Cocoa powder with synergic retention of activity and flavor as well as preparation method and application of cocoa powder

Abstract

The invention discloses cocoa powder with synergic retention of activity and flavor and a preparation method and application thereof, and the preparation method comprises the following steps: (1) alkalization treatment: mixing natural cocoa powder with food-grade alkali liquor, and carrying out alkalization treatment; (2) neutralizing and washing: after the reaction is finished, immediately neutralizing to be neutral, and carrying out solid-liquid separation and washing to thoroughly remove residual alkali liquor and salt; and (3) performing drying treatment: performing infrared-microwave combined drying on the washed wet cocoa powder to finally obtain the alkalized cocoa powder. By optimizing the alkalization and drying processes, the flavor quality of the cocoa powder is remarkably improved while the high retention rate of active substances is achieved; meanwhile, the cocoa powder with high activity and high flavor retention rate can be used for preparing biscuit products with excellent oxidation resistance and prolonged shelf life.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, and in particular to a cocoa powder that synergistically retains activity and flavor, its preparation method, and its application in antioxidant biscuits. Background Technology

[0002] Biscuits are a popular food due to their convenience and long shelf life. However, their high fat content, especially unsaturated fatty acids, makes them prone to oxidation during storage. This oxidation leads to increased acid value (AV) and peroxide value (POV), producing off-flavor substances such as aldehydes and ketones, causing rancidity and severely affecting the product's flavor, color, texture, and food safety. Traditional methods for delaying lipid oxidation rely heavily on synthetic antioxidants (such as BHA, BHT, and TBHQ). However, with increasing consumer demand for clean-label and natural health foods, the application of synthetic antioxidants is becoming increasingly limited.

[0003] Cocoa powder is rich in bioactive substances such as polyphenols, flavonoids, and proanthocyanidins, possessing excellent antioxidant potential and considered an ideal natural inhibitor of lipid oxidation. Furthermore, the volatile flavor compounds in cocoa powder, such as pyrazines and esters, are key to its unique sensory qualities. However, to improve its solubility, color, and flavor, most commercially available cocoa powder undergoes alkalization treatment. This process, while altering its physicochemical properties, also severely damages the structure of phenolic compounds, leading to a significant decrease in core antioxidant activity. Studies have shown that alkalization treatment can cause a loss of over 90% of proanthocyanidins in cocoa powder, greatly limiting its application value as a highly effective natural antioxidant.

[0004] Furthermore, hot air drying technology is currently widely used in the drying process of alkalized cocoa powder. Existing research (e.g., Feng Yun, Jiangnan University, 2008) shows that this drying method often takes place at high temperatures for extended periods, resulting in low thermal efficiency and uneven heating. Its surface-to-interior heat transfer method easily leads to surface hardening and difficulty in internal moisture migration, thus not only accelerating the degradation of heat-sensitive active ingredients but also causing significant losses of key flavor compounds (such as pyrazines and esters) and the formation of undesirable flavor compounds (such as aldehydes), becoming a dual technical bottleneck restricting the preparation of high-activity, high-flavor cocoa powder.

[0005] Therefore, under the current industrial context, there is an urgent need to develop a new cocoa powder processing method that can retain the natural antioxidant active ingredients and characteristic flavor substances to the maximum extent after alkalization treatment. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, this invention provides a cocoa powder with synergistic preservation of activity and flavor, its preparation method, and its applications. By optimizing the alkalization and drying processes, this invention achieves high retention rates of active substances while significantly improving the flavor quality of cocoa powder. Furthermore, the highly active cocoa powder with high flavor retention can be used to prepare biscuit products with excellent antioxidant properties and extended shelf life.

[0007] The technical solution of the present invention is as follows: The first objective of this invention is to provide a method for preparing cocoa powder that synergistically retains activity and flavor, comprising the following steps: (1) Alkalization treatment: Mix natural cocoa powder with food-grade alkali solution and carry out alkalization treatment; (2) Neutralization and washing: After the reaction is completed, neutralize to neutral immediately, and perform solid-liquid separation and washing to thoroughly remove residual alkali and salt; (3) Drying treatment: The washed wet cocoa powder is dried by infrared-microwave combined drying to finally obtain alkalized cocoa powder. In one embodiment of the present invention, the natural cocoa powder raw material may be any commercially available cocoa powder of varieties such as Forastero, Criollo, or Trinitario, and its place of origin may include, but is not limited to, China, Ghana, Cambodia, and Côte d'Ivoire.

[0008] In one embodiment of the present invention, in step (1), the mass concentration of the food-grade alkali solution is 0.5%-1.0%; the mass ratio of natural cocoa powder to food-grade alkali solution is 1:3-5.

[0009] In one embodiment of the present invention, in step (1), the alkalization treatment conditions are: reaction at 60-70℃ and pH 7.8-8.2 for 30-50 min.

[0010] In one embodiment of the present invention, in step (3), the conditions for infrared-microwave combined drying are: infrared radiation controls the surface temperature of the material to be 75-85℃, microwave power is 2-3 W / g, and combined drying time is 10-15 min.

[0011] The second objective of this invention is to provide a cocoa powder prepared by the above-described method that retains both activity and flavor synergistically.

[0012] A third objective of this invention is to provide an application of the cocoa powder that synergistically retains the above-mentioned activity and flavor, for the preparation of cocoa powder antioxidant biscuits.

[0013] The fourth objective of this invention is to provide a method for preparing the above-mentioned cocoa powder antioxidant biscuits, comprising the following steps: S1, by weight percentage, weigh 20%~25% palm oil, 40%-50% low-gluten flour, 15%-20% powdered sugar, 3%-5% white sugar, 0.3%-0.8% edible salt, 0.3%-0.8% baking soda, 5%-10% purified water and 3%-8% cocoa powder that retains the above-mentioned activity and flavor synergistically; S2, add sifted low-gluten flour to softened palm oil, along with granulated sugar, powdered sugar, salt, baking soda, purified water, and cocoa powder that retains the activity and flavor of the above ingredients, and mix them into a dough using a cutting or folding method. S3, roll the dough to the required thickness at a low temperature and shape it with a mold; place the shaped dough in an oven to bake to achieve cooking and shaping; S4, after cooling to room temperature, quickly seal and store using packaging materials with high oxygen barrier and light barrier properties, such as aluminum foil composite bags.

[0014] In one embodiment of the present invention, in step S2, the conditions for mixing into dough are: a mixing speed of 80-150 r / min and a mixing time of 3-8 min, in order to avoid excessive gluten formation and overheating of the mixture.

[0015] In one embodiment of the present invention, in step S3, the low temperature environment is 2-8 ℃.

[0016] In one embodiment of the present invention, in step S3, the baking temperature is 150-200 °C and the time is 10-20 min, in order to minimize the degradation of heat-sensitive active substances.

[0017] The beneficial technical effects of this invention are as follows: The method of this invention significantly improves the retention rate of active substances and flavor substances while taking into account the excellent processing characteristics and sensory quality of alkalized products. Therefore, it can be effectively applied to high-fat food systems, delaying oxidative deterioration while improving the flavor quality of the product.

[0018] This invention introduces infrared-microwave combined drying technology into the field of cocoa powder processing, achieving synergistic improvement of active ingredients, sensory quality, and flavor substances while efficiently dehydrating the cocoa powder.

[0019] The highly active, high-sensory-quality cocoa powder prepared by this invention, when applied to biscuit systems, imparts excellent and long-lasting antioxidant properties to biscuits. It can effectively quench free radicals, block the chain reaction of lipid oxidation, and improve the oxidative stability of biscuits, thereby extending shelf life and having significant commercial value.

[0020] This invention employs a purely physical processing method. By precisely controlling the process parameters of infrared-microwave combined drying, it simultaneously achieves high retention of cocoa powder's activity and high sensory quality without relying on any synthetic antioxidants. This aligns with the consumer trend towards clean labels and provides a clear technical path and raw material selection basis for developing high-end, healthy functional baked goods. Attached Figure Description

[0021] Figure 1 The graph shows the change in acid value of the biscuits prepared in Example 2 and Comparative Examples 6-11 of this invention.

[0022] Figure 2 The graph shows the change in peroxide value of the biscuits prepared in Example 2 and Comparative Examples 6-11 of this invention.

[0023] Figure 3 This is a graph showing the change in oxidative stability index of the biscuits prepared in Example 2 and Comparative Examples 6-11 of the present invention.

[0024] Figure 4 This is a graph showing the change in hexanal content in the biscuits prepared in Example 2 and Comparative Examples 6-11 of the present invention.

[0025] Figure 5 The graph shows the changes in the DPPH free radical scavenging ability of the biscuits prepared in Example 2 and Comparative Examples 6-11 of this invention.

[0026] Figure 6 The graph shows the changes in the FRAP free radical scavenging ability of the biscuits prepared in Example 2 and Comparative Examples 6-11 of this invention.

[0027] Figure 7 The graph shows the changes in the ABTS free radical scavenging ability of the biscuits prepared in Example 2 and Comparative Examples 6-11 of this invention. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] The reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field.

[0030] The processing method and measurement method involved in this invention (1) Extraction of oil from biscuits The fat in shortbread biscuits was extracted using the Soxhlet extraction method as described in the national standard GB-5009.6-2016 "Determination of Fat in Food". The biscuits were crushed as finely as possible, and 100 g of the extract was placed in a filter paper tube and soaked in petroleum ether for extraction. The solvent was then removed by rotary evaporation, and the biscuits were dried in an oven. Finally, the extract was weighed and used for subsequent experimental analysis.

[0031] (2) Sensory evaluation of cocoa powder The sensory evaluation of cocoa powder was conducted with reference to the national standard GB / T 20706-2023 and appropriate modifications. Fifteen trained personnel (eight women and seven men, with an average age of 24 ± 3 years) served as testers to evaluate the cocoa powder. The maximum score was 10 points, and the final score was the average of the 15 scores. The sensory evaluation criteria for cocoa powder are shown in Table 1.

[0032] Table 1

[0033] (3) Volatile flavor compounds in cocoa powder Sample pretreatment: Take 2 g of cocoa powder sample and place it in a headspace vial. Add 5 μL of 4-methyl-2-pentanone as an internal standard with a mass concentration of 90 ug / mL.

[0034] Solid-phase microextraction conditions: After sealing the headspace vial, equilibrate in a 50°C water bath for 30 min, then remove the extraction head and insert it into the 250°C injection port for analysis for 5 min.

[0035] Chromatographic conditions: DB-WAX capillary column, 60 m long, 0.25 mm inner diameter, 0.25 μm film thickness. Initial temperature 40°C, hold for 6 min, ramp to 200°C at 5°C / min, ramp to 240°C at 10°C / min, hold for 10 min. Mass spectrometry conditions: Electron impact (EI) ion source, electron energy 70 eV, ion source temperature 230°C, interface temperature 250°C. Signal acquisition was performed in full scan mode, scan range 40–500 m / z.

[0036] Qualitative and quantitative analysis of volatile substances: Compounds detected by HS-SPME-GC-MS were compared with the NIST14 spectral library, retaining compounds with a match greater than 80%. Quantification was performed by comparing the peak area of ​​the compound with that of the internal standard compound to obtain the content of flavor substances. The calculation formula is: C i =S i / S 内标 ×C 内标 In the formula, C i The mass fraction of the analyte is expressed in ng / g; S i Peak area representing the unknown substance; S 内标 Peak area representing the internal standard compound; C 内标 The mass fraction of the internal standard is ng / g.

[0037] (4) Determination of acid value and peroxide value of fats in biscuits The acid value was determined by referring to the national standard GB 5009.229-2016 "National Food Safety Standard - Determination of Acid Value in Food"; the peroxide value was determined by referring to GB5009.227-2023 "National Food Safety Standard - Determination of Peroxide Value in Food". The acid value and peroxide value of the oil extracted from the biscuits were determined.

[0038] (5) Oxidation induction time of fats in biscuits Oxidation induction time: Tested using the Rancimat method (GB / T 21121-2007). 3.00 g of oil extracted from shortbread biscuits was weighed into a test tube. Test conditions were: air flow rate 20 L / min, oxidation temperature 120°C.

[0039] (6) Detection of hexanal content Sample pretreatment: Weigh 1 g of biscuit sample into a headspace vial, prepare a 1 mg / mL hexanal standard stock solution, and dilute the stock solution with ultrapure water to a gradient concentration (0.1, 0.5, 1.0, 5, 10 μg / mL). Place the headspace vial in a constant temperature water bath shaker and equilibrate at 80℃ for 30 minutes. After equilibration, let it stand for 5 minutes, and then inject the headspace gas.

[0040] Chromatographic conditions: DB-WAX capillary column, 60 m in length, 0.25 mm in inner diameter, and 0.25 μm in film thickness. Initial temperature 40°C, held for 3 minutes, increased to 120°C at a rate of 8°C / min, increased to 240°C at a rate of 15°C / min, and held for 10 minutes.

[0041] Mass spectrometry conditions: Electron impact (EI) ion source, electron energy 70 eV, ion source temperature 230 °C, interface temperature 250 °C.

[0042] (7) Determination of total phenol content The Folin-Ciocalteu colorimetric method was used. An appropriate amount of the sample powder was accurately weighed and dissolved in a methanol-water solution of a specific concentration. After ultrasonic-assisted extraction, the sample was extracted for a certain period of time in the dark at a predetermined temperature. Subsequently, it was centrifuged in a high-speed refrigerated centrifuge, and the supernatant was collected as the test solution. 1 mL of the supernatant was pipetted into a cuvette, 2.5 mL of Folin-Ciocalteu reagent was added, and the mixture was shaken well. Then, 2.5 mL of 15% Na₂CO₃ solution was added, and water was added to the mark and shaken well. The reaction was carried out at 40℃ for 60 minutes, and the absorbance was measured at 750 nm. A standard curve was prepared using gallic acid (GAE) solution at concentrations of 0, 4, 8, 12, 20, and 30 mg / L. The absorbance was measured using the same method to construct the standard curve. The final results are expressed as gallic acid equivalents (mg GAE / g).

[0043] (8) Determination of total flavonoid content The total flavonoid content in biscuits was determined using the aluminum trichloride colorimetric method. 0.25 mL of the supernatant was pipetted into a cuvette, and 4.75 mL of 70% methanol and 2 mL of 0.1 mol / L aluminum trichloride solution were added, followed by 3 mL of 1 mol / L potassium acetate solution. The mixture was allowed to react at room temperature for 30 min, and the absorbance was measured at 420 nm. Using rutin as a standard, standard curves were constructed at concentrations of 0, 0.005, 0.01, 0.02, 0.03, and 0.04 mg / mL using the same method. The flavonoid content in the biscuits was calculated based on the rutin standard curve.

[0044] (9) Determination of proanthocyanidin content Take 1 mL of the supernatant, add 6 mL of hydrochloric acid-n-butanol solution and 0.2 mL of ferric ammonium sulfate solution, mix well, seal with pliers, heat in a boiling water bath for 40 minutes, remove, and immediately cool to room temperature in ice water. Measure the absorbance at 546 nm. Prepare a series of standard working solutions with concentrations of 0, 10, 25, 50, 100, 150, 200, and 250 μg / mL, and measure the absorbance values ​​using the same procedure. Plot a standard curve with absorbance as the ordinate and proanthocyanidin concentration as the abscissa.

[0045] (10) Determination of DPPH free radical scavenging ability Prepare a 0.2 mmol / L DPPH solution, and adjust the absorbance at 517 nm to 0.700 ± 0.002 with 95% ethanol. Store in the dark until ready for use. Prepare Trolox standard working solutions with concentrations of 0, 100, 200, 300, 400, 500, 600, and 700 μmol / L. Take 0.1 mL of Trolox standard working solution and the diluted extract into a 10 mL amber volumetric flask, mix with 3.9 mL of DPPH solution, and incubate at room temperature in the dark for 30 min. Use 95% ethanol as a blank control. Measure the absorbance at 517 nm. Construct a standard curve based on the concentration and absorbance of the Trolox standard working solution, and evaluate the DPPH radical scavenging ability of the sample based on the absorbance of the extract.

[0046] (11) Determination of ABTS free radical scavenging ability Prepare a 7 mmol / L ABTS stock solution, mix it with 2.45 mmol / L potassium persulfate, and let it stand at room temperature for 12 h. Then, add an appropriate amount of 95% ethanol at 734 nm to adjust the absorbance of the working solution to 0.700 ± 0.002, obtaining the ABTS solution, which is stored in the dark for later use. Prepare Trolox standard working solutions with concentrations of 0, 100, 200, 300, 400, 500, 600, and 700 μmol / L. Take 0.1 mL of Trolox standard working solution and the diluted extract into a 10 mL brown volumetric flask, mix it with 3.9 mL of ABTS solution, and let it stand in the dark at room temperature for 30 min. Measure the absorbance at 734 nm. Construct a standard curve based on the concentration and absorbance of the Trolox standard working solution, and evaluate the ABTS radical scavenging ability of the sample based on the absorbance of the extract.

[0047] (12) Determination of FRAP free radical scavenging ability Add 250 mL of acetate buffer (pH 3.6), 25 mL of 10 mmol / L TPTZ, and 25 mL of 20 mmol / L FFeCl3. Mix thoroughly with 6H₂O (10:1:1, v / v / v), preheat in a 37 ℃ water bath for 10 min in the dark, and use immediately. Prepare Trolox standard working solutions with concentrations of 0, 100, 200, 300, 400, 500, 600, and 700 μmol / L. Take 0.1 mL of Trolox standard working solution and the diluted extract into a 10 mL amber volumetric flask, mix with 3.9 mL of FRAP solution, and incubate at room temperature in the dark for 30 min. Measure the absorbance at 593 nm. Construct a standard curve based on the concentration and absorbance of the Trolox standard working solution, and evaluate the FRAP radical scavenging ability of the sample based on the absorbance of the extract.

[0048] Example 1 A method for preparing alkalized cocoa powder with high activity retention rate, the preparation method is as follows: (1) Mix natural cocoa powder with a food-grade potassium carbonate aqueous solution of 0.8% (w / w) at a mass ratio of 1:4. The pH value of the mixture is kept stable within the range of 8.0. Stir continuously for 45 min at 60 °C.

[0049] (2) After the reaction is complete, immediately neutralize to neutral and perform solid-liquid separation and washing to thoroughly remove residual alkali and salt.

[0050] (3) The washed wet cocoa powder was dehydrated and dried by infrared-microwave combined drying. The infrared radiation controlled the surface temperature of the material at 80 ℃, the microwave power was controlled at 2 W / g, and the combined drying time was 12 min, finally obtaining alkalized cocoa powder.

[0051] Comparative Example 1 The only difference from Example 1 is that the drying method is infrared drying only, the material surface temperature is controlled at 80℃, and the drying time is 12 minutes.

[0052] Comparative Example 2 The only difference from Example 1 is that the drying method is microwave drying only, the microwave power density is controlled at 2 W / g, and the drying time is 12 minutes.

[0053] Comparative Example 3 The only difference from Example 1 is that the infrared-microwave combined drying parameters are different: infrared radiation controls the material surface temperature at 90 ℃, microwave power density is maintained at 2 W / g, and the combined drying time is 12 min.

[0054] Comparative Example 4 The only difference from Example 1 is that the infrared-microwave combined drying parameters are different: infrared radiation controls the material surface temperature at 100 ℃, microwave power density is maintained at 2 W / g, and the combined drying time is 12 min.

[0055] Comparative Example 5 The only difference from Example 1 is that the drying method used is the traditional oven drying method, with a temperature of 100 ℃ and a drying time of 12 min.

[0056] The content of active substances in cocoa powder after alkalization in Examples 1 and Comparative Examples 1-5 is shown in Table 2.

[0057] Table 2

[0058] As shown in Table 2, by employing the drying process described in this invention and controlling the materials within the optimal range, the total phenol content, total flavonoid content, and proanthocyanidin content of the prepared cocoa powder are all significantly better than those of the comparative example. Among them, the cocoa powder of Example 1 has the highest content of active substances, with a total phenol content of 35.81±2.18 mg GAE / g, a total flavonoid content of 96.73±1.34 μg / g, and a proanthocyanidin content of 14.05±0.32 mg / g, all of which are the highest values ​​among all groups and far superior to the highest level in the comparative example. Compared with the traditional oven drying process (Comparative Example 5), the total phenol content increased by 2.02 times, indicating that the drying process of this invention can effectively retain the active substances in cocoa powder. Infrared drying alone can also improve the retention rate of active substances, with the total phenol content increasing by 1.19 times compared to Comparative Example 5; when microwave drying is used alone, the total phenol content increases by 46.28%. Although Comparative Examples 3 and 4 also used infrared-microwave combined drying technology, the excessively high drying temperature led to a significant degradation of the active substances, indicating that this combined technology requires precise control of process parameters. Comparative Example 5, using a traditional oven drying process, showed poor retention of active substances, with total phenol content of 11.84±1.09 mg GAE / g, total flavonoid content of 71.35±0.56 μg / g, and proanthocyanidin content of 0.05±0.00 mg / g.

[0059] To comprehensively evaluate the impact of different drying technologies on the final quality of cocoa powder, a systematic sensory evaluation was conducted on the prepared cocoa powder. The sensory evaluation scores of the cocoa powders in Example 1 and Comparative Examples 1-5 are shown in Table 3.

[0060] Table 3

[0061] As shown in Table 3, the infrared-microwave combined drying technology used in Example 1 of this invention exhibits significant advantages in all sensory indicators, resulting in the best overall quality. The alkalized cocoa powder prepared in Example 1 scored significantly higher than other comparative examples in terms of color (8.92±0.31), aroma (9.12±0.20), and solubility (9.32±0.31), indicating that this combined drying process can retain the natural sensory properties of cocoa powder to the maximum extent while efficiently dehydrating it. This superior performance is attributed to the synergistic effect of infrared and microwave energy. Infrared radiation provides gentle heating from the surface to the interior, effectively maintaining the integrity of the surface structure of cocoa powder particles, which is beneficial to the stability and presentation of color; while the volumetric heating characteristics of microwave energy promote the rapid migration of internal moisture, shortening the total drying time and reducing the volatilization and deterioration of heat-sensitive flavor substances caused by prolonged heating, thereby achieving a high aroma score. In addition, the combined effect of the two energies may cause uniform and subtle morphological changes on the particle surface, increasing the specific surface area and hydrophilicity, thereby significantly improving its dispersibility and dissolution rate in the aqueous phase.

[0062] In contrast, single infrared or microwave drying (Comparative Examples 1 and 2) suffers from significant shortcomings in color, aroma, and solubility due to uneven heat distribution or a single mode of action. While Comparative Examples 3 and 4 employ the same combined method, the higher infrared temperature exacerbates thermal damage, leading to a systematic decline in sensory quality. This demonstrates that precise control of process parameters is crucial to achieving the advantages of this invention. Traditional oven drying (Comparative Example 5), due to prolonged high-temperature treatment, performs the worst across all sensory dimensions, further highlighting the advanced nature and practicality of the infrared-microwave combined drying method described in this invention in improving the overall sensory quality of alkalized cocoa powder.

[0063] The volatile flavor compounds of cocoa powder prepared by different drying processes were analyzed. The results of volatile flavor compounds of cocoa powder from Example 1 and Comparative Examples 1-5 are shown in Table 4 below.

[0064] Table 4

[0065] As can be clearly seen from Table 4, the infrared-microwave combined drying process used in Example 1 of the present invention has significant advantages in the retention and control of flavor substances, which further explains why it has the highest sensory evaluation score.

[0066] Regarding pyrazines, these compounds are important products of the Maillard reaction, directly imparting characteristic aromas of popcorn, nuts, and chocolate to cocoa powder. The total amount (1520.34 ± 23.33 ng / g) and the content of the key flavor monomer 2-methylpyrazine (680.22 ± 22.12 ng / g) in Example 1 were significantly higher than in other groups, exhibiting a pronounced popcorn flavor. The combined drying process employed in this invention, under a suitable combination of temperature and time, not only effectively promotes the conversion of precursor substances into pyrazines but also, through the synergistic effect of infrared and microwave, avoids the volatilization and decomposition of flavor compounds caused by localized overheating or prolonged heating.

[0067] Aldehydes are markers of oil oxidation and flavor degradation, producing grassy or rancid tastes. In Example 1, the total aldehyde content (285.34 ± 18.34 ng / g) was the lowest among all groups, lower than that of microwave drying and infrared drying alone. This result indicates that the combined drying method described in this invention, through the synergy of gentle surface heating by infrared radiation and rapid volumetric heating by microwaves, may achieve rapid moisture removal in a short time, thereby inhibiting the activity of lipid oxidases and possibly altering the oxidation reaction pathway, effectively delaying the formation of undesirable flavor compounds.

[0068] Esters are important components constituting the characteristic flavor of cocoa, typically contributing pleasant aromas such as floral, fruity, sweet, and creamy notes. Their content directly reflects the richness and quality of the product's flavor. The total ester content (420.34 ± 30.09 ng / g) in Example 1 (optimal infrared-microwave combined drying) was significantly higher than all other groups. It was not only about 35% higher than infrared drying alone, about 50% higher than microwave drying alone, but also four times higher than traditional oven drying. This indicates that the drying process of the present invention not only effectively preserves the inherent ester flavor compounds in the raw materials, but may also promote the formation or transformation of certain ester compounds by controlling the thermal effects and moisture migration behavior during the drying process, thereby significantly enhancing the flavor profile and quality of the product.

[0069] Example 2 A method for preparing an antioxidant biscuit containing cocoa powder with synergistic preservation of activity and flavor includes the following steps: (1) Weigh out 23% palm oil, 41% low-gluten flour, 18% powdered sugar, 4% white sugar, 0.5% edible salt, 0.6% baking soda, 8% purified water and 4.9% cocoa powder prepared in Example 1 with synergistic preservation of activity and flavor by mass percentage.

[0070] (2) After softening the palm oil at room temperature, place it in a mixing bowl along with sifted low-gluten flour, then add granulated sugar, powdered sugar, salt, baking soda, purified water, and cocoa powder (which synergistically preserves activity and flavor). Use a paddle mixer to mix at 120 rpm for 3 minutes, combining cutting and folding to evenly form a dough. This medium-speed, short-duration mixing condition aims to mix the materials evenly while avoiding excessive gluten formation and overheating of the mixture.

[0071] (3) Roll the dough to a thickness of about 4 mm at a low temperature of 4°C and shape it with a mold. Place the raw cookie dough in an oven preheated to 175°C for the top heat and 170°C for the bottom heat and bake for 20 min. This mild baking condition is intended to allow the cookies to mature and set and to minimize the damage to the heat-sensitive active substances in the cocoa powder.

[0072] (4) After baking, the cookies are allowed to cool naturally to room temperature, and then quickly sealed in aluminum foil composite bags with high oxygen barrier and light barrier to ensure the stability of product quality during storage.

[0073] The biscuits prepared in Example 2 were stored in a constant temperature and humidity chamber at 50°C (75% RH) for 30 days, with samples taken every five days for performance testing. Acid value, peroxide value, oxidative stability index, hexanal, DPPH radical scavenging ability, FRAP radical scavenging ability, and ABTS radical scavenging ability were measured. The results are as follows: Figures 1-7 As shown.

[0074] Comparative Example 6 Same as Example 2, except that the cocoa powder was prepared from Comparative Example 1.

[0075] Comparative Example 7 Same as Example 2, except that the cocoa powder was prepared from Comparative Example 2.

[0076] Comparative Example 8 Same as Example 2, except that the cocoa powder was prepared from Comparative Example 3.

[0077] Comparative Example 9 Same as Example 2, except that the cocoa powder was prepared from Comparative Example 4.

[0078] Comparative Example 10 Same as Example 2, except that the cocoa powder was prepared from Comparative Example 5.

[0079] Comparative Example 11 Same as Example 2, except that the added cocoa powder is replaced with low-gluten wheat flour, that is, biscuits without added cocoa powder.

[0080] like Figure 1 The accelerated storage test results showed that the acid value of all samples increased with prolonged storage time. However, the acid value of the biscuits with added cocoa powder was significantly higher than that of the control group (Comparative Example 11). This phenomenon is mainly because cocoa powder contains a certain amount of oil; a higher fatty acid content means that more free fatty acids can be generated during the accelerated storage test, resulting in a higher overall acid value. In the sample group with added cocoa powder, the biscuits prepared using cocoa powder with high activity retention rate showed significantly lower levels of oil hydrolysis and rancidity compared to the control group. This indicates that the biscuit system with added cocoa powder with high activity retention rate can effectively inhibit the process of oil hydrolysis and rancidity. The high-temperature infrared-microwave combined drying method used in Comparative Examples 8 and 9 resulted in the loss of antioxidant active substances in the cocoa powder, making it impossible to provide effective antioxidant protection for the biscuits. The final acid value of Comparative Example 10 was between that of Comparative Examples 8 and 9, further illustrating the limitations of traditional processes in retaining active substances.

[0081] Peroxide value is a key indicator for measuring the primary oxidation products of oils and fats. The resulting hydroperoxides decompose, forming small-molecule compounds such as aldehydes, ketones, and acids. For example... Figure 2As shown, the peroxide value of all samples increased with prolonged storage time, with Comparative Example 11 exhibiting the most significant rate of increase. On day 30 of storage, its peroxide value was 0.088 ± 0.001 g / 100 g, the highest among all groups. This clearly demonstrates that without additional antioxidant measures, the oil oxidation process in biscuits is very rapid, resulting in a short shelf life. The peroxide values ​​of Comparative Examples 8-10 were lower than those of Examples 2 and 6 and 7, possibly because the oil oxidation process involves the decomposition of hydroperoxides.

[0082] The Oxidative Stability Index (OSI) is a direct indicator of an oil's resistance to oxidation. A higher OSI indicates stronger antioxidant stability and a longer shelf life potential. For example... Figure 3 As shown, the OSI values ​​of Examples 2 and Comparative Examples 6-7 were higher than those of other sample groups, indicating that the oil system was stable and difficult to oxidize. The OSI data of Comparative Example 10 showed that traditional oven drying technology resulted in low retention of active substances. Comparative Example 11 had the lowest OSI value among all groups, exhibiting the most significant decrease in OSI value during the entire storage period, with a decrease rate of 46.43%. This further verifies the positive effect of highly active cocoa powder on improving the oxidative stability of biscuits.

[0083] Hexanal is a core volatile aldehyde produced during the oxidation and rancidity of oils and fats. It is a key marker for measuring the degree of secondary oxidation products and flavor deterioration in oils and fats. Higher hexanal content indicates a deeper degree of oxidation, and more pronounced rancid or paint-like odors in the product. Figure 4 As shown, in Example 2, the hexanal content remained at a certain level, demonstrating a good inhibitory effect on oil oxidation. The hexanal growth rate in Comparative Examples 8-9 was faster than in the Examples, corresponding to their lower retention rate of active substances. In Comparative Example 10, the hexanal content was higher than in Comparative Examples 8 and 9, indicating a faster oxidation rate and highlighting the limitations of traditional oven drying technology in preserving the active substances in cocoa powder. Comparative Example 11 showed the most significant increase in hexanal content, with an increase rate of 99.98%, and after 30 days of storage at 50°C, it had the highest content among all groups. This clearly demonstrates that without effective antioxidant protection, oil oxidation in biscuits proceeds rapidly, producing large amounts of unpleasant volatile aldehydes, resulting in an extremely short flavor shelf life.

[0084] DPPH radical scavenging capacity is a classic indicator for quantitatively characterizing the in vitro antioxidant activity of a sample. According to... Figure 5As shown, Example 2 exhibited the highest free radical scavenging ability, indicating its superior antioxidant effect. After 30 days of storage, its free radical scavenging ability was 1.61 ± 0.03 μM TEAC / g, significantly higher than that of the traditional oven drying method. Furthermore, the DPPH free radical scavenging ability of Example 2 was significantly higher than that of Comparative Examples 6-11, consistent with its polyphenol content retention rate. Comparative Examples 8 and 9 used high-temperature infrared-microwave combined drying, which caused the cocoa powder raw material to lose most of its antioxidant active substances due to high-temperature treatment, resulting in a weak contribution to the free radical scavenging ability of the biscuit system after addition. Comparative Example 10 used cocoa powder obtained through traditional oven drying, which had weak free radical scavenging ability, with a value of only 0.23 ± 0.01 μM TEAC / g after 30 days of storage. Comparative Example 11 was a blank control biscuit without added cocoa powder, exhibiting almost no free radical scavenging ability, relying solely on trace amounts of natural components in the flour, resulting in limited free radical scavenging capacity.

[0085] The FRAP method is a classic method for assessing the total antioxidant capacity of a sample. Its principle is to measure the ability of antioxidants to reduce ferric iron (Fe3+) to ferrous iron (Fe2+). This indicator directly reflects the reducing potential of antioxidant components in biscuits. Figure 6 Data shows that samples prepared using specific process parameters exhibit significant differences in FRAP activity. Example 2 demonstrates high reducing ability, indicating the formation of a stable antioxidant protection system within the product. Comparative Examples 8 and 9, prepared using high-temperature infrared-microwave combined drying, initially showed some reducing ability, but due to process parameters deviating from the optimal range, the active substances were destroyed, leading to a sharp decrease in FRAP, verifying the crucial influence of process parameters on activity maintenance. Comparative Example 11 showed the lowest FRAP value among all samples during storage, with a FRAP value of only 0.22 ± 0.02 μM TEAC / g after 30 days of storage, indicating the fastest oxidation rate and shortest shelf life.

[0086] ABTS free radical scavenging capacity is another authoritative indicator for evaluating the total antioxidant activity of a sample; it measures the amount of ABTS that antioxidants can scavenge. • + The antioxidant capacity of free radical cations, including both hydrophilic and lipophilic antioxidant components, was highly consistent with the DPPH and FRAP results, providing final verification of the comprehensive antioxidant strength of the biscuit products of this invention. Example 2 showed a high overall free radical scavenging ability, indicating that this process has good retention rate of active substances and antioxidant capacity. In contrast, Comparative Examples 8 and 9 used high-temperature infrared-microwave combined drying, and as the infrared drying temperature increased, the active substances decreased accordingly, and the free radical scavenging ability weakened. Comparative Example 11, a sample without added cocoa powder, had lower antioxidant capacity than other sample groups. This indicates that this process technology can improve the antioxidant capacity of biscuit samples and extend the shelf life of the product.

[0087] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing cocoa powder that synergistically preserves activity and flavor, characterized in that, Includes the following steps: (1) Alkalization treatment: Mix natural cocoa powder with food-grade alkali solution and carry out alkalization treatment; (2) Neutralization and washing: After the reaction is completed, neutralize to neutral immediately, and perform solid-liquid separation and washing to thoroughly remove residual alkali and salt; (3) Drying treatment: The washed wet cocoa powder is dried by infrared-microwave combined drying to finally obtain alkalized cocoa powder.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass concentration of the food-grade alkali solution is 0.5%-1.0%; the mass ratio of natural cocoa powder to food-grade alkali solution is 1:3-5.

3. The preparation method according to claim 1, characterized in that, In step (1), the alkalization treatment conditions are: reaction at 60-70 ℃ and pH 7.8-8.2 for 30-50 min.

4. The preparation method according to claim 1, characterized in that, In step (3), the conditions for infrared-microwave combined drying are: infrared radiation controls the surface temperature of the material to 75-85 ℃, microwave power is 2-3 W / g, and combined drying time is 10-15 min.

5. A cocoa powder with synergistic preservation of activity and flavor, prepared by the method according to any one of claims 1-4.

6. The application of the cocoa powder with synergistic preservation of activity and flavor as described in claim 5, characterized in that, Used to make cocoa powder antioxidant cookies.

7. A method for preparing cocoa powder antioxidant biscuits as described in claim 6, characterized in that, Includes the following steps: S1, by weight percentage, weigh 20%~25% palm oil, 40%-50% low-gluten flour, 15%-20% powdered sugar, 3%-5% white granulated sugar, 0.3%-0.8% edible salt, 0.3%-0.8% baking soda, 5%-10% purified water and 3%-8% cocoa powder with synergistic preservation of activity and flavor as described in claim 5; S2, add sifted low-gluten flour to softened palm oil, along with granulated sugar, powdered sugar, edible salt, baking soda, purified water, and cocoa powder that synergistically preserves activity and flavor as described in claim 5, and mix them into a dough using a cutting or folding method. S3, roll the dough to the required thickness at a low temperature and shape it with a mold; place the shaped dough in an oven to bake to achieve cooking and shaping; S4, after cooling to room temperature, quickly seal and store using packaging materials with high oxygen barrier and light barrier properties, such as aluminum foil composite bags.

8. The preparation method according to claim 7, characterized in that, In step S2, the conditions for mixing into dough are: mixing speed of 80-150 r / min and mixing time of 3-8 min.

9. The preparation method according to claim 7, characterized in that, In step S3, the low-temperature environment is 2-8 ℃.

10. The preparation method according to claim 7, characterized in that, In step S3, the baking temperature is 150-200℃ and the time is 10-20 min.

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