Ozone was first discovered in 1840. It was first used in sewage treatment and subsequently used in medical and health, food, breeding, aquaculture, storage and preservation, chemical production, and tap water disinfection. In recent years, the tendency to apply ozone in the food industry has been increasing, and its application range has been expanding. In particular, research on the application of ozone in the storage and preservation of aquatic products and processing has been increasing. This paper expounds the nature, production, sterilization mechanism and the advantages of ozone sterilization of food. It summarizes the application research of ozone in the preservation of aquatic products at home and abroad, in order to provide a theoretical reference for the preservation of aquatic products in China.
1. The nature of ozone
Ozone has a molecular formula of 03 and is an allotrope of oxygen (O2). Pure ozone, boiling point of ¬-119.7 ± 0.3 ° C, melting point of -192.7 ± 0.2 ° C, at room temperature is a light blue gas, but usually looks colorless, irritating astringent, a trace when there is a "Fresh" smell. Ozone is unstable and easily decomposes into oxygen. Its half-life in water decomposition depends mainly on water quality and temperature. At 20 ° C, the half-life of ozone in distilled water is about 25 min, about 20 min in low-hardness groundwater; when the water temperature drops to 0 ° C, the ozone becomes quite stable; the half-life of ozone in air is generally 20-50 min. The higher the temperature, the greater the humidity, the faster the decomposition; in dry and low temperature air, the half-life can reach several hours. The redox potential of ozone is second only to fluorine (Table 1), and it has strong oxidizing ability. This property can be used for sterilization, disinfection, deodorization and preservation.
2. Ozone production
The generation of ozone can be carried out by a corona discharge method, an electrolysis method, and an ultraviolet method. At present, corona discharge method and electrolysis method are more used, and the ultraviolet method is less applied.
2.1 Corona discharge method
The principle is to ionize air or oxygen with high-voltage, high-frequency current to produce ozone. The method is to pretreat oxygen or air through drying, etc., and then enter the discharge chamber to ionize. This method can only obtain a mixed gas containing ozone, can not obtain pure ozone, has high equipment cost, and can produce toxic nitrogen oxides.
At present, such ozone generators are used in both plate type and tube type. The plate type ozone generator forms a discharge space between the high voltage electrode plate and the low pressure electrode plate, and ionizes oxygen molecules in the air into ions, oxygen ions and oxygen molecules. Combined with ozone, its ozone production is high. In the tubular ozone generator, air passes through the corona discharge space around the tube, which produces ozone, but the yield is low.
2.2 Electrolysis
In recent years, foreign countries have used electrolysis to produce ozone. The law was initiated in 1840. The principle is to electrolyze water with low-voltage direct current to oxidize it at the special anode interface to produce ozone. The electrolysis method precipitates ozone at the anode and hydrogen gas at the cathode. The generator can produce ozone with high concentration, and the product has no harmful nitrogen oxides, so it has broad application prospects, and has been developed and produced in China.
2.3 UV method
Ultraviolet light having a wavelength shorter than 200 nm can ionize oxygen molecules in the air to generate ozone. High-ozone ultraviolet light is the use of ultraviolet light to produce ozone, which is sterilized by the synergy of ultraviolet light and ozone. The amount of ozone produced by this method is low.
3. Ozone sterilization mechanism
Ozone sterilization or bacteriostatic action is usually a combination of physical, chemical and biological aspects. The mechanism of action can be summarized as follows: (1) acting on the cell membrane, causing an increase in the permeability of the cell membrane, efflux of the intracellular material, and deactivating the cell; (2) inactivating the enzyme necessary for cell activity. These enzymes include both basal metabolic enzymes and enzymes that synthesize important cellular components; (3) disrupting or rendering the genetic material in the cytoplasm. Ozone killing virus is accomplished by directly destroying RNA (ribonucleic acid) or DNA (deoxyribonucleic acid) substances; while killing bacteria and mold microorganisms, ozone first acts on the cell membrane, causing damage to the composition of the cell membrane, leading to metabolic disorders. And inhibit its growth, ozone continues to penetrate and destroy the tissue inside the membrane until death.
4, the advantages of food ozone sterilization
The use of ozone for food sterilization has the following advantages: (1) Ozone oxidizing and disinfecting ability is stronger than the most commonly used fungicide chlorine, which can inactivate many microorganisms including the most stubborn spores, viruses, etc. (2) Ozone Unlike chemical synthetic products, it is decomposed into oxygen after handling food, does not leave any harmful substances, and does not affect human health. Even in the United States with high safety requirements, it is approved as “GRAS†(generally considered safe) (3) Ozone avoids heat sterilization, which preserves the original nutrients (vitamins, minerals, etc.) of the food, while effectively avoiding the texture, flavor and taste of the food caused by heat treatment. (4) Ozone is easy to prepare. Only the ozone generator can be used, and the cost is low.
5. Research progress in the application of ozone in the preservation of aquatic products
In foreign countries, as early as the beginning of the 20th century, the application and research work of ozone in the preservation of aquatic products began. In 1936, Sa1mon et al. found that fresh fish were placed in ozone-treated ice, and their storage time could be almost doubled. Washing fish with ozonized water can extend the storage time by 5 days and accelerate the contaminated oysters. The speed of disinfection and purification of mussels and other shellfish. However, in the following thirty years, there has been little research report on the use of ozone to preserve aquatic products to extend their shelf life. Until 1969, Japanese scholar Hara Uchi et al. reported that the fish was immersed in a 30% NaCI solution containing 0.6 mg/m 303 every 2 d to prolong the storage time of 1.2 to 1.6 d; and only the raw material was washed with ozone water. The storage period of the squid cannot be significantly prolonged without any treatment during storage. In 1982, B1ogos1awski found that disinfecting scallops with ozone water can reduce the total number of bacteria by 90% to 94%. The storage of frog fish with ozonized ice can extend the storage period by 2 to 3 days. Nelson extended the storage period of Alaskan frog fish with ozonized ice and used unozonated ice as a control. The total number of frog fish in ozonized ice (94×103) was only 3% of the control sample (2.7×10). Ozonized ice kept the freshness of Pacific frogs above 6d, while the control group only lasted for 4 days. In 1984, DeWitt et al reported that ozonized ice can prolong the storage period of the Gulf of Mexico shrimp for l~2d. In 1986, Sassen et al. used ozone water and ozone ice to extend the storage period of shrimp (sandshrimp). In 1988, Kayama et al reported that the use of ozone-preserved black mites (Acanthopagrusschlegeli), small shrimp (Trachypenaeus curvirostris), squid (Scomberjaponicus), sardines (Sardinopsme1anssticata), oysters (Crassostreagigas) can effectively inhibit the increase of K value and the decrease of 1MP content. The effect is slightly worse than the amino acid preservative (ca11ed PichiPichi, PP), but superior to chloride. In 1990, Brooks et al. reported that ozone was used instead of chlorine for the commercial processing of salmon (Icta1uruspunctatus), which is believed to have the potential to extend the shelf life of salmon. In 1992, Chen et al. used ozone for the preservation of shrimps and found that the ozonation of the salt solution was more effective than the water containing organic matter. After the muscle was ozonated, no deterioration was found. In the same year, Dondo et al reported that ozone can reduce the number of microbes on the surface of fish, reduce the content of trimethylamine, and improve the sensory quality. In 1996, Sakamoto et al. washed the soy-impregnated frog fish with ozone water and then chilled at 5 ° C. The results showed that the life span of the frog fish was extended by 3 days. In 1998, Silva et al. achieved good results in using ozone gas to improve the sensory quality of the horse mackerel (Trachurustrachurus) and reduce the number of microorganisms. In 2000, FishingNews International reported that an ozone ice manufacturing facility developed by the Polaris Ice Equipment Company in Seattle, USA, has been installed on fishing vessels in Norway. The ozone flake ice or slurry ice produced by the equipment (which can be made to flow by a pump) has a good bactericidal effect and can significantly prolong the shelf life of benthic fish, fresh fish and other fish. However, some scholars have reported that ozone treatment has no obvious effect on prolonging the shelf life of aquatic products. For example, Ravesi et al reported that the combination of ozonized ice packaging, ozone water or seawater rinsing to store Atlantic fresh fish did not extend the shelf life, ie ozone treatment had no significant effect. Ktter et al. (1997) reported that although the ozonation of water during the transportation of fresh fish reduced the number of bacteria and extended the shelf life by nearly 36 h, the laboratory simulation experiments gave different results.
Domestically, the application of ozone in the processing of aquatic products has been a relatively mature technology. It is mainly used for sterilization of aquatic products in cold storage, sterilization of air, equipment and supplies in processing workshops, sterilization of processing water, deodorization, processing of raw materials before packaging and packaging, etc., and is widely used. At present, many domestic aquatic product processing plants have begun to adopt ozone sterilization technology. In recent years, the application of ozone in the preservation of aquatic products has also been continuously carried out. For example, some domestic enterprises have begun to use ozone for the preservation of fresh aquatic products and for sterilization before freezing. Wang Guoli and other reports reported that ozone disinfection was used in the processing of aquatic products such as scallops in some enterprises in Changdao, Shandong Province, which prolonged the storage time of raw materials. Zhou Xiangyang and others used ozone water to control the microbes of frozen shrimp. The results showed that the total number of bacteria in frozen shrimp was greatly reduced, and the incidence of other common pathogens was also effectively inhibited, and the sensory characteristics were not significantly changed. It has also been reported that the use of ozone water to spray aquatic products such as shrimp can effectively control the amount of microorganisms. Qin Cheng et al observed the oxidation of aquatic products and the preservation effect of high-concentration ozone water. It was found that the preservation effect of ozone water was significantly better than that of sodium hypochlorite, and there was no significant difference in surface oxidation.
6 outlook
There are three main ways in which ozone can be used to preserve aquatic products: ozone water, ozone ice, and ozone gas. Ozone water has a strong oxidizing power, and it can reduce the number of original bacteria in aquatic products. However, the researchers' conclusions are not consistent with whether or not they can prolong their storage period. Therefore, the research work in this area needs further research. . The active ozone in ozone ice can be slowly released with the melting of ice, which has a great inhibitory effect on the bacteria in the mucus of the fish body. Therefore, it can be used to preserve aquatic products and achieve good preservation effect. This is a predecessor. The research confirmed. In addition, the regular use of ozone gas to preserve aquatic products has also achieved good preservation effect. China is a big fishing country in the world. With the improvement of living standards, consumers are increasingly demanding the quality of aquatic products, and the preservation of aquatic products has received unprecedented attention. The concept of “freshness†is value has been accepted by more and more aquatic workers. Therefore, the development of new and safe methods for preserving aquatic products has become a topic of great concern. Aquatic products can be sterilized by ozone water before storage, which can reduce the amount of original microorganisms. During storage, high-concentration ozone ice is used or a certain amount of ozone gas is used, which is expected to achieve better preservation effect. It can be expected that with the in-depth research in this field, ozone preservation will become an important way for the preservation of aquatic products in China.