CN108271989B

CN108271989B - Non-thermal sterilization micro-processing chamber, sterilization system and sterilization method for blueberry juice

Info

Publication number: CN108271989B
Application number: CN201810036056.0A
Authority: CN
Inventors: 孙爱东; 朱宁; 于宁; 韦玉龙; 朱月; 张嘉颖; 雷雨晴
Original assignee: Beijing Forestry University
Current assignee: Beijing Forestry University
Priority date: 2018-01-15
Filing date: 2018-01-15
Publication date: 2021-06-29
Anticipated expiration: 2038-01-15
Also published as: CN108271989A

Abstract

The invention provides a blueberry juice non-thermal sterilization micro-processing chamber, and a sterilization system and a sterilization method using the micro-processing chamber, wherein the micro-processing chamber has the advantages that the electrode spacing is shortened by virtue of a microchip, the volume is smaller, the voltage is greatly reduced on the premise of ensuring the same sterilization effect, a series of equipment such as a voltage amplifier and the like can be replaced, and compared with the traditional high-voltage pulse electric field sterilization, the operability is obviously improved, and the cost is effectively reduced; in the treatment process, the temperature rise amplitude is small, no pressure change exists, secondary pollution is avoided, the sensory quality of the blueberry juice is not influenced, and the anthocyanin can be promoted to be dissolved out, so that the high-quality blueberry juice is obtained while microorganisms are effectively killed; meanwhile, due to the precision of the microchip, the experimental precision is greatly improved, the sterilization parameters can be strictly controlled, and the possibility is provided for the digital sterilization of factories.

Description

Non-thermal sterilization micro-processing chamber, sterilization system and sterilization method for blueberry juice

Technical Field

The invention belongs to the technical field of fruit juice sterilization, and particularly relates to a non-thermal sterilization micro-processing chamber, a sterilization system and a sterilization method for blueberry juice.

Background

Blueberries are enjoyed by consumers due to their rich nutritional value and health-care function, but due to their seasonality and poor storage, about fifty percent of the world's blueberries are processed into juices or other products. For heat-sensitive fruit juice represented by blueberry juice, heat sterilization has certain influence on the nutrition and sensory quality of the blueberry juice, so that a non-heat processing technology is derived.

High-voltage Pulse Electric Field (PEF) is used as a non-thermal sterilization technology for achieving commercial sterility of food by destroying microbial cell membranes, has small temperature rise and no pollution to the environment, can reduce the damage to the sensory and nutritional quality of the food to the maximum extent, can effectively kill most microbes, and arouses the research interest of domestic and foreign industry people, but the pulse electric field sterilization technology has the following problems in practical application: (1) high voltage is generally required to obtain high field strength, and the high voltage pulse generator is high in cost; (2) the PEF treatment chamber consists of two electrodes and an insulating material, wherein the electrodes are easily electrolyzed under high voltage to generate strong oxidizing substances which may form substances harmful to human bodies and damage the components of treatment liquid, and meanwhile, the electrode electrolysis can also influence the service life of the system; (3) the defects of inaccurate control of operation parameters, high cost, large volume and the like exist in the actual operation. Based on the above problems, how to overcome the disadvantages of the conventional processing chamber and implement the sterilization technology under low voltage becomes one of the hot spots in the current PEF research field.

With the maturation and development of micro-electro-mechanical technology, microchips and biochips have gained much attention in the field of application of pulsed electric fields. The microchip has the advantages of high efficiency, high analysis speed, integration of multiple functions and the like, so that the pulse electric field technology based on the microchip is widely applied in the field of biochemistry. The electrode spacing of the processing chamber of the lab-scale PEF sterilization system is at least several millimeters, the voltage needs to reach several kilovolts to several tens kilovolts to obtain high sterilization rate, and such a pulse generator is very costly and difficult to manufacture. Because the electrode spacing of the microchip is in the micron level, the required voltage is low, and the high surface-to-volume ratio of the microchip is favorable for heat dissipation and can reduce the heat effect, the microchip has ideal development space for researching pulsed electric field sterilization.

Disclosure of Invention

In order to solve the technical problems, the invention provides a non-thermal sterilization micro-processing chamber, a sterilization system and a sterilization method for blueberry juice.

The specific technical scheme of the invention is as follows:

the invention provides a blueberry juice non-thermal sterilization micro-processing chamber which comprises a bottom plate and a packaging plate arranged above the bottom plate, wherein a microelectrode is etched on the top of the bottom plate, a juice channel is etched on the bottom of the packaging plate, a juice inlet and a juice outlet which are communicated with the juice channel are respectively arranged at two ends of the top of the packaging plate, which are positioned at two ends of the juice channel, and the extending direction of the juice channel is the same as the current circulation line of the microelectrode.

The blueberry juice non-thermal sterilization micro-processing chamber provided by the invention utilizes a microchip pulse electric field to sterilize blueberry juice, and after a bottom plate and a packaging plate are buckled and sealed, a juice channel and the bottom plate can form a path for juice circulation; because the extending direction of the juice channel is the same as the current flowing direction of the microelectrode, all blueberry juice flowing through the juice channel can be subjected to sterilization treatment by an electric field, and the sterilization efficiency is effectively improved.

Further, the micro-electrode is an interdigital electrode structure formed by a pair of comb-shaped electrodes in a crossed arrangement.

The comb-shaped electrode comprises a positive electrode and a negative electrode, and the structure of the interdigital electrode can greatly reduce the distance between the positive electrode and the negative electrode, so that the volume of the electrode is reduced, and the comb-shaped electrode is convenient to use; the edge electrodes on the two sides of the interdigital electrode can be thickened so as to reduce the phenomenon of edge field intensity reduction; the microelectrode can be made of a copper-plated material, has good stability, is not easy to electrolyze, does not generate pollutants or substances harmful to human bodies, and is suitable for long-term use.

Further, the distance between the positive electrode and the negative electrode of the microelectrode is 100 μm, the width of the center comb teeth is 30 μm, and the width of the edge comb teeth is not less than that of the center comb teeth.

Further, the juice channel comprises n transverse grooves and n +1 longitudinal grooves perpendicular to the transverse grooves, two ends of each transverse groove are respectively communicated with one end of each two adjacent longitudinal grooves, and n is a natural number not less than 2; the 1 st keep away from on the vertical groove the one end of horizontal groove with the fruit juice import intercommunication, the n +1 th keep away from on the vertical groove the one end of horizontal groove with the fruit juice export intercommunication.

Through the setting, make the fruit juice passageway be snakelike arranging, greatly increased the total length of fruit juice passageway to the time that blueberry juice passes through the fruit juice passageway under the same velocity of flow has been prolonged, made blueberry juice can obtain abundant sterilization process.

Further, the widths of the longitudinal grooves and the transverse grooves are both 3mm, and the distance between every two adjacent longitudinal grooves is 0.5 mm.

The invention also provides a non-thermal sterilization system for blueberry juice, which comprises the micro-processing chamber and also comprises the following parts which are respectively and electrically connected with the micro-processing chamber:

the single-pulse power supply is used for providing pulse voltage for the micro-processing chamber;

the sample injection system is connected with the fruit juice inlet and is used for conveying the blueberry juice sample into the micro-processing chamber;

and the sample outlet system is connected with the juice outlet and is used for outputting and collecting the blueberry juice sample subjected to pulse processing from the micro-processing chamber.

The single pulse power supply used by the system is a customized square wave pulse power supply, the single voltage is 220V +/-10%, the frequency is 50Hz/60Hz +/-5%, and the rated current is 4A, so that the pulse low voltage required by sterilization can be provided; the sample injection system can adopt a digital injection pump and a digital injector so as to accurately control the flow rate of the blueberry juice.

Further, the sterilization system further comprises a monitoring system, and the monitoring system comprises the following parts:

the pulse monitoring device is electrically connected with the micro-processing chamber and is used for monitoring the pulse generation condition of the micro-processing chamber in real time;

and the temperature monitoring device is connected with the tail end of the sample outlet system and used for monitoring the temperature change condition of the blueberry juice sample collected by the sample outlet system.

The invention also provides a non-thermal sterilization method for blueberry juice by applying the sterilization system, which comprises the following steps:

s1: sterilizing the micro-processing chamber, conveying the blueberry juice into the micro-processing chamber through the sample introduction system, and performing pulse processing, wherein the width of a pulse is 0.14-0.16 ms, and the voltage is 330-370V;

s2: and outputting the blueberry juice subjected to pulse treatment from the micro-processing chamber through the sample outlet system, and collecting to obtain the sterilized blueberry juice.

The pulse width and the voltage are optimized, so that bacteria and fungi in the blueberry juice can be effectively killed, the content of total phenols and anthocyanin in the blueberry juice can not be reduced, the sterilization effect is ensured, and the excellent quality of the blueberry juice can be maintained.

Further, the flow rate of the blueberry juice sample entering the micro-processing chamber is 9 mL/min.

The flow rate is optimized, so that the blueberry juice can be fully sterilized, the sterilization efficiency can be ensured as far as possible, and the sterilization time can be shortened.

Further, the method of sterilizing the micro-processing chamber is as follows:

firstly, injecting 75% ethanol solution into the micro-processing chamber through the sample injection system, enabling the ethanol solution to flow out of the sample outlet system, and then washing with sterile distilled water for 3-5 times.

The invention has the following beneficial effects: the invention provides a blueberry juice non-thermal sterilization micro-processing chamber, and a sterilization system and a sterilization method using the micro-processing chamber, wherein the micro-processing chamber has the advantages that the electrode spacing is shortened by virtue of a microchip, the volume is smaller, the voltage is greatly reduced on the premise of ensuring the same sterilization effect, a series of equipment such as a voltage amplifier and the like can be replaced, and compared with the traditional high-voltage pulse electric field sterilization, the operability is obviously improved, and the cost is effectively reduced; in the treatment process, the temperature rise amplitude is small, no pressure change exists, secondary pollution is avoided, the sensory quality of the blueberry juice is not influenced, and the anthocyanin can be promoted to be dissolved out, so that the high-quality blueberry juice is obtained while microorganisms are effectively killed; meanwhile, due to the precision of the microchip, the experimental precision is greatly improved, the sterilization parameters can be strictly controlled, and the possibility is provided for the digital sterilization of factories.

Drawings

FIG. 1 is a top view of a bottom plate of a non-thermal sterilization micro-processing chamber for blueberry juice in example 1;

FIG. 2 is a bottom view of the package plate in the non-thermal sterilization micro-processing chamber for blueberry juice as described in example 1;

FIG. 3 is a top view of a bottom plate of a non-thermal sterilization micro-processing chamber for blueberry juice in example 2;

FIG. 4 is a bottom view of the package plate in the non-thermal sterilization micro-processing chamber for blueberry juice as described in example 2;

FIG. 5 is a schematic structural diagram of a non-thermal blueberry juice sterilization system in embodiment 5;

FIG. 6 shows the variation of viable count of live bacteria in blueberry juice with voltage in Experimental example 1;

FIG. 7 shows the content of total phenols and anthocyanins in blueberry juice varying with voltage in Experimental example 1;

FIG. 8 shows the variation of the number of viable bacteria in blueberry juice with pulse width in Experimental example 2;

FIG. 9 shows the content of total phenols and anthocyanins in blueberry juice varying with pulse width in Experimental example 2;

FIG. 10 shows the variation of viable count of live bacteria in blueberry juice with the flow rate of sample injection in Experimental example 3;

FIG. 11 shows the content of total phenols and anthocyanidin in blueberry juice varying with the flow rate of sample injection in Experimental example 3;

FIG. 12 shows the PCA results of the different treatments of the blueberry juice odor of Experimental example 5;

FIG. 13 shows DFA results of blueberry juice odor treated by different methods in Experimental example 5;

FIG. 14 shows the SIMCA results of the blueberry juice odor treated by different methods in Experimental example 5;

FIG. 15 shows SQC results of blueberry juice odor treated by different methods in Experimental example 5;

FIG. 16 shows the PCA results of the mouthfeel of blueberry juices processed by different methods in Experimental example 5;

FIG. 17 shows DFA results of the mouthfeel of blueberry juice treated by different methods in Experimental example 5;

FIG. 18 shows the SIMCA results of the mouthfeel of blueberry juices processed by different methods in Experimental example 5;

FIG. 19 shows SQC results of the mouthfeel of blueberry juices treated by different methods in Experimental example 5.

Wherein: 1. a base plate; 11. a microelectrode; 2. a package board; 21. a juice passageway; 22. a fruit juice inlet; 23. a fruit juice outlet; 24. a transverse groove; 25. a longitudinal groove; 3. a single pulse power supply; 4. a sample introduction system; 41. a digital syringe pump; 42. a digital injector; 43. a sample introduction pipeline; 5. a sample outlet system; 51. a sample outlet pipeline; 52. a collection device; 6. a monitoring system; 61. a pulse monitoring device; 62. and a temperature monitoring device.

Detailed Description

The present invention will be described in further detail with reference to the following examples and drawings.

Example 1

As shown in fig. 1, embodiment 1 of the present invention provides a non-thermal sterilization micro-processing chamber for blueberry juice, which includes a bottom plate 1 and an encapsulation plate 2 disposed above the bottom plate 1, wherein a micro-electrode 11 is etched on a top of the bottom plate 1, a juice channel 21 is etched on a bottom of the encapsulation plate 2, a juice inlet 22 and a juice outlet 23, which are respectively communicated with the juice channel 21, are respectively disposed at two ends of the juice channel 21 on the top of the encapsulation plate 2, and an extending direction of the juice channel 21 is the same as a current flow path of the micro-electrode 11.

When the blueberry juice packaging device is used, after the bottom plate 1 and the packaging plate 2 are buckled and sealed, the juice channel 21 can be combined with the bottom plate 1 to form a path for juice to flow, and after blueberry juice is injected from the juice inlet 22, the blueberry juice can flow along the path and finally flow to the juice outlet 23; because the extending direction of the juice channel 21 is the same as the current flowing direction of the microelectrode 11, all blueberry juice flowing through the juice channel 21 can be subjected to sterilization treatment by an electric field, and the blueberry juice can also be subjected to the action of the electric field in the whole process of flowing through the juice channel 21, so that the sterilization efficiency is effectively improved.

Example 2

As shown in FIG. 2, this example 2 provides a non-thermal sterilization micro-processing chamber for blueberry juice based on example 1, and this example 2 further defines that the micro-electrode 12 is an interdigitated electrode structure formed by a pair of comb-shaped electrodes arranged in a crossing manner, the distance between the positive and negative electrodes of the micro-electrode 12 is 100 μm, and the width of the comb teeth is 30 μm.

Juice passageway 21 include 4

cross slots

24 and 5 with cross slot 24 vertically indulges groove 25, every cross slot 24 both ends communicate with the one end of two adjacent vertical slots 25 respectively, and the one end and the juice import intercommunication of keeping away from cross slot 24 on the 1 st vertical slot 25, and the one end and the juice export 23 intercommunication of keeping away from cross slot 24 on the 5 th vertical slot 25.

Example 3

Example 3 a non-thermal sterilization micro-processing chamber for blueberry juice is provided on the basis of example 2, and example 3 further defines that the distance between the positive electrode and the negative electrode of the microelectrode 12 is 100 μm, the width of the center comb teeth is 30 μm, and the width of the edge comb teeth is 40 μm; the widths of the longitudinal grooves 25 and the transverse grooves 24 are both 3mm, and the distance between adjacent longitudinal grooves 25 is 0.5 mm.

Example 4

This embodiment 4 provides a non-thermal sterilization system of blueberry juice, includes the little processing chamber that embodiment 1 provided, still includes the following part of being connected with little processing chamber electricity respectively:

the single pulse power supply 3 is used for providing pulse voltage for the micro-processing chamber;

the sample injection system 4 is connected with the fruit juice inlet 22 and is used for conveying the blueberry juice sample into the micro-processing chamber;

and the sample outlet system 5 is connected with the juice outlet 23 and is used for outputting and collecting the blueberry juice sample subjected to pulse processing from the micro-processing chamber.

The sample injection system 4 used in the present embodiment comprises a digital injection pump 41 (a digital injection pump of RSP01-E model is adopted), a digital injector 42 (a digital injector of W-HDS88411 model can be used), and a sample injection pipeline 43, and can accurately control the flow rate of the blueberry juice sample; the sample outlet system 5 comprises a sample outlet pipe 51 and a collecting device 52.

Example 5

As shown in fig. 3, this embodiment 5 provides a non-thermal blueberry juice sterilization system, which includes the micro-processing chamber provided in embodiment 2 and the portions provided in embodiment 4, and further includes a monitoring system 6, where the monitoring system 6 includes the following portions:

the pulse monitoring device 61 is electrically connected with the micro-processing chamber and is used for monitoring the pulse generation condition of the micro-processing chamber in real time;

and the temperature monitoring device 62 is connected with the tail end of the sample outlet system 5 and is used for monitoring the temperature change condition of the blueberry juice sample collected by the sample outlet system 5.

The pulse monitoring device 61 used in this embodiment is an oscilloscope (an oscilloscope of SDS 1122E type may be used), and the temperature monitoring device 62 may be a general thermometer.

Example 6

This example 6 provides a non-thermal blueberry juice sterilization system comprising the micro-processing chamber provided in example 3 and the parts provided in example 5.

Example 7

This embodiment 7 provides a non-thermal blueberry juice sterilization method using the sterilization system of embodiment 4, which includes the following steps:

s1: sterilizing the micro-processing chamber, conveying the blueberry juice into the micro-processing chamber through a sample introduction system 4, and performing pulse processing, wherein the width of the pulse is 0.15ms, and the voltage is 350V;

s2: and outputting the blueberry juice subjected to pulse treatment from the micro-treatment chamber through a sample outlet system 5, and collecting to obtain the sterilized blueberry juice.

Example 8

This example 8 provides a non-thermal blueberry juice sterilization method using the sterilization system of example 5, including the steps provided in example 7, and further defining the flow rate of the blueberry juice sample into the micro-processing chamber to be 9 mL/min.

In step S1, the method of sterilizing the micro-processing chamber is as follows:

firstly, injecting a 75% ethanol solution into a micro-processing chamber through a sample injection system, enabling the ethanol solution to flow out of the sample outlet system, and then washing with sterile distilled water for 3-5 times.

Example 9

This embodiment 9 provides a non-thermal blueberry juice sterilization method using the sterilization system described in embodiment 6, which includes the steps provided in embodiment 8.

Comparative example 1

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 7, wherein the voltage of the pulse treatment is 50V.

Comparative example 2

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 7, wherein the voltage of the pulse treatment is 100V.

Comparative example 3

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 7, wherein the voltage of the pulse treatment is 150V.

Comparative example 4

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 7, wherein the voltage of the pulse treatment is 200V.

Comparative example 5

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 7, wherein the voltage of the pulse treatment is 250V.

Comparative example 6

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 7, wherein the voltage of the pulse treatment is 300V.

Comparative example 7

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 7, wherein the voltage of the pulse treatment is 400V.

Comparative example 8

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 8, wherein the pulse width is 0.1 ms.

Comparative example 9

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 8, wherein the pulse width is 0.125 ms.

Comparative example 10

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 8, wherein the pulse width is 0.175 ms.

Comparative example 11

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 8, wherein the pulse width is 0.2 ms.

Comparative example 12

A non-thermal blueberry juice sterilization method comprising the steps provided in example 9, wherein the flow rate of a blueberry juice sample into the micro-processing chamber is 6 mL/min.

Comparative example 13

A non-thermal blueberry juice sterilization method comprising the steps provided in example 9, wherein the flow rate of a blueberry juice sample into the micro-processing chamber is 7 mL/min.

Comparative example 14

A non-thermal blueberry juice sterilization method comprising the steps provided in example 9, wherein the flow rate of a blueberry juice sample into the micro-processing chamber is 8 mL/min.

Comparative example 15

A non-thermal sterilization method for blueberry juice, comprising the steps provided in embodiment 9, wherein the flow rate of the blueberry juice sample into the micro-processing chamber is 10 mL/min.

Experimental example 1

Comparison of treatment effects for different voltages

Taking the method provided by the embodiment 7 as an experimental group 1, taking the methods provided by the comparison examples 1-7 as comparison groups 1-7 respectively, taking untreated fresh blueberry juice as a blank control, and performing sterilization treatment on blueberry juice from the same source by adopting the methods respectively, and performing the following detection after the sterilization is finished:

(1) measuring the total number of viable bacteria of each group of blueberry juice, adopting a plate counting agar to coat a plate for detecting the total number of bacterial colonies, and culturing for 24 hours at 37 ℃; and (3) detecting the total amount of the mold and the yeast, selecting a malt extract powder agar culture medium, and culturing for 3-4 days at 28 ℃.

As shown in fig. 6, the total number of bacteria and the total number of fungi were gradually decreased as the voltage was increased, and when the voltage was increased to 350V, the presence of viable bacteria was not detected. The voltage is not lower than 350V, so that the good sterilization effect can be achieved.

(2) And (3) determining the total phenol content and the anthocyanin content of each group of blueberry juice: the determination of total phenol adopts Folin-Ciocalteu colorimetry, the absorbance value at 765nm is determined, and the total phenol content is calculated according to a pyrogallic acid standard curve; the measurement of anthocyanin was carried out by the pH differential method, in which the sample was added to buffers of pH1.0 and pH4.5, and absorbance values at 520nm and 700nm were measured, respectively, and the absorbance of anthocyanin was (a520nm-a700nm) pH1.0- (a520nm-a700nm) pH 4.5.

As shown in fig. 7, as the voltage was increased, no significant change in total phenol content occurred; the anthocyanin content firstly shows a rising trend, reaches a maximum value at 350V and then begins to greatly decline. The possible reason is that the voltage rise can promote the dissolution of the anthocyanin, and the overhigh voltage can destroy the structure of the anthocyanin, thereby causing the change of the content of the anthocyanin.

In summary, when the pulse voltage is 350V, the sterilization effect is the best, and the content of anthocyanin is the highest, so 350V is selected as the optimal sterilization voltage.

Experimental example 2

Comparison of treatment effects for different pulse widths

The method provided by the embodiment 8 is used as an experimental group 1, the methods provided by the comparison examples 8-11 are used as comparison groups 1-4, untreated fresh blueberry juice is used as a blank comparison, the blueberry juice from the same source is sterilized by the methods, and after sterilization is finished, the total viable count, the total phenol content and the anthocyanin content of each group of blueberry juice are detected according to the method provided by the experimental example 1.

As shown in fig. 8, the total number of bacteria and the total number of fungi were gradually decreased as the pulse width was increased, and when the pulse width was increased to 0.15ms, the presence of viable bacteria was not detected. The pulse width is not less than 0.15ms, so that a good sterilization effect can be achieved.

As shown in fig. 9, as the pulse width increased, no significant change in total phenol content occurred; the anthocyanin content first shows a rising trend, reaches a maximum value at 0.15ms, and then begins to gradually decline. The possible reason is that the increase of the pulse width can promote the dissolution of the anthocyanin, and the excessive pulse width can destroy the structure of the anthocyanin, thereby causing the change of the content of the anthocyanin.

As described above, when the pulse width is 0.15ms, the sterilization effect is the best, and the content of anthocyanin is the highest, so 0.15ms is selected as the optimal pulse width.

Experimental example 3

Comparison of treatment effects at different sample introduction flow rates

The method provided by the embodiment 9 is used as an experimental group 1, the methods provided by the comparison examples 12-15 are used as comparison groups 1-4, untreated fresh blueberry juice is used as a blank comparison, the blueberry juice from the same source is sterilized by the methods, and the total viable count, the total phenol content and the anthocyanin content of each group of blueberry juice are detected according to the method provided by the experimental example 1 after sterilization.

As shown in FIG. 10, when the flow rate does not exceed 9mL/min, no viable bacteria can be detected in each group of blueberry juice; when the flow rate reached 10mL/min, viable fungi began to be detected. The possible reasons are that the blueberry juice cannot sufficiently receive the sterilization effect of the electric field due to the excessively high flow speed, and the fungus resistance is stronger than that of bacteria, so that the situation of incomplete sterilization is easy to occur.

As shown in fig. 11, as the flow rate was increased, no significant change in total phenol content occurred; the anthocyanin content did not change significantly at the beginning, but decreased when the flow rate reached 10 mL/min. The probable reason is that the blueberry juice cannot sufficiently receive the action of an electric field due to the too high flow rate, so that the dissolution of anthocyanin is influenced, and the content of anthocyanin is changed.

In conclusion, when the flow rate of the sample injection is not more than 9mL/min, a good sterilization effect can be obtained, and the content of anthocyanin is high; however, in view of shortening the treatment time, saving time cost and equipment loss, 9mL/min was selected as the optimum flow rate of the sample.

Experimental example 4

Comparison of influences of different sterilization methods on physical and chemical quality of blueberry juice

The method provided in example 9 (hereinafter referred to as MPEF) was used as experimental group 1, and conventional heat treatment methods (95 ℃, 15s high temperature short time sterilization) and high-pressure pulse field PEF sterilization methods (30KV, 60 μ s) were used as

control groups

1 and 2, respectively, to sterilize blueberry juice from the same source, and Vc, anthocyanin, titratable acid, total phenols, soluble reducing sugar, and soluble solid (Brix%) of each group of blueberry juice were measured and compared, respectively, using untreated fresh blueberry juice as positive control. The results are shown in Table 1.

TABLE 1 Effect of different sterilization modes on the physicochemical Properties of blueberry juice

As can be seen from Table 1, the heat treatment has a large influence on the physicochemical indexes of the blueberry juice, the contents of Vc, anthocyanins and total phenols are all lower than those of other groups, and the contents of soluble reducing sugar and soluble solid matter are higher than those of other groups; the MPEF and the PEF have small influence on various indexes of the blueberry juice, wherein the physical and chemical indexes of the MPEF group blueberry juice have the minimum change, and meanwhile, the anthocyanin content is increased. The MPEF method provided by the invention is adopted to sterilize the blueberry juice, so that the physical and chemical indexes of the blueberry juice can be retained to the maximum extent, and the physical and chemical quality of the blueberry juice is ensured.

Experimental example 5

Comparison of influence of different sterilization methods on sensory quality of blueberry juice

The method provided in example 9 (hereinafter referred to as MPEF) was used as an experimental group a, and a high-temperature short-time sterilization method HTST (95 ℃, 15s) was used as a control group b, blueberry juice from the same source was sterilized, and the sensory quality of each group of blueberry juice was measured as follows using untreated fresh blueberry juice as a positive control c:

(1) electronic nose for measuring blueberry juice odor

The sample injection speed is 300mL/min, the carrier gas speed is 300mL/min, the measurement time is 100s, and the cleaning time is 1000 s. Data obtained for the electronic sensor panels were compared using Principal Component Analysis (PCA), Discriminant Function Analysis (DFA), soft independent model analysis (SIMCA), and statistical quality control analysis (SQC), respectively. The experimental results are shown in FIGS. 12 to 15.

Fig. 12 shows PCA results for three groups of blueberry juice odors. The contribution rate of the principal component 1 is 83.303%, the contribution rate of the principal component 2 is 12.699%, and the two-term accumulated contribution rate is 96%, which indicates that the selected principal component can well reflect the overall information of the sample. The differentiation index for the three groups of blueberry juices was 92, indicating that PCA could completely differentiate the 3 groups of blueberry juice samples that were subjected to different treatments. Comparing the abscissa positions of the samples in the three groups a, b and c, the distance between the group a and the group b is closer, and the distance between the group c is farther, which shows that the odor difference between the HTST-treated blueberry juice and the freshly squeezed blueberry juice is larger, and the MPEF treatment has smaller influence on the odor of the blueberry juice.

Fig. 13 is DFA results for three groups of blueberry juice odors. The abscissa discrimination factor is 97.613%, the ordinate discrimination factor is 2.387%, and the sum of the discrimination factors is 100%, that is, the correct discrimination rate is 100%. The size of the discrimination factor is in direct proportion to the distinguishing capability of the electronic nose, and the discrimination factor shows that the DPA analysis technology can effectively distinguish three types of blueberry juice treated differently. The three groups of blueberry juice are obviously divided into two groups, wherein the group a is closer to the group b, and the group c is divided into one group separately, which shows that the flavor of the MPEF-treated blueberry juice is closer to that of freshly squeezed blueberry juice.

Figure 14 is the SIMCA results for three groups of blueberry juice odors. The soft independent model verifies that the score is 90 points, which shows that the method can well distinguish the odors of the three groups of blueberry juices. As can be seen from the figure, the freshly squeezed blueberry juice and the MPEF-treated blueberry juice are in the same interval, and the HTST-treated blueberry juice is separately divided outside the interval, which shows that the HTST-treated blueberry juice has a larger difference with the freshly squeezed blueberry juice and the MPEF-treated blueberry juice, and the MPEF-treatment has a smaller influence on the odor of the blueberry juice.

Figure 15 is the SQC analysis of the odor of three groups of blueberry juices. The recognition index was 87, it is visually apparent from the figure that the HTST treatment group is far from the scent unit of the freshly extracted blueberry juice, indicating that HTST treatment has a greater impact on the flavor of the freshly extracted blueberry juice.

Therefore, the flavor of the MPEF-treated blueberry juice is considered to be closer to that of freshly extracted blueberry juice.

(2) Electronic tongue for measuring mouth feel of blueberry juice

Using a mixture of 30mmol/L KCl and 0.3mmol/L tartaric acid as reference solutions, the taste sensor was immersed in the sample to be tested (Vt) and the reference solution (Vr), respectively, and the difference in potential between the two was used to evaluate the taste value. The aftertaste is measured by washing the sensor with a reference solution and then soaking the sensor in the reference solution again, wherein the potential is Vr ', and the Vr' -Vr is the aftertaste. When the measurement of one sample is finished, the sensor is cleaned by alcohol with a certain concentration, substances adsorbed on the sensor are completely removed, and then the next sample to be measured is measured. Data obtained for the electronic sensor panels were compared using Principal Component Analysis (PCA), Discriminant Function Analysis (DFA), soft independent model analysis (SIMCA), and statistical quality control analysis (SQC), respectively. The experimental results are shown in FIGS. 16 to 19.

Fig. 16 shows PCA results of the mouthfeel of three groups of blueberry juices. The contribution rate of the principal component 1 is 97.049%, the contribution rate of the principal component 2 is 2.951%, and the two-term cumulative contribution rate is 100%, which shows that the selected principal component can well reflect the overall information of the sample. The differentiation index for the three groups of blueberry juices was 87, indicating that PCA could completely differentiate the differently treated 3 groups of blueberry juice samples. Comparing the abscissa positions of the samples in the three groups a, b and c, the distance between the group a and the group b is closer, and the distance between the group c is farther, which shows that the taste difference between the HTST-treated blueberry juice and the freshly squeezed blueberry juice is larger, and the MPEF treatment has smaller influence on the smell of the blueberry juice.

Fig. 17 shows DFA results of the mouthfeel of three groups of blueberry juices. The abscissa discrimination factor is 99.828%, the ordinate discrimination factor is 0.172%, and the sum of the discrimination factors is 100%, i.e., the correct discrimination rate is 100%. The size of the discrimination factor is in direct proportion to the distinguishing capability of the electronic tongue, and the discrimination factor shows that the DPA analysis technology can effectively distinguish three types of blueberry juice treated differently. The three groups of blueberry juice are obviously divided into two groups, wherein the group a is closer to the group b, and the group c is divided into one group separately, which shows that the MPEF treated blueberry juice is closer to the fresh blueberry juice in taste.

FIG. 18 shows the SIMCA results for three groups of blueberry juices. The soft independent model verifies that the score is 83 points, which shows that the method can well distinguish the tastes of the three groups of blueberry juice. As can be seen from the figure, the freshly squeezed blueberry juice and the MPEF-treated blueberry juice are in the same interval, and the HTST-treated blueberry juice is separately divided outside the interval, which shows that the HTST-treated blueberry juice has a larger difference with the freshly squeezed blueberry juice and the MPEF-treated blueberry juice, and the MPEF-treatment has a smaller influence on the taste of the blueberry juice.

FIG. 19 shows SQC analysis results for three groups of blueberry juices. The identification index was 82, it is visually apparent from the figure that the HTST treatment group is located far from the scent unit of the freshly extracted blueberry juice, indicating that HTST treatment has a greater impact on the flavor of the freshly extracted blueberry juice.

Therefore, the mouthfeel of the MPEF-treated blueberry juice is considered to be closer to that of the freshly squeezed blueberry juice.

By combining the analysis, the MPEF method provided by the invention can be used for sterilizing the blueberry juice, so that the smell and the taste of the fresh blueberry juice can be better kept, and the sensory quality of the blueberry juice is ensured.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A non-thermal sterilization method for blueberry juice is characterized by being carried out through a non-thermal sterilization system, and the non-thermal sterilization system comprises the following parts:

the micro-processing chamber comprises a bottom plate (1) and a packaging plate (2) arranged above the bottom plate (1), wherein a microelectrode (11) is etched on the top of the bottom plate (1), a fruit juice channel (21) is etched on the bottom of the packaging plate (2), a fruit juice inlet (22) and a fruit juice outlet (23) which are communicated with the fruit juice channel (21) are respectively arranged at two ends of the fruit juice channel (21) on the top of the packaging plate (2), and the extending direction of the fruit juice channel (21) is the same as the current flow path line of the microelectrode (11);

the microelectrode (11) is an interdigital electrode structure formed by a pair of comb-shaped electrodes in a crossed arrangement manner; the distance between the positive electrode and the negative electrode of the microelectrode (11) is 100 micrometers, the width of the center comb teeth is 30 micrometers, and the width of the edge comb teeth is not less than that of the center comb teeth;

the juice channel (21) comprises n transverse grooves (24) and n +1 longitudinal grooves (25) perpendicular to the transverse grooves (24), two ends of each transverse groove (24) are respectively communicated with one end of each two adjacent longitudinal grooves (25), and n is a natural number not less than 2; one end of the 1 st longitudinal groove (25) far away from the transverse groove (24) is communicated with the fruit juice inlet, and the other end of the n +1 th longitudinal groove (25) far away from the transverse groove (24) is communicated with the fruit juice outlet (23); the widths of the longitudinal grooves (25) and the transverse grooves (24) are both 3mm, and the distance between every two adjacent longitudinal grooves (25) is 0.5 mm;

a single pulse power supply (3) for providing a pulse voltage to the micro-processing chamber;

a sample injection system (4) connected to the juice inlet (22) for delivering a blueberry juice sample into the micro-processing chamber;

the sample outlet system (5) is connected with the juice outlet (23) and is used for outputting and collecting the pulse-processed blueberry juice sample from the micro-processing chamber;

the method comprises the following steps:

s1: sterilizing the micro-processing chamber, conveying the blueberry juice into the micro-processing chamber through the sample introduction system (4), and performing pulse processing, wherein the width of the pulse is 0.14-0.16 ms, the voltage is 330-370V, and the flow rate of the blueberry juice sample entering the micro-processing chamber is 9 mL/min;

s2: and outputting the blueberry juice subjected to pulse treatment from the micro-treatment chamber through the sample outlet system (5), and collecting to obtain the sterilized blueberry juice.

2. The non-thermal sterilization method for blueberry juice according to claim 1, wherein the sterilization system further comprises a monitoring system (6), and the monitoring system (6) comprises the following parts:

the pulse monitoring device (61) is electrically connected with the micro-processing chamber and is used for monitoring the pulse generation condition of the micro-processing chamber in real time;

and the temperature monitoring device (62) is connected with the tail end of the sample outlet system (5) and is used for monitoring the temperature change condition of the blueberry juice sample collected by the sample outlet system (5).

3. The non-thermal sterilization method for blueberry juice as set forth in claim 1, wherein the sterilization method for the micro-processing chamber is as follows: