In 1801, German physicist Ritter found thatsunlightThe outer section of the purple end of the spectrum can makeSilver bromideThe existence of ultraviolet ray was discovered because of the sensitivity of the photographic negative of.[1]
Research progress
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Ultraviolet (UV) is the general term for radiation with a wavelength from 10 to 400 nm in the electromagnetic spectrum.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 rays (100 ～ 200nm).Short wave ultraviolet belongs to the range of bactericidal wave band, which 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 the function of cells, and ultimately leading to cell death.It can improve the quality of food preservation 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, the treatment of potato with 254nm UV-C can reduce the dry rot caused by Fusarium solani during storage, and does not affect the content and composition of starch in potato.The United States has developed a UV-C treatment equipment suitable for postharvest treatment and processing of fruits and vegetables.
In China, although this technology has not yet been developed for commercial use, it has a very good prospect for commercial treatment of fruits and vegetables.Moreover, UV-C processing has the advantages of simple operation, small investment and noChemical ReagentsIn recent years, it has become a research hotspot in the field of fresh-keeping.
Study on Ultraviolet Radiation in Postharvest Preservation of Fruits and Vegetables
Fruits and vegetables are an indispensable part of people's life.However, due to geographical and time constraints, many of them are decayed during transportation and storage, and the annual losses caused by them are unimaginable.About 30% of postharvest fruits and vegetables in developed countries such as the United States are lost due to decay. In China, postharvest decay is more serious due to insufficient postharvest processing capacity and refrigeration facilities. Therefore, a suitable and efficient fresh-keeping technology for fruits and vegetables is very important for us.At present, the traditional and common fresh-keeping technology includes air conditioning and refrigeration, but its cost is relatively high and its effect is also limited.In recent years, as a new type of preservation technology, ultraviolet radiation has appeared in people's vision. Some scholars and researchers have also conducted relevant experiments and achieved corresponding research results.The fruit treated by ultraviolet light can reduce the incidence of fruit and improve the quality of fruits and vegetables.For example, Wang Kaizhi irradiated mature mangoes with UV-C for 10 min, which increased the content of polyamines in mango skin tissue and prevented mangoes from rotting.
Wu Fangfang et al reported that low-dose UV-C irradiation can reduceApple bitter rot Incidence, inhibit the occurrence of postharvest apple anthracnose.The research results of Yang Zhenfeng et al. showed that when strawberry fruits were stored at 10 ℃ for 12 days, 3 kJ/mtwoUV-C treatment could significantly inhibit the occurrence of postharvest decay and the accumulation of MDA of strawberry fruits, and delay the reduction of weight loss, hardness and soluble solids content of strawberry fruits.At the same time, it can also slow down the decline of antioxidant components in strawberry fruit, and maintain a higher nutritional quality of the fruit.In addition, the research results of Wang Zhongyuan and others showed that the treatment of UVB could significantly delay the decline of cassava hardness and color change, maintain the storage quality of fruit, and delay the ripening and softening process of fruit.
Jiang Zitao et al. reported that UV treatment could slow down the rise of weight loss rate and relative conductivity of longan, maintain the storage quality of longan, and delay the maturation and softening process of longan.Ultraviolet ray has a certain effect on the preservation of vegetables and fungi.Research by Lu Jiandong et al. shows that UV － C3kJ/mtwoIrradiation with treatment dose can significantly inhibit the weight loss of Pleurotus eryngii, and inhibit theLipid peroxidationIt can reduce the accumulation of MDA during storage and maintain the antioxidant activity of Pleurotus eryngii 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 also different for different kinds of fruits and vegetables. Therefore, there should be corresponding UV-C treatment process for different kinds of fruits and vegetables, which is also an area that needs further research.
Study on Ultraviolet in Fresh cut 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. Because of their freshness, health, hygiene, convenience and other characteristics, they occupy an increasingly important position in the fruit and vegetable processing industry. Especially in most developed countries, the demand for fresh cut fruits and vegetables is increasing,It has become one of the fastest growing retail food sales.However, fruits and vegetables are prone to tissue browning, nutrient loss, microbial infection and other undesirable phenomena after cutting, resulting in great losses and waste.Therefore, the key to the processing technology of fresh cut fruits and vegetables is to maintain the quality and extend the fresh-keeping period.
At present, the commonly used fresh-keeping technologies in China mainly include modified atmosphere, the application of edible film, cold storage and the use of preservatives.These traditional fresh-keeping technologies usually require a large one-time investment and a long time, and some fresh-keeping methods can also cause chemical residues on the surface of fruits and vegetables, endangering human health.Compared with traditional fresh-keeping technology, ultraviolet irradiation fresh-keeping is a physical fresh-keeping method, which does not add any chemical reagents and has no residues.Ultraviolet irradiation can only penetrate the surface tissue of fruits and vegetables, destroy the DNA of bacteria, viruses and other microorganisms remaining in fruits and vegetables, so as to extend the fresh-keeping time of fruits and vegetables.Ultraviolet radiation treatment can inhibit the growth of microorganisms and improve the shelf life of fresh cut fruits and vegetables.
Allende and other research results show that 4.74 and 8.14kJ/mtwoThe amount of UV-C can significantly reduce the number of microorganisms (total colonies, lactic acid bacteria, yeast) in the cut lettuce, and does not affect the quality.Lamikanra et al. showed that UV-C treatment of cut melon could induce anaphylactic defense reaction, lead to the accumulation of ascorbic acid and peroxidase, reduce esterase activity, reduce respiration, delay the decline of hardness, and improve shelf life.Francisco et al. showed that UV-C treatment could inhibit the growth of microorganisms on fresh cut watermelon and significantly enhance its antioxidant capacity.Geng Yajuan et al. showed that different doses of ultraviolet radiation had different effects on the nutritional quality of fresh cut apples during storage.The 20 W ultraviolet light irradiation for 15 min was beneficial to maintain the good nutritional quality of fresh cut apples during storage.
Ultraviolet combined with traditional preservation technology
Fresh keeping has always been a hot topic in people's life, and has always been closely linked with us.With the development of science and technology, fresh-keeping technology has become more and more advanced, but it still can not stop the pace of living decay and aging, so we have also been advancing on this road.At present, the technologies that have been widely used include: mechanical refrigeration storage and fresh-keeping technology, controlled atmosphere storage and fresh-keeping technology, traditional cellar storage and fresh-keeping technology as well as fresh-keeping agent and coating technology.
Ke Fansheng and others extended the fresh-keeping period of sturgeon slices by combining modified atmosphere packaging (MAP) with ultraviolet.In addition, the research results of Wang Juan et al. showed that the coating and UV treatment can better maintain the color of fresh cut papaya, inhibit browning, maintain a high content of soluble solids, reduce water loss during storage, and inhibit the growth of mold, yeast and bacteria.The composite coating formula and ultraviolet treatment can make the shelf life reach at least 6 days, providing technical reference for fresh cut papaya.The traditional preservation technology combined with ultraviolet ray provides a reference for preservation. As for whether it can be widely used, it needs further exploration and verification.
Security and Outlook
At present, UV treated food is generally considered safe.US Food and Drug Administration(FDA) and the United States Department of Agriculture (USDA) have determined that UV is safe.In 2000, FDA approved that UV-C could be used in juicePasteurizationIn 2002, UV-C was approved for food surface disinfection.FDA issued 21CFR179.41 regulation to approve the use of pulsed UV-C in food production, processing and processing.Canada conducted a safety assessment of UV-C treatment of apple juice.It is believed that there is no human safety problem with the processed juice.
UV-C has been used in water and air disinfection in the food industry in Europe.As a physical fresh-keeping technology, UV fresh-keeping technology has no disadvantages of chemical fresh-keeping, no pollution, no residue, and is deeply loved by people.And its cost has great advantages over other preservation technologies, so UV preservation will gradually expand its coverage and become a mainstream.In the future, we will study different irradiation conditions for different fruits and vegetables, or apply ultraviolet ray preservation to more fields, or combine it with other preservation technologies to create more simple, practical and efficient preservation methods, opening up a new way for the preservation field.[2]
Harm of ultraviolet ray
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Why does ultraviolet radiation inactivate cells?
It is known that ultraviolet radiation on skin can not only kill bacteria, but also regulate and improve nerves, endocrine, digestion, circulation, respiration, bloodimmune systemAnd promotevitamin DGenerated function.However, in recent years, people have gradually realized that excessive ultraviolet radiation causesPhotochemical reactionIt can cause a series of changes in human function, especially harm to human skin, eyes and immune system.In recent years, in the United States, CanadaAustraliaAnd some cities in China have begun to releaseUltraviolet index predictionTo remind the public to take corresponding protective measures.A few days ago,world health organizationThe experts ofskin。
Ultraviolet rays have the most obvious effect on human skin and eyes.The absorption of ultraviolet rays by skin is related to its wavelength.The shorter the wavelength, the more penetrating
The smaller the depth of the skinMelanosisWeak;The longer the wavelength, the greater the penetration depth into the skin, and the stronger the melanin deposition after irradiation.Due toPhotochemical reactionThe role of,energy levelHigher photon flow can cause intracellularNucleoproteinAnd denaturation of some enzymes.Therefore, after being exposed to ultraviolet radiation, it takes 6-8 hours for the cells to change and show symptoms, including dry pain of the skin, shrinking of the epidermis, and even blistering and falling off.Because the penetration of ultraviolet rays to tissues is very weak, the deep tissues under the skin are less injured.However, severe ultraviolet rays can cause fatigueLow fever, drowsiness and other systemic reactions.Some people's skinUltraviolet allergy, occurs after illuminationSolar dermatitis(also known asSunburn）, exposure areaskin Itch, tingling, skinDesquamation, and may ulcerate and form scabs.The actual observation shows that in the plateau area at an altitude of 3500 meters (the ultraviolet radiation is usually 3-4 times that of the plain area), the exposed skin will be exposed to ultraviolet radiation around noon for 20-40 minutes, and the skin will feel burning and peeling;For 40-80 minutes, the skin will risepapuleIt is like a blister and causes various pathological changes.
Long term and repeated exposure can cause actinic keratosis (actinic keratosis) of skin and mucosa, which is manifested in exposed parts (such as foreheadBuccal region、nose, lipsEyelidConjunctiva) appear single and multiple flat topCornification layerThickening.According to medical analysis, this is a precancerous change.Research shows that ultraviolet rays can causenucleuswithinDeoxyribonucleic acid(DNA) damage. Due to the inherent defects of the body, cells can not repair the damaged DNA, thus causing mutationdna replication , if theimmune systemIt can not be rejected in time to eliminate this variant cell, namely the bodyImmune surveillanceIf the function is defective, the cells with this variant DNA will proliferate and eventually lead to the formation of tumors.Therefore, ultraviolet ray is an important part of skinCarcinogenic factors。
Prevent skin damage caused by ultraviolet radiation, mainly to prevent ultraviolet radiationUVBRadiation of;And preventUVAUltraviolet rays are used to avoid sunburn.In Europe and the United States, people believe that dark skin is a symbol of fitness, so instead, tanning agents should be added to cosmetics, without considering the protection of UVA.In recent years, this view has changed. People have begun to strengthen the protection against UVA because they realize that UVA may cause long-term serious damage to the human body.[1]
