PHYSICOCHEMICAL COMPOSITION AND SENSORY ANALYSIS OF WHOLE JUICE EXTRACTED FROM GRAPES IRRADIATED WITH ULTRAVIOLET C 1

Grape juice has been widely studied due to the presence of phenolic compounds and its beneficial effects on human health. Ultraviolet irradiation C (UV-C) can increase the content of phenolic compounds and anthocyanins and contribute to sensory acceptability. The aim of this study was to evaluate the effect of different doses of ultraviolet irradiation C (UV-C) on ‘Trebbiano’, ‘Niagara Branca’, ‘Isabel’ and ‘Cabernet Sauvignon’ grapes, as well as effect of the storage period. Juices were elaborated and evaluated for physicochemical analyses, and for the sensorial analysis in irradiated samples. In ‘Niagara Branca’ and ‘Trebbiano’ cultivars, storage and irradiation promoted few physicochemical alterations, and sensorially, irradiation reduced the intensity of flavor and color attributes. In juices from ‘Isabel’ and ‘Cabernet Sauvignon’ cultivars, the storage period led to the concentration of sugars and irradiation influenced physicochemical parameters and increased the intensity of aroma attribute at dose of 2 kJ m-2. Thus, UV-C irradiation contributes little for the improvement of white grape juices; however, it favors some sensory attributes in red grape juice, requiring further studies to elucidate the influence of UV-C irradiation on the phenolic and volatile composition of grape juice.


INTRODUCTION
In Brazil, grape juice is made from American cultivars of Vitis labrusca species, due to consumer preference for aroma, color and flavor.Cultivars of Vitis vinifera species are preferentially used for the production of fine wines, as well as for the production of juice (CAMARGO; MAIA; RITSCHEL, 2010), especially 'Cabernet Sauvignon' cultivar (DUTRA et al., 2014).
Grape juice has been widely studied due to the presence of phenolic compounds and its potential beneficial effect on human health.The intake of foods rich in polyphenols has contributed to slow the onset of chronic and cardiovascular diseases and cancer (YAMAGATA; TAGAMI; YAMORI, 2015;RUIZ;HERNÁNDEZ, 2014;TANGNEY;RASMUSSEN, 2013).The main pathways of action of polyphenols are through their anti-inflammatory activity and antioxidant capacity (ANDROUTSOPOULOS, et al., 2010).
Grapes coming from Vitis vinifera and Vitis labrusca species are mainly different regarding the resistance to fungal diseases such as anthracnose, mildew and powdery mildew, as well as to climate adaptation and processing possibilities (PINTO et al., 2016;ÇETIN et al., 2011).However, when dealing with postharvest losses, both are highly perishable, leading to the need for the use of new technologies to reduce losses.
Ultraviolet irradiation C (UV-C) is widely known as abiotic elicitor due to its germicidal action in grapes especially in the control of fungal contamination (SCHUMPP et al., 2012, TYUNIN andKISELEV, 2016).This technology can also stimulate the secondary metabolism of plants, favoring the production of defense chemicals without leaving residues that could be a risk to human health (MARTI et al., 2014;PINTO et al., 2016;50 SHEN et al., 2013).
In addition to its effect on the control of postharvest diseases in grapes, UV-C irradiation stimulates the production of phenolic compounds in fruits after 4-6 days stored at 20ºC (CANTOS et al., 2002;SAUTTER et al).In wines produced with Vitis vinifera cultivars, better acceptance regarding the aroma of wines produced from irradiated 'Trebbiano' grapes was observed (BERTAGNOLLI et al., 2007).
Considering that the use of UV-C radiation can stimulate the production of bioactive compounds (TYUNIN; KISELEV, 2016), and that one of the major forms of grape consumption in Brazil is through juice (IBRAVIN, 2015), the importance of evaluating the physical and chemical parameters resulting from the application of this technology to grapes is justified.
In addition, there are only few studies on its use due the fact that it is a recent technology (MARTI et al., 2014;PINTO et al., 2016).Thus, the present study aimed to evaluate the postharvest effect of different doses of ultraviolet irradiation C (UV-C) on 'Trebbiano', 'Niagara Branca', 'Isabel' and 'Cabernet Sauvignon' grapes, as well as the effect of the storage period.
Grape clusters were transported to the Núcleo Integrado de Desenvolvimento em Análises Laboratoriais (NIDAL), Universidade Federal de Santa Maria, and acclimated for 6 hours at 20 ºC.Stems were then removed with a pair of scissors, kept with a peduncle and stored for 24 hours at 20 ° C for healing of tissues.
The experiment was applied independently in 'Niagara Branca', 'Trebbiano', 'Isabel' and 'Cabernet Sauvignon' cultivars.The experimental design was the completely randomized consisting of the initial grape sample (without storage and without irradiation) and four UV-C irradiation treatments at doses 0, 1, 2 and 3 kJ m -2 followed by five days of storage with four replicates per treatment.The experimental unit consisted of 500 g of grape clusters, originating 20 sample units yielding 480 mL of juice.The juice was analyzed for the physicochemical composition in the initial samples and in samples treated with UV-C irradiation.For sensory analysis, only juices from grapes treated with UV-C irradiation were analyzed.
The irradiation method used was that described in Sautter et al. (2008) with adaptations, according to Treptow (2012).The sample units were placed on reflective aluminum trough without overlapping clusters for exposure to UV-C radiation.Irradiation occurred at a distance of 29 cm from the source to the surface in an anti-reflective chamber DOI 10.1590/0100-29452017 579 Jaboticabal -SP PHYSICOCHEMICAL COMPOSITION AND SENSORY ANALYSIS OF WHOLE JUICE... with ultraviolet irradiation C (UV-C) (Phillips ® , model TUV15W-G15T8 Longe Life, power 15 W) with air circulation at 25 ° C to deplete the ozone, thus avoiding a second elicitor.Irradiance of 3.048 W m -2 at wavelength of 254 nm was measured using spectroradiometer (International Light®, model RPS900).Doses were calculated by integrating exposure time and source irradiance, using the OringinTM version 5.0 package.Grape clusters received doses of 0, 1, 2 and 3 kJ m -2 and remained stored in heated chamber at 20 ° C for 5 days for the development of the physiological response.
The storage time after the five-day UV-C irradiation was based on preliminary studies, where the best responses were found for the physicochemical parameters, which was also reported as the best period by researchers such as Cantos et al. (2002).
Juices were elaborated based on the method of Flanzy, with cold sulphurous maceration process described by Manfroi (1999).Juice was packed in 500 ml glass bottles, where soluble solids (SS) content was determined by refractometry at temperature of 20°C.Titratable total acidity was determined according to methodology described by Amerine and Ough (1980), and the results were expressed as tartaric acid per 100 milliliters of juice (g 100 mL -1 ).The determination of total anthocyanins was performed by spectrophotometry, as described by Di Stefano (1989), with results expressed in grams of malvidin per 100 milliliters of juice (g 100 mL -1 ).Total polyphenols were determined according to method of Singleton and Rossi Junior (1965) and expressed in grams of gallic acid per 100 milliliters of juice (g 100 mL -1 ).The determination of total, reducing and non-reducing sugars was carried out using the colorimetric method of Somogyi and Nelson (NELSON, 1944) and results were expressed in grams of glucose per 100 milliliters of juice (g 100 mL -1 ).
Sensory analysis was carried out by applying the ordering test, in which each judge received four juice samples (referring to the different UV-C doses of 0, 1, 2 and 3 kJ m -2 ) of each cultivar, ordering samples in decreasing order regarding color intensity, aroma and flavor (IAL, 2008).
Analyses were carried out at the Laboratory of Sensory Analysis, Departamento de Tecnologia e Ciência dos Alimentos and at the Núcleo Integrado de Desenvolvimento em Análises Laboratoriais, both at the Universidade Federal de Santa Maria -RS.The panel consisted of 60 untrained judges, and the analyses of juices from each cultivar were performed on alternate days, and each judge randomly received samples coded with three digits in the amount of 20 mL in transparent acrylic cup, forms to be filled, water and crackers for cleaning taste buds, and coffee for cleaning the smell, between samples.The research was approved by the Ethics Research Committee of the Universidade Federal de Santa Maria, under numbers: 23081.020467/ 2010-07 and CAAE: 0388.0.243.000-10.
Data obtained from physicochemical analyses were used to study two effects.The first effect was on storage between initial sample and the dose of 0 kJ m -2 as determined by Student's t-test (p<0.05).The second effect was of UV-C irradiation determined by the analysis of variance, followed by the Tukey test at 5% error probability.The statistical software used for both tests was Statistica® 9.0.The results of the sensory analysis for color, aroma and flavor attributes were analyzed using the Friedman test and the table of Newell and MacFarlane (MEILGAARD et al., 1987), considering 5% error probability.

RESULTS AND DISCUSSION
The juice produced from non-irradiated 'Niagara Branca' grapes showed reduction in the concentration of total sugars during the five-day storage period (Table 1).However, when considering postharvest UV-C irradiation, it was observed that the dose of 3 kJ m -2 promoted a decrease in the content of non-reducing sugars and an increase in the content of reducing sugars (Table 1), indicating a probable homeostasis process, since there were no changes in total polyphenols in the same period.This has already been discussed by Shama and Alderson (2005), who showed that low-dose irradiation can stimulate vital processes within cells and trigger homeostasis.
In addition, sugars may represent components of the primary metabolism and be used as energy sources to maintain berries, or assist in the production of substances of the secondary metabolism, such as phenolic compounds (ALI et al., 2010;PINTO et al., 2016;PALA;TOKLUCU, 2013).According to Vermerris and Nicholson (2006), the precursors of phenolic compounds can be derived from the catabolic process of glycolysis.
The results of 'Niagara Branca' juice showed an increase in the concentration of total sugars at doses of 2 and 3 kJ m -2 (Table 1).Sensory analysis only showed a significant difference (p <0.05) for flavor and color attributes of the juice at dose of 3 kJ m -2 , presenting a lower intensity when compared to dose of 0 kJ m -2 of UV-C (Figures 1A and 1C).This result may be related to the fact that the sweetness sensation, although important, is not the only DOI 10.1590/0100-29452017579 Jaboticabal -SP T. C. TREPTOW et al.
responsible for the formation of flavor, which may be influenced by other substances that have undergone alterations due to UV-C irradiation treatment.
In the 'Trebbiano' juice, the initial sample had higher SS concentrations when compared to the dose of 0 kJ m -2 of UV-C (Table 1).These results agree with Detoni et al. (2005), who also found a decrease of SS in stored grapes.This reduction in SS content, observed in other studies, is associated with the use of sugars in the respiratory activity (COOMBE et al., 1992).
At the irradiation dose of 2 kJ m -2 for 'Trebbiano' cultivar, higher SS concentration was observed, when compared to the dose of 0 kJ m -2 of UV-C and a reduction in the concentration of total sugars (Table 1).In the ordering test carried out in the sensory analysis of this cultivar, it was observed that in samples treated with doses of 0, 1 and 2 kJ m -2 , there were no significant differences for color and aroma attributes (p<0.05)(Figure 1A and  1B), and at the dose of 3 kJ m -2 , samples presented lower intensity in both attributes.Bertagnolli et al. (2007), in a similar work, reported that wines from 'Trebbiano' cultivar elaborated from berries irradiated with UV-C showed greater acceptability, representing 56.66% of judges in attribute aroma.
A reduction of SS content, total sugars, total anthocyanins and total polyphenols was observed in treatments of 'Isabel' grapes with UV-C irradiation (Table 1).In spite of the reduction of total anthocyanins, it was observed in the ordination test (p <0.05) that juices produced from irradiated berries obtained the highest intensity scores in attribute color (Figure 1A).In this ordering test, a significant increase in aroma (p<0.05) was observed, especially in juices made from grapes treated with UV-C dose of 2 kJ m -2 (Figure 1B).
In the 'Cabernet Sauvignon' juice, it was observed from the initial analysis that the dose of 0 kJ m -2 of UV-C with five days storage, there was an increase in SS concentration, total acidity, nonreducing sugars and total polyphenols, possibly because in the postharvest period, the respiratory activity may have increased, consequently dehydrating berries and concentrating these compounds.During the storage period, a decrease in reducing sugars was also observed.This may indicate that there was consumption by metabolism for conversion to energy and production of polyphenols, since there was a 3.5 times increase in the concentration of total polyphenols (Table 1).
With UV-C irradiation, there was a decrease in the content of non-reducing sugars and an increase in reducing sugars (Table 1).This change in sugars was not observed in the ordering test, since there was no statistical difference (p<0.05) in flavor attribute (Figure 1 C).However, a statistical difference (p<0.05) in aroma attribute with dose of 2 kJ m -2 was observed, being referred to as "the most intense" when compared to UV-C dose of 0 kJ m -2 (Figure 1B).
Normative Instruction No. 01 of January 7, 2000 refers to the technical regulation that establishes identity and quality standards for grape juice.In the present study, juices made from grapes irradiated with UV-C presented concentrations of total sugars within values allowed by the Brazilian legislation, except for 'Cabernet Sauvignon' juices that remained with exceeding values (23.9 ± 1.1 to 27.3 ± 0.6 g 100 mL -1 ), which could be explained by the fact that it is a cultivar with high oenological potential.Regarding total acidity, only 'Trebbiano' (0.35 ± 0.0 to 0.40 ± 0.0 g 100 mL -1 ) and 'Cabernet Sauvignon' juices (0.30 ± 0.0 to 0, 35 ± 0.0 g 100 mL -1 ) presented values below the minimum required.Regarding soluble solids, it was observed that 'Niagara Branca', 'Trebbiano' and 'Isabel' juices remained below values established by Normative Instruction No. 01 of 2000, which determines minimum of 14°Brix (Table 1).In the SS / TA ratio, it was observed that only 'Cabernet Sauvignon' juices (62.3 ± 2.4 to 86.9 ± 3.4)

*
presented very high values according to Ordinance No. 55 of 2004, indicating juices in sensory imbalance, being extremely sweetSS / TA -Soluble solids / total acidity ratio, Initial analysis -samples without storage and UV-C irradiation, n.a.-not analyzed ** Means differ only between initial sample and 0 kJ m -2 by the t-test (p <0.05), reflecting the effect of the five days of storage.*** Means followed by the same letter, in the same cultivar, do not differ from each other with UV-C irradiation doses by the Tukey test at 5% error probabilityTABLE 1 -Physicochemical analysis of the juice from different cultivars under UV-C irradiation plus five days of storage.

FIGURE 1 -
FIGURE 1 -Results of the ordering test of color (A), aroma (B) and flavor (C) parameters of juice from 'Niagara Branca', 'Trebbiano', 'Isabel' and 'Cabernet Sauvignon' grapes submitted to different doses of UV-C irradiation.1Means followed by the same letter, in the same cultivar, do not differ from each other with UV-C irradiation doses by the Friedman test and the Newell and MacFarlane table at 5% error probability.