Can ultraviolet light be used to disinfect food
Ultraviolet rays can kill bacteria and have a certain carcinogenic ability. So, can food treated with ultraviolet light be eaten?
Ultraviolet light is defined as electromagnetic radiation with wavelengths between 10 and 400 nanometers. However, in practical applications, the wavelength used is generally more than 100 nanometers. UVA wavelengths between 315 and 409 nanometers typically tan the skin, UVB wavelengths between 280 and 315 nanometers can burn the skin and increase the risk of skin cancer, UVC wavelengths between 200 and 280 nanometers are effective in killing bacteria and viruses, and UV wavelengths between 100 and 200 nanometers are absorbed by oxygen in the air. Therefore, it can only work in a vacuum or at least a completely oxygen-free environment, which is not suitable for practical sterilization. Traditional ultraviolet sterilization uses a wavelength of 254 nanometers. Ultraviolet disinfection, mainly uses the appropriate wavelength of ultraviolet light to destroy the DNA molecular structure in the cells of the microbial body, resulting in the death of growth cells or regenerative cells, to achieve the effect of sterilization, in this process will not appear harmful substances, the sterilized food can be eaten normally.
From left to right are X-rays and ultraviolet light. Visible light, infrared light, the wavelength of light increases in turn. The commonly used sterilization wavelength of 6254 nm is located in the far ultraviolet (UVC) band of ultraviolet light.
When UV rays are absorbed by bacteria or viruses, they damage DNA, rendering them incapable of multiplying. In terms of sterilization results, it is the same as heating or treating with chemicals. However, ultraviolet light does not heat, and it does not destroy nutrients - because DNA is not a nutrient component of food, and those substances that the body needs are not destroyed. In addition, it will not destroy the natural flavor of the food. Chemical fungicides or preservatives, after all, introduce new substances, and sometimes bring some "odors." The DNA molecules destroyed by ultraviolet light enter the human body and will be broken down, and will not produce harmful substances. Therefore, although ultraviolet light has the ability to cause cancer, food treated with ultraviolet light is not safe.
Any food processing method will have a certain degree of "destruction" of food. Uv treatment is much less damaging than the most conventional heating. For some foods that want to stay in their "natural state," such as fruit juice, it has a big advantage.
The ability of UV to kill bacteria is not only related to the wavelength, but also depends on the energy that is radiated to the food. At the selected wavelength of 254 nm, the bactericidal effect and energy intensity show a stretched S-shape. In other words, at low energy, the bactericidal effect is very poor, because bacteria or viruses, like the human body, have a certain ability to repair DNA damage. When the irradiation energy is low, the damaged DNA is repaired in time, and bacteria and viruses can continue to proliferate. When the energy is high to a certain extent, the DNA repair system is really busy, and the DNA damage increases sharply, which is shown in the macro that the bacteria or viruses are "killed". Beyond this energy intensity, with each increase, the sterilization capacity will be greatly increased. However, when it increases to a certain extent, it enters the second platform - and continues to increase the energy, and the bactericidal effect increases very little. This "tail" in sterilization effect may be due to the fact that some microorganisms are resistant to UV attack, or it may be due to the fact that some of the treated samples cannot be irradiated.
Because of the existence of this "tail", ultraviolet sterilization is difficult to achieve as complete a kill as heating or chemical fungicides. It is usually used to reduce the value of 4 pairs as the "sterilization standard", that is, one in 10,000 bacteria survive. Pasteurization of fresh milk - treated at 72 degrees Celsius for 15 seconds a batch - is usually reduced by five pairs, that is, at most one in 100,000 bacteria survive. If it is ultra-high temperature sterilization of normal temperature milk, the reduced pair value is more than 12, almost no bacteria can survive.
Different microorganisms have different sensitivity to ultraviolet light, and some will be killed in large numbers at lower energy intensity, while others require higher energy. By lowering the value of four pairs, some of the bacteria tested in the study required only a few tens of joules per square meter of energy, while others required more than 300 joules per square meter. We don't know what bacteria are present in real food, and how many of them there are, so we always target the toughest one and kill the others. Therefore, the energy intensity used in ultraviolet sterilization needs to be above 400 joules per square meter.
The sterilization effect of various sterilization techniques will be affected by the physical and chemical properties of food. For example, heating or autoclaving, temperature, pH and pressure all have a big impact. In ultraviolet sterilization, these factors are less important. The key to UV sterilization is that UV rays can reach bacteria, so penetration is key. Factors such as the composition of food, solid content, color and other factors will affect the absorption of ultraviolet light, thus affecting the thickness of its penetration, which has a great impact on the bactericidal effect. If the food is uniform and transparent, the penetration of ultraviolet light is good, the sterilization effect will be good; On the contrary, if the food is cloudy, then the ultraviolet light will be scattered, the energy will be reduced in the penetration, and the sterilization effect will be poor.
It should be noted that the penetration of ultraviolet light is relatively weak, the thickness of a printing paper can not penetrate, and it can only kill bacteria, microorganisms and viruses on the surface of food for food disinfection, and can not sterilize the bacteria in the deep layer of food. It is still challenging to get solid foods to receive UV radiation uniformly in a thin layer. This congenital defect greatly limits its scope of application.
The reason why I am keen on using ultraviolet disinfection is that it can achieve the effect of heating disinfection, and will not destroy the nutrients and natural flavor of the food, and now some restaurants will buy ultraviolet lamps to disinfect the surface of plates, bowls, chopsticks and so on, the effect is very good.
At present, there are three main applications of ultraviolet sterilization in the food industry
The first is the disinfection of food processing equipment. For the equipment, the microorganisms always only stay on the surface, and the weakness of poor ultraviolet penetration is not urgently needed, and the advantages of not heating and not introducing other substances (including water) are fully played.
The second is the pretreatment of food processing water. In order to reduce the microorganisms that may be introduced in the production process, sterilization pretreatment of processing water is a measure that gets twice the result with half the effort. Compared with the "chemical means" of adding chlorine or chloride, ultraviolet sterilization without the introduction of chemicals can avoid the risk of sterilization byproducts and avoid the odor caused by fungicides.
Third, at present, the use of ultraviolet sterilization in direct food is mainly fruit juice. The flavor of juice is easily changed by heat, so "non-thermal processing" is attractive in juice production. The name of the fungicide alone does not make consumers like it, so the ultraviolet sterilization that does not change the flavor and does not introduce "chemical composition" has a great use.
