The aim of this work was to investigate the effect of the UV-C radiation on grape juice turbidity, sensoric properties and microbial count.

Ultraviolet C (UV-C) irradiation is one of the emerging techniques for the inactivation of microorganisms in liquid food products, and it holds considerable promise also for treatment of wine. This application can be of particular interest to reduce or even eliminate the use of sulphur dioxide as a preservative in winemaking, given its potential health risks (Rizzotti et al., 2011).

Ultraviolet radiation involves the use of radiation from the electromagnetic spectrum from 100 to 400 nm and is categorized as UV-A (320 – 400 nm), UV-B (280 – 320 nm) and UV-C (200 – 280 nm) (Guerrero-Beltrán and Barbosa-Cánovas, 2004).

UV-C radiation is considered to be germicidal against microorganisms such as bacteria, viruses, protozoa, yeasts, moulds and algae, where the highest germicidal effect is obtained between 250 and 270 nm (Bintsis, Litopoulou- Tzanetaki, and Robinson, 2000).

Microbial inactivation caused by UV-C (254 nm) radiation is based on the rearrangement of the microorganism’s nucleic acid which directly interferes with the ability of microorganisms to reproduce (Bintsis et al., 2000; Thompson, 2003; Tran and Farid, 2004; Gabriel and Nakano, 2009).

The UV-C rays damage the structure of DNA, rendering microorganisms incapable of reproduction. Each type of microorganism requires a specific dose for destruction. In general, bacteria die at doses greater than 20 mj/cm², while molds can tolerate up to 300 mj/cm². Germicidal ultraviolet lamps gradually loose power with use. In order to stabilize the quantity of rays emitted in terms of time- surface units, the input power is increased as a function of the length of time in use (around a total of 10,000 hours) (Delfini and Formica, 2001).

Cleaning and disinfection are important operations in food processing because of the significant contributions to product hygiene and food safety. The UV-C treatment is a physical method, which can be applied for this purpose (Otto et al., 2011).

Ultraviolet rays fall perpendicular to the surface being irradiated but can not pass through any type of material, including glass. The surfaces to be treated must be smooth to avoid casting shadows in which microorganisms could be protected. In oenology UVC irradiation could be used to keep the mouth of bottles clean during transport from the sterilizer to the bottling line, and to the corker. UV irradiation could provide partial sanitation of metallic capsules of corks, as well the air around the bottler and corker (Delfini and Formica, 2001).

UV-C radiation has offered a wide spectrum of effective inactivation of wine-associated microorganisms such as Brettanomyces, Saccharomyces, Acetobacter, Lactobacillus, Pediococcus and Oenococcus and therefore may hold promise as an alternative technology to inactivate spoilage microorganisms at different stages of ^{vinification in conjunction with reduced SO}2 ^{levels. From} practical point of view, further studies pertaining to the long and short term effect of UV-C radiation on the sensorial and chemical properties of wine are imperative (Fredericks, du Toit and Krügel, 2011).

The application of the UV-C treatment to different grape juice and wine samples in five diverse wineries assured the desired decrease of viable microorganisms (Lorenzini et al., 2010).

Microbial reduction is in correlation with the UV-C dosage (J L^-1): higher microbial reductions were obtained with exposure to higher UV-C dosages (J L^-1). As a result, the highest microbial reduction was obtained after 3672 J L^-1 (Fredericks, du Toit and Krügel, 2011).

Ultraviolet treatment is performed at low temperatures and is classified as a non-thermal disinfection method (Tran and Farid, 2004).

The penetration effect of UV-C radiation depends on the type of liquid, its UV-C absorptivity, soluble solids and suspended matter in the liquid. The greater the amount of soluble solids, the lower the intensity of penetration of the UV-C light in the liquid (Guerrero-Beltrán & Barbosa- Cánovas, 2005).

The UV-C treatment did not to alter the color and chemical parameters of grape juice and wine, even in the case of prolonged treatments (Lorenzini et al., 2010).

The advantages associated with UV-C radiation used as a non-thermal method is that no known toxic or significant nontoxic byproducts are formed during the treatment, certain organic contaminants can be removed, no off taste or odor is formed when treating water, and the treatment requires very little energy when compared to thermal pasteurization processes. Fruit juice that undergo thermal pasteurization or sterilization tend to change color and lose some of its aromas and vitamins during the process of heating (Choi and Nielsen, 2005).

The usage of UV-C treatment needs aware staff and requires clean equipments and facilities to keep must and wine stable during storage in barrels and in bottles. Indeed, after the treatment, the samples could be newly contaminated by spoilage microorganisms in poorly sanitized containers. The promising results reported here demonstrated that physical methods, such as UV-C, an incoming technology already commercially available, could exert a highly positive impact in the winemaking ^{industry by eliminating or reducing the use of SO}2 ^{in the} near future (Lorenzini et al., 2010).

Unluturk and Atilgan (2015) were investigated the effects of UV-C irradiation on the inactivation of Escherichia coli and on the shelf life of freshly squeezed turbid white grape juice. UV exposure was not found to alter pH, total soluble solid, and titratable acidity of juice. There was a significant effect on turbidity, absorbance coefficient, color, and ascorbic acid content. The microbial shelf life was doubled after UV-C treatment, whereas the quality of juice was adversely affected similarly observed in the control samples.

The effect of the UV-C radiation treatment on the grape juice microbial counts is presented in the Table 1 and Figure 2. The effect of UV-C radiation treatment on the grape juice turbidity is presented in the Table 2 and Figure 3. The effect of UV-C radiation treatment on the grape juice sensory properties is presented in Table 3, Table 4, Figure 4 and Figure 5.

The effect of UV-C radiation (254 nm) was studied to reduce the microbial count in different grape juices with or ^{without addition of SO}2^{. UV-C radiation is considered to} be germicidal against microorganisms such as bacteria (Bintsis, Litopoulou-Tzanetaki, and Robinson, 2000). We agree, the application of UV-C radiation reduced the microbial count in grape juices (Table 1). In grape juice A, an aplicaiton of 0.68 kJ L^-1 UV-C reduced the log of microbial count from initial log 7.37 to log 4.53, dose 6.83 kJ L^-1 to log 3.86 and dose 13.67 kJ L^-1 to log 2.83. In grape juice B, an aplicaiton of 0.68 kJ L^-1 UV-C reduced the log of microbial count from initial log 7.21 to log 3.93, dose 6.83 kJ L^-1 to log 3.55 and dose 13.67 kJ L^-1 to log 1.33. In grape juice C, an aplicaiton of 0.68 kJ L^-1 UV-C reduced the log of microbial count from initial log 7.47 to log 6.53, dose 6.83 kJ L^-1 to log 6.00 and dose 13.67 kJ L^-1 to log 4.13. The reduction of log microbial counts with ^{addition of SO}2 ^{was more effective (}Figure 2^{). The} microbial counts in grape juice D was reduced to log 0, because this grape juice was sampled 96 hours after ^{sedimentation and was effectively treated with SO}2^. Application of UV-C treatment in order to reduce microorganism counts in clarified grape juices in small demijohns, which are used by small producers is questionable according to our research. Some microbial counts can survive the treatment. The growth and spoiling capacity of the surviving microbes should be investigated in further research.

Lorenzini et al., (2010) found more effective method of treatment. These authors used reactor with 40 UV-C (254 nm) germicidal lamps in series, and exploits an advanced turbulent flow system to optimize the penetration of UV-C and improve microbial inactivation. In their study, grape juice and wine batches were circulated at a constant flow rate of 4000 L.h^-1 by means of an eccentric screw pump and the dosage was 1000 J L^-1. Also, the fluid systems described in (Fredericks, du Toit and Krügel, 2011) was effective. Rizzotti et al., 2015 was applied UV-C light treatment to ten different white and red wines during winemaking, for the first time at industrial scale, using a commercial turbulent flow system. The effect of 1.0 kJ L^-1

dosage treatment on the viability of the natural microbial population, (total yeasts, lactic acid bacteria and acetic acid bacteria), was investigated. Data indicated that the UV-C irradiation was effective in reducing microbial counts for up to five log CFU mL^-1, depending on the wine.

The main aim of our study was to determine whether the UV-C radiation (254 nm) affects the sensory properties of grape juices.

According to Fredericks, du Toit and Krügel (2011) further studies pertaining to the long and short term effect of UV-C radiation on the sensorial and chemical properties of wine are imperative.

Lorenzini et al., (2010) were investigated the effect of UV-C treatment on chemical composition of grape juice and wine. Authors of this study found, UV-C treatment did not to alter the color and chemical parameters of grape juice and wine, even in the case of prolonged treatments. ^{In contrast to our study, these authors didn't use the SO}2 for grape juice treatment. Authors reported, after UV-C irradiation no changes were observed for alcohol, reducing sugars, glycerine content, total acidity, pH and color in all the samples, including the red wines, which were subjected to higher UV-C dosage. These authors didn't study the sensory properties of treated grape juice.

In our study, we have used lower doses (0.68 kJ L^-1 and 1.37 kJ L^-1) and higher doses (6.83 kJ L^-1 and 13.67 kJ L^-1) to study the effect of UV-C treatment on the sensory properties of grape juice.

Unfortunatelly, we have found that UV-C treatment of grape juice has affected the sensory properties both in lower and higher doses.

The effect of UV-C radiation on grape juice turbidity is presented in Figure 3. We have observed incrase in turbidity in all UV-C treated grape juices with or without ^{addition of SO}2^{. In average, an application of 0.68 kJ L-1} UV-C increased the turbidity 1.1 times, dose 6.83 kJ L^-1 1.2 times and dose 13.67 kJ L^-1 1.3 times.

The sensory properties, the smell (Table 3) and taste (Table 4) were changed immediately when grape juices ^{were treated with SO}2^{. The sensory properties of grape} juices sampled 24 and 96 hours after sedimentation ^{without addition of SO}2 ^{was changed slightly after 1 min} of treatment (UV-C dose 0.68 kJ L^-1) and changed markedly (p-value <0.001) after 2 min of treatment (UV-C dose 1.37 kJ L^-1). We can describe the smell and taste after the treatment like baked and strongly simmilar to hydrogen sulphide. This smell and taste was very unpleasant and nasty.

The Principal Components Analysis of four grape juices with and without addition of sulphur dioxide according to the different UV-C treatment times is presented in Figure 6. This figure contains four groups of data that are separated by a distance, which indicates clearly that the UV-C radiation treatment affected the turbidity of grape juices. The turbidity of grape juices with and without ^{addition of SO}2 ^{was increased in relation to the length of} UV-C treatment (p <0.05). This findig is in agreement with Hartly (2008). All the wines absorb strongly upper end of the UV spectrum. Wavelengths of 375 and 440 nm have been identified as critical in promoting harmful reactions.

TExposure of wine to light results in what is known as light-struck flavours and aromas. These are produced by the initiation of chemical reactions in the wines, resulting in the formation of sulphurous compounds with an unpleasant smell and taste. The reactions can occur within minutes of exposure to light and a tiny amount of the sulphurous compounds can impart a noticeable (bad) taste and aroma to a wine.

The subject of further investigation may be the effect of fermentation on grape juices treated with UV-C radiation. It would be useful to found how the changed sensory properties of grape juice affect the final product.

The UV-C (254 nm) radiation increases the turbidity of grape juices (p <0.001). This effect was observed in all grape juices with or without addition of sulphur dioxide and also in clarified or not clarified grape juices.

We found UV-C radiation negatively affect the sensory properties of grape juices (p <0.001). This effect was more pronounced in grape juices treated with sulphur dioxide. The smell and taste were significantly negatively changed. Exposure of grape juice treated with sulphur dioxide to UV-C radiation can probably lead to arising the sulphur compounds, which affects the smell and taste of grape juices. Also, it is very likely that the negative change in taste and smell may negatively affect the quality of produced wines. For this reason, we do not recommend to use UV-C light for the grape juice treatment. It will be interesting to conduct a detail analysis of the grape juices composition before and after UV-C radiation treatment in next work.