Method for processing coffee beans through combination of freezing and dipping and flavor coffee beans produced by method

Abstract

The invention discloses a method for treating coffee beans through combination of freezing and dipping and flavor coffee beans produced through the method. The method comprises the following steps: grading and screening coffee beans, mixing the coffee beans with exogenous additives (such as coconut milk, pure milk and the like) according to a ratio of (1-1.11): 1, freezing at-20 DEG C for 20-30 hours, unfreezing and soaking at 25 DEG C for 16 hours, then drying until the water content is 10-12%, and finally baking at 190-210 DEG C until the Eilkstrong value is 35. According to the working principle, the structure of coffee beans is destroyed through low temperature, exogenous additives enter the coffee beans, the content of flavor precursors is changed, the baking thermal chemical reaction is affected, and meanwhile the exogenous additives give unique fragrance. Coconut milk treatment is taken as an example, the content of sugar and protein can be increased, fragrance and sweetness can be improved, bitter and sour feeling can be reduced, and coffee with mellow and balanced coconut fragrance can be obtained. The method can effectively improve coffee quality and produce coffee beans with brand new flavor.

Description

Technical Field

[0001] This invention relates to the field of coffee bean processing technology, and more specifically, to a method for freezing combined with maceration of coffee beans and the flavored coffee beans produced therefrom, particularly a method for freezing combined with maceration of coffee beans optimized for coconut flavor. Background Technology

[0002] The continued growth in coffee consumption not only reflects expanding market demand but also highlights consumers' increasing emphasis on coffee quality and diverse flavors. The younger generation has a higher demand for experimentation and variety in coffee, with unique flavor combinations, plant-based beverages, and innovative coffee drinks gaining popularity. As flavor is one of the core factors attracting consumers, research in the field of flavorful coffee has been on the rise in recent years.

[0003] In coffee cultivation, sustainable development is achieved by improving varieties through hybridization breeding, molecular breeding, and other methods, while enhancing disease resistance and preserving high-quality flavor characteristics.

[0004] In terms of processing, in addition to the four traditional methods of sun-drying, washing, honey processing, and wet hulling, a variety of innovative processing methods have been developed, such as anaerobic fermentation, directional fermentation by inoculation of microorganisms, and decaffeination. These methods are combined with various auxiliary technologies such as solar drying, microwave drying, and ultra-low temperature induction to influence the flavor of coffee. These processes mainly affect the basic flavor of coffee beans, such as acidity, sweetness, and body, but it is difficult to directly impart other distinct flavors to coffee beans.

[0005] Today, many advanced methods are used to improve the flavor of coffee beans. Among them, the most natural flavor enhancement can be achieved by adjusting the composition of the beans before roasting. For example, volatile components or their precursors can be added at different stages, or aromatic substances with their own aroma components can be used to impregnate coffee beans before roasting. For example, Chinese patent CN118177269A discloses a method for pre-treating and roasting coffee beans with a coconut aroma. In this application, coffee beans and coconut oil mixed in a certain ratio are pre-treated by ultrasound and then roasted to obtain coconut-flavored black coffee. However, the antioxidant capacity of the coconut-flavored black coffee processed by this method is inferior to that of untreated coffee. Therefore, there is an urgent need to provide a new coffee bean processing method that imparts a distinct additional flavor to coffee beans without affecting the quality of the coffee, and to apply this method to the production of coffee beans with special flavors. Summary of the Invention

[0006] To achieve the above objectives, this application uses exogenous additives to impregnate green coffee beans, combined with low-temperature freezing, allowing the exogenous additives to penetrate the interior of the coffee beans, altering the content of flavor precursors and thus affecting the thermochemical reactions during roasting. Simultaneously, the exogenous additives, as natural aroma components, can impart unique aroma and flavor to the coffee, thereby improving coffee quality and obtaining a completely new flavored coffee. The specific technical solution is as follows:

[0007] One object of the present invention is to provide a method for freezing combined with maceration of coffee beans, comprising the following steps:

[0008] (1) Raw material pretreatment: The coffee beans are graded and screened to remove impurities and substandard beans;

[0009] (2) Impregnation: Selected coffee beans are added to the same exogenous additive in a ratio of coffee beans to exogenous additive of (1-1.11): 1 to obtain mixture A; the exogenous additive is a solution containing flavor;

[0010] (3) Low temperature treatment: Place the mixture A in a constant temperature freezer at -20℃ and treat it at low temperature for 20-30 h to allow the exogenous additives to enter the coffee beans and change the content of flavor precursors in the coffee beans.

[0011] (4) Thawing and soaking treatment: Place the frozen mixture A into a constant temperature chamber for thawing and soaking;

[0012] (5) Drying: The soaked mixture A is transferred to a constant temperature drying oven for drying. (6) Baking: Baking at a temperature of 190℃-210℃ until the Egerzhuang value reaches 35.

[0013] Furthermore, the method also includes:

[0014] (7) Screening and packaging: Screen the roasted flavored coffee beans to remove under-roasted or over-roasted coffee beans and residual impurities, and then package them.

[0015] Furthermore, the flavored solution includes any one of coconut milk, whey protein solution, whole milk sweetened milk powder solution, and pure milk.

[0016] Further, in step (4), the temperature is set to 25°C, and the product is thawed and soaked for 16 hours.

[0017] Furthermore, in step (5), the product is dried at 25°C until the moisture content reaches 10%~12%.

[0018] Furthermore, the baking temperature in step (6) is 199°C.

[0019] Furthermore, the flavored solution is coconut milk, and the amount of coconut milk added is 201.5 mL of coconut milk per 200 g of coffee beans, with a low-temperature treatment time of 24 h 8 min and a roasting temperature of 199℃.

[0020] Furthermore, the coffee beans used are Catimor coffee beans.

[0021] Another object of the present invention is to produce a flavored coffee bean according to the above method.

[0022] Furthermore, the working principle of the coconut-flavored coffee beans is as follows: Raw coffee beans themselves have a porous microstructure. During the roasting process, under high temperature, the moisture in the coffee beans evaporates rapidly, and the contents undergo a series of thermochemical reactions. A large amount of water vapor, volatile flavor components, and CO2 are generated and accumulate inside the coffee beans, leading to an increase in internal pressure until the gas breaks through and the overall volume of the coffee beans expands, and the microstructure changes: the pore diameter increases and the pore spacing decreases.

[0023] The porosity of coffee after roasting determines its flavor to a certain extent. A small porosity indicates insufficient pyrolysis of the coffee beans and inadequate generation of flavor components. At the same time, a small porosity inhibits the release of aroma components, which further leads to insufficient aroma of the coffee beans. Secondly, during the coffee brewing process, porosity determines the contact area and penetration speed between water and the flavor substances inside the coffee grounds, thus affecting the extraction efficiency and flavor of the coffee.

[0024] During low-temperature processing, ice crystal growth disrupts the structure of coffee beans, increasing porosity and allowing coconut milk to penetrate. Under high temperatures, these substances react to form a black or brown viscous substance that remains in the pores, giving the coffee beans a unique coconut milk flavor. Simultaneously, the coconut milk immersion process alters the composition of the coffee beans (significantly increasing reducing sugars and soluble proteins, and decreasing flavonoids and caffeine), intensifying the Maillard reaction, caramelization, and other thermal reactions during roasting. This generates even more flavor compounds while further increasing the porosity of the roasted beans.

[0025] In summary, the combined effects of low-temperature freezing and coconut milk soaking result in a darker color, increased aroma and sweetness, and decreased bitterness and acidity in roasted beans, resulting in a coffee with a coconut milk flavor that is rich, smooth, and balanced.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: the soaking in coconut milk and the low-temperature treatment can affect the texture and content of coffee beans, thereby deepening the thermal reaction during the roasting process, promoting the generation and expression of flavor components, and ultimately affecting the aroma and brewing flavor of the beans, thus creating a coconut-flavored coffee.

[0027] Compared to untreated beans, beans treated with coconut milk have similar moisture and caffeine content, but also have higher levels of reducing sugars, soluble proteins, polyphenols, and chlorogenic acid. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method for freezing and impregnating coffee beans according to the present invention;

[0029] Figure 2 The effect of different exogenous additives on coffee cupping scores;

[0030] Figure 3 The effects of different amounts of coconut milk (a), different freezing times (b), and different roasting temperatures (c) on coffee cupping scores;

[0031] Figure 4 A Nightingale Rose illustration for coffee cup scoring;

[0032] Figure 5 Response surface plot of coconut milk addition amount and freezing time to coffee cup scores;

[0033] Figure 6 Response surface plot of coconut milk addition amount and roasting temperature to coffee cup measurements;

[0034] Figure 7 The response surface plot of freezing time and roasting temperature to coffee cup measurements;

[0035] Figure 8 The effects of coconut milk soaking and long-term storage on coffee cupping scores;

[0036] Figure 9 Microstructure of coffee beans from different samples;

[0037] Figure 10 The results of the Gezhuang numerical detection;

[0038] Figure 11 A bar chart showing the moisture content test results;

[0039] Figure 12 This is the standard curve for reducing sugars;

[0040] Figure 13 The results are for the detection of reducing sugar content;

[0041] Figure 14 This is a standard curve for soluble proteins;

[0042] Figure 15 This is the result of the soluble protein content test;

[0043] Figure 16 The standard curve for total flavonoids;

[0044] Figure 17 The results are for the total flavonoid content test.

[0045] Figure 18 For polyphenol standard curve;

[0046] Figure 19 The results are for the detection of polyphenol content;

[0047] Figure 20 Results for chlorogenic acid content;

[0048] Figure 21 This is the result of a caffeine content test. Detailed Implementation

[0049] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0050] The following experiments were conducted from July 1, 2024 to May 1, 2025 in the laboratory of the College of Modern Coffee Industry, Yunnan Agricultural University.

[0051] Example 1: Screening test of exogenous additives

[0052] Table 1 Raw materials and sources

[0053] Catim coffee beans 2024 Production - Yunnan Baoshan Huke Manor Co., Ltd. Coconut milk Yunnan Eurasia Dairy Co., Ltd. Instant full-fat sweetened milk powder Yunnan Eurasia Dairy Co., Ltd. pure milk Yunnan Eurasia Dairy Co., Ltd.

[0054] 200g of coffee beans were weighed and impregnated with four different exogenous additives as shown in Table 1, at a 1:1 ratio of beans to solution (Group A: 2% whey protein solution, Group B: 12.5% ​​whole milk sweetened milk powder solution, Group C: whole milk, Group D: coconut milk, control group: water). The beans were then frozen for 24 hours, thawed, and impregnated for 16 hours. Afterward, they were dried in a 35℃ constant temperature drying oven until the moisture content reached 10%-12%. A medium roast (210℃) was then performed. Finally, sensory evaluation was conducted on the five groups of coffee beans after grinding and brewing to determine the optimal exogenous additive.

[0055] The results are as follows Figure 2As shown in Figure 2, the effects of four different exogenous additives on coffee cupping scores are illustrated. The figure shows that the five groups of beans scored similarly in terms of consistency and acidity. Beans treated with whey protein exhibited superior cleanliness but lacked a strong finish. Treatment with whole-fat sweetened milk powder gave the beans excellent sweetness, flavor, and balance, but reduced cleanliness. Beans treated with pure milk showed balanced performance across all attributes. Beans treated with coconut milk performed well in aroma, flavor, finish, body, and overall evaluation. In conclusion, the four different exogenous additives positively impacted the aroma, flavor, finish, body, balance, sweetness, and overall evaluation of coffee beans, but negatively affected cleanliness. Coconut milk resulted in the highest overall cupping score, with the best overall flavor and mouthfeel.

[0056] Therefore, coconut milk was selected as the exogenous additive. A single-factor experiment was designed with sensory evaluation as the dependent variable to study the effects of coconut milk addition amount, freezing time, and roasting temperature on coconut-flavored coffee.

[0057] Example 2: Single-factor experiment

[0058] (1) Coconut milk addition test

[0059] Weigh 200g of coffee beans and set 6 levels with the amount of coconut milk added as the independent variable (A1: 180 mL, A2: 190 mL, A3: 200 mL, A4: 210 mL, A5: 220 mL, A6: 230 mL). Then freeze for 24 hours, thaw, dry, and then roast at a medium temperature (210℃).

[0060] The effect of different amounts of coconut milk added on coffee cupping scores is shown in the figure. Figure 3 As shown in the figure, when coconut milk is used as an exogenous additive, under the conditions of fixed freezing time and roasting temperature, the cupping score shows a trend of first increasing and then decreasing with the increase of coconut milk addition. The highest cupping score is achieved when the amount of coconut milk added is 200 mL. When the amount of coconut milk added is small, it has no significant impact on the flavor of coffee. When the amount of coconut milk added is too large, it not only increases the cost but also masks the original flavor characteristics of coffee, resulting in the loss of the original taste of coffee. Therefore, three gradients of 190 mL, 200 mL, and 210 mL were selected for subsequent response surface methodology optimization.

[0061] (2) Freezing time test

[0062] Weigh 200 g of coffee beans and add 200 mL of coconut milk. Using freezing time as the independent variable, set 6 levels (T1: 20 h, T2: 22 h, T3: 24 h, T4: 26 h, T5: 28 h, T6: 30 h) for freezing treatment. After thawing, dry the beans and then perform medium roasting (210℃).

[0063] The effect of different freezing times on coffee cupping scores is shown in the figure. Figure 3 b. As shown in the figure, with coconut milk as an exogenous additive, under the condition of fixed coconut milk addition and roasting temperature, the cupping score shows an increasing trend with the extension of freezing time. When the freezing time exceeds 24 h, the cupping score fluctuates slightly with the increase of freezing time, but the peak value remains at 24 h; this is because short-term freezing is insufficient for ice crystals to affect the texture of coffee, thus the maceration effect of coconut milk is not significantly manifested; when the freezing time is close to 24 h, ice crystal growth has reached saturation, so even if the freezing time is extended, it will not have a significant impact on the score; therefore, considering all factors, 22 h, 24 h, and 26 h are selected for subsequent response surface optimization.

[0064] (3) Baking temperature test

[0065] Weigh 200 g of coffee beans, add 200 mL of coconut milk, freeze for 24 hours, dry after thawing, and roast at 5 levels (D1: 190℃, D2: 200℃, D3: 210℃, D4: 220℃, D5: 230℃) with roasting temperature as the independent variable.

[0066] The effect of different roasting temperatures on coffee cupping scores is shown in [link to relevant documentation]. Figure 3c. As shown in the figure, when coconut milk is used as an exogenous additive, under the condition of fixed coconut milk addition and freezing time, the cupping score shows a trend of first increasing and then decreasing with the increase of roasting temperature. The optimal cupping score is achieved at 200℃. This is because lower roasting temperatures lead to incomplete pyrolysis during coffee roasting, resulting in less pronounced flavor characteristics. With increasing roasting temperature, proteins and sugars react to produce aldehydes, ketones, and other substances, while amino acids decompose to produce furans, pyridines, etc., giving coffee excellent flavor characteristics. Furthermore, other flavor regulators in coffee beans, such as caffeine, chlorogenic acid, fats, and organic acids, also change with increasing roasting temperature. Low-temperature roasted coffee has higher acidity, while high-temperature roasted coffee has a stronger bitterness. However, when the roasting temperature is too high, excessive pyrolysis causes undesirable flavor characteristics such as burnt taste, or even high carbonization, rendering the coffee worthless for evaluation. Therefore, considering all factors, three temperature gradients of 190℃, 200℃, and 210℃ were selected for subsequent response surface methodology optimization.

[0067] Example 3: Response Surface Experiment

[0068] Based on the above experimental results, coconut milk, which has the most distinctive flavor, was selected as the additive. The amount of coconut milk added (A), freezing time (B), and roasting temperature (C) were used as single factors. Following a Box-Benhnken central composite design, sensory scores were used as the response values ​​to conduct a 3-factor, 3-level response surface methodology analysis. This optimized the process parameters and yielded the best processing technology for coconut-flavored coffee. The experimental factors and levels are shown in Table 2.

[0069] Data analysis was performed using Design-Expert 13.0 software. Three experiments were conducted on the final results to compare the actual values ​​with the theoretical values ​​and verify the reliability of the model.

[0070] Table 2 Box-Benhnken Experimental Design Table

[0071]

[0072] The experiment was conducted according to the above plan, and the results are detailed in Table 3. Figure 4 :

[0073] Table 3 Results of response surface optimization experiments

[0074] Standard order Random order Coconut milk addition amount Freezing time Baking temperature Cupping score 6 1 210 24 190 78.25 17 2 200 24 200 78.9 4 3 210 26 200 78.35 8 4 210 24 210 78.13 1 5 190 22 200 77.9 14 6 200 24 200 79.27 15 7 200 24 200 79.08 16 8 200 24 200 79.08 3 9 190 26 200 77.98 7 10 190 24 210 77.69 2 11 210 22 200 78.06 13 12 200 24 200 78.96 11 13 200 22 210 77.67 12 14 200 26 210 78.17 9 15 200 22 190 78.23 5 16 190 24 190 78.08 10 17 200 26 190 77.98

[0075] Model regression equation: Y = -318.878 + 1.73725A + 3.70175B - 1.79C + 0.002625AB + 0.000675AC + 0.009375BC - 0.004803A 2- 0. 126313B 2 - 0.005402C 2

[0076] The influence of the interactions of each factor on the cupping test scores, from largest to smallest, is BC > AC > AB.

[0077] Table 4. Analysis of variance of the regression model based on coffee cupping scores

[0078] Source of variance sum of squares Degrees of freedom Mean Square F value p-value Significance Model 4. 14 9 0.4596 37.61 <0.0001 significant A-Coconut milk addition amount 0.1625 1 0.1625 13.30 0.0082 ** B - Freezing time 0.0481 1 0.0481 3.93 0.0878 C - Baking temperature 0.0968 1 0.0968 7.92 0.0260 * AB 0.0110 1 0.0110 0.9023 0.3738 AC 0.0182 1 0.0182 1.49 0.2615 BC 0.1406 1 0.1406 11.51 0.0116 * A² 0.9711 1 0.9711 79.48 <0.0001 ** B² 1.07 1 1.07 87.97 <0.0001 ** C² 1.23 1 1.23 100.58 <0.0001 ** Residual 0.0855 7 0.0122 Lack of Fit 0.0051 3 0.0017 0.0837 0.9654 notsignificant Pure Error 0.0805 4 0.0201 Cor Total 4.22 16

[0079] The structure of the ANOVA for the regression model based on coffee cupping scores is shown in Table 4. As the table shows, the F-test result is 37.61 (P < 0.01), indicating that the regression model is highly significant. The lack-of-fit term, P = 0.9654 > 0.05, is not significant. The model's coefficient of variation (CV) is 14.11%, and the coefficient of determination R0 is... 2 = 0.9797, prediction coefficient R 2 adj = 0.9537 and adjustment factor R 2 pre = 0.9511 is basically consistent (difference less than 0.2), and the signal-to-noise ratio (adeqprecision) is 16.7554 (>4), indicating that the model fit is very good, there is good overall consistency between the actual value and the predicted value, and it has high credibility.

[0080] The p-values ​​indicate that the amount of coconut milk added had a highly significant impact on the cupping score (P < 0.01), and the interaction between baking temperature and freezing time had a significant impact on the cupping score (P < 0.05). However, freezing time, the amount of coconut milk added, the interaction between the amount of coconut milk added and baking temperature, and freezing time had no significant impact on the cupping score (P > 0.05). 2 B 2 C 2 It has a highly significant impact on cupping scores.

[0081] At fixed baking temperature and freezing time, due to the interaction between the amount of coconut milk added and freezing time, the cupping scores showed a trend of first increasing and then decreasing within the range of 190 mL-210 mL of coconut milk added. When the baking temperature and amount of coconut milk added were fixed, the 3D response surface graph showed a trend of first increasing and then decreasing within the freezing time range of 22 h-26 h. Figure 5 The steepness of the surface indicates that, under the influence of the interaction, both factors have a significant impact on the cupping score, and their influence patterns are similar, with no significant interaction.

[0082] like Figure 6 As shown, under fixed baking temperature and freezing time, due to the interaction between the amount of coconut milk added and baking temperature, the cupping score initially increases and then decreases within the range of 190 mL-210 mL of coconut milk added. When the freezing time and amount of coconut milk added are fixed, the 3D response surface plot shows an initial increase followed by a decrease within the baking temperature range of 190℃-210℃. Based on the steepness of the surface, it can be concluded that under the influence of the interaction, both factors have a significant impact on the cupping score, and their influence patterns are similar, indicating that the interaction is not significant.

[0083] like Figure 7 As shown, with fixed amounts of coconut milk and freezing time, the cupping scores initially increased and then decreased within the baking temperature range of 190℃-210℃ due to the interaction between freezing time and baking temperature. When baking temperature and coconut milk amount were fixed, the 3D response surface graph showed an initial increase followed by a decrease within the freezing time range of 22 h-26 h. Based on the steepness of the 3D graph, it can be concluded that both factors significantly affected the cupping scores under the influence of the interaction, with baking temperature having a greater impact than freezing time.

[0084] Cupping was conducted according to the SCA-102 coffee value assessment. Roasted samples were stored in the dark for 8 hours to allow the aroma components in the coffee beans to fully volatilize. Following the Specialty Coffee Association (SCA) cupping system, the coffee beans were ground to a fineness of 70%–75%. The ground coffee was poured into a standard cupping cup for dry aroma assessment. A rapid brewing process was performed using 10 g of coffee powder to 181.8 mL of water at 93°C. Timing was started 4 minutes after pouring, followed by breaking and skimming off the grounds. The coffee was then tasted and scored after cooling to a suitable temperature. Sensory evaluation was conducted using the SCA (Specialty Coffee Association of America Coffee Cupping Form) on ten attributes: dry / wet aroma, flavor, finish, acidity, body, consistency, balance, cleanliness, sweetness, and overall impression. Each attribute score incremented by 0.25, with a score range of 6–10. The final score was the sum of the ten scores minus any defective items. After the scoring is completed, the final scores of each sample are compiled and the average score is calculated.

[0085] In summary, the optimal processing method for coffee beans is: 201.461 mL of coconut milk added, 24.138 h of freezing time, and 199.191℃ of roasting temperature. Considering practical operation and production feasibility, the optimal process is adjusted as follows:

[0086] Coconut milk addition: 201.5 mL; freezing time: 24 h 8 min; baking temperature: 199℃.

[0087] Three sets of repeatability tests were conducted under these process conditions, and the final cupping score was 79.12, which is within the range of 78.9411 to 79.1749 (confidence = 95%), proving that the model is reliable.

[0088] Example 4: Effects of coconut milk soaking and long-term storage on coffee beans

[0089] During storage, the composition and content of coffee beans' components change, leading to undesirable flavors and a decline in quality. Therefore, a controlled experiment was designed to study the effects of exogenous additives on the sensory properties, texture, and component content of coffee during long-term storage.

[0090] 1. Sample pretreatment

[0091] Based on the optimal solution derived from response surface methodology, 200 g of coffee beans were weighed, 201.5 mL of coconut milk was added for soaking, and the mixture was frozen at -20℃ for 24 h 8 min. After thawing and soaking for 16 h, the mixture was dried in a constant temperature drying oven until the moisture content was reduced to 10%~12%. The final roasting temperature was 199℃. This group is designated as the coconut milk group.

[0092] Weigh 200 g of coffee beans, add 201.5 mL of coconut milk for soaking, freeze for 24 h 8 min, thaw and soak for 16 h, then dry in a constant temperature drying oven to a moisture content of 10%~12%, and finally roast at 199℃. After roasting, store in a sealed container at room temperature for about 70 days, and this is designated as the storage group.

[0093] Weigh 200 g of coffee beans, add 201.5 mL of drinking water for soaking, freeze for 24 h 8 min, thaw and soak for 16 h, place in a constant temperature drying oven to dry to 10%~12% moisture content, and finally roast at 199℃. This is recorded as the control group.

[0094] To facilitate accurate weighing and testing, the three samples were ground to a fineness of 70% to 75%, meaning the coffee powder particle size reached 0.85 mm.

[0095] 2. Coffee quality was assessed using cupping methods, and the results are as follows: Figure 8 The graph showing the effects of coconut milk immersion and long-term storage on coffee cupping scores indicates that coffee beans treated with coconut milk scored higher than untreated beans in aroma, flavor, aftertaste, acidity, sweetness, and overall evaluation. However, coffee beans that underwent long-term storage showed a decrease in scores for all attributes except cleanliness and consistency, with the most significant declines in body and balance. In conclusion, coconut milk immersion can improve the sensory evaluation of coffee beans, but long-term storage will lead to a decline in flavor and mouthfeel.

[0096] 3. Scanning electron microscopy (SEM): Coffee bean samples with dimensions less than 10 mm were selected. The samples were cut transversely, and the cross-sections were observed using a scanning electron microscope at magnifications of 100x (100 μm), 300x (30 μm), 500x (20 μm), and 1000x (10 μm). Three loci were recorded for each sample group. The results are as follows: Figure 9 As shown: untreated beans have a coarser cross-section, with unevenly distributed porosity, smaller pores, and larger gaps. Beans treated with coconut milk but stored for a long time are also coarser than unstored beans, with many tiny pores distributed within the porosity. Furthermore, substances resembling coconut milk residue from high-temperature roasting were observed in the porosity of beans treated with coconut milk.

[0097] 4. Determination of Roast Level: Take an appropriate amount of sample and measure it using a coffee roaster. Repeat the measurement four times for each sample group, calculate the average value, and compare it with the Agtro number to analyze the differences in coffee bean roasting. The results are as follows: Figure 10 As shown, beans treated with coconut milk but not stored had significantly lower Eigron values ​​than the control group (P < 0.01) and significantly lower than the stored group (P < 0.01). Beans treated with coconut milk but stored for a long period also had significantly higher Eigron values ​​than the control group (P < 0.01). In conclusion, coconut milk maceration and long-term storage can affect the degree of coffee roasting.

[0098] 5. Moisture content determination: Weigh 5-6g of sample and measure the moisture content using a moisture meter. Repeat the test three times for each sample group. Calculate the average value. The results are shown below. Figure 11 As shown, coffee beans treated with coconut milk and stored for a long period had significantly higher moisture content than the control group (P < 0.01) and significantly higher moisture content than the coconut milk group (P < 0.01). There was no significant difference between the control group and the coconut milk group (P > 0.05). In conclusion, coconut milk immersion treatment does not significantly affect the moisture content of coffee beans, but coffee beans stored for a long period will have a significantly increased moisture content.

[0099] 6. Determination of total reducing sugar content: The reducing sugar content was determined by colorimetric analysis using the 3,5-dinitrosalicylic acid (DNS) method.

[0100] Sample preparation and color development: Accurately weigh 1.0 g of sample and dissolve it in 20.0 mL of ultrapure water. Take 0.5 mL of sample solution into a test tube, add 1.0 mL of DNS reagent under ice-water bath conditions, mix thoroughly, and then boil in a water bath for 5 min. After cooling to room temperature, add 3.5 mL of ultrapure water and mix well. Set the wavelength of the microplate reader to 540 nm, detect and record the absorbance value.

[0101] Preparation of standard solution: Accurately weigh 0.1 g of glucose sample, add an appropriate amount of pure water to dissolve it, pour it into a 100 mL volumetric flask, and add water to make up to 100 mL to obtain a standard glucose solution (1 mg / mL).

[0102] Construction of the standard curve: Take 0, 0.1, 0.2, 0.3, 0.4, and 0.5 mL of glucose standard solution into 10.0 mL centrifuge tubes, equivalent to 0, 0.1, 0.2, 0.3, 0.4, and 0.5 mg of anhydrous glucose solid, respectively. Add distilled water to bring the volume to 0.5 mL and perform color development according to the sample color development procedure. Using the final glucose content (mg) in the sample as X and the absorbance value as Y, plot the standard curve (…). Figure 12 The standard curve regression equation is: y = 1.5343x + 0.0368 (R²) 2 =0.9998).

[0103] Calculation results: The total reducing sugar content in the sample is expressed as the glucose equivalent per gram of sample, and can be calculated using the following formula:

[0104]

[0105] In this calculation formula:

[0106] ω — the content of reducing sugars in the sample (mg / g);

[0107] m—After measuring the absorbance of the sample, it is substituted into the standard curve to calculate the corresponding glucose content (mg).

[0108] A—Sampling ratio;

[0109] M — Mass of the sample taken (g).

[0110] Figure 13 shows the results of reducing sugar content detection in the three groups of coffee samples. The reducing sugar content of beans treated with coconut milk but not stored for a long period was significantly higher than that of the stored group (P < 0.01) and significantly higher than that of the control group (P < 0.01). The reducing sugar content of the stored group was also significantly higher than that of the control group (P < 0.01). In conclusion, coconut milk maceration can increase the reducing sugar content in coffee beans, and although the reducing sugar content decreases after long-term storage, it is still higher than that of untreated coffee beans.

[0111] 7. Determination of soluble protein content

[0112] Sample preparation and color development: Accurately weigh 1.0 g of sample and dissolve it in 20.0 mL of ultrapure water. Take 1.0 mL of sample solution into a test tube and add 9.0 mL of pure water. Transfer 20 μL to a 96-well plate, add 200 μL of 1×G250 staining solution to each well, incubate at room temperature for 5 minutes, and measure the absorbance using a microplate reader at 595 nm. Record the absorbance value.

[0113] Preparation of staining solution: Invert 5×G250 staining solution 5 times to mix it well, take 1 mL into a centrifuge tube, add 4 mL of ultrapure water and mix thoroughly to obtain 1×G250 staining solution.

[0114] Preparation of standard solution: Accurately weigh 10 mg bovine serum albumin sample, dissolve it in ultrapure water, pour it into a 50 mL volumetric flask, add ultrapure water to make up to the mark, and obtain standard protein solution (0.2 mg / mL).

[0115] Standard curve preparation: Take 0, 2, 4, 6, 8, 12, 16, and 20 μL of bovine serum albumin (BSA) solids into 96-well plates, corresponding to 0, 0.4, 0.8, 1.2, 1.6, 2.4, 3.2, and 4.0 μg, respectively. Add ultrapure water to a final volume of 20 μL. Perform color development according to the sample color development procedure. Using the final BSA content (μg) in the sample as X and the absorbance of the protein-Coomassie brilliant blue staining solution conjugate as Y, plot the standard curve. Figure 14 The standard curve regression equation is: y = 0.1284x + 0.4728 (R2 = 0.9951).

[0116] Calculation results: The content of soluble protein in the sample is expressed as bovine serum albumin equivalent per gram of sample, which can be calculated using the following formula:

[0117]

[0118] In this calculation formula:

[0119] ω — the content of soluble protein in the sample (ωg / g);

[0120] C—After measuring the absorbance of the sample, it is substituted into the standard curve to calculate the corresponding protein content (ųg).

[0121] V—Total volume of extract (mL);

[0122] V1—Sampling volume (mL) during measurement;

[0123] M—Mass of the sample taken (g);

[0124] The results of the soluble protein content detection in the three groups of coffee samples are as follows: Figure 15 As shown, coffee beans treated with coconut milk and not stored for a long period had significantly higher soluble protein content than the stored group (P < 0.01) and significantly higher than the control group (P < 0.01). In conclusion, coconut milk maceration can increase the soluble protein content of coffee beans, while the soluble protein content of coffee beans stored for a long period decreases.

[0125] 8. Determination of flavonoid content – ​​using the sodium nitrite-aluminum nitrate method

[0126] Sample processing and color development: Take 3 mL of the extracted and diluted solution and place it in a 10 mL colorimetric tube. Add 0.5 mL of 5% sodium nitrite solution, shake well and let stand for 6 min. Then add 0 mg of anhydrous rutin sample, dissolve it in 80% ethanol and pour it into a 50 mL volumetric flask. Dilute to the mark to obtain the rutin standard solution (0.2 mg / mL).

[0127] Standard curve preparation: Place 0, 0.25, 0.50, 1.00, 2.00, 3.00, 4.00, and 5.00 mL of rutin standard solution into test tubes, equivalent to 0, 0.05, 0.10, 0.20, 0.40, 0.60, 0.80, and 1.00 mg of anhydrous rutin samples, respectively. Add 0.5 mL of 10% aluminum nitrate solution according to the sample concentration, shake well again, and let stand for 6 min. Add 4.00 mL of 4% sodium hydroxide, and make up to 10 mL with pure water. Shake thoroughly and let stand for 20 min. Set the microplate reader wavelength to 510 nm, measure and record the absorbance values.

[0128] Preparation of standard solution: Accurately weigh 1 μL of the standard solution and proceed with the colorimetric steps. The final rutin content (mg) in the sample is recorded as X, and the absorbance value is Y. Plot a standard curve (…). Figure 16 The standard curve regression equation is: y = 0.6352x + 0.0264 (R²)2 = 0.9980).

[0129] Calculation results: The total flavonoid content in the sample is expressed as the rutin equivalent per gram of sample, which can be calculated using the following formula:

[0130]

[0131] In this formula:

[0132] ω — Flavonoid content in the sample (mg / g);

[0133] m—After measuring the absorbance of the sample, it is substituted into the standard curve to calculate the corresponding rutin content (mg).

[0134] V—The volume (mL) of the sample extracted to a fixed volume;

[0135] V1—The volume of test solution transferred during the test (mL);

[0136] M—mass of the sample taken;

[0137] Figure 17 shows the flavonoid content detection results of the three groups of coffee samples. The flavonoid content of the control group without coconut milk treatment was significantly higher than that of the coconut milk group (P < 0.01). However, the flavonoid content of beans treated with coconut milk but stored for a long time was significantly higher than that of the unstored coconut milk group (P < 0.01). In conclusion, under the same processing conditions, coconut milk immersion treatment reduces the flavonoid content of coffee beans, while long-term storage increases the flavonoid content.

[0138] 9. Determination of polyphenol content – ​​using the Follin-Ciocalteu method.

[0139] Sample preparation and color development: Take 0.25 mL of the diluted solution and place it in a 25 mL colorimetric tube. Add 4 mL of Folin-phenol reagent, mix well, and let stand for 30 min. Slowly add 8 mL of 12% sodium carbonate solution, shake thoroughly to remove air bubbles, and add pure water to bring the volume to the 25 mL mark. Incubate in the dark for 4 h. Measure and record the absorbance at a wavelength of 765 nm.

[0140] Construction of the standard curve: Take 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, and 1.75 mL of gallic acid standard solution (1.0 mg / mL) into 25 mL stoppered colorimetric tubes. These correspond to 0, 0.025, 0.050, 0.075, 0.100, 0.125, 0.150, and 0.175 mg of standard gallic acid solid, respectively. Process the sample according to the colorimetric procedure. The final gallic acid concentration (μg / mL) in the sample is recorded as X, and the absorbance value is recorded as Y. Plot the standard curve (…). Figure 18 The standard curve regression equation is: y = 0.0077x + 0.0427 (R2 = 0.9996).

[0141] Calculation results: The polyphenol content in the sample is expressed as gallic acid equivalent per gram of sample, which can be calculated using the following formula:

[0142]

[0143] In this formula:

[0144] ω — the content of polyphenols in the sample (mg / g);

[0145] C—After measuring the absorbance of the sample, it is substituted into the standard curve to calculate the corresponding gallic acid concentration (ųg / mL).

[0146] V1—The volume (mL) used for sample extraction;

[0147] V2—The volume (mL) used for testing;

[0148] V3—Volume aspirated during testing (mL);

[0149] N—Dilution factor;

[0150] M—Mass of the sample taken (g);

[0151] The results of polyphenol content detection in the three coffee samples are shown in Figure 19.

[0152] like Figure 19 As shown, the polyphenol content in the untreated control group was significantly lower than that in the treated coconut milk group and the storage group (P < 0.01). Furthermore, after long-term storage following coconut milk treatment, the polyphenol content also decreased significantly (P < 0.01). In conclusion, coconut milk immersion treatment increases the polyphenol content in coffee beans, while the polyphenol content decreases during long-term storage.

[0153] 10. Chlorogenic acid was determined according to the method in NT / T 3514-2019. The results are as follows: Figure 20 As shown, the chlorogenic acid content of beans treated with coconut milk was significantly higher than that of the control group without coconut milk treatment (P < 0.01). However, after long-term storage following coconut milk maceration, the chlorogenic acid content in the stored group was significantly reduced (P < 0.01). In conclusion, coconut milk maceration increases the chlorogenic acid content in coffee beans, while long-term storage reduces the chlorogenic acid content.

[0154] 11. The caffeine content was determined according to the method in GB 5009.139—2014, and the results are as follows: Figure 21 As shown, the caffeine content in the control group (without coconut milk treatment) was not significantly different from that in the coconut milk group (P > 0.05). However, the caffeine content was significantly reduced after long-term storage following the addition of coconut milk for immersion treatment (P < 0.01).

[0155] In summary, by disrupting the structure of coffee beans through low-temperature processing, coupled with coconut milk immersion, the coconut milk permeates the beans, giving the roasted beans a unique coconut aroma. Simultaneously, coconut milk immersion alters the content of the coffee beans' components, increasing the levels of important flavor precursors such as sugars and proteins. This influences the Maillard and caramelization reactions during roasting, resulting in a darker color, enhanced aroma and sweetness, and reduced bitterness and acidity in the roasted beans. The result is a coffee with a coconut milk flavor and a full-bodied, balanced taste. Furthermore, while flavonoids, phenolic compounds, and caffeine in coffee have antioxidant properties, a decrease in polyphenol and caffeine content in coffee beans reduces their antioxidant capacity. However, although the flavonoid content in coffee beans prepared using this method is lower due to coconut milk immersion, it increases with long-term storage. Therefore, the antioxidant capacity of these coffee beans gradually increases over a fixed storage period.

Claims

1. A method of freeze combining impregnation treatment of coffee beans, characterized in that, The method comprises the following steps: (1) raw material pretreatment: grading and screening coffee beans, removing impurities and defective beans; (2) soaking: adding the selected coffee beans to the exogenous additive to obtain a mixture A according to a ratio of 1-1.11:1; the exogenous additive is a solution containing flavors; (3) low-temperature treatment: placing the mixture A into a constant-temperature freezing room at-20℃ for 20-30 h, so as to make the exogenous additive enter the coffee beans and change the content of flavor precursors in the coffee beans; (4) thawing and soaking treatment: placing the frozen mixture A into a constant-temperature oven for thawing and soaking; (5) drying: moving the soaked mixture A into a constant-temperature drying oven for drying treatment; (6) roasting: roasting at a roasting temperature of 190-210℃ until the Agtron value reaches 35.

2. The method of claim 1, wherein, Further comprising: (7) screening and packaging: screening the roasted flavored coffee beans, removing the under-roasted or over-roasted coffee beans and residual impurities, and packaging.

3. The method of claim 1, wherein, The solution containing flavors comprises any one of coconut milk, whey protein solution, full-fat sweet milk powder solution and pure milk.

4. The method of claim 1, wherein, In the step (4), the temperature is set to 25℃, and the thawing and soaking are performed for 16 h.

5. The method of claim 1, wherein, In the step (5), the drying treatment is performed at 25℃ until the water content reaches 10-12%.

6. The method of claim 1, wherein, The roasting temperature in the step (6) is 199℃.

7. The method of claim 3, wherein, The solution containing flavors is coconut milk, and the coconut milk is added according to a ratio of 201.5 mL of coconut milk to 200 g of coffee beans, the low-temperature treatment time is 24 h 8 min, and the roasting temperature is 199℃.

8. The method of claim 1, wherein, The coffee beans are KATIE coffee beans.

9. Flavored coffee beans produced by the method according to any one of claims 1-8.

10. The flavored coffee bean according to claim 9, characterized in that, The flavored coffee beans are coconut-flavored coffee beans.

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