Quality parameters of currant berries from three different cluster positions

Scientia Horticulturae 210 (2016) 188–196

Contents lists available at ScienceDirect

Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti

Quality parameters of currant berries from three different cluster positions Maja Mikulic-Petkovsek a,∗ , Darinka Koron b , Robert Veberic a a Biotechnical Faculty, Department of Agronomy, University of Ljubljana, Chair for Fruit, Vine and Vegetable Growing, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia b Agricultural institute of Slovenia, Hacquetova ulica 17, SI-1000 Ljubljana, Slovenia

a r t i c l e

i n f o

Article history: Received 30 March 2016 Received in revised form 22 July 2016 Accepted 23 July 2016 Keywords: Ribes Fruit Colour characteristics Sugars Organic acids Phenolic compounds

a b s t r a c t The challenge in the production of currants is the definition of the optimum harvest time due to successive ripening of berries over the entire length of cluster. The study focused on detecting the differences in quality parameters among individual positions of berries in the cluster. A red, black and white currant cultivar (‘Rovada’, ‘Tsema’ and ‘Blanka’) were selected for the experiment as they all develop long clusters and are used for fresh consumption. The berry mass, colour parameters and pH of the juice were recorded and sugar and organic acids contents were determined using HPLC. A detailed analysis of individual phenolic compounds was performed on HPLC–MS. The results of the study indicate that berries from the basal part of the cluster contain higher levels of sugars, organic acids and vitamin C in comparison with berries positioned at apical cluster sections. A similar pattern was observed for phenolic components: berries of the ‘Rovada’ cultivar contained almost twice the amount of total anthocyanins (TA) in berries from the basal cluster section compared to berries positioned at the apical part of the cluster. The differences were even more prominent (2.8 fold more TA in basal cluster section) in black currant ‘Tsema’. Significant differences in the content of all identified phenolic groups have been determined between the basal and apical position of berries in the cluster: berries from the basal part contained from 1.6 to 2.2 fold more hydroxycinnamic acids, from 1.7 to 2.2 fold more flavonol glycosides and from 1.5 to 1.8 fold more flavanols (catechin, epicatechin and procyanidin). The results of the study may be useful to the producers who strive to improve their production technology, for food and processing industry and for consumers as it was pointed out that the quality of berries at the apical part of the currant clusters is decreased compared to berries from the basal part of the cluster. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Ribes rubrum and R. nigrum currant species represent important shares in berry fruit production and in food industry. Both species are cultivated in colder climates and are abundant in regions of Northern Europe. Global currant production reached 706910 tons in 2013 with main cultivation areas located in Russia (53% global production) and Poland (28% global production) (FAOSTAT, 2016). Currant fruit is consumed fresh or processed into juices, jams, preserves, teas and liqueurs. Berries are frequently used for production of natural food colorants and various health-promoting additives (Savikin et al., 2009; Savikin et al., 2014).

∗ Corresponding author. E-mail address: [email protected] (M. Mikulic-Petkovsek). http://dx.doi.org/10.1016/j.scienta.2016.07.030 0304-4238/© 2016 Elsevier B.V. All rights reserved.

The content of sugars, organic acids, vitamin C and phenolic compounds affect the organoleptic properties of red, white and black currants. Fructose and glucose are the prevalent sugars in fruit of both currant species, which also accumulate low levels of sucrose. The abundancy and diversity of organic acids in fruit greatly influence their taste, colour and aroma. Organic acids indirectly affect phenolic metabolism as they regulate cell sap pH level and act as phenolic precursors (Flores et al., 2012). Mikulic-Petkovsek et al. (2013) reported malic and citric acids the predominant organic acids in Ribes fruit. Red, black and white currant fruit accumulate various phenolic compounds from the groups of anthocyanins, flavonols and hydroxycinnamic acids. The phenolic profile differs among currant species and cultivars (Maatta et al., 2001; Wojdylo et al., 2013). Rubinskiene et al. (2005) identified the following anthocyanins in black currants: cyanidin-3-rutinoside (33–38%), delphinidin-3-rutinoside (27–34%), cyanidin-3-glucoside (8–10%) and delphinidin-3- gluco-

M. Mikulic-Petkovsek et al. / Scientia Horticulturae 210 (2016) 188–196

side (8–10%). Monomeric flavanols, such as catechin and its isomer (epicatechin) and oligomeric and polymeric flavanols (proanthocyanidins, condensed tannins) have been determined in Ribes berries (Laaksonen et al., 2015). Among flavonols, Milivojevic et al. (2012) confirmed the presence of myricetin, quercetin, isorhamnetin and kaempferol glycosides in selected currant species and cultivars. From the group of hydroxycinnamic acids, different derivatives of ferulic, p-coumaric and caffeic acids have been detected in currant berries (Jakobek et al., 2007; Mitic et al., 2011). Currants are valued for their health-promoting properties as several studies report beneficial effects of currant consumption on reducing age-related symptoms and inhibiting the progression of degenerative diseases such as cancer and cardiovascular disorders (Bishayee et al., 2011; Folmer et al., 2014). Specifically, the role of phenolic compounds and vitamin C has been highlighted in a study of Szajdek and Borowska (2008), who investigated antioxidative function of currant products. Currant berries are combined in a cluster (raceme) and different cultivars are characterized by the number of clusters per bud, the size of individual berries in the cluster, the length of the cluster, time of maturity, fruit taste and other features. One of the challenges in currant production is the definition of optimal harvest time as individual berries ripen consecutively over the entire length of the cluster. The decision on the adequate time of harvest is reached when berries at the lowest part of the cluster develop characteristic cultivar-specific colour. Generally, berries located at apical parts of the cluster ripen later than those at the basal positions. Therefore, it often happens that some currant cultivars are harvested too early or too late resulting in apical quality fruits. The most reliable method of optimum berry ripeness determination is the analysis of their organoleptic properties. The present study aimed to determine significant differences in the quality parameters (external fruit characteristics and chemical composition) of currant berries collected at three different positions in the cluster. Red, white and black currant cultivars were included in the experiment and their clusters were harvested in their optimum ripeness. We expected differences among three cluster positions in terms of berry mass, their colour parameters and pH of berry juice and also in the content of sugars, vitamin C, organic acids and phenolic compounds. A detailed analysis of individual sugars and acids was performed with HPLC and individual phenolic compounds were determined by using HPLC–MS. The content of total phenolics was assessed spectrophotometrically.

2. Materials and methods 2.1. Chemicals Sugars and organic acids were quantified by the use of the following standards: sucrose, fructose and glucose; citric, malic and fumaric acid from Fluka Chemie (Buchs, Switzerland), and shikimic acid from Sigma-Aldrich Chemie GmbH (Steinheim, Germany). Phenolic compounds, cyanidin-3-glucoside, neochlorogenic acid (3-caffeoylquinic acid), petunidin-3-O-glucoside and quercetin-3-O-rutinoside were obtained from Sigma-Aldrich Chemie GmbH; caffeic and ferulic acid, (−)-epicatechin, quercetin3-O-galactoside, quercetin-3-O-glucoside, p-coumaric acid, procyanidin B1, cyanidin-3-O-galactoside, cyanidin-3-O-rutinoside, apigenin-7-glucoside and kaempferol-3-O-glucoside from Fluka Chemie GmBH (Buchs, Switzerland), peonidin-3-O-glucoside from Extrasynthese (Genay Cedex, France), (+)-catechin from Roth (Karlsruhe, Germany), and quercetin-3-O-xyloside from Apin Chemicals (Abingdon, UK). Phenolics were extracted with methanol acquired from Sigma. The chemicals for the mobile phases were HPLC–MS grade acetonitrile and formic acid from Fluka Chemie GmbH. Water

189

for mobile phase was double distilled and purified with the Milli-Q system (Millipore, Bedford, MA, USA). For the total phenolic content, Folin-Ciocalteu phenol reagent (Fluka Chemie GmBH), sodium carbonate (Merck, Darmstadt, Germany), gallic acid (Sigma) and ethanol (Sigma) were used. 2.2. Plant material Black currant ’Tsema’, red currant ’Rovada’ and white currant ’Blanka’ bushes were planted in 2006 at the experimental station of Agricultural Institute of Slovenia, located at Brdo pri Lukovici (latitude: 46◦ 10 N, longitude: 14◦ 41 E). The location and soil are optimal for soft fruit production (North South orientation; high organic matter, slightly acidic soil, optimal phosphorous and potassium content). Black currants were planted in bush training system in row spacing of 3 m × 1.5 m with five to seven trunks per bush. Red and white currants were planted in cordon training system in row spacing of 3 m × 0.75 m with three trunks (vertical cordons). Fruit of red and white currants are normally harvested for fresh market and black currant berries for processing although several cultivars have been developed for fresh consumption. Plants were planted on slightly elevated beds, covered with agrotextile. Ribes, grown for fresh consumption requires intensive pruning, which stimulates the plants to produce long, uniform and healthy clusters with long stems. ‘Rovada’ is a vigorous, late-ripening Dutch red currant cultivar with long clusters and large berries. ‘Tsema’ is a vigorous, early-ripening blackcurrant cultivar with long clusters and large, tasteful berries suitable for fresh consumption. ‘Blanka’ is an extremely vigorous and high-yielding Slovakian white currant cultivar, which ripens relatively late in season and produces very long clusters and medium to large berries. All currant cultivars were harvested when all berries in the cluster reached full coloration. Ribes fruits were collected in year 2015 at their optimal maturity (organoleptically determined), which differed among cultivars analyzed. Fruits of white currant ‘Blanka’ and black currant ‘Tsema’ were collected on June 29th and fruits of red currant ‘Rovada’ were collected on July 10th. Approx. 250 g of fruits were collected for one repetition from different bushes growing at a single location. Ten repetitions per cultivar were separately stored in plastic bags and transported to the lab facility in a cooler. Individual clusters were separated into three sections:1. Basal part of the cluster, 2. Medial part and, 3. Apical part of the cluster (Fig. 1). The number of berries in each section was counted and their mass was recorded as well as the colour parameters using the colorimeter. Extracts were prepared from berries in order to determine the content of vitamin C, sugars, organic acids and phenolic compounds. Extracts of individual cultivars were prepared in ten replicates for each treatment by combining several berries. 2.3. Measurement of fruit colour, soluble solids and pH of currants Fruit colour was measured using a portable colorimeter (CR-10 Chroma; Minolta, Osaka, Japan) with L*, C* and h◦ values. Colour was measured in the equatorial region of the berry fruit (two replicates per berry and thirty fruits per berry position in the cluster for each cultivar analyzed) to ensure equal measurement conditions. The colorimeter was calibrated with a standard plate before measurements. Chroma (C*) records fruit colour intensity and L value corresponds to a dark-bright scale from 0 (black colour) to 100 (white colour). The hue angle (h◦ ) is expressed in degrees from 0 to 360, where 0◦ depicts red color, 90◦ yellow, 180◦ green and 270◦ corresponds to blue colour of the sample (McGuire, 1992). Total soluble solids were determined using a digital hand held refractometer (30PX, Mettler Toledo, United States) and pH value was measured with a pH-meter (inoLab pH/Cond 720, WTW, Germany). Fruit firmness was evaluated on the surface of berries using a penetrometer

190

M. Mikulic-Petkovsek et al. / Scientia Horticulturae 210 (2016) 188–196

filtrated through polytetrafluoroethylene (PTFE) filters (20 ␮m) into vials. Phenolic compounds were analyzed on an HPLC system equipedded with DAD detector set on 280 nm, 350 nm and 530 nm. The elution solvents were aqueous 0.1% formic acid in double distilled water (A) and 0.1% formic acid in acetonitrile (B). For phenolic determination a Gemini C18 (Phenomenex) column was used, operated at 25 ◦ C. Samples were eluted according to linear gradients reported by Wang et al. (2002). Phenolics were identified by comparing their UV–vis spectra and retention times with standards and also confirmed using a mass spectrometer (Thermo Scientific, LCQ Deca XP MAX) with an electrospray interface (ESI) operating in negative and positive ion modes (for anthocyanins). Full scan data-dependent MSn scanning from m/z 115–1400 was performed. All conditions on mass spectrometer were the same as reported by Mikulic-Petkovsek et al. (2015). Phenolic contents were expressed in mg/kg fresh weight (FW) of fruits and the values were calculated for 100 berries. 2.6. Extraction and determination of vitamin C

Fig. 1. Individual clusters of different currants were separated into three sections:1. Basal part of the cluster, 2. Medial part and, 3. Apical part of the cluster.

(T.R. Turoni srl, Forlì, Italy) with a 1 mm-diameter needle (Newton, N).

Currant fruits were crushed to a paste in a mortar chilled with liquid nitrogen and 3 g was extracted with 15 mL of 2% m-phosphoric acid. The mixture was left for 40 min at room temperature, and the extract was centrifuged and filtrated through 0.20 ␮m cellulose filters into vials. Identification of ascorbic acid was based on the HPLC method reported by Mikulic-Petkovsek et al. (2013). The column was a Rezex ROA − organic acid H+ (8%) heated to 20 ◦ C, the mobile phase was 4 mM sulfuric acid and the flow rate maintained at 0.6 mL min−1 . The contents of ascorbic acid were expressed in g/kg FW and their values were calculated for 100 currant berries.

2.4. Extraction and determination of sugars and organic acids

2.7. Determination of total phenolic content

Primary metabolites (sugars and organic acids) in currant berries were analyzed according to the protocol described by Mikulic-Petkovsek et al. (2012a). 5 g of fruits were macerated and immersed in 25 mL of double distilled water with a homogenizer (Ultra-Turrax, Ika Labortechnik). Fruit samples were left for half an hour at room temperature with frequent stirring. The extracts were centrifuged and filtrated through a 0.20 ␮m cellulose ester filters into glass vials. The samples were analyzed using high performance liquid chromatography (HPLC; Thermo Scientific, San Jose, CA, USA). The determination of sugars was performed on a Rezex RCM-monosaccharide Ca+ (2%) column (Phenomenex) heated to 65 ◦ C equipped with a RI detector. The mobile phase was double distilled water and the flow rate maintained at 0.6 mL min−1 . Organic acids were monitored on the same HPLC system, equipped with a UV detector (210 nm), the column was a Rezex ROA − organic acid H+ (8%) heated to 65 ◦ C, mobile phase 4 mM sulfuric acid and the flow rate 0.6 mL min−1 . Carbohydrates and acids were identified by their retention time characteristics. External standards were used to calculate the contents of individual primary metabolites in samples. Their contents were expressed in g/kg FW and values were calculated for 100 currant berries (a handful of berries, frequently consumed in a single helping).

Extraction for total phenolics was performed according to a similar protocol used for individual phenolics, without the addition of BHT. Total phenolic content (TPC) of extracts was evaluated by using the Folin-Ciocalteau phenol reagent method (Singleton et al., 1999). To 100 ␮L of the sample extracts (extract of black currants was diluted 1: 9 (v/v) with MeOH), 6 mL of double distilled water and 500 ␮L of Folin-Ciocalteau reagent were added; after waiting for 4 min at room temperature, 1.5 mL of sodium carbonate (20% w/v) was added. The extracts were mixed and left for half an hour at 40 ◦ C. Then the absorbance was measured at 765 nm in three repetitions. The mixture of methanol and reagents was used for blank. Total phenolic content was expressed as gallic acid equivalents (GAE) in mg kg−1 fresh weight of fruit and then the values were calculated for 100 berries.

2.5. Extraction and determination of individual phenolic compounds using HPLC-DAD-MSn analysis

2.8. Statistical analysis Statgraphics Plus 4.0 program (Manugistics. Inc.; Rockville, Maryland, USA) was used for data analysis. Data were tested for differences in analysed parameters among different cluster (basal part of the cluster, medial of the cluster and apical part of the cluster) using one-way analysis of variance (ANOVA) separately for each cultivar. Differences in the content levels of analyzed metabolites among treatments were tested with LSD test. p-Values of less than 0.05 were considered statistically significant. 3. Results

Phenolic compounds in Ribes fruits were extracted as reported by Mikulic-Petkovsek et al. (2012b). Fruits were crushed to a smooth paste and 3 g of samples were extracted with 7 mL methanol containing 1% (w/v) 2.6-di-tert-butyl-4-methylphenol (BHT) in ultrasonic bath for 50 min. Extracts were centrifuged and

3.1. The characteristics of currant berries The mass of 100 red ‘Rovada’ berries ranged from 60.65 g (apical part of the cluster) to 94.06 g (basal part of the cluster) (Table 1).

Different letters in rows denote significant differences in analyzed parameters among different cluster sections for each individual currant cultivar (p < 0.05). Mean ± standard errors are presented.

24.10 ± 0.11b 0.73 ± 0.05b 259.3 ± 5.13a 2.93 ± 0.02b 0.85 ± 0.08a 148.21 ± 4.17c 0.92 ± 0.07a 23.96 ± 0.07b 0.67 ± 0.04ab 259.8 ± 3.47a 2.97 ± 0.03b 0.83 ± 0.04a 106.58 ± 4.44b 1.63 ± 0.07c

Medial Apical

23.48 ± 0.11a 0.57 ± 0.05a 256.7 ± 6.76a 2.48 ± 0.01a 0.81 ± 0.07a 73.90 ± 2.87a 1.34 ± 0.09b 28.74 ± 0.14a 28.50 ± 0.59a 8.01 ± 0.23a 2.75 ± 0.03a 0.40 ± 0.07a 94.06 ± 2.93c 1.26 ± 0.05a

Basal Apical

55.50 ± 0.41b 26.30 ± 0.68a 71.86 ± 0.82a 2.94 ± 0-20b 0.70 ± 0.09a 66.30 ± 3.22c 0.90 ± 0.05a 55.54 ± 0.36b 25.77 ± 0.56a 71.90 ± 0.60a 2.97 ± 0.23b 0.76 ± 0.11a 56.22 ± 2.34b 3.03 ± 0.07b 52.18 ± 0.51a 26.14 ± 0.55a 71.37 ± 0.69a 2.87 ± 0.008a 0.71 ± 0.55a 41.32 ± 1.77a 4.07 ± 0.10b L (lightness) C (chroma) H (hue angle) pH of juice Firmness Mass of 100 berries (g) Number of berries per cm of cluster

Basal Medial Apical

Medial

29.22 ± 0.16ab 30.29 ± 0.61a 8.52 ± 0.29ab 2.76 ± 0.01a 0.52 ± 0.07a 79.32 ± 2.11b 3.49 ± 0.09c

Black currant Red currant White currant

Table 1 Characteristics of berries from different cluster sections in white (‘Blanka’), red (‘Rovada’) and black (‘Tsema’) currants.

29.36 ± 0.31b 32.21 ± 0.73b 9.15 ± 0.32b 2.79 ± 0.002a 0.60 ± 0.05a 60.65 ± 2.00a 2.63 ± 0.12b

Basal

M. Mikulic-Petkovsek et al. / Scientia Horticulturae 210 (2016) 188–196

191

White currant cv. ‘Blanka’ was characterized by comparably smaller berries: average mass of 100 berries from the apical part was 41.32 g and a 1.6 fold higher mass was recorded for 100 berries from the basal part of the cluster. Similar differences were recorded in black currant cv. ‘Tsema’, which developed significantly heavier berries (larger mass) in the basal section of the cluster (148.21 g per 100 berries). The mass of the berries positioned at the lowest cluster section was twofold lower (Table 1). Correspondingly, the number of berries was significantly lower at the basal part of cluster (Table 1). No significant differences in berry firmness have been detected among individual sections (Table 1). Berry firmness ranged from 0.40 N in the cv. ‘Rovada’ to 0.85 N in the cv. ‘Tsema’. Higher firmness of black currant berries could be attributed to thicker skin of the ‘Tsema’ cultivar. The measured pH value of the juice indicates that white and black currant berries from the upper two thirds of the cluster are characterized by significantly higher pH compared to the berries located at the apical section of the cluster (Table 1). No statistical differences in the pH value of the juice have been detected among the position of berries in the cluster in red currants. Fruit colour is an essential indicator for determination of berry ripeness and an important parameter of their quality. It is wellknown that perfect colouration is a key factor of fruit acceptance by the consumers next to taste and aroma. In order to determine potential differences in colour parameters among berries from individual cluster sections, the following parameters were measured: L* (lightness), C (chroma) and hue angle (h◦ ). In white currants h◦ ranged from 71.37 to 71.90 indicating light yellow colour of berries; in red currants the values ranged from 8.01 to 9.15, which signifies red colour and in black currants the values ranged from 256.7 to 259.3, indicating dark blue hues. No statistical differences in hue angle values have been detected among the three positions in the cluster with the exception of red currants. Berries of the ‘Rovada’ cultivar from the basal section were characterized by lower h◦ compared to berries from the basal part of the cluster. Chroma of black currant berries ranged from 0.57 to 0.73, of red currants from 28.50 to 32.21 and of white currants from 25.77 to 26.30. Significant differences in chroma values have been detected between the lowest position of red currant berries (6–12% higher chroma values) and fruit located higher along the cluster (basal and medial part). Contrary, significant differences have also been observed in black currants, which were characterized by 22% higher chroma of berries from the basal part of the cluster compared to fruit located at positions 2 and 3 (medial and apical part). The position of berries in the cluster also affected the value of L* parameter. White and black currant berries located in the medial or basal part of the cluster had a significantly higher L*. Contrary, red currant berries from the basal position were characterized by slightly lower L* parameter in comparison with berries from the lowest cluster section. Average L* parameter of black currants ranged from 23.48 to 24.10, of red currants from 28.74 to 29.36 and of white currants from 52.18 to 55.54. 3.2. Composition and contents of sugars, organic acids and vitamin C in currant berries Sugars, organic acids and vitamin C were analysed from the group of primary metabolites in different currant cultivars. The major sugars in black, red and white currants were fructose and glucose in similar levels accounting approx. 97% of total sugars (Table 2). Sucrose represented the remaining part (less than 1 g/kg FW, results not shown). Fruit of white currant cv. ‘Blanka’ accumulated less sugars (from 50.5 to 57.1 g/kg FW) compared to red currant cv. ‘Rovada’ berries (66.5–71.3 g/kg FW). The highest sugar levels have been measured in black currant berries (from 90.1 to 99.4 g/kg FW; data not shown). Significant differences in individual

192

M. Mikulic-Petkovsek et al. / Scientia Horticulturae 210 (2016) 188–196

Table 2 The content of sugars (g per 100 fresh berries), organic acids (g per 100 fresh berries or mg per 100 fresh berries for shikimic and fumaric acid) and vitamin C (mg per 100 fresh berries) in different cluster sections of white (‘Blanka’), red (‘Rovada’) and black (‘Tsema’) currants. White currant

Sucrose Fructose Glucose Total sugars Citric acid Malic acid Shikimic acid Fumaric acid Total acids Sugars/acids Vitamin C

Red currant

Black currant

Apical

Medial

Basal

Apical

Medial

Basal

Apical

Medial

Basal

0.07 ± 0.02a 1.04 ± 0.05a 0.97 ± 0.04a 2.09 ± 0.05a 0.64 ± 0.03a 0.15 ± 0.008a 14.27 ± 0.26a 0.35 ± 0.05a 0.81 ± 0.04a 2.61 ± 0.17a 11.65 ± 0.90a

0.06 ± 0.002a 1.61 ± 0.06b 1.42 ± 0.06b 3.11 ± 0.12b 0.78 ± 0.05b 0.18 ± 0.007b 16.53 ± 0.72b 0.40 ± 0.02a 0.98 ± 0.006b 3.24 ± 0.31ab 13.12 ± 1.77a

0.06 ± 0.003a 1.91 ± 0.05c 1.80 ± 0.06c 3.78 ± 0.08c 0.82 ± 0.02b 0.18 ± 0.005b 16.72 ± 0.57b 0.53 ± 0.02b 1.02 ± 0.02b 3.70 ± 0.15b 17.92 ± 1.21b

0.030 ± 0.003a 2.16 ± 0.02a 1.87 ± 0.02a 4.06 ± 0.04a 0.84 ± 0.02a 0.13 ± 0.004b 13.47 ± 0.47a 0.34 ± 0.03a 0.98 ± 0.02a 4.13 ± 0.07a 11.94 ± 0.44a

0.057 ± 0.008b 2.78 ± 0.04b 2.43 ± 0.03b 5.28 ± 0.07b 1.04 ± 0.02b 0.14 ± 0.01a 16.84 ± 0.93b 0.46 ± 0.02b 1.24 ± 0.02b 4.23 ± 0.07a 12.67 ± 0.47a

0.83 ± 0.11c 3.54 ± 0.07c 3.08 ± 0.07c 6.71 ± 0.08c 1.03 ± 0.03b 1.46 ± 0.15a 22.74 ± 0.33c 0.66 ± 0.04c 1.19 ± 0.04b 5.65 ± 0.23b 17.74 ± 0.52b

1.47 ± 0.03a 3.04 ± 0.10a 2.31 ± 0.06a 6.83 ± 0.17a 1.74 ± 0.03a 0.37 ± 0.007a 12.07 ± 0.47a 1.45 ± 0.06a 2.13 ± 0.04a 3.20 ± 0.10a 107.66 ± 6.27a

2.41 ± 0.03b 4.81 ± 0.06b 3.52 ± 0.07b 10.75 ± 0.14b 2.61 ± 0.03b 0.54 ± 0.01b 20.55 ± 0.45b 2.81 ± 0.07b 3.18 ± 0.04b 3.38 ± 0.03a 159.22 ± 9.59b

2.97 ± 0.04c 6.79 ± 0.9c 4.99 ± 0.14c 14.75 ± 0.35c 3.22 ± 0.04c 0.62 ± 0.01c 25.51 ± 0.91c 3.36 ± 0.13c 3.87 ± 0.05c 3.81 ± 0.09b 154.78 ± 6.26b

Different letters in rows denote significant differences in analyzed parameters among different cluster sections for each individual currant cultivar (p < 0.05). Mean ± standard errors are presented. Bold characterized letters in rows denote significant differences in Sum of single primary group among different cluster sections for each individual currant cultivar.

and total sugars have also been detected among the three cluster sections. Berries from the basal part of the cluster contained significantly highest levels of fructose and glucose and, consequently 1.6–2.1 fold more total sugars compared to the other two cluster sections (Table 2). Berries from the basal part of the cluster contained 3.78 g total sugars per 100 berries in white currants, 6.71 g in red currants and 14.75 g in black currants. Among organic acids citric acid was the prevalent acid detected in currant fruits as it represented 80–85% total organic acids analysed. Malic acid was the second major organic acid representing 10–20% of total acids, followed by shikimic and fumaric acids (less than 2% of total acids). White currants cv. ‘Blanka’ contained from 0.81 to 1.02 g total acids per 100 berries, red currants cv. ‘Rovada’ contained from 0.98 to 1.24 g and black currants cv. ‘Tsema’ from 2.13 to 3.87 g total acids per 100 currant berries (Table 2). A similar pattern has also been observed in organic acids levels. Berries positioned in the medial or basal part of the cluster accumulated significantly more individual organic acids and a 1.3–1.8 fold higher content of total organic acids compared to berries from the apical cluster section. Fruits characterized by a higher sugars/organic acids ratio develop a sweeter taste in comparison with those with a lower ratio. 50% higher sugar and acid ratio was measured in red currant cv. ‘Rovada’ berries from the basal cluster section compared to white and black currants from the same position indicating sweeter taste of the former. Generally, significantly higher sugar/acid ratio was measured in fruits located in the basal cluster section compared to fruits from the lowest section regardless of the cultivar (Table 2). Vitamin C content of white and red currants ranged from 11.65 to 17.94 mg per 100 berries. Significantly higher content has been measured in black currant fruits, i.e. from 107.66 to 154.78 mg per 100 berries (Table 2). Berries positioned in the basal part of the cluster were characterized by highest vitamin C content in all cultivars analyzed. Vitamin C content was 40–50% higher in berries from the basal cluster section compared to berries positioned at its lowest part. 3.3. Composition and contents of phenolic compounds in currant berries Phenolic compounds are one of the major groups of bioactive constituents contributing to the quality and specific taste of individual fruit species. Phenolic compounds were analysed at three wavelengths (280, 350 and 530 nm), characteristic for distinct phenolic groups. Ribes species differ in composition and occurrence of selected phenolic groups. Based on their characteristic fragmentation pattern, UV spectra and comparison with standards 40

different phenolic compounds were identified in selected currant cultivars. To facilitate the presentation of differences among cultivars and cluster sections individual compounds were combined to phenolic groups. Anthocyanins were the major phenolic group in black currant berries as they accounted 87% of total phenolic compounds analysed (Table 3). A slightly lower share of anthocyanins (70% total phenolics) has been recorded in red currant berries (Table 4). Contrary, no anthocyanins have been detected in white currants (Table 5). Nine different anthocyanins have been identified in black currant fruit the prevalent delphinidin-3-glucoside and delphinidin-3-rutinoside (approx. 55% total anthocyanins) and cyanidin-3-glucoside and cyanidin-3-rutinoside (approx. 45% total anthocyanins). Peonidin and petunidin glycosides represented the remaining share in black currants. Several cyanidin glycosides have been quantified in red currants, contributing to their characteristic bright red colour. Other anthocyanidin aglycones have not been identified in red currants. ‘Rovada’ berries from the basal cluster section contained almost twofold levels of total anthocyanins (TA) and black currant berries from the basal position 2.8 fold levels of TA compared to fruit from lowest positions (Table 3). Numerous flavonol glycosides have been identified in analysed currant cultivars: 15 in ‘Tsema’ berries, 12 in ‘Blanka’ and 13 different flavonols in ‘Rovada’ fruit. Glycosides of quercetin represented the highest share of flavonol glycosides in all cultivars: 50–60% total flavonols (TF) in black currants, 77% TF in red currants and 86–93% TF in white currants. The major flavonols in white currants were quercetin-3-rutinoside (50–70% TF) and quercetin3-glucoside (approx. 15% TF; data not shown). In addition to glycosides of quercetin glycosides of kaempferol and myricetin have been quantified in all cultivars analysed; however, their levels were significantly higher in black currants compared to white and red currant fruit. The content of kaempferol and myricetin glycosides ranged from 9.35 to 21.72 mg per 100 black currant berries and less than 1 mg per 100 red and white currant berries (Tables 3, 4, and 5). Two isorhamnetin derivatives, i.e. isorhamnetin-3rutinoside and isorhamnetin-3-glucoside, have been identified in black currants. Other Ribes cultivars did not contain any isorhamnetin glycosides. Berries from the basal cluster section contained from 1.7 to 2.2 fold higher flavonol levels compared to berries positioned at the apical part of the cluster regardless of the cultivar analysed. Flavanols, i.e. catechin, epicatechin and several procyanidin dimers have additionally been identified in currant berries. Epicatechin has only been detected in black currant fruits while catechin and procyanidin dimers were identified in fruits of red and white currants. The content of total flavanols was comparable among

M. Mikulic-Petkovsek et al. / Scientia Horticulturae 210 (2016) 188–196

193

Table 3 Content of phenolic compounds (mg per 100 fresh berries) in different cluster sections of black currant cv. ‘Tsema’. Cluster section Apical Epicatechin (flavanols) Derivatives of caffeic acid Derivatives of p-coumaric acid Derivatives of ferulic acid Total hydroxycinnamic acids Ellagic acid Kaempferol glycosides Myricetin glycosides Quercetin glycosides Isorhamnetin glycosides Total flavonols Aurones Cyanidin glycosides Delphinidin glycosides Peonidin glycosides Petunidin glycosides Total anthocyanins

2.15 ± 0.11 13.17 ± 1.18 3.77 ± 0.17 0.081 ± 0.004 17.03 ± 1.34 2.09 ± 0.18 3.22 ± 0.19 6.13 ± 0.75 14.38 ± 1.06 0.191 ± 0.021 23.93 ± 1.97 0.044 ± 0.003 99.28 ± 14.53 122.91 ± 16.42 0.45 ± 0.10 0.50 ± 0.21 223.14 ± 30.63

Medial a a a a a a a a a a a a a a a a a

2.62 ± 0.11 18.75 ± 2.31 5.46 ± 0.14 0.117 ± 0.004 24.33 ± 2.43 3.32 ± 0.14 4.47 ± 0.21 10.31 ± 1.27 19.60 ± 0.79 0.320 ± 0.031 34.72 ± 2.09 0.063 ± 0.003 170.23 ± 28.49 197.30 ± 30.81 2.52 ± 0.66 2.58 ± 0.43 373.01 ± 59.41

Basal a b b b b b b b b b b b a a ab b a

3.30 ± 0.31 29.22 ± 1.71 7.83 ± 0.48 0.157 ± 0.009 37.21 ± 2.13 5.07 ± 0.54 5.45 ± 0.28 16.27 ± 1.70 23.61 ± 1.22 0.354 ± 0.024 45.70 ± 3.11 0.073 ± 0.003 278.17 ± 28.70 347.98 ± 29.20 3.38 ± 0.12 1.11 ± 0.48 630.66 ± 58.85

b c c c c c c c c b c b b b b a b

Different letters in rows denote significant differences in individual phenolic compounds among different cluster sections (p<0.05). Mean ± standard errors are presented. Bold characterized letters in rows denote significant differences in Sum of single phenolic group among different cluster sections.

Table 4 Content of phenolic compounds (mg per 100 fresh berries) in different cluster sections of red currant cv. ‘Rovada’. Cluster section Apical catechin Procyanidins Total flavanols Derivatives of caffeic acid Derivatives of p-coumaric acid Total hydroxycinnamic acids Kaempferol glycosides Myricetin glycosides Quercetin glycosides Total flavonols Apigenin glycosides Total anthocyanins

1.05 ± 0.10 0.767 ± 0.064 1.82 ± 0.14 0.622 ± 0.060 0.775 ± 0.089 1.39 ± 0.14 0.313 ± 0.031 0.081 ± 0.008 1.34 ± 0.15 1.74 ± 0.18 0.119 ± 0.014 11.76 ± 1.22

Medial a a a a a a a a a a a a

1.10 ± 0.11 0.678 ± 0.071 1.78 ± 0.18 0.593 ± 0.063 0.824 ± 0.106 1.42 ± 0.16 0.232 ± 0.024 0.061 ± 0.007 1.03 ± 0.14 1.33 ± 0.17 0.097 ± 0.012 13.97 ± 0.85

Basal a a a a a a a a a a a a

2.11 ± 0.14 1.315 ± 0.102 3.42 ± 0.23 1.097 ± 0.079 1.761 ± 0.105 2.85 ± 0.17 0.507 ± 0.057 0.149 ± 0.013 2.43 ± 0.31 3.08 ± 0.37 0.220 ± 0.028 22.99 ± 2.55

b b b b b b b b b b b b

Different letters in rows denote significant differences in individual phenolic compounds among different cluster sections (p<0.05). Mean ± standard errors are presented. Bold characterized letters in rows denote significant differences in Sum of single phenolic group among different cluster sections.

Table 5 Content of phenolic compounds (mg per 100 fresh berries) in different cluster sections of white currant cv. ‘Blanka’. Cluster section Apical catechin Procyanidins Total flavanols Derivatives of caffeic acid Derivatives of p-coumaric acid Total hydroxycinnamic acids Kaempferol glycosides Myricetin glycosides Quercetin glycosides Total flavonols

1.07 ± 0.07 0.605 ± 0.035 1.62 ± 0.10 0.89 ± 0.04 0.62 ± 0.02 1.64 ± 0.07 0.226 ± 0.018 0.038 ± 0.002 2.22 ± 0.28 2.49 ± 0.28

Medial a a a a a a a a a a

1.41 ± 0.09 0.850 ± 0.061 2.26 ± 0.15 1.28 ± 0.08 0.92 ± 0.06 2.36 ± 0.14 0.341 ± 0.017 0.059 ± 0.002 2.64 ± 0.31 3.04 ± 0.31

Basal b b b b b b b b a a

1.56 ± 0.07 0.887 ± 0.039 2.44 ± 0.11 1.42 ± 0.05 1.05 ± 0.05 2.61 ± 0.11 0.322 ± 0.021 0.041 ± 0.003 5.11 ± 0.40 5.47 ± 0.42

b b b b b b b a b b

Different letters in rows denote significant differences in individual phenolic compounds among different cluster sections (p < 0.05). Mean ± standard errors are presented. Bold characterized letters in rows denote significant differences in Sum of single phenolic group among different cluster sections.

the cultivars analysed. Currants contained from 1.62 to 3.42 mg total flavanols per 100 berries and the position within the cluster affected the accumulation of flavanols. The content of this phenolic group was 50–80% higher in berries from the basal cluster section as opposed to berries positioned at the apical part of the cluster. Numerous hydroxycinnamic acids (HCA) have been determined in currant berries: two p-coumaroylhexoses and two

caffeoylhexoses were identified in all cultivars. ‘Tsema’ additionally accumulated neochlorogenic acid and 3-p-caffeoylquinic acid. Neochlorogenic acid represented 35% of total hydroxycinnamic acids (TAH) in black currant fruit, which were also abundant in derivatives of caffeic acid (40% TAH) and derivatives of p-coumaric acid (approx. 25% TAH). Feruloylhexose represented approximately 0.5% TAH (results not shown) in all analysed cultivars. Similar lev-

194

M. Mikulic-Petkovsek et al. / Scientia Horticulturae 210 (2016) 188–196

els of caffeic and p-coumaric acid derivatives were detected in red and white currants. Black currant berries from the medial cluster section accumulated 40% more HCA in comparison with those at apical positions. However, 50% higher HCA levels were recorded in berries at basal part, compared to the medial section (Table 3). The pattern was similar in white currants; however, only 10% increase in HCA levels has been measured between medial and basal cluster sections (Table 5). Contrary, no significant differences in HCA content levels have been determined between berries from apical and medial parts of the cluster in red currants (Table 4). The differences in individual phenolic compound accumulation along the cluster were also reflected in the levels of total phenolics (TPC). TPC of berries from the basal cluster section was significantly higher in red and white currants compared to total phenolics measured in the medial and apical part of the cluster. Moreover, TPC of black currant berries differed significantly among the three analysed cluster sections. Berries from the medial section were characterized by 56% higher TPC compared to berries from the apical section and berries from the basal section accumulated 38% more total phenolics compared to berries from the medial cluster section.

4. Discussion Fruit quality may be affected by several factors such as genotype, fruit maturity and different external factors (Mikulic-Petkovsek et al., 2013). In the present analysis, currant clusters were collected before the parameters of apical berries reached the values measured in basal berries. With the progression of ripening along the entire cluster basal berries would eventually lose their quality (gloss, colour, firmness). Over ripening also depends on the weather conditions during the final stages of berry fruit maturation. Fruit size (determined as berry weight) is the most important trait of currants intended for fresh consumption (Sasnauskas et al., 2012). The results of the study suggest that berries positioned at the basal part of the cluster develop significantly larger mass compared to berries from the apical cluster section. This may be related to the fact that berries located at the basal cluster section develop from flowers, which bloom earlier. The time of currant flowering mainly depends on weather conditions and generally, currant flowers in basal part of the cluster open 3–10 days earlier than flowers at apical positions. Consequently, berries located in basal cluster sections start to develop and accumulate assimilates sooner (and for a prolonged time) compared to berries in apical positions. Moreover, the number of berries at the basal part of the cluster is usually smaller than at its apical sections (Table 1). Proietti et al. (2006) reported that fruit size depends on the availability of photoassimilates, which is in tight connection with fruit load. Similarly, negative correlation between fruit mass and the number of fruits has been recorded in apricots (Roussos et al., 2011). Firmness is frequently utilized for prediction of fruit maturity. Data analysis in the present study did not detect any differences in berry firmness among individual positions in the cluster. This indicates comparable maturity stage among the sampled berries. Chroma is a measure of colour intensity of the sample and ranges from dull grey to intense colour (McGuire, 1992). Slight differences in the parameter C* have been measured among the analyzed cluster sections, but as they were not significant visual differences in color of the berries cannot be confirmed. Glucose and fructose were the major sugars in Ribes fruits, while sucrose only represented approx. 3% total sugars as previously reported by Famiani et al. (2005). The presence and abundancy of sugars in plants have been linked to the expression of different genes (Gonzali et al., 2006). Sugars may act as signal molecules and their function is similar to that of hormones (Rolland et al., 2006).

From our results it is evident that berries positioned in the basal part of the cluster contained from 1.6 to 2.1 fold higher total sugar levels compared to berries at the apical cluster section (Table 2). Similar results have been observed in the content of organic acids as white and red currant berries positioned at the basal cluster section contained 20% higher total organic acid levels than berries at apical positions. A positive relationship between sugars and organic acids was previously observed in kiwifruit (Famiani et al., 2012). Moreover, 80% higher total organic acid levels have been determined in black currant berries from the basal cluster section in comparison with berries located at apical sections. Sugars and organic acids ratio are greatly responsible for the taste of the fruit (Kafkas et al., 2007; Famiani et al., 2015). As a result berries located in basal cluster sections were sweeter since they were characterized by a higher sugar/organic acids ratio (Table 2). It is well-known that fruit thinning can alter the source/sink balance of plants (Pastore et al., 2011; Zhuang et al., 2014). Apples with little or no crop decrease the rate of photosynthesis as they retain the accumulation of carbohydrates in leaves (Veberic et al., 2002). The content of primary metabolites was significantly higher in larger berries near the stem and a similar pattern has been observed for vitamin C levels. The latter is formed from glucose and berries located in the basal part of the cluster contained 40–50% more vitamin C than berries in apical cluster sections. One of the reasons for low contents of primary metabolites in berries located in apical cluster sections may be an increased number of smaller berries produced in the apical part of the cluster. Therefore, assimilates have to be distributed among a greater number of sinks. Correspondingly, Milivojevic et al. (2012) measured higher levels of sugars and organic acids in currant fruits in the first experimental year compared to the second year of the experiment when bushes developed more fruit clusters and consequently, more berries. Correspondingly, sugar and organic acid contents were negatively related to fruit load of kiwi (Famiani et al., 2012). It has been determined that the level of assimilates in Ribes berries depends primarily on the position of berries in the cluster. The berries in the basal part of the cluster are the first sinks for assimilates transported from nearby leaves. The remaining assimilates are then relocated over the length of the cluster and finally accumulated in berries in the lowest cluster section. The sink activity of berries is physiologically determined and thus affected by different parameters and enzymes in carbohydrate metabolism and their accumulation (Lemoine et al., 2013). As mentioned earlier, berries from the basal part of the cluster develop first and are therefore characterized by extended period of assimilate accumulation compared to other berries along the cluster. Similarly, Gouthu et al. (2014) determined a significant correlation between grape maturity stages within the cluster and relative sink activity of the berries depending on their size, availability of assimilates as well as metabolic (photosynthetic) activity. The content of phenolic compounds was significantly higher in berries positioned at the basal part of the cluster. These berries contained from 1.6 to 2.2 fold higher levels of hydroxycinnamic acids, from 1.5 to 1.8 fold more flavanols and from 1.7 to 2.2 more flavonols compared to berries situated in the apical part of the cluster. Significant differences in anthocyanin levels have also been determined among the positions of berries in the cluster. Anthocyanins belonging to the group of flavonoids were the predominant phenolics in black and red currant fruit. Black currants contained from 223.14 to 630.66 mg of total anthocyanins per 100 berries and red currants from 11.76 to 22.99 mg of total anthocyanins per 100 berries. Anthocyanins were not identified in white currants. Red currant berries positioned at the basal part of the cluster accumulated almost twofold levels of anthocyanins compared to berries positioned at the apical cluster section. The differences were even greater in black currants since the berries in

M. Mikulic-Petkovsek et al. / Scientia Horticulturae 210 (2016) 188–196

195

and are used for fresh consumption. The results indicate that berries positioned at the basal part of the cluster contain significantly more sugars, organic acids, vitamin C, and phenolic compounds in comparison with the berries positioned at its bottom. Considering that consumers favour currant cultivars with intensely coloured, aromatic and larger berries evenly distributed over the entire length of the cluster, it would be necessary to introduce adequate techniques (pruning, training system, thinning of cluster,. . .) for the regulation of quantity and quality of yield in the production of currants for fresh consumption. In further investigations various measures influencing the production of larger berries shall be tested on several currant cultivars.

Acknowledgements The research was supported by Research programmes P4-00130481 Horticulture from the Slovenian Research Agency (ARRS). Fig. 2. The content of total phenolics (mg GAE per 100 fresh berries) in different cluster sections of white (‘Blanka’), red (‘Rovada’) and black (‘Tsema’) currants. Different letters denote significant differences in analyzed parameters among different cluster sections for each individual currant cultivar (p < 0.05). Mean ± standard errors are presented (for interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

the basal part of the cluster contained 2.8 fold more anthocyanins than berries at its apical part. Higher contents of anthocyanins in berries located in the basal part of the cluster may be related to their higher sugar levels. It has namely been reported that sugars can modulate genes involved in anthocyanin biosynthesis (Zheng et al., 2009). Similarly, higher contents of all analysed polyphenols in berries located in the basal cluster section are probably related to their higher levels of primary metabolites. It is wellknown that primary metabolites are the substrates affecting the synthesis of secondary metabolites. Sugar transporters, cell wall invertases and sugar-degrading enzymes modulate several molecular activities which regulate the sink strength, and their actions can be dynamically changed throughout berry growth (Balibrea et al., 2003). A similar pattern as in our study was demonstrated in grape berries, which accumulated increased levels of anthocyanins, flavonols and flavanols when plants were subjected to various thinning treatments (Avizcuri-Inac et al., 2013). Berries positioned at the basal part of the currant cluster are considered the first sinks for photosynthetic assimilates produced in the leaves and are their most intensive consumers. Therefore, it may be concluded that berries positioned at apical cluster sections secure a smaller quantity of assimilates which are then distributed to numerous berries. Consequently, decreased synthesis of phenolic compounds is characteristic for berries in apical parts of the cluster. The results are in accordance with the reports on grapes, in which the berries from the tips of the grape cluster (apical part of cluster) contain 11% less anthocyanins and 1.6% less flavonols in comparison with berries from the shoulders (basal part of the cluster) (FigueiredoGonzalez et al., 2012). Total phenolic content of red currant berries positioned at the basal parts of the cluster was 30% higher than in the berries positioned at the bottom of the cluster (Fig. 2). In white currants 50% higher TPC was recorded between basal and apical part of the cluster and in black currants berries located in the basal part of the cluster were characterized by 2.2 fold higher TPC compared to berries positioned at the apical part of the cluster. 5. Conclusion The analysed ‘Blanka’, ‘Rovada’ and ‘Tsema’ cultivars were deliberately chosen for the investigation as they all develop long clusters

References Avizcuri-Inac, J.M., Gonzalo-Diago, A., Sanz-Asensio, J., Martinez-Soria, M.T., Lopez-Alonso, M., Dizy-Soto, M., Echavarri-Granado, J.F., Vaquero-Fernandez, L., Fernandez-Zurbano, P., 2013. Effect of cluster thinning and prohexadione calcium applications on phenolic composition and sensory properties of red wines. J. Agric. Food Chem. 61, 1124–1137. Balibrea, M.E., Cuartero, J., Bolarin, M.C., Perez-Alfocea, F., 2003. Sucrolytic activities during fruit development of Lycopersicon genotypes differing in tolerance to salinity. Physiol. Plant. 118, 38–46. Bishayee, A., Mbimba, T., Thoppil, R.J., Haznagy-Radnai, E., Sipos, P., Darvesh, A.S., Folkesson, H.G., Hohmann, J., 2011. Anthocyanin-rich black currant (Ribes nigrum L:) extract affords chemoprevention against diethylnitrosamine-induced hepatocellular carcinogenesis in rats. J. Nutr. Biochem. 22, 1035–1046. FAOSTAT, 2016. Food and Agriculture Organization of the United Nations http://faostat3fao.org/home/E. Famiani, F., Cultrera, N.G.M., Battistelli, A., Casulli, V., Proietti, P., Standardi, A., Chen, Z.H., Leegood, R.C., Walker, R.P., 2005. Phosphoenolpyruvate carboxykinase and its potential role in the catabolism of organic acids in the flesh of soft fruit during ripening. J. Exp. Bot. 56, 2959–2969. Famiani, F., Baldicchi, A., Farinelli, D., Cruz-Castillo, J.G., Marocchi, F., Mastroleo, M., Moscatello, S., Proietti, S., Battistelli, A., 2012. Yield affects qualitative kiwifruit characteristics and dry matter content may be an indicator of both quality and storability. Sci. Hortic. 146, 124–130. Famiani, F., Battistelli, A., Moscatello, S., Cruz-Castillo, J.G., Walker, R.P., 2015. The organic acids that are accumulated in the flesh of fruits: occurrence, metabolism and factors affecting their contents − a review. Rev. Chapingo Ser. Hortic. 21, 97–128. Figueiredo-Gonzalez, M., Simal-Gandara, J., Boso, S., Martinez, M.C., Santiago, J.L., Cancho-Grande, B., 2012. Anthocyanins and flavonols berries from Vitis vinifera L: cv. Brancellao separately collected from two different positions within the cluster. Food Chem. 135, 47–56. Flores, P., Hellin, P., Fenoll, J., 2012. Determination of organic acids in fruits and vegetables by liquid chromatography with tandem–mass spectrometry. Food Chem. 132, 1049–1054. Folmer, F., Basavaraju, U., Jaspars, M., Hold, G., El-Omar, E., Dicato, M., Diederich, M., 2014. Anticancer effects of bioactive berry compounds. Phytochem. Rev. 13, 295–322. Gonzali, S., Loreti, E., Solfanelli, C., Novi, G., Alpi, A., Perata, P., 2006. Identification of sugar-modulated genes and evidence for in vivo sugar sensing in Arabidopsis. J. Plant Res. 119, 115–123. Gouthu, S., O’Neil, S.T., Di, Y.M., Ansarolia, M., Megraw, M., Deluc, L.G., 2014. A comparative study of ripening among berries of the grape cluster reveals an altered transcriptional programme and enhanced ripening rate in delayed berries. J. Exp. Bot. 65, 5889–5902. Jakobek, L., Seruga, M., Novak, I., Medvidovic-Kosanovic, M., 2007. Flavonols, phenolic acids and antioxidant activity of some red fruits. Deut. Lebensm. Rundsch. 103, 369–378. Kafkas, E., Kosar, M., Paydas, S., Kafkas, S., Baser, K.H.C., 2007. Quality characteristics of strawberry genotypes at different maturation stages. Food Chem. 100, 1229–1236. Laaksonen, O.A., Saiminen, J.P., Makila, L., Kallio, H.P., Yang, B.R., 2015. Proanthocyanidins and their contribution to sensory attributes of black currant juices. J. Agric. Food Chem. 63, 5373–5380. Lemoine, R., La Camera, S., Atanassova, R., Deedaldeechamp, F., Allario, T., Pourtau, N., Bonnemain, J.L., Laloi, M., Coutos-Theevenot, P., Maurousset, L., Faucher, M., Girousse, C., Lemonnier, P., Parrilla, J., Durand, M., 2013. Source-to-sink transport of sugar and regulation by environmental factors. Front. Plant Sci. 4, 272.

196

M. Mikulic-Petkovsek et al. / Scientia Horticulturae 210 (2016) 188–196

Maatta, K., Kamal-Eldin, A., Torronen, R., 2001. Phenolic compounds in berries of black, red, green, and white currants (Ribes sp.). Antioxid. Redox Signal. 3, 981–993. McGuire, R.G., 1992. Reporting of objective color measurements. Hortscience 27, 1254–1255. Mikulic-Petkovsek, M., Schmitzer, V., Slatnar, A., Stampar, F., Veberic, R., 2012a. Composition of sugars, organic acids, and total phenolics in 25 wild or cultivated berry species. J. Food Sci. 77, C1064–C1070. Mikulic-Petkovsek, M., Slatnar, A., Stampar, F., Veberic, R., 2012b. HPLC-MSn identification and quantification of flavonol glycosides in 28 wild and cultivated berry species. Food Chem. 135, 2138–2146. Mikulic-Petkovsek, M., Slatnar, A., Schmitzer, V., Stampar, F., Veberic, R., Koron, D., 2013. Chemical profile of black currant fruit modified by different degree of infection with black currant leaf spot. Sci. Hortic. 150, 399–409. Mikulic-Petkovsek, M., Ivancic, A., Todorovic, B., Veberic, R., Stampar, F., 2015. Fruit phenolic composition of different elderberry species and hybrids. J. Food Sci. 80, C2180–C2190. Milivojevic, J., Slatnar, A., Mikulic-Petkovsek, M., Stampar, F., Nikolic, M., Veberic, R., 2012. The influence of early yield on the accumulation of major taste and health related compounds in black and red currant cultivars (Ribes spp.). J. Agric. Food Chem. 60, 2682–2691. Mitic, M.N., Obradovic, M.V., Kostic, D.A., Naskovic, D.C., Micic, R.J., 2011. Phenolics content and antioxidant capacity of commercial red fruit juices. Hem. Ind. 65, 611–619. Pastore, C., Zenoni, S., Tornielli, G.B., Allegro, G., Dal Santo, S., Valentini, G., Intrieri, C., Pezzotti, M., Filippetti, I., 2011. Increasing the source/sink ratio in Vitis vinifera (cv Sangiovese) induces extensive transcriptome reprogramming and modifies berry ripening. BMC Genomics 12. Proietti, P., Nasini, L., Famiani, F., 2006. Effect of different leaf-to-fruit ratios on photosynthesis and fruit growth in olive (Olea europaea L.). Photosynthetica 44, 275–285. Rolland, F., Baena-Gonzalez, E., Sheen, J., 2006. Sugar sensing and signaling in plants: conserved and novel mechanisms. Annu. Rev. Plant Biol., 675–709. Roussos, P.A., Sefferou, V., Denaxa, N.K., Tsantili, E., Stathis, V., 2011. Apricot (Prunus armeniaca L:) fruit quality attributes and phytochemicals under different crop load. Sci. Hortic 129, 472–478.

Rubinskiene, M., Viskelis, P., Jasutiene, I., Viskeliene, R., Bobinas, C., 2005. Impact of various factors on the composition and stability of black currant anthocyanins. Food Res. Int. 38, 867–871. ˇ 2012. Evaluation of Sasnauskas, A., Siksnianas, T., Stanys, V., Bobinas, C., agronomical characters of blackcurrant cultivars and selections in Lithuania. Acta Hortic. 946, 189–194. Savikin, K., Zdunic, G., Jankovic, T., Tasic, S., Menkovic, N., Stevic, T., Dordevic, B., 2009. Phenolic content and radical scavenging capacity of berries and related jams from certificated area in Serbia. Plant Food Hum. Nutr. 64, 212–217. Savikin, K., Zdunic, G., Jankovic, T., Godevac, D., Stanojkovic, T., Pljevljakusic, D., 2014. Berry fruit teas: phenolic composition and cytotoxic activity. Food Res. Int. 62, 677–683. Singleton, V.L., Orthofer, R., Lamuela-Raventos, R.M., 1999. Analysis of total phenols and other oxidation substrates and antioxidants by means of Folin-Ciocalteu reagent. In: Packer, L. (Ed.), Oxidants and Antioxidants, Pt A. Elsevier Academic Press Inc, San Diego, pp. 152–178. Szajdek, A., Borowska, E.J., 2008. Bioactive compounds and health-promoting properties of berry fruits: a review. Plant Food Hum. Nutr. 63, 147–156. Veberic, R., Stampar, F., Vodnik, D., 2002. Autumn photosynthesis of ‘Golden Delicious’ apple trees − the effects of picking and fertilisation treatment. Gartenbauwissenschaft 67, 92–98. Wang, S.Y., Zheng, W., Galletta, G.J., 2002. Cultural system affects fruit quality and antioxidant capacity in strawberries. J. Agric. Food Chem. 50, 6534–6542. Wojdylo, A., Oszmianski, J., Milczarek, M., Wietrzyk, J., 2013. Phenolic profile: antioxidant and antiproliferative activity of black and red currants (Ribes spp.) from organic and conventional cultivation. Int. J. Food Sci. Technol. 48, 715–726. Zheng, Y.J., Tian, L., Liu, H.T., Pan, Q.H., Zhan, J.C., Huang, W.D., 2009. Sugars induce anthocyanin accumulation and flavanone 3-hydroxylase expression in grape berries. Plant Growth Regul. 58, 251–260. Zhuang, S.J., Tozzini, L., Green, A., Acimovic, D., Howell, G.S., Castellarin, S.D., Sabbatini, P., 2014. Impact of cluster thinning and basal leaf removal on fruit quality of Cabernet Franc (Vitis vinifera L.) grapevines grown in cool climate conditions. Hortscience 49, 750–756.