Method for increasing caffeine content and crude fat content in coffee extract by combining subcritical water extraction with ethanol

Abstract

The invention discloses a method for increasing caffeine content and crude fat content in coffee extract liquor through combination of subcritical water extraction and ethanol. The method comprises the following steps: mixing coffee bean powder with an ethanol water solution, sequentially carrying out programmed heating, staged pressure and temperature control subcritical water extraction, cooling, carrying out solid-liquid separation, and carrying out reduced pressure distillation on filtrate to recover ethanol, thereby finally obtaining the coffee extract. Through ethanol concentration regulation and control in combination with staged temperature control, the content of crude fat is increased to be greater than or equal to 12mg / g while the content of caffeine is greater than or equal to 18mg / g. According to the method, the defect of low crude fat content in traditional subcritical extraction is overcome through the synergistic effect of polarity adjustment of ethanol and subcritical water, and efficient enrichment of two components is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural product extraction, and particularly relates to a method for subcritical water extraction combined with ethanol to improve the contents of caffeine and crude fat in coffee extract. Background Art

[0002] As the core alkaloid in coffee, the extraction technology of caffeine has always been a research hotspot in the fields of food and chemical engineering. Traditional caffeine extraction methods mainly include ethyl acetate method, liquid-liquid extraction method, boiling water decaffeination method, etc. However, these methods generally have problems such as low selectivity, high risk of solvent residue, or serious loss of flavor substances. For example, although the boiling water method is simple to operate, high temperature easily causes the degradation of heat-sensitive flavor components in coffee, and the caffeine extraction rate is relatively low (usually <10 mg / g coffee bean powder); while the supercritical carbon dioxide extraction method (SFE) has high selectivity (the caffeine removal rate can reach 98%) and green environmental protection characteristics, but its equipment cost is high, the operating pressure is extremely high (>7.38 MPa), and it is necessary to pre-wet the coffee beans to enhance permeability, which limits its industrial application.

[0003] In recent years, subcritical fluid extraction technology has attracted attention due to its mild process conditions (low pressure, low temperature) and high mass transfer characteristics. Research shows that subcritical extraction can selectively extract target components and retain natural active substances by adjusting solvent types (such as dimethyl ether, etc.), temperature and pressure parameters. For example, when using subcritical butane to extract plant essential oils, more than 90% of the aroma components can be retained below 50°C; similarly, when subcritical dimethyl ether is used for fish oil extraction, the solvent residue is significantly lower than that of the traditional n-hexane process. However, in the prior art, there are few studies on the synergistic optimization of high-efficiency extraction of caffeine and flavor retention.

[0004] In addition, the caffeine extraction methods mentioned in existing patents or literatures mostly focus on removal rather than enrichment. For example, the supercritical carbon dioxide method is mainly used to produce decaffeinated coffee, and although traditional organic solvents (such as ethyl acetate) can extract caffeine, the residual solvent may affect the product safety, and there is a lack of directional retention of the flavor components required for coffee extract. Some studies have tried to optimize the extraction efficiency through multi-stage extraction, but the equipment complexity and energy consumption are still relatively high.

[0005] Therefore, there is a need to study a safe and low-cost method for efficiently enriching caffeine and crude fat particles in coffee extract while maintaining coffee flavor. Summary of the Invention

[0006] To solve the problems of low selectivity, high solvent residue, serious flavor loss, and high equipment cost in the existing caffeine extraction technology, the present invention provides a method for subcritical water extraction combined with ethanol to increase the caffeine and crude fat contents in coffee extract. This method combines an ethanol assistant with a process of controlling pressure and temperature in stages, uses ethanol as an assistant to adjust the polarity of the solvent, and directly utilizes the unique dissolution characteristics of subcritical water to achieve high-selectivity extraction (≥18 mg / g), enrichment of caffeine and crude fat, and directional retention of characteristic flavor substances. At the same time, the solvent residue (ethanol residue rate ≤ 0.3%) and equipment cost are significantly reduced, which is suitable for the green industrial production of coffee extract.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A method for subcritical water extraction combined with ethanol to increase the caffeine and crude fat contents in coffee extract, comprising the following steps:

[0009] Use a polar solvent as an assistant to adjust the polarity of the aqueous solution of coffee bean powder, and then perform subcritical extraction with pressure and temperature control in stages, and separate the solid and liquid to obtain coffee extract.

[0010] Preferably, the polarity of the polar solvent is less than that of water, more preferably at least one of ethanol and ethyl acetate, and most preferably ethanol.

[0011] Preferably, the percentage of the assistant in the total volume of the assistant and the aqueous solution of coffee bean powder is 3 - 21% (v / v); more preferably 6 - 21% (v / v).

[0012] Preferably, in the aqueous solution of coffee bean powder, the mass ratio of coffee bean powder to the total volume of the assistant and water is 20:(80 - 240) g / mL; more preferably 20:(120 - 240) g / mL.

[0013] Preferably, the process of subcritical extraction with pressure and temperature control in stages is as follows: the temperature in the first stage is 100 - 130 °C, and the pressure is 1.5 - 3.5 MPa; the temperature in the second stage is 140 - 180 °C, and the pressure is 2.5 - 4.5 MPa.

[0014] More preferably, the temperature in the first stage is 110 - 130 °C, and the pressure is 1.5 - 2.5 MPa.

[0015] More preferably, the temperature in the second stage is 150 - 170 °C, and the pressure is 2.5 - 3.5 MPa.

[0016] More preferably, the time in the first stage is 10 - 30 min, and even more preferably 15 - 20 min.

[0017] More preferably, the time of the second stage is 10 to 50 min, even more preferably 20 to 50 min; most preferably 30 to 50 min.

[0018] Preferably, the solid-liquid mixture obtained after extraction is cooled before solid-liquid separation.

[0019] Preferably, the method of solid-liquid separation includes filtration by a filter bag filter.

[0020] Preferably, the pore size of the filter bag used for solid-liquid separation is 0.1 to 0.5 μm.

[0021] The above method for subcritical water extraction combined with ethanol to improve the caffeine and crude fat contents in coffee extract includes the following steps:

[0022] (1) Mix the coffee bean powder and water evenly, and then add a polar solvent to obtain a mixed solution;

[0023] (2) Perform staged pressure and temperature controlled subcritical extraction on the mixed solvent. In the first stage, perform subcritical extraction at 100 - 130 °C and 1.5 - 3.5 MPa for 10 - 30 min. In the second stage, perform subcritical extraction at 140 - 180 °C and 2.5 - 4.5 MPa for 10 - 50 min, cool, and perform solid-liquid separation to obtain coffee extract.

[0024] Preferably, the mass ratio of the coffee bean powder in step (1) to the total volume of water and polar solvent is 20:(80 - 240) g / mL; even more preferably 20:(120 - 240) g / mL.

[0025] Preferably, the volume percentage of the polar solvent in the mixed solution in step (1) is 3 - 21% (v / v).

[0026] Preferably, after the solid-liquid separation in step (2), it is also necessary to perform vacuum distillation. The conditions for vacuum distillation are a temperature of 55 - 65 °C, a vacuum degree of -0.07 to -0.1 MPa, an ethanol recovery rate ≥ 92%, and a residual ethanol content ≤ 0.3%.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] Through the combination of an ethanol assistant and a process of controlling pressure and temperature in stages, the present invention realizes the co-extraction of highly selective extraction of caffeine (≥18 mg / g) and crude fat. Ethanol, as a co-solvent, can adjust the polarity of the system: low-concentration ethanol (<9%) destroys the plant cell wall through hydrogen bonding, enhancing the dissolution rate of caffeine, but having limited solubilization effect on crude fat; high-concentration ethanol (>12%) enhances the extraction of fat-soluble components, but weakens the hydrogen bond binding efficiency of caffeine due to the decrease in solvent polarity (dielectric constant <60). Experiments show that when the ethanol concentration is between 9% and 12%, the dielectric constant is stable in the range of 45 - 55, which can not only dissolve crude fat through moderate hydrophobicity but also maintain a high mass transfer rate of caffeine, achieving the co-extraction of the two components. Compared with the prior art, this method significantly reduces the solvent residue (ethanol residue rate ≤0.3%) and equipment investment cost while retaining the characteristic flavor substances of coffee, providing a new idea for the green industrial production of coffee. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a trend chart of the extraction rate of caffeine and the extraction rate of crude fat at different ethanol concentrations in the embodiment of the present invention;

[0030] Figure 2 It is a trend chart of the extraction rate of caffeine and the extraction rate of crude fat at different solid-liquid ratios in the embodiment of the present invention;

[0031] Figure 3 It is a trend chart of the extraction rate of caffeine and the extraction rate of crude fat at different second-stage temperatures in the embodiment of the present invention;

[0032] Figure 4 It is a trend chart of the extraction rate of caffeine and the extraction rate of crude fat at different second-stage times in the embodiment of the present invention;

[0033] Figure 5 It is a trend chart of the extraction rate of caffeine and the extraction rate of crude fat under different condition differences in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The present invention will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0035] For those not specified in the embodiments of the present invention, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The raw materials, reagents, etc. without indicating the manufacturer can be obtained as conventional products through commercial purchase.

[0036] Example 1

[0037] A method for extracting a high-caffeine tobacco coffee flavor adjuvant from coffee bean powder, comprising:

[0038] Mix 20 g of coffee bean powder with 160 mL of an aqueous solution containing 3% ethanol (v / v) to obtain a mixed solution; transfer the mixed solution to a high-temperature and high-pressure autoclave for subcritical extraction, and the subcritical extraction is carried out in two stages.

[0039] First-stage subcritical extraction: Treat at 130 °C and 2.5 MPa for 15 min;

[0040] Second-stage subcritical extraction: Raise the temperature to 160 °C and treat at 3.5 MPa for 30 min;

[0041] After cooling to 60 °C, perform solid-liquid separation using a 0.1-μm pore size bag filter;

[0042] The filtrate is distilled under reduced pressure at a temperature of 60 °C and a vacuum of -0.08 MPa until the residual ethanol content is ≤ 0.3% to obtain a coffee extract.

[0043] Example 2

[0044] This example is the same as Example 1 in all conditions except that the concentration of ethanol is 6% (v / v).

[0045] Example 3

[0046] This example is the same as Example 1 in all conditions except that the concentration of ethanol is 9% (v / v).

[0047] Example 4

[0048] This example is the same as Example 1 in all conditions except that the concentration of ethanol is 12% (v / v).

[0049] Example 5

[0050] This example is the same as Example 1 in all conditions except that the concentration of ethanol is 15% (v / v).

[0051] Example 6

[0052] This example is the same as Example 1 in all conditions except that the concentration of ethanol is 18% (v / v).

[0053] Example 7

[0054] This example is the same as Example 1 in all conditions except that the concentration of ethanol is 21% (v / v).

[0055] Example 8

[0056] Mix 20 g of coffee bean powder with 80 mL of an aqueous solution containing 9% ethanol (v / v) to obtain a mixed solution; transfer the mixed solution to a high-temperature and high-pressure autoclave for subcritical extraction, and the subcritical extraction is carried out in two stages.

[0057] First-stage subcritical extraction: Treat for 15 min at 130°C and 2.5 MPa;

[0058] Second-stage subcritical extraction: Raise the temperature to 160°C and treat for 30 min at 3.5 MPa;

[0059] After cooling to 60°C, perform solid-liquid separation using a bag filter with a pore size of 0.1 μm;

[0060] The filtrate is distilled under reduced pressure at a temperature of 60°C and a vacuum of -0.08 MPa until the residual ethanol content is ≤0.3% to obtain the coffee extract.

[0061] Example 9

[0062] In this example, except that the volume of the ethanol aqueous solution is 120 ml, the other conditions are the same as those in Example 8.

[0063] Example 10

[0064] In this example, except that the volume of the ethanol aqueous solution is 200 ml, the other conditions are the same as those in Example 8.

[0065] Example 11

[0066] In this example, except that the volume of the ethanol aqueous solution is 240 ml, the other conditions are the same as those in Example 8.

[0067] Example 12

[0068] Mix 20 g of coffee bean powder with 160 mL of an aqueous solution containing 9% ethanol (v / v) to obtain a mixed solution; transfer the mixed solution to a high-temperature and high-pressure autoclave for subcritical extraction, and the subcritical extraction is carried out in two stages.

[0069] First-stage subcritical extraction: Treat for 15 min at 130°C and 2.5 MPa;

[0070] Second-stage subcritical extraction: Raise the temperature to 140°C and treat for 30 min at 3.5 MPa;

[0071] After cooling to 60°C, perform solid-liquid separation using a bag filter with a pore size of 0.1 μm;

[0072] The filtrate is distilled under reduced pressure at a temperature of 60°C and a vacuum of -0.08 MPa until the residual ethanol content is ≤0.3% to obtain the coffee extract.

[0073] Example 13

[0074] In this example, except that the temperature in the second stage of subcritical extraction is 150°C, the other conditions are the same as those in Example 13.

[0075] Example 14

[0076] In this example, except that the temperature in the second stage of subcritical extraction is 170 °C, the other conditions are the same as those in Example 13.

[0077] Example 15

[0078] In this example, except that the temperature in the second stage of subcritical extraction is 180 °C, the other conditions are the same as those in Example 13.

[0079] Example 16

[0080] Mix 20 g of coffee bean powder with 160 mL of an aqueous solution containing 9% ethanol (v / v) to obtain a mixed solution; transfer the mixed solution to a high-temperature and high-pressure autoclave for subcritical extraction, and the subcritical extraction is carried out in two stages.

[0081] First-stage subcritical extraction: Treat at 130 °C and 2.5 MPa for 15 min;

[0082] Second-stage subcritical extraction: Raise the temperature to 160 °C and extract at 3.5 MPa for 10 min;

[0083] After cooling to 60 °C, carry out solid-liquid separation using a 0.1 μm pore size filter bag filter;

[0084] The filtrate is distilled under reduced pressure at a temperature of 60 °C and a vacuum degree of -0.08 MPa until the residual ethanol content is ≤ 0.3% to obtain a coffee extract.

[0085] Example 17

[0086] In this example, except that the extraction time in the second stage of subcritical extraction is 20 min, the other conditions are the same as those in Example 18.

[0087] Example 18

[0088] In this example, except that the extraction time in the second stage of subcritical extraction is 40 min, the other conditions are the same as those in Example 18.

[0089] Example 19

[0090] In this example, except that the extraction time in the second stage of subcritical extraction is 50 min, the other conditions are the same as those in Example 18.

[0091] Example 20

[0092] A method for extracting high-caffeine tobacco-use coffee flavor adjuvant from coffee bean powder, comprising:

[0093] Mix 20 g of coffee bean powder with 160 mL of an aqueous solution containing 9% ethanol (v / v) to obtain a mixed solution; transfer the mixed solution to a high-temperature and high-pressure autoclave for subcritical extraction, and the subcritical extraction is carried out in two stages.

[0094] First-stage subcritical extraction: Treat at 110 °C and 1.5 MPa for 20 min;

[0095] Second-stage subcritical extraction: Raise the temperature to 160 °C and treat at 2.5 MPa for 30 min;

[0096] After cooling to 60 °C, perform solid-liquid separation using a 0.1-μm pore size filter bag filter;

[0097] The filtrate is distilled under reduced pressure at a temperature of 60 °C and a vacuum degree of -0.08 MPa until the residual ethanol content is ≤ 0.3% to obtain a coffee extract.

[0098] The caffeine extraction rate obtained in this example is 20.3 mg / g, and the crude fat extraction rate is 11.7 mg / g.

[0099] Comparative Example 1 (compared with Example 3, single-stage extraction)

[0100] A method for extracting a high-caffeine tobacco-use coffee flavor adjuvant from coffee bean powder, comprising:

[0101] Mix 20 g of coffee bean powder with 160 mL of an aqueous solution containing 9% ethanol (v / v) to obtain a mixed solution; transfer the mixed solution to a high-temperature and high-pressure autoclave for subcritical extraction.

[0102] Subcritical extraction: Raise the temperature to 160 °C and treat at 3.5 MPa for 30 min;

[0103] After cooling to 60 °C, perform solid-liquid separation using a 0.1-μm pore size filter bag filter;

[0104] The filtrate is distilled under reduced pressure at a temperature of 60 °C and a vacuum degree of -0.08 MPa until the residual ethanol content is ≤ 0.3% to obtain a coffee extract. Comparative Example 2 (compared with Example 3, supercritical CO2 extraction)

[0105] A method for extracting a high-caffeine tobacco-use coffee flavor adjuvant from coffee bean powder, comprising:

[0106] Mix 20 g of coffee bean powder with 160 mL of an aqueous solution containing 9% ethanol (v / v) to obtain a mixed solution; transfer the mixed solution to a high-temperature and high-pressure autoclave for supercritical CO2 extraction.

[0107] Supercritical CO2 extraction: Pressure 30 MPa, temperature 50 °C, time 2 h.

[0108] After cooling to 60°C, solid-liquid separation is carried out using a filter bag filter with a pore size of 0.1 μm;

[0109] The filtrate is distilled under reduced pressure at a temperature of 60°C and a vacuum of -0.08 MPa until the residual ethanol content is ≤0.3% to obtain a coffee extract.

[0110] Comparative Example 3 (compared with Example 3, without ethanol additive)

[0111] A method for extracting a high-caffeine tobacco-use coffee flavor auxiliary from coffee bean powder, comprising:

[0112] Mix 20 g of coffee bean powder with 160 mL of water to obtain a mixed solution; transfer the mixed solution to a high-temperature and high-pressure autoclave for subcritical extraction, and the subcritical extraction is carried out in two stages.

[0113] First-stage subcritical extraction: Treat at 130°C and 2.5 MPa for 15 min;

[0114] Second-stage subcritical extraction: Heat up to 160°C and 3.5 MPa and treat for 30 min;

[0115] After cooling to 60°C, solid-liquid separation is carried out using a filter bag filter with a pore size of 0.1 μm;

[0116] The filtrate is distilled under reduced pressure at a temperature of 60°C and a vacuum of -0.08 MPa until the residual ethanol content is ≤0.3% to obtain a coffee extract.

[0117] Test for crude fat content:

[0118] Referring to GB 5009.6-2016 "National Food Safety Standard - Determination of Fat in Foods", the Soxhlet extraction method is used for testing. Weigh 5 g - 10 g of the coffee extracts obtained from

Examples 1 - 20

Comparative Examples 1 - 3

[0119] Put the filter paper thimble into the extraction cylinder of the Soxhlet extractor, connect the receiving bottle that has been dried to a constant weight, add petroleum ether from the upper end of the condenser of the extractor to two-thirds of the bottle volume, heat on a water bath to make the petroleum ether reflux and extract continuously (6 - 8 times / h), generally extract for 6 - 10 h. At the end of the extraction, use a frosted glass rod to pick up 1 drop of the extract, and if there is no oil spot on the frosted glass rod, it indicates that the extraction is complete.

[0120] Remove the receiving flask, recover petroleum ether. When there is 1 - 2 mL of solvent left in the receiving flask, evaporate it to dryness on a water bath, then dry it at 100°C ± 5°C for 1 h, cool it in a desiccator for 0.5 h and then weigh it. Repeat the above operations until constant weight (until the difference between two weighings does not exceed 2 mg).

[0121] The fat content in the extraction product is calculated according to the following formula:

[0122] Where: X - the fat content in the sample, in grams per hundred grams (g / 100g);

[0123] m1 - the content of the receiving flask and fat after constant weight, in grams (g);

[0124] m0 - the mass of the receiving flask, in grams (g);

[0125] m2 - the mass of the sample, in grams (g);

[0126] 100 - the conversion factor. The calculation result is expressed to one decimal place.

[0127] Quantitative detection method for caffeine in coffee extract:

[0128] Liquid chromatography conditions: Agilent Eclipse XDB - C18 (4.6 mm × 250 mm, 5 μm); mobile phase: acetonitrile - 0.1% acetic acid aqueous solution (10%:90%, isocratic elution), flow rate: 1.0 mL / min; detection wavelength: 0 - 5.5 min (254 nm), 5.5 - 9.5 min (320 nm) and 9.5 - 15.0 min (254 nm); column temperature: 35°C; injection volume: 10 μL.

[0129] Examples 1 - 7 and Comparative Example 3, that is, the test results of the extraction solutions obtained at different ethanol concentrations are shown in Table 1 and Figure 1 as follows.

[0130] Table 1 Test results of extraction solutions obtained at different ethanol concentrations

[0131]

[0132] As shown in Table 1 and Appendix Figure 1As shown, within the range of 3% - 9% ethanol concentration, the caffeine extraction rate significantly increases from 18.0 mg / g to 21.3 mg / g, and the crude fat extraction rate increases from 9.8 mg / g to 12.0 mg / g. However, when the ethanol concentration exceeds 9% (such as 15%), the caffeine extraction rate drops to 20.0 mg / g, while the crude fat extraction rate continues to slowly rise to 12.8 mg / g. The caffeine and crude fat extraction rates of Comparative Example 3 (0% ethanol) are only 13.7 mg / g and 6.3 mg / g respectively, indicating that the solubilization effect of ethanol on fat-soluble components is crucial.

[0133] This may be due to the dual regulatory effects of ethanol on solvent polarity and selectivity. Low-concentration ethanol (3 - 9%) disrupts the cellulose structure of the coffee bean cell wall through hydrogen bonding, increasing the porosity and enhancing the solvent permeability. At the same time, the addition of ethanol reduces the dielectric constant of the aqueous phase, enhancing the solubility of moderately polar substances (such as caffeine). However, when the ethanol concentration is too high (>9%), the solvent polarity further decreases (dielectric constant < 60), weakening the hydrogen bonding between caffeine and the solvent, resulting in a decrease in its dissolution efficiency. Crude fat, due to its stronger hydrophobicity, follows the "like dissolves like" principle and its solubility continues to increase at high ethanol concentrations.

[0134] The test results of the extraction liquids obtained under different solid-liquid ratios are shown in Table 2 and Figure 2 as follows.

[0135] Table 2 Test results of the extraction liquids obtained under different solid-liquid ratios

[0136]

[0137] As shown in Table 2 and the appendix Figure 2 as follows, when the solid-liquid ratio increases from 20:80 to 20:160, the caffeine extraction rate rises from 18.5 mg / g to 21.3 mg / g, and the crude fat extraction rate increases from 9.5 mg / g to 12.0 mg / g. However, when the liquid volume continues to increase (20:240), the extraction rate decreases instead (caffeine 19.5 mg / g, crude fat 10.5 mg / g). This non-linear relationship reflects the dynamic equilibrium of mass transfer kinetics: when the solvent is insufficient, the solute diffusion is limited by local concentration saturation; excessive solvent reduces the solute concentration gradient and decreases the diffusion driving force. Excessive solvent (such as 20:240) causes a dilution effect, resulting in a decrease in the solute concentration per unit volume, prolonging the equilibrium time and increasing energy consumption.

[0138] The test results of the extraction liquids obtained at different second-stage extraction temperatures are shown in Table 3 and Figure 3 as follows.

[0139] Table 3 Test results of the extraction liquids obtained at different second-stage extraction temperatures

[0140]

[0141]

[0142] As shown in Table 3 and the appendix Figure 3 As shown, when the temperature rises from 140 °C to 160 °C, the caffeine extraction rate increases from 19.0 mg / g to 21.3 mg / g, and the crude fat extraction rate increases from 11.0 mg / g to 12.0 mg / g; however, when the temperature exceeds 160 °C (such as 180 °C), the caffeine extraction rate drops to 19.3 mg / g, and the crude fat extraction rate remains at 11.5 mg / g.

[0143] Although high temperature accelerates molecular movement through the Arrhenius effect, exceeding 160 °C will cause the degradation of thermosensitive aroma components (such as furfuryl mercaptan). The dielectric constant of subcritical water decreases with increasing temperature. At 160 °C, the dielectric constant is about 30, close to the polarity range of ethanol. At this time, the selectivity of the solvent for caffeine reaches its peak. When the temperature further increases (such as 180 °C), the solvent polarity weakens excessively (dielectric constant < 25), which instead inhibits the dissolution of caffeine. In addition, high temperature may trigger the Maillard reaction, generating colloidal substances and affecting the clarity of the extract.

[0144] The test results of the extracts obtained at different times in the second-stage extraction are shown in Table 4 and Figure 4 as shown.

[0145] Table 4 Test results of the extracts obtained at different times in the second-stage extraction

[0146]

[0147] As shown in Table 4 and the appendix Figure 4 As shown, when the time increases from 10 min to 30 min, the caffeine extraction rate increases from 16.8 mg / g to 21.3 mg / g, and the crude fat extraction rate increases from 8.6 mg / g to 12.0 mg / g; when the time is extended to 50 min, the extraction rate tends to be stable (caffeine 21.2 mg / g, crude fat 13.5 mg / g). This phenomenon conforms to the first-order kinetic model: the first 30 min is the rapid diffusion stage (rate constant k = 0.042 / min), and then it enters the equilibrium stage (k = 0.015 / min). At 30 min, the caffeine concentration in the solvent is close to saturation (about 80%). Continuing to extend the extraction time only marginally increases the yield (Δ < 0.8 mg / g / 10 min), and the energy consumption will also increase.

[0148] The test results of the extracts obtained by different extraction methods are shown in Table 5 and Figure 5 as shown.

[0149] Table 5 Test results of the extracts obtained by different extraction methods

[0150]

[0151] As shown in Table 5 and the appendix Figure 5 As shown, the two-stage subcritical extraction method (caffeine 21.3 mg / g, crude fat 12.0 mg / g) is significantly superior to single-stage subcritical water extraction (17.1 mg / g, 9.0 mg / g) and supercritical CO2 (1.3 mg / g, 79.8 mg / g). The low affinity of supercritical CO2 for polar components (Brunner, 2005) results in insufficient caffeine extraction rate, while the two-stage method realizes efficient selective extraction through staged temperature control (breaking the cell wall first and then selective extraction) and the synergism of ethanol additives.

[0152] From the above examples and comparative examples, it can be seen that the present invention realizes efficient extraction of caffeine (≥18 mg / g) through the synergism of ethanol additives and two-stage subcritical extraction at 160 °C and 3.5 MPa. At the same time, vacuum distillation (residual ethanol ≤0.3%) and membrane pore size control (0.1 μm) ensure the safety of tobacco additives.

[0153] The above examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for subcritical water extraction combined with ethanol to increase the caffeine and crude fat contents in coffee extract, characterized in that, It includes the following steps: Using a polar solvent as an auxiliary agent to adjust the polarity of the aqueous coffee bean powder solution, and then performing staged pressure and temperature controlled subcritical extraction, followed by solid-liquid separation to obtain a coffee extract.

2. The method according to claim 1, wherein The polarity of the polar solvent is less than that of water; and / or, the percentage of the polar solvent in the total volume of the polar solvent and the aqueous coffee bean powder solution is 3-21%.

3. The method according to claim 2, characterized in that, The polar solvent is at least one of ethanol and ethyl acetate; and / or, the percentage of the polar solvent in the total volume of the polar solvent and the aqueous coffee bean powder solution is 6-21%.

4. The method according to claim 1, wherein In the aqueous coffee bean powder solution, the mass ratio of the coffee bean powder to the total volume of the auxiliary agent and water is 20:(80-240) g / mL.

5. The method according to claim 4, characterized in that, In the aqueous coffee bean powder solution, the mass ratio of the coffee bean powder to the total volume of the auxiliary agent and water is 20:(120-240) g / mL.

6. The method according to claim 1, wherein The process of the staged pressure and temperature controlled subcritical extraction is as follows: the temperature in the first stage is 100-130°C, and the pressure is 1.5-3.5 MPa; the temperature in the second stage is 140-180°C, and the pressure is 2.5-4.5 MPa; and / or, the time in the first stage is 10-30 min; and / or, the time in the second stage is 10-50 min.

7. The method according to claim 6, wherein The temperature in the first stage is 110-130°C, and the pressure is 1.5-2.5 MPa; and / or, the temperature in the second stage is 150-170°C, and the pressure is 2.5-3.5 MPa; and / or, the time in the first stage is 15-20 min; and / or, the time in the second stage is 20-50 min.

8. The method according to claim 7, wherein The time in the second stage is 30-50 min.

9. The method according to any one of claims 1 to 8, characterized in that, It includes the following steps: (1) Mix the coffee bean powder and water evenly, and then add a polar solvent to obtain a mixed solution; (2) Perform staged pressure and temperature controlled subcritical extraction on the mixed solvent. In the first stage, perform subcritical extraction at 100-130°C and 1.5-3.5 MPa for 10-30 min. In the second stage, perform subcritical extraction at 140-180°C and 2.5-4.5 MPa for 10-50 min. Cool, and perform solid-liquid separation to obtain a coffee extract.

10. The method according to claim 9, wherein After the solid-liquid separation in step (2), it is also necessary to perform vacuum distillation. The conditions for the vacuum distillation are a temperature of 55-65°C, a vacuum degree of -0.07 to -0.09 MPa, an ethanol recovery rate ≥ 92%, and a residual ethanol content ≤ 0.3%; and / or, the pore size of the filter bag used for the solid-liquid separation in step (2) is 0.1-0.5 μm.

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