 2 It can be seen that the extraction rate is highest when the solid-liquid ratio is 1:5, because when the solid-liquid ratio is small, the slurry can not only fully absorb water but also absorb oil, resulting in insufficient release of oil and a low extraction rate; as the solid-liquid ratio increases, more water is absorbed, more free oil is replaced, and the extraction rate is increased. However, when the solid-liquid ratio exceeds a certain ratio, the excess water will emulsify with oil, pulp residue, etc. to form more emulsions, making it difficult to separate oil and reduce the extraction rate. Therefore, the appropriate solid-liquid ratio is selected as 1:5, which is consistent with the results of Wang Wei's water substitution method for extracting Xikang almond oil.

[0085] 2.3 Effect of pH on extraction rate

[0086] Depend on Figure 3It can be seen that the pH in the range of 7.0 to 11.0 has a greater impact on the extraction rate, and the overall trend is first rising and then falling. The extraction rate is the highest at pH 10.0. In an alkaline environment, the average particle size of cyperus oleiferus protein decreases with the increase of pH, and the protein is more evenly dispersed in the solution system. As the pH increases, the emulsification and surface hydrophobicity of cyperus oleiferus protein first decrease and then increase. Therefore, it is possible that the emulsification and surface hydrophobicity of protein in the solution system are the lowest at pH 10.0, so that the protein can fully combine with water molecules to replace more free oil, making the extraction rate the highest at this time. As the pH increases, the surface hydrophobicity and emulsification of the protein increase, which is not conducive to the replacement of oil and fat, resulting in a decrease in the extraction rate and an increase in the emulsion. Therefore, the appropriate pH is selected as 10.0.

[0087] 2.4 Effect of extraction time on extraction rate

[0088] Depend on Figure 4 It can be seen that the extraction time increases first and then decreases within 2 to 6 hours, and the extraction rate reaches the highest at 4 hours, indicating that the extraction time should not be too long. Within the range of 2 to 4 hours, as time increases, the material cells are further destroyed, so that the free oil in them is fully released. However, after more than 4 hours, since the oil in the raw material is fully released, if the reaction continues, the free oil in the system will combine with proteins and other substances to aggravate the emulsification phenomenon and reduce the extraction rate. There is no significant difference in the extraction rate at 3 hours and 4 hours. In order to save time cost, 3 hours is selected as the optimal extraction time.

[0089] 2.5 Effect of extraction temperature on extraction rate

[0090] Depend on Figure 5 It can be seen that temperature has a significant effect on the extraction rate of cyperus oleifera oil. The extraction temperature shows a trend of first increasing and then decreasing in the range of 40-80°C, and the extraction rate is highest at 50°C. This is because when the temperature is low, the slurry is viscous and the oil is difficult to separate; when the temperature rises, the movement between oil molecules is intensified, and collisions occur in the system to aggregate into larger oil droplets and free them. At the same time, the viscosity of the oil decreases, and the slurry becomes thinner, making it easier to separate the oil; when the temperature is higher than 50°C, as the temperature increases, the evaporation of water accelerates, the solid-liquid ratio gradually decreases, and the slurry becomes viscous, resulting in a continuous decrease in the extraction rate of free oil. Therefore, the suitable extraction temperature is 50°C.

[0091] 2.6 Effect of freezing time on extraction rate

[0092] Depend on Figure 6As shown, the oil extraction rate reaches the maximum at 20h of freezing, indicating that the demulsification effect is better with the extension of freezing time. The extraction rate increases rapidly from 8 to 12h, and the extraction rate increases slowly from 12 to 20h, indicating that the oil phase crystals form rapidly in the emulsion from 8 to 12h, and the formation of oil phase crystals in the emulsion from 12 to 20h gradually saturates and reaches the maximum value at 20h. The oil phase crystals pierce the water phase and the interface membrane at the same time, thereby destroying the stability of the emulsion, thereby releasing and aggregating the small oil droplets. Therefore, the optimal freezing time is 20h.

[0093] 2.7 Effect of freezing temperature on extraction rate

[0094] Depend on Figure 7 It can be seen that as the freezing temperature decreases, the oil extraction rate continues to increase, and the extraction rate is highest when the temperature reaches -25°C. This is because under freezing conditions, the oil in the emulsion undergoes oil phase crystallization, and the oil phase crystals pierce the interface membrane to destroy the interfacial tension of the emulsion, causing the oil droplets to aggregate, thereby achieving the purpose of increasing the oil extraction rate.

[0095] 2.8 Effect of thawing temperature on extraction rate

[0096] like Figure 8 As shown in the figure, in the range of 40-80℃, with the increase of thawing temperature, the extraction rate of jatropha oil first increased and then decreased. When the temperature reached 70℃, the extraction rate was the highest. This may be because after the oil phase crystals were completely dissolved due to excessively high temperature, part of the oil and protein combined again to re-form an emulsion, resulting in a decrease in the extraction rate.

[0097] 2.9 Effect of thawing time on extraction rate

[0098] like Fig. 9 As shown in the figure, within the range of 10 to 30 minutes, the extraction rate increases with the extension of thawing time, reaching the maximum value at 20 minutes, indicating that as the thawing time increases, the oil phase crystals can be fully dissolved to release oil droplets, thereby increasing the oil extraction rate; but when the thawing time exceeds 20 minutes, the time for oil to combine with protein molecules will increase, forming an emulsion, and the oil extraction rate will decrease. Therefore, the appropriate thawing time is 20 minutes.

[0099] 3. Plackett-Burman Design Test

[0100] The advantage of PBD test is that the most significant influencing factors can be selected from a large number of influencing factors with the least number of experiments, which reduces the factors to be considered and the number of experiments for the response surface optimization process, while also being accurate. Through single-factor experiments, solid-liquid ratio (A), pH (B), extraction temperature (C), extraction time (D), freezing time (E), freezing temperature (F), thawing temperature (G), and thawing time (H) were selected as reference factors, and the extraction rate of jatropha oil was used as the evaluation index for experimental design. The factor level table is shown in Table 1.

[0101] Table 1Plackett-Burman Design factor level table

[0102]

[0103]

[0104] 3.1 Factors affecting PBD test screening

[0105] The PBD experimental design and results are shown in Table 2, and the experimental variance analysis is shown in Table 3.

[0106] Table 2 Experimental design and results of Plackett-Burman Design

[0107]

[0108] Table 3 Analysis of variance of Plackett-Burman Design test

[0109] Table3 Variance analysis ofPlackett-Burman Design

[0110]

[0111] As shown in Table 2, there are 12 groups of PBD tests with solid-liquid ratio (A), pH (B), extraction temperature (C), extraction time (D), freezing time (E), freezing temperature (F), thawing temperature (G), and thawing time (H) as factors and extraction rate as response value. The highest extraction rate of group 12 is 80.30%. As shown in Tables 3-5, the model is significant (p<0.05), indicating that the model is reliable. The factors that have a significant impact on the extraction rate are ranked in order of influence ability as A>H>B>D, that is, solid-liquid ratio>thawing time>pH>extraction time. According to the results of single factor test and PBD test, the central composite test was carried out to determine that the solid-liquid ratio, thawing time, pH, and extraction time are the main factors affecting the extraction rate, and the oil extraction process was further optimized.

[0112] 4. Central Composite Design

[0113] On the basis of PBD test, CCD test was used to further optimize the process conditions, and the significant influencing factors obtained through PBD test, namely, solid-liquid ratio (A), pH (B), extraction time (D), and thawing time (H), were selected as independent variables, and the extraction rate of cyperus oleifera oil was used as the evaluation index for optimization test. The factor level table is shown in Table 4. According to the experimental design, a total of 30 groups of experiments were obtained, and each group was repeated 3 times.

[0114] Table 4 Central Composite Design factor level table Table 2 Central Composite Design Factor level table

[0115]

[0116]

[0117] 4.1 Establishment and analysis of central composite test regression model

[0118] The central composite test results are shown in Table 5. The corresponding regression equation for the extraction rate of cyperus oleifera oil obtained by the central composite test is:

[0119] Y (extraction rate / %) = +84.62-3.71*A+1.07*B-0.82*H-2.29*D+0.14*AB+0.44*AH+0.48*AD+0.17*BH-1.33*BD-1.30*HD-2.43*A2-1.94*B2-2.91*H2-4.11*D2.

[0120] Table 5 Experimental design and results of Central Composite Design

[0121]

[0122]

[0123] Table 5

[0124]

[0125] Table 6 Variance analysis of Central Composite Design

[0126]

[0127]

[0128] As shown in Table 6, the regression model p<0.0001, indicating that the model is extremely significant; the lack of fit term p=0.5088>0.05, the difference is not significant, indicating that the model has a good fit and can be used to optimize the process of extracting cyperus oleiferus oil by water-based freezing and thawing method; the determination coefficient R2=97.79%, the correction coefficient R2Adj=95.73%, and the prediction coefficient R2Pred=90.35% of the model are all greater than 90%, indicating that the model has good stability, and 97.79% of the change in cyperus oleiferus oil extraction rate comes from the variables, and the actual value is relatively mild compared with the model prediction value. Therefore, the model can be used to analyze and predict the situation of extracting cyperus oleiferus oil by water-based freezing and thawing method. From the significance analysis of Table 3-7, it can be seen that the order of factors affecting the extraction rate of jatropha oil is solid-liquid ratio > thawing time > pH > extraction time; in the model, BD, HD, A2, B2, H2, and D2 have extremely significant effects on the extraction rate of jatropha oil (p<0.01), indicating that there is a certain interactive relationship between thawing time and pH and extraction time.

[0129] Normal probability plots, the ratio of residuals to the number of test runs, and the ratio of actual test results to predicted values ​​are used to verify the adequacy of the established model and to illustrate the interaction between actual and predicted values. The normal probability plot indicates whether the residuals follow a normal distribution. Fig.10(a) is the normal probability distribution diagram of the model. It can be seen from the figure that the response residuals of the extraction rate of jatropha oil are normally distributed, and the data points are located on both sides of this line. The residuals and the number of experimental runs can be used to check for hidden variables that may affect the actual response during the extraction process. These variables should be randomly distributed. Fig.10 (b) is a graph of residuals and test run order. It can be seen from this graph that the model established in this study fits well, and all points are randomly distributed within a certain range (±3). Fig.10 (c) is the actual test value and the predicted value graph. It can be seen from the graph that the data points are close to the straight line, indicating that the determined value is consistent with the predicted value. The results show that the model can better optimize the process conditions for extracting cyperus oleifera oil by water-freeze-thaw method.

[0130] 3. Response surface test results and analysis

[0131] 3.1 Effects of interactions among various factors on the extraction rate of jatropha oil

[0132] The three-dimensional response surface diagram reflects the interaction between factors on the extraction rate of jatropha oil. In the extraction process of jatropha oil, the interaction between pH and extraction time, thawing time and extraction time has a significant effect on the extraction rate (p<0.05). Fig.11 As shown. Fig.11 (a) It can be seen that when other extraction conditions are fixed, the effects of pH and extraction time on the extraction rate are quadratic. The extraction rate of cyperus oleifera oil increases with the increase of extraction time, and then decreases slightly. Prolonging the extraction time and increasing the pH will lead to the formation of more emulsions during the oil extraction process, reducing the extraction rate. Fig.11 (b) It can be seen that when other extraction conditions are fixed, there is an obvious quadratic curve relationship between the extraction time and the thawing time. When the thawing time is 20 minutes, the extraction rate of jatropha oil first increases and then decreases with the increase of extraction time.

[0133] 3.2 Verification test

[0134] According to the Soxhlet extraction method in GB 5009.6-2016, the oil content of cyperus oleifera is 20.27%. The formula for calculating the oil extraction rate of cyperus oleifera is as follows:

[0135]

[0136] Wherein: M represents the mass of cyperus juncea powder in g, and m represents the mass of cyperus juncea oil extracted in g.

[0137] Table 7 Verification test

[0138] Table 7 Validation tests

[0139]

[0140] In order to verify the reliability of the model, experiments were carried out under the optimal extraction conditions with slight modifications according to the actual situation. The experimental conditions and results are shown in Table 7. The experimental results (86.07±0.38%) were statistically consistent with the predicted values ​​(86.76%), indicating that the established model is reliable.

[0141] This chapter optimizes the process of extracting cyperus oleifera oil by water-freeze-thaw method through single factor test, PBD and CCD test, and obtains the best process conditions. The results are as follows:

[0142] (1) This study used a water-based method combined with freeze-thaw to extract cyperus oleifera oil. The optimal values ​​of solid-liquid ratio (1:5), pH (10.0), extraction temperature (50℃), extraction time (3h), freezing time (20h), freezing temperature (-20℃), thawing temperature (70℃), and thawing time (20min) for cyperus oleifera oil extraction rate were determined through single factor experiments.

[0143] (2) Based on the single factor, the PBD test was used to screen out four factors that have a significant impact on the extraction rate of jatropha oil from the factors such as solid-liquid ratio, pH, extraction temperature, extraction time, freezing time, freezing temperature, thawing temperature, and thawing time, namely, solid-liquid ratio, thawing time, pH, and extraction time.

[0144] (3) Based on the PBD test, the CCD test was conducted to further optimize the water-freeze-thaw process, and the optimized conditions were: solid-liquid ratio 1:4, extraction temperature 50℃, extraction time 2.63h, pH 10.40, freezing temperature -20℃, freezing time 20h, thawing temperature 70℃, thawing time 20min. Under the optimal conditions, the extraction rate of cyperus oleifera oil was 86.07%, which was slightly lower than the predicted value (86.76%).

[0145] 3. Performance analysis of cyperus oleifera oil prepared by the present invention

[0146] The cyperus juncea oil prepared by the present invention was compared with the cyperus juncea oil sold on the market, wherein the commercially available cyperus juncea oil comes from Xinjiang Sanli Grain and Oil Co., Ltd. and is stored in a refrigerator at 4°C.

[0147] 1. Fatty acid composition and content

[0148] Table 8 Fatty acid composition and content of water-freeze-thawed cyperus oleifera oil

[0149] Table 8Fatty acid composition and contentoftiger nut oilby aqueousmedium-freezing and

[0150] thawing

[0151]

[0152] As shown in Table 8, there are five fatty acids in cyperus olei oil, namely palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid. There is no significant difference in the fatty acid composition of cyperus olei oil from different processes (p>0.05). The oleic acid content in cyperus olei oil is the highest, followed by palmitic acid and linoleic acid. The relative percentage of oleic acid (79.08%) and unsaturated fatty acids (87.36%) in water-freeze-thawed cyperus olei oil is higher than that in commercial oil (71.85%, 84.48%). The absolute content of oleic acid (533.01 mg / g) and unsaturated fatty acids (586.79 mg / g) in water-freeze-thawed cyperus olei oil is higher than that in commercial oil (474.84 mg / g, 558.28 mg / g). The fatty acid contents of water-based frozen-thawed cyperus juncea oil and commercially available cyperus juncea oil were 673.22 mg / g and 660.78 mg / g, respectively. The fatty acid content of water-based frozen-thawed cyperus juncea oil was higher than that of commercially available cyperus juncea oil.

[0153] 2. Content of lipid accompaniments

[0154] Tocopherol (VE) is a fat-soluble vitamin, mostly found in vegetable oils. It is a natural antioxidant that can inhibit the oxidation and deterioration of oils. Tocopherol exists in oils and fats mainly in four forms: α, δ, γ and β. Among them, α-tocopherol has the strongest biological activity and high content, while γ and β tocopherols have lower content. Therefore, this experiment conducted a qualitative and quantitative analysis of the four types of tocopherols, α, δ, γ and β, in water-based frozen-thawed jatropha oil. β and γ were not separated and were combined for calculation. Table 4-4 shows the composition and content of tocopherol in water-based frozen-thawed oil and commercially available jatropha oil. Both oils contain α, δ, γ and β tocopherols, and there is a significant difference in the tocopherol content of the two oils (p<0.05), indicating that different processes will affect the content of tocopherol in oils and fats. The contents of α-tocopherol (170.03 mg / kg) and total tocopherol (229.13 mg / kg) in water-based frozen-thawed oil were higher than those in commercially available oil (112.11 and 213.36 mg / kg).

[0155] Table 9 Lipid concomitants of jatropha nut oil by aqueous medium-freezing and thawing

[0156]

[0157] As shown in Table 9 above, there are significant differences in the total phenol and squalene contents between the two types of cyperus oleifera oils (p<0.05), and the total phenol and total tocopherol contents of the water-freeze-thawed cyperus oleifera oil are higher than those of the commercially available oil.

[0158] 3. Free radical scavenging ability

[0159] As shown in Table 10, the scavenging rate of polar components and whole oil in water-freeze-thawed cyperus oleifera oil on ABTS+ was slightly higher than that of commercial oil, but there was no significant difference between the two (p>0.05). The scavenging rate of water-freeze-thawed cyperus oleifera oil on DPPH· was higher than that of commercial oil.

[0160] Table 10 Free radical scavenging ability of tiger nut oil by aqueous medium-freezing and thawing

[0161]

[0162]

[0163] 4. Oxidation stability index

[0164] from Fig.12 It can be seen that at the same temperature, the OSI of water-based frozen-thawed cyperus rotundus oil is always greater than the OSI value of commercial oil. For example, at 100°C, the OSI of commercial oil is 11.48h, and the OSI of water-based frozen-thawed oil is 38.63h, which is 3.37 times that of commercial oil. During the accelerated oxidation process at 90°C to 130°C, the OSI of water-based frozen-thawed oil is 2.85 to 3.90 times that of commercial oil, indicating that the oxidation stability of water-based frozen-thawed cyperus rotundus oil is better than that of commercial cyperus rotundus oil. As the oxidation temperature increases from 90°C to 130°C, the OSI value of cyperus rotundus oil gradually decreases, and the OSI of oil and fat decreases by half almost every 10°C increase. During the entire heating process, the difference between the OSI values ​​of the two oil samples is reduced exponentially, and the higher the temperature, the closer the OSI values ​​of the two oil samples are, indicating that under the condition of a certain amount of oxygen, the oxidation stability of oil and fat is more sensitive to changes in temperature. The reason why the water-based frozen-thawed cyperus oleic oil has better oxidative stability than the commercial oil may be that the water-based frozen-thawed cyperus oleic oil contains more oleic acid, and the high oleic acid content has better oxidative stability because the oxidation rates of linoleic acid and linolenic acid are 12 and 25 times that of oleic acid.

[0165] 5. Types and contents of flavor substances

[0166] The composition and content of volatile organic compounds (VOCs) in water-based frozen-thawed cyperus juncea oil and commercially available cyperus juncea oil were analyzed and determined using HS-GC-MS.

[0167] Depend on Fig.13 and 14 It can be seen that a total of 77 VOCs were identified in commercially available cyperus juncea oil, including 22 aldehydes, 13 alcohols, 13 ketones, 5 esters, 8 acids, 5 alkanes, 6 alkenes, 3 furans and 2 other compounds. Among them, aldehydes had the highest relative percentage, accounting for 72.22% of the total, followed by alcohols, accounting for 14.81% of the total. These two types of substances together accounted for 87.03% of the total VOCs in commercially available cyperus juncea oil. The content of hydrocarbons, esters and other substances was relatively low, accounting for about 2.24% of the total, indicating that aldehydes and alcohols are the main VOCs in commercially available cyperus juncea oil. A total of 84 VOCs were identified in water-based frozen-thawed cyperus juncea oil, including 19 aldehydes, 8 alcohols, 13 ketones, 8 esters, 6 acids, 14 alkanes, 9 alkenes, 2 ethers, 3 furans and 24 other compounds. Among them, aldehydes, ketones and olefins had relatively high percentages, accounting for 36.85%, 25.06% and 11.61% of the total, respectively. These three types of substances accounted for 73.52% of the total VOCs in water-based frozen-thawed cyperus juncea oil, alcohols accounted for 4.25%, esters accounted for 3.78%, acids accounted for 5.23%, alkanes accounted for 7.36%, and other substances accounted for 4.90%. The content of ethers and furans was relatively low, accounting for about 0.97% of the total, indicating that aldehydes and ketones were the main volatile substances in water-based frozen-thawed cyperus juncea oil. It can be seen that the flavor substances in the jatropha oil prepared by the present invention are more than those in the existing jatropha oil.

[0168] In summary, the present invention provides a green, environmentally friendly method for preparing cyperus juncea oil with a high extraction rate by combining a water-based method with a freeze-thaw method. The optimal extraction factor is finally selected through the selection of various factors, and the extraction rate reaches 86%. The extracted cyperus juncea oil has more flavor substances than the existing cyperus juncea oil, a higher total tocopherol content, a stronger free radical scavenging ability, and better oxidative stability.

Claims

1. A method for preparing cyperus oleifera oil by water-freezing and thawing: characterized in that: The following steps are involved: (1) removing impurities and washing the cyperus oleifera, drying at 45° C. to constant weight, and crushing through a 40-120 mesh sieve; (2) Weigh 30 g of the cyperus oleifera flour prepared in step (1) into a conical flask, add distilled water at a solid-liquid ratio of 1:4-1:7, place the flask in a water bath oscillator and shake and heat to 60° C., then take the flask out and cool to room temperature; (3) adjusting the pH to 7.00-11.00, incubating in a water bath shaker at 40-80°C for 2-6 h, centrifuging at 5000 r / min for 5 min, and taking the upper oil layer and the emulsion layer into a 50 mL plastic centrifuge tube; (4) Freeze at -5 to -25°C for 8 to 24 hours, take out and thaw in warm water at 40 to 80°C for 10 to 30 minutes, centrifuge at 7000 r / min for 15 minutes, and collect the supernatant.

2. The preparation method according to claim 1, characterized in that: The solid-liquid ratio in step (1) is 1:5; the pH in step (3) is 10.0, the extraction temperature of water bath oscillation is 50°C, and the incubation extraction time is 3 hours; the freezing time in step (4) is 20 hours, the freezing temperature is -20°C, the thawing temperature is 70°C, and the thawing time is 20 minutes.

3. The preparation method according to claim 1, characterized in that: The solid-liquid ratio in step (1) is 1:4; the pH in step (3) is 10.4, the extraction temperature of water bath oscillation is 50°C, and the incubation extraction time is 2.63h; the freezing time in step (4) is 20h, the freezing temperature is -20°C, the thawing temperature is 70°C, and the thawing time is 20min.

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