Preparation method of lactobacillus fermented blueberry juice

Abstract

The invention discloses a preparation method of lactobacillus fermented blueberry juice, and belongs to the technical field of microbial production. The probiotic function of lactic acid bacteria and the nutritional function of blueberries are effectively combined, the pH of the fermented blueberry juice is reduced to 3.2 from 4.25 through the preparation method, and the viable count is increased by 23.82%; phenolic substances and flavonoid substances in the blueberry juice are increased by 30.05% and 34.47% respectively; meanwhile, the antioxidant activity is obviously enhanced and is superior to that of an unfermented group; the lactobacillus fermented blueberry juice enhances the oxidation resistance, improves the quality of the blueberry juice, and is a beverage product which is more suitable for the market and has flavor and nutrition.

Description

Technical Field

[0001] The invention relates to a method for preparing blueberry juice fermented by lactic acid bacteria, and belongs to the technical field of microbial production. Background Art

[0002] At present, there are many types of blueberry products in the domestic market, and processing can increase the added value of blueberry production. The manufacturing process of this product can be divided into two different development stages: primary and deep processing. Among them, primary products are mainly made by peeling, core removal or slicing fruits and then steaming and fermenting them. Primary processed products include preserved fruits, candied fruits and jellies, and deep processed products include pulp, pectin, fruit wine and fruit vinegar. Primary processed products are generally produced by manual or semi-mechanical methods. In order to improve the quality and taste of primary processed products, the method of adding frozen fruits and pure pulp is often used; after the pomace is crushed, compound enzymes or other additives are added to make it a functional food with certain nutritional value, such as fruit tea, fruit powder, fruit juice drinks, etc.

[0003] The processing of blueberries mainly includes the following aspects: Washing: Soak the picked blueberries in clean water to remove impurities and surface dust. Stem removal: Remove the berry stems to reduce the content of the stems. Selection: Select good quality berries according to the size and color of the blueberries. Drying: Put the cleaned blueberries into the dryer for drying to remove most of the water. Pulping: Pulp the dried blueberries through a pulper to remove the seeds and peels to obtain pure juice. Filtration: Filter the blueberry juice obtained by pulping through a precision filter to obtain seedless and residue-free blueberry juice. Processing: Blueberry juice can be made into paste, jelly, jam and other products as needed.

[0004] At present, the domestic blueberry processing technology is still imperfect. Most companies have a small scale of blueberry processing and production, a single product flavor, simple processing technology, and there is a lot of room for improvement in product quality. Although there are many varieties of blueberries in my country, the processing technology content is relatively low. At present, my country's blueberry processing technology has not kept up with the pace of technology introduced in the 1980s, resulting in its processing capacity and product quality failing to reach the world's leading level. At the same time, the international market demand for blueberries and their products continues to grow, and domestic companies face huge opportunities and challenges in increasing R&D efforts, improving processing technology, and improving product quality. Summary of the invention

[0005] The invention uses blueberry juice as the main raw material to inoculate lactic acid bacteria for fermentation, optimizes the lactic acid bacteria fermentation process of blueberry juice through single factor and response surface experiments, and studies the changes of functional substance content and physical and chemical indicators before and after fermentation under the optimal fermentation process.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A method for preparing blueberry juice fermented by lactic acid bacteria comprises the following steps:

[0008] Step 1: Activation and preservation of strains. The plant lactobacillus selected in this experiment was inoculated into MRS liquid culture medium at 5% (v / v), cultured at 37°C for 24 hours, and then three-zoned. After picking a single colony for culture, the purified bacterial liquid was obtained, and the bacterial liquid was mixed with 80% sterile glycerol in a ratio of 3:1 for seed preservation and stored at -80°C for later use. The method for preparing blueberry juice is as follows: After washing the blueberries, water and blueberries are mixed in a ratio of 1:2, then crushed with a juicer, and finally an 80-mesh filter is used for efficient filtration. Use 120°C high-temperature steam sterilization for 15 minutes to inactivate enzymes and harmful bacteria in blueberry juice. After sterilization, the juice is cooled to 37°C, and then inoculated and fermented according to the initial number of live bacteria of 1.0×107CFU / mL.

[0009] Step 2: Optimize fermentation conditions. The total antioxidant capacity of fermented blueberry juice is affected by three main factors: fermentation time, fermentation temperature and initial inoculum size. Through single factor experiment and response surface experiment, the fermentation temperature of blueberry juice was determined to be 37.5℃, the fermentation time was 30h, and the initial inoculum size was 2.5%.

[0010] Step 3: Preparation of fermented blueberry juice. The blueberry juice was squeezed and filtered, sterilized at 120° C. with high-temperature steam for 15 minutes, and cooled to 37° C. The fermented blueberry juice was prepared according to the fermentation conditions obtained in step 2.

[0011] The fermented blueberry juice prepared by the invention has high phenol and flavonoid contents.

[0012] The beneficial effects achieved by the present invention are as follows: after the blueberry juice is fermented by lactic acid bacteria, the contents of phenolic substances and flavonoids show a trend of gradual increase, increasing by 30.05% and 34.47% respectively, the number of live bacteria increases by 23.82%, and the pH drops from 4.25 to 3.2. DETAILED DESCRIPTION

[0013] The present invention is further described below. The following examples are only used to more clearly illustrate the technical solution of the present invention, and are not intended to limit the protection scope of the present invention.

[0014] A method for preparing blueberry juice fermented by lactic acid bacteria comprises the following steps:

[0015] Step 1: Activation and preservation of strains. The plant lactobacillus selected in this experiment was inoculated into MRS liquid culture medium at 5% (v / v), cultured at 37°C for 24 hours, and then three-zoned. After picking a single colony for culture, the purified bacterial liquid was obtained, and the bacterial liquid was mixed with 80% sterile glycerol in a ratio of 3:1 for seed preservation and stored at -80°C for later use. The method for preparing blueberry juice is as follows: After washing the blueberries, water and blueberries are mixed in a ratio of 1:2, then crushed with a juicer, and finally an 80-mesh filter is used for efficient filtration. Use 120°C high-temperature steam sterilization for 15 minutes to inactivate enzymes and harmful bacteria in blueberry juice. After sterilization, the juice is cooled to 37°C, and then inoculated and fermented according to the initial number of live bacteria of 1.0×107CFU / mL.

[0016] Step 2: Optimize fermentation conditions. The total antioxidant capacity of fermented blueberry juice is affected by three main factors: fermentation time, fermentation temperature and initial inoculum size. Through single factor experiment and response surface experiment, the fermentation temperature of blueberry juice was determined to be 37.5℃, the fermentation time was 30h, and the initial inoculum size was 2.5%.

[0017] Step 3: Preparation of fermented blueberry juice. The blueberry juice was squeezed and filtered, sterilized at 120° C. with high-temperature steam for 15 min, and cooled to 37° C. Fermented blueberry juice was prepared according to the fermentation conditions obtained in step 2, and the obtained fermented blueberry juice was subjected to subsequent physical and chemical experiments.

[0018] pH: The pH of the juice was measured directly by a pH meter.

[0019] Viable bacteria count detection: The viable bacteria count was determined by plate count method.

[0020] Flavonoid content detection: The total flavonoid content in blueberry juice was determined by ultraviolet spectrophotometry. Take 1g (accurate to 0.01g) of the sample and put it in a 25mL volumetric flask. After mixing evenly with ethanol, ultrasonic extraction for 20min was placed at room temperature for 30min. 1mL of the supernatant was aspirated and placed in a 25mL colorimetric tube and then fixed to volume with methanol and mixed evenly. The reference substance was rutin. 109.7mg (content of 92.4%) of rutin standard was accurately weighed and placed in a 100mL volumetric flask. After being fixed to the scale with methanol, the standby reagent was obtained. The dilution concentrations were 1.01μg / mL, 2.03μg / mL, 3.04μg / mL, 4.06μg / mL, 5.07μg / mL, and 6.08μg / mL of rutin reference reagents, respectively. The zero point was methanol solution, and the absorbance was measured at 360nm. The concentration of total flavonoids in the test solution was calculated according to the standard curve.

[0021] Detection of phenolic substance content: The content of phenolic substances was detected by the Folin phenol colorimetric method. Take 2.5mL of sample extract and place it in a 50mL beaker, add 15mL of 60% ethanol solution and ultrasonicate for 10 minutes, then use 60% ethanol solution to make up to 25mL, mix well and filter. Add 1.0mL of filtrate to a 10mL colorimetric tube, add 2.5mL of Folin phenol reagent, mix well, add 2.5mL of 15% Na2CO3 solution to the colorimetric tube, add water to make up to the scale and mix well, take out and cool for 20 minutes after 60 minutes in a 40℃ water bath, and measure the absorbance value. Use the standard curve to calculate the overall concentration of polyphenols in the test solution.

[0022] Determination of total antioxidant capacity (T-AOC)

[0023] The total antioxidant capacity was determined using a total antioxidant capacity kit and calculated according to the following formula.

[0024]

[0025] Note: A—Dilution multiple of reaction system

[0026] B—Dilution multiple of sample before testing

[0027] Changes in basic indicators

[0028] After determining the fermentation process of blueberry juice, the physical and chemical indicators after fermentation were tested. As shown in Table 1, after 2.5% lactic acid bacteria were inoculated into the blueberry juice matrix and cultured at a constant temperature of 37.5°C for 30 hours, as the number of lactic acid bacteria increased rapidly, its growth rate was rapid, and the accumulation rate of metabolites also accelerated, resulting in a rapid decrease in pH value from 4.25 to 3.2.

[0029] UV spectrophotometer method for detecting functional substances "In order to explore the effect of lactic acid bacteria fermentation on the active ingredients in blueberry juice, the total phenol and total flavonoid contents after fermentation were detected. The test results are shown in Table 2. The test results show that after the blueberry juice was fermented with lactic acid bacteria, the content of flavonoids in the blueberry juice increased significantly, with a growth rate of 34.47%; the content of phenolic substances also increased to a certain extent, with a growth rate of 30.05%.

[0030] After testing the active substances and pH value of blueberry juice before and after fermentation, it was observed that the contents of phenolic substances and flavonoids showed a gradual increase, increasing by 30.05% and 34.47% respectively, the number of viable bacteria increased by 23.82%, and the pH dropped from 4.25 to 3.2. In summary, this study helps to gain a deeper understanding of the impact of lactic acid bacteria fermentation on blueberry juice and provide reference and technical guidance for subsequent development.

[0031] Table 1 Detection of fermentation process Table 3-3 Detection offering process

[0032]

[0033] Tab.3-4Comparison of functional substances before and after fermentation

[0034]

[0035] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing blueberry juice fermented by lactic acid bacteria, characterized in that: The fermentation temperature was 37.5°C, the fermentation time was 30 h, and the initial inoculation amount was 2.5%.

2. The method for preparing blueberry juice fermented by lactic acid bacteria according to claim 1, characterized in that: Lactic acid bacteria fermented blueberry juice has excellent flavor and can enhance the body's own antioxidant capacity.

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