Method for preparing high-quality probiotic fermented strawberry juice based on magnetic field assistance

Abstract

The present application belongs to the technical field of fermented fruit juice, and particularly relates to a method for preparing high-quality probiotic fermented strawberry juice based on magnetic field assistance. The present application first uses Lactobacillus plantarum CTCF-LP-1 to perform static fermentation on the strawberry juice to be fermented in a fermentation device for more than 24 hours, and then places the fermentation device in a static magnetic field. The static magnetic field reduces the generation of organic acid components by Lactobacillus plantarum during the fermentation process of the strawberry juice, reduces the acidity, and improves the fermentation quality of the strawberry juice. The magnetic field strength of the static magnetic field is 1.0-2.5 mT, and the fermentation time in the static magnetic field is 0.5-1.5 h. After the static fermentation and the magnetic field treatment, the content of malic acid, isocitric acid, glutaconic acid and other organic acid components in the fermented strawberry juice is significantly reduced, while the content of alcohol and ester components such as n-octanol, 2-phenylethanol, methyl benzoate, 3-hexyl hexanoate and butyl valerate is increased, the types of aroma components are more abundant, and the taste and quality of the strawberry juice are significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fermented fruit juice, and particularly relates to a method for preparing high-quality probiotic fermented strawberry juice based on magnetic field assistance. BACKGROUND

[0002] Research shows that the influence of a magnetic field on microorganisms is related to the induced current generated by cells under the action of a magnetic field. Under an applied magnetic field, charged particles in the cells are affected by the Lorentz force, thereby affecting the normal physiological functions of the cells.

[0003] At the present stage, magnetic fields are more commonly applied to the preservation of fresh-cut fruits and vegetables in food processing. For example, patent CN112826076A discloses a high-pressure magnetic field system to assist Bacillus natto in producing homologous polypeptides and metabolites with antibacterial effects, thereby improving the antibacterial and color protection efficiency and effect. This technology mainly uses the strong inhibition of a magnetic field to kill bacteria, thereby achieving the effect of prolonging the preservation period.

[0004] In fact, a magnetic field can be divided into three types, i.e., strong, medium and weak, according to its magnetic induction strength. Different magnetic field strengths have different effects on the growth and metabolism of microorganisms. Under a suitable magnetic induction strength, the growth of microbial cells is promoted, and the metabolic activity is enhanced, which is beneficial to the generation of beneficial metabolites such as polysaccharides, proteins, antibiotics, functional active substances and flavor substances.

[0005] Patent CN111903883A discloses a dynamic magnetic field stirring fermentation process. The action of a dynamic magnetic field stimulates the improvement of the extracellular enzyme decomposition capacity of microorganisms, while inhibiting the decline period of microbial cells, thereby enhancing the activity of the cells and shortening the fermentation time.

[0006] Patent CN110693007A uses red light, blue light and alternating magnetic field treatment to ensure that Aspergillus niger and Aspergillus oryzae are always in a strong growth vigor, thereby continuously and efficiently producing a variety of high-activity enzymes.

[0007] Strawberry, containing rich vitamins, aspartic acid, folic acid, iron, calcium and other nutrients, is known as "Queen of Fruits", especially the content of vitamin C, which is 7-10 times higher than that of apple and grape. However, the storage period of strawberry is very short, which will rot in 1-2 days at room temperature, causing great waste of raw materials and seriously affecting the development of strawberry industry. Since the fruit and vegetable products fermented by probiotics can meet the increasing health and nutritional needs of people, it has become an inevitable trend of fruit and vegetable processing. Using strawberry as raw material, the production of fermented strawberry juice based on probiotic fermentation technology will be an important direction to promote the development of strawberry industry. However, the traditional probiotic fermentation technology for preparing fermented strawberry juice will produce a large amount of organic acid. When the content of organic acid is high, it will make the strawberry juice produce a sour taste, which will give people a wrong idea of strawberry juice rancidity, and then seriously affect the taste of strawberry juice product. Whether the magnetic field intervention can be applied to the preparation of probiotic fermented strawberry juice to reduce the production of undesirable flavors and other components in the probiotic fermentation process has not been studied. SUMMARY

[0008] In order to solve the above technical problems, the application provides a method for preparing high-quality probiotic fermented strawberry juice based on magnetic field assistance.

[0009] The applicant of the present application found in a long-term research that by adjusting the strength of the magnetic field and the time of the magnetic field action, the generation of a certain type of component in the probiotic fermentation process can be weakened or strengthened to a certain extent. If the magnetic field can be used to interfere with the probiotics, guide the probiotics to reduce or reduce the production of undesirable organic acid components or decompose and transform them during the fermentation of strawberry juice, and at the same time, the content of other aroma components such as esters or alcohols is increased on the basis of the original, then the taste and aroma of strawberry juice will be greatly improved.

[0010] Therefore, the present application provides a method for preparing high-quality probiotic fermented strawberry juice based on magnetic field assistance. The content of undesirable organic acid components in the high-quality probiotic fermented strawberry juice provided is significantly lower than that of the fermented strawberry juice under the traditional non-magnetic field intervention condition, and the content of aroma components in the strawberry juice will be significantly improved.

[0011] The method for preparing high-quality probiotic fermented strawberry juice based on magnetic field assistance provided by the application is specifically as follows: first, Lactobacillus plantarum is used to ferment the strawberry juice to be fermented in a fermentation device for 24-36 h, and then the fermentation device is placed in a static magnetic field for further fermentation, so as to obtain high-quality probiotic fermented strawberry juice; the magnetic field strength of the static magnetic field is 1.0-2.5 mT, and the fermentation time in the static magnetic field is 0.5-1.5 h; the Lactobacillus plantarum CTCF-LP-1 was preserved in the China General Microbiological Culture Collection Center on September 1, 2023, the address is No. 1, Beichen West Road, Hua-yuan Community, Beijing, and the Institute of Microbiology of the Chinese Academy of Sciences, the preservation number is CGMCC NO. 28329, and the classification name is Lactobacillus plantarum. If there is no special description below, the Lactobacillus plantarum mentioned refers to the Lactobacillus plantarum with the above preservation number.

[0012] In the application, the static magnetic field is introduced, and the interference of the static magnetic field is used to reduce the generation of organic acid components of probiotics in the fermentation process of strawberry juice, reduce the acidity, and improve the fermentation quality of strawberry juice.

[0013] Preferably, the inoculation volume of the Lactobacillus plantarum CTCF-LP-1 is 1.8-2.5% of the volume of the strawberry juice to be fermented.

[0014] More preferably, the inoculation volume of the Lactobacillus plantarum CTCF-LP-1 is 2.0% of the volume of the strawberry juice to be fermented.

[0015] Preferably, the magnetic field strength of the static magnetic field is 2.0 mT.

[0016] Preferably, the fermentation time in the static magnetic field is 1.0 h.

[0017] Further, the method for preparing high-quality probiotic fermented strawberry juice based on magnetic field assistance provided by the application comprises the following steps:

[0018] (1) Fresh strawberries are washed and pulped to obtain strawberry pulp;

[0019] (2) Pectinase is added to the strawberry pulp in (1) for enzymolysis, and the enzymolysis is carried out at 30-40℃ for 1.5-3 h, and then centrifugation is carried out for 3-5 min, and the supernatant strawberry juice is taken;

[0020] (3) The supernatant strawberry juice obtained in (2) is adjusted in sugar content and pH, sterilized, and the strawberry juice to be fermented is obtained;

[0021] (4) placing the to-be-fermented strawberry juice obtained in (3) into a fermentation device, first using Lactobacillus plantarum CTCF-LP-1 to perform static fermentation on the to-be-fermented strawberry juice for 24-36 h, then placing the fermentation device in a static magnetic field with a magnetic field strength of 1.0-2.5 mT to continue fermentation for 0.5-1.5 h, and obtaining high-quality probiotic fermented strawberry juice.

[0022] In the above preparation method of high-quality fermented strawberry juice:

[0023] Preferably, in (2), pectinase is used to enzymatically hydrolyze the strawberry pulp at 30-40 DEG C for 2 h.

[0024] Preferably, the pectinase is purchased from Novozymes Company, and the model of the pectinase is XXL.

[0025] Preferably, in (3), glucose is used to adjust the sugar degree of the strawberry juice to 10-13 DEG Brix, sodium citrate is used to adjust the pH to 4.5-5.5, and the adjusted strawberry juice is sterilized in a water bath at 75-90 DEG C for 30 min.

[0026] Preferably, in (3), glucose is used to adjust the sugar degree of the strawberry juice to 12 DEG Brix, and sodium citrate is used to adjust the pH to 5.0.

[0027] Preferably, in (4), the inoculation volume of Lactobacillus plantarum CTCF-LP-1 is 1.8-2.5% of the volume of the to-be-fermented strawberry juice.

[0028] The present application has the following beneficial effects:

[0029] Firstly, the present application introduces a static magnetic field in the fermentation process of the strawberry juice, and the metabolism of Lactobacillus plantarum CTCF-LP-1 is intervened by the magnetic field to affect the composition and yield of the fermentation product of the bacteria on the strawberry juice, so that the content of organic acids, including malic acid, isocitric acid, glutaconic acid, etc., in the fermented strawberry juice is greatly reduced compared with the strawberry juice without magnetic field intervention, at the same time, the content of typical aroma substances such as n-octanol, 2-phenylethanol, methyl benzoate, 3-hexanoic acid hexyl ester, and butyl valerate is increased, so that the aroma composition and types of the fermented strawberry juice are more abundant, and the taste and quality of the strawberry juice are significantly improved.

[0030] Secondly, through the principal component analysis model, it is shown that there is obvious separation between the metabolic products of the magnetic field assisted fermentation group and the static fermentation group, the contribution rate of the principal component 1 (PC1) is 78%, the contribution rate of the principal component 2 (PC2) is 8.50%, and the total contribution rate is 86.50%, based on the results of the orthogonal partial least squares-discriminant analysis, it is found that 32 kinds of metabolic substances are identified as differential metabolites (VIP>1, P<0.05), including 8 kinds of organic acids, 4 kinds of amino acids, 4 kinds of sugar and its derivatives, 8 kinds of alcohol and ester substances, 3 kinds of ketone and aldehyde substances, and 6 kinds of other metabolites. There are 20 kinds of up-regulated substances and 12 kinds of down-regulated substances in the magnetic field assisted fermentation group, the up-regulated substances account for 62.50% of the total differential metabolites, and the down-regulated substances account for 37.50% of the total differential metabolites; the pathway analysis of the differential metabolites shows that the top 5 metabolic pathways with significant influence (impact>1, P<0.05) are as follows: (1) Biosynthesis of amino acid, mainly including benzoic acid methyl ester, n-octanol, etc. (2) Glyoxalic acid and dicarboxylic acid metabolism, mainly including L-histidine, malic acid, isocitric acid, etc. (3) Biosynthesis of phenylpropanoids, mainly including 4-hydroxybenzaldehyde, 2-phenylethanol. (4) Flavonoid biosynthesis, mainly including dihydroquercetin, procyanidin B2, etc. (5) Sphingolipid metabolism, mainly including sphingosine, phosphoethanolamine 2 metabolic components.

[0031] Thirdly, after the optimal magnetic field assisted process is adopted in the application, the total acid of the strawberry juice is 4.36g / L, the sensory score is 2.32, the flavonoid content is 0.18mg / mL, the total phenol content is 1.03mg / mL, the DPPH free radical scavenging rate is 84.33%, and the hydroxyl radical scavenging rate is 66.12%. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The influence of the magnetic field intensity on the components in the fermented strawberry juice in example 2 of the application;

[0033] Figure 2 The influence of the magnetic field treatment time on the components in the fermented strawberry juice in example 3 of the application;

[0034] Figure 3Principal component and OPLS-DA analysis results of metabolites of non-fermented (WFJ), static fermentation (J-24), and magnetic field assisted fermentation strawberry juice (MF-24) in Example 5.1 of the present application;

[0035] Figure 4 Principal component and OPLS-DA analysis results of metabolites of static fermentation (J-24) and magnetic field assisted fermentation strawberry juice (MF-24) in Example 5.1 of the present application;

[0036] Figure 5 Heat map of differential metabolites of non-fermented (WFJ), static fermentation (J-24), and magnetic field assisted fermentation strawberry juice (MF-24) in Example 5.2 of the present application;

[0037] Figure 6 Heat map of differential metabolites of static fermentation (J-24) and magnetic field assisted fermentation strawberry juice (MF-24) in Example 5.2 of the present application;

[0038] Figure 7 Volcano plot of differential metabolites of static fermentation (J-24) and magnetic field assisted fermentation strawberry juice (MF-24) in Example 5.2 of the present application;

[0039] Figure 8 Metabolic pathway enrichment in Example 5.3 of the present application;

[0040] Figure 9 Bubble chart of metabolic pathway impact factors in Example 5.3 of the present application. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the present application, the present application will be further described in conjunction with specific embodiments.

[0042] Example 1

[0043] A method for preparing high-quality probiotic fermented strawberry juice based on magnetic field assistance, comprising the following steps:

[0044] (1) Fresh strawberries are washed and pulped to obtain strawberry pulp;

[0045] (2) Pectinase XXL (sold by Novozymes) is added to the strawberry pulp in (1), and the enzyme preparation is used in an amount of 200 ppm. Enzymolysis is carried out at a temperature of 37°C, and after 120 minutes of enzymolysis, centrifugation is performed, and the supernatant strawberry juice is taken;

[0046] (3) The sugar content of the supernatant strawberry juice is adjusted to 12°Brix using glucose, and the pH is adjusted to 5.0 using sodium citrate. Sterilization is performed to obtain the fermented strawberry juice;

[0047] (4) placing the strawberry juice to be fermented obtained in (3) in a fermentation device, first using Lactobacillus plantarum CTCF-LP-1 to stand for fermentation for 24 h, and then placing the fermentation device in a static magnetic field to continue fermentation for 1 h, wherein the inoculation volume of Lactobacillus plantarum CTCF-LP-1 is 2% of the volume of the strawberry juice to be fermented, the fermentation temperature is 36℃, the fermentation is performed for 24 h, the strength of the static magnetic field is 2.0 mT, and the fermentation is performed for 1 h.

[0048] Finally, the obtained strawberry juice is red, bright in color, uniform in tissue state, has fresh fruit aroma and fermentation characteristic flavor, and is suitable in sourness and sweetness.

[0049] Example 2

[0050] In this embodiment, the influence of the magnetic field strength on fermentation is mainly investigated.

[0051] Steps (1)-(3) are the same as in Example 1, and in step (4), the magnetic treatment strength is set to 1.0 mT, 2.0 mT, 3.0 mT, 4.0 mT and 5.0 mT, respectively.

[0052] Under the conditions of different magnetic field strengths, the contents of various active ingredients in the fermented strawberry juice obtained by using Lactobacillus plantarum CTCF-LP-1 to ferment the strawberry juice are shown in Table 1, and the influence of the magnetic field strength on various active ingredients and the comprehensive score of the strawberry juice are shown in the accompanying Figure 1

[0053] Table 1 Quality analysis of fermented strawberry juice under different magnetic field strengths

[0054]

[0055] As shown in Table 1 and the accompanying Figure 1 With the increase of the magnetic induction strength, the contents of flavonoids, polyphenols and total acids in the fermented strawberry juice all show a certain degree of reduction. When the magnetic field strength is 1.0 mT, the contents of various components are almost the highest. However, since flavonoids, total acids and other components all have a certain degree of bitterness and astringency, and Lactobacillus plantarum CTCF-LP-1 may also ferment other undesirable flavor substances under this magnetic field strength, thus leading to the fact that although the contents of flavonoids, total phenols and total acids in the fermented strawberry juice under the conditions of magnetic field strengths of 1.0 mT and 2.0 mT are not much different, the taste of the strawberry juice shows a very significant difference. When the magnetic field strength is 1.0 mT, the sensory score of the strawberry juice is far lower than that when the magnetic field strength is 2.0 mT. Therefore, the most suitable magnetic induction strength for fermentation is 2.0 mT in terms of the comprehensive score.

[0056] ​From the above data, it can be inferred that as the magnetic induction intensity continues to increase, the growth of the bacterial body is further intensified, in order to maintain normal life activities, some active ingredients such as flavonoids, polyphenols, total acids and the like produced in the previous stage of fermentation are consumed by the metabolism of microorganisms, and therefore, too high a magnetic induction intensity is not conducive to the fermentation of Lactobacillus plantarum CTCF-LP-1 on strawberry juice, but instead causes the loss of active ingredients. However, although a lower magnetic induction intensity is conducive to the fermentation of microorganisms to produce more active ingredients to some extent, under a lower magnetic field intensity, Lactobacillus plantarum CTCF-LP-1 can produce some undesirable flavor components, thereby seriously affecting the taste of the strawberry juice.

[0057] Example 3

[0058] In this example, the effect of the time of magnetic field intervention on fermentation is investigated.

[0059] Different from Example 1, in step (4), the magnetic induction intensity is adjusted to 2.0 mT, and the magnetic field treatment time is 0.5 h, 1.0 h, 1.5 h, 2 h and 2.5 h, respectively.

[0060] The quality of the strawberry juice obtained under different fermentation times of magnetic field treatment is identified and detected, and the results are shown in Table 2 and FIG. 2. Figure 2

[0061] Table 2 Content of each component of the strawberry juice fermented under magnetic field intervention at different times

[0062]

[0063] Note: Different lowercase letters represent significant differences P < 0.05 (the same below)

[0064] The results show that as the magnetic field treatment time is prolonged, the total acid content in the fermented strawberry juice gradually decreases, and the sensory score shows a slow increasing trend.

[0065] That is, the polyphenol and flavonoid contents in the strawberry juice reach a peak when the magnetic treatment time is 1 h, and when the magnetic field treatment time is further prolonged on the basis of 1.5 h, the polyphenol and flavonoid contents begin to show a negative growth. This can be due to the fact that magnetic field assisted treatment can change the cell membrane permeability, and the cell membrane permeability is continuously increased, which is conducive to the secretion of enzymes and the transmembrane transport of cell material components, thereby releasing more phenolic substances. However, when the magnetic field treatment time is prolonged to a certain extent, the magnetic field environment can cause irreversible damage to the cell membrane, and also inhibit the activity of microorganisms. Therefore, when the magnetic treatment time is 1 h, the comprehensive score reaches the highest, and therefore, the magnetic treatment time of 1 h is the most suitable fermentation time for assisted fermentation.

[0066] Example 4 ​

[0067] The quality of the strawberry juice prepared in Example 1 was analyzed, and the unfermented, non-magnetic field assisted fermentation was used as a control, and the results are shown in Table 3 below.

[0068] Table 3 Changes in physicochemical properties of strawberry juice under different fermentation conditions

[0069]

[0070] From the data in Table 3, it can be seen that the pH of the strawberry juice decreased from 5.00 before fermentation to 3.89, and the total acid content after fermentation was 5.91 g / L and 4.36 g / L, respectively, and the reducing sugar content was 86.37 mg / mL and 89.36 mg / mL, respectively. There was no significant difference in polyphenol content between the two groups. In addition, the flavonoid content was 0.15 mg / mL and 0.18 mg / mL, respectively, and the flavonoid content and antioxidant activity were significantly higher than those of the unfermented strawberry juice.

[0071] That is, under the optimal process conditions of magnetic field assistance: magnetic treatment time of 1 h, magnetic assistance intensity of 2.0 mT, the total acid content of the strawberry juice was 4.36 g / L, the sensory score was 2.32, the flavonoid content was 0.18 mg / mL, the total phenol content was 1.03 mg / mL, the DPPH free radical scavenging rate was 84.33%, and the hydroxyl radical scavenging rate was 66.12%.

[0072] Further, by comparing the data of the strawberry juice obtained from the non-magnetic field fermentation group and the magnetic field fermentation group, it can be seen that the accumulation of organic acids in the non-magnetic field fermentation group leads to an imbalance in the ratio of sweet and sour, and thus the sensory score of the fermentation group is lower than that of the magnetic field assisted fermentation group. Magnetic field assisted fermentation can increase the content of reducing sugar to a certain extent, while reducing the accumulation of organic acids, which is conducive to improving the taste score of the fermented strawberry juice.

[0073] Example 5

[0074] Example 1 prepared fermented strawberry juice, magnetic field assisted fermentation (MF-24) metabolomics research, unfermented (WFJ) as control example 1, non-magnetic field normal standing fermentation (J-24) as control example 2 comparison.

[0075] 5.1 Principal component analysis

[0076] The principal component analysis of metabolites of the strawberry juice prepared in different ways was carried out.

[0077] The metabolites of the three groups of samples (WFJ, J-24, MF-24) and the two groups of samples (J-24, MF-24) were combined in positive ion mode and negative ion mode, respectively, and principal component analysis was carried out, and the results are shown in Figures Figure 3 , 4 ​

[0078] Figure 3 As can be seen in the score plot of PCA, the contribution rate of the first principal component (PC1) in the samples of the three groups was 82%, and the contribution rate of the second principal component (PC2) was 6.5%. The samples of the three groups showed a relatively obvious separation trend, indicating that the flavors of the strawberry juice fermented by the magnetic field and the strawberry juice fermented by static placement were significantly different. The distribution of the samples of the MF-24 group and the J-24 group was relatively close, and the difference with the samples of the WFJ group was large. The total cumulative contribution rate of the principal components was 88.5%, and thus it can be seen that the metabolites changed obviously before and after fermentation.

[0079] Figure 4 As can be seen in the score plot of PCA, the contribution rate of the first principal component (PC1) in the samples of the three groups was 82%, and the contribution rate of the second principal component (PC2) was 6.5%. The samples of the three groups showed a relatively obvious separation trend, indicating that the flavors of the strawberry juice fermented by the magnetic field and the strawberry juice fermented by static placement were significantly different. The distribution of the samples of the MF-24 group and the J-24 group was relatively close, and the difference with the samples of the WFJ group was large. The total cumulative contribution rate of the principal components was 88.5%, and thus it can be seen that the metabolites changed obviously before and after fermentation.

[0080] 5.2 Screening and analysis of metabolic differences

[0081] The analysis of the differential metabolites of the strawberry juice obtained in Example 1 and Comparative Examples 1-2 showed that the differential metabolites of the strawberry juice before and after fermentation were different, as shown in Table 4 and the data in the accompanying Figure 5

[0082] Table 4 Differential metabolites of the strawberry juice before and after fermentation

[0083] Comparison between sample groups Total amount of metabolites identified Total amount of different metabolites between groups Total amount of up-regulated metabolites Total amount of down-regulated metabolites J-24 VS WFJ 499 74 40 34 MF-24 VS WFJ 499 74 43 31 MF-24 VS J-24 499 32 20 12

[0084] Table 4 and the data in the accompanying Figure 5 The data in Table 4 and the accompanying data showed that the total amount of the differential metabolites identified in the three groups was 74 substances. Compared between the two groups, the up-regulated substances in the magnetic field fermentation group relative to the unfermented group were 20, and the down-regulated substances were 12. It was found through PCA and OPLS-DA analysis that the unfermented group, the static fermentation group and the magnetic field assisted fermentation group showed a relatively obvious separation trend, and the model was stable.

[0085] In summary, the amount of up-regulated substances after fermentation was relatively large, indicating that the metabolites produced after fermentation by Lactobacillus plantarum LP121 were more abundant.

[0086] In addition, based on the OPLS-DA model analysis of non-magnetic field fermentation and magnetic field fermentation, a total of 32 differential metabolites were identified, as shown in Table 5. In order to more clearly observe the changes of the differential metabolites in the two fermentation methods, a heat map was prepared, as shown in the accompanying Figure 6 ,​Figure 6 The metabolic distribution can be visually divided into up-regulation and down-regulation. Red indicates up-regulation in the magnetic field-assisted fermentation group, and light color indicates down-regulation substances.

[0087] Table 5 Comparison of differential metabolites of strawberry juice fermented by two methods

[0088]

[0089]

[0090] Overall, the change trend of differential metabolites can be roughly divided into two regions. The differential metabolites in the red region in the lower half are mainly enriched in the magnetic field-assisted fermentation sample group, including 3 ester substances, 4 alcohol substances, 2 aldehyde substances, 3 acid substances, 2 flavonoid substances, and 6 other substances.

[0091] Similarly, the content of some differential metabolites in the blue region in the upper half is significantly reduced compared to the red region, indicating that the intervention of the magnetic field during the fermentation of strawberry juice has a certain inhibitory effect on the acid-producing performance of Lactobacillus plantarum LP121. The production of amino acids such as L-asparagine, dimethylglycine, and L-histidine will also decrease.

[0092] At the same time, compared with the non-magnetic field fermentation group sample, 20 metabolites are up-regulated, mainly including alcohol and ester substances, including 6 substances such as methyl benzoate, butyl valerate, 3-ethyl hexanoate, phenethyl alcohol, n-octanol, and lanosterol. In addition, there are also 3 substances such as dihydroquercetin and procyanidin B2.

[0093] Figure 7 The volcano plot of differential metabolites between non-magnetic field fermentation and magnetic field fermentation is shown in the figure. Many points are distributed in the figure, including red, blue, and gray. Each point represents a substance. Red indicates an increased content, blue indicates a reduced content, and gray indicates a common substance between the two groups. The horizontal coordinate represents the logarithmic value of the quantitative difference between the two groups, and the vertical coordinate represents the negative logarithmic value of P. The larger the vertical coordinate value, the more significant the differential expression, and the more reliable the results.

[0094] Figure 7 The top 5 metabolites are shown in the figure, which are malic acid, pentenedioic acid, hexyl hexanoate, n-octanol, and dihydroquercetin. Among them, malic acid and pentenedioic acid are down-regulated, and the remaining 3 substances are up-regulated.

[0095] It can be seen that after the magnetic field assisted strength of 2.0 mT and the magnetic treatment time of 1 h, compared with the strawberry juice fermented without the magnetic field, the strawberry juice fermented with the magnetic field has increased alcohol and ester substances such as n-octanol, 2-phenylethanol, methyl benzoate, 3-hexyl hexanoate and butyl valerate, the types of aroma components are more abundant, the organic acid components such as malic acid, isocitric acid and pentenoic acid are obviously down-regulated, the magnetic field assistance has an improving effect on the aroma components of the Lactobacillus plantarum LP121 fermented strawberry juice, the total flavonoid content is significantly increased, the production of organic acids is inhibited, and the quality of the fermented strawberry juice is significantly improved.

[0096] 5.3 KEGG metabolic pathway enrichment analysis

[0097] The KEGG system is used for pathway enrichment research on the differential metabolites between the strawberry fermented in the magnetic field and the strawberry fermented by standing, and the metabolic pathways with P<0.05 are selected as the metabolic pathways in which the differential metabolites are significantly enriched. The 32 kinds of differential metabolites screened are mapped into the KEGG database, and the top 20 metabolic pathways annotated are shown in Figure 8-9 .

[0098] The top five pathways in which the number of differential metabolites is most enriched are: (1) Biosynthesis of amino acid, mainly including methyl benzoate, n-octanol, etc. (2) Glyoxalic acid and dicarboxylic acid metabolism, mainly including L-histidine, malic acid, isocitric acid, etc. (3) Biosynthesis of phenylpropanoids, mainly including 4-hydroxybenzaldehyde and 2-phenylethanol. (4) Flavonoid biosynthesis, mainly including dihydroquercetin and procyanidin B2. (5) Sphingolipid metabolism, mainly including sphingosine and phosphoethanolamine.

[0099] It can be seen from the figure that the top five metabolic pathways verify the mechanism analysis that the magnetic field assisted probiotic fermented strawberry juice increases n-octanol, 2-phenylethanol, methyl benzoate, 3-hexyl hexanoate, butyl valerate and other alcohol and ester typical aroma substances, and reduces malic acid, isocitric acid, pentenoic acid and other irritating organic acids.

Claims

1. A method for the preparation of high quality probiotic fermented strawberry juice based on magnetic field assistance, characterized by, The steps include the following: (1) Fresh strawberries are washed and pulped to obtain strawberry pulp; (2) Pectinase is added to the strawberry pulp in (1), and enzymolysis is performed at 30-40 DEG C for 1.5-3 h, and the supernatant strawberry juice is obtained by centrifugation for 3-5 min; (3) The supernatant strawberry juice obtained in (2) is adjusted in sugar content and pH, and sterilized to obtain strawberry juice to be fermented; (4) The strawberry juice to be fermented obtained in (3) is placed in a fermentation device, and first subjected to static fermentation for 24-36 h by Lactobacillus plantarum CTCF-LP-1, and then subjected to continuous fermentation for 1.0 h in a static magnetic field with a magnetic field intensity of 2.0 mT to obtain high-quality probiotic fermented strawberry juice; The inoculation volume of the Lactobacillus plantarum CTCF-LP-1 is 1.8-2.5% of the volume of the strawberry juice to be fermented; the Lactobacillus plantarum CTCF-LP-1 is preserved in the China General Microbiological Culture Collection Center on September 1, 2023, and the preservation number is CGMCC NO. 28329, and the classification name is Lactobacillus plantarum Lactobacillus plantarum .

2. The method for preparing high quality probiotic fermented strawberry juice based on magnetic field assistance according to claim 1, characterized in that, In (2), the strawberry pulp is subjected to enzymolysis by 50-300 ppm of pectinase at 30-40 DEG C for 2 h.

3. The method for preparing high-quality probiotic fermented strawberry juice based on magnetic field assistance according to claim 1, characterized in that, In (3), the sugar content of the supernatant strawberry juice is adjusted to 10-13 DEG Brix by using glucose, and the pH is adjusted to 4.5-5.5 by using sodium citrate, and the adjusted strawberry juice is sterilized in a water bath at 75-90 DEG C for 30 min.

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