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1、Anthocyanins and fruit colour in plums (Prunus domestica L.) during ripeningUniversity of Ljubljana, Biotechnical Faculty, Agronomy Department, Chair for Fruit Growing, Jamnikarjeva 101, Ljubljana, SloveniaAbstract；The accumulation of anthocyanins and the evolution of fruit colour were investigated
2、during ripening of Prunus domestica L. Using HPLC, the fruit of the Jojo, Valor, Cacanska rodna and Cacanska najbolja cul-tivars were quantied for anthocyanins during a 25-day period of ripening (a 33-day period in the case ofJojo). The major anthocyanin was cyanidin 3-rutinoside which, in ripe frui
3、ts, ranged from 4.1 to 23.4 mg/100 g FW (from 52.6% to 73.0%). It was followed by peonidin 3-rutinoside (from 6.5% to 37.9%), cyanidin3-glucoside (from 1.8% to 18.4%), cyanidin 3-xyloside (from 4.7% to 7.8%) and peonidin 3-glucoside (from0.0% to 0.4%). The ripening process resulted in a concentratio
4、n increase of total anthocyanins and changed the ratios amongst the anthocyanins. The colour parameters, L*, a*, b*, chroma and hue angle, of partially ripe plums were higher than those in the ripe fruit, but the CIRG index of partially ripe fruit was always lower than that of ripe fruit. The total
5、anthocyanins were weakly correlated with each of the colour parameters; their relationships varied between cultivars and ripening stage. Correlation coefcients between individual anthocyanins and colour parameters in ripe plums were cultivar-dependent.2008 Elsevier Ltd. All rights reserved.1. Introd
6、uction Anthocyanins represent a group of widespread natural phenolic compounds in plants, and are responsible for their colours (Mazza & Miniati, 1993). Colour is the most important indicator of matu-rity and quality in many fruit species (Drake, Proebsting, & Spayd,1982). It is mainly inuenced by t
7、he concentration and distribution of various anthocyanins in the skin (Gao & Mazza, 1995), as well as by other factors, such as light, temperature, ethylene, and cultural practices (Lancaster, Lister, Reay, & Trigs, 1997). The inuence of ripeness on the accumulation of anthocyanins and on the evolut
8、ion of colour has been analysed in sweet cherries (Gonalves et al.,2007) and grapes (Ryan & Revilla, 2003). The chromatic parame-ters, L*, a*, b*, chroma and hue angle, correlated negatively with the total anthocyanin levels in sweet cherry (Gonalves et al.,2007). The total levels of anthocyanin are
9、 higher in ripe sweet cherries than in partially ripe ones (Gonalves et al., 2004).Plums are the most numerous and diverse group of fruit tree species (Blazek, 2007), but the amount of research data does not reect this abundance. The literature on research into anthocyanincomposition in European (Pr
10、unus domestica L.) plums is limited. More data are available for P. salicina plums. Cyanidin 3-glucoside, cyanidin 3-rutinoside, cyanidin 3-galactoside and cyanidin 3-acet-yl-glucoside were detected in plum cultivars (P. salicina) Ange-leno, Black Beaut, Santa Rosa, Red Beaut and Wickson(Toms-Barber
11、n et al., 2001). In two plum cultivars, Sugar andPresident, Piga, del Caro, and Corda (2003) identied cyanidin3-glucoside, cyanidin 3-rutinoside and an unidentied antho-cyanin compound. Five anthocyanins were identied in plumssampled directly from the US market (cyanidin 3-galactoside,cyanidin 3-glu
12、coside, cyanidin 3-rutinoside, cyanidin 3-xyloside and cyanidin 3-(600 -acetoyl) glucoside (Wu & Prior, 2005).The aim of our study was to analyse the inuence of ripeness on the accumulation of anthocyanins in European plum (P. domestica L.) and to nd correlations between anthocyanin composition and
13、colour measurements.2. Material and methods2.1. Plant material Fruit of the Jojo, Valor, Cacanska rodna and Cacanska najbol-ja plum cultivars (P. domestica L.), grafted on rootstock Myrobolan( P. cerasifera Ehrh.), were collected in 2006 from the 4-year-old experimental orchard of the Agricultural I
14、nstitute Slovenia. The planting density was 4 m 2.5 m. The year 2006 was comparable to a long-term average regarding the temperature and bright sun-shine duration. Only August was slightly cooler and with less sun- shine compared to the long-term period. All other months were slightly warmer and wit
15、h more sunshine. Since the fruits devel-oped typical cultivar coloration, it is assumed, that the weather conditions in the ripening period were favourable for development of the colour. Ten samples of fruit were randomly selected at each sampling date from the same tree. The fruit were picked at ve
16、 dif-ferent times (Valor, Cacanska rodna and Cacanska najbolja) or at six different times (Jojo) at six- to eight-day intervals during mat-uration (date 1 (t1): 17th of August, date 2 (t2): 23rd of August,date 3 (t3): 29th of August, date 4 (t4): 4th of September, date 5(t5): 11th of September and d
17、ate 6 (t6): 19th of September) in 2006. The number of days elapsed from t1 to t2 is 6, from t1 to t3, 12 days, from t1 to t4, 18 days, from t1 to t5, 25 days and from t1 to t6, 33 days. The last picking date of each cultivar coincided with fruit drop. For each time and cultivar, four plums were rand
18、omly selected amongst the 10 for skin colour measurements and anthocyanin concentration measurements on HPLC. After colour measurements,samples were packed in plastic bags, frozen and kept at 20 C un-til the extraction. Anthocyanins were analysed from the whole edi-ble part of fruit. For each cultiv
19、ar, four repetitions were carried out(n = 4); each repetition included one fruit. Data for colour measure-ment and anthocyanin concentration were obtained from the same fruit.2.2. Extraction and HPLC analysis of anthocyanins. Samples were prepared according to the method described by Escarpa and Gon
20、zalez (2000): 5 g of sample were extracted with 25 ml of MeOH containing 1% HCl and 1% 2.6-di-tert-butyl-4-meth-ylphenol (BHT) using an ultrasonic bath. An HPLC analysis was per-formed using a Surveyor HPLC system and a diode array detector,controlled by a CromQuest 4.0 chromatography workstation so
21、ft-ware system (Thermo Finnigan, San Jose, CA). The anthocyanins were analysed at 530 nm. The column used was a Phenomenex Gemini C18 (150 4.6 mm 3 micron), operated at 25 C. The elu-tion solvents were aqueous 0.01 M phosphoric acid (A) and 100%methanol (B). The samples were eluted according to the
22、linear gra-dient described by Escarpa and Gonzalez (2000). The injection amount was 20 ll, and the ow rate was 1 ml/min. Anthocyanins in the plum extracts were identied by HPLC/MS (LCQ Deca XP MAX, Thermo Finnigan). The concentrations of the anthocyanins identied, namely, cyanidin 3-glucoside (cy 3-
23、glucoside), cyanidin 3-rutinoside (cy 3-rutinoside) and peonidin 3-glucoside (peo 3-glucoside), were assessed from the peak areas and expressed in mg per 100 g of fresh weight (FW). The concentrations of the cyani-din 3-xyloside (cy 3-xyloside) were calculated as equivalents of cyanidin 3-glucoside
24、(CGE) and peonidin 3-rutinoside (peo 3-ruti-noside) as equivalents of cyanidin-3-rutinoside (CRE). The sum of anthocyanins was calculated from the values of individual anthocyanins.2.3. Colour analyses The skin colour variables were measured on four fruit samples immediately after picking. The CIELA
25、B colour system (Commission Internationale de lEclairage, 1986) is extensively used to evaluate food colour. Fruit colour was measured with a Konica Minolta CR-10 Chroma Meter (Minolta, Japan) on the site opposite the fruit su-ture. Values L*, a*, b*, chroma (C*) and hue angle (h) were measured to d
26、escribe the colour of the plums. Also, the CIRG index (CIRG),based on the CIELAB values, on the parameters L* (lightness), h (hue angle) and C* (chroma), was calculated: (180h)/(L* + C*). Hvalues between 360 and 270 were considered as negative (e.g.346 was taken as 14) (Carreo, Martnez, Almela, & Fe
27、rnn-dez-Lpez, 1995).2.4. Statistical analysis Statistical analysis was conducted with the programme Stat-graphics Plus 4.0 (Statgraphics, Herndon, VA). One-way ANOVA was used for analysis of the effect of ripening on anthocyanin con-centration and colour parameters. Differences between sampling date
28、s were estimated with the Duncan test (p 0.05). Linear regression was performed between anthocyanin concentrationand colour parameters. The relationships were tested at p 6 0.05.3. Results and discussion3.1. Anthocyanin content of plums The HPLC chromatograms of plum extracts obtained at 530 nm reve
29、aled four peaks (Fig. 1), which corresponded to the ve antho-cyanins: cyanidin 3-xyloside (peak 1), cyanidin 3-glucoside (peak1), cyanidin 3-rutinoside (peak 2), peonidin 3-glucoside (peak 3),and peonidin 3-rutinoside (peak 4). Five anthocyanins were identi-ed. Wu and Prior (2005) also found ve anth
30、ocyanins, while Toms-Barbern et al. (2001) found four anthocyanins in P. salicina.Toms-Barbern et al. (2001) did not identify any peonidin deriva-tive. Piga et al. (2003) found three anthocyanins in the President(P. domestica) cultivar.3.2. Inuence of ripeness on skin colour There were signicant dif
31、ferences in colour parameters L*, a*,b*, C, h and CIRG between the four cultivars and at different ripe-ness stages. The chromatic characteristics of the fruit of four culti-vars during ripening are shown in Table 2. The chroma and hue angle of partially ripe plums were always higher than those in t
32、he ripe fruit of all cultivars, as has previously been reported forsweet cherries (Gonalves et al., 2007), but the CIRG index of par-tially ripe fruits was always lower than that of ripe fruits. A de-crease in chroma means an increase in the tonality of the fruitcolour (Gonalves et al., 2007). The r
33、esults show a signicant inu-ence of cultivar on CIRG. The highest CIRG was measured Cacanska najbolja and the lowest in Cacanska rodna. Cacanskarodna is the least highly coloured cultivar amongst these cultivars. The different correlation coefcients between individual antho-cyanins and colour parame
34、ters obtained for different cultivars of ripe fruits mean that the evolution of colour is cultivar-dependent(Table 3). The variation in the anthocyanin levels in different sweet cherry cultivars induces variation in the degree of correlation be-tween total anthocyanins and colour parameters (Gonalve
35、set al., 2007). Our results do not conrm the ndings of McGuire(1992) and Gonalves et al. (2007) that better correlation between hue angle and chroma and pigment concentrations could be ob-tained than when pigment concentrations were compared directly with the values of L*, a* and b*. Only in Valor w
36、ere parameters L* and b* correlated in a statis-tically signicantly manner with cyanidin 3-glucoside, cyanidin3-rutinoside and peonidin 3-rutinoside (p 0.05). At the last sam-pling date, the concentrations of mentioned anthocyanins were also the highest, resulting in the lowest value in the negative
37、 range of parameter b* that indicates blue colour of the fruits. Since antho-cyanin was not strongly correlated with at least one chromatic parameter in all four differently coloured plum cultivars, we can-not decide which anthocyanin or group of anthocyanins is respon-sible for the typical colour o
38、f each plum cultivar. Although not signicant, amongst these cultivars, a* was the most strongl A wide range of variability between plum cultivars (P. domestica L.) in their concentrations of anthocyanins and chromatic parame-ters at fruit maturity also exist during fruit ripening. The ripening proce
39、ss resulted in increased concentrations of anthocyanins,which darkens plums, and in changed relationships between indi-vidual anthocyanins. With plum cultivars, the levels of total and individual anthocyanins were weakly correlated (mainly not statis-tically signicant) with colour parameters.Acknowledgement This work is part of the programme Horticulture No. P4-0013-0481, granted by the Slovenian Ministry of Higher Education, Sci-ence and Technology.
