4. Efficacy of UV light on dairy products

#### 4.1. Liquid dairy products

Raw milk from healthy cows contains relatively few bacteria, but can be contaminated easily during handling and/or storage from a variety of sources (persons, containers, machines, pipelines etc.). Milk is also suitable for the growth of many pathogenic microorganisms carrying potential risk of transferring diseases from animals to humans. The storage conditions of milk before further processing influence the microbial population. To limit the bacterial population in the raw milk, applying effective cooling and good hygiene practices are essential. Heat application is traditionally used to kill the pathogenic bacteria and reduce the others, and extend the shelf life of milk. The success and convenience of heat treatment is proved for milk. Thus, the alternative technologies to heat treatment cannot be integrated into dairy industry easily despite studies in this field.

In literature, the results of the application of UV light technology as an alternative to thermal processing are contradictory. Some authors reported that UV light can be used effectively for the reduction of certain bacterial pathogens in milk. Cilliers et al. [22] showed the similar level of microbial efficacy obtained in milk processed with pasteurization (high temperature short time), UV light and their combination. Similarly, Crook et al. [23] investigated the effect of UV-C light on the inactivation of seven milkborne pathogens such as Listeria monocytogenes, Serratia marcescens, Salmonella senftenberg, Yersinia enterocolitica, Aeromonas hydrophila, Escherichia coli and Staphylococcus aureus. Of the seven milkborne pathogens tested, L. monocytogenes was the most UV resistant, requiring 2000 J/L of UV-C exposure to reach a 5-log reduction, and the most sensitive bacteria was S. aureus, requiring only 1450 J/L to reach a 5-log reduction. Matak et al. [24] reported that UV-C treatment could be used for the reduction of L. monocytogenes in goat's milk and application of a cumulative UV dose of 15.8 1.6 mJ/cm2 to goat milk led to more than

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, 2.38 and 2.95 log respectively [28].

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

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 reactor by Singh and Ghaly [36].

Table 2 summarizes the microbial inactivation and technical characteristics of UV light system used for milk that were reported in the studies cited above.

#### 4.2. Surface applications of dairy products

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

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

Raw milk from healthy cows contains relatively few bacteria, but can be contaminated easily during handling and/or storage from a variety of sources (persons, containers, machines, pipelines etc.). Milk is also suitable for the growth of many pathogenic microorganisms carrying potential risk of transferring diseases from animals to humans. The storage conditions of milk before further processing influence the microbial population. To limit the bacterial population in the raw milk, applying effective cooling and good hygiene practices are essential. Heat application is traditionally used to kill the pathogenic bacteria and reduce the others, and extend the shelf life of milk. The success and convenience of heat treatment is proved for milk. Thus, the alternative technologies to heat treatment cannot be integrated into dairy industry

In literature, the results of the application of UV light technology as an alternative to thermal processing are contradictory. Some authors reported that UV light can be used effectively for the reduction of certain bacterial pathogens in milk. Cilliers et al. [22] showed the similar level of microbial efficacy obtained in milk processed with pasteurization (high temperature short time), UV light and their combination. Similarly, Crook et al. [23] investigated the effect of UV-C light on the inactivation of seven milkborne pathogens such as Listeria monocytogenes, Serratia marcescens, Salmonella senftenberg, Yersinia enterocolitica, Aeromonas hydrophila, Escherichia coli and Staphylococcus aureus. Of the seven milkborne pathogens tested, L. monocytogenes was the most UV resistant, requiring 2000 J/L of UV-C exposure to reach a 5-log reduction, and the most sensitive bacteria was S. aureus, requiring only 1450 J/L to reach a 5-log reduction. Matak et al. [24] reported that UV-C treatment could be used for the reduction of L. monocytogenes in goat's milk and application of a cumulative UV dose of 15.8 1.6 mJ/cm2 to goat milk led to more than

polypropylene/cast polypropylene (OPP/CPP).

10 Technological Approaches for Novel Applications in Dairy Processing

after cleaning processes of the dairy equipment.

4. Efficacy of UV light on dairy products

3.3.2. Food contact surfaces

4.1. Liquid dairy products

easily despite studies in this field.

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


and cause undesirable changes that may reduce shelf life of the product. To prolong shelf life and reduce microbial growth and oxidative degradation of dairy products, some types of preservatives are used according to legislation limits. However, a negative public reaction is growing over the addition of chemical preservatives to foods. Although UV light application is limited for liquid dairy products because of the confirmed success of heat treatment, it is very

Type of UV reactor UV treatment Test microorganisms Results/achieved inactivation Studies

Mycobacterium avium

Mycobacterium avium

paratuberculosis

Listeria innocua Mycobacterium smegmatis, Salmonella serovar typhimurium E. coli S. aureus Streptococcus agalactiae Acinetobacter baumannii

Not an alternative to current

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

Not an alternative to current

sterilization of whey if the proper reactor gap size and the appropriate residence

Significant reduction for all bacterial species tested except [33]

13

[34]

[35]

[37]

pasteurization

pasteurization

time are used

M. smegmatis.

Total viable count May be used on-line

subsp. paratuberculosis

ssp.

Light exposure of solid foods affects only a thin surface layer of the product, while a minimum light dose can reach its internal part [11]. Due to low penetration depth, UV light is suitable for inactivation of surface microorganisms to ensure product safety and extend shelf life with minor effects on chemical and nutritional values in dairy products. However, limited data are available on the effects of UV light on the surface decontamination, quality and organoleptic

In the surface applications of UV light, all targeted surfaces of the food must be exposed to UV light. For this purpose, flat products can be turned to allow exposure of both sides or placed on a supporting net or a film. Additional lamps can also be placed on the product sides [11].

One of the most common problems in cheese technology is molding on the surface. Application of UV light on cheese surface just before packaging can be a good solution to prevent mold growth. Lacivita et al. [38] reported 1–2 log reduction on Pseudomonas spp. and Enterobacteriaceae by applying UV light on the surface of cheese without changes in color, texture and surface

promising for the surface applications of dairy products instead of using chemicals.

properties of dairy products.

Whole and semiskim milk

Cheese whey

Sterile whole milk

Laboratory-scale Dose: 1000 mJ/ml

UHT milk Pilot-scale Doses: 0–1836 mJ/

Pilot-scale UV light continuous flowthrough unit

min

ml

Tubular-type Gap sizes: 18, 13,

Table 2. Efficacy of UV light application for liquid dairy products.

Flow rate: 168 ml/

Flow rate: 4000 l/h 30 W UV C output

and 6 mm

Dose: 45 J/cm<sup>2</sup> Flow rate: 65 l/min


Table 2. Efficacy of UV light application for liquid dairy products.

Type of UV reactor UV treatment Test microorganisms Results/achieved inactivation Studies

Similar level of microbial efficacy with high temperature short time heat treatment

Potential as a non-thermal method to reduce microorganisms

L. monocytogenes in goat's milk

inactivation of Staphylococcus

Higher resistance of B. cereus endospores to UV than E. coli

Higher inactivation efficiencies of both bacteria in skimmed milk than full fat raw milk

and lower reactivation ratio at 254 nm than 222 and 282 nm

Suggested for reducing of bacteria not susceptible to thermal treatment and psychrotrophic in refrigerated milk stored for prolonged

Lower counts in UV-treated

aureus in milk

W1485 cells,

E. coli O157:H7 Higher inactivation efficiency

periods

milk

Total viable count 2.3 log reduction [31]

A major effect on total coliforms, E. coli and Staphylococcus spp.

Listeria monocytogenes Suggested for the reduction of

Staphylococcus aureus A potential method for

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

Coliform bacteria

Aerobic mesophilic

Listeria monocytogenes Serratia marcescens Salmonella senftenberg Yersinia enterocolitica Aeromonas hydrophila

Mesophilic aerobics Coliform bacteria

Staphylococcus spp. Yeasts/Molds

Escherichia coli W1485, Bacillus cereus endospores

Total viable count, Psychrotrophics Coliform bacteria Thermodurics

Aerobic plate count

Aerobic sporeformers Coliform bacteria

E. coli

Dose: 430 mJ/cm<sup>2</sup> Aerobic plate count

E. coli

spores Anaerobic mesophilic spores Aerobic thermophilic

spores Anaerobic thermophilic spores

Dose: 0–5000 J/L Flow rate: 4300 L/h

13.87 J/mL (per single pass) Flow rate: 1090 mL/min

Flow rates: 20, 30, 40 ml/min Polychromatic 100–1100 nm

Doses: 0–20 mJ/cm2

mJ/cm2 Intensity: 1.375 mW/cm2

5–20 mJ/cm2 Wavelength: 222, 254, 282 nm

0.93, 1.9, 3.7, 7.4 and 1.5 kJ/L Flow rate: 1.1 L/s

Doses: 880 and 1760 J/L

Dose: 16.822 mJ/

cm2 Intensity: 1.375 mW/cm2

Bovine milk-full cream

Surepure40 turbulent flow commercial system

12 Technological Approaches for Novel Applications in Dairy Processing

Milk Thin-film turbulent

system

Goat milk CiderSure 3500 apparatus

Raw milk Pulsed light

Bovine milk

Full fat raw milk and skimmed milk

Bovine milk

Raw cow milk

Cow's Milk

Raw cow milk

flow-through pilot

sterilization system

Custom-made Intensity:

Coiled tube Dose: 11.187

— Dose:

Continuous turbulent flow

Continuous flow coiled tube

Pure UV system Doses: 0.23, 0.46,

and cause undesirable changes that may reduce shelf life of the product. To prolong shelf life and reduce microbial growth and oxidative degradation of dairy products, some types of preservatives are used according to legislation limits. However, a negative public reaction is growing over the addition of chemical preservatives to foods. Although UV light application is limited for liquid dairy products because of the confirmed success of heat treatment, it is very promising for the surface applications of dairy products instead of using chemicals.

Light exposure of solid foods affects only a thin surface layer of the product, while a minimum light dose can reach its internal part [11]. Due to low penetration depth, UV light is suitable for inactivation of surface microorganisms to ensure product safety and extend shelf life with minor effects on chemical and nutritional values in dairy products. However, limited data are available on the effects of UV light on the surface decontamination, quality and organoleptic properties of dairy products.

In the surface applications of UV light, all targeted surfaces of the food must be exposed to UV light. For this purpose, flat products can be turned to allow exposure of both sides or placed on a supporting net or a film. Additional lamps can also be placed on the product sides [11].

One of the most common problems in cheese technology is molding on the surface. Application of UV light on cheese surface just before packaging can be a good solution to prevent mold growth. Lacivita et al. [38] reported 1–2 log reduction on Pseudomonas spp. and Enterobacteriaceae by applying UV light on the surface of cheese without changes in color, texture and surface appearance. Authors concluded that this treatment showed an interesting surface microbial decontamination and prolonged cheese shelf-life with minimum transmittance inside the product. Similarly, Sık et al. [39] used different UV doses on the surface of Kashar cheese and application of UV-C (≥1.926 kJ/m2 ) was able to achieve approximately 2–3 log reduction in mold population. Can et al. [40] investigated the efficacy of pulsed UV light for inactivation of inoculated Penicillium roqueforti and Listeria monocytogenes of hard cheeses packaged and unpackaged. The reduction of P. roqueforti was 1.32 log and 1.24 log in packaged and unpackaged cheeses, respectively. L. monocytogenes was reduced by over 2.8 log for packaged and unpackaged cheeses. They reported that pulsed UV light has potential to inactivate P. roqueforti and L. monocytogenes on the surface of hard cheeses. Proulx et al. [41] examined the effectiveness of pulsed-light (PL) treatment on the inactivation of the spoilage microorganisms on cheese surface in order to determine the effects of inoculum level and cheese surface topography and the presence of clear polyethylene packaging. Inoculated cheese samples were exposed to PL doses of 1.02–12.29 J/cm2 . Listeria innocua was the least sensitive with a maximum inactivation level of 3.37 log, followed by P. fluorescens with a maximum inactivation of 3.74 log and Escherichia coli ATCC 25922 with a maximum reduction of 5.41 log. The inactivation reached a plateau after three pulses (3.07 J/cm2 ). The authors concluded that PL treatments through UVtransparent packaging and without packaging consistently resulted in similar inactivation levels.

through plastic film packaging and the thickness of packaging film are important parameters for eliminating or controlling growth of foodborne pathogens on the surfaces. Ha et al. [21] applied UV-C light for inactivation of food-borne pathogens on sliced cheese packaged with different types and thicknesses of plastic films. The authors' results showed that adjusted 0.07 mm thick PP or PE film packaging in conjunction with UV-C radiation can be effectively used for controlling

Ultraviolet Light Applications in Dairy Processing http://dx.doi.org/10.5772/intechopen.74291 15

There has been really limited research carried on the surface decontamination of other dairy products with UV-light. Similar to cheese, post-processing contamination of the mold on set type yoghurt shortens its shelf life. That is why, the surface of set-type yoghurt samples contaminated naturally were exposed to UV light at different doses in a batch UV light cabinet to inactivate the mold at Ege University by chapter authors Koca and Saatli [42]. They indicated that UV light can be promising for mold inactivation of surface set-type of yoghurt and that higher doses of UV light increased oxidation levels slightly in yoghurt. Studies about the

Milk is rich in protein, unsaturated fatty acids, metal ions, oxidases and other pro-oxidants that induce oxidative changes for lipids or protein in raw milk [43]. Dairy products are known as light sensitive products and light may decrease the nutritional value, the content of unsaturated fatty acids and vitamins especially riboflavin and α-tocopherol of the product [44, 45]. Figuring out the suitable UV doses which reduce the microbial growth enough without causing any sensorial defects is challenging. Consumer acceptance of UV treated dairy product will ultimately determine the acceptability of UV technology as an alternative

Limited research has been carried out on the effects of UV treatment on a biochemical and chemical perspective of dairy products. Some authors concluded that chemical composition of milk is not significantly affected by UV light application [43, 46]. Similarly, Cilliers et al. [22] concluded that UV light application to bovine milk did not affect most of the macro and micro-components, but reduced the cholesterol level compared to pasteurized milk. UV light application produced no change in raw milk with regard to the composition, free fatty acid profile, oxidation, or protein profile [46]. Another study showed that UV treatment to raw milk increased pH and reduced lightness, but did not change soluble

Lipid oxidation is known to be dependent on light exposure. In general, as the UV light dose increases, the oxidation degree and accordingly off-flavor increase in dairy products. In relation to oxidative changes of milk with UV light, increase in UV dose resulted in an increase in TBARs and acid degree values of the goat milk samples [47]. Similarly, higher values of malondialdehyde and other reactive substances in UV-treated raw cow milk were reported as an indication of oxidative degradation by Bandla et al. [31]. In contrast, Hu et al. [43] found no change in the values of TBARs of UV-C treated raw milk (11.8 W/m<sup>2</sup> dose), but an increase in

foodborne pathogens including E. coli O157:H7, S. Typhimurium, and L. monocytogenes.

surface application of UV light to dairy products are summarized in Table 3.

5. Quality effects of UV light on dairy products

or adjunct to commercial thermal treatment.

solids content [43].

its protein oxidation.

After packaging of cheese, application of UV-C would be a good safety method to inactivate hazardous microorganisms on cheese surfaces. For this application, the transmission of UV light


Table 3. Effects of surface application of UV light on different dairy products.

through plastic film packaging and the thickness of packaging film are important parameters for eliminating or controlling growth of foodborne pathogens on the surfaces. Ha et al. [21] applied UV-C light for inactivation of food-borne pathogens on sliced cheese packaged with different types and thicknesses of plastic films. The authors' results showed that adjusted 0.07 mm thick PP or PE film packaging in conjunction with UV-C radiation can be effectively used for controlling foodborne pathogens including E. coli O157:H7, S. Typhimurium, and L. monocytogenes.

There has been really limited research carried on the surface decontamination of other dairy products with UV-light. Similar to cheese, post-processing contamination of the mold on set type yoghurt shortens its shelf life. That is why, the surface of set-type yoghurt samples contaminated naturally were exposed to UV light at different doses in a batch UV light cabinet to inactivate the mold at Ege University by chapter authors Koca and Saatli [42]. They indicated that UV light can be promising for mold inactivation of surface set-type of yoghurt and that higher doses of UV light increased oxidation levels slightly in yoghurt. Studies about the surface application of UV light to dairy products are summarized in Table 3.
