CN117491526A - A method for monitoring the process of lactic acid fermentation of fruit and vegetable juices - Google Patents

Abstract

The invention relates to a monitoring method of fruit and vegetable juice lactic acid fermentation process, which takes component A (acetoin and 2, 3-butanedione) as a marker of total colony number change in the fruit and vegetable juice lactic acid fermentation process, determines the component A content of different time points in the fermentation process through HS-GC-I MS analysis, judges the fermentation process according to the acetoin or 2, 3-butanedione content change condition of different time points, and determines the fermentation end point through the component A content reaching a certain value. The monitoring method for the fruit and vegetable juice lactic acid fermentation process can monitor the fruit and vegetable juice lactic acid fermentation process in real time and judge the fermentation end point, and overcomes the defect that the fermentation process is judged to be lagged by calculating the total number of bacterial colonies through a plate counting method; on the other hand, the defect that the fermentation degree cannot be accurately reflected due to more interference in pH value detection is overcome.

Description

A method for monitoring the process of lactic acid fermentation of fruit and vegetable juices

Technical field

The invention relates to the field of fermentation, and in particular to a method for monitoring the process of lactic acid fermentation of fruit and vegetable juices.

Background technique

After fermentation of fruit and vegetable juices by lactic acid bacteria, some bioactive ingredients will be produced, which can enrich the nutritional value of fruit and vegetable juices and improve their sensory properties. At the same time, the fermented juices are rich in lactic acid bacteria and can regulate intestinal flora. Therefore, fermented juices have received more and more attention and research, and more and more products are on the market.

At present, in the fermentation process of probiotic juice, pH value, number of viable bacteria and lactic acid content are usually used as indicators to measure the degree of fermentation. The detection of viable bacteria count and lactic acid content is complex and time-consuming, and the fermentation process cannot be monitored in real time. For example, the plate counting method is now used to detect the number of viable bacteria. This method has a large sampling volume (200g) and a long detection cycle, often requiring 36 hours. Above, the number of viable lactic acid bacteria during the fermentation process cannot be monitored in real time. Although pH can be monitored in real time, it is affected by many factors. For example, organic acids in the juice, bacterial contamination and other factors will cause pH changes, making it unable to reflect the fermentation degree of lactic acid bacteria well.

Flavor substances are substances that stimulate people's sense of smell and taste and elicit feelings. It brings flavor to food, and flavor is one of the important indicators of the sensory quality of food. The fermentation process uses the growth and metabolic activities of microorganisms to convert complex organic compounds into simple compounds and can produce certain volatile compounds. Solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS), as a mature volatile compound analysis technology, is widely used in food analysis. It can fully extract volatile components and relatively quantify the detected substances through internal standard substances, helping us understand the contribution of each compound to the flavor of the product. However, the extraction method of this technology is time-consuming, the detection limit is relatively high, and it cannot be used to monitor the fermentation process in real time.

In recent years, headspace-gas chromatography-ion mobility spectroscopy (HS-GC-IMS) is a new volatile compound analysis technology that has the characteristics of high sensitivity and no need for sample pretreatment. It has been widely used in the food field, such as in Food freshness evaluation, food flavor identification, etc., but it has not yet been applied in the fermentation process of fruit and vegetable juices.

Contents of the invention

In order to make up for the deficiencies in the prior art, the present invention provides a method for monitoring the lactic acid fermentation process of fruit and vegetable juices, which can more accurately and in real time monitor the lactic acid fermentation process of fruit and vegetable juices and determine the fermentation end point, overcoming the deficiencies in the prior art.

The technical solutions adopted by the present invention to solve the above technical problems are:

A method for monitoring the process of lactic acid fermentation of fruit and vegetable juices. Component A is used as a marker for changes in the total number of bacterial colonies during the lactic acid fermentation of fruit and vegetable juices. HS-GC-IMS analysis is used to determine the content of component A at different time points during the fermentation process. The fermentation process is judged by the content changes of component A at different time points, and the fermentation end point is determined by the content of component A reaching a certain value;

Among them, component A is acetoin or 2,3-butanedione.

Further, the gas phase ion mobility spectrum of the fermentation sample was obtained through HS-GC-IMS analysis, and the peak volume of component A in the spectrum was calculated to obtain the corresponding component A content.

Further, the HS-GC-IMS analysis conditions are as follows: take 2 mL of the sample to be tested and put it into a 20 mL headspace bottle. The incubation temperature is 40-50°C, the incubation time is 10-30 min, and the incubation speed is 350-550 rpm; non-polar chromatographic separation is used. Capillary chromatography column, perform gas chromatography separation at 38-45°C, use nitrogen with a purity of 99.99% as the carrier gas, run at 2mL/min for 5-8min, 10mL/min for 5-10min, and 50mL/min for 2-8min. , run at 150mL/min for 2-8 minutes; IMS ionization temperature is 45°C.

Further, the HS-GC-IMS analysis conditions are as follows: take 2 mL of the sample to be tested and put it into a 20 mL headspace bottle. The incubation temperature is 45°C, the incubation time is 20 min, and the incubation speed is 500 rpm. The chromatographic separation uses a Multicapillary SE-54 capillary chromatography column (0.32 mm×30m, 0.25μm), perform gas chromatography separation at 40°C, use nitrogen with a purity of 99.99% as the carrier gas, run at 2mL/min for 5min, 10mL/min for 10min, 50mL/min for 5min, and 150mL/min. Run for 5 minutes; IMS ionization temperature is 45°C.

Furthermore, the shorter the sample sampling interval, the more accurate the result. The interval can be 2h\4h\6h, but considering the actual operation and monitoring accuracy, 6h is preferred.

Furthermore, the fruit and vegetable juice can be selected from one of tart cherry juice, apple juice, pear juice, kiwi juice, and peach juice, but is not limited to these types. Among them, sour cherry juice uses Lactobacillus plantaru (LP) or Lactobacillus rhamnosus GG (LGG) lactic acid fermentation; apple juice, pear juice, kiwi juice, and peach juice use LGG lactic acid fermentation.

The present invention adopts the above structure and has the following advantages: in this monitoring method, the volatile metabolite acetoin or 2-pentanone is used as a marker for changes in the total number of bacterial colonies during the lactic acid fermentation of fruit and vegetable juices, and the monitoring method uses HS-GC-IMS The analysis can quickly obtain the content of acetoin or 2-pentanone, so as to understand the changes in the content of acetoin or 2-pentanone during the fermentation process, and thus better judge the fermentation process and fermentation end point. The above monitoring method, on the one hand, overcomes the disadvantage of lagging behind in judging the fermentation process by calculating the total number of bacterial colonies by plate counting; on the other hand, it overcomes the disadvantage of not being able to accurately reflect the degree of fermentation due to the presence of too much interference in pH value detection.

This monitoring method can not only accurately monitor the number of viable bacteria in lactic acid fermented fruit and vegetable juices in real time, but also represent the changing trend of the overall flavor to a certain extent, and better realize the monitoring of the lactic acid bacteria fermentation process.

Description of drawings

Figure 1 is a summary diagram of the characteristic peaks of flavor substances during the fermentation process of apple juice lactic acid bacteria LGG;

Figure 2 is an analysis chart of the change trend of the total number of fermentation colonies of apple juice lactic acid bacteria LGG and acetoin;

Figure 3 is a correlation analysis diagram between the total number of fermentation colonies of apple juice lactic acid bacteria LGG and acetoin;

Figure 4 Correlation analysis diagram of the total number of fermentation colonies of apple juice lactic acid bacteria LGG and 2,3-butanedione, 2-heptanone and 2-pentanone respectively;

Figure 5 is a PCA analysis chart of volatile components during the fermentation process of apple juice lactic acid bacteria LGG;

Figure 6 is a pH change diagram during the fermentation process of apple juice lactic acid bacteria LGG;

Figure 7 is a summary diagram of the characteristic peaks of flavor substances during the fermentation process of sour cherry juice lactic acid bacteria LP;

Figure 8 is an analysis chart of the total number of colonies fermented by Lactobacillus LP in sour cherry juice and the change trend of acetoin;

Figure 9 is a correlation analysis diagram between the total number of colonies fermented by Lactobacillus LP in sour cherry juice and acetoin;

Figure 10 is a correlation analysis diagram of the total number of fermentation colonies of sour cherry juice lactic acid bacteria LP and 2,3-butanedione, 2-heptanone and 2-pentanone respectively;

Figure 11 is a PCA analysis chart of volatile components during the fermentation process of sour cherry juice lactic acid bacteria LP;

Figure 12 is a pH change diagram during the fermentation process of sour cherry juice lactic acid bacteria LP;

Figure 13 is a color view of Figure 1;

Figure 14 is a color view of Figure 3;

Figure 15 is a color view of Figure 4;

Figure 16 is a color view of Figure 7;

Figure 17 is a color view of Figure 9;

Figure 18 is a color view of Figure 10.

Detailed ways

In order to clearly explain the technical features of this solution, the present invention will be described in detail below through specific implementation modes and in conjunction with the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present application. However, the present application can also be implemented in other ways different from those described here. Therefore, the protection scope of the present application is not limited to the specific implementation disclosed below. Example limitations.

This application provides a method for monitoring the process of lactic acid fermentation of fruit and vegetable juices. Specifically, component A (acetoin or 2,3-butanedione) is used as a marker for changes in the total number of bacterial colonies during the lactic acid fermentation of fruit and vegetable juices. Through HS -GC-I MS analysis quickly determines the content of component A at different time points during the fermentation process, to judge the fermentation process through the changes in the content of component A at different time points, and to determine the fermentation end point when the content of component A reaches a certain value. Specifically, the following examples demonstrate that component A can be used as a marker for changes in the total number of bacterial colonies during the lactic acid fermentation of fruit and vegetable juices.

Example 1:

Lactobacillus LGG is used to ferment apple juice. Specifically, the prepared apple juice raw materials are put into a sterilization pot and sterilized at 90°C for 10 minutes. The purpose is to kill other bacteria in the apple juice raw material liquid and provide a sterile environment for fermentation. Then, the sterilized and cooled apple juice raw material liquid was inoculated with LGG lactic acid bacteria at an inoculation amount of 4% (v:v), and fermented at 37°C for 48 hours. The above fermentation process is an existing technology and will not be described in detail here.

During the above fermentation process, samples were taken and monitored every 6 hours. The number of samples at each time point is 3. One sample is used to calculate the total number of colonies using the existing plate counting method; one sample is used to measure pH; one sample is analyzed by HS-GC-IMS to obtain the gas phase ions of volatile substances. Migration spectrum, N-ketone C4-C9 (Sinopharm Beijing Chemical Reagent Co., Ltd.) was used to calculate the retention index (RI) of volatile compounds, and each volatile compound was analyzed by comparing with the retention time and drift time of the GC-IMS library. Qualitatively, the content of each volatile compound is obtained by calculating the peak volume of volatile compounds in the gas phase ion mobility spectrum.

The HS-GC-IMS analysis conditions are as follows: take 2 mL of the sample to be tested and put it into a 20 mL headspace bottle. The incubation temperature is 45°C, the incubation time is 20 min, and the incubation speed is 500 rpm. The chromatographic separation uses a Multicapillary SE-54 capillary chromatography column (0.32 mm × 30 m, 0.25μm), perform gas chromatography separation at 40°C, using nitrogen with a purity of 99.99% as the carrier gas, running at 2mL/min for 5min, 10mL/min for 10min, 50mL/min for 5min, and 150mL/min for 5min; IMS ionization temperature is 45°C.

1.1 In order to intuitively express the changing rules of volatile substances during the above fermentation process, a summary chart of the characteristic peaks of volatile substances was drawn, as shown in Figure 1 and Figure 13.

It can be seen from Figure 1 or Figure 13 that the flavor substances change greatly during the fermentation process of apple juice. The newly formed products of fermentation include 2,3-butanedione and acetoin, with obvious peaks appearing at 18 hours of fermentation. These two products are derived from pyruvate metabolism.

1.2 Taking acetoin as an example, based on the number of colonies and acetoin content measured at each fermentation time point, draw a graph showing the changes in the number of colonies and acetoin as the fermentation time changes. See Figure 2 for details. It should be noted that during the HS-GC-IMS analysis and detection process, some acetoin monomers will be converted into acetoin dimers, so Figure 2 plots acetoin monomers and acetoin dimers respectively. The content change curve with fermentation time, and the acetoin content during the fermentation process is actually the sum of the content of acetoin monomer and acetoin dimer.

It can be seen from Figure 2 that the lactobacillus LGG has a pre-lag period of 0-12h in apple juice, and the changes in the number of colonies and acetoin tend to be gentle; it enters the logarithmic growth phase after 12h; it basically enters the stable phase after 36h, and the number of colonies basically does not change. Further increasing, the number of colonies of lactic acid bacteria LGG reached the maximum at 36h, increasing from the initial colony number of 7.93log CFU/mL to 8.98log CFU/mL. A similar trend was seen for acetoin, with its content increasing slowly from 12 to 18h. It increases rapidly from 18 to 36h, and when it reaches 36h, its growth rate slows down. This shows that acetoin can be used as a marker for changes in the number of fermentation colonies of apple juice lactic acid bacteria LGG.

1.3 Results of Pearson correlation analysis on markers

(1) In order to clarify the conclusion in 1.2, Pearson correlation analysis was performed on acetoin monomer and acetoin dimer and the number of colonies of lactic acid bacteria LGG respectively, and the fermentation data of acetoin and colony number were processed through graphpad software. , the results are shown in Figure 3 or Figure 14. It can be seen from Figure 3 or Figure 14 that the Pearson correlation coefficients r between acetoin monomer and acetoin dimer and the number of colonies are 0.92 and 0.90 respectively; where P1=0.0041 (acetoin), P2= 0.001 (acetoin dimer), P values are all less than 0.05. The above results show that there is a positive and close correlation between acetoin monomers and acetoin dimers and the number of colonies. There is a significant correlation between the changes in the number of colonies of acetoin and lactic acid bacteria LGG in apple juice, which illustrates that acetoin Aiolin can be used as a marker for changes in the number of colonies fermented by lactic acid bacteria LGG in apple juice.

(2) In order to show that 2,3-butanedione can also be used as a marker for changes in the number of fermentation colonies of apple juice lactic acid bacteria LGG, Pearson correlation analysis was performed on 2,3-butanedione, and the fermentation of the marker and colony number was The data is processed through graphpad software, and the results are shown in Figure 4 or Figure 15.

For 2,3-butanedione, the Pearson correlation coefficient r between it and the number of colonies is 0.91; P=0.00068 (2,3-butanedione), which is less than 0.05. The above results show that there is a positive and close correlation between 2,3-butanedione and the number of colonies. There is a significant correlation between 2,3-butanedione and the number of colonies of lactic acid bacteria LGG in apple juice, which illustrates that 2,3 -Diacetyl can be used as a marker for changes in the number of fermentation colonies of lactic acid bacteria LGG in apple juice.

1.4 Perform PCA analysis on apple juice from two replicate samples at different times. The analysis results are shown in Figure 5.

It can be seen from Figure 5 that the sum of the first two principal components PC1 (70%) and PC2 (13%) is 83%, which is greater than 70%. This shows that the first two principal components can represent the overall information of the sample, and the PCA results are valid. The distances between the two samples in the section are close to each other, which shows that the repeatability of the two samples in this experiment is relatively good. For any sample, from 0 to 12h, since the lactic acid bacteria LGG is in the pre-lag phase, the analyzed samples of the first three groups are more clustered in the PCA chart, and the flavors between the groups are similar; starting from 18h, the flavor difference between the groups becomes larger ; When reaching the end of the logarithmic growth phase, due to the decrease in growth metabolism rate, the flavor substances change slowly, and the PCA plots of fermentation 42h and 48h are also relatively close. The above results show that the change in the total number of bacterial colonies can represent the change trend of the overall flavor to a certain extent, and indirectly illustrates that the change trend of acetoin content during the fermentation process can represent the change trend of the overall flavor. The above results are consistent with the changes in Figure 2.

1.5 In order to further demonstrate the accuracy of using acetoin as a total bacterial colony marker to judge the fermentation process, the pH of the samples at each time period was tested. The test results are shown in Figure 6.

During the lactic acid fermentation process, lactic acid bacteria will produce lactic acid and accumulate in the fermentation broth, causing the pH of the fermentation broth to continuously decrease. As can be seen from Figure 6, the change in pH of the fermentation broth shows a continuous decline. The decline in pH is related to the accumulation of lactic acid and the Increased numbers of lactic acid bacteria. After 0-12h and 36h, the number of viable bacteria increases slowly and relatively steadily. During the above two time periods, the changes in pH value are more consistent with the changes in the number of viable bacteria. Therefore, it can be said that the changes in pH are consistent with the changes in the number of viable bacteria. Related, but between 12-30h, the changes in pH are not very consistent with the number of viable bacteria. This also shows that pH does not reflect the fermentation process well, but acetoin can be used as a marker for the total number of bacterial colonies. To judge the fermentation process in real time.

Example 2:

Lactobacillus LP is used to ferment tart cherry juice. Specifically, the prepared tart cherry juice raw materials are put into a sterilization pot and sterilized at 90°C for 10 minutes. The purpose is to kill other bacteria in the tart cherry juice raw material liquid and provide a sterile environment for fermentation. . Then, the sterilized and cooled sour cherry juice raw material liquid was added with LP lactic acid bacteria at an inoculation amount of 4% (v:v), and fermented at 37°C for 48 hours. The above fermentation process is an existing technology and will not be described in detail here.

During the above fermentation process, samples were taken and monitored every 6 hours. The number of samples at each time point is 3. One sample is used to calculate the total number of colonies using the existing plate counting method; one is used to measure the pH value, and one sample is analyzed by HS-GC-I MS to obtain the gas phase of volatile substances. Ion mobility spectrum, N-ketone C4-C9 (Sinopharm Beijing Chemical Reagent Co., Ltd.) was used to calculate the retention index (RI) of volatile compounds. By comparing with the retention time and drift time of the GC-IMS library, each volatile compound Qualitatively, the content of each volatile compound is obtained by calculating the peak volume of volatile compounds in the gas phase ion mobility spectrum.

The HS-GC-IMS analysis conditions are as follows: take 2 mL of the sample to be tested and put it into a 20 mL headspace bottle. The incubation temperature is 45°C, the incubation time is 20 min, and the incubation speed is 500 rpm. The chromatographic separation uses a Multicapillary SE-54 capillary chromatography column (0.32 mm × 30 m , 0.25μm), perform gas chromatography separation at 40°C, using nitrogen with a purity of 99.99% as the carrier gas, running at 2mL/min for 5min, 10mL/min for 10min, 50mL/min for 5min, and 150mL/min for 5min. ;IMS ionization temperature 45℃.

2.1 In order to visually express the changing rules of volatile substances during the above fermentation process, the fingerprint of volatile substances was drawn, as shown in Figure 7 or 16.

It can be seen from Figure 7 that lactic acid bacteria consume aldehydes during the fermentation process, such as benzaldehyde, hexanal, and heptanal. The dimers of benzaldehyde and hexanal almost disappear after 24 hours of fermentation, and aldehyde metabolites such as 1-heptanol, 1- The hexanol content tends to increase over a period of time, and the content of some alcohols such as 1-butanol decreases because of participation in the esterification reaction. In addition, the content of 2-heptanone increased significantly at 42 h of fermentation compared with the initial level. At the same time, an obvious monomer peak appeared in 2-pentanone at 36 h of fermentation, indicating that lactic acid bacteria LP can generate the corresponding methyl ketones through fatty acid oxidation, but compared with LGG, the metabolism of fatty acids is not that intense, especially for 2-heptanone, the content growth trend is not obvious throughout the fermentation process, and the content growth is only observed at the end of the fermentation. Although LP and LGG are both lactic acid bacteria, their genes are not exactly the same, so theoretically, there are some differences in metabolism. Regarding sugar metabolism, similar to LGG, 2,3-butanedione and acetoin were generated through pyruvate metabolism, with obvious peaks appearing at 18h and 24h of fermentation respectively.

2.2 Taking acetoin as an example, based on the number of colonies and acetoin content measured at each fermentation time point, draw a graph showing the changes in the number of colonies and acetoin as the fermentation time changes. See Figure 8 for details. It should be noted that during the HS-GC-IMS analysis and detection process, some acetoin monomers will be converted into acetoin dimers, so Figure 8 plots acetoin monomers and acetoin dimers respectively. The content change curve with fermentation time, and the acetoin content during the fermentation process is actually the sum of the contents of acetoin monomer and acetoin dimer.

It can be seen from Figure 8 that after 48 hours of fermentation, the number of colonies increased from 8.08 log CFU/mL to 8.82 log CFU/mL. LP is in the pre-lag phase from 0 to 12 hours. At this time, the metabolic activity of lactic acid bacteria is not strong, and the changes in acetoin It is not obvious either; after 12 hours of fermentation, LP enters the logarithmic growth phase, reproduces in large quantities, and has strong growth and metabolism. At the same time, the content of acetoin also begins to increase; when fermented for 30 hours, the content of acetoin monomer decreases. This is because When the substance reaches a certain amount, the monomer content begins to decrease. After 42 hours of fermentation, the number of colonies tends to level off. This shows that acetoin can most likely be used as a marker for changes in the total number of colonies fermented by Lactobacillus LP in sour cherry juice.

2.3 Results of Pearson correlation analysis on markers

(1) In order to clarify the conclusion in 2.2, Pearson correlation analysis was performed on acetoin monomer and acetoin dimer and the number of colonies of lactic acid bacteria LP respectively, and the fermentation data of acetoin and colony number were processed through graphpad software. , the results are shown in Figure 9 or Figure 17. It can be seen from Figure 9 or Figure 17 that the Pearson correlation coefficient r between acetoin monomer and acetoin dimer and the number of colonies is 0.80 and 0.99 respectively; its P1=0.01 (acetoin monomer), P2=9.3×10 ^-6 (acetoin dimer), both values are less than 0.05. The above results show that there is a positive and close correlation between acetoin monomers and acetoin dimers and the number of colonies. There is a significant correlation between the changes in acetoin content in tart cherry juice and the changes in the number of lactic acid bacteria LP colonies. This It shows that acetoin can be used as a marker for changes in the number of colonies fermented by Lactobacillus LP in sour cherry juice.

(2) In order to show that 2,3-butanedione can also be used as a marker for changes in the number of fermentation colonies of sour cherry juice Lactobacillus LP, Pearson correlation analysis was performed on the marker, and the fermentation data of the marker and colony number were passed through graphpad Software processing, the results are shown in Figure 10 or Figure 18.

For 2,3-butanedione, the Pearson correlation coefficient r between it and the number of colonies is 0.97; its P=0.000018 (2,3-butanedione), which is less than 0.05. The above results show that there is a positive and close correlation between 2,3-butanedione and the number of colonies. There is a significant correlation between the changes in the content of 2,3-butanedione in tart cherry juice and the changes in the number of lactic acid bacteria LP colonies. This shows that It was found that 2,3-butanedione can be used as a marker for changes in the number of colonies fermented by Lactobacillus LP in tart cherry juice.

2.4 Perform PCA analysis on tart cherry juice from two replicate samples at different times. The analysis results are shown in Figure 11.

It can be seen from Figure 11 that the sum of the first two principal components PC1 (70%) and PC2 (13%) is 83%, which is greater than 70%. This shows that the first two principal components can represent the overall information of the sample, and the PCA results are valid. Two The distance between the samples in the PCA plot at 12 h may be due to differences in the starting times of logarithmic growth cycles in different experiments, or due to time measurement errors and other reasons, resulting in large flavor differences between the two samples in a short period of time. For any sample, from 0 to 12 hours, because the lactic acid bacteria LP is in the early lag phase, the distribution of the first three groups of analyzed samples in the PCA chart is relatively clustered, and the flavors between the groups are similar; when it reaches the end of the logarithmic growth phase, due to the growth The metabolic rate decreases, the flavor substances change slowly, and the PCA plots of fermentation 42h and 48h are also relatively close. The above results indicate that changes in the total number of bacterial colonies can represent the changing trend of the overall flavor to a certain extent. This indirectly illustrates that the changing trend of acetoin content during the fermentation process can also represent the changing trend of the overall flavor. The above results are consistent with the changes in Figure 8.

2.5 In order to further demonstrate the accuracy of using acetoin as a marker for total bacterial colony count to judge the fermentation process, the pH of the samples at each time period was measured. The test results are shown in Figure 12.

From Figure 12, we can see that the change in pH is similar to the change in bacterial colony number. Specifically, there is little change from 0 to 12 hours, and it begins to decrease significantly after 12 hours. It tends to change slowly after 42 hours, and the pH drops to 3.92 after 48 hours of fermentation. The changes in pH further verified that acetoin can be used as a marker of the total number of bacterial colonies to judge the fermentation process.

The above specific embodiments cannot be used to limit the scope of the present invention. For those skilled in the art, any substitutions, improvements or transformations made to the embodiments of the present invention fall within the scope of the present invention. Things not described in detail in the present invention are all well-known technologies to those skilled in the art.

Claims (7)

1. A monitoring method for the lactic acid fermentation process of fruit and vegetable juice is characterized in that a component A is used as a marker for the total number change of bacterial colonies in the lactic acid fermentation process of the fruit and vegetable juice, the content of the component A at different time points in the fermentation process is determined through HS-GC-IMS analysis, the fermentation process is judged according to the content change condition of the component A at different time points, and the fermentation end point is determined through the fact that the content of the component A reaches a certain value;

wherein, the component A is acetoin or 2, 3-butanedione.

2. The method for monitoring the lactic acid fermentation process of fruit and vegetable juice according to claim 1, wherein the gas-phase ion mobility spectrogram of the fermentation sample is obtained through HS-GC-IMS analysis, and the peak volume of the component A in the spectrogram is calculated to obtain the corresponding content of the component A.

3. The method for monitoring the lactic acid fermentation process of fruit and vegetable juice according to claim 2, wherein the analysis conditions of the HS-GC-IMS are as follows: 2mL of sample to be tested is taken and put into a 20mL headspace bottle, the incubation temperature is 40-50 ℃, the incubation time is 10-30min, and the incubation rotating speed is 350-550rpm; the chromatographic separation is carried out by adopting a nonpolar capillary chromatographic column, carrying out gas chromatographic separation at 38-45 ℃, taking nitrogen with the purity of 99.99% as carrier gas, and carrying out the chromatographic separation according to 2mL/min for 5-8min,10mL/min for 5-10min,50mL/min for 2-8min and 150mL/min for 2-8 min; IMS ionization temperature 45 ℃.

4. A method for monitoring the lactic acid fermentation process of fruit and vegetable juice according to claim 3, wherein the HS-GC-IMS analysis conditions are as follows: 2mL of the sample to be tested is taken and put into a 20mL headspace bottle, the incubation temperature is 45 ℃, the incubation time is 20min, and the incubation rotating speed is 500rpm; the chromatographic separation is carried out by adopting a Multicapillary SE-54 capillary chromatographic column (0.32 mm multiplied by 30m,0.25 μm), carrying out gas chromatographic separation at 40 ℃, taking nitrogen with the purity of 99.99% as carrier gas, and carrying out operation at 2mL/min for 5min,10mL/min for 10min,50mL/min for 5min and 150mL/min for 5 min; IMS ionization temperature 45 ℃.

5. The method for monitoring the lactic acid fermentation process of fruit and vegetable juice according to claim 2, wherein the sampling interval is 2-6 h.

6. The method for monitoring the lactic acid fermentation process of fruit and vegetable juice according to claim 5, wherein the sampling interval is 6h.

7. The method for monitoring the lactic acid fermentation process of fruit and vegetable juice according to claim 1, wherein the fruit and vegetable juice is one of sour cherry juice, apple juice, pear juice, kiwi fruit juice and peach juice.