2. UV light technology

processing in food industry. Ultraviolet (UV) light, which is a non-thermal technology, has recently attracted a lot attention to improvement of food safety. Compared to thermal processing, this promising technology can provide consumers with minimally processed, microbiologically safe and fresh-like products with minor effects on the nutritional and sensory properties of the product. On the other hand, this technology must not replace hygiene,

UV light application can also be introduced as an alternative to the use of chemicals in food industry. Besides, the use of UV light does not generate chemical residues. Additionally, it offers some technological advantages especially in developing countries in a small-scale production due to its low maintenance cost, low installation cost and low operational cost with minimal energy use. The operation and cleaning of the treatment is quite easy. In spite of its many advantages, its low penetration power restricts the area of use in food industry. Furthermore, its inactivation efficiency may be reduced or prevented because of physical features of food. At high doses, it can create negative effects on quality and some vitamins. In order to

UV irradiation of milk was first used in the mid-1900s for the purpose of vitamin D enrichment [1]. Efficacy of UV light treatment has been studied in recent years and more and more research has also been carried out to evaluate the potential applications of UV light as a non-thermal alternative to thermal processing of milk. On the other hand, due to the confirmed success and convenience of thermal processing, potential processing alternatives for milk are still limited. The use of UV light must not only be considered for microbial inactivation but also for the development of novel dairy products. The UVtreated pasteurized cow's milk was authorized as a novel food in market by European Commission. It is reported that the treatment of the pasteurized milk with UV radiation results in an increase in the vitamin D3 (cholecalciferol) concentrations by conversion of

Contamination of dairy products with microorganisms may occur at several stages of production, originating from a variety of sources during production. Although heat treatment is applied for inactivation of foodborne pathogens, dairy products especially cheese can be contaminated with undesirable microorganisms. After pasteurization process, handling of the curd, equipment, processing lines, packaging or storage rooms can result in cross-contamination with a variety of microorganisms. Even if good manufacturing practices are applied, surface applications of antimicrobial agents before packaging are commonly used to prevent spoilage and extend storage life for some dairy products. Instead of chemical preservatives, additional solution is needed to control the growth of microorganisms just before or after packaging of dairy products. Surface application of UV light after production can offer an attractive alternative method to eliminate or control the growth of postprocessing contamination. Other promising uses of UV light are the disinfection of air and water used in dairy plant, and surface decontamination of food contact surfaces and packaging materials. A lot of research is mainly focused on the application of UV light to reduce microorganisms in milk, and relatively little research focuses on the decontamination of the surfaces of solid dairy products. There is lack of information about the relation of quality and safety of dairy products. Thus, the application of UV light for various dairy products needs to be investigated in

obtain effective results, applications should be made considering these situations.

good manufacturing or agricultural practice.

4 Technological Approaches for Novel Applications in Dairy Processing

7-dehydrocholesterol to vitamin D3 [2].

#### 2.1. Principles of UV light technology

UV light includes the wavelengths from 100 to 400 nm on the electromagnetic spectrum. UV light can be subdivided into four regions according to their wavelength: UV-A (315–400 nm), UV-B (280–315 nm), UV-C (200–280 nm) and vacuum UV (100–200 nm). UV-C light has the most effective germicidal effect on microorganisms, such as bacteria, viruses, protozoa, fungi and algae [3, 4]. UV-C radiation in the range of 250–260 nm has the highest germicidal effect and ultraviolet energy at a wavelength of 253.7 nm shows the maximum effect, at which the absorption of DNA is stronger [3].

In principle, the photochemical reactions of biomolecules of microorganism primarily result in germicidal effect leading to inhibition of microbial growth or to inactivation of the cell. Germicidal effect of UV light on microorganisms occurs because of cross-linking between the bases of adjacent pyrimidine dimers in the same DNA strand [5]. This situation leads to inhibition of transcription and replication of nucleic acids, which is called clonogenic death [6, 7]. In some conditions, the metabolism can repair the DNA damage by photoreactivation or darkreactivation depending on the microorganism. Nevertheless, at high UV doses, the repair cannot be possible because of the wider damage [8].

#### 2.2. Factor affecting the efficacy of UV light in food industry

The UV light efficacy depends on several factors related to UV equipment, UV sources, operating and measuring conditions, target microorganisms and material or food to be exposed in food industry, which are summarized as:


The germicidal effects of UV radiation primarily depend on the UV dose (J/m2 ) which refers to the UV irradiance or UV intensity flux and is defined as the function of the intensity and time of exposure. The UV intensity (W/m2 ) is the total radiation from the specified area. In most cases, as the exposure time and intensity of UV light increase and the distance from light source to target decreases, inhibition rate of cells increases. In addition, whether the sample is located directly under lamp or not affects the inhibition ratio of microorganisms for a group of samples.

smooth surfaces is more effective than rough surfaces. The dirtiness and roughness can cause to form shadows and prevents direct access of light to the microorganism. Viscosity and density determine the effectiveness of the transfer and flow model of the liquid in the system, while optical properties affect the UV light transmittance [9]. Light transmission of food and packaging material in UV application to the surface of unpacked and packaged food is a critical factor for decontamination. Higher absorbsion of light is obtained in dark foods,

Ultraviolet Light Applications in Dairy Processing http://dx.doi.org/10.5772/intechopen.74291 7

Choosing the right UV source can increase the efficiency of microbial inactivation by increasing UV light penetration. The first and natural source of UV light is the Sun. The Sun emits radiation across a wide range of wavelengths. Other UV light sources are lamps. Many alternative UV light sources have been developed, such as low pressure mercury (LPM), medium pressure mercury (MPM), low pressure high output mercury lamp-amalgam type, mercury free amalgam lamps, pulsed-light (PL) and excimer lamps. LPM lamps are commonly

Mercury lamps have been the sources of radiation in most UV-based disinfection systems. The low and medium pressure mercury UV lamp sources are reliable sources for disinfection applications which are beneficial for their performance, and low cost. They are based on the vapor pressure of mercury while the lamps are operating. LPM lamps are designed to deliver a continuous monochromatic light at 254 nm. MPM lamps emit germicidal polychromatic light between 200 and 300 nm [9]. A breakthrough for economic UVC generation is the discovery of low pressure amalgam lamps [15]. This technology has recently been developed and incorporated into disinfection applications. The mercury emissions from lamps to the environment have encouraged the investigation of mercury-free lamps [9]. Xenon lamps are used in the Pulsed light UV technology. These lamps emit flashes in a short period of time. They have a broad spectrum of radiation between 180 and 1100 nm. Another UV light source is excimer lamps, which can emit pulsed light at 248 nm. It is possible to emit light in desired wavelength by using various gases such as He, Ne, Ar, Kr, Xe in the excimer lamps. The excimer lamps can

UV light applications are carried out with different equipment for solids or liquids: UV reactor designs for liquids according to flow types and UV cabinet designs for solids. It is necessary to increase the absorbed energy to the maximum level by developing the design of UV light

Reactors are devices used for UV light application to liquids. UV reactor contains UV lamps inside. Each UV lamp is in a separate protective quartz tube to prevent the direct contact with liquid. The liquid flowing through the UV reactor is exposed to UV rays emitted from lamps.

device with appropriate lamp and size in order to achieve the desired effect.

causing decrease of available energy for microbial inactivation [11].

2.3. UV light sources

used in food applications [14].

2.4. UV light devices

2.4.1. Reactors

be operated even at very low surface temperatures [7].

The UV light sensitivity of the target microorganism is an important parameter for the selection of the UV light dose. Microorganisms have different structures due to their many characteristics. The necessary energy can vary for a certain species of microorganism according to strain, growth medium and stage of the culture. Therefore, different doses are needed for inactivation of various microorganisms. UV doses as D values required for reducing populations of various microbial groups are reported by Koutchma [9] in Table 1. Besides the sensitivity of microorganism its contamination level also affects the decontamination degree. In fact, in our research on decontamination of mold on the yoghurt surface, the population of mold affected the decontamination level of mold. This can be attributed to overlapping of microorganisms which prevents UV light from reaching the population at the lower layer.

In dairy industry, one of the most important problems for dairy industry is biofilm formation which occurs with colonization of microorganisms on the surface. These biofilms block the light transmission, act as a protective barrier for microorganisms against the light and reduce the efficacy of UV treatment [10, 11].

Physical, compositional and surface properties such as thickness, viscosity, density, optical properties, color differences, dirtiness, roughness etc. can change the process efficiency. UV light has a restricted penetrability. Transparent fluids such as water are effectively disinfected by UV light, whereas opaque fluids such as milk are affected less due to poor penetration depth of light, and microorganisms cannot be affected directly [11, 12]. The composition of target is also important for the efficacy of UV light. Dissolved solids, suspended particles, organic solutes, macromolecules especially proteins and fat globules in food have shadowing effect on target microorganisms and limit the penetration and efficacy of light [11–13] Treatment efficacy also depends on the characteristics of surface exposed to light and application to


\* The D value is a measure of the resistance of a microorganism. It is given as the dose needed for an exponential decay of the target microorganism.

Table 1. UV inactivation doses measured at 253.7 nm for various microbial groups [9].

smooth surfaces is more effective than rough surfaces. The dirtiness and roughness can cause to form shadows and prevents direct access of light to the microorganism. Viscosity and density determine the effectiveness of the transfer and flow model of the liquid in the system, while optical properties affect the UV light transmittance [9]. Light transmission of food and packaging material in UV application to the surface of unpacked and packaged food is a critical factor for decontamination. Higher absorbsion of light is obtained in dark foods, causing decrease of available energy for microbial inactivation [11].

#### 2.3. UV light sources

of exposure. The UV intensity (W/m2

6 Technological Approaches for Novel Applications in Dairy Processing

the efficacy of UV treatment [10, 11].

Microbial group D Value (mJ/cm2

Table 1. UV inactivation doses measured at 253.7 nm for various microbial groups [9].

Enteral bacteria 2–8 Cocci and micrococci 1.5–20 Spore formers 4–30 Enteric viruses 5–30 Yeast 2.3–8 Fungi 30–300 Protozoa 60–120 Algae 300–600

\*

the target microorganism.

) is the total radiation from the specified area. In most cases,

) \*

as the exposure time and intensity of UV light increase and the distance from light source to target decreases, inhibition rate of cells increases. In addition, whether the sample is located directly under lamp or not affects the inhibition ratio of microorganisms for a group of samples. The UV light sensitivity of the target microorganism is an important parameter for the selection of the UV light dose. Microorganisms have different structures due to their many characteristics. The necessary energy can vary for a certain species of microorganism according to strain, growth medium and stage of the culture. Therefore, different doses are needed for inactivation of various microorganisms. UV doses as D values required for reducing populations of various microbial groups are reported by Koutchma [9] in Table 1. Besides the sensitivity of microorganism its contamination level also affects the decontamination degree. In fact, in our research on decontamination of mold on the yoghurt surface, the population of mold affected the decontamination level of mold. This can be attributed to overlapping of microorganisms which prevents UV light from reaching the population at the lower layer.

In dairy industry, one of the most important problems for dairy industry is biofilm formation which occurs with colonization of microorganisms on the surface. These biofilms block the light transmission, act as a protective barrier for microorganisms against the light and reduce

Physical, compositional and surface properties such as thickness, viscosity, density, optical properties, color differences, dirtiness, roughness etc. can change the process efficiency. UV light has a restricted penetrability. Transparent fluids such as water are effectively disinfected by UV light, whereas opaque fluids such as milk are affected less due to poor penetration depth of light, and microorganisms cannot be affected directly [11, 12]. The composition of target is also important for the efficacy of UV light. Dissolved solids, suspended particles, organic solutes, macromolecules especially proteins and fat globules in food have shadowing effect on target microorganisms and limit the penetration and efficacy of light [11–13] Treatment efficacy also depends on the characteristics of surface exposed to light and application to

The D value is a measure of the resistance of a microorganism. It is given as the dose needed for an exponential decay of

Choosing the right UV source can increase the efficiency of microbial inactivation by increasing UV light penetration. The first and natural source of UV light is the Sun. The Sun emits radiation across a wide range of wavelengths. Other UV light sources are lamps. Many alternative UV light sources have been developed, such as low pressure mercury (LPM), medium pressure mercury (MPM), low pressure high output mercury lamp-amalgam type, mercury free amalgam lamps, pulsed-light (PL) and excimer lamps. LPM lamps are commonly used in food applications [14].

Mercury lamps have been the sources of radiation in most UV-based disinfection systems. The low and medium pressure mercury UV lamp sources are reliable sources for disinfection applications which are beneficial for their performance, and low cost. They are based on the vapor pressure of mercury while the lamps are operating. LPM lamps are designed to deliver a continuous monochromatic light at 254 nm. MPM lamps emit germicidal polychromatic light between 200 and 300 nm [9]. A breakthrough for economic UVC generation is the discovery of low pressure amalgam lamps [15]. This technology has recently been developed and incorporated into disinfection applications. The mercury emissions from lamps to the environment have encouraged the investigation of mercury-free lamps [9]. Xenon lamps are used in the Pulsed light UV technology. These lamps emit flashes in a short period of time. They have a broad spectrum of radiation between 180 and 1100 nm. Another UV light source is excimer lamps, which can emit pulsed light at 248 nm. It is possible to emit light in desired wavelength by using various gases such as He, Ne, Ar, Kr, Xe in the excimer lamps. The excimer lamps can be operated even at very low surface temperatures [7].

#### 2.4. UV light devices

UV light applications are carried out with different equipment for solids or liquids: UV reactor designs for liquids according to flow types and UV cabinet designs for solids. It is necessary to increase the absorbed energy to the maximum level by developing the design of UV light device with appropriate lamp and size in order to achieve the desired effect.

#### 2.4.1. Reactors

Reactors are devices used for UV light application to liquids. UV reactor contains UV lamps inside. Each UV lamp is in a separate protective quartz tube to prevent the direct contact with liquid. The liquid flowing through the UV reactor is exposed to UV rays emitted from lamps. Thus, the microorganisms in the liquid become ineffective. In the selection of UV reactors, the physical, chemical and microbiological properties of the liquid to be disinfected and the amount of the liquid passing through are the most important parameters. In this context, the UV light dose should be determined according to the nature of the fluid and the target microorganism. In addition, to increase the efficiency of disinfection, parameters such as sediment and turbidity in liquid should be removed with sensitive filters.

2.4.3. Pulsed UV light

Pulsed UV light is a modified and improved version of the UV-C light. Pulsed UV light is an application using devices containing ultraviolet lamps that emit ultraviolet light at high power at regular intervals. It is applied in a very short time (1 μs–0.1 s) in the range of 200–1100 nm [7]. In this technology, combined effect of photochemical, photothermal and photophysical

Ultraviolet Light Applications in Dairy Processing http://dx.doi.org/10.5772/intechopen.74291 9

Clean and fresh air is necessary for food processing area. UV technology can be used for preventing the spread of airborne diseases by inhibition of airborne pathogenic microorganisms in the field of production, packaging, cooling, storage and ripening. For this purpose, low pressure mercury vapor lamps are successfully used as UV light sources. The efficiency of this

UV-C light has been used to disinfect water for several years and has become a successful process that eliminates several types of microorganisms. UV-C technology is a good alternative to chlorine disinfection. In dairy industry, it is possible to use the UV systems for the disinfec-

In food industry, the use of UV light for decontamination of packaging material is becoming widespread. The number of microorganisms on the surfaces of packaging materials such as boxes, cartons, foils, films, wrappings, containers, bottles, caps, closures and lids can be reduced or eliminated by applying the appropriate UV light doses. The packages can be treated with UV light before filling or closing the lid or the packaged food can be exposed to UV-C light. The effectiveness of UV treatment is better on smooth surfaces. On the other hand,

Plastic materials such as polyethylene terephthalate (PET), polyvinylchloride (PVC), polypropylene (PP) and polyethylene (PE) are increasingly being used as packaging materials for dairy products. These materials have many advantages such as availability, low cost, transparency, thermal adhesiveness and being a good barrier against oxygen, carbon dioxide, anhydrite and aromatic compounds [21]. Due to different constructions, thicknesses and various properties of these packages, their UV-C permeability is different. When the packaged food is UV treated, this permeability becomes more important. The UV permeability of PP/PP (50 μm), bone

the UV light cannot reach every spot because of shadowing on irregular surfaces.

conditions occurs and microorganisms become ineffective [20].

3. The applications of UV light in dairy industry

process depends on the volume of the area and the power of the UV lamp.

3.1. Disinfection of air in the production area

3.2. Disinfection of water used during processing

3.3.1. Packaging materials

tion of drinking water, process water, waste water and brine.

3.3. Surface applications of packaging materials and equipment

The flow pattern of liquid in the UV reactor has also significant effect on total UV dose due to the differences in the position and residence times of the microorganisms in certain regions of the irradiated field [9]. The inactivation of microorganisms increases using turbulent flow in continuous flow UV reactors [16, 17].

The first reactor design is a thin film UV reactor. Thin-film reactors are characterized by laminar flow with a parabolic velocity profile [16]. Another reactor having laminar flow is laminar Taylor-Couette UV reactor. In both reactors, the two cylinders in the system are intertwined. While the system is running, the gap between the cylinders is filled with liquid product. In the thin film reactor, the UV lamps are placed in the inner cylinder, whereas in laminar Taylor-Couette UV reactor the lamps are placed on the outer cylinder and the inner cylinder turns around by creating whirlpools [18, 19]. The second design approach is turbulent flow reactors. They increase the turbulence within the reactor in order to make the liquid close to UV light source. In another approach, the UV reactor called Dean flow reactor includes a coiled Teflon tube with UV lamps and reflectors placed both inside and outside the tube, which are used to promote additional turbulence and to create a secondary swirling flow, also known as "Dean effect" [9].

#### 2.4.2. UV cabinets and tunnels

UV cabinets are devices developed for UV light applications on the surface of solids. The number and position of lamps in the UV cabinet are the most critical factors for the disinfection of entire food surfaces. The UV processing units for solid food was well schematized by Manzocco and Nicoli [11]. If one side of the solid food is exposed to UV light, the food is placed on a support. For the exposure to the top and bottom sides, the food can be placed on a film or turned upside down during treatment. If all the surfaces of the solid food are exposed to the UV light at the same time, it is needed to increase the number of lamps and place the food on a film. For example, in dairy industry, only upper surface of the yoghurt in package is enough to be treated by UV light while all surfaces are exposed for many cheeses. If there is no food support, the product flows near the lamps coated with waterproof quartz tubes in a vessel containing water.

It is also possible to design a tunnel with a dynamic system moving with the food. In this type of cabinet system or tunnel, the food material is conveyed through UV tunnel and taken from the other end. The width and height of the tunnel are designed according to expectations of user. UV application time is adjusted by conveyor speed. Such tunnels provide convenience for industrial use. They are added to the desired point of production line and their use in the system is practical.

#### 2.4.3. Pulsed UV light

Thus, the microorganisms in the liquid become ineffective. In the selection of UV reactors, the physical, chemical and microbiological properties of the liquid to be disinfected and the amount of the liquid passing through are the most important parameters. In this context, the UV light dose should be determined according to the nature of the fluid and the target microorganism. In addition, to increase the efficiency of disinfection, parameters such as

The flow pattern of liquid in the UV reactor has also significant effect on total UV dose due to the differences in the position and residence times of the microorganisms in certain regions of the irradiated field [9]. The inactivation of microorganisms increases using turbulent flow in

The first reactor design is a thin film UV reactor. Thin-film reactors are characterized by laminar flow with a parabolic velocity profile [16]. Another reactor having laminar flow is laminar Taylor-Couette UV reactor. In both reactors, the two cylinders in the system are intertwined. While the system is running, the gap between the cylinders is filled with liquid product. In the thin film reactor, the UV lamps are placed in the inner cylinder, whereas in laminar Taylor-Couette UV reactor the lamps are placed on the outer cylinder and the inner cylinder turns around by creating whirlpools [18, 19]. The second design approach is turbulent flow reactors. They increase the turbulence within the reactor in order to make the liquid close to UV light source. In another approach, the UV reactor called Dean flow reactor includes a coiled Teflon tube with UV lamps and reflectors placed both inside and outside the tube, which are used to promote additional turbulence and to create a secondary swirling flow, also

UV cabinets are devices developed for UV light applications on the surface of solids. The number and position of lamps in the UV cabinet are the most critical factors for the disinfection of entire food surfaces. The UV processing units for solid food was well schematized by Manzocco and Nicoli [11]. If one side of the solid food is exposed to UV light, the food is placed on a support. For the exposure to the top and bottom sides, the food can be placed on a film or turned upside down during treatment. If all the surfaces of the solid food are exposed to the UV light at the same time, it is needed to increase the number of lamps and place the food on a film. For example, in dairy industry, only upper surface of the yoghurt in package is enough to be treated by UV light while all surfaces are exposed for many cheeses. If there is no food support, the product flows near the lamps coated with waterproof quartz tubes in a

It is also possible to design a tunnel with a dynamic system moving with the food. In this type of cabinet system or tunnel, the food material is conveyed through UV tunnel and taken from the other end. The width and height of the tunnel are designed according to expectations of user. UV application time is adjusted by conveyor speed. Such tunnels provide convenience for industrial use. They are added to the desired point of production line and their use in the

sediment and turbidity in liquid should be removed with sensitive filters.

continuous flow UV reactors [16, 17].

8 Technological Approaches for Novel Applications in Dairy Processing

known as "Dean effect" [9].

2.4.2. UV cabinets and tunnels

vessel containing water.

system is practical.

Pulsed UV light is a modified and improved version of the UV-C light. Pulsed UV light is an application using devices containing ultraviolet lamps that emit ultraviolet light at high power at regular intervals. It is applied in a very short time (1 μs–0.1 s) in the range of 200–1100 nm [7]. In this technology, combined effect of photochemical, photothermal and photophysical conditions occurs and microorganisms become ineffective [20].
