Ultraviolet rays can kill bacteria and have certain carcinogenic capacity. So, can food treated with ultraviolet rays be eaten?

What is ultraviolet

Ultraviolet is defined asElectromagnetic radiation with wavelengths ranging from 10 nm to 400 nm。 However, in practical applications, the wavelength used is generally more than 100 nm. With wavelengths between 315 and 409 nmUVA usually Tan the skinAt wavelengths of 280 to 315 nmUVB can burn the skin and increase the risk of skin cancerThe wavelength is 200 to 280 nmUVC can effectively kill bacteria and virusesUltraviolet rays with wavelengths between 100 and 200 nanometers can be absorbed by oxygen in the air, so they can only work in vacuum or at least completely anaerobic environment, which is not suitable for practical sterilization.The wavelength of 254 nm is selected for traditional UV sterilization。

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 254 nm is located in the ultraviolet (UVC) band.

Principles and advantages of ultraviolet sterilization

When ultraviolet light is absorbed by bacteria or viruses, theDNA damageTo make themLoss of proliferative capacity。 In terms of sterilization results,It's the same as heating or chemical treatment。 But ultraviolet lightIf you don't heat it, you don't destroy the nutrients——Because DNA is not a nutrient in food, and the molecules that the human body needs are not destroyed. In addition,It will not destroy the natural flavor of food。 After all, chemical fungicides or preservatives introduce new substances, and sometimes bring some "peculiar smell". The DNA molecules destroyed by ultraviolet rays will be decomposed when they enter the human body and will not produce harmful substances. SoDespite the carcinogenic potential of ultraviolet rays, food treated with ultraviolet rays has no safety problems.

Any food processing means will have a certain degree of "damage" to food. Compared with the most conventional heating, UV treatedThe damage is much less。 For some foods that want to keep their natural state, it has a great advantage over juice.

UV sterilization is used for juice treatment.

How about the effect of ultraviolet sterilization

The ability of UV sterilization is not only related to the wavelength, but also depends on the energy radiated from food. At the selected 254 nm wavelength, the germicidal efficacy and energy intensity present a stretched S-shape. in other words,At low energy, the sterilization effect is very poorThis is 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 rapidly. On the macro level, bacteria or viruses are "killed".Beyond this energy intensity, each increase in sterilization capacity will greatly increase. But when it reaches a certain level, it will enter the second platform, and if we continue to increase the energy, the bactericidal effect will increase little。 The "tail" of the sterilization effect may be due to the fact that some microorganisms are resistant to UV attack, or some of the treated samples cannot be irradiated.

Ultraviolet rays can cause DNA damage.

Because of the existence of this "tail", ultraviolet sterilizationIt's hard to kill as thoroughly as heat or chemical fungicides。 Generally, the reduction of 4 logarithms is regarded as the "sterilization standard", that is, there are alsoOne in ten thousand bacteria survived。 Pasteurization of fresh milk - treated at 72 ℃ for 15 seconds - usually reduces by five logarithms, meaning that at most one in 100000 bacteria survive. If it is the ultra-high temperature sterilization of normal temperature milk, the logarithm value is more than 12, almost no bacteria can survive.

Influencing factors of sterilization effect

Different microorganisms have different sensitivity to ultraviolet raysSome of them will be killed in a large number at lower energy intensity, while others need higher energy. To reduce four logarithms as the standard, some of the bacteria detected in the study only need tens of joules per square meter, while others need more than 300 joules per square meter. We don't know which bacteria exist in real food, and how many bacteria there are, soAlways take the most tenacious one as the target, and kill the others by the way. Therefore, the energy intensity of ultraviolet sterilization should be more than 400 joules per square meter.

Factory sterilization operation.

The sterilization effect of various sterilization technologies will beAffected by the physical and chemical properties of food。 For example, heating or high pressure sterilization, temperature, pH and pressure will have a great impact. In UV sterilization, these factors are not so important. The key to UV sterilization is that UV can reach bacteria, soPenetrabilityIt's the key. Such as the composition of food, solid content, color and other factors will affect the absorption of ultraviolet ray, thus affecting the thickness of its penetration, which has a great impact on the sterilization effect. If the food is uniform and transparent, and the ultraviolet ray penetration is good, the sterilization effect will be good; on the contrary, if the food is turbid, the ultraviolet light will be scattered, the energy will be reduced in the penetration, and the sterilization effect will be relatively poor.

In general, the penetration of ultraviolet rays is relatively poor, and it can usually penetrate two or three centimeters in thickness. It is still a challenging task for solid food to receive ultraviolet radiation evenly in a thin layer. This congenital defect greatly limits its application.

High pressure sterilization equipment.

Application of ultraviolet sterilization in food industry

There are three main categories:

The first is the disinfection of food processing equipment. For equipment, microorganisms always stay on the surface, and the weakness of poor UV penetration is irrelevant. The advantages of no heating and no introduction of other substances (including water) are fully utilized.

The second is the pretreatment of water for food processing. In order to reduce the possible introduction of microorganisms in the production process, the sterilization pretreatment of processing water is twice the result with half the effort. Compared with chlorine or chloride, ultraviolet sterilization without chemical substances can avoid the risk of sterilization by-products and avoid the odor caused by fungicides.

Schematic diagram of ultraviolet sterilization of water.

Third, & nbsp;At present, fruit juice is the main UV sterilized food.The flavor of juice is easily changed by heating, so "non thermal processing" is very attractive in juice production. The name of the fungicide alone can't make consumers like it. Therefore, ultraviolet sterilization without changing flavor and introducing "chemical components" will have a great use.

φ conclusion

There is no safety problem when food is sterilized by UV with proper wavelength. And for some foods that want to keep their natural state, ultraviolet sterilization has more advantages than juice.

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