What Is Ultraviolet Irradiation?

Ultraviolet (English name: ultraviolet ray; UVR): Part of the solar radiation, it is composed of three different wavelengths in the ultraviolet spectral region, from short-wave UV C to long-wave UV A.

UV is

Ultraviolet (UV) is a general term for radiation in the electromagnetic spectrum with a wavelength from 10 to 400 nm. According to the different wavelengths of ultraviolet rays, ultraviolet rays can be divided into long-wave ultraviolet rays (315-400nm, UV-A), medium-wave ultraviolet rays (280-315nm, UV-B), short-wave ultraviolet rays (200-280nm, UV-C), and vacuum. Ultraviolet light (100-200nm). Short-wave UV belongs to the sterilizable band and can kill bacteria and viruses. UV-C (especially the wavelength of 254 nm) can penetrate the cell membrane of microorganisms, causing cross-linking between adjacent thymine and cytosine in the same DNA chain, resulting in blocked DNA translation and replication, endangering cell function, and ultimately leading to Cell death. It can improve the preservation quality of food by killing surface microorganisms and stimulating abiotic stress effects. UV-C treatment can induce fresh agricultural products to improve disease resistance, produce functional components, delay maturity and aging, and inhibit the growth and reproduction of pathogenic microorganisms. For example, treatment of potatoes with UV-C at 254nm can reduce the dry rot caused by Fusarium solani during storage, and does not affect the starch content and composition in potatoes. The United States has developed UV-C processing equipment suitable for post-harvest processing and processing of fruits and vegetables, which has been used in apple post-harvest processing with good results.

In China, although this technology has not been developed for commercial use, it has a very good prospect for its commercial application in fruits and vegetables. In addition, UV-C treatment has the advantages of simple operation, small investment, and no chemical reagent residues, so it has become a research focus in the field of fresh preservation in recent years.

Research on Ultraviolet in Postharvest Preservation of Fruits and Vegetables

Fruits and vegetables are an essential part of people's lives. However, because of geographical and time constraints, many are rotten during transportation and storage, and the annual losses caused by it are unimaginable. About 30% of the harvested vegetables in the United States and other developed countries are lost due to decay. Due to insufficient post-harvest processing capacity and cold storage facilities, post-harvest decay is more serious. Therefore, a suitable and efficient fruit and vegetable preservation technology is important to us. At present, the traditional and popular fresh-keeping technology includes modified atmosphere and refrigeration, but its cost is relatively high and the effect is also limited. In recent years, ultraviolet radiation has appeared in people's field of vision as a new preservation technology. Some scholars and researchers have also conducted relevant experiments and achieved corresponding research results. After UV treatment, fruits can reduce the incidence of fruits and improve the quality of fruits and vegetables. For example, Wang Kaizhi irradiated the ripe mango with UV-C for 10 min, which increased the polyamine content in the mango skin tissue and played a role in preventing the mango from decaying.

Wu Fangfang et al. Reported that low-dose UV-C irradiation can reduce the incidence of anthracnose in apples to a certain extent and inhibit the occurrence of anthracnose in apples after harvest. The results of research by Yang Zhenfeng and others showed that strawberry fruit stored at 10 for 12 days, 3kJ / m ² UV-C treatment could significantly inhibit the occurrence of strawberry fruit post-harvest rot and MDA accumulation, delay fruit weight loss, hardness and soluble solids content. reduce. At the same time, it can also delay the decrease of the content of antioxidant components in strawberry fruits and maintain high nutritional quality of the fruits. In addition, Wang Zhongyuan and other research results show that short-wave UV treatment can significantly delay the decline of cassava hardness and color change, maintain the quality of fruit storage, and delay the ripening and softening process of fruit.

Reports by Jiang Ziyu and others: UV treatment can slow the increase in weight loss and relative conductivity of longan, maintain the quality of longan storage, and delay the maturation and softening process of longan. Ultraviolet rays have certain effects on the preservation of vegetables and fungi. Studies by Lu Jiandong and others show that irradiation with UV-C3kJ / m ² treatment dose can significantly inhibit the weight loss of Pleurotus eryngii, inhibit the lipid peroxidation of Pleurotus eryngii, reduce the accumulation of MDA during storage, and make Pleurotus eryngii resistant to The oxide activity is maintained at a relatively high level.

UV-C treatment will have a certain fresh-keeping effect on fruits and vegetables. Of course, the effect of UV-C treatment is different for different varieties of fruits and vegetables. Therefore, corresponding UV-C treatment should be applied to different types of fruits and vegetables. Process is also an area that needs further research.

Study on Ultraviolet in Fresh-keeping Fruits and Vegetables

Fresh-cut fruits and vegetables are also called micro-processed fruits and vegetables, light (shallow) processed fruits and vegetables, cut fruits and vegetables, semi-processed fruits and vegetables, and conditioned fruits and vegetables. Due to their freshness, health, hygiene and convenience, they have occupied more and more fruits and vegetables processing industry. The more important position, especially in most developed countries, the increasing demand for fresh-cut fruit and vegetable products has become one of the fastest growing retail foods. However, fruits and vegetables are very prone to tissue browning, loss of nutrients, and microbial infection after cutting, which cause great losses and waste. Therefore, maintaining the quality and extending the fresh-keeping period is the key to the processing technology of fresh-cut fruits and vegetables.

At present, the commonly used fresh-keeping technologies in China mainly include modified atmosphere, application of edible film, refrigeration and use of preservatives. These traditional fresh-keeping technologies usually have large one-time investment and take a long time, and some fresh-keeping methods also cause chemical residues on the surface of fruits and vegetables, which endangers human health. Compared with the traditional preservation technology, UV irradiation preservation is a physical preservation method without adding any chemical reagents and without any residue. Ultraviolet radiation can only penetrate the surface tissues of fruits and vegetables, and destroy the DNA of bacteria, viruses and other microorganisms remaining in the fruits and vegetables, thereby achieving the effect of extending the fresh-keeping time of fruits and vegetables. Ultraviolet irradiation treatment can inhibit the growth of microorganisms and improve the shelf life of fresh-cut fruits and vegetables.

The results of Allende et al. Showed that the UV-C doses of 4.74 and 8.14 kJ / m ² can significantly reduce the number of microorganisms (total colony, lactic acid bacteria, yeast) that cut the lettuce without affecting quality. Lamikanra and other studies have shown that UV-C treatment can be used to induce allergic defense reactions by cutting melon, leading to the accumulation of ascorbic acid and peroxidase, reducing esterase activity, reducing breathing, delaying hardness decline, and improving shelf life. Studies by Francisco and others show that UV-C treatment can inhibit the growth of microorganisms on fresh-cut watermelon and significantly enhance its antioxidant capacity. Studies by Geng Yajuan and others showed that the treatment with different doses of ultraviolet irradiation had different effects on the nutritional quality of fresh-cut apples during storage. The 20W UV lamp is irradiated for 15min, which is beneficial to maintaining good nutritional quality of fresh-cut apples during storage.

UV combined traditional preservation technology

Preservation has always been a hot topic in people's lives and has always been closely related to us. With the development of science and technology, fresh-keeping technology is becoming more and more advanced, but it still cannot stop the pace of living body decay and aging, so we have been moving forward on this road. At present, the technologies that people have widely used are: mechanical refrigeration storage fresh-keeping technology, modified atmosphere storage fresh-keeping technology, traditional cellar storage fresh-keeping technology, fresh-keeping agent, and coating film fresh-keeping technology.

Ke Fansheng and others combined the modified atmosphere packaging (MAP) freshness and UV to extend the freshness period of Shi's catfish fillets. In addition, the research results by Wang Juan and others show that: coating and UV treatment can better maintain the color of fresh-cut papaya, inhibit browning, maintain a high soluble solid content, reduce water loss during storage, and inhibit Growth of mold, yeast and bacteria. The composite coating film formula and ultraviolet treatment can make the shelf life reach at least 6 days, providing a technical reference for fresh-cut papaya preservation. The traditional preservation technology combined with ultraviolet light provides a reference for preservation. As to whether it can be widely used, further investigation and verification are needed.

Security and Outlook

UV-treated foods are currently considered safe. The US Food and Drug Administration (FDA) and the United States Department of Agriculture (USDA) have determined that UV is safe. In 2000, the FDA approved UV-C for pasteurization of fruit juices. In 2002, UV-C was approved for food surface disinfection. The FDA has promulgated 21CFR179.41, approving the use of pulsed UV-C in food production, processing and processing. A safety assessment of UV-C apple juice was conducted in Canada. The treated juice is considered to be free of human safety issues.

Europe has used UV-C for water and air disinfection in the food industry. As a kind of physical fresh-keeping technology, ultraviolet fresh-keeping technology has no drawbacks of chemical fresh-keeping, no pollution, no residue, and is deeply loved by people. And its cost has great advantages compared to other fresh-keeping technologies, so ultraviolet fresh-keeping will gradually expand its coverage and become a mainstream. In the future, it is necessary to study different irradiation conditions according to the needs of different fruits and vegetables, or apply ultraviolet preservation to more fields, or combine it with other preservation technologies to create more convenient, practical and efficient preservation methods for preservation. The field opens a new path. ^[2]

Why does UV irradiation nucleus make cells inactive?

It is known that, in addition to bactericidal effects, directly irradiating the skin with ultraviolet rays also has the functions of regulating and improving nerves, endocrine, digestion, circulation, breathing, blood, immune system and promoting vitamin D production. However, in recent years, people have gradually realized that excessive ultraviolet rays cause photochemical reactions, which can cause a series of changes in human body functions, especially causing damage to the human skin, eyes, and immune system. In recent years, in the United States, Canada, Australia and other countries and some cities in China, UV index forecasts have been issued to remind the public to take corresponding protective measures. A few days ago, experts from the World Health Organization urged people engaged in outdoor activities to avoid prolonged exposure to the sun, and to pay special attention to protecting the skin when vacationing at the seaside and districts.

Ultraviolet rays have the most obvious effects on human skin and eyes. The skin's absorption of ultraviolet light is related to its wavelength. The shorter the wavelength, the smaller the depth of penetration into the skin, and the weaker the melanin deposition after irradiation; the longer the wavelength, the greater the depth of penetration into the skin, and the stronger the melanin deposition after irradiation. Due to the effect of photochemical reactions, higher energy levels of photon flow can cause the degeneration of nuclear proteins and some enzymes in cells. Therefore, after being exposed to ultraviolet rays, it takes 6-8 hours of incubation period before cell changes and symptoms occur, including dry and sore skin, epidermal shrinkage, and even blistering. Due to the weak penetration of ultraviolet light into tissues, deep tissues under the skin are less injured. However, severe ultraviolet rays can cause systemic reactions such as fatigue, low fever, and lethargy. Some people's skin is allergic to ultraviolet rays, and solar dermatitis (also known as sunburn) occurs after exposure to light. Itching, tingling, and scaling of the skin in exposed areas may also cause crusting. Actual observations show that in high-altitude areas at an altitude of 3500 meters (ultraviolet rays are usually 3-4 times that of plain areas), bare skin is exposed to ultraviolet rays around noon for about 20-40 minutes, and the skin has a burning sensation and peeling; lasting 40-80 Minutes, the skin will pimples like blisters and cause various lesions.

Long-term and multiple exposures can cause solar keratosis (photokeratosis) of the skin and mucous membranes, manifested in single and multiple appearances in exposed areas (such as the forehead, cheeks, nose tip, lips, eyelids, conjunctiva). Thickened horny layers. According to medical analysis, this is a precancerous change. Studies have shown that ultraviolet rays can cause DNA damage in the nucleus of cells. Due to internal defects in the body, the cell cannot repair the damaged DNA, which causes the replication of mutant DNA. If the body's immune system cannot reject it in time The elimination of such mutated cells means that the body's immune surveillance function is defective. Such mutated DNA cells will proliferate and eventually lead to the formation of tumors. Therefore, UV is an important carcinogen for the skin.

To prevent skin damage caused by ultraviolet radiation, the main purpose is to prevent UVB radiation; and to prevent UVA is to prevent skin tanning. In Europe and the United States, it is considered that dark skin is a symbol of bodybuilding, so tanning agents should be added to cosmetics without considering the protection of long-wave ultraviolet rays. In recent years, this view has changed. As people realize that long-wave ultraviolet rays may cause serious long-term damage to the human body, people have begun to strengthen protection against long-wave ultraviolet rays. ^[1]