5. Quality effects of UV light on dairy products

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

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

vation 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

transparent packaging and without packaging consistently resulted in similar inactivation levels. 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

Dairy product UV treatment Test microorganisms Results/achieved inactivation Studies

Escherichia coli O157:

Pseudomonas spp., Enterobacteriaceae

Penicillium roqueforti, Listeria monocytogenes

Pseudomonas fluorescens, Escherichia coli ATCC 25922, Listeria innocua

H7, Salmonella Typhimurium, Listeria monocytogenes

) was able to achieve approximately 2–3 log reduction in mold

. Listeria innocua was the least sensitive with a maximum inacti-

). The authors concluded that PL treatments through UV-

Suggested use of PP or PE films in conjunction with UV-C radiation for controlling foodborne pathogens

About 1–2 log reduction without changes in color, texture and surface

of pasta-filata cheese, but off-flavor at

Suggested use of pulsed UV light for inactivation of P. roqueforti and L. monocytogenes on the surface of hard

Suggested application for PL for decontamination of the cheese surface through UV-transparent packaging

of yoghurt, but increased oxidation levels and off-flavor at high doses

and without packaging

appearance

Molds Promising for surface mold reduction

high doses

cheeses

Molds Promising for surface mold reduction

[21]

[38]

[39]

[40]

[41]

[42]

application of UV-C (≥1.926 kJ/m2

14 Technological Approaches for Novel Applications in Dairy Processing

to PL doses of 1.02–12.29 J/cm2

Sliced cheddar cheese

Fiordilatte cheese

White American cheese

Cheddar, process cheese

Set-type yoghurt

plateau after three pulses (3.07 J/cm2

5 UV-C lamps Intensity: 3.04 mW/cm<sup>2</sup> Treatment time: 1 min

Intensity: 20 W/m2 Treatment time: up to

Treatment time: up to

Pulsed Light Sterilization

Distances: 5, 8, and 13 cm Treatment time: up to 60 s

Bench top pulsed light unit

1.02 to 12.29 J/cm2

Batch UV light cabinet Intensity: 32.1 W/m2 Treatment time: up to

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

750 s

Kashar cheese Intensity: 32.1 W/m2

300 s

System

Doses:

600 s

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 or adjunct to commercial thermal treatment.

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 solids content [43].

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 its protein oxidation.

The nutritional value and sensory attributes of dairy products may change with the light exposure depending on the oxidation of lipids and protein and light sensitivity. Jung et al. [48] reported 'sunlight' flavor, which is characterized by a burnt and oxidized odor in milk after 2 or 3 days of UV application. Oxidized flavor in milk perceived as off-flavor results from oxidation of unsaturated fatty acid residues in milk lipids and phospholipids. The photodegradation of proteins also results in off-flavors and organoleptic changes in milk [14].

treated milk due to the effects of UV light on the molecular properties of proteins in milk sample. It is noted that UV treatment to raw milk limits the inactivation of native enzymes and the denaturation of whey proteins and the defects in products related to high initial bacterial counts, and shortens the ripening period of cheese. In contrast, Cilliers et al. [22] found no significant differences in the enzyme activity, α-amino acid contents and protein profiles of UV

Ultraviolet Light Applications in Dairy Processing http://dx.doi.org/10.5772/intechopen.74291 17

There are few data on the quality changes for surface application of UV light on dairy products such as cheese and yoghurt. Cheese treated with pulsed light at moderate (30 s at 8 cm) and extreme (40 s at 5 cm) conditions had higher values of TBARs compared to mild (5 s at 13 cm) treated and untreated samples, and the changes in color and chemical quality of cheeses were not significantly different after mild treatments. Additionally, when compared with packaged samples, unpackaged samples had slightly higher malondialdehyde values [40]. The application of UV light to surface of Kashar cheese slightly increased redness and yellowness values as the dosage of UV light increased, but these slight changes were not perceptible by the panelists [39]. However, they found that exposure of higher doses (9.630

) of UV-C light led to photo-oxidation and accordingly caused flavor defects. In the other study, UV light application in batch UV cabinet to set-type yoghurt surface did not cause any significant changes with respect to hardness and color parameters [42]. On the other hand, the off-flavor was detected by panelists for the yoghurt samples treated at high

6. Legislations on UV light application in the production, processing and

The Food and Drug Administration, Department of Health and Human Services (US FDA) approved the use of UV radiation for controlling surface microorganisms of food or food product, sterilization of water used in production and reduction of human pathogens and other microorganisms in juice products under specific conditions defined by Code 21CFR179.39 [54]. These conditions are limited to the use of low pressure mercury lamps emitting 90% of the emission at a wavelength of 253.7 nm. If the pulsed UV is considered, in code 21CFR179.41, US FDA [55] approves the use of pulsed UV light for the surface microorganism control at doses not exceeding 12 J/cm<sup>2</sup> using xenon flashlamps, which are designed to emit broadband radiation consisting of wavelengths covering the range of 200–1100 nm, and operated no longer than 2 milliseconds for pulse duration. In addition, the minimum treatment

In European Union, UV light is accepted as irradiation [14]. The use of irradiation is limited but authorized in many European countries. According to European Commission, treating food with ionizing radiation may be authorized if there is reasonable technological need, it poses no health hazard and benefits consumers, and if it does not replace hygiene, health or good manufacturing or agricultural practice. Irradiated food or ingredients must be labeled. The UV-treated of pasteurized cow's milk was authorized as novel food in market by EC

required to obtain intended technical effect is used for food.

treated and pasteurized milk.

kJ/m<sup>2</sup>

dosages of UV light.

handling of food

UV-C treatment has the potential to accelerate the formation of the volatile compounds in milk. In fact, Hu et al. [49] found an increase in the variety and content of volatile compounds of cow milk by the application of UV light (at 254 nm, 11.8 W/m2 ). Nevertheless, no major differences were observed in terms of aroma-active compounds of milk following the UV treatment, but some new volatiles were generated [25]. In another study, no difference was found between the odor of untreated and UV treated cow milk but after 1 day of storage the UV-C treated sample had a significantly different smell from that of untreated milk [31]. The flavor defects in cow milk were clearly differentiated by panelists [30]. Cilliers et al. [22] noted the 'tallowy' flavor descriptor for the UV treated milk. In another study, odor of UV treated milk was described by panelists as manure, stinky, barnyard, and goaty [47].

Vitamin A, carotenes, vitamin B12, vitamin D, folic acid, vitamin K, riboflavin (vitamin B2) tocopherols (vitamin E), tryptophan, and unsaturated fatty acid residues in oils, solid fats, and phospholipids are well known as light sensitive nutrients [50]. The first research was carried out the increase in Vitamin D in milk. European Food Safety Authority (EFSA) concluded that the treatment of the pasteurized milk with UV radiation results in an increase in Vitamin D. The effects of UV light on vitamins A, B2, C, and E in cow and goat milk were assessed by Guneser and Karagul Yüceer [51]. UV light sensitivities of vitamins for the milk samples were found as C > E > A > B2. Authors concluded that UV light application reduces the vitamin content and their reduction levels depend on the initial amount of vitamins and the number of passes through the system. In contrast to most research, Cappozzo et al. [46] found that UV light, HTST and UHT processing of raw milk caused to decrease in vitamin D content to undetectable levels. UV light treatment reduced the content of vitamin A from 24.5 at 1045 J/L to 14.9% at 2090 J/L, but HTST and UHT processes resulted in a large reduction (96.8 and 100%, respectively). In bovine milk, vitamin B12 and riboflavin were not reduced by UV application in contrast to thermal treatment [22].

Protein oxidation in dairy systems has an important effect on protein properties and functionalities. UV light can cause the degradation or modification of proteins that lead to changes in solubility, sensitivity to heat, mechanical properties, and digestion by proteases [14]. In fact, Semagoto et al. [52] found changes in the solubility and color of milk protein concentrate. UV induced photo-oxidation decreased the solubility and contributed to the discoloration of milk protein concentrate during storage. Furthermore, exposure to UV irradiation resulted in denaturation of whey proteins but this denaturation degree is low when compared to UHT or HTST [53].

Application of UV light to raw milk used in the production of dairy products may also influence the quality of product. Some changes in rheological properties of yoghurt from UV treated milk were generated by UV treatment [25]. In this research, higher viscosity and lower syneresis were found in the sample made from UV-treated milk compared to that of heat treated milk due to the effects of UV light on the molecular properties of proteins in milk sample. It is noted that UV treatment to raw milk limits the inactivation of native enzymes and the denaturation of whey proteins and the defects in products related to high initial bacterial counts, and shortens the ripening period of cheese. In contrast, Cilliers et al. [22] found no significant differences in the enzyme activity, α-amino acid contents and protein profiles of UV treated and pasteurized milk.

The nutritional value and sensory attributes of dairy products may change with the light exposure depending on the oxidation of lipids and protein and light sensitivity. Jung et al. [48] reported 'sunlight' flavor, which is characterized by a burnt and oxidized odor in milk after 2 or 3 days of UV application. Oxidized flavor in milk perceived as off-flavor results from oxidation of unsaturated fatty acid residues in milk lipids and phospholipids. The photodegradation of

UV-C treatment has the potential to accelerate the formation of the volatile compounds in milk. In fact, Hu et al. [49] found an increase in the variety and content of volatile compounds of cow

were observed in terms of aroma-active compounds of milk following the UV treatment, but some new volatiles were generated [25]. In another study, no difference was found between the odor of untreated and UV treated cow milk but after 1 day of storage the UV-C treated sample had a significantly different smell from that of untreated milk [31]. The flavor defects in cow milk were clearly differentiated by panelists [30]. Cilliers et al. [22] noted the 'tallowy' flavor descriptor for the UV treated milk. In another study, odor of UV treated milk was described by panelists

Vitamin A, carotenes, vitamin B12, vitamin D, folic acid, vitamin K, riboflavin (vitamin B2) tocopherols (vitamin E), tryptophan, and unsaturated fatty acid residues in oils, solid fats, and phospholipids are well known as light sensitive nutrients [50]. The first research was carried out the increase in Vitamin D in milk. European Food Safety Authority (EFSA) concluded that the treatment of the pasteurized milk with UV radiation results in an increase in Vitamin D. The effects of UV light on vitamins A, B2, C, and E in cow and goat milk were assessed by Guneser and Karagul Yüceer [51]. UV light sensitivities of vitamins for the milk samples were found as C > E > A > B2. Authors concluded that UV light application reduces the vitamin content and their reduction levels depend on the initial amount of vitamins and the number of passes through the system. In contrast to most research, Cappozzo et al. [46] found that UV light, HTST and UHT processing of raw milk caused to decrease in vitamin D content to undetectable levels. UV light treatment reduced the content of vitamin A from 24.5 at 1045 J/L to 14.9% at 2090 J/L, but HTST and UHT processes resulted in a large reduction (96.8 and 100%, respectively). In bovine milk, vitamin B12 and riboflavin were not reduced by UV application

Protein oxidation in dairy systems has an important effect on protein properties and functionalities. UV light can cause the degradation or modification of proteins that lead to changes in solubility, sensitivity to heat, mechanical properties, and digestion by proteases [14]. In fact, Semagoto et al. [52] found changes in the solubility and color of milk protein concentrate. UV induced photo-oxidation decreased the solubility and contributed to the discoloration of milk protein concentrate during storage. Furthermore, exposure to UV irradiation resulted in denaturation of whey proteins but this denaturation degree is low when compared to UHT or HTST [53]. Application of UV light to raw milk used in the production of dairy products may also influence the quality of product. Some changes in rheological properties of yoghurt from UV treated milk were generated by UV treatment [25]. In this research, higher viscosity and lower syneresis were found in the sample made from UV-treated milk compared to that of heat

). Nevertheless, no major differences

proteins also results in off-flavors and organoleptic changes in milk [14].

milk by the application of UV light (at 254 nm, 11.8 W/m2

16 Technological Approaches for Novel Applications in Dairy Processing

as manure, stinky, barnyard, and goaty [47].

in contrast to thermal treatment [22].

There are few data on the quality changes for surface application of UV light on dairy products such as cheese and yoghurt. Cheese treated with pulsed light at moderate (30 s at 8 cm) and extreme (40 s at 5 cm) conditions had higher values of TBARs compared to mild (5 s at 13 cm) treated and untreated samples, and the changes in color and chemical quality of cheeses were not significantly different after mild treatments. Additionally, when compared with packaged samples, unpackaged samples had slightly higher malondialdehyde values [40]. The application of UV light to surface of Kashar cheese slightly increased redness and yellowness values as the dosage of UV light increased, but these slight changes were not perceptible by the panelists [39]. However, they found that exposure of higher doses (9.630 kJ/m<sup>2</sup> ) of UV-C light led to photo-oxidation and accordingly caused flavor defects. In the other study, UV light application in batch UV cabinet to set-type yoghurt surface did not cause any significant changes with respect to hardness and color parameters [42]. On the other hand, the off-flavor was detected by panelists for the yoghurt samples treated at high dosages of UV light.
