Method for preparing passion fruit peel red sour soup by enzyme-bacterium coupling

Abstract

The invention discloses a method for preparing passion fruit peel red sour soup through enzyme-bacterium coupling. The method comprises the steps of pretreatment and enzymolysis, burdening, material stirring, inoculation and sealing and fermentation. The passion fruit peel red sour soup is prepared through enzyme-bacterium coupling, traditional waste fruit peel is converted into a high-added-value sour soup seasoning, and resource waste is remarkably reduced; meanwhile, the fermentation process is precisely regulated and controlled by adopting a compound leavening agent, so that the production period is greatly shortened and the operation process is simplified while the product quality consistency is ensured; the passion fruit peels are utilized to break through the limitation of the flavor of traditional sour soup, the red sour soup is endowed with unique fruity composite sour taste and distinct layered flavor, and the red sour soup has nutrition enrichment and health care values. Efficient utilization of resources and product innovation are achieved, and the market prospect is wide.

Description

Technical Field

[0001] The present invention belongs to the technical field of food processing, and particularly relates to a method for preparing passion fruit peel red sour soup by enzyme-fungus coupling. Background Art

[0002] Passion fruit is a national geographical indication agricultural product. Among them, the passion fruit peel accounts for 50-60% of the total fruit weight and contains rich bioactive substances, with a large amount available for utilization. However, the peel contains macromolecular components such as cellulose and pectin that are difficult to degrade, resulting in difficult utilization and waste of resources. Moreover, discarding it into the environment will cause pollution. Red sour soup is a unique sour condiment in Guizhou cuisine and also a national geographical indication product, deeply loved by the public. The passion fruit peel is large in quantity and rich in various nutrients such as sugars, flavonoids, and dietary fiber, having the potential to develop sour soup.

[0003] The pectin, cellulose, etc. in the passion fruit peel have relatively large molecular weights, resulting in a low processing utilization rate of passion fruit despite its abundant production. The domestic processing technology is relatively backward. The sales of passion fruit are still mainly based on fresh fruit consumption, with a low processing ratio, and the processed products are relatively primary. High-value-added deep-processed products such as pectin and fruit seed oil are almost blank. In addition, the production of red sour soup is mainly carried out in family production and small handwork workshops, with a strong regional consumption. It is rarely seen in the catering industry outside Guizhou Province. And most of the red sour soup made at home generally has unstable quality due to difficult control of fermentation conditions. The commercially available red sour soup has problems such as low content of organic acids produced by natural fermentation, sour taste irritation, and single flavor, which deviate from the characteristics of traditional red sour soup of "sour, fresh, and fragrant" and cannot restore the true flavor quality of traditional red sour soup.

[0004] The pectin, cellulose, etc. in the passion fruit peel have relatively large molecules and are difficult to be utilized by microorganisms during fermentation. Therefore, based on the processing applicable characteristics of the passion fruit peel, the passion fruit peel can be pretreated with enzymes to enable microorganisms to better utilize and absorb the nutrients in the passion fruit peel for fermentation. Secondly, after the enzymatic hydrolysis process, most of the strains used in traditional fermentation inoculation come from endogenous bacteria, that is, the strains extracted and separated from the sour soup itself. By using a compound fermentation agent, industrialization can be better achieved, and the operability and repeatability can be improved. At the same time, by studying the fermentation of the fermentation agent in the passion fruit peel matrix, a compound fermentation agent suitable for passion fruit peel fermentation can be screened out, further optimizing the fermentation process and developing high-quality passion fruit peel sour soup.

[0005] The patent "A method for preparing red sour soup with whole industrial chain control applicable to Guizhou region" with the publication number CN118104532A discloses a method for making red sour soup that combines the local climate characteristics of Guizhou and forms a whole industrial chain control and stable quality through the process control of time, temperature, and humidity. The patent "A method for making Qianbei red sour soup" with the publication number CN119157240A discloses a method for preparing red sour soup using tomatoes, whose fragrance and flavor are much higher than those of the red sour soup made by traditional processes and are suitable for large-scale compound production. Thus, it can be seen that currently, since the raw materials for making red sour soup are mostly tomatoes, there are no reports on improving the flavor of red sour soup made from passion fruit peel based on enzyme bacteria.

[0006] Currently, the method of enzymatically hydrolyzing passion fruit peel still stays at the stage of solely using enzymes, and there is rarely a method of using the coupling of enzyme bacteria to prepare red sour soup. The formation of the quality of fermented foods is the result of multiple complex effects, and natural fermentation or single microorganisms are difficult to meet the high-quality requirements of fermented foods.

[0007] Therefore, fermenting passion fruit peel with the coupling of enzymes and bacteria to form red sour soup is of great significance for improving the utilization rate of passion fruit peel and the flavor and quality of red sour soup. Summary of the Invention

[0008] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, the abstract of the specification, and the title of the invention to avoid obscuring the purpose of this part, the abstract of the specification, and the title of the invention, and such simplifications or omissions shall not be used to limit the scope of the present invention.

[0009] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0010] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing red sour soup from passion fruit peel using the coupling of enzyme bacteria.

[0011] To solve the above technical problems, the present invention provides the following technical solutions: Provide a method for preparing red sour soup from passion fruit peel using the coupling of enzyme bacteria, including,

[0012] Boil the passion fruit in boiling water, remove the pulp and retain the peel. After the peel is broken, add distilled water and homogenize to make a pulp to obtain passion fruit liquid;

[0013] Add cellulase to the passion fruit liquid for enzymatic hydrolysis, and then add pectinase for enzymatic hydrolysis to obtain an enzymatic hydrolysate;

[0014] Extract juice from tomatoes, add salt and white wine to the tomato juice, and stir until evenly mixed;

[0015] Tomato juice added with table salt, liquor and glucose is mixed with the enzymolysis solution, and a mixed material is obtained after stirring the materials.

[0016] After the baking powder is inoculated into the mixed material, it is bottled and sealed to obtain the sour soup.

[0017] Among them, the mass ratio of the passion fruit liquid to the tomato is 1:5 to 20, the addition amount of the table salt is 5 to 10% of the mass of the tomato, the addition amount of the liquor is 2 to 10% of the mass of the tomato, and the addition amount of the glucose is 2 to 10% of the mass of the tomato; the enzymolysis solution is 20 to 25% of the mass of the tomato.

[0018] As a preferred scheme of the method of the present invention, wherein: the passion fruit is boiled in boiling water for 10 to 15 minutes, the sponge layer is removed after cooling, homogenized and pulped with a high-speed homogenizer, and after pulping, it is diluted according to the volume ratio of the fruit pulp to distilled water of 1:3 to 5, and shaken and mixed evenly.

[0019] As a preferred scheme of the method of the present invention, wherein: the cellulase enzymolysis includes first adjusting the pH of the passion fruit liquid to 3.0, keeping it warm in a water bath at 37 to 40 °C for 20 to 30 minutes, adding 3 to 10 mg of cellulase with 50000 U / g after the insulation ends, immediately putting it into a shaking table for shaking enzymolysis for 45 to 60 minutes, and immediately inactivating the enzyme in a boiling water bath for 15 to 20 minutes after the enzymolysis ends; the parameters of the shaking table are 37 to 40 °C and 300 to 400 r / min.

[0020] As a preferred scheme of the method of the present invention, wherein: the pectinase enzymolysis includes, after the cellulase enzymolysis ends, readjusting the pH to 3.0, keeping it warm in a water bath at 50 to 55 °C for 20 to 30 minutes, adding 5 to 40 mg of pectinase with 30000 U / g after the insulation ends, and then immediately putting it into a shaking table for shaking enzymolysis for 45 to 60 minutes; the parameters of the shaking table are 50 to 55 °C and 300 to 400 r / min. Immediately inactivate the enzyme in a boiling water bath for 15 to 20 minutes after the enzymolysis ends.

[0021] As a preferred scheme of the method of the present invention, wherein: the baking powder is one or more of high-activity dry yeast, pickled vegetable lactic acid bacteria baking powder and compound leavening agent.

[0022] As a preferred scheme of the method of the present invention, wherein: the inoculation mass ratio of the high-activity dry yeast and the pickled vegetable lactic acid bacteria in the baking powder is 1 to 5:9 to 5.

[0023] As a preferred scheme of the method of the present invention, wherein: the dosage of the leavening agent is 1 to 3% of the mass of the mixed material.

[0024] As a preferred embodiment of the method of the present invention, the bottling and sealing step includes inoculating the mixed material with baking powder, filling it into a fermentation bottle until it reaches 80-85% of the bottle volume, compacting it, and then sealing it for fermentation.

[0025] As a preferred embodiment of the method of the present invention, the fermentation temperature is 30-35°C, and the fermentation time is 7-10 days.

[0026] Another object of the present invention is to overcome the deficiencies in the prior art and provide a red sour soup made from passion fruit peel.

[0027] Advantages of the present invention:

[0028] (1) The present invention converts the passion fruit peel, which is usually regarded as waste, into a high-value-added condiment - red sour soup made from passion fruit peel, fully exploiting the potential of passion fruit peel in food processing. At the same time, through enzymatic hydrolysis, the macromolecular components in the passion fruit peel are effectively degraded, making it more easily fermented and utilized by microorganisms, thereby reducing the huge economic losses caused by the waste of passion fruit peel every year and injecting new vitality into the local passion fruit industry.

[0029] (2) The present invention selects a compound starter. Thanks to the cultivation and screening of the compound starter, it has specific functionality and repeatability, and can effectively ensure the quality consistency of the sour soup under the same conditions. Appropriate compound strains can accelerate the fermentation process, shorten the fermentation time, improve production efficiency, and meet the market's demand for rapid product listing. At the same time, the use of the compound starter reduces the dependence on microbial sources, overcomes geographical limitations, simplifies the operation process, and reduces the requirements for environmental conditions. Moreover, the present invention is easy to realize industrialized and large-scale production, and has broad market prospects.

[0030] (3) The fermentation of passion fruit peel in the present invention significantly enhances the flavor and nutritional components of the red sour soup. Passion fruit peel is rich in pectin, cellulose, and various active ingredients. Its unique aroma and sweet and sour taste bring rich fruit flavors to the red sour soup (the content of ester flavor substances after fermentation increases by 1 time), making the product more attractive to consumers and breaking through the flavor limitations of traditional sour soup. In addition, passion fruit peel is rich in flavonoids with anti-inflammatory and antioxidant effects, and the content increases by 4 times after fermentation, effectively enhancing the health value of the red sour soup, increasing its market attractiveness, and improving product competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the process flow chart in Example 1 of the present invention.

[0032] Figure 2 It is the graph of the reducing sugar content of passion fruit peel after enzymatic hydrolysis with different amounts of cellulase in Example 2 of the present invention.

[0033] Figure 3 It is the diagram of the reducing sugar content of passion fruit peels after enzymatic hydrolysis with different amounts of pectinase in Example 3 of the present invention.

[0034] Figure 4 It is the diagram of the pH change and total acid content change of the sour soup added with different compound starters during the fermentation process in Example 4 of the present invention.

[0035] Figure 5 It is the diagram of the pH change of the sour soup added with different proportions of high - activity dry yeast and pickled cabbage lactic acid bacteria fermentation powder during the fermentation process in Example 5 of the present invention.

[0036] Figure 6 It is the diagram of the pH change of the sour soup added with different passion fruit peel enzymatic hydrolysates during the fermentation process in Example 6 of the present invention.

[0037] Figure 7 is the diagram of the number of lactic acid bacteria colonies and the number of yeast colonies of the sour soup of different treatment groups during the fermentation process in Examples 1, 7 - 10 of the present invention.

[0038] Figure 8 is the diagram of the pH and reducing sugar changes of the sour soup of different treatment groups during the fermentation process in Examples 1, 7 - 10 of the present invention.

[0039] Figure 9 It is the diagram of the types and contents of organic acids of the sour soup of different treatment groups during the fermentation process in Examples 1, 7 - 10 of the present invention.

[0040] Figure 10 It is the PCA analysis diagram of the sour soup of different treatment groups on the 7th day of fermentation in Examples 1, 7 - 10 of the present invention. Figure 11 It is the bubble diagram of the change in the types and contents of volatile flavor substances of the sour soup of different treatment groups during the fermentation process in Examples 1, 7, 8 of the present invention. Figure 12 It is the heat map of volatile compounds of the sour soup of different treatment groups during the fermentation process in Examples 1, 7, 8 of the present invention. Figure 13 It is the composition and content of flavor substances of the sour soup of different treatment groups during the fermentation process in Examples 1, 7, 8 of the present invention. Detailed implementation manners

[0041] To make the above - mentioned objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific implementation manners of the present invention is made in combination with the embodiments of the specification.

[0042] In the following description, many specific details are set forth to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0043] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure or characteristic that may be included in at least one implementation manner of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or alternative embodiments that are mutually exclusive of other embodiments.

[0044] Raw materials and reagents in the present invention:

[0045] Golden passion fruit, provided by Qixiang Agricultural Investment and Development Co., Ltd., Congjiang County, Guizhou Province; vegetable tomato, iodized refined salt, purchased from Tianhui Supermarket Co., Ltd.; Red Star Erguotou liquor, 56 degrees, produced by Beijing Red Star Co., Ltd., purchased from Tianhui Supermarket Co., Ltd.; glucose, food grade, purchased from Heilongjiang NHU Biotech Co., Ltd.; Yeast extract peptone dextrose (YPD) liquid medium, De man rogosa sharpe (MRS) broth medium for lactic acid bacteria, gallnut acid, sodium carbonate, aluminum nitrate, potassium acetate, FoLin-CiocaLteu reagent, all purchased from Wuxi Huachuan Meitong Technology Co., Ltd.; pectinase at 30,000 U / g, food grade, purchased from Nanning Pangbo Bioengineering Co., Ltd.; cellulase at 50,000 U / g, food grade, purchased from Zhengzhou Mingxin Chemical Products Co., Ltd.; Angel high-activity dry yeast, Baizuan yogurt starter (Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus salivarius subsp. thermophilus), food grade, purchased from Angel Yeast Co., Ltd.; pickled cabbage and sauerkraut lactic acid bacteria fermentation powder (Lactobacillus plantarum, Lactobacillus acidophilus, Lactobacillus rhamnosus), probiotic natto fermentation powder (Lactobacillus plantarum), lactic acid bacteria yogurt fermentation powder (Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus casei), food grade, purchased from Beijing Chuanxiu International Trade Co., Ltd.; 2,4,6-trimethylpyridine, tetrahydrofuran, methanol, acetonitrile, hydrochloric acid, ether, all purchased from Shanghai Titan Scientific Co., Ltd.; trichloroacetic acid solution, sodium acetate, triethylamine, rutin, phenolphthalein solution, all purchased from Sinopharm Chemical Reagent Co., Ltd.; sulfosalicylic acid purchased from Yuanye Bio-Technology Co., Ltd.; sodium hydroxide solution purchased from Shandong Keyuan Biochemical Co., Ltd. All other chemicals and organic solvents used in this study are of analytical grade.

[0046] Experimental methods:

[0047] Determination of reducing sugar content: Fehling's reagent method. First, a glucose standard curve needs to be plotted. After mixing Fehling's reagent in a 1:1 ratio, 3 mL is pipetted into a test tube. 0, 4, 5, 6, and 7 mL of the glucose standard solution are added, and 7, 3, 2, 1, and 0 mL of water are added correspondingly. The test tube is stoppered and sealed, and then heated in a boiling water bath in an iron pot for 20 - 30 min. When obvious red precipitate forms in the test tube and the quantity is relatively stable, it is taken out and cooled with tap water, and then centrifuged at 1500 r / min for 15 min in a centrifuge. The supernatant is taken, the absorbance is read, and the standard curve is plotted. Since the reducing sugar concentration in passion fruit puree is relatively high, dilution steps are required. After multiple experiments, a more appropriate ratio is obtained: passion fruit peel puree: deionized water = 1:2. Next, the pH of the dilution is adjusted to 4.3 - 5.0, and it is shaken several times during this period to fully extract the reducing sugar. 1 mL of the test solution is pipetted, 6 mL of deionized water is added, and then 3 mL of Fehling's reagent is added to prepare the test solution. Other operations are the same as those for the standard curve, and the absorbance is read at a wavelength of 590 nm. The absorbance of the blank arm without the sample is subtracted from the absorbance of the sample tube, and the reducing sugar content is found on the standard curve.

[0048] Determination of crude fiber content: Refer to the national standard GB / T 5009.10 - 2003. First, 2 - 3 g of the mashed sample is weighed and transferred into a 50 mL conical flask. 20 mL of boiling 1.25% sulfuric acid is added, and it is heated to a gentle boil, maintaining a constant volume for 30 min. The conical flask is shaken once every 5 min to fully mix the substances in the flask. The conical flask is removed, immediately filtered through linen cloth, and washed with boiling water until the solution is no longer acidic. Then, 20 mL of boiling 1.25% potassium hydroxide solution is used to wash the residue on the linen cloth into the original conical flask, heated to a gentle boil for 30 min, the conical flask is removed, immediately filtered through linen cloth, washed 2 - 3 times with boiling water, and then transferred into a pre - dried and weighed G2 sintered glass crucible or a sintered glass funnel of the same model, and suction - filtered. After being washed thoroughly with hot water, it is suction - dried. Then, it is washed once with ethanol and once with ether in sequence. The crucible and its contents are dried in an oven at 105 °C and weighed. The operation is repeated until a constant weight is obtained.

[0049] Determination of total sugar content: Total polysaccharides are extracted by the water - extraction and alcohol - precipitation method, and the total polysaccharide content is determined by the phenol - sulfuric acid method. First, 0.05 g of the sample is weighed, 1 mL of water is added and homogenized thoroughly, extracted in a water bath at 100 °C for 2 h, cooled, and centrifuged at 10000 g for 10 min. The supernatant is taken, 0.2 mL of the supernatant is pipetted, 0.8 mL of absolute ethanol is slowly added, mixed well, and left to stand overnight at 4 °C. Then, it is centrifuged at 10000 g for 10 min, the supernatant is discarded, 1 mL of water is added to the precipitate, and after mixing well to dissolve the precipitate, it is ready for testing. 200 μL of the test sample is taken, 100 μL of the reagent and 0.5 mL of concentrated sulfuric acid are added, mixed well, heated in a water bath at 90 °C for 20 min, cooled with running water, 200 μL is taken and added to an enzyme - linked immunosorbent assay (ELISA) plate, and the absorbance value is measured at 490 nm.

[0050] Determination of pectin content: Carbazole colorimetric method. Prepare six 50 mL centrifuge tubes. Pipette 1.0 mL of galacturonic acid standard working solutions with concentrations of 0.0 mg / L, 20.0 mg / L, 40.0 mg / L, 60.0 mg / L, 80.0 mg / L, and 100.0 mg / L into the centrifuge tubes respectively. Add 0.25 mL of carbazole ethanol solution to each tube, which will produce white flocculent precipitates. Shake the centrifuge tubes continuously, and then quickly add 5.0 mL of sulfuric acid and mix well. Immediately place the centrifuge tubes in a water bath at 85 °C for 20 min and shake them from time to time. After taking them out, quickly cool them in cold water. Within 1.5 h, measure the absorbance of the standard solutions at a wavelength of 525 nm using a spectrophotometer. Plot a standard curve with the galacturonic acid concentration on the abscissa and the absorbance value on the ordinate. Pipette 1 mL of the filtrate into a 25 mL glass test tube, add 0.25 mL of carbazole ethanol solution for color development. Measure the absorbance at 525 nm using a spectrophotometer within 1.5 h, and calculate the pectin content in the filtrate according to the standard curve.

[0051] Determination of total phenol content: Folin-Ciocateu method. Using gallic acid as the standard, the total phenol content is expressed as mg gallic acid equivalents (GAE) / 100 g. Dissolve 0.5000 g of gallic acid in 10 mL of distilled water and make up the volume to 100 mL. Pipette 0 mL, 1 mL, 2 mL, 3 mL, 5 mL, and 7 mL respectively into 100 mL volumetric flasks and make up the volume. Pipette 1.0 mL from the above standard solutions with different concentrations into 100 mL volumetric flasks respectively, add 60 mL of water, mix, then add 5 mL of Folin-Ciocateu reagent and mix. Within 0.5 min - 8 min, add 15 mL of 20% sodium carbonate solution and make up the volume with water. After leaving the above standard solutions at 20 °C for 2 h, measure the absorbance at a wavelength of 765 nm and plot a standard curve. Accurately pipette 1 mL of the extract into a 100 mL volumetric flask, and measure its absorbance at a wavelength of 765 nm according to the above standard curve measurement method. Calculate the corresponding total phenol content from the above standard curve.

[0052] Determination of total flavonoid content: Aluminum oxide-sodium nitrite colorimetric method. Using rutin as the standard, the flavonoid content is expressed as mg of rutin equivalent mgRE / 100g. Pipette 20 mL of the sample into a 100 mL triangular flask dried to a constant weight, weigh it (accurate to 1 mg) for subsequent determination. Add about 30 mL of absolute ethanol and shake the sample well. Place the shaken sample in an ultrasonic cleaner for ultrasonic extraction for 1 h, and shake the solution every 20 min during this period. Pipette 1 mL, 2 mL, 3 mL, 4 mL, and 5 mL of the rutin standard working solution into 50 mL volumetric flasks respectively. Add absolute ethanol to a total volume of 15 mL, successively add 1 mL of aluminum nitrate solution and 1 mL of potassium acetate solution, shake well, add water to the scale, and shake well. Let it stand for 1 h, use a 1 cm colorimetric cell, at a wavelength of 420 nm, with 30% ethanol solution as the blank, and measure the absorbance. Use the mass of rutin (mg) in 50 mL as the abscissa and the absorbance as the ordinate to draw a standard curve. Pipette 1.0 mL of the sample precisely into a 50 mL volumetric flask. According to the above standard curve determination method, measure its absorbance value at a wavelength of 765 nm. The blank test solution is the same as the previous steps except that no sample is added. Using the blank test solution as the reference, use a 1 cm colorimetric cup to measure the absorbance of the test solution at a wavelength of 420 nm. Calculate the content of flavonoid compounds in the test solution from the above standard curve.

[0053] Example 1

[0054] This example provides a method for preparing passion fruit peel red sour soup by enzyme-fungus coupling.

[0055] (1) Pretreatment of passion fruit:

[0056] Select fruits with dark purple color, slightly wrinkled peel, heavy feel, and strong aroma. Boil the passion fruits in boiling water for 10 min, cool, remove the sponge layer, homogenize and pulp with a high-speed homogenizer. After pulping, dilute according to pulp: distilled water = 1:3, shake well to obtain a passion fruit liquid sample.

[0057] After collecting the samples, measure the reducing sugar, crude fiber, total sugar, pectin, total phenol, and total flavonoid. A series of physicochemical indexes of passion fruit peel are shown in Table 1.

[0058] Table 1

[0059]

[0060] (2) Take 5 g of the sample, adjust the pH to 3.0, keep it warm in a water bath at 37 °C for 20 min. After the insulation, add 10 mg of cellulase at 50000 U / g, and then immediately put it into a shaker for enzymatic hydrolysis for 45 min; the shaker parameters are 37 °C and 300 r / min. After the enzymatic hydrolysis, immediately inactivate the enzyme in a boiling water bath for 15 min.

[0061] (3) After enzymatically hydrolyzing the diluted pulp of passion fruit peel with cellulase for 45 min, the pH was readjusted to 3.0, and it was incubated at 50 °C in a water bath for 20 min. After the incubation, 30 mg of pectinase at 30,000 U / g was added, and then it was immediately placed in a shaker and shaken for enzymatic hydrolysis for 45 min. The shaker parameters were 50 °C and 300 r / min. After the enzymatic hydrolysis, it was immediately inactivated in a boiling water bath for 15 min.

[0062] (4) 100 g of tomatoes were cut into 5 g pieces and then juiced with a juicer. Then, salt, liquor, and glucose were added to the tomato juice. Among them, the addition amount of salt was 6.7% of the mass of tomatoes, which was 6.7 g, the addition amount of liquor was 2% of the mass of tomatoes, which was 2 g, and the addition amount of glucose was 2% of the mass of tomatoes, which was 2 g. The tomato juice with salt, liquor, and glucose added was mixed to prepare a tomato homogenate sample.

[0063] (5) Take a 100 mL blue-capped bottle and add 60 g of fresh tomato homogenate, and then add the enzymatic hydrolysate and the compound fermentation agent. Among them, the enzymatic hydrolysate of passion fruit peel was 20% of the mass of tomato homogenate, which was 12 g, and the addition amount of the compound fermentation agent was 1.7% of the mass of tomato homogenate, which was 1.02 g. The compound fermentation agent was composed of high-activity dry yeast and lactic acid bacteria of pickled vegetables and pickled cabbages, and the ratio of the two was 1:9. It was placed in an incubator at 30 °C for 7 days. The process flow chart is as Figure 1 shown, and the red sour soup of passion fruit peel of this example was obtained.

[0064] Example 2

[0065] This example was used to explore the effect of the dosage of cellulase on the red sour soup of passion fruit peel.

[0066] Take 5 g of the passion fruit liquid sample obtained in step 1) of Example 1, adjust the pH to 3.0, incubate at 37 °C in a water bath for 20 min. After the incubation, 3 mg, 6 mg, 8 mg, and 10 mg of cellulase at 50,000 U / g were added respectively;

[0067] It was immediately placed in a shaker and shaken for enzymatic hydrolysis for 45 min. The shaker parameters were 37 °C and 300 r / min;

[0068] After the enzymatic hydrolysis, it was immediately inactivated in a boiling water bath for 15 min to obtain the red sour soup of passion fruit peel of this example.

[0069] After enzymatic hydrolysis, the samples were collected and the reducing sugar content was measured. The changes in reducing sugar in each group are shown in Figure 2 .

[0070] Figure 2It shows that the content of reducing sugar in the sample after enzymatic hydrolysis with 8 - 10 mg of cellulase is the highest, indicating that the amount of reducing sugar (glucose) produced by cellulose decomposition is the largest, that is, the enzymatic hydrolysis effect is the best. Thus, it increases the nutrients available to microorganisms in the compound fermenting agent and the raw materials, and the growth will be better, which is more beneficial to the fermentation process. Therefore, 8 - 10 mg of cellulase is preferably used for enzymatic hydrolysis in the final food process.

[0071] Example 3

[0072] This example is used to explore the effect of the dosage of pectinase on the red sour soup of passion fruit peel.

[0073] Take 5 g of the passion fruit liquid sample obtained in step 1) of Example 1, adjust the pH to 3.0, keep it warm in a water bath at 37 °C for 20 min. After the insulation is completed, add 10 mg of cellulase with 50000 U / g, and then immediately put it into a shaker and shake for enzymatic hydrolysis for 45 min. The shaker parameters are 37 °C and 300 r / min. After the enzymatic hydrolysis is completed, immediately inactivate the enzyme in a boiling water bath for 15 min;

[0074] After enzymatic hydrolysis of the diluted slurry of passion fruit peel with cellulase for 45 min, readjust the pH to 3.0, keep it warm in a water bath at 50 °C for 20 min. After the insulation is completed, add 5 mg, 10 mg, 15 mg, 20 mg, 25 mg, 30 mg, 35 mg, 40 mg of pectinase respectively;

[0075] Immediately put it into a shaker and shake for enzymatic hydrolysis for 45 min. The shaker parameters are 50 °C and 300 r / min;

[0076] After the enzymatic hydrolysis is completed, immediately inactivate the enzyme in a boiling water bath for 15 min to obtain the red sour soup of passion fruit peel in this example.

[0077] Collect the samples after enzymatic hydrolysis and measure the content of reducing sugar. The changes in reducing sugar in each group are shown in Figure 3 .

[0078] Figure 3 It shows that when the addition amount of pectinase is 25 mg, the content of reducing sugar is the highest, indicating that the amount of reducing sugar (glucose) produced by pectin decomposition is the largest, that is, the enzymatic hydrolysis effect is the best. Thus, it increases the nutrients available to microorganisms in the compound fermenting agent and the raw materials, and the growth will be better, which is more beneficial to the fermentation process. Therefore, 25 - 30 mg of pectinase is preferably used for enzymatic hydrolysis in the final fermentation process of the red sour soup food.

[0079] Example 4

[0080] This example is used to explore the effect of different compound fermenting agents on the red sour soup of passion fruit peel.

[0081] (1) Blank group: Cut 100 g of tomatoes into 5 g pieces and juice them with a juicer. Then, add salt, white liquor, and glucose to the tomato juice. Among them, the salt addition amount is 6.7% of the tomato mass, which is 6.7 g, the white liquor addition amount is 2% of the tomato mass, which is 2 g, and the glucose addition amount is 2% of the tomato mass, which is 2 g. Mix the tomato juice with added salt, white liquor, and glucose to prepare a tomato homogenate sample. Add 60 g of fresh tomato homogenate to a 100 mL blue-capped bottle and place it in an incubator at 30 °C for 8 days.

[0082] (2) Pickled cabbage and sauerkraut lactic acid bacteria fermentation powder group: Cut 100 g of tomatoes into 5 g pieces and juice them with a juicer. Then, add salt, white liquor, and glucose to the tomato juice. Among them, the salt addition amount is 6.7% of the tomato mass, which is 6.7 g, the white liquor addition amount is 2% of the tomato mass, which is 2 g, and the glucose addition amount is 2% of the tomato mass, which is 2 g. Mix the tomato juice with added salt, white liquor, and glucose to prepare a tomato homogenate sample. Add 60 g of fresh tomato homogenate and 1 g of pickled cabbage and sauerkraut lactic acid bacteria fermentation powder to a 100 mL blue-capped bottle, mix well, and place it in an incubator at 30 °C for 8 days.

[0083] (3) High-activity dry yeast group: Cut 100 g of tomatoes into 5 g pieces and juice them with a juicer. Then, add salt, white liquor, and glucose to the tomato juice. Among them, the salt addition amount is 6.7% of the tomato mass, which is 6.7 g, the white liquor addition amount is 2% of the tomato mass, which is 2 g, and the glucose addition amount is 2% of the tomato mass, which is 2 g. Mix the tomato juice with added salt, white liquor, and glucose to prepare a tomato homogenate sample. Add 60 g of fresh tomato homogenate and 1 g of high-activity dry yeast to a 100 mL blue-capped bottle, mix well, and place it in an incubator at 30 °C for 8 days.

[0084] (4) Classic probiotic yogurt starter group: Cut 100 g of tomatoes into 5 g pieces and juice them with a juicer. Then, add salt, white liquor, and glucose to the tomato juice. Among them, the salt addition amount is 6.7% of the tomato mass, which is 6.7 g, the white liquor addition amount is 2% of the tomato mass, which is 2 g, and the glucose addition amount is 2% of the tomato mass, which is 2 g. Mix the tomato juice with added salt, white liquor, and glucose to prepare a tomato homogenate sample. Add 60 g of fresh tomato homogenate and 1 g of classic probiotic yogurt starter to a 100 mL blue-capped bottle, mix well, and place it in an incubator at 30 °C for 8 days.

[0085] (5) Lactobacillus yogurt fermentation powder group: Cut 100 g of tomatoes into 5 g pieces and juice them with a juicer. Then add salt, liquor, and glucose to the tomato juice. Among them, the salt addition amount is 6.7% of the tomato mass, which is 6.7 g, the liquor addition amount is 2% of the tomato mass, which is 2 g, and the glucose addition amount is 2% of the tomato mass, which is 2 g. Mix the tomato juice with added salt, liquor, and glucose to prepare a tomato homogenate sample. Add 60 g of fresh tomato homogenate and 1 g of Lactobacillus yogurt fermentation powder to a 100 mL blue-capped bottle, mix well, and place it in an incubator at 30 °C for 8 days.

[0086] (6) Probiotic natto fermentation powder group: Cut 100 g of tomatoes into 5 g pieces and juice them with a juicer. Then add salt, liquor, and glucose to the tomato juice. Among them, the salt addition amount is 6.7% of the tomato mass, which is 6.7 g, the liquor addition amount is 2% of the tomato mass, which is 2 g, and the glucose addition amount is 2% of the tomato mass, which is 2 g. Mix the tomato juice with added salt, liquor, and glucose to prepare a tomato homogenate sample. Add 60 g of fresh tomato homogenate and 1 g of probiotic natto fermentation powder to a 100 mL blue-capped bottle, mix well, and place it in an incubator at 30 °C for 8 days.

[0087] During the fermentation process of each group inoculated with different compound starters, the changes in the pH and total acid content of the red sour soup are shown in Figure 4 . Figure 4 It shows that in the first four days of fermentation, only the inoculated group inoculated with pickled cabbage Lactobacillus fermentation powder can quickly reduce the pH value, produce acid rapidly, reach a lower pH value, and the low-acid food environment system can effectively inhibit the growth of spoilage bacteria and pathogenic bacteria, ensuring the safety of fermented foods. This may be because the pickled cabbage Lactobacillus fermentation powder is mainly composed of Lactobacillus plantarum, Lactobacillus acidophilus, and Lactobacillus rhamnosus, and its optimal growth pH value range is 4.0 - 6.5, which is close to the natural pH of tomatoes (about 4.0 - 4.5). The acidic environment in the early stage of fermentation is conducive to its growth and reproduction. Moreover, as the fermentation progresses, the oxygen content becomes less and less, further inhibiting the growth and reproduction of aerobic bacteria and promoting the growth of Lactobacillus. Considering both flavor and acid production, the final determined red sour soup food fermentation process is a mixed fermentation method of using pickled cabbage Lactobacillus fermentation powder to produce acid and high-activity dry yeast to enhance flavor.

[0088] Example 5

[0089] This example is used to explore the influence of the compound starter ratio on the red sour soup of passion fruit peel

[0090] (1) Take 5 g of the sample in step (2) of Example 1, adjust the pH to 3.0, keep it warm at 37 °C in a water bath for 20 min. After the insulation, add 10 mg of cellulase at 50000 U / g, and then immediately put it into a shaker for enzymatic hydrolysis for 45 min; the shaker parameters are 37 °C and 300 r / min. After the enzymatic hydrolysis, inactivate the enzyme in a boiling water bath for 15 min immediately.

[0091] (2) After enzymatic hydrolysis of the diluted pulp of passion fruit peel with cellulase for 45 min, readjust the pH to 3.0, keep it warm at 50 °C in a water bath for 20 min. After the insulation, add 30 mg of pectinase at 30000 U / g, and then immediately put it into a shaker for enzymatic hydrolysis for 45 min; the shaker parameters are 50 °C and 300 r / min; after the enzymatic hydrolysis, inactivate the enzyme in a boiling water bath for 15 min immediately.

[0092] (3) Cut 100 g of tomatoes into pieces of 5 - 10 g and then juice them with a juicer. Then add salt, white wine and glucose to the tomato juice. Among them, the addition amount of salt is 6.7% of the mass of tomatoes, which is 6.7 g, the addition amount of white wine is 2% of the mass of tomatoes, which is 2 g, and the addition amount of glucose is 2% of the mass of tomatoes, which is 2 g. Mix the tomato juice added with salt, white wine and glucose to prepare a tomato homogenate sample.

[0093] (4) Take a 100 mL blue cap bottle, add 60 g of fresh tomato homogenate, and then add the enzymatic hydrolysate and the compound fermenting agent. Among them, the enzymatic hydrolysate of passion fruit peel is 20% of the mass of tomatoes, which is 12 g, and the addition amount of the compound fermenting agent is 1.7% of the mass of tomatoes, which is 1 g. In the experimental design, the ratios of high - activity dry yeast to pickled Chinese cabbage lactic acid bacteria fermentation powder in the compound fermenting agent are 1:9, 2:8, 3:7, 4:6, 5:5 respectively.

[0094] (5) Place it in an incubator at 30 °C for 4 days.

[0095] The changes in pH values during the fermentation process of each group inoculated with different ratios of high - activity dry yeast and pickled Chinese cabbage lactic acid bacteria fermentation powder are shown in Figure 5 .

[0096] Figure 5 It shows that in the early stage of fermentation, the pH change of the inoculation group with the ratio of high - activity dry yeast to pickled Chinese cabbage lactic acid bacteria fermentation powder of 1:9 is the largest and can rapidly reduce the pH value, quickly producing acid. The low - acid food environment system can effectively inhibit the growth of spoilage bacteria and pathogenic bacteria, ensuring the safety of fermented foods; in the later stage of fermentation, the pH and total acid basically tend to be stable. This is because the yeast under this ratio can consume appropriate oxygen and will not over - produce alcohol substances, which is more conducive to the growth and acid production of lactic acid bacteria.

[0097] The sensory evaluation of different groups is shown in Table 2.

[0098] Table 2

[0099]

[0100]

[0101] Note: Different letters in the same row indicate significant differences between different samples (P < 0.05).

[0102] Table 2 shows that by comparing the sensory evaluation results of the five fermentation groups, it can be seen that the overall sensory evaluation of the group with the ratio of high - activity dry yeast to pickled cabbage lactic acid bacteria fermentation powder of 1:9 is the highest, and it is significantly different from other groups. The red sour soup obtained from this fermentation group has a red color, luster, a suitable sour taste, a prominent unique flavor of sour soup, a light sweet taste from yeast fermentation, and is in a liquid state when flowing, with the best overall quality. This may be because the lactic acid bacteria grow well at this ratio, quickly produce acid, effectively reduce the pH value, making the red sour soup show a bright red color. The pH values of other experimental groups are relatively high, and the color is easily affected by it, showing a darker color. And at this ratio, the yeast ferments to produce appropriate alcohol substances, which will not overly cover the original flavor of the red sour soup, but can appropriately enhance it on this basis, making the flavor more layered. Figure 5 As can be seen from Table 2 and considering both quality and sensory evaluation, it is finally determined that the compound ferment in the food fermentation process of red sour soup is a mixture of high - activity dry yeast and pickled cabbage lactic acid bacteria fermentation powder in a ratio of 1:9.

[0103] Example 6

[0104] This example is used to explore the influence of the mass ratio of passion fruit peel enzymolysis solution to tomatoes on passion fruit peel red sour soup.

[0105] (1) Take 5 g of the passion fruit liquid sample obtained in step 1) of Example 1, adjust the pH to 3.0, keep it warm in a water bath at 37 °C for 20 min. After the insulation is completed, add 10 mg of cellulase with an activity of 50000 U / g, and then immediately put it into a shaker and shake for enzymatic hydrolysis for 45 min; the shaker parameters are 37 °C and 300 r / min. After the enzymatic hydrolysis is completed, immediately inactivate the enzyme in a boiling water bath for 15 min.

[0106] (2) After enzymatic hydrolysis of the diluted slurry of passion fruit peel with cellulase for 45 min, readjust the pH to 3.0, keep it warm in a water bath at 50 °C for 20 min. After the insulation is completed, add 30 mg of pectinase with an activity of 30000 U / g, and then immediately put it into a shaker and shake for enzymatic hydrolysis for 45 min. The shaker parameters are 50 °C and 300 r / min. After the enzymatic hydrolysis is completed, immediately inactivate the enzyme in a boiling water bath for 15 min.

[0107] (3) Cut 100 g of tomatoes into small pieces of 5 - 10 g and juice them using a juicer. Then, add salt, white liquor, and glucose to the tomato juice. Among them, the addition amount of salt is 6.7% of the mass of tomatoes, which is 6.7 g; the addition amount of white liquor is 2% of the mass of tomatoes, which is 2 g; the addition amount of glucose is 2% of the mass of tomatoes, which is 2 g. Mix the tomato juice with the added salt, white liquor, and glucose to prepare a tomato homogenate sample.

[0108] (4) Take a 100 mL blue - capped bottle and add 60 g of fresh tomato homogenate, then add enzyme - hydrolyzed solution and compound fermentation agent. Among them, the addition amount of the compound fermentation agent is 1.7% of the mass of tomatoes, which is 1 g. The ratio of high - activity dry yeast to pickled cabbage lactic acid bacteria fermentation powder in the fermentation agent is 1:9. The experimental design of the enzyme - hydrolyzed solution of passion fruit peel is 5%, 10%, 15%, 20%, 25% of the mass of tomatoes, which are 3 g, 6 g, 9 g, 12 g, 15 g respectively.

[0109] (5) Place it in an incubator at 30 °C for 10 days to obtain the passion fruit peel red sour soup of this example.

[0110] The pH value changes during the fermentation process of each group with different proportions of added passion fruit peel enzyme - hydrolyzed solution are shown in Figure 6 ; It can be seen from Figure 6 that when the addition amount of the enzyme - hydrolyzed solution is 20 - 25%, the pH change is the largest, and it can quickly reduce the pH value and produce acid rapidly. The low - acid food environment system can effectively inhibit the growth of spoilage bacteria and pathogenic bacteria, ensuring the safety of fermented foods. Therefore, the optimal addition amount of the enzyme - hydrolyzed solution should be 20 - 25%. This phenomenon may be due to the fact that an appropriate amount of passion fruit enzyme - hydrolyzed solution can bring more carbohydrate substances, which is more conducive to the growth and acid production of lactic acid bacteria. Considering both cost and quality, the red sour soup fermentation food process is to add the enzyme - hydrolyzed solution of passion fruit peel accounting for 20 - 25% of the mass of tomato homogenate.

[0111] Example 7

[0112] This example is used to explore the influence of the compound fermentation agent on the passion fruit peel red sour soup. Specifically:

[0113] The difference between this example and Example 1 is that in step (5), adding the enzyme - hydrolyzed solution and the compound fermentation agent is replaced by adding only the enzyme - hydrolyzed solution, that is, not adding the compound fermentation agent. Among them, the enzyme - hydrolyzed solution is 20% of the mass of tomato homogenate, which is 12 g.

[0114] The remaining steps of the process are all referred to Example 1 to obtain the passion fruit peel red sour soup of this example.

[0115] Example 8

[0116] This example takes the fermentation of single tomato juice as a comparison. Specifically:

[0117] (1) Cut 100 g of tomatoes into 5 g small pieces and juice them with a juicer. Then, add salt, liquor, and glucose to the tomato juice. Among them, the addition amount of salt is 6.7% of the mass of tomatoes, which is 6.7 g, the addition amount of liquor is 2% of the mass of tomatoes, which is 2 g, and the addition amount of glucose is 2% of the mass of tomatoes, which is 2 g. Mix the tomato juice added with salt, liquor, and glucose to prepare a tomato homogenate sample.

[0118] (2) Take a 100 mL blue-capped bottle, add 60 g of fresh tomato homogenate, and place it in an incubator at 30 °C for 7 days to obtain the tomato sour soup of this example.

[0119] Example 9

[0120] This example is used to explore the influence of the addition amount of the compound starter on the red sour soup of passion fruit peel. Specifically:

[0121] The difference between this example and Example 1 is that in step (5), the addition amount of the compound starter is 1.7% of the mass of tomatoes, which is replaced by the addition amount of the compound starter being 2.2% of the mass of tomatoes, which is 1.32 g.

[0122] The process of the remaining steps is all referred to Example 1 to obtain the red sour soup of passion fruit peel of this example.

[0123] Example 10

[0124] This example is used to explore the influence of the addition amount of the compound starter on the red sour soup of passion fruit peel. Specifically:

[0125] The difference between this example and Example 1 is that in step (5), the addition amount of the compound starter is 1.7% of the mass of tomatoes, which is replaced by the addition amount of the compound starter being 2.7% of the mass of tomatoes, which is 1.62 g.

[0126] The process of the remaining steps is all referred to Example 1 to obtain the red sour soup of passion fruit peel of this example.

[0127] The changes in the number of lactic acid bacteria colonies in the sour soup during the fermentation process of Examples 1, 7 - 10 are shown in Figure 7a . The changes in yeast in the sour soup during the fermentation process of each group are shown in Figure 7bAs can be seen from Figure 7, from the 1st day to the 5th day of fermentation, the growth of lactic acid bacteria and yeast in the fermentation group with a tomato inoculation amount of 1.7% of the passion fruit peel enzymatic hydrolysate was the best. The growth of the fermentation group with a tomato inoculation amount of 2.2% of the passion fruit peel enzymatic hydrolysate and the fermentation group with a tomato inoculation amount of 2.7% of the passion fruit peel enzymatic hydrolysate was similar. This may be because the nutrients in the fermentation bottle were limited, and too large an inoculation amount made the competition among microorganisms more intense, resulting in poor growth. An appropriate inoculation amount can enable microorganisms to fully absorb the nutrients in the fermentation bottle. Since no compound starter was inoculated, the growth of microorganisms in the natural tomato fermentation group and the natural tomato fermentation group of the passion fruit peel enzymatic hydrolysate was much worse than that in the inoculation group. However, the growth of lactic acid bacteria in the natural tomato fermentation group of the passion fruit peel enzymatic hydrolysate was slightly better than that in the natural tomato fermentation group, probably because the acidity of the passion fruit peel enzymatic hydrolysate was relatively high, making the pH of the fermentation environment lower, which was beneficial to the growth of lactic acid bacteria. The growth of yeast in the natural tomato fermentation group was better than that in the natural tomato fermentation group of the passion fruit peel enzymatic hydrolysate, also because the pH of the fermentation environment in the natural tomato fermentation group of the passion fruit peel enzymatic hydrolysate was lower, which was not conducive to the growth of yeast. After the 5th day, the growth of microorganisms was slow.

[0128] The pH changes during the fermentation process of each group are shown in Figure 8a As shown in the figure, during the fermentation process, the pH of the natural tomato fermentation group of the passion fruit peel enzymatic hydrolysate was the lowest because the pH of the passion fruit peel enzymatic hydrolysate itself had reached 2.74, and many original microorganisms in the tomato itself, such as Enterobacter and Pichia, could hardly grow normally in such a highly acidic environment. Therefore, the low pH here was mainly due to the added passion fruit peel enzymatic hydrolysate. The pH of the inoculation groups all decreased rapidly and tended to be stable in the later stage of fermentation, indicating that they could all produce acid quickly. Among them, the pH of the fermentation group with a tomato inoculation amount of 1.7% of the passion fruit peel enzymatic hydrolysate decreased the fastest and had the lowest pH, mainly because the nutrients in the fermentation bottle were limited, and too large an inoculation amount made the competition among microorganisms more intense, resulting in poor growth. An appropriate inoculation amount can enable microorganisms to fully absorb the nutrients in the fermentation bottle and thus produce acid quickly, and their pH values were all lower than 4.6, which could effectively inhibit spoilage bacteria and pathogenic bacteria and ensure the safety of fermented foods. The pH of the natural tomato fermentation group also decreased, but not as fast as that of the inoculation group, indicating that the acid production effect of natural fermentation was worse than that of inoculation fermentation.

[0129] The changes in reducing sugar during the fermentation process of each group are shown in Figure 8bAs shown in the figure, during the fermentation process, the reducing sugar content in all groups decreased, indicating that the reducing sugar was utilized by the growth and reproduction of microorganisms. The overall trend was a rapid decrease first, and then it tended to be stable in the later stage of fermentation (starting from the 6th day). The nutrients in the fermentation flask were insufficient, which was not conducive to the rapid growth of microorganisms. Among them, the reducing sugar content in the fermentation group with 1.7% inoculum of tomato in the enzymolysis solution of passion fruit peel decreased the fastest and was the lowest, indicating that more reducing sugar was utilized by microorganisms and the growth of microorganisms was also the best.

[0130] The sensory evaluation of different groups is shown in Table 3.

[0131] Table 3

[0132]

[0133] Note: Different letters in the same row indicate significant differences between different samples (P < 0.05).

[0134] Table 3 shows that when comparing the sensory evaluation results of the five fermentation groups, the overall sensory evaluation of the fermentation group of tomato with the addition of enzymolysis solution of passion fruit peel and an inoculum of 1.7% was the highest, and there were significant differences between this group and other groups. The red sour soup obtained from this fermentation group was red, shiny, with a suitable sour taste, prominent fermented wine fragrance and sweet flavor, had the unique flavor of sour soup, flowed in a liquid state, and had the best overall quality. This may be because an appropriate amount of passion fruit enzymolysis solution can bring more sugar substances. Under this environmental system, lactic acid bacteria grow well and produce acid rapidly, effectively reducing the pH value, making the red sour soup show a bright red color. The pH values of some other experimental groups were relatively high, and the color was easily affected by it, showing a darker color. And the yeast fermentation at this ratio produced appropriate alcohol substances, which would not overly cover the original flavor of the red sour soup, but could appropriately enhance it on this basis, making the flavor more layered. Considering the quality and sensory evaluation comprehensively, the food process of red sour soup was finally determined as adding 20 - 25% enzymolysis solution of passion fruit peel and additionally inoculating 1.7% compound fermentation agent (the ratio of high - activity dry yeast to pickled cabbage lactic acid bacteria fermentation powder was 1:9).

[0135] The types and content changes of organic acids during the fermentation process are shown in Figure 9 Citric acid is the main organic acid, followed by malic acid and lactic acid.

[0136] Compared with the natural fermentation group of tomatoes, the inoculated fermentation group of tomatoes with passion fruit peel enzymolysis liquid had slightly more citric acid, malic acid, and lactic acid, but the difference was not significant, indicating that the inoculation of the starter and the addition of passion fruit peel enzymolysis liquid had little effect on the accumulation of these organic acids. However, the contents of tartaric acid and acetic acid in the inoculated fermentation group of tomatoes with passion fruit peel enzymolysis liquid increased significantly. Acetic acid can promote flavor formation as a flavor substance or odor precursor, and tartaric acid can make the overall sour taste of the sour soup more intense and distinct, stimulating the taste buds and stimulating appetite. Moreover, it can endow the sour soup with a fresh, refreshing, slightly astringent sour taste, enriching the flavor level of the sour soup.

[0137] The PCA analysis of the electronic nose on the 7th day of fermentation was as Figure 10 . Two principal components (PC1: 95.766%, PC2: 3.9%) were extracted to explain more than 99% of the data variables. The discriminant index was -367, indicating good odor separation between samples.

[0138] The changes in the content of free amino acids (mg / mL) during the fermentation process are shown in Table 4.

[0139] Table 4

[0140]

[0141]

[0142]

[0143] Note: Different letters in the same row indicate significant differences between different samples on the same day (P < 0.05).

[0145] As shown in Table 4, during the fermentation of the sour soup, the content of almost all free amino acids in the tomato inoculated fermentation group with the enzymolysis solution of passion fruit peel was much higher than that in the tomato natural fermentation group. Among them, the content of glutamic acid was the highest, followed by aspartic acid and proline, all of which were umami and sweet amino acids. This indicates that the tomato inoculated fermentation group with the enzymolysis solution of passion fruit peel can produce a better taste compared to the tomato natural fermentation group. After consulting relevant research, it was found that the microbial enzymes in the starter play an important role in the release of free amino acids; in the tomato natural fermentation group with the enzymolysis solution of passion fruit peel, due to the too low pH value, it is not conducive to the growth of microorganisms, so the content of free amino acids did not increase, and even decreased. This is because free amino acids react with substances such as organic acids and metal ions in the sour soup, or the solubility of free amino acids decreases due to changes in conditions such as pH, causing them to form precipitates and resulting in a decrease in content. However, the content of glutamic acid and aspartic acid in the tomato natural fermentation group with the enzymolysis solution of passion fruit peel was very high at the initial stage of fermentation. The content of glutamic acid reached 55.06 mg / mL, and that of aspartic acid was 14.11 mg / mL, both of which were umami and sweet amino acids. Therefore, the addition of the enzymolysis solution of passion fruit also contributed to the taste and flavor of the tomato inoculated fermentation group with the enzymolysis solution of passion fruit peel.

[0146] The types and proportions of volatile flavor compounds on the 0th day, 1st day, 3rd day, 5th day, and 7th day during the fermentation process are shown in Figures 11 to 13 .

[0147] As Figure 12 can be seen, a total of 149 volatile compounds were detected during the fermentation of the sour soup, including 40 esters, 12 terpenoids, 5 alkanes, 20 ketones, 4 acids, 9 aldehydes, 1 quinone, 13 aromatics, 32 alcohols, and 13 others. The formation of the flavor of fermented foods is a complex process, involving protein hydrolysis, carbohydrate metabolism, lipid oxidation, and spice factors, etc.

[0148] Ester volatile compounds play an important role in fermented sour soup due to their low thresholds and good ester aroma flavors. In the three treatment groups, the types and contents of most ester compounds increased with time, while a small number of ester compounds showed fluctuating changes. Among them, in the natural tomato fermentation group with passion fruit peel enzymatic hydrolysate added and the tomato fermentation group with passion fruit peel enzymatic hydrolysate added and an inoculum amount of 1.7%, the types and contents of ester compounds increased with time. Passion fruit itself is rich in various organic acids and alcohols. During the fermentation process, these substances generate ester compounds through esterification reactions. For example, after fermentation, the ethyl acetate content in the tomato fermentation group with passion fruit peel enzymatic hydrolysate added and an inoculum amount of 1.7% reached 623.58 μg / g, while that in the natural tomato fermentation group was only 464.75 μg / g. The addition of passion fruit peel and the compound starter also brought ester substances such as isobutyl acetate, ethyl 2-methylbutyrate, and 2-methylbutyl acetate to the sour soup. These ester substances have strong fruity and floral scents and low thresholds. Therefore, in the sensory evaluation, the sour soup with passion fruit peel added can clearly smell a fresh fruity aroma. Compared with the ordinary natural tomato fermented sour soup, the aroma is more abundant and the layers are more distinct. This unique ester aroma flavor adds a special flavor characteristic to the sour soup. Alcohol compounds show dynamic changes during the fermentation process, and the change in their content may be related to their participation in the esterification reaction to form ester substances. During the sensory evaluation, these alcohol compounds give the sour soup a faint mellow aroma, which blends with other flavor substances, making the sour soup with passion fruit peel added taste more mellow. Compared with the sour soup without addition, there is an obvious improvement in the coordination and fullness of the flavor. In the initial stage of fermentation, since the microbial activity has just started, the types and contents of volatile flavor substances are relatively low. The initial ethyl acetate in the tomato fermentation group with passion fruit peel enzymatic hydrolysate added and an inoculum amount of 1.7% was only 61.42 μg / g. In the middle stage of fermentation, as the fermentation progresses, the microbial metabolic activity increases, generating more volatile compounds, especially the contents of ester and alcohol substances increase significantly, such as ethyl acetate, ethyl oleate, ethyl palmitate, etc. These substances usually have fruity aromas and can improve the flavor of the sour soup. In the late stage of fermentation, the contents of volatile substances such as ethyl oleate may reach a peak and then start to decline because some substances are further metabolized or transformed into other compounds, and the contents of acid and aldehyde substances increase. These substances usually have sour and pungent odors and have an important impact on the overall flavor of the sour soup. Adding passion fruit peel enzymatic hydrolysate may introduce additional enzymes, microorganisms, and flavor precursor substances, which will accelerate the fermentation process and increase the generation of specific volatile flavor substances. At the same time, the inoculated group will also accelerate the fermentation process of the sour soup and increase the generation of flavor substances due to the adjustment of the microbial population structure and metabolic activities. From the fruity aroma of esters, the mellow aroma of alcohols to the fresh aroma of alkenes, in the sensory evaluation, whether it is the richness and layering of the aroma or the mellow degree of the taste, it shows a unique flavor different from the ordinary natural tomato fermented sour soup, greatly improving the flavor quality of the sour soup.

[0149] Collect the samples of Example 1, and take the samples on the 0th day and the 7th day of fermentation. Measure the contents of total phenols, total flavonoids, total acids and reducing sugars in the samples and make comparisons, as shown in Table 5. Collect the samples after 7 days of fermentation in Example 1 and Example 8, measure the contents of total phenols, total flavonoids, total acids and reducing sugars in the samples and make comparisons, as shown in Table 6.

[0150] Table 5

[0151]

[0152] Note: Different letters in the same row indicate significant differences among different samples (P < 0.05).

[0153] Table 6

[0154]

[0155] Note: Different letters in the same row indicate significant differences among different samples (P < 0.05).

[0156] As can be seen from Tables 5 and 6, during the fermentation process of sour soup, the contents of total phenols, total flavonoids and total acids all increase. The total flavonoids increase by 10 mg / kg, the total phenols increase by about 56.25%, and the total acids increase by 13%. Basically, each physical and chemical index has significant differences before and after fermentation, indicating that microorganisms convert some components in the raw materials into phenolic and flavonoid substances during the fermentation process. For example, lactic acid bacteria can hydrolyze glycoside substances in the raw materials to release free flavonoid compounds. At the same time, the organic acids produced by the metabolites of lactic acid bacteria will also promote the release of some bound phenolic substances in the raw materials; while during the fermentation process of red sour soup, yeast can produce some enzymes through its own metabolic activities. These enzymes can decompose macromolecular compounds in the raw materials, making the phenolic and flavonoid components in them easier to be extracted, and yeast may synthesize some secondary metabolites with similar phenolic or flavonoid structures during the metabolic process, increasing the contents of total phenols and total flavonoids in red sour soup. During the fermentation process, the content of reducing sugar decreases because microorganisms consume it as a nutrient during the fermentation process.

[0157] Comparing the red sour soup made from passion fruit peel in Comparative Example 1 with the naturally fermented red sour soup of tomatoes, it was found that the contents of total phenols, total flavonoids and total acids in the red sour soup made from passion fruit peel in Example 1 were all higher than those of the naturally fermented red sour soup. The total phenols and total flavonoids were increased by no less than 10 times, and the total acid was increased by nearly 20%. The reducing sugar after fermentation in the commercial starter culture group with an inoculation amount of 1.7% was only 1 / 3 of that in the natural fermentation group. There were significant differences in most physicochemical indexes between the two treatment groups. One reason was that a compound starter culture was inoculated in the red sour soup made from passion fruit peel under the optimal conditions, and there were more microorganisms, and their metabolic activities promoted the release of nutritional components such as total phenols. The other reason was that the enzymolysis solution of passion fruit peel was added, making the environment more acidic, which helped the flavonoid and phenolic compounds to be released from the cell structure of the raw materials, because acid could destroy structures such as cell walls and cell membranes, making the flavonoid and phenolic components originally encapsulated in the cells more easily dissolved.

[0158] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the present invention.

Claims

1. A method for preparing passion fruit peel red sour soup by enzyme-fungus coupling, characterized in that: Including, Boil passion fruit in boiling water, remove the pulp and keep the peel. After the peel is broken, add distilled water, homogenize to make pulp, and obtain passion fruit liquid; Add cellulase to the passion fruit liquid for enzymatic hydrolysis, and then add pectinase for enzymatic hydrolysis to obtain an enzymatic hydrolysate; Extract tomato juice, add salt, white wine and glucose to it, and stir until evenly mixed to obtain tomato homogenate; Mix the tomato homogenate with the enzymatic hydrolysate to obtain a mixture, where the enzymatic hydrolysate is 20-25% of the mass of the tomato. Add compound fermentation powder to the mixture, and after sealed fermentation, the red sour soup of passion fruit peel is obtained; In the tomato homogenate, calculated by mass percentage, the addition amount of salt is 5-10% of the mass of the tomato, the addition amount of white wine is 2-10% of the mass of the tomato, and the addition amount of glucose is 2-10% of the mass of the tomato.

2. The method according to claim 1, wherein: Boil the passion fruit in boiling water for 10-15 min, remove the sponge layer after cooling, homogenize and beat the pulp with a high-speed homogenizer, and dilute it according to the volume ratio of the pulp to distilled water of 1:3-5 after beating, and shake and mix evenly.

3. The method according to claim 1, characterized in that: The cellulase enzymatic hydrolysis includes: first adjust the pH of the passion fruit liquid to 3.0, keep it warm in a water bath at 37-40 °C for 20-30 min, add 3-10 mg of cellulase with an activity of 50000 U / g after the insulation ends, immediately put it into a shaker and shake for enzymatic hydrolysis for 45-60 min, and immediately inactivate the enzyme in a boiling water bath for 15-20 min after the enzymatic hydrolysis ends; the shaker parameters are 37-40 °C, 300-400 r / min.

4. The method according to any one of claims 1 or 3, characterized in that: The pectinase enzymatic hydrolysis includes: after the cellulase enzymatic hydrolysis, readjust the pH to 3.0, keep it warm in a water bath at 50-55 °C for 20-30 min, add 5-40 mg of pectinase with an activity of 30000 U / g after the insulation ends, and then immediately put it into a shaker and shake for enzymatic hydrolysis for 45-60 min; the shaker parameters are 50-55 °C, 300-400 r / min, and immediately inactivate the enzyme in a boiling water bath for 15-20 min after the enzymatic hydrolysis ends.

5. The method according to claim 1, characterized in that: The compound fermentation powder is composed of high-activity dry yeast and pickled cabbage lactic acid bacteria fermentation powder.

6. The method according to any one of claims 1 or 5, characterized in that: In the compound fermentation powder, the inoculation mass ratio of high-activity dry yeast to pickled cabbage lactic acid bacteria is 1-5:9-5.

7. The method according to any one of claims 1 or 5, characterized in that: The dosage of the compound fermentation powder starter is 1-3% of the mass of the mixture.

8. The method according to claim 1, wherein: The sealed fermentation is to seal the bottle. The mixture added with the compound fermentation powder is filled to 80-85% of the bottle volume, compacted and then sealed for fermentation.

9. The method according to claim 1, characterized in that: The temperature of the sealed fermentation is 30-35 °C, and the fermentation time is 7-10 d.

10. The red sour soup of passion fruit peel prepared by the method according to any one of claims 1-3, 5, 8 or 9.

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