The Application of Micro-nano Ozone Bubble Water in The Cleaning of Fruits And Vegetables

The Application of Micro-nano Ozone Bubble Water in the Cleaning of Fruits and Vegetables

In the field of fresh food, fresh-cut fruits and vegetables are deeply favored by consumers for their cleanliness, freshness, and convenience of consumption. However, microbial contamination seriously affects their quality and safety. How to effectively clean and disinfect fruits and vegetables has become a key issue. This article will introduce a new type of bubble cleaning and disinfection technology - the application of micro-nano ozone bubble water in the cleaning and disinfection of fruits and vegetables.

01 The Current Situation and Challenges of Fresh-cut Fruits and Vegetables

In recent years, fresh-cut fruits and vegetables have mushroomed in major and medium-sized supermarkets and online fresh food stores. It is a new type of fruit and vegetable processed product that is supplied to consumers for direct consumption or simple processing after being washed, disinfected, cut and sorted. It integrates preservation and processing technologies. This processing method meets consumers' demands for convenient and fresh food and has become a rapidly developing new field in the fresh food industry.

However, during the processing, circulation, storage, and shelf placement of fresh-cut fruits and vegetables, microbial contamination has become the biggest factor affecting the quality of fruits and vegetables. Microbial contamination mainly comes from multiple aspects. For example, field infection during the planting process, where the soil contains bacteria, actinomycetes, molds, yeasts and other microorganisms, and the use of unfermented crude farmyard manure during planting, which contains a large number of Escherichia coli, Salmonella and other microorganisms that can adhere to or invade the fruits and vegetables. The harvesting, sorting and processing stages are also the main stages of microbial contamination. During this process, the cell tissues of fruits and vegetables are easily damaged, causing nutrients to flow out, providing conditions for microbial growth. At the same time, the surface of fruits and vegetables is exposed to the air, making them prone to contamination by bacteria, molds, yeasts and other microorganisms. During storage and transportation, due to factors such as packaging materials, changes in storage and transportation temperatures, storage warehouse environments, and cross-contamination between fresh-cut fruits and vegetables products, the number of microorganisms on the surface of fruits and vegetables gradually increases, directly affecting the shelf life of fresh-cut fruits and vegetables.

02 Conventional Methods for Cleaning Fruits and Vegetables

At present, there are mainly three types of devices used for cleaning fresh-cut products in the processing of fruits and vegetables. Traditional cleaning machines mainly complete the cleaning process through soaking, physical cleaning and spraying. Physical cleaning methods include brush cleaning, mechanical vibration cleaning and paddle cleaning, etc. This type of cleaning machinery is mainly suitable for the cleaning of fruits and vegetables such as potatoes, tomatoes and carrots, but it causes relatively large damage to leafy vegetables. Because the tissue structure of leafy vegetables is relatively fragile, during the processes of brush cleaning and mechanical vibration, it is very easy for the leaves to be damaged or broken, which affects the appearance and quality of leafy vegetables.

Bubble cleaning machines usually adopt the bottom air supply method, using an air pump to add gas (air) with a certain positive pressure into a flowing or static water tank. The added positive pressure gas generates positive pressure bubbles. When the bubbles rise and burst, the resulting pressure changes continuously adsorb and impact impurities on the surface of vegetables, thus achieving the cleaning purpose. Compared with traditional cleaning machines, bubble cleaning machines can be used for the cleaning of leafy vegetables and cause less damage. This is because the impact of bubbles is relatively gentle and will not cause excessive mechanical damage to leafy vegetables. The cleaning characteristics of ultrasonic cleaning machines are fast speed, good effect and easy industrial control, and they can clean various vegetables and fruits such as root and stem vegetables and leafy vegetables. However, during the cleaning process, the ultrasonic generator will produce strong vibrations and rapid temperature rise of the water solution. When used for the cleaning of fruits and vegetables, the strong vibration and high temperature can easily cause damage to plant cells, resulting in the loss of nutrients.

03 Conventional Methods for Disinfecting Fruits and Vegetables

For the disinfection of fruits and vegetables, the most widely used sterilization method currently is to add sodium hypochlorite as a disinfectant in the washing, spraying and washing tanks. Sodium hypochlorite has strong oxidizing properties, is low in cost, and can effectively and broadly kill microorganisms. In large-scale fruit and vegetable processing enterprises, sodium hypochlorite is widely used in the fruit and vegetable disinfection process due to its price advantage and sterilization effect. However, in recent years, researchers have found that chlorine-containing disinfectants can combine with some organic substances to form toxic by-products, such as chloramines, polychlorinated biphenyls, and trihalomethanes, which are all potential carcinogens and can cause harm to human health. Long-term intake of fruits and vegetables containing these toxic by-products may increase the risk of diseases such as cancer.

Ozone is a new, efficient and broad-spectrum sterilizer with a high oxidation-reduction potential, second only to fluorine, and has strong oxidizing properties. In June 2001, the FDA (Food and Drug Administration of the United States) approved ozone as an antibiotic additive for the processing, storage and processing of foods including meat and poultry, and it can also be used in the preparation, packaging and storage of primary agricultural products. The sterilization effect of ozone water is mainly determined by the concentration of ozone in water and the duration of action. Studies have shown that a certain concentration of ozone water can achieve a high sterilization rate in a short time. However, ozone disinfection and sterilization also have disadvantages, mainly due to its instability. The decomposition rate of ozone in water is faster than in air, and ozone decomposes into oxygen in water solutions containing impurities. Reducing water temperature, adjusting water quality and pH can increase the stability of ozone, but it is not practical in actual applications.

04 Characteristics of Micro-nano Ozone Bubble Water 

Micro-nano ozone bubble water is a product that combines micro-nano bubble generation technology with ozone generation technology. Using air as the raw material, pure oxygen is separated by an oxygen generator and then converted into ozone gas through an ozone generator. The ozone gas is then used as the gas source and mixed with water through a micro-nano bubble generator to form a gas-liquid mixed fluid. The concentration of ozone in water and its effective dissolution efficiency are influenced by multiple factors such as water temperature, pH value, ozone quantity, gas-liquid ratio, and gas-liquid mixing methods. Researchers compared four gas-liquid mixing methods: micro-nano bubble devices, gas-liquid mixing pumps, sand core aeration heads, and Venturi tubes. The results showed that the ozone dissolution efficiency was the highest when using micro-nano bubble devices.

After being subjected to high-speed rotation and shearing in the micro-nano bubble generator, the ozone gas dissolves in water in the form of micro-nano bubbles, with a particle size ranging from 100 nanometers to 10 micrometers. This increases the contact area between the gas and water, facilitating the dissolution of ozone in the water. Additionally, the slow upward movement of micro-nano bubbles in water helps maintain a more stable ozone concentration in the water. Compared with ultrasonic ozone water cleaning, although ultrasonic waves can also form small bubbles to promote the dispersion of ozone and enhance sterilization effects, the intense vibration during ultrasonic cleaning causes the water temperature to rise rapidly, reducing the solubility of ozone in water. In contrast, micro-nano ozone bubble water avoids this issue and can better exert the sterilization and disinfection effects of ozone.

05 The Advantages of Micro-nano Ozone Bubble Water in the Cleaning of Fruits and Vegetables 

Washing fruits and vegetables with micro-nano ozone bubble water is a type of bubble cleaning method. This method causes the least damage to fruits and vegetables and can be applied to leafy vegetables. Different from traditional bubble cleaning, micro-nano bubbles have a small particle size and can penetrate into the tiny spaces where fruits and vegetables overlap, cleaning the hard-to-reach areas with conventional methods more thoroughly and achieving a better cleaning effect. When cleaning leafy vegetables with closely overlapping leaves, micro-nano bubbles can enter the gaps between the leaves, removing dust, impurities and microorganisms, ensuring the cleanliness of the fruits and vegetables.

Micro-nano ozone bubble water has strong oxidizing properties. It can not only quickly kill eggs, bacteria, viruses, etc., but also decompose pesticide residues on the surface of fruits and vegetables, keeping them fresh and crisp and extending their shelf life. After ozone decomposes, it forms oxygen and leaves no residue on the surface of fruits and vegetables, making it a safe and reliable disinfection method. For consumers, eating fruits and vegetables that have been washed and disinfected with micro-nano ozone bubble water is more reassuring, as they don't have to worry about the harm caused by pesticide residues and microbial contamination to their health. Moreover, this cleaning method can effectively maintain the quality and taste of fruits and vegetables, allowing consumers to enjoy fresher and more delicious fruits and vegetables.