Red date and Chinese wolfberry fruit compound fruit vinegar and fermentation process thereof

Abstract

The invention relates to the technical field of beverage fermentation production, in particular to red date and fructus lycii compound fruit vinegar and a fermentation process thereof. The preparation method comprises the following steps: weighing raw materials by mass, and then pretreating the raw materials to obtain mixed slurry; adding an enzyme preparation into the mixed pulp, and carrying out alcoholic fermentation treatment and acetic fermentation treatment to obtain an acetic acid solution; adding honey, table salt, lactic acid and malic acid into the acetic acid solution, and sealing and ageing in a dark place to generate a stock solution; suspended impurities in the stock solution are removed, and then pasteurization is performed to obtain the compound fruit vinegar. According to the method, acidity loss space is reserved through excessive fermentation, acid substance volatilization in the after-ripening stage and the sterilization stage is counteracted, lactic acid and malic acid are compounded to form a wide-area pH buffer system, then honey and salt are added, fructose and glucose in the honey enhance osmotic pressure, infectious microbe breeding is inhibited, and the taste is improved. The salt stabilizes the dissociation state of acid substances through an ion effect, so that the acidity of the prepared compound fruit vinegar beverage reaches the standard.

Description

Technical Field

[0001] The present invention relates to the technical field of beverage fermentation production, and specifically, to a red date and wolfberry compound fruit vinegar and its fermentation process. Background Art

[0002] Fruit vinegar beverage is a healthy drink brewed by modern biotechnology with fruits as the main raw material. The fruit vinegar beverage not only retains the nutritional components of fruits, but also has the sour taste and health care function of vinegar. It is a new type of drink integrating functions such as nutrition, health care, and diet therapy.

[0003] For example, CN106465816A involves a production process of fruit vinegar beverage. Its special feature is that adding Oenococcus oeni reduces the acidity of fruit juice during fermentation, greatly reducing the bitter taste, retaining the natural fruit aroma to the greatest extent, with a long-lasting fruit wine aroma, and improving the quality of raw materials. The problem is that in step two of this production process, "pumping the obtained fruit juice into a normal-temperature alcohol fermentation tank, adding 0.5 - 0.7 kg / t of sulfurous acid aqueous solution for sterilization, acid increase, and clarification, adding 0.15 kg / t of purified yeast strain; then adding 100 - 200 U / L of extracellular β-glucosidase and 300 - 400 U / L of extracellular naringinase, adding granulated sugar in batches, adjusting the total sugar content of the fruit juice to 150 - 200 g / L, and stirring evenly". In this step, using sulfurous acid aqueous solution for sterilization, its residue will inhibit the activities of subsequent fermentation strains such as yeast and acetic acid bacteria, resulting in reduced fermentation efficiency or abnormal metabolites, incomplete fermentation, large fluctuations in acidity indicators, and the acidity of the finished fruit vinegar beverage not meeting the standard. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that the acidity of the finished fruit vinegar beverage does not meet the standard due to incomplete fermentation in the existing fruit vinegar production process.

[0005] The purpose of the present invention is to provide a red date and wolfberry compound fruit vinegar and its fermentation process, which can produce a compound fruit vinegar beverage with the acidity of the beverage meeting the standard by over-fermenting to reserve space for acidity loss and offsetting the volatilization of acid substances in the post-ripening and sterilization stages.

[0006] To achieve the above purpose, one of the purposes of the present invention is to provide a red date and wolfberry compound fruit vinegar, including raw materials with the following mass percentages:

[0007] Red dates 20 - 22%, wolfberries 5 - 6%, fructose syrup 8 - 10%, enzyme preparation 0.03 - 0.05%, honey 1 - 2%, table salt 0.08 - 0.12%, lactic acid 0.05 - 0.10%, malic acid 0.03 - 0.06%, and the balance is drinking water.

[0008] As a further improvement of the present technical solution, the enzyme preparation includes a pectinase preparation and a cellulase preparation, and the mass ratio of the pectinase preparation to the cellulase preparation is 3:2.

[0009] The second object of the present invention is to further provide a fermentation process for producing the above-mentioned red date and wolfberry compound fruit vinegar, which includes the following steps:

[0010] Step S1: Weigh the raw materials according to the mass ratio, and first perform raw material pretreatment on red dates and wolfberries respectively to obtain red date pulp and wolfberry pulp;

[0011] Then mix the red date pulp and the wolfberry pulp, and then add fructose syrup to adjust the sugar content to produce a mixed pulp;

[0012] Step S2: Add the enzyme preparation to the mixed pulp and enzymatically hydrolyze it at 50°C for 2 hours to obtain an enzymolysis solution;

[0013] Subsequently, perform alcohol fermentation on the enzymolysis solution to obtain an alcohol fermentation solution, and then perform acetic acid fermentation on the alcohol fermentation solution to obtain an acetic acid solution;

[0014] Step S3: Add honey, salt, lactic acid and malic acid to the acetic acid solution, and stir for 30 minutes until fully mixed, then seal and store the acetic acid solution in the dark for 10 - 15 days to produce a stock solution;

[0015] Coarsely filter the stock solution to remove large particle precipitate impurities;

[0016] Step S4: First remove the suspended impurities in the stock solution by diatomaceous earth filtration, then intercept bacteria and macromolecular substances through an ultrafiltration membrane, and then perform pasteurization on the stock solution at 70°C for 15 minutes to obtain the compound fruit vinegar;

[0017] Sterilize and can the compound fruit vinegar.

[0018] As a further improvement of the present technical solution, in the step S1, the raw material pretreatment is to wash the red dates, then pre-cook them at 80°C for 10 minutes, then beat them into pulp, remove the cores and pass through a 60-mesh sieve to obtain red date pulp;

[0019] Soak the wolfberries in warm water at 40°C for 4 hours, then beat them into pulp and remove the residue by centrifugal filtration to obtain wolfberry pulp.

[0020] As a further improvement of the present technical solution, in the step S2, the pH value of the mixed pulp during enzymatic hydrolysis is 3.8 - 4.2.

[0021] As a further improvement of the technical solution, in step S2, the alcohol fermentation treatment is to add wine yeast into a solution containing 2% sucrose at 35°C, let it stand for 30 minutes to produce an activated bacterial solution, add the activated bacterial solution into the enzymolysis solution, and the volume of the added activated bacterial solution is 0.8% of the volume of the enzymolysis solution, and perform anaerobic fermentation treatment under closed conditions at 28±1°C;

[0022] During fermentation, the enzymolysis solution is detected in real time. When the residual sugar in the enzymolysis solution ≤ 2°Bx and the alcohol content ≥ 8% vol, the enzymolysis solution is centrifuged to remove residues, removing yeast mud and fruit residues to obtain an alcohol fermentation broth.

[0023] As a further improvement of the technical solution, in step S2, the acetic acid fermentation treatment is that the alcohol fermentation broth is inoculated with acetic acid bacteria and oxygen is introduced to oxidize ethanol in the alcohol fermentation broth into acetic acid until the acidity ≥ 50 g / L and the alcohol residue ≤ 0.3% vol to produce acetic acid solution.

[0024] As a further improvement of the technical solution, the temperature during the acetic acid fermentation treatment is 32 - 34°C.

[0025] As a further improvement of the technical solution, in step S4, the temperature during sealed light - proof aging is 10 - 15°C.

[0026] As a further improvement of the technical solution, in step S4, the filtration accuracy of the ultrafiltration membrane is 0.20 - 0.30 μm.

[0027] In the present invention, through the complete conversion of sugars by alcohol fermentation and the directional oxidation control of acetic acid fermentation, the efficient conversion of fermentation substrates and the long - term stability of acidity are achieved, so as to be applicable to the industrial production of high - quality red date and wolfberry compound fruit vinegar, with both efficiency and quality controllability.

[0028] Compared with the prior art, the beneficial effects of the present invention:

[0029] In the red date and wolfberry compound fruit vinegar and its fermentation process, with the residual sugar ≤ 2°Bx and the alcohol content ≥ 8% vol as the termination standard, it is ensured that sugars are completely converted into alcohol, avoiding the interference of residual sugars on subsequent acetic acid fermentation; through excessive fermentation, that is, exceeding the acidity requirement of the finished product, a space for acidity loss is reserved to offset the volatilization of acid substances in the after - ripening and sterilization stages, and a wide - range pH buffer system is formed by compounding lactic acid and malic acid to reduce the acidity fluctuation during the storage period. Then, honey and salt are added. Fructose and glucose in honey enhance the osmotic pressure and inhibit the growth of miscellaneous bacteria, and salt stabilizes the dissociation state of acid substances through ionic effects, thereby ensuring that the acidity of the prepared compound fruit vinegar beverage meets the standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] One of the purposes of the present invention is to provide a red date and wolfberry compound fruit vinegar, which comprises raw materials with the following mass ratios:

[0033] Red dates 20-22%, wolfberries 5-6%, fructose syrup 8-10%, enzyme preparation 0.03-0.05%, honey 1-2%, salt 0.08-0.12%, lactic acid 0.05-0.10%, malic acid 0.03-0.06%, and the balance is drinking water.

[0034] Furthermore, the enzyme preparation includes pectinase preparation and cellulase preparation, and the mass ratio of the pectinase preparation to the cellulase preparation is 3:2, which is used to improve the juice yield and clarity.

[0035] Please refer to Figure 1 As shown, another purpose of the present invention is to provide a fermentation process for producing the above-mentioned red date and wolfberry compound fruit vinegar, which comprises the following steps:

[0036] Step S1: Weigh 20-22% of red dates, 5-6% of wolfberries, 8-10% of fructose syrup, 0.03-0.05% of enzyme preparation, 1-2% of honey, 0.08-0.12% of salt, 0.05-0.10% of lactic acid, 0.03-0.06% of malic acid according to the mass ratio, and the balance is drinking water. First, pre-treat the red dates and wolfberries respectively to obtain red date pulp and wolfberry pulp. Specifically, the raw material pre-treatment is to wash the red dates, then pre-cook them at 80°C for 10 min (to soften pectin), then beat them into pulp, remove the cores and pass through a 60-mesh sieve to obtain red date pulp.

[0037] Soak the wolfberries in warm water at 40°C for 4 h, then beat them into pulp and remove the residue by centrifugal filtration to obtain wolfberry pulp.

[0038] Then mix the red date pulp and wolfberry pulp, and then add fructose syrup to adjust the sugar content to produce a mixed pulp.

[0039] Step S2: Add the enzyme preparation to the mixed pulp and enzymatically hydrolyze it at 50°C for 2 h to obtain an enzymatic hydrolysate. When enzymatically hydrolyzing, the pH value of the mixed pulp is 3.8-4.2.

[0040] Subsequently, the enzymolysis solution is subjected to alcohol fermentation treatment to obtain an alcohol fermentation solution. Specifically, the alcohol fermentation treatment is to add wine yeast to a solution containing 2% sucrose at 35°C (yeast:solution = 1:10), and let it stand for 30 min to produce an activated bacterial solution (the viable bacteria count after activation ≥ 1×10^8 CFU / mL). Then add the activated bacterial solution to the enzymolysis solution, and the volume of the added activated bacterial solution is 0.8% of the volume of the enzymolysis solution, and carry out anaerobic fermentation treatment under sealed conditions at 28 ± 1°C.

[0041] During fermentation, the enzymolysis solution is detected in real time. When the residual sugar in the enzymolysis solution ≤ 2°Bx and the alcohol content ≥ 8% vol, the enzymolysis solution is centrifuged to remove residues (4000 r / min, centrifugation for 10 min) to remove yeast mud and fruit residues (reduce miscellaneous bacteria and autolytic products) to obtain an alcohol fermentation solution.

[0042] Then, the alcohol fermentation solution is subjected to acetic acid fermentation treatment to obtain an acetic acid solution. Among them, the acetic acid fermentation treatment is carried out at 32 - 34°C. The alcohol fermentation solution is inoculated with acetic acid bacteria and an appropriate amount of oxygen is introduced to oxidize ethanol in the alcohol fermentation solution into acetic acid until the acidity ≥ 50 g / L and the alcohol residue ≤ 0.3% vol to produce an acetic acid solution, ensuring that the acidity is stably up to standard.

[0043] Step S3: Add honey, salt, lactic acid, and malic acid to the acetic acid solution, and stir for 30 min until fully mixed. Then, seal the acetic acid solution and age it in the dark for 10 - 15 days to produce a stock solution. The temperature during aging in the dark is 10 - 15°C.

[0044] The stock solution is roughly filtered to remove large - particle precipitate impurities.

[0045] Step S4: First, remove suspended impurities in the stock solution through diatomaceous earth filtration to achieve preliminary clarification, then intercept bacteria and macromolecular substances through an ultrafiltration membrane to complete fine sterilization, and then carry out pasteurization at 70°C for 15 min to kill residual microorganisms and retain flavor components to ensure the safety and stability of the product, and obtain a compound fruit vinegar. The filtration accuracy of the ultrafiltration membrane is 0.20 - 0.30 μm.

[0046] The compound fruit vinegar is sterilized and canned.

[0047] The following further illustrates a red - date and wolfberry compound fruit vinegar and its fermentation process provided by the present invention through specific examples.

[0048] Example 1

[0049] Step S1: Weigh 20% of red dates, 6% of wolfberries, 8% of fructose syrup, 0.05% of enzyme preparation, 1% of honey, 0.12% of salt, 0.05% of lactic acid, and 0.06% of malic acid according to the mass ratio. The balance is drinking water. First, pre-treat the red dates and wolfberries respectively to obtain red date pulp and wolfberry pulp. Specifically, the raw material pre-treatment is to wash the red dates, then pre-cook them at 80 °C for 10 min, then beat the pulp to remove the pits and pass through a 60-mesh sieve to obtain red date pulp.

[0050] Soak the wolfberries in warm water at 40 °C for 4 h, then beat the pulp and remove the residue by centrifugal filtration to obtain wolfberry pulp.

[0051] Then mix the red date pulp and wolfberry pulp, and then add fructose syrup to adjust the sugar content to produce a mixed pulp.

[0052] Step S2: Add the enzyme preparation to the mixed pulp and enzymatically hydrolyze it at 50 °C for 2 h to obtain an enzymatic hydrolysate. The pH value of the mixed pulp during enzymatic hydrolysis is 3.8.

[0053] Subsequently, perform alcohol fermentation treatment on the enzymatic hydrolysate to obtain an alcohol fermentation broth. Specifically, the alcohol fermentation treatment is to add wine yeast to a solution containing 2% sucrose at 35 °C (yeast:solution = 1:10), let it stand for 30 min to produce an activated bacterial solution, add the activated bacterial solution to the enzymatic hydrolysate, and the volume of the added activated bacterial solution is 0.8% of the volume of the enzymatic hydrolysate, and perform anaerobic fermentation treatment in a sealed manner at 28 ± 1 °C.

[0054] During fermentation, the enzymatic hydrolysate is detected in real time. When the residual sugar in the enzymatic hydrolysate ≤ 2 °Bx and the alcohol content ≥ 8% vol, the enzymatic hydrolysate is centrifuged to remove the residue (4000 r / min, centrifuge for 10 min) to remove yeast mud and fruit residues to obtain an alcohol fermentation broth.

[0055] Then perform acetic acid fermentation treatment on the alcohol fermentation broth to obtain acetic acid solution. Among them, the acetic acid fermentation treatment is to inoculate acetic acid bacteria and introduce appropriate oxygen into the alcohol fermentation broth at 34 °C, oxidize ethanol in the alcohol fermentation broth to acetic acid until the acidity ≥ 50 g / L and the alcohol residue ≤ 0.3% vol to produce acetic acid solution.

[0056] Step S3: Add honey, salt, lactic acid, and malic acid to the acetic acid solution, and stir for 30 min until fully mixed, then seal and age the acetic acid solution in the dark for 10 days to produce a stock solution. The temperature during sealing and aging in the dark is 15 °C.

[0057] Coarsely filter the stock solution to remove large particle precipitate impurities.

[0058] Step S4: First, remove suspended impurities in the stock solution by diatomaceous earth filtration, then intercept bacteria and macromolecular substances through an ultrafiltration membrane, and then perform pasteurization at 70 °C for 15 min to obtain compound fruit vinegar. The filtration accuracy of the ultrafiltration membrane is 0.20 μm.

[0059] Sterilize and can the compound fruit vinegar.

[0060] Example 2

[0061] Step S1: Weigh 20% red dates, 5% wolfberries, 10% fructose syrup, 0.04% enzyme preparation, 2% honey, 0.10% salt, 0.08% lactic acid, 0.05% malic acid according to the mass ratio, and the balance is drinking water. First, pretreat the raw materials of red dates and wolfberries respectively to obtain red date pulp and wolfberry pulp. Specifically, the raw material pretreatment is to wash the red dates, then pre-cook them at 80°C for 10 min, then beat them into pulp, remove the pits and pass through a 60-mesh sieve to obtain red date pulp.

[0062] Soak the wolfberries in warm water at 40°C for 4 h, then beat them into pulp and remove the residue by centrifugal filtration to obtain wolfberry pulp.

[0063] Then mix the red date pulp and wolfberry pulp, and then add fructose syrup to adjust the sugar content to produce a mixed pulp.

[0064] Step S2: Add the enzyme preparation to the mixed pulp and enzymatically hydrolyze it at 50°C for 2 h to obtain an enzymatic hydrolysate. When enzymatically hydrolyzing, the pH value of the mixed pulp is 4.0.

[0065] Subsequently, perform alcoholic fermentation on the enzymatic hydrolysate to obtain an alcoholic fermentation broth. Specifically, the alcoholic fermentation treatment is to add wine yeast to a solution containing 2% sucrose at 35°C (yeast:solution = 1:10), let it stand for 30 min to produce an activated bacterial solution, add the activated bacterial solution to the enzymatic hydrolysate, and the volume of the added activated bacterial solution is 0.8% of the volume of the enzymatic hydrolysate, and perform anaerobic fermentation treatment under airtight conditions at 28±1°C.

[0066] During fermentation, the enzymatic hydrolysate is detected in real time. When the residual sugar in the enzymatic hydrolysate ≤ 2°Bx and the alcohol content ≥ 8% vol, centrifuge the enzymatic hydrolysate to remove the residue (4000 r / min, centrifuge for 10 min) to remove the yeast mud and fruit residue to obtain an alcoholic fermentation broth.

[0067] Then perform acetic acid fermentation on the alcoholic fermentation broth to obtain an acetic acid solution. Among them, the acetic acid fermentation treatment is to inoculate acetic acid bacteria and introduce appropriate oxygen into the alcoholic fermentation broth at 33°C, oxidize ethanol in the alcoholic fermentation broth to acetic acid until the acidity ≥ 50 g / L and the alcohol residue ≤ 0.3% vol to produce an acetic acid solution.

[0068] Step S3: Add honey, salt, lactic acid and malic acid to the acetic acid solution, and stir for 30 min until fully mixed, then seal the acetic acid solution and age it in the dark for 12 days to produce a stock solution. The temperature during aging in the dark is 12°C.

[0069] Coarsely filter the stock solution to remove large particle precipitate impurities.

[0070] Step S4: First, remove the suspended impurities in the stock solution by diatomite filtration, then retain bacteria and macromolecular substances through an ultrafiltration membrane, and then perform pasteurization at 70 °C for 15 min to obtain the compound fruit vinegar. The filtration accuracy of the ultrafiltration membrane is 0.22 μm.

[0071] Sterilize and can the compound fruit vinegar.

[0072] Example 3

[0073] Step S1: Weigh 22% red dates, 5% wolfberries, 10% fructose syrup, 0.03% enzyme preparation, 2% honey, 0.08% salt, 0.10% lactic acid, and 0.03% malic acid by mass ratio, and the balance is drinking water. First, pre-treat the raw materials of red dates and wolfberries respectively to obtain red date pulp and wolfberry pulp. Specifically, the raw material pre-treatment is to wash the red dates, then pre-cook them at 80 °C for 10 min, then beat them into pulp, remove the pits, and pass through a 60-mesh sieve to obtain red date pulp.

[0074] Soak the wolfberries in warm water at 40 °C for 4 h, then beat them into pulp and remove the residue by centrifugal filtration to obtain wolfberry pulp.

[0075] Then mix the red date pulp and wolfberry pulp, and then add fructose syrup to adjust the sugar content to produce a mixed pulp.

[0076] Step S2: Add the enzyme preparation to the mixed pulp and enzymatically hydrolyze it at 50 °C for 2 h to obtain an enzymatic hydrolysate. When enzymatically hydrolyzing, the pH value of the mixed pulp is 4.2.

[0077] Subsequently, perform alcoholic fermentation on the enzymatic hydrolysate to obtain an alcoholic fermentation broth. Specifically, the alcoholic fermentation treatment is to add wine yeast to a solution containing 2% sucrose at 35 °C (yeast:solution = 1:10), let it stand for 30 min to produce an activated bacterial solution, add the activated bacterial solution to the enzymatic hydrolysate, and the volume of the added activated bacterial solution is 0.8% of the volume of the enzymatic hydrolysate, and perform anaerobic fermentation treatment under closed conditions at 28 ± 1 °C.

[0078] During fermentation, the enzymatic hydrolysate is detected in real time. When the residual sugar in the enzymatic hydrolysate ≤ 2 °Bx and the alcohol content ≥ 8% vol, centrifuge and remove the residue (4000 r / min, centrifuge for 10 min) from the enzymatic hydrolysate to remove yeast mud and fruit residues to obtain an alcoholic fermentation broth.

[0079] Then perform acetic acid fermentation on the alcoholic fermentation broth to obtain an acetic acid solution. Among them, the acetic acid fermentation treatment is to inoculate acetic acid bacteria and introduce appropriate oxygen into the alcoholic fermentation broth at 32 °C, oxidize ethanol in the alcoholic fermentation broth to acetic acid until the acidity ≥ 50 g / L and the alcohol residue ≤ 0.3% vol to produce an acetic acid solution.

[0080] Step S3: Add honey, salt, lactic acid, and malic acid to the acetic acid solution, and stir for 30 min until fully mixed. Then, seal the acetic acid solution and age it in the dark for 15 days to produce the stock solution. The temperature during aging in the dark is 10°C.

[0081] Coarsely filter the stock solution to remove large particle sediment impurities.

[0082] Step S4: First, remove suspended impurities in the stock solution by diatomite filtration, then intercept bacteria and macromolecular substances through an ultrafiltration membrane, and then perform pasteurization at 70°C for 15 min to obtain the compound fruit vinegar. The filtration accuracy of the ultrafiltration membrane is 0.30 μm.

[0083] Sterilize and can the compound fruit vinegar.

[0084] According to Examples 1-3, prepare the compound fruit vinegar, and then use the acid-base titration method to detect the total acid content of the compound fruit vinegar. The principle is to use phenolphthalein as an indicator and titrate the total acid (calculated as acetic acid) in the sample with a standard sodium hydroxide solution. Calculate the total acid content based on the volume of NaOH consumed. Specifically, take 10 mL of the compound fruit vinegar sample, dilute it to 100 mL with distilled water, then filter to remove suspended matter to obtain the dilution. Take 25 mL of the dilution in a conical flask, add 2-3 drops of phenolphthalein indicator, and then titrate with 0.1 mol / L standard sodium hydroxide solution until the solution turns slightly red (does not fade within 30 seconds). The formula for calculating the total acid is as follows:

[0085]

[0086] In the formula, C 氢氧化钠 is the concentration of the sodium hydroxide solution (mol / L), V 氢氧化钠 is the volume of sodium hydroxide consumed in the titration (L), 60.5 is the molar mass of acetic acid (g / mol), V 样品 is the actual volume of the sample used for titration (L). Record the measured total acid in Table 1.

[0087] Table 1 Total acid of the compound fruit vinegar prepared in Examples 1-3

[0088] Example 1 Example 2 Example 3 Total acid / (g / L) 50.4 51.8 51.2

[0089] It can be seen from Table 1 that the total acid of the compound fruit vinegar prepared in Examples 1-3 is not less than 50.4 g / L, indicating that the acidity of the compound fruit vinegar prepared by the fermentation process provided by the present invention meets the standards.

[0090] In the present invention, an enzyme preparation is used to decompose the pulp cell wall, release fermentable sugars, and increase the initial sugar content to provide sufficient substrate for yeast, avoiding residual sugar. Macromolecular impurities are removed by filtration to reduce fermentation inhibitors and ensure the metabolic efficiency of the strain. Then, with the residual sugar ≤ 2 °Bx and alcohol content ≥ 8% vol as the termination criteria, it is ensured that the sugars are completely converted into alcohol, avoiding interference from residual sugars in subsequent acetic acid fermentation. Through excessive fermentation, that is, exceeding the required acidity of the finished product, a space for acidity loss is reserved to offset the volatilization of acidic substances during the after-ripening and sterilization stages. Additionally, a wide-range pH buffer system is formed by compounding lactic acid and malic acid to reduce acidity fluctuations during storage. Then, honey and salt are added. The fructose and glucose in honey enhance the osmotic pressure and inhibit the growth of miscellaneous bacteria, while salt stabilizes the dissociation state of acidic substances through ionic effects, thus ensuring that the acidity of the prepared compound fruit vinegar beverage meets the standard.

[0091] Example 4

[0092] In the present invention, a wide-range buffer system is formed by compounding lactic acid and malic acid, covering a wider pH range and stabilizing the total acid at the target value. Among them, lactic acid has a mild acidity and provides a lasting sour taste, while malic acid has a sharp sour taste, rapidly reducing the pH and enhancing the sour taste impact. After acetic acid fermentation, some acetic acid may volatilize. By adding lactic acid and malic acid, the acidity can be compensated to ensure that the acidity of the finished product meets the standard. Moreover, organic acids can chelate minerals such as calcium and iron, improving the bioavailability of nutrients in red dates and goji berries. Lactic acid and malic acid have high thermal stability (decomposition temperature > 160 °C) and have no loss during pasteurization (70 °C), ensuring acidity consistency.

[0093] To prove that lactic acid and malic acid are one of the important components for the fermentation process provided by the present invention to produce compound fruit vinegar with a qualified acidity, and to prove that the mass ratio of lactic acid of 0.05 - 0.10% and the mass ratio of malic acid of 0.03 - 0.06% are one of the important factors for the fermentation process provided by the present invention to produce compound fruit vinegar with a qualified acidity, based on Example 2 above, the mass ratios of lactic acid and malic acid in the compound fruit vinegar are changed, and then the compound fruit vinegar is prepared and tested according to the total acid test method provided in the above examples. The test results are recorded in Table 2.

[0094] Table 2 Comparison of the total acid of compound fruit vinegar at different mass ratios of lactic acid and malic acid

[0095] Mass percentage of lactic acid / % 0 0.02 0.05 0.08 0.10 0.12 0.15 Mass percentage of malic acid / % 0.10 0.08 0.06 0.05 0.03 0.02 0 Total acid / (g / L) 48.7 48.8 50.6 51.8 50.9 47.3 46.9

[0096] As can be seen from Table 2, when the mass ratio of lactic acid is 0% or the mass ratio of malic acid is 0%, the total acid of the prepared compound fruit vinegar decreases. Moreover, when the mass ratio of lactic acid is 0.02%, 0.12%, 0.15% or when the mass ratio of malic acid is 0.02%, 0.08%, 0.10%, the total acid of the prepared compound fruit vinegar is lower than that when the mass ratio of lactic acid is 0.05 - 0.10% and the mass ratio of malic acid is 0.03 - 0.06%. Therefore, it can be proved that lactic acid and malic acid are one of the important components for the fermentation process provided by the present invention to produce compound fruit vinegar with qualified acidity, and it is also proved that the mass ratio of lactic acid of 0.05 - 0.10% and the mass ratio of malic acid of 0.03 - 0.06% are one of the important factors for the fermentation process provided by the present invention to produce compound fruit vinegar with qualified acidity.

[0097] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A fermentation process for red date and wolfberry compound fruit vinegar, characterized in that, It includes the following steps: Step S1: Weigh 20 - 22% of red dates, 5 - 6% of Chinese wolfberries, 8 - 10% of fructose syrup, 0.03 - 0.05% of enzyme preparation, 1 - 2% of honey, 0.08 - 0.12% of salt, 0.05 - 0.10% of lactic acid, 0.03 - 0.06% of malic acid according to the mass ratio, and the balance is drinking water. First, pre-treat the red dates and Chinese wolfberries respectively to obtain red date pulp and Chinese wolfberry pulp; Then mix the red date pulp and Chinese wolfberry pulp, and then add fructose syrup to adjust the sugar content to produce a mixed pulp; Step S2: Add the enzyme preparation to the mixed pulp and enzymatically hydrolyze it at 50 °C for 2 h to obtain an enzymolysis solution; Subsequently, perform alcoholic fermentation on the enzymolysis solution to obtain an alcoholic fermentation liquid, and then perform acetic acid fermentation on the alcoholic fermentation liquid to obtain an acetic acid solution; Step S3: Add honey, salt, lactic acid, and malic acid to the acetic acid solution, and stir for 30 min until fully mixed, then seal and store the acetic acid solution in the dark for 10 - 15 days to produce a stock solution; Coarsely filter the stock solution to remove large particle sediment impurities; Step S4: First, remove suspended impurities in the stock solution by diatomaceous earth filtration, then intercept bacteria and macromolecular substances through an ultrafiltration membrane, and then perform pasteurization at 70 °C for 15 min to obtain a compound fruit vinegar; Sterilize and can the compound fruit vinegar.

2. The fermentation process of the red date and wolfberry compound fruit vinegar according to claim 1, characterized in that: In the said step S1, the enzyme preparation includes pectinase preparation and cellulase preparation, and the mass ratio of pectinase preparation to cellulase preparation is 3:

2.

3. The fermentation process of the red date and wolfberry compound fruit vinegar according to claim 1, characterized in that: In the said step S1, the raw material pre-treatment is to wash the red dates, then pre-cook them at 80 °C for 10 min, then beat them into pulp, remove the pits, and pass through a 60 - mesh sieve to obtain red date pulp; Soak the Chinese wolfberries in warm water at 40 °C for 4 h, then beat them into pulp and remove the residue by centrifugal filtration to obtain Chinese wolfberry pulp.

4. The fermentation process of the red date and wolfberry compound fruit vinegar according to claim 1, characterized in that: In the said step S2, the pH value of the mixed pulp during enzymatic hydrolysis is 3.8 - 4.

2.

5. The fermentation process of the red date and wolfberry compound fruit vinegar according to claim 1, characterized in that: In the said step S2, the alcoholic fermentation treatment is to add wine yeast to a solution containing 2% sucrose at 35 °C, let it stand for 30 min to produce an activated bacterial solution, add the activated bacterial solution to the enzymolysis solution, and the volume of the added activated bacterial solution is 0.8% of the volume of the enzymolysis solution, and perform anaerobic fermentation treatment in a sealed state at 28 ± 1 °C; During fermentation, the enzymolysis solution is detected in real time. When the residual sugar in the enzymolysis solution ≤ 2 °Bx and the alcohol content ≥ 8% vol, centrifuge the enzymolysis solution to remove the residue, remove the yeast mud and fruit residue to obtain an alcoholic fermentation liquid.

6. The fermentation process of the red date and wolfberry compound fruit vinegar according to claim 1, characterized in that: In the said step S2, the acetic acid fermentation treatment is that the alcoholic fermentation liquid is inoculated with acetic acid bacteria and oxygen is introduced to oxidize ethanol in the alcoholic fermentation liquid to acetic acid until the acidity ≥ 50 g / L and the alcohol residue ≤ 0.3% vol to produce an acetic acid solution.

7. The fermentation process of the red date and wolfberry compound fruit vinegar according to claim 6, characterized in that: The temperature during the said acetic acid fermentation treatment is 32 - 34 °C.

8. The fermentation process of the red date and wolfberry compound fruit vinegar according to claim 1, characterized in that: In the said step S4, the temperature during sealed storage in the dark is 10 - 15 °C.

9. The fermentation process of the red date and wolfberry compound fruit vinegar according to claim 1, wherein: In the said step S4, the filtration accuracy of the ultrafiltration membrane is 0.20 - 0.30 μm.

10. A red date and Chinese wolfberry compound fruit vinegar produced by the fermentation process according to any one of claims 1 - 9.

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