Ultraviolet light sterilization

Sterilization. In some processes, such as food and beverage and pharmaceutical processes, water might need to be sterilized before it is reused or recycled. Chemical oxidation (e.g. ozonation) can be used. Ultraviolet light is an alternative for lightly contaminated water. Alternatively, a combination of chemical oxidation and UV light can be... 

UV-C technology is widely used as an alternative to chemical sterilization and microorganism reduction in food products (Lamikanra 2002 Fan and others 2008). Ultraviolet light also induces biological stress in plants and defense mechanisms in plant tissues with the consequent production of phytochemical compounds (Lee and Kader 2000). Phytoalexin accumulation could be accompanied by other inducible defenses such as cell-wall modifications, defense enzymes, and antioxidant activity, which have been reported with health benefits (Gonzalez-Aguilar and others 2007). It is well documented that UV-C irradiation has an effect in secondary metabolism. 

Many cellular materials absorb ultraviolet light, leading to DNA damage and consequently to cell death. Wavelengths around 265 nm have the highest bactericidal efficiency. However, ultraviolet rays have very little ability to penetrate matter. Therefore, their use is limited to the reduction of microbial population in a room where sterility needs to be maintained, such as hospital operating rooms or clean chambers in a laboratory. X-rays are lethal to microorganisms and have penetration ability. However, they are impractical as sterilization tools due to their expense and safety concerns. 

Photochemistry involves the interaction of visible and ultraviolet light with cellulose whereas radiation chemistry involves its interaction with high-energy radiations, such as from y-radiation. Light promotes the deterioration of cellulosic products, particularly cotton fabrics, and certain dyes or other additives greatly accelerate this process known as phototendering. Ionizing radiation is used to sterilize medical and bioproducts many of which are cellulosic. Several authoritative reviews are available [511-514]. 

Ultraviolet light is frequently employed to reduce airborne microbial contamination. Surface sterilization is usually achieved by employing a mercury vapor lamp with an emitted light of 253.7 run. 

Persistence in the soil is generally low (half-life under aerobic and anaerobic conditions is 21 and 68 days, respectively). In sterile soil, the half-life is almost 1 year. Azinphos-methyl adsorbs strongly to soil particles and has low solubility in water. Biodegradation and evaporation are the primary routes of elimination from soil but azinphos-methyl is also degraded by ultraviolet light. Degradation is more rapid at higher temperatures. Azinphos-methyl has a short half-life in surface waters (2 days). Hydrolysis is more prominent under alkaline conditions but the compound is relatively stable in water below pH 10. The half-life on crops is 3-5 days under normal conditions. 

Singh, S. and Schaaf, N.G. 1989. Dynamic sterilization of titanium implants with ultraviolet light. Int. ]. Oral MaxiUofac. Implants 4 139. 

Sterilization of the surfaces of vessels, pipes and valves may be achieved by heat, radiation or chemicals [81]. The use of steam has already been mentioned apart from cost it tends to be a slow procedure for sterilizing brewery vessels when steam pressures are low. Furthermore, it may carry undesirable particles and odours while the condensate is often drained unsatisfactorily. Radiation sterilization is rare although ultraviolet light irradiation is used for the treatment of water on a continuous basis. One of the simplest chemicals used for sterilization is ozone but this has proved corrosive [82]. More widely employed is hydrogen peroxide which, with peracetic acid, is added to soak baths for flexible pipes and items of fermentation equipment. 

For these materials to be utilized in biomedical in vivo and in vitro applications, it is imperative that the material be sterilized before use. Sterilization of these materials can be performed using a variety of methods such as ethylene oxide gas [48-50], ultraviolet light [51,52], ethanol washing [53], and autoclaving [12,54], An alternative approach to sterilization of the formed ICPs is the polymerization of the ICP under sterile conditions. This approach was utilized by Richardson et al. [55] to prepare PPy-coated electrodes for use in auditory nerve studies. 

In order to conduct this test, erythrocytes are separated from plasma and the buffy coat and washed three times with five volumes of phosphate buffer saline (PBS, pH = 7.4). The RBCs are collected in a centrifuge under specified conditions (3000 g for 10 min at 25°C). The compacted cells are then suspended in four volumes of PBS for the experiment. The surfaces of all the experimental samples are sterilised for 30 min in ultraviolet light under a sterile laminar air hood. 

Water samples are normally collected in clean, sterile, pretreated plastic bottles. If there is an excessive amount of suspended organic matter in the water, pretreatment of the samples using ultraviolet light and an ozone bubbler or sodium hypochlorite is necessary. Filtration is carried out using standard laboratory glassware, usually through a 25 mm-diameter filter of an appropriate material. The filter type depends on the microscope used for further analysis. 

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