UV light in the fight against bacteria in packaging

For microbiologically demanding packaged goods such as foodstuffs, pharmaceuticals or cosmetics, hygienic packaging is vital to ensure that the goods maintain their quality. These packaging materials can be disinfected using a variety of methods. Compared with chemical and thermal processes, UV irradiation is an environmentally friendly and economical method.

While taking into account different design and construction criteria and with sufficiently high irradiation power, UV disinfection can be used as a simple, fast and reliable process for continuous operation in filling equipment. Generally with this disinfection process, it is a matter of disinfection of packaging and not sterilisation.

Disinfection with ultraviolet light

Ultraviolet light at wavelengths of 254 nm is more energy-rich than the terrestrial UV light of the sun. This especially short wave UV light destroys the DNA of all microorganisms. When installed purposefully, viruses are disabled in seconds and microorganisms such as bacteria, yeasts and fungi are killed in an environmentally friendly manner, without the addition of chemicals. For a whole series of microorganisms, the lethal dose of UV radiation is known and this is the dose after which the cells can no longer maintain their metabolism and can also no longer multiply. Because of the cell structure, the lethal dose for different pathogens is distinctly high. Consequently, bacteria such as Salmonella and E. coli, which have a comparatively thin cell wall and can thus only slightly block the UV radiation, are extremely vulnerable and are very easily destroyed. On the other hand, mould spores protect themselves against UV radiation with a thick cell wall, which can even be pigmented. To kill these, a UV dose which is 10 to 100 times higher than that required for bacteria is needed.

The required lethal UV dose is an important parameter in the design and selection of suitable UV radiation sources.

Machine speed, geometry and shape of the packaging (for example, cup or sealing foil) are further criteria in the design of an effective disinfection process. The necessary UV dose is calculated by multiplying the irradiation power (intensity) of the UV lamp by the length of time that irradiation takes place. The intensity of the radiation is also dependent on the distance between the UV cassette and the packaging. The UV intensity of a lamp decreases with the increase in operating hours. At the end of the lamp operating life there must still be sufficient high UV intensity to ensure a suitable disinfection power and the necessary lethal dose in the given radiation time.

Experience with yoghurt filling, for example, has shown that pots of a depth of 150 mm can be effectively disinfected within six seconds and sealing foils in two seconds at the same intensity.

UV disinfection is used especially for the packaging of acidic fresh milk products, such as yoghurt and kefir, which are kept in the cool chain, in order to improve shelf life. This means that the dairy has significantly fewer returns of spoiled product, saving time, effort and cost of disposal.

Heraeus Noblelight UV disinfection modules have been specially developed for the disinfection of packaging and surfaces. For example, they can be installed in filling and sealing machines for milk and other drink products. Various shapes of pots and cups for milk products, sealing foils or bags, caps for glasses or bottle necks can be effectively disinfected with UV radiation. At the same time, combination processes of UV radiation and hydrogen peroxide can also be used. Even though the UV cassettes generate a high radiation power, the UV radiation itself is cold. The packaging is not heated. As a result, the disinfection process is particularly suitable for heat-sensitive materials.

BlueLight UV cassettes are fitted with UV amalgam lamps, which offer high intensity. Compared with modules with conventional emitters, irradiation power can be increased by 40% for the same irradiation time. Low capital and operating costs ensure a very economical disinfection method.

The UV modules are immediately ready for operation when supplied and are available in different sizes with two, eight or 10 emitters. The complete module consists of the UV disinfection cassette with the UV emitters, a power supply and a ventilation system. BlueLight cassettes are simply cooled by means of a fan and air tubes. The compact design of the cassettes allows rapid retrofit of the disinfection module in existing filling and sealing machines.

The quartz glass windows of the UV cassettes are fitted with a breakage detector and are thus within the Hazard Analysis Critical Control Point (HACCP) concept. On breakage of the window, the detector sends a signal to ensure immediate stoppage of the filling system. Moreover, the rounded edges of the window make for simple and thorough cleaning. This saves time when cleaning the complete machine.

The UV module requires a power supply of 50 to 60 Hz and a voltage of 195 to 260 V so that it can be connected to mains supplies in most countries. The electrical function of the emitters is monitored and reported in pairs and the UV intensity of the cassette can be simply controlled with a UV hand meter.

Disinfection with BlueLight UV modules is an economical and reliable method of disinfecting foodstuff packaging. It also has many applications away from the production line, where surface disinfection is important to ensure the destruction of pathogens in an environmentally friendly manner.