A kind of sterilization method of freshly squeezed juice

Abstract

The present invention relates to a method for sterilizing freshly squeezed fruit juice, and specifically to a treatment method of pulsed electric field coordinated with medium temperature and natural antibacterial agent, and belongs to the technical field of fruit juice processing. A method for sterilizing freshly squeezed fruit juice comprises adding vanillin to the freshly squeezed fruit juice, treating the fruit juice containing vanillin at a water bath temperature of 40 to 60°C for 3 to 5 minutes; and treating the treated fruit juice in a high-voltage pulsed electric field. The product obtained by the sterilization method of the present invention, without adding preservatives, is stored at room temperature (25°C) for more than 40 days, and the number of bacteria, molds, and yeasts thereof remains within the national standard range, while showing good color and transparency. The high-voltage pulsed electric field cold sterilization cabinet used is more suitable for industrial and enterprise processing, rather than being limited to laboratory applications.

Description

Technical Field

[0001] The invention relates to a sterilization method for freshly squeezed juice, in particular to a treatment method using a pulse electric field in coordination with medium temperature and a natural antibacterial agent, and belongs to the technical field of juice processing. Background Art

[0002] In recent years, as consumers' demand for healthy food increases, the quality and safety of juice, as a nutritious drink, have also received more and more attention. During processing and storage, juice is often contaminated by microorganisms, among which mold and yeast are the main causes of juice spoilage. The nutritional content and flavor of freshly squeezed juice have a great impact on consumer acceptance. Traditional thermal sterilization methods may destroy the nutritional content and flavor of the juice while killing microorganisms. Therefore, it is necessary to find a method that can effectively sterilize and protect the nutritional content and flavor of juice.

[0003] Among natural compounds, vanillin is a natural antibacterial substance extracted from vanilla beans of the Rutaceae family. It can participate in the signal transmission between bacterial cells. When combined with pulsed electric fields to treat juice, it can significantly improve the sterilization effect on bacteria, molds and yeasts, and further prevent the loss of nutritional value and flavor of juice. The method of sterilizing juice by pulsed electric fields combined with medium-temperature natural antibacterial agents is intended to solve the problem of microbial contamination during juice processing and storage, while maximally protecting the nutritional components and flavor of juice, meeting consumers' demand for healthy food, and promoting the healthy development of the juice industry. CN202010893880.5 discloses a method for sterilizing fresh juice, which includes adding vanillin at a concentration of 2.0 to 6.4 mg / mL to the juice, and then subjecting the juice to thermal ultrasound treatment, with an ultrasonic power of 150 to 300 W, a heating temperature of 40-55 ° C, and a heating time of 15 to 60 min. The method uses thermal ultrasound and vanillin for combined treatment, synergistic sterilization, and achieves an ideal sterilization effect on common Gram-negative pathogens in juice, but the method has a long heating time and a high vanillin concentration, which has an adverse effect on the color and flavor of fresh juice. At present, most of the research on vanillin at home and abroad is applied to flavors, and there are few reports on the sterilization of fresh juice in combination with pulsed electric fields. And most juices are stored at low temperature (-4 ° C) after cold sterilization. Summary of the invention

[0004] The present invention mainly discloses a method for treating fruit juice by using a high-voltage pulse electric field in coordination with a medium temperature and a natural antibacterial agent. The method can effectively inactivate the total number of bacteria and the number of molds and yeasts in the fruit juice, significantly increase the content of phenolic substances in the fruit juice, effectively inactivate the activity of PPO and POD enzymes, maintain the quality of the fruit juice, and extend its shelf life.

[0005] A method for sterilizing freshly squeezed fruit juice comprises the following steps: adding vanillin to the freshly squeezed fruit juice, treating the fruit juice containing vanillin at a water bath temperature of 40 to 60 DEG C for 3 to 5 minutes; and treating the treated fruit juice in a high-voltage pulse electric field to obtain the obtained fruit juice.

[0006] In the above technical solution, the vanillin is used to inhibit the synthesis of biomacromolecules in microbial cells, and the phenolic group therein can inhibit the formation of membrane pores and cell wall biosynthesis of microbial cell membranes in juice. In addition, the addition of vanillin is used to increase the content of polyphenols in juice, thereby improving the antioxidant capacity of juice as a whole.

[0007] In the above technical solution, the water bath is used to change the cell membrane structure and fluidity of the microorganisms, increase the sensitivity of the microorganisms to the pulsed electric field, and further increase the inactivation effect.

[0008] In the above technical solution, the high-voltage pulse electric field treatment is used to make vanillin more easily enter the microbial cells, act on the enzyme or functional protein system, destroy the microbial genetic material, inhibit the microbial respiratory system, and achieve the purpose of synergistic sterilization.

[0009] In the above technical scheme, high voltage pulse electric field (HPEF) technology is one of the non-thermal treatment technologies that sterilizes by generating pulse electric field. It not only has a good sterilization effect, but also can well maintain the nutritional value and flavor of juice. Its sterilization principle is mainly to kill microorganisms through electric shock and electroporation. When microorganisms are exposed to pulse electric fields, the electric field produces a strong electric shock effect on the cell membrane, resulting in the rupture of the cell membrane and the leakage of cell contents. In addition, the pulse electric field can also produce electroporation, that is, forming small holes in the cell membrane, thereby destroying the ion balance of the cell and further inhibiting the respiratory activity of the cell. These two effects together lead to the death of microorganisms, thereby achieving the purpose of sterilization. The pulse electric field is combined with medium temperature treatment, and the cell membrane of the microorganism loses mechanical resistance, making it more susceptible to electroporation, and the internal components of the microorganism are more likely to leak out, further damaging the viability of the microorganism.

[0010] Preferably, vanillin is added to freshly squeezed juice, and the juice containing vanillin is treated at a water bath temperature of 55° C. for 3 minutes; the treated juice is treated in a high-voltage pulse electric field to obtain the product.

[0011] Preferably, the concentration of vanillin in the juice is 0.32-1.6 mg / mL; most preferably, the concentration of vanillin in the juice is 1.6 mg / mL.

[0012] Preferably, the high-voltage pulse electric field strength is 20-40 KV / cm; most preferably, the high-voltage pulse electric field strength is 40 KV / cm.

[0013] Preferably, the high-voltage pulse electric field treatment time is 10 to 80 seconds.

[0014] Preferably, the freshly squeezed juice is directly squeezed from fresh fruits, 0.15% pectinase is added, the juice is water-bathed at 45° C. for 90 minutes, filtered, centrifuged at 4500 r / min for 15 minutes, and vanillin is directly added to the supernatant.

[0015] Preferably, the juice is red raspberry, blueberry or strawberry juice.

[0016] Preferably, the high-voltage pulse electric field treatment is carried out in a high-voltage pulse electric field cold sterilization cabinet.

[0017] The beneficial effects of the present invention are as follows: the present invention uses a high-voltage pulse electric field in coordination with medium temperature and a natural antibacterial agent (vanillin) to treat fruit juice, effectively killing bacteria, molds, and yeasts therein, and effectively inhibiting the activity of polyphenol oxidase and peroxidase in the fruit juice, and can significantly increase the total phenol content and protein concentration in the fruit juice. The product obtained by the sterilization technology of the present invention, without adding preservatives, is stored at room temperature (25°C) for more than 40 days, and the number of bacteria, molds, and yeasts remains within the national standard range, while showing good color and transparency. The high-voltage pulse electric field cold sterilization cabinet used is more suitable for industrial and enterprise processing, rather than being limited to laboratory applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 (A) shows the lethality of the total bacteria in red raspberry juice treated with pulsed electric field in combination with medium temperature and vanillin (20-40 KV / cm, 40 s, 50°C, 0.96 mg / ml) and pulsed electric field alone (20-40 KV / cm, 40 s) in Example 1.

[0019] Figure 1 (B) shows the lethality of total bacteria, molds and yeasts in red raspberry juice treated with pulsed electric field in combination with medium temperature and vanillin (20-40KV / cm, 40s, 50°C, 0.96mg / ml) in Example 1

[0020] Figure 1 (C) is a comparison of the protein content in raspberry juice treated with pulsed electric field synergistically with medium temperature and vanillin (40 KV / cm, 40 s, 50°C, 0.96 mg / ml), pulsed electric field alone (40 KV / cm, 40 s) and pasteurization (85°C, 10 min) in Example 1.

[0021] Figure 1 (D) is a comparison of the total phenol content in raspberry juice treated with pulsed electric field synergistically with medium temperature and vanillin (40 KV / cm, 40 s, 50°C, 0.96 mg / ml) in Example 1, pulsed electric field (40 KV / cm, 40 s) treatment, vanillin treatment (0.96 mg / ml) treatment alone, and pasteurization treatment (85°C, 10 min).

[0022] Figure 2 The lethality of the total number of bacteria, molds and yeasts in red raspberry juice treated with pulsed electric field in combination with medium temperature and vanillin (40 KV / cm, 40 s, 50°C, 0.32-1.6 mg / ml) in Example 2.

[0023] Figure 3 The lethality of the total number of bacteria, molds and yeasts in red raspberry juice treated with pulsed electric field in combination with medium temperature and vanillin (40 KV / cm, 40 s, 40-60°C, 1.6 mg / ml) in Example 3.

[0024] Figure 4 The lethality of the total number of bacteria, molds and yeasts in red raspberry juice treated with pulsed electric field in combination with medium temperature and vanillin (40 KV / cm, 10-80 s, 55°C, 1.6 mg / ml) in Example 4.

[0025] Figure 5 This is the effect of different treatment methods on the number of bacteria, molds and yeasts in juice under room temperature (25°C) storage conditions in Example 5.

[0026] Figure 6 The changes in juice color and turbidity under different treatment conditions under room temperature (25° C.) storage conditions in Example 5 are shown. DETAILED DESCRIPTION

[0027] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0028] The test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0029] Embodiment 1:

[0030] S1: Vanillin was added to freshly squeezed red raspberry juice to prepare raspberry juice with a final vanillin concentration of 0.96 mg / ml.

[0031] S2: The juice treated with vanillin was placed in a 50°C water bath for 3 min.

[0032] S3: After the water bath, the juice is immediately sterilized in a high-voltage pulse electric field cold sterilizer. The electric field strengths are 20, 25, 30, 35, and 40 KV / cm, respectively, and the treatment time is 40 s.

[0033] To illustrate the effect of the present invention, this example compares the sterilization effect of the method of the present invention with the following methods:

[0034] Treatment conditions: no vanillin, no water bath, electric field strength of 20, 25, 30, 35, 40 KV / cm, treatment for 40 s.

[0035] The plate counting method was used to count the total number of bacteria, molds and yeasts in the raspberry juice before and after treatment. The lethal effects of different treatment methods on microorganisms were analyzed by calculating the logarithmic lethality of bacteria, molds and yeasts.

[0036] lgS=lg(N 0 / N)

[0037] N 0 is the number of microorganisms before PEF treatment, CFU / ml; N is the number of microorganisms after PEF treatment, CFU / ml

[0038] The comparison results are shown in Figure 1. As shown in Figure 1 (A), with the increase of electric field intensity, the lethality of the total bacteria in raspberry juice is gradually increasing. The lethality of the total bacteria in the pulse electric field combined with medium temperature and vanillin treatment increases from 0.86 logarithms to 2.06 logarithms, and the lethality of the total bacteria in the pulse electric field alone increases from 0.54 to 1.57 logarithms. The bactericidal effect is best when the electric field intensity is 40KV / cm. The lethality of the total bacteria in the pulse electric field combined with medium temperature and vanillin treatment is higher than that in the pulse electric field alone. It can be seen that the pulse electric field combined with medium temperature and natural antibacterial agents can increase the lethality of bacteria by 0.48 logarithms. And compared with the group treated with the pulse electric field alone, the lethality achieved when the 40KV / cm treatment is alone can be achieved when the pulse electric field is combined with 35KV / cm, which not only saves energy, but also improves the inactivation effect of microorganisms. As shown in Figure 1(B), the mortality rate of the pulsed electric field combined with medium temperature and vanillin treatment for the total number of molds and yeasts is significantly higher than that for the total number of bacteria. This is because the bacterial cell wall is thicker and more complex, and the types of microorganisms determine the different composition structures of the cell wall and cell membrane, and the sensitivity to the pulsed electric field is different.

[0039] As shown in Figure 1(C), the protein concentration of raspberry juice treated with pulsed electric field alone was significantly increased compared with the untreated group, while the protein concentration of the group treated with pulsed electric field synergistically with medium temperature and vanillin was significantly higher than that of the group treated with pulsed electric field alone. The protein concentration of the pasteurization treatment group was the highest, indicating that pulsed electric field synergistic treatment can cause the leakage of cell contents, thereby increasing the protein concentration in the juice.

[0040] As shown in Figure 1 (D), pasteurization of juice (85°C, 15min) will lead to a decrease in the total phenol content in the juice, reducing the overall antioxidant capacity of the juice. There is no significant difference between the pulsed electric field alone treatment and the control group, indicating that the pulsed electric field treatment will not reduce the polyphenol content in the juice, while the vanillin alone treatment group and the pulsed electric field synergistic medium temperature and vanillin treatment group significantly increase the polyphenol content in the juice, confirming that the increase in the polyphenol content in the juice is due to the addition of vanillin, and the content of phenolic substances has increased, and some of the polyphenols are more conducive to the inactivation of microorganisms in the juice. The enzyme activities of PPO and POD in the red raspberry juice treated with pulsed electric field synergistic medium temperature and vanillin (40KV / cm, 40s, 50°C, 0.96mg / ml) treated in Example 1 decreased by 98% and 96% respectively compared with the control group, which can effectively inhibit the enzyme activities of PPO and POD in the juice.

[0041] Example 2

[0042] S1: Vanillin was added to freshly squeezed red raspberry juice to prepare raspberry juices with final vanillin concentrations of 0.32, 0.64, 0.96, 1.28, and 1.6 mg / ml, respectively.

[0043] S2: Same as Example 1

[0044] S3: After the water bath, the juice is immediately sterilized in a high-voltage pulse electric field cold sterilizer with an electric field strength of 40 KV / cm and a treatment time of 40 s.

[0045] like Figure 2 As shown, with the increase of vanillin concentration, the lethality to microorganisms also increases. When the vanillin concentration is added to 1.6 mg / ml, the lethality effect is the best, with the lethality to the total bacteria reaching 1.96 logarithms, and the lethality to molds and yeasts reaching 2.35 logarithms.

[0046] Example 3

[0047] S1: Vanillin was added to freshly squeezed red raspberry juice to prepare raspberry juice with a final vanillin concentration of 1.6 mg / ml.

[0048] S2: The juice treated with vanillin was placed in a water bath at 40, 45, 50, 55, and 60 °C for 3 min.

[0049] S3: Same as Example 2

[0050] like Figure 3As shown in the figure, as the water bath temperature increases, the lethality of the total bacteria, molds, and yeasts gradually increases, until the temperature rises to 55°C, the total bacteria, molds, and yeasts are completely killed, the lethality of the total bacteria reaches 2.02 logarithms, and the lethality of molds and yeasts reaches 2.40 logarithms. As the temperature rises, the fluidity of the cell membrane increases, and the microorganisms are more sensitive to the pulsed electric field, thereby achieving the purpose of killing more microorganisms.

[0051] Example 4

[0052] S1: Same as Example 3

[0053] S2: Place the fruit juice containing vanillin in a water bath at 55°C for 3 min.

[0054] S3: After the water bath, the juice is immediately sterilized in a high-voltage pulse electric field cold sterilizer with an electric field strength of 40 KV / cm and treatment times of 10, 20, 40, 60, and 80 s, respectively.

[0055] like Figure 4 As shown in the figure, with the extension of the pulse electric field treatment time, the logarithmic lethality of the total number of bacteria, molds and yeasts also increased. When the treatment time reached 80s, the lethality of the total number of bacteria reached 2.16 logarithmic values, and the lethality of the molds and yeasts reached 2.57 logarithmic values.

[0056] Example 5

[0057] S1: Vanillin was added to freshly squeezed red raspberry juice to prepare raspberry juice with a final vanillin concentration of 1.28 mg / ml.

[0058] S2: Same as Example 4.

[0059] S3: After the water bath, the juice is immediately sterilized in a high-voltage pulse electric field cold sterilizer with an electric field strength of 40 KV / cm and a treatment time of 60 s.

[0060] The plate counting method was used to count the total number of bacteria, molds and yeasts in the raspberry juice before and after treatment.

[0061] N=(c / V)×M

[0062] N: Total colony count of the sample, CFU / ml

[0063] c: Average colony count (CFU) on the plate at a certain dilution

[0064] V: Volume of diluent used to coat the plate (ml)

[0065] M: dilution multiple

[0066] Table 1 Effects of different treatments on the total number of bacteria in raspberry juice stored at 25℃

[0067]

[0068] Note: - indicates total colony count ≥ 100 CFU / ml, 0 day indicates initial colony count after different treatments. Values ​​are expressed as mean ± SD (n = 3)

[0069] As can be seen from Table 1, the raspberry juice treated by the method of the present invention can be stored for more than 40 days at room temperature (25° C.) without adding preservatives, which is unattainable by the pasteurization method disclosed in the prior art.

[0070] Table 2 Effects of different treatments on the total number of molds and yeasts in raspberry juice stored at 25℃

[0071]

[0072] Note: - indicates total colony count ≥ 100 CFU / ml, 0 day indicates the initial colony count after treatment in different ways, and the values ​​are expressed as mean ± SD (n = 3)

[0073] As shown in Tables 1, 2 and Figure 5 As shown in the results, under the storage condition of 25℃, the total number of bacteria, mold and yeast in the juice treated with pulsed electric field in combination with medium temperature and natural antibacterial agent can be kept less than 100 CFU / ml for more than 40 days. Compared with mold and yeast, this method has better killing effect on bacteria. The total number of colonies in the group treated with PEF alone still exceeded the standard during the subsequent storage process. PEF alone can cause sublethal damage to microorganisms, and sublethal damaged microorganisms can recover to normal cells under suitable environmental conditions, and then continue to multiply to cause food spoilage or foodborne diseases. The number of bacteria, mold and yeast in the group treated with vanillin alone exceeded the standard after 4 days, and the effect was not as good as that of PEF+V+50℃ group. After 20 days, the number of colonies in the pasteurization group exceeded the standard. Until 40 days later, the number of colonies in the PEF+V+50℃ group was still within the national standard range, which was better than the other 7 groups.

[0074] Table 3 Effects of different treatments on the turbidity of raspberry juice under storage conditions of 25℃

[0075]

[0076] Note: Values ​​are expressed as mean ± SD (n = 3)

[0077] As shown in Tables 3, 4 and Figure 6As shown in the figure, the turbidity changes of raspberry juice under different treatments were measured on the 0th day and the 8th day. It can be clearly observed that on the 8th day, the PEF+V+50℃ group can achieve the same effect as the pasteurization group, and it is still clear and transparent, which is significantly different from the control group. The untreated group and the PEF group alone cannot keep the juice clear. On the 25th day, the PEF+V+50℃ group was significantly different from the other groups and had the smallest turbidity and was the clearest. Pasteurization also became turbid with the extension of storage time, which was significantly different from the control group. There was no significant difference between the untreated group and the PEF group alone, which shows that PEF sterilization alone cannot keep the juice clear. The PEF+V+50℃ group had the best effect and was better than the other 7 groups.

Claims

1. A method for sterilizing freshly squeezed juice, characterized in that: Vanillin is added to freshly squeezed juice, and the juice containing vanillin is treated at a water bath temperature of 55°C for 3 minutes; the treated juice is treated in a high-voltage pulse electric field to obtain the method; the concentration of the vanillin in the juice is 0.32-1.6 mg / mL, the intensity of the high-voltage pulse electric field is 20-40 KV / cm, and the high-voltage pulse electric field treatment time is 10-80 s.

2. The method according to claim 1, characterized in that: The concentration of vanillin in the juice was 1.6 mg / mL.

3. The method according to claim 1, characterized in that: The high voltage pulse electric field strength is 40KV / cm.

4. The method according to claim 1, characterized in that: The freshly squeezed juice is directly squeezed from fresh fruits, 0.15% pectinase is added, the juice is water-bathed at 45° C. for 90 minutes, filtered, centrifuged at 4500 r / min for 15 minutes, and then the supernatant is directly added with vanillin.

5. The method according to claim 1, characterized in that: The fruit juice is red raspberry, blueberry or strawberry juice.

6. The method according to claim 1, characterized in that: The high-voltage pulse electric field treatment is carried out in a high-voltage pulse electric field cold sterilization cabinet.

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