Method for cleaning and disinfecting fruits and vegetables through intermittent ultrasonic enhanced micro-nano bubbles

Abstract

The invention provides an intermittent ultrasonic enhanced micro-nano bubble fruit and vegetable cleaning and disinfecting method, which comprises the following steps: introducing an active oxygen solution and gas into a micro-nano bubble generator, and placing a water inlet and a water outlet of the micro-nano bubble generator in the same cleaning pool; placing fruits and vegetables to be treated in the cleaning pool, starting the micro-nano bubble generator, and applying intermittent periodic ultrasonic treatment to the cleaning pool by using an ultrasonic device so as to clean and disinfect the fruits and vegetables to be treated. According to the method, micro-nano bubbles, ultrasound and active oxygen are combined, the method can be efficiently used for sterilizing the surfaces of fruits and vegetables, and the sterilizing effect on natural flora on the surfaces of the fruits and vegetables can reach 99.99%. Meanwhile, the combination of the three can also significantly inhibit browning of the fruits and vegetables, and has no negative influence on the quality (such as hardness and chromaticity) and nutritional ingredients of the fruits and vegetables.

Description

Technical Field

[0001] The present application relates to the field of fruits and vegetables. Specifically, the present application relates to a method for cleaning and disinfecting fruits and vegetables by intermittent ultrasound-enhanced micro-nano bubbles. Background Art

[0002] Traditional fruit and vegetable cleaning and disinfection technologies mainly include chlorine-based disinfectants (such as sodium hypochlorite), ozone water treatment, acidic electrolyzed water, and ultraviolet irradiation, etc. Among them, chlorine cleaning has the advantages of broad-spectrum sterilization and low cost, but it is easy to react with organic substances to generate carcinogenic by-products such as trihalomethanes, and residual chlorine may affect the sensory quality; ozone water achieves high-efficiency sterilization through strong oxidation and has no chemical residue, but ozone has poor stability, high equipment investment, and excessive use is likely to cause oxidative damage to vegetable tissues; acidic electrolyzed water can effectively inactivate microorganisms by virtue of low pH and high redox potential, and is environmentally friendly but has a short action time and requires high corrosion resistance of equipment; ultraviolet technology has no chemical pollution and is easy to operate, but is limited by weak penetration and has poor inactivation effect on microorganisms on complex surfaces and inside. Therefore, it is crucial to develop a fruit and vegetable cleaning and disinfection method that can well balance the sterilization efficiency, safety, and quality maintenance.

[0003] The micro-nano bubble technology can generate micron-sized (1-100 μm) and nano-sized (1-1000 nm) bubble clusters, which can carry gases such as O, CO, O, etc. Its high specific surface area significantly improves the gas mass transfer efficiency, and the micro-jet and reactive oxygen species (such as ·OH, etc.) generated when the bubbles collapse can synergistically enhance the cleaning efficiency. Therefore, it has become an emerging technology in the cleaning and processing of agricultural products. However, in current research, it is found that except for ozone micro-nano bubbles, the bactericidal effect of single micro-nano bubbles of air, oxygen, carbon dioxide, etc. for cleaning fruits and vegetables is very limited and has no difference from water treatment. Therefore, more research is to use micro-nano bubbles in combination with chemical substances such as HO. Although it can reduce microbial residues to a certain extent, the effect still needs to be improved. Summary of the Invention

[0004] The present application aims to solve at least to some extent the technical problems existing in the prior art.

[0005] It should be noted that the present application is based on the inventor's discovery and recognition of the following facts and problems:

[0006] A small number of studies have confirmed the effectiveness of the combined use of air micro-nano bubbles, ozone micro-nano bubbles and hydrogen peroxide in wastewater treatment, organic matter degradation, etc., mainly due to the generation of more reactive oxygen free radicals that are beneficial to oxidation and decomposition. Some studies have also found that the combined use of air micro-nano bubbles and laccase will significantly increase the degradation rate of bisphenol. However, when ultrasound is applied in this system, the degradation rate of bisphenol significantly decreases after 180 minutes of ultrasound. It is speculated that the bubble rupture during the ultrasound process may reduce the concentrations of oxygen and ·OH, but the specific mechanism is not yet clear. There are also studies using the combined use of micro-nano bubbles, disinfectants (a mixture of citric acid, hydrogen peroxide and anionic surfactants) and ultrasound to clean and remove microorganisms on the egg surface. This treatment effect is better than the combined use of disinfectants and ultrasound or the combined use of disinfectants and micro-nano bubbles, mainly because the synergy between ultrasound and micro-nano bubbles enhances the cavitation effect and is conducive to the disinfectant contacting the eggshell pores faster. However, the disinfectants used in this technology are relatively complex (such as adding anionic surfactants, etc.) and are not suitable for fruit and vegetable cleaning, especially fresh-cut vegetables, as they are likely to remain on the vegetables.

[0007] In view of this, the inventors of the present application have found through research that under the treatment conditions of low-frequency and intermittent ultrasound, bubble bursting can be effectively induced directionally, increasing the interaction among bubbles, ultrasound and microorganisms, thereby improving the bactericidal effect. Generally, micro-nano bubbles rise and aggregate to the liquid surface and then burst, but this surface bursting cannot effectively act on microorganisms or other target substances in the liquid to achieve an effective cleaning and disinfection effect. By using the method of intermittent ultrasound, bubbles have enough time to generate in the liquid. After achieving uniform distribution, directional bursting induction is immediately implemented through the action of ultrasound, and the controllability is greatly improved. In addition, if the resonance radius of micro-nano bubbles is similar to that of ultrasound, this interaction may also be enhanced, further increasing the cell membrane permeability and facilitating the entry of the reactive oxygen solution into the microbial cells, synergistically enhancing the microbial bactericidal efficiency on the surface of fruits and vegetables.

[0008] Thus, the combined advantages of micro-nano bubbles, ultrasound and reactive oxygen are fully utilized, which can be efficiently used for the sterilization of the surfaces of fruits and vegetables, and the bactericidal effect on the natural flora on the surfaces of fruits and vegetables can be as high as 99.99%. At the same time, the combined use of these three technologies can also significantly inhibit the browning of fruits and vegetables, and has no negative impact on the quality (such as hardness, chromaticity) and nutritional components of the fruits and vegetables.

[0009] According to the embodiments of the present application, the above-mentioned method for cleaning and disinfecting fruits and vegetables may also have the following additional technical features:

[0010] According to an embodiment of the present application, the power of the ultrasonic treatment is 20 kHz to 100 kHz, and exemplarily 20 kHz, 30 kHz, 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz, 100 kHz; the power of the ultrasonic treatment is 100 W to 500 W, and exemplarily 100 W, 150 W, 200 W, 250 W, 300 W, 350 W, 400 W, 450 W, 500 W; each intermittent period is 5 s to 30 s of working and 1 s to 60 s of intermittent, and exemplarily working for 5 s, 10 s, 15 s, 20 s, 25 s, 30 s, and intermittent for 1 s, 15 s, 25 s, 45 s, 60 s, wherein 60 s is the time when micro-nano bubbles can reach a uniform and stable distribution in the cleaning pool. Thus, it is beneficial to generate more micro-scale bubbles close to the ultrasonic resonance radius, thereby more efficiently achieving the bactericidal effect. In addition, it is also beneficial to delay the browning of fruits and vegetables.

[0011] According to an embodiment of the present application, the gas is carbon dioxide gas. Carbon dioxide gas in the micro-nano bubble generator is more likely to generate micro-nano bubbles (with a size of 50 - 100 μm) close to the ultrasonic resonance radius obtained under the above ultrasonic conditions compared to other gases (such as air), increasing the permeability of the bacterial cell membrane, thereby facilitating the entry of the reactive oxygen solution into the microbial cell and increasing the intracellular oxidative stress level, synergistically improving the bactericidal efficiency on the surface of fruits and vegetables.

[0012] According to an embodiment of the present application, the flow rate of the gas is 10 mL / min to 100 mL / min, and exemplarily 10 mL / min, 20 mL / min, 40 mL / min, 50 mL / min, 60 mL / min, 80 mL / min, 100 mL / min. Thus, it is beneficial to improve the bactericidal effect on the surface of fruits and vegetables.

[0013] In this text, the term "reactive oxygen solution" refers to a solution containing hydrogen peroxide or other reactive oxygen components. According to an embodiment of the present application, the reactive oxygen solution is selected from hydrogen peroxide solutions, and the concentration of the hydrogen peroxide solution is 0.1 vol% to 2 vol%, and exemplarily 0.1 vol%, 0.5 vol%, 1 vol%, 1.5 vol%, 2 vol%. Thus, it is beneficial to fully disinfect the microorganisms on the surface of fruits and vegetables, while significantly delaying the browning of fruits and vegetables, maintaining their chromaticity and hardness during the shelf life, and not affecting the content of nutrients in the lotus root slices, such as total phenols.

[0014] According to an embodiment of the present application, the outlet pressure of the micro-nano bubble generator is 0.3 MPa to 0.7 MPa, and exemplarily it is 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa. Thereby, the stable generation and uniform distribution of micro-nano bubbles are effectively ensured, and the bubbles are prevented from bursting due to excessive pressure during the generation process, thereby improving the stability of the bubbles, and further improving the sterilization and cleaning effects.

[0015] According to an embodiment of the present application, the fruits and vegetables to be processed are placed in the cleaning pool for 5 min to 20 min, and exemplarily it is 5 min, 10 min, 15 min, 20 min. Thereby, it is convenient to fully disinfect the microorganisms on the surface of the fruits and vegetables, delay the browning of the fruits and vegetables, maintain their chromaticity and hardness during the shelf life, and does not affect the content of nutrients therein.

[0016] According to an embodiment of the present application, the fruits and vegetables include lotus root slices. The method of the present application has a better sterilization effect on the surface of lotus root slices in particular, and can delay its browning, maintain its chromaticity and hardness during the shelf life, and does not affect the content of nutrients in the lotus root slices.

[0017] In addition, the present application provides a method for cleaning and disinfecting lotus root slices. According to an embodiment of the present application, the method includes: introducing 1% by volume of hydrogen peroxide solution and carbon dioxide gas into a micro-nano bubble generator, the flow rate of the carbon dioxide gas is 100 mL / min, and the inlet and outlet of the micro-nano bubble generator are placed in the same cleaning pool; placing the lotus root slices to be processed in the cleaning pool, and placing the cleaning pool in an ultrasonic device; turning on the micro-nano bubble generator and the ultrasonic device, the outlet pressure of the micro-nano bubble generator is 0.6 MPa to 0.65 MPa, the carbon dioxide flow rate is 100 mL / min, intermittent periodic ultrasonic treatment is adopted, each cycle is 15 s of working and 60 s of intermittent, the ultrasonic power is 240 W, and the frequency is 40 kHz. After the lotus root slices are processed as a whole for 10 min, the lotus root slices are taken out, rinsed with water and dried. The method of the present application combines micro-nano bubbles, ultrasound and reactive oxygen, and can be efficiently used for sterilizing the surface of fruits and vegetables, and the sterilization effect on the natural flora on the surface of fruits and vegetables can be as high as 99.99%. At the same time, the combination of these three can also significantly inhibit the browning of fruits and vegetables, and has no negative impact on the quality (such as hardness, chromaticity) and nutrient components of the fruits and vegetables.

[0018] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. Description of the Drawings

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of embodiments in conjunction with the accompanying drawings, in which:

[0020] Figure 1 Shows the device diagram for fruit and vegetable cleaning and disinfection of the present application;

[0021] Figure 2 Shows the micro-nano bubble size distribution diagram;

[0022] Figure 3 Shows the analysis diagram of the reduction amount of Escherichia coli;

[0023] Figure 4 Shows the removal effect of the natural microbiota of lotus root slices;

[0024] Figure 5 Shows the analysis diagram of delaying browning. Detailed implementation manners

[0025] The solution of the present invention will be explained below in conjunction with embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product instructions. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0026] Example 1

[0027] As Figure 1 shown, carbon dioxide gas and 1% hydrogen peroxide solution are simultaneously introduced into the micro-nano bubble generator. The water inlet and outlet of the micro-nano bubble generator are placed in the same cleaning pool. At the same time, the pressure at the outlet of the micro-nano bubble generator is controlled to be 0.6 - 0.65 MPa, the carbon dioxide flow rate is 100 mL / min, and the addition amount of hydrogen peroxide is 1%. The lotus root slices are placed in the same cleaning pool as the outlet and inlet of the micro-nano bubbles, and the cleaning pool is placed in an ultrasonic bath (240 W, 40 kHz), and the ultrasonic waves are applied intermittently and periodically, working for 15 s / interval for 60 s. The lotus root slices are processed in the cleaning pool for 10 min and then taken out.

[0028] Example 2

[0029] The difference from Example 1 is that carbon dioxide gas is replaced by air.

[0030] Example 3

[0031] The difference from Example 1 is that the condition of applying ultrasonic waves intermittently and periodically is replaced by working for 15 s / interval for 25 s.

[0032] Comparative Example 1

[0033] The difference from Example 1 is that ultrasonic treatment is not applied.

[0034] Comparative Example 2

[0035] The difference from Example 1 is that the intermittent periodic application of ultrasound is replaced by continuous ultrasound (started throughout the process).

[0036] Test Example

[0037] 1. The in-situ real-time particle size and concentration analysis of microbubbles (>1μm) in the micro-nano bubble systems of Experimental Group 1 and Experimental Group 2 below was carried out using a focused beam reflectance measurement instrument.

[0038] Experimental Group 1: Air was introduced into the micro-nano bubble generator. The water inlet and outlet of the micro-nano bubble generator were placed in the same cleaning pool. At the same time, the pressure at the outlet of the micro-nano bubble generator was controlled to be 0.6 - 0.65 MPa, and the flow rate of air gas was 30 mL / min.

[0039] Experimental Group 2: Carbon dioxide gas was introduced into the micro-nano bubble generator. The water inlet and outlet of the micro-nano bubble generator were placed in the same cleaning pool. At the same time, the pressure at the outlet of the micro-nano bubble generator was controlled to be 0.6 - 0.65 MPa, and the carbon dioxide flow rate was 100 mL / min.

[0040] The results are as Figure 2 shown. Compared with air, the particle size of carbon dioxide micro-nano bubbles is closer to the resonance radius of ultrasound, and when used in combination with ultrasound, it is more conducive to improving the bactericidal effect.

[0041] 2. Cleaning effect of microorganisms on the surface of lotus root slices

[0042] (I) Cleaning effect of inoculating Escherichia coli on the surface of lotus root slices

[0043] (1) The method of inoculating Escherichia coli is as follows: After the overnight-cultured Escherichia coli bacterial solution was washed and resuspended with an equal volume of phosphate buffer solution (PBS, pH 7.4), the bacterial suspension was taken and spot-inoculated on the lotus root slices. After inoculation, the samples were placed in a clean bench and air-dried aseptically to obtain a contamination model with an initial bacterial load of 7 - 8 log CFU / slice.

[0044] (2) The lotus root slices inoculated with a high concentration of Escherichia coli in the previous step were subjected to the cleaning and disinfection treatments of Examples 1 - 3, Comparative Example 1, Comparative Example 2, Experimental Group 1, and Experimental Group 2.

[0045] (3) The lotus root slices treated in the previous step were put into a sterile homogenization bag containing phosphate buffer solution (PBS) and were thoroughly beaten with a beating homogenizer. The homogenized samples were serially diluted, spread on EMB medium, and cultured at 37°C for 24 hours for counting.

[0046] The results are as follows Figure 3 As shown, intermittent ultrasound is used to obtain more micro-nano bubbles close to the resonance radius. After they are fully in contact with the microorganisms, ultrasound is applied to the system to promote the interaction between ultrasound and bubbles, resulting in a better sterilization effect.

[0047] (II) Cleaning effect of natural flora of lotus root slices

[0048] (1) The lotus root slices (containing natural bacterial flora on the surface) are cleaned and disinfected according to Example 1 and the water washing method.

[0049] (2) Place the lotus root slices treated in the previous step into a sterile homogenization bag filled with phosphate buffered saline (PBS) and beat them thoroughly with a beating homogenizer. Dilute the homogenized sample in a gradient manner, spread it on PCA medium, and culture it at 37°C for 48 hours for counting.

[0050] The results are as follows Figure 4 As shown, it can be seen that the method of the present application has a better sterilization effect.

[0051] (2) The lotus root slices in Example 1 are natural lotus root slices with natural bacteria on the surface, and water-washed lotus root slices are used as a control.

[0052] The results are as follows Figure 4 As shown, it can be seen that the method of the present application has a better sterilization effect.

[0053] 3. The lotus root slices and washed lotus root slices treated in Example 1 were subjected to browning detection, and the specific steps were as follows:

[0054] After treatment, the lotus root slices were rinsed with deionized water for 20 seconds, and the surface moisture was absorbed by sterile absorbent paper. The slices were packed in sterile PE sampling bags and stored at 4°C and relative humidity of 40-60% for 16 days. The quality of the lotus root slices was tested every 4 days, and the browning index was calculated.

[0055] The results are as follows Figure 5 As shown, it can be seen that the method of the present application can effectively delay the browning of lotus root slices.

[0056] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. An intermittent ultrasound-enhanced fruit and vegetable cleaning and disinfection method using micro-nano bubbles, characterized in that Comprising: Introduce the reactive oxygen solution and gas into the micro-nano bubble generator, and place the water inlet and outlet of the micro-nano bubble generator in the same cleaning pool; Place the fruits and vegetables to be treated in the cleaning pool, Turn on the micro-nano bubble generator and apply intermittent periodic ultrasonic treatment to the cleaning pool by using an ultrasonic device, so as to clean and disinfect the fruits and vegetables to be treated.

2. The method according to claim 1, characterized in that The frequency of the ultrasonic treatment is 20 kHz to 100 kHz; The power of the ultrasonic treatment is 100 W to 500 W; Each intermittent period is 5 s to 30 s of working and 1 s to 60 s of intermittent; 3. The method according to claim 1, wherein The gas is carbon dioxide gas.

4. The method according to claim 1 or 3, characterized in that, The flow rate of the gas is 10 mL / min to 100 mL / min.

5. The method according to claim 1, wherein The reactive oxygen solution is selected from hydrogen peroxide solution, and the concentration of the hydrogen peroxide solution is 0.1 vol% to 2 vol%.

6. The method according to claim 1, wherein The outlet pressure of the micro-nano bubble generator is 0.3 MPa to 0.7 MPa.

7. The method according to claim 1, wherein Place the fruits and vegetables to be treated in the cleaning pool for 5 min to 20 min.

8. The method according to claim 1, wherein, The fruits and vegetables include lotus root slices.

9. A method for cleaning and disinfecting lotus root slices, characterized in that, Comprising: Introduce 1 vol% hydrogen peroxide solution and carbon dioxide gas into the micro-nano bubble generator, the flow rate of the carbon dioxide gas is 100 mL / min, and place the water inlet and outlet of the micro-nano bubble generator in the same cleaning pool; Place the lotus root slices to be treated in the cleaning pool, and place the cleaning pool in the ultrasonic device; Turn on the micro-nano bubble generator and the ultrasonic device, the outlet pressure of the micro-nano bubble generator is 0.6 MPa to 0.65 MPa, the carbon dioxide flow rate is 100 mL / min, adopt intermittent periodic ultrasonic treatment, each period is 15 s of working and 60 s of intermittent, the ultrasonic power is 240 W, the frequency is 40 kHz. After the lotus root slices are treated integrally for 10 min, take out the lotus root slices, rinse with water and dry.

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