Preparation method of ultrasonic-assisted high-antioxidant-activity coffee leaf Kangpu tea

Abstract

The invention belongs to the technical field of tea beverages, and particularly relates to an ultrasonic-assisted preparation method of coffee leaf Kangpu tea with high antioxidant activity. The method mainly comprises the following steps: firstly, screening and cleaning coffee leaves, drying and crushing to obtain coffee leaf powder; extracting the coffee leaf powder with boiling water, and filtering to obtain a coffee leaf extract; kombucha is inoculated into the coffee leaf leach liquor, and seed liquor is obtained after culture; mixing the coffee leaf extracting solution with cane sugar, sterilizing, cooling the sterilized mixed solution to room temperature, and adjusting the pH value to obtain the pH-adjusted mixed solution; inoculating a seed solution into the pH-adjusted mixed solution to obtain an inoculated mixed solution, performing ultrasonic treatment to obtain the inoculated mixed solution subjected to ultrasonic treatment, and finally performing fermentation to obtain the coffee leaf Kangpu tea with high antioxidant activity. The flavor characteristics of the Kangpu tea and the coffee leaves are greatly integrated; in addition, the content of bioactive substances in the coffee leaf Kangpu tea is remarkably increased, and the oxidation resistance of the coffee leaf Kangpu tea is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of tea beverages, and particularly relates to a method for preparing coffee leaf kombucha with high antioxidant activity assisted by ultrasound. Background Art

[0002] Kombucha is a beverage made from tea leaves, sugar, and a symbiotic culture of bacteria and yeast, with excellent nutritional value and potential health benefits. Black tea is the traditional base for kombucha fermentation, but in recent years, a variety of plant extracts such as azalea, turmeric, and pomegranate have been added to the fermentation base to prepare kombucha with different flavors and functional properties.

[0003] Coffee leaves are a byproduct of the abundant coffee tree. They are usually discarded in the field during the regular pruning of coffee trees, which not only causes a waste of resources but also increases the environmental burden. Coffee leaves contain many bioactive ingredients, such as caffeine, trigonelline, chlorogenic acid, caffeic acid, p-coumaric acid, ferulic acid, catechins, epicatechin, rutin, chlorogenic acid, amino acids and other bioactive substances. These phytochemical ingredients have functional properties such as antioxidant activity, anti-inflammatory activity, and anti-cancer activity. At present, coffee leaves have been processed into coffee leaf tea for human consumption. Compared with traditional tea leaves, coffee leaves have low caffeine content, but high polyphenol content and antioxidant activity. Therefore, coffee leaves are a potential healthy matrix for making kombucha. However, research on the production of kombucha by fermentation using coffee leaves as a matrix is ​​still very lacking.

[0004] At present, kombucha is mainly prepared by traditional fermentation methods using kombucha. Traditional fermentation methods have disadvantages such as low yield, long duration, and high risk of contamination. As an emerging physical processing technology, ultrasound can improve fermentation efficiency and yield by promoting microbial growth, increasing enzyme activity and metabolic capacity, and improving mass transfer processes. Therefore, ultrasound-assisted fermentation is an effective means to improve the antioxidant activity of kombucha. At present, research on ultrasound in kombucha preparation mainly focuses on using ultrasound to prepare extracts for fermentation, while there are few reports on the use of ultrasound to pretreat kombucha before fermentation. There are also no reports on the preparation of coffee leaf kombucha by ultrasound-assisted fermentation of kombucha and how to obtain coffee leaf kombucha with high antioxidant activity by screening ultrasound conditions. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing coffee leaf kombucha with high antioxidant activity assisted by ultrasound; the obtained coffee leaf kombucha has a unique flavor of kombucha, and its unique sweet and sour taste neutralizes and dilutes the herbal smell of coffee leaves, forming a more distinctive sensory characteristic. Therefore, the purpose of this study is to improve the antioxidant activity of coffee leaf kombucha through ultrasound-assisted fermentation; at the same time, the grassy taste of coffee leaves is diluted through kombucha fermentation, so as to obtain a functional coffee leaf kombucha with high antioxidant activity and unique flavor.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for preparing coffee leaf kombucha with high antioxidant activity assisted by ultrasound comprises the following steps:

[0008] Step 1: Pretreatment of coffee leaves:

[0009] (1) Pretreatment: The freshly picked coffee leaves are destemmed, and leaves without insect holes and in complete shape are selected, followed by washing and draining to obtain pretreated coffee leaves;

[0010] (2) Drying: drying the pretreated coffee leaves to obtain dried coffee leaves;

[0011] (3) crushing: crushing the dried coffee leaves to obtain coffee leaf powder;

[0012] Step 2: Preparation of inoculation mixture:

[0013] (1) Preparation of coffee leaf extract: adding the coffee leaf powder obtained in step 1 (3) into boiling water, extracting with boiling water, and collecting the filtrate through gauze to obtain a coffee leaf extract;

[0014] (2) mixing the coffee leaf extract and sucrose and sterilizing them under high pressure, cooling the sterilized mixed solution to room temperature, and then adjusting the pH of the mixed solution to obtain a mixed solution after the pH is adjusted;

[0015] (3) inoculating kombucha into the coffee leaf extract obtained in step 2 (1) to obtain a seed solution after culturing; and then inoculating the seed solution into the mixed solution after adjusting the pH in step 2 (2) to obtain an inoculated mixed solution;

[0016] Step 3: Ultrasonic-assisted preparation of coffee leaf kombucha:

[0017] (1) Ultrasonic treatment: ultrasonically treating the inoculated mixed solution in step 2 (3) to obtain an ultrasonically treated inoculated mixed solution;

[0018] (2) fermenting the inoculated mixed solution treated with ultrasound in step 3 (1) to obtain coffee leaf kombucha with high antioxidant activity.

[0019] Preferably, the drying temperature in step (2) is 160° C. and the drying time is 20-25 min.

[0020] Preferably, in step 2 (1), the amount of coffee leaf powder to boiling water is 3-11 g:1 L; and the boiling water extraction time is 10-15 min.

[0021] Preferably, in step 2 (2), the amount of sucrose and coffee leaf extract is 30-70 g:1 L; the pH of the mixed solution is adjusted using sterilized sodium citrate or sodium bicarbonate solution to a pH of 3.0-5.0; the sterilization conditions are 121° C. and 15-20 min.

[0022] Preferably, in step 2 (3), the inoculation amount of kombucha fungus in the coffee leaf extract is 10 g:100 mL; and the volume ratio of the seed solution to the mixed solution after pH adjustment is 3:50-7:50.

[0023] Preferably, the ultrasonic treatment in step 3 (1) is performed after the inoculated mixed solution has been statically cultured for 0-7 days, wherein 0 days refers to the direct ultrasonic treatment of the inoculated mixed solution after obtaining it, and 1 day refers to the ultrasonic treatment of the inoculated mixed solution after static culture for 24 hours, and so on for 2-7 days; the static culture temperature is 32°C.

[0024] Preferably, in step 3 (1), the ultrasonic power density is 4-38W / L; the ultrasonic time is 5-60min; the ultrasonic frequency is single frequency, dual frequency or triple frequency; wherein the single frequency is 20-40kHz; the dual frequency is two frequencies simultaneously processed, including 20kHz and 28kHz simultaneously processed, 20kHz and 40kHz simultaneously processed or 28kHz and 40kHz simultaneously processed; the triple frequency is three frequencies simultaneously processed, including 20kHz, 28kHz and 40kHz simultaneously processed. More preferably, the ultrasonic power density is 8W / L, the ultrasonic time is 20min, and the ultrasonic frequency is a single frequency of 40kHz.

[0025] Preferably, in step 3 (2), the fermentation is carried out in an incubator at a temperature of 25-36° C. for 6-12 days. More preferably, the fermentation temperature is 32° C. for 9 days.

[0026] Beneficial effects:

[0027] (1) The present invention uses coffee leaves instead of black tea to ferment and prepare coffee leaf kombucha, thereby improving the antioxidant activity of kombucha and giving kombucha a unique flavor.

[0028] (2) The present invention prepares kombucha from coffee leaves, thereby increasing the total phenol content of kombucha. Meanwhile, the caffeine content of kombucha is lower than that of traditional black tea kombucha, thereby achieving substantial technical effects and providing consumers with a functional beverage with low caffeine content, which has broad market application prospects.

[0029] (3) The present invention improves the antioxidant activity and vitamin C content of coffee leaf kombucha through ultrasound-assisted fermentation, achieving unexpected substantial results, while also further improving its functions and health characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The electronic nose analysis results of coffee leaf kombucha from different embodiments.

[0031] Figure 2 The principal component analysis results of sensory evaluation of coffee leaf kombucha from different embodiments are shown. DETAILED DESCRIPTION

[0032] The present invention is explained in more detail by the following examples. The following examples are merely illustrative, and the present invention is not limited to these examples.

[0033] The commercially available black tea and black tea fungus mentioned in this example were purchased from Anqing Mingxun Tuosen Trading Co., Ltd.

[0034] Comparative Example 1:

[0035] Step 1: Pretreatment of coffee leaves:

[0036] (1) Pretreatment: The freshly picked coffee leaves are destemmed, and leaves without insect holes and in complete shape are selected, followed by washing and draining to obtain pretreated coffee leaves;

[0037] (2) Drying: drying the pretreated coffee leaves in an oven at 160° C. for 24 min to obtain dried coffee leaves;

[0038] (3) Grinding: placing the dried coffee leaves in a grinder and grinding them to obtain coffee leaf powder;

[0039] Step 2: Preparation of coffee leaf extract:

[0040] The coffee leaf powder was extracted with boiling water at a solid-liquid ratio of 5 g / L for 10 min, and then filtered through four layers of gauze to obtain the extract.

[0041] Comparative Example 2:

[0042] Step 1: Pretreatment of coffee leaves:

[0043] (1) Pretreatment: The freshly picked coffee leaves are destemmed, and leaves without insect holes and in complete shape are selected, followed by washing and draining to obtain pretreated coffee leaves;

[0044] (2) Drying: drying the pretreated coffee leaves in an oven at 160° C. for 24 min to obtain dried coffee leaves;

[0045] (3) Grinding: placing the dried coffee leaves in a grinder and grinding them to obtain coffee leaf powder;

[0046] Step 2: Preparation of coffee leaf extract:

[0047] The coffee leaf powder was extracted with boiling water at a solid-liquid ratio of 5 g / L for 10 min, and then filtered through four layers of gauze to obtain the extract.

[0048] Step 3: Preparation of Coffee Leaf Kombucha:

[0049] According to the dosage relationship of 50 g / L, sucrose is added to the extract obtained in step 2, and after being sterilized by high pressure (121° C., 20 min) and cooled to room temperature, the pH is adjusted to 4.5 by a sterilized sodium citrate solution to obtain a mixed solution after the pH is adjusted;

[0050] The kombucha fungus was inoculated into the extract at an inoculation amount of 10 g:100 mL; the seed solution was obtained after culturing at 28° C. for 9 days; the seed solution was then inoculated into the mixed solution after the pH was adjusted at a volume ratio of 4:50 (v / v), the bottle mouth was wrapped with a sealing film and sterilized gauze, and the solution was placed in an incubator at 32° C. for culturing for 9 days to obtain coffee leaf kombucha.

[0051] Comparative Example 3:

[0052] The operation is the same as that of Comparative Example 2, except that the coffee leaf powder in step 2 of Comparative Example 2 is replaced by commercially available black tea; and finally black tea kombucha is prepared.

[0053] Embodiment 1:

[0054] Step 1: Pretreatment of coffee leaves:

[0055] (1) Pretreatment: The freshly picked coffee leaves are destemmed, and leaves without insect holes and in complete shape are selected, followed by washing and draining to obtain pretreated coffee leaves;

[0056] (2) Drying: drying the pretreated coffee leaves in an oven at 160° C. for 24 min to obtain dried coffee leaves;

[0057] (3) Grinding: placing the dried coffee leaves in a grinder and grinding them to obtain coffee leaf powder;

[0058] Step 2: Preparation of coffee leaf extract:

[0059] The coffee leaf powder was extracted with boiling water at a solid-liquid ratio of 5 g / L for 10 min, and then filtered through four layers of gauze to obtain the extract.

[0060] Step 3: Preparation of Coffee Leaf Kombucha:

[0061] According to the dosage relationship of 50 g / L, sucrose is added to the extract obtained in step 2, and after being sterilized by high pressure (121° C., 20 min) and cooled to room temperature, the pH is adjusted to 4.5 by a sterilized sodium citrate solution to obtain a mixed solution after the pH is adjusted;

[0062] The red tea fungus was inoculated into the extract at an inoculation amount of 10 g: 100 mL; after culturing at 28°C for 9 days, the seed solution was obtained; then, the seed solution was inoculated into the mixed solution after pH adjustment at a volume ratio of 4:50 to obtain an inoculated mixed solution, the bottle mouth was wrapped with a sealing film and sterilized gauze, and the solution was placed in an incubator and fermented at 28°C for 3 days, 6 days, 9 days, 12 days, and 15 days to obtain coffee leaf kombucha. The antioxidant activity of coffee leaf kombucha was then measured, and the results are shown in Table 1:

[0063] Table 1 Effect of fermentation time on antioxidant activity of coffee leaf kombucha

[0064]

[0065] It can be seen from Table 1 that with the increase of culture time, the antioxidant activity of coffee leaf kombucha reached the highest on the 9th day. If the fermentation time is further extended, the antioxidant activity will gradually decrease. Therefore, the fermentation time is preferably 9 days.

[0066] Embodiment 2:

[0067] The operation was the same as in Example 1, and the fermentation time was determined to be 9 days; the difference was that the material-liquid ratio was adjusted from 5 g / L to 3 g / L, 7 g / L, 9 g / L, and 11 g / L in sequence. The antioxidant activity results of coffee leaf kombucha are shown in Table 2:

[0068] Table 2 Effect of solid-liquid ratio on antioxidant activity of coffee leaf kombucha

[0069]

[0070] It can be seen from Table 2 that with the increase of the solid-liquid ratio, the antioxidant activity of coffee leaf kombucha gradually increases; however, if the solid-liquid ratio is too high, it will affect the flavor and taste of kombucha; and according to the standard food specifications of the US Food and Drug Administration, the amount of tea added to kombucha is generally 4-5g / L; therefore, after comprehensive consideration, a 5g / L solid-liquid ratio was selected for fermentation.

[0071] Embodiment 3:

[0072] The operation was the same as in Example 1, and the fermentation time was determined to be 9 days; the difference was that the amount of sucrose added was adjusted from 50 g / L to 30 g / L, 40 g / L, 60 g / L, and 70 g / L in sequence. The antioxidant activity results of coffee leaf kombucha are shown in Table 3:

[0073] Table 3 Effect of sucrose addition on antioxidant activity of coffee leaf kombucha

[0074]

[0075] It can be seen from Table 3 that when the sucrose addition amount is 50 g / L, the antioxidant activity of coffee leaf kombucha has the highest value, so the addition amount is selected to be 50 g / L.

[0076] Example 4: The operation is the same as that of Example 1, and the fermentation time is determined to be 9 days; the difference is that the volume ratio of the seed liquid to the mixed solution after pH adjustment is adjusted from 4:50 to 3:50, 5:50, 6:50, and 7:50 in sequence. The antioxidant activity results of coffee leaf kombucha are shown in Table 4:

[0077] Table 4 Effect of volume ratio on antioxidant activity of coffee leaf kombucha

[0078]

[0079] It can be seen from Table 4 that with the increase of seed liquid inoculation amount, the antioxidant activity of coffee leaf kombucha showed a trend of increasing and then decreasing. At a volume ratio of 4:50, the antioxidant activity of coffee leaf kombucha reached the highest, so the optimal condition was a volume ratio of 4:50.

[0080] Embodiment 5:

[0081] The operation was the same as in Example 1, and the fermentation time was determined to be 9 days; the difference was that the pH was adjusted from 4.5 to 3.0, 3.5, 4.0, and 5.0 in sequence. The antioxidant activity results of coffee leaf kombucha are shown in Table 5:

[0082] Table 5 Effect of pH on the antioxidant activity of coffee leaf kombucha

[0083]

[0084] It can be seen from Table 5 that as the initial pH increases, the antioxidant activity of coffee leaf kombucha gradually increases, reaches the highest when the initial pH is 4.5, and then begins to decrease. Therefore, the initial pH of coffee leaf kombucha was adjusted to 4.5 for fermentation.

[0085] Embodiment 6:

[0086] The operation was the same as in Example 1, and the fermentation time was determined to be 9 days; the difference was that the fermentation temperature was adjusted from 28°C to 20°C, 24°C, 32°C, and 36°C in sequence. The antioxidant activity results of coffee leaf kombucha are shown in Table 6:

[0087] Table 6 Effect of fermentation temperature on antioxidant activity of coffee leaf kombucha

[0088]

[0089] It can be seen from Table 6 that with the increase of fermentation temperature, the antioxidant activity of coffee leaf kombucha showed a trend of increasing and then decreasing, reaching a peak value when the fermentation temperature was 32°C. Therefore, the fermentation temperature was selected as 32°C.

[0090] Through the single factor test of Examples 1-6, it was found that the optimal conditions were: 5 g / L solid-liquid ratio, 50 g / L sucrose addition, volume ratio 4:50, pH 4.5, fermentation temperature 32°C, and fermentation time 9 days. The prepared coffee leaf kombucha had the highest antioxidant activity, and subsequent ultrasonic tests were carried out on this basis.

[0091] Embodiment 7:

[0092] Step 1: Pretreatment of coffee leaves:

[0093] (1) Pretreatment: The freshly picked coffee leaves are destemmed, and leaves without insect holes and in complete shape are selected, followed by washing and draining to obtain pretreated coffee leaves;

[0094] (2) Drying: drying the pretreated coffee leaves in an oven at 160° C. for 24 min to obtain dried coffee leaves;

[0095] (3) Grinding: placing the dried coffee leaves in a grinder and grinding them to obtain coffee leaf powder;

[0096] Step 2: Preparation of coffee leaf extract:

[0097] The coffee leaf powder was extracted with boiling water at a solid-liquid ratio of 5 g / L for 10 min, and then filtered through four layers of gauze to obtain the extract.

[0098] Step 3: Preparation of inoculation mixture:

[0099] According to the dosage relationship of 50 g / L, sucrose is added to the extract obtained in step 2, and after being sterilized by high pressure (121° C., 20 min) and cooled to room temperature, the pH is adjusted to 4.5 by a sterilized sodium citrate solution to obtain a mixed solution after the pH is adjusted;

[0100] The kombucha fungus was inoculated into the extract at an inoculation amount of 10 g:100 mL; the seed solution was obtained after culturing at 28° C. for 9 days; and the seed solution was then inoculated into the mixed solution after the pH was adjusted at a volume ratio of 4:50 to obtain an inoculated mixed solution.

[0101] Step 4: Ultrasonic-assisted fermentation to prepare kombucha:

[0102] After obtaining the inoculated mixed solution, ultrasonic treatment was directly performed (recorded as 0 day), wherein the ultrasonic power density was 8 W / L, the ultrasonic frequency was 28 kHz, and the ultrasonic time was 5 min, 15 min, 30 min, 45 min, and 60 min, respectively, and then fermented in an incubator at 32° C. for 9 days to obtain coffee leaf kombucha;

[0103] The antioxidant activity of coffee leaf kombucha was determined and the results are shown in Table 7.

[0104] Table 7 Effect of ultrasound time on antioxidant activity of coffee leaf kombucha

[0105]

[0106] As can be seen from Table 7, with the increase of ultrasonic time, the antioxidant activity of coffee leaf kombucha showed a trend of first increasing and then decreasing; when the ultrasonic time was 15 minutes, coffee leaf kombucha achieved good antioxidant activity.

[0107] Embodiment 8:

[0108] The operation was the same as in Example 7, and the ultrasonic time was determined to be 15 min; the difference was that the power density was adjusted from 8 W / L to 4 W / L, 13 W / L, 21 W / L, 29 W / L, and 38 W / L in sequence.

[0109] The results of the antioxidant activity of coffee leaf kombucha are shown in Table 8:

[0110] Table 8 Effect of power density on antioxidant activity of coffee leaf kombucha

[0111]

[0112] As can be seen from Table 8, the coffee leaf kombucha under the 13 W / L power density treatment had the highest antioxidant activity; secondly, under the 13 W / L power density treatment, the coffee leaf kombucha had a higher antioxidant activity.

[0113] Embodiment 9:

[0114] The operation is the same as that in Example 7, the ultrasonic time is determined to be 15 min, and the power density is determined to be 13 W / L; the difference is that the ultrasonic frequency is adjusted from 28 kHz to 20 kHz, 40 kHz, 20 / 28 kHz, 20 / 40 kHz, 28 / 40 kHz, and 20 / 28 / 40 kHz in sequence.

[0115] The results of the antioxidant activity of coffee leaf kombucha are shown in Table 9:

[0116] Table 9 Effect of ultrasonic frequency on antioxidant activity of coffee leaf kombucha

[0117]

[0118] It can be seen from Table 9 that the antioxidant activity of coffee leaf kombucha reached the highest when the ultrasonic frequency was 40 kHz, and other frequencies had no significant effect on the antioxidant activity of coffee leaf kombucha.

[0119] Embodiment 10:

[0120] The operation was the same as in Example 7, with an ultrasonic time of 15 min, a power density of 13 W / L, and an ultrasonic frequency of 40 kHz; the difference was that the period of ultrasonic application was adjusted from direct ultrasonic treatment (0 day) to 1 day, 3 days, 5 days, and 7 days. The antioxidant activity results of coffee leaf kombucha are shown in Table 10:

[0121] Table 10 Effect of ultrasound period on antioxidant activity of coffee leaf kombucha

[0122]

[0123] As can be seen from Table 10, when directly sonicated (day 0), the coffee leaf kombucha obtained had the highest antioxidant activity.

[0124] Embodiment 11:

[0125] The operation was the same as in Example 7, except that the ultrasonic time was determined to be 15 min, the power density was determined to be 13 W / L, the power frequency was determined to be 40 kHz, and the coffee leaf kombucha was obtained during direct ultrasonication (0 day).

[0126] Embodiment 12:

[0127] On the basis of the above single-factor test results, a two-factor four-level test was conducted on ultrasound time and power density to further explore the synergistic effect of the two.

[0128] Step 1, step 2 and step 3 are the same as those in Example 7;

[0129] Step 4: Ultrasonic-assisted fermentation to prepare kombucha:

[0130] The inoculated mixed solution in step 3 was ultrasonicated under the combined conditions of ultrasonic frequency 40kHz, ultrasonic time and power density as shown in Table 11, and then fermented in a 32°C incubator for 9 days to measure the antioxidant activity of the fermentation liquid. The results of the two-factor four-level test are shown in Table 11:

[0131] Table 11 Two-factor four-level experimental design and results

[0132]

[0133] Note: CTL refers to the experimental control group without ultrasonic treatment.

[0134] Minitab was used to perform response optimization prediction, and the optimal ultrasound-assisted fermentation process was determined to be an ultrasound time of 20 min and a power density of 8 W / L. Kombucha coffee leaves prepared under the optimal conditions were used as the final product of Example 12; under these conditions, the fitted value of ABTS scavenging capacity was 6.54 μmol Trolox / mL, which was close to the experimental value of 6.55±0.15 μmol Trolox / mL, and the composite desirability was 0.87.

[0135] The total phenol content and ABTS free radical scavenging ability as well as caffeine and vitamin C content of the coffee leaf extract and kombucha produced by the production processes of Examples 11 and 12 of the present invention and Comparative Examples 1, 2 and 3 are shown in Table 12.

[0136] Table 12 Determination of total phenol content, antioxidant activity, caffeine content and vitamin C content

[0137]

[0138] The total phenol content and ABTS of Comparative Example 1, Comparative Example 2, Example 11 and Example 12 show the same trend, and the values ​​increase successively, which indicates that fermentation and ultrasound can increase the antioxidant activity of coffee leaf extract. At the same time, the antioxidant activity of Example 12 is 27.18% higher than that of Example 11. In addition, the vitamin C content of Example 12 is significantly increased relative to that of Comparative Example 1, Comparative Example 2 and Example 11, and the caffeine content of Examples 11 and 12 is significantly lower than that of Comparative Example 3 (black tea kombucha). The total phenol content, ABTS free radical scavenging ability and vitamin content of Comparative Example 2, Example 11 and Example 12 are all higher than those of Comparative Example 3, indicating that coffee leaf kombucha produced by fermentation with coffee leaves as the matrix has higher biological activity than black tea kombucha produced with black tea as the matrix, and has achieved substantial technical effects.

[0139] In addition, the aroma characteristics of the products produced by the production processes of Example 12 of the present invention and Comparative Examples 1, 2, and 3 were analyzed using an electronic nose. Figure 1 . Figure 1 The volatile compounds detected by the ten probes are: W1C (aromatic compounds), W5S (nitrogen oxides), W3C (ammonia, aromatic molecules), W6S (hydrides), W5C (olefins, aromatics, polar molecules), W1S (short-chain alkanes), W1W (inorganic sulfides), W2S (alcohols, aldehydes and ketones, some aromatic compounds), W2W (aromatic compounds, organic compounds of sulfur) and W3S (long-chain alkanes and aliphatic hydrocarbons). Electronic nose analysis found that the W1W (inorganic sulfides) and W5S (nitrogen oxides) of Comparative Example 1 were significantly lower than those of Comparative Example 2 and Example 1, indicating that proper fermentation can enhance the volatile aroma substances of coffee leaf kombucha. The products produced by the production processes of Example 12 of the present invention and Comparative Examples 1 and 2 were subjected to sensory evaluation and compared with commercially available black tea kombucha. The sensory evaluation score table is shown in Table 13. The sensory evaluation results are shown in Table 13. Figure 2 shown.

[0140] Comparison of the four samples revealed that Comparative Example 1 was distributed in the second and third quadrants, with tea aroma and a slight bitterness; Example 12 and Comparative Example 2 were distributed in the first quadrant, and the commercially available black tea kombucha was distributed in the fourth quadrant. Among them, the taste of Comparative Example 2 was sweet and sour; and the flavor of Example 12 was richer and had a sense of hierarchy. Therefore, the coffee leaf kombucha prepared by ultrasound assistance in the present invention not only had a rich flavor, but also had higher antioxidant activity.

[0141] Table 13 Sensory evaluation score table

[0142]

[0143] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; therefore, although this specification has described the present invention in detail with reference to the above embodiments, a person skilled in the art should understand that the present invention can still be modified or replaced by equivalents; and all technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing coffee leaf kombucha with high antioxidant activity assisted by ultrasound, characterized in that: The following steps are involved: Step 1: Pretreatment of coffee leaves: (1) Pretreatment: The freshly picked coffee leaves are destemmed, and leaves without insect holes and in complete shape are selected, followed by washing and draining to obtain pretreated coffee leaves; (2) Drying: drying the pretreated coffee leaves to obtain dried coffee leaves; (3) crushing: crushing the dried coffee leaves to obtain coffee leaf powder; Step 2: Preparation of inoculation mixture: (1) Preparation of coffee leaf extract: adding the coffee leaf powder obtained in step 1 (3) into boiling water, extracting with boiling water, and collecting the filtrate through gauze to obtain a coffee leaf extract; (2) mixing the coffee leaf extract and sucrose and sterilizing them under high pressure, cooling the sterilized mixed solution to room temperature, and then adjusting the pH of the mixed solution to obtain a mixed solution after the pH is adjusted; (3) inoculating kombucha into the coffee leaf extract obtained in step 2 (1) to obtain a seed solution after culturing; and then inoculating the seed solution into the mixed solution after adjusting the pH in step 2 (2) to obtain an inoculated mixed solution; Step 3: Ultrasonic-assisted preparation of coffee leaf kombucha: (1) Ultrasonic treatment: ultrasonically treating the inoculated mixed solution in step 2 (3) to obtain an ultrasonically treated inoculated mixed solution; (2) fermenting the inoculated mixed solution treated with ultrasound in step 3 (1) to obtain coffee leaf kombucha with high antioxidant activity.

2. The method for preparing an ultrasound-assisted coffee leaf kombucha with high antioxidant activity according to claim 1, characterized in that: The drying temperature in step 1 (2) is 160° C. and the drying time is 20-25 min.

3. The method for preparing an ultrasound-assisted coffee leaf kombucha with high antioxidant activity according to claim 1, characterized in that: In step 2 (1), the amount of coffee leaf powder and boiling water is 3-11 g:1 L; and the boiling water extraction time is 10-15 min.

4. The method for preparing an ultrasound-assisted coffee leaf kombucha with high antioxidant activity according to claim 1, characterized in that: In step 2 (2), the dosage of sucrose and coffee leaf extract is 30-70 g:1 L; the pH of the mixed solution is adjusted to 3.0-5.0 using sterilized sodium citrate or sodium bicarbonate solution; the sterilization conditions are 121° C. and 15-20 min.

5. The method for preparing coffee leaf kombucha with high antioxidant activity assisted by ultrasound according to claim 1, characterized in that: In step 2 (3), the inoculation amount of kombucha inoculated into the coffee leaf extract is 10 g:100 mL; the culture temperature is 20-36° C., and the time is 3-15 days; the volume ratio of the seed solution to the mixed solution after adjusting the pH is 3:50-7:

50.

6. The method for preparing coffee leaf kombucha with high antioxidant activity assisted by ultrasound according to claim 1, characterized in that: The ultrasonic treatment in step 3 (1) is performed after the inoculated mixed solution has been statically cultured for 0-7 days, wherein 0 days refers to the direct ultrasonic treatment of the inoculated mixed solution after obtaining it, and 1 day refers to the ultrasonic treatment of the inoculated mixed solution after static culture for 24 hours, and so on for 2-7 days; the static culture temperature is 32°C.

7. The method for preparing an ultrasound-assisted coffee leaf kombucha with high antioxidant activity according to claim 1, characterized in that: In step three (1), the ultrasonic power density is 4-38W / L; the ultrasonic time is 5-60min; the ultrasonic frequency is single frequency, dual frequency or triple frequency; the single frequency is 20-40kHz; the dual frequency is two frequencies processed simultaneously, including 20kHz and 28kHz, 20kHz and 40kHz, or 28kHz and 40kHz; the triple frequency is three frequencies processed simultaneously, including 20kHz, 28kHz and 40kHz.

8. The method for preparing coffee leaf kombucha with high antioxidant activity assisted by ultrasound according to claim 7, characterized in that: The ultrasonic power density was 8W / L, the ultrasonic time was 20min, and the ultrasonic frequency was single frequency 40kHz.

9. The method for preparing coffee leaf kombucha with high antioxidant activity assisted by ultrasound according to claim 1, characterized in that: In step 3 (2), the fermentation is carried out in an incubator at a temperature of 25-36° C. and a fermentation time of 6-12 days.

10. The method for preparing coffee leaf kombucha with high antioxidant activity assisted by ultrasound according to claim 9, characterized in that: The fermentation temperature was 32°C and the fermentation time was 9 days.

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