3. The applications of UV light in dairy industry

#### 3.1. Disinfection of air in the production area

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

#### 3.2. Disinfection of water used during processing

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

#### 3.3. Surface applications of packaging materials and equipment

#### 3.3.1. Packaging materials

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

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 guard bags (BG) (25 μm), polyamide/polyethylene (PA/PP) (40 μm) and oriented polypropylene (OPP) (40 μm) were reported as 64, 67, 8 and 83%, respectively, by Manzocco and Nicoli [11]. However, there was no UV-C permeability of OPP/PE, PET/PE, Polyester and oriented polypropylene/cast polypropylene (OPP/CPP).

5 log reduction in L. monocytogenes. Engin and Karagul Yuceer [25] reported the UV irradiation was as effective against certain microorganisms as heat treatment. The authors applied the UV light as an alternative to heat treatment to bovine milk using a custom-made UV system and the growth of coliform bacteria, E. coli and Staphylococcus spp. was completely reduced by UV treatment. Similar results were found for inactivation of S. aureus in milk using pulsed UV light treatment by Krishnamurthy et al. [26]. It was shown that the pulsed UV light can be used as an alternative method to inactivate S. aureus in milk. Choudhary et al. [27] showed that E. coli W1485 was reduced by 7.8 log in skimmed milk, but 4.1 log in full-fat raw milk with UV light treatment by using coiled tube reactor. They also reported that Bacillus cereus endospores were more resistant than E. coli W1485 and that these endospores were reduced by only 2.72 and 2.65 log in skimmed milk and full fat milk, respectively. In another study, inactivation of E. coli O157: H7 in bovine milk exposed at 254 nm was higher than at 222 and 282 nm at the same UV doses. The reductions in E. coli O157:H7 at 254 nm using the doses of 5, 10 and 20 mJ/cm2 were 1.81,

Ultraviolet Light Applications in Dairy Processing http://dx.doi.org/10.5772/intechopen.74291 11

UV light efficacy on the reduction of total number of microorganisms is also proved in different studies [29–31]. Reinemann et al. [29] reported that UV treatment to raw cow's milk achieved more than 3 log reduction in total numbers of bacteria. The highest reduction was found for coliform bacteria followed by pyschrotrophs, thermodurics and spore formers. Microbial counts of UV treated milk (continuous turbulent flow system, 880 and 1760 J/L doses) were lower compared to those of control milk [30]. UV-C treatment of raw cow milk was capable of reducing total viable count by 2.3 log [31]. UV light treatment in milk can be used as a method to reduce the number of psychrotrophic bacteria to prolong the storage period of cooled raw milk [9, 22, 26, 32]. In contrast, Altic et al. [33] and Donaghy et al. [34] concluded that the UV light technology cannot be an alternative to current pasteurization process for milk. The authors found less than 1 log reduction in Mycobacterium avium ssp. paratuberculosis in milk by UV treatment. In both studies, the use of UV light was not very

UV radiation may be used for an alternative to pasteurization of cheese whey, valuable liquid dairy product, if the lamp fouling problem is solved [35]. In their study, for destruction of microbial population of 5.95 <sup>10</sup><sup>6</sup> cells/ml in cheese whey, more than 3.3, 2.1 and 0.8 h residence times were needed in the first, second and third UV reactors, respectively. However, fouling was seen as a major problem when the temperature of cheese whey increased. As a solution to the fouling problem, coil reactor series were recommended instead of conventional

Table 2 summarizes the microbial inactivation and technical characteristics of UV light system

Surface of dairy products such as cheese, yoghurt, etc. is the primary location for microbial access and quality depletion during processing and storage period. Most of the chemical, oxidative, microbial and enzymatic reactions take place on the surface of the dairy product

effective in reducing the number of Mycobacterium avium ssp. paratuberculosis.

2.38 and 2.95 log respectively [28].

reactor by Singh and Ghaly [36].

4.2. Surface applications of dairy products

used for milk that were reported in the studies cited above.

#### 3.3.2. Food contact surfaces

The cross-contamination of microorganisms from equipment to the products is an important issue in dairy technology. UV light can be used to provide disinfection of surfaces of conveyor and other equipment used in preparation, production and, storage areas. For an effective inhibition, microorganisms must be exposed to UV light directly. There should be no obstruction between the UV source and the surface to be sterilized. The success of this application also depends on the cleanliness of the material surfaces because dirt would absorb the radiation and hence protect the bacteria. Therefore, it is possible to say that UV light must be applied after cleaning processes of the dairy equipment.
