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Article

Effect of Postharvest Ripening on the Phytochemical Composition and Antioxidant Properties of Fruits from Ten Plum (Prunus domestica L.) Cultivars

by
Monika Mieszczakowska-Frąc
*,
Niall John Dickinson
and
Dorota Konopacka
Fruit and Vegetable Storage and Processing Department, The National Institute of Horticultural Research, Konstytucji 3 Maja 1/3, 96-100 Skierniewice, Poland
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(6), 1351; https://doi.org/10.3390/agronomy15061351
Submission received: 3 May 2025 / Revised: 28 May 2025 / Accepted: 29 May 2025 / Published: 30 May 2025
(This article belongs to the Section Horticultural and Floricultural Crops)
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Abstract

The purpose of this study was to determine the effect of postharvest ripening on the concentration of phenolic compounds and antioxidant activity in fruits of ten plum cultivars. The degree of ripeness was defined as the CIRG index, based on the CIE Lab color values and ranging from 1.05 to 10.04, soluble solids (12.9 to 20.7%), and firmness (4.47 to 13.64 N). Fruits were analyzed directly after harvest and after 3 and 6 days of storage at 18 °C. The CIRG index increased by 2% to 23% after 3 days of storage, and by as much as 64% after 6 days, depending on the cultivar. Ripening resulted in increased concentration of phenolic compounds and in higher antioxidant activity. The predominant compounds in the majority of the cultivars were proanthocyanidins, which constituted over 50% of the total polyphenols, at concentrations between 30 and 453 mg 100 g−1 FW. Additionally, postharvest ripening caused the proanthocyanidins to increase up to 76%. The polymerization of proanthocyanidins ranged from 6.6 to 20.0. For some cultivars, the concentration of anthocyanins approximately doubled after 6 days of fruit storage. Fruits of ‘Čačanska Najbolja’ and ‘Čačanska Lepotica’ were characterized by the highest concentration of bioactive compounds and the highest antioxidant activity.

1. Introduction

Plum (Prunus domestica L.) is one of the most popular species of fruit grown in Europe. According to the Food and Agriculture Organization of the United Nations (FAO), plums and sloes had the 10th largest production quantity for fruit in 2023 within the EU, 1.5 m tons, for which Poland was the 5th largest contributor within the bloc at over 127,000 tons of production, with an estimated value of over $78 million [1]. The same organization found plums to have been dedicated the 5th largest area of cultivation of fruit, over 157,000 hectares, within the EU. Plums are highly regarded for their taste and dietary value and are usually consumed as fresh fruit or after drying as prune-type plums [2], though they can also be used to prepare preserves such as jams and chutneys. The nutritional composition of plums has been widely reported and reviewed in the literature [3,4,5,6,7,8,9]. Plums contain simple carbohydrates such as glucose, fructose, sucrose, and sorbitol, organic acids, such as malic and citric acid, fibre in the form of pectins, minerals such as potassium, calcium, magnesium, and phosphorus, and vitamins A, B1, B2, and C [3,10]. Plums also contain high concentrations of boron, which may play a significant role in the prevention of osteoporosis [11]. They also contain significant amounts of polyphenolic compounds [12,13], such as anthocyanin compounds with antioxidant properties, which are known to promote good health through the sequestration of free radicals and reactive oxygen species (ROS) [14,15]. Exposure to free radicals and ROS is linked to an increased risk in the development of cancer [16], atherosclerosis and other inflammatory diseases [17], heart disease and stroke [18,19], and neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease [20,21,22]. While plums are rich in carbohydrates, their consumption does not result in a significant increase in blood glucose or insulin levels after consumption [4] due to their high fiber content, and are therefore a suitable sweet snack for diabetics. The high levels of dietary fibre, as well as the sorbitol contained in plums, help in the regulation of bowel functions [3]. Indeed, the European Food Safety Authority (EFSA) approved a health claim for dried plums of ‘prune’ cultivars related to their maintenance of normal bowel function (Commission Regulation (EU) 536/2013 of 11 June 2013 [23]). Plum consumption has also been linked to the lowering of serum cholesterol [24,25].
Several studies have shown that red fruits, such as plums, have health-promoting properties [26,27,28,29,30] because of high concentrations of antioxidants, such as phenolic compounds [31,32,33], which are secondary plant metabolites. Some studies have revealed that plums exhibit one of the highest antioxidant activities among fruit species [34,35]. Moreover, the phenolic compounds present in plums are reported to have antimicrobial [36,37], anti-inflammatory [37,38], anti-obesity, and anticardiovascular disease properties [39,40]. However, the information on plum antioxidants gathered so far is not sufficient for EFSA to grant fresh plums a health claim on their beneficial physiological effects.
The phenolic compounds occurring in plums include mainly hydroxycinnamic acids, such as neochlorogenic acid, chlorogenic acid, and anthocyanins (cyanidin-3-rutinoside, cyanidin-3-glucoside, and peonidin-3-rutinoside [31,41,42]), as well as proanthocyanidins [27,43]. The composition of phenolic phytochemicals found in the fruit is affected by fruit maturity [44], cultivar [45], horticultural practices [46], and geographic origin [47,48]. Phenolic compounds contribute greatly to the sensory quality of fresh fruit, e.g., due to their astringency [49,50]. Despite the health benefits of plums, their consumption in the fresh state remains low compared to other fruits, often due to problems with uneven ripening on the tree [51] and cold storage injury [52]. This has led to the publishing of a consumer quality index to facilitate optimal harvesting with a view to increasing global consumption [53]. Some of the parameters indicating fruit maturity include soluble solids concentration (SSC) [54], acidity (TA) [55], and the SSC:TA ratio [56]. However, their utility depends on the cultivar, geographic area, and season [57]. The skin color of plums is one of the most important criteria of ripeness [54]. Usenik et al. [58] reported that the CIRG index, based on color measurements, is a very useful indicator for estimating fruit ripeness. According to Crisosto and Kader [59], fresh plums in California are picked based on color when at least 50% of the fruit surface is red or purple. Fresh plums can be stored under optimal conditions (−1.1 to 0 °C) for 2 to 5 weeks, depending on the cultivar [60]. For most cultivars, the optimal temperature for ripening is up to 20 °C, and plums are known to develop more color after a few days of storage at this temperature [61].
There is scant information in the literature on how short-term storage at a moderately high temperature may influence the degree of ripeness and the levels of antioxidants in plums. The purpose of this study was to determine the effect of the degree of fruit ripeness after harvest on the concentration and composition of phenolic compounds and on the antioxidant activity in the fruit of ten plum cultivars under the market storage conditions.

2. Materials and Methods

2.1. Fruit Material

Fruits of ten plum cultivars were studied, nine with red-purple or dark blue skin, ‘Diana’, ‘Węgierka Dąbrowicka’, ‘Čačanska Lepotica’, ‘Haganta’, ‘Valjevka’, ‘Węgierka Zwykła’, ‘Jojo’, ‘Amers’, and ‘Čačanska Najbolja’, and one with yellow skin, ‘Żółta Afaska’.
Plums were grown at the Experimental Orchard of the National Institute of Horticultural Research in Skierniewice, Poland, at harvest maturity (at least 50% of the fruit surface exhibited coloration characteristic of the respective cultivar), as recommended by [60]. The fruits of each cultivar were divided into three batches: freshly harvested plums (0 days of storage), and those designated for 3 and 6 days of storage at 18 °C (simulation of market conditions). Samples containing 25 randomly selected fruits from each cultivar and batch were used for measurements of skin color, soluble solids content, and firmness. Additionally, after each storage period, about 1 kg of plums (perfectly healthy) were washed (after removing stems), drained, and frozen at −25 °C. To prepare for the analyses, plums were hand-pitted using a ceramic knife and disintegrated in the frozen state. The disintegrated samples were used for the determination of the concentrations of phenolic compounds and levels of antioxidant activity, performed in triplicate.

2.2. Chemicals

All HPLC solvents were gradient grade (Mallinckrodt Baker Ltd., Deventer, The Netherlands). ABTS (2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt) and Trolox ((±)-6-hydroxy-2,5,7,8-tetra-methylchromane-2-carboxylic acid) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Standards of phenolic compounds were purchased from Extrasynthèse (Genay Cedex, France).

2.3. Measurements

2.3.1. Fruit Ripeness Determination

Fruit ripeness was estimated with the CIRG index based on the CIE Lab color values using the following parameters: L*—lightness, h—hue angle, and C*—chroma. Fruit color was measured on two sides of each fruit using a CM-2600d hand-held colorimeter (Konica Minolta Sensing Inc., Tokyo, Japan). The ripeness index was calculated according to Equation (1) [62]:
CIRG = (180 − h)/(L* + C*)
where h values between 360° and 270° were considered as negative (e.g., 346° was taken as −14°).
In addition, the following indicators of ripeness were measured: soluble solids concentration (SSC), evaluated with a RE50 refractometer (Mettler-Toledo, Tokyo, Japan) at 20 °C, and reported as percentage; and firmness (F), measured by puncture test using an Instron machine, model 4303 (Instron Ltd., High Wycombe, UK) equipped with a 500 N load cell and a 3.2 mm Magness-Tylor probe at 50 mm min−1 cross-head speed. Firmness measurements were carried out on a side surface at the largest fruit diameter. Results are expressed in Newtons (N) as the force needed to puncture the skin of the fruit.

2.3.2. Extraction and HPLC Analyses of Phenolic Compounds

Samples for HPLC analyses were prepared as follows: frozen plum samples were lyophilized and homogenized in an IKA A11 grinder (IKA-Werke, Staufen, Germany) using liquid nitrogen to afford a homogenous powdered sample. The 100 mg of lyophilized material was extracted with 1200 µL of 1% formic acid in 60% methanol using an ultrasonic water bath for 20 min. Centrifugation of the resulting solutions (3000× g; 10 min) and filtration of the supernatant (0.45 µm PTFE filter) afforded the samples for HPLC analysis.
The procedure for the HPLC analysis of phenolic compounds was as described by [63], with some modifications. The analysis was performed with an Agilent HPLC Model HP 1200 (Agilent Technologies, Waldbronn, Germany) equipped with a DAD Detector (Diode Array Detector). Separation was achieved using a Synergi 4 µm Fusion-RP 80 Å, LC Column 250 mm × 4.6 mm (Phenomenex, Torrance, CA, USA). HPLC method parameters were as follows: mobile phase A (5% aq. Formic acid) and mobile phase B (acetonitrile), flow rate—1 mL min−1. Gradient program: 0–5 min, isocratic 3% B; 5–32 min, 10% B; 32–54 min, 33% B; 54–58 min, 90% B; 58–62 min, isocratic 90% B. A post-run program of 15 min was used to re-equilibrate the column to 3% mobile phase B. The detection wavelengths were as follows: 280 nm (flavan-3-ols), 360 nm (flavonols), 320 nm (phenolic acids), and 520 nm (anthocyanins). The column thermostat temperature was −25 °C. The injection volume was 5 µL. Phenolic compounds were quantified by calibration with the standards of catechin, quercetin-3-rutinoside, chlorogenic acid, cyanidin-3-glucoside, peonidin-3-rutinoside, and cyanidin-3-rutinoside, and expressed in mg 100 g−1 FW (fresh weight).

2.3.3. Extraction and HPLC Analyses of Proanthocyanidins

Quantification of proanthocyanidins was performed as described by [64], using phloroglucinol as a trapping reagent. A 800 µL volume of a methanolic solution containing phloroglucinol (75 g·L−1) with L-ascorbic acid (15 g·L−1) and a second solution of 0.3 N hydrochloric acid in anhydrous methanol in the volume of 400 µL were added to an accurately weighed sample (approx. 100 mg) of freeze-dried powdered plum sample and mixed. The sample was incubated at 50 °C for 30 min in a water bath. A total of 700 µL of the sample and 700 µL of 0.2 M buffered sodium acetate solution were mixed to terminate the trapping. The sample was then centrifuged for 7 min (3000× g), and filtration of the supernatant (0.45 µm PTFE filter) afforded the samples for HPLC analysis. HPLC separation was performed as described in Section 2.3.2 above. Concentration of proanthocyanidins was quantified according to the catechin standard curve and expressed in mg 100 g−1 FW. Equation (2) was used to calculate the average degree of polymerization (DPn) of proanthocyanidins.
DPn = (Σ extension subunit + Σ terminal subunit)/(Σ terminal subunit)

2.3.4. Antioxidant Activity Measurement

A total of 10 g of plum (frozen, ground material) was suspended in 50 mL of 70% aq. methanol and then homogenized for 2 min. Then, gravity filtration (Whatman No. 3 filter paper) afforded the filtrate.
Free-radical scavenging activity was determined as described by [65], using ABTS●+ radical cation, and the detailed measurement procedure was according to [66]. An ABTS●+ solution (5 mL) was added to the filtrate (500 µL), mixed, and stored in the dark at room temperature (6 min). Absorbance at 734 nm (Cary 3000 Bio UV-Visible spectrophotometer, Varian, Las Vegas, NV, USA) was measured for each sample. A minimum of four measurements at different concentrations were made to reduce the initial absorbance of the ABTS●+ solution in the range 20% to 80%. A linear regression method was applied to calculate the concentration of the sample, resulting in a 50% decrease in the absorbance of the ABTS●+ solution, and expressed as Trolox equivalents in mg per g FW.

2.4. Statistical Analysis

The results were subjected to analysis of variance (ANOVA) using STATISTICA 13.1 (Dell Inc., Tulsa, OK, USA, StatSoft Polska, Kraków, Poland). The one-way analysis was applied for parameters of fruit ripeness, and the content of phenolic components and antioxidant activity were subjected to two-way statistical analysis. The significance of the differences between storage periods and cultivars was estimated with Tukey’s HSD test at p = 0.05.

3. Results and Discussion

3.1. Fruit Ripeness

The values of the index for the 10 plum cultivars after postharvest storage (ripening) at 18 °C are shown in Table 1. The CIRG index for the yellow-skinned cultivar, ‘Żółta Afaska’, was 1.05 at harvest and increased to 1.15 after 6 days of storage. The lowest CIRG index among the investigated red-purple or dark blue plum cultivars immediately after harvest was recorded for ‘Amers’ (3.68), and the highest for ‘Čačanska Najbolja’ (8.77). The other cultivars were characterized by CIRG values between 5.27 and 7.12. This range is in agreement with the data presented by [67]. The CIRG index increased significantly after 6 days of storage, except for two cultivars: ‘Haganta’ and ‘Węgierka Zwykła’. The greatest increase (by about 64%) in the color index was observed for ‘Amers’, followed by ‘Čačanska Lepotica’ (43%), ‘Węgierka Dąbrowicka’ (38%), and ‘Diana’ (32%). It may be concluded that the changes in color were highly dependent on cultivar characteristics but were not related to the initial value of the CIRG index. A similar conclusion was drawn by [68] with respect to Japanese-type plums.
On the harvest day, soluble solids content (SSC) of the fruit varied from 12.9% for ‘Čačanska Lepotica’ to 20.7% for ‘Węgierka Zwykła’ (Table 1). According to [69], early-season plum cultivars are characterized by lower fruit SSC than the late-season ones, which was confirmed by the results of the present study. Fruit of early cultivars, ‘Diana’ and ‘Čačanska Lepotica’, contained the lowest concentration of soluble solids (13%), while late cultivars, ‘Haganta’, ‘Valjevka’, and ‘Węgierka Zwykła’, were characterized by the highest SSC, above 19%. This parameter increased significantly during postharvest storage, except for two cultivars, ‘Węgierka Zwykła’ and ‘Żółta Afaska’, which exhibited a statistically non-significant increase of SSC during storage at 18 °C.
There were significant changes in firmness during plum storage, with the exception of cultivar ‘Węgierka Zwykła’. According to Valero et al. [70], plums with firmness lower than 13 N are more accepted by consumers, and therefore, fruits of such firmness are classified as “ready to eat”. In our study, the highest firmness on the harvest day was 13.6 N for ‘Valjevka’, suggesting that fruits of all tested cultivars were harvested at consumer maturity state. The lowest firmness (4.47 N at harvest and 2.56 N after 6 days of storage) was recorded for fruit from ‘Diana’, which is a common dessert plum cultivar. Firmness decreased quite rapidly during fruit storage. The largest decrease in firmness after 6 days of storage was found for cultivars ‘Čačanska Lepotica’ (4.5-fold), ‘Węgierka Dąbrowicka’ (3.8-fold), and ‘Čačanska Najbolja’ (3.3-fold). For most cultivars (with the exception of ‘Węgierka Zwykła’), it was observed that with storage time, the CIGR index increases and, simultaneously, the plum firmness decreases. However, an increase in the CIGR index was at the same time associated with an increase in soluble solids.

3.2. Proanthocyanidins

The phenolic composition and the concentration of total phenols, as determined by HPLC, are shown in Table 2. The predominant compounds quantified in plums, irrespective of cultivar and storage period, were proanthocyanidins (PAnt), which in most cases constituted over 50% of total polyphenols, as reported by [41]. The highest proanthocyanidin concentrations were found in two cultivars: ‘Čačanska Najbolja’ (328 to 453 mg 100 g−1 FW) and ‘Čačanska Lepotica’ (233 to 259 mg 100 g−1 FW), whereas the lowest were found in ‘Amers’ (30 to 52 mg 100 g−1 FW). The concentration of PAnt in the other cultivars ranged from 49 to 102 mg 100 g−1 FW. Therefore, it may be concluded that the concentration of PAnt strongly depends on the plum cultivar. Nunes et al. [58] also reported a wide range of concentrations of PAnt in plums: 88 to 320 mg 100 g−1 FW. According to [27], the average PAnt concentration in plums is 215.9 ± 50.7 mg 100 g−1 FW, which means that plums are one of the best sources of proanthocyanidins among fruit species. The differences between cultivars are significant from the point of view of flavor because proanthocyanidins are responsible for the astringency of plums [31]. The degree of fruit ripeness had a significant effect on the concentration of PAnt, but there was no consistent trend during postharvest ripening. In most of the investigated cultivars, the process of ripening at 18 °C resulted in an increase in PAnt concentration, except for ‘Valjevka’ and ‘Żółta Afaska’, which, after 3 days of storage, contained less PAnt than directly after harvest. For five cultivars (‘Węgierka Dąbrowicka’, ‘Haganta’, ‘Węgierka Zwykła’, ‘Jojo’, and ‘Čačanska Najbolja’), the higher increase in PAnt concentration was observed after 3 days of storage rather than after 6 days.
The process of the postharvest ripening, for a few plum cultivars, caused a significant increase in PAnt concentration compared to fruit at harvest day: 76% more after 6 days for ‘Amers’, and 34–38% more for ‘Węgierka Zwykła’, ‘Żółta Afaska’, and ‘Čačanska Najbolja’. The statistical analysis suggests that the degree of ripeness did not have a significant effect on the degree of polymerization (DPn) of PAnt (p = 0.9961). This parameter depended primarily on the plum cultivar. Proanthocyanidins with the lowest DPn (6.6 to 8.1) were found in the fruit of the cultivars ‘Diana’, ‘Jojo’, and ‘Amers’, whereas the highest DPn (around 20) was determined for ‘Čačanska Lepotica’ (Table 3). The remaining cultivars contained proanthocyanidin chains consisting of at least 10 to 14 units. Prior and Gu [27] reported that the average DPn for plum, determined by thiolysis, was 7.2. The large variations in PAnt polymerization occurring in the flesh and skin of plums (DPn of 4.5 to 8.5 and 4.0 to 5.8, respectively) were recorded by [58]. The authors also observed a high impact of the origin on the degree of PAnt polymerization in plum. By comparison, one of the most commonly consumed fruits, such as apples, contains proanthocyanidins with a degree of polymerization of 5 to 7 [71].
From among monomers of flavan-3-ols, only catechin was identified in the investigated plum cultivars (Table 2). Additionally, ‘Węgierka Dąbrowicka’, ‘Čačanska Lepotica’, ‘Jojo’, and ‘Čačanska Najbolja’ contained dimers of flavan-3-ols. The concentrations of the monomers and dimers of flavan-3-ols were not dependent on the degree of fruit ripeness.

3.3. Phenolic Acids and Flavonols

The next dominant class of phenolic compounds identified in plums was hydroxycinnamic acid derivatives, mainly neochlorogenic acid [72]. The highest concentration of neochlorogenic acid was detected in ‘Jojo’ (50.3 to 55.4 mg 100 g−1 FW) and ‘Čačanska Najbolja’ (39.8 to 55.5 mg 100 g−1 FW). The found values of neochlorogenic acid are comparable to those reported by [41], which, depending on the cultivar, ranged from trace amounts to 52.2 mg 100 g−1 FW. Fruits of all cultivars (except for ‘Valjevka’) also contained chlorogenic acid, but at a concentration lower than neochlorogenic acid, as well as other hydroxycinnamic acid derivatives (Table 2). The trend of lower concentration of chlorogenic acid with respect to neochlorogenic acid was also observed by [8,41], who also reported a similar ratio of chlorogenic acid to neochlorogenic acid for plum fruits, specifically for the cultivar ‘Čačanska Lepotica’. Postharvest ripening mainly affected neochlorogenic acid, causing both increasing and decreasing concentrations during storage, depending on the plum cultivar.
Concentrations of glycosides of quercetin in plums varied from 2 to 10 mg 100 g−1 FW, depending on the cultivar. These values are significantly higher than those reported by [73] in their analysis of six Norwegian plum cultivars (0.14–1.06 mg 100 g−1 FW). During postharvest storage, concentrations of quercetin glycosides changed slightly, mostly not statistically significantly.

3.4. Anthocyanins

HPLC chromatograms at 520 nm revealed that the plums contained four different anthocyanins: cyanidin-3-glucoside, cyanidin-3-rutinoside (the predominant one), peonidin-3-glucoside, and peonidin-3-rutinoside (Table 2). These results correspond with those of [7,8,31,74]. In their investigations on the impact of rootstock on the chemical characteristics of the variety ‘Čačanska Lepotica’, [8] reported findings which generally match ours. For cyanidin-3-rutinoside (8.5–14.5 mg 100 g−1 FW) and peonidin-3-rutinoside (2.0–3.2 mg 100 g−1 FW), good agreement was seen (0.4 fold and 2.5 fold higher, respectively, for mean values for our values), while for cyanidin-3-glucoside (4.9–16.9 mg 100 g−1 FW) and peonidin-3-glucoside (0.6–1.6 mg 100 g−1 FW), the values we report are significantly higher (6.3 fold and 5.0 fold higher, respectively, for mean values for our values). As can be seen from our results, fruit maturity can significantly affect the chemical composition of fruits. The anthocyanins concentration increased during postharvest ripening (Figure 1); however, for ‘Haganta’, ‘Węgierka Zwykła’, and ‘Jojo’, the changes were not statistically significant. Miletić et al. [75] proved that there is a significant correlation between anthocyanin concentration in plum and maturity stage (on-tree ripening). The strongest effect of plum ripening on the concentration of anthocyanins (cyanidin-3-glucoside, cyanidin-3-rutinoside, and peonidin-3-rutinoside) was observed for ‘Diana’ after 3 days of storage, and for ‘Amers’ after 6 days of storage at 18 °C. Compared to the concentrations on the harvest day, the greatest increase in cyanidin-3-glucoside was about 2.4 and 4.3 times after 3 and 6 days of storage, respectively. In cyanidin-3-rutinoside, the increase was 1.8 and 2.7 times after 3 and 6 days, respectively, and in peonidin-3-rutinoside, it was 1.4 and 2.5 times after 3 and 6 days, respectively. In the case of peonidin-3-glucoside, the greatest increase was observed for ‘Čačanska Lepotica’ after 3 and 6 days of storage.
Plums of ‘Čačanska Najbolja’ and ‘Valjevka’ were the richest in anthocyanins, at 69.5 mg 100 g−1 FW and 50.8 mg 100 g−1 FW, respectively, after 6 days of storage (Figure 1). On the other hand, the lowest concentrations were found for the following cultivars: ‘Węgierka Zwykła’, ‘Amers’, and ‘Haganta’. The early plum cultivars like ‘Diana’, ‘Węgierka Dąbrowicka’, and ‘Čačanska Lepotica’ revealed very high increases in anthocyanins concentration after 6 days of postharvest ripening, with values of 108%, 133%, and 128%, respectively. The experiment showed that the CIRG index for plum fruit should be at least 6 for ‘Diana’, ‘Amers’, ‘Čačanska Lepotica’, and ‘Haganta’; above 7 for ‘Węgierka Dąbrowicka’, ‘Valjevka’, and ‘Jojo’; and at least 9 for ‘Čačanska Najbolja’, considering the high concentration of anthocyanins. There was a positive correlation between the CIRG index and anthocyanin concentration (R2 = 0.663, Figure 2A).

3.5. Antioxidant Activities

The fruit of tested cultivars differed considerably in antioxidant activity. The highest scavenging properties (ABTS●+ method) were exhibited by two cultivars: ‘Čačanska Najbolja’ (4.27 to 5.87 mg Trolox g−1 FW) and ‘Čačanska Lepotica’ (2.09 to 2.58 mg Trolox g−1 FW) (Table 4). Trendafolova et al. [8] reported ‘Čačanska Lepotica’ cultivar to have a value of 0.88–0.92 mg Trolox g−1, which is quite close to our observations. These two cultivars were also characterized by presenting the highest concentrations of polyphenols. The level of antioxidant activity in ‘Čačanska Najbolja’ coincided with the data presented by [76], who reported 22 µM Trolox g−1 (equivalent of 5.51 mg Trolox g−1 FW). Our results confirmed a strong correlation between the concentration of total polyphenols and antioxidant activity (R2 = 0.9183, Figure 2B). The yellow-skinned cultivar ‘Żółta Afaska’ was characterized by the lowest antioxidant activity (0.53 to 0.61 mg Trolox g−1 FW), whereas the ABTS●+ activity of the remaining seven cultivars was in the range 0.72 to 1.83 mg Trolox g−1 FW.
The degree of ripeness did not exhibit a linear relationship with the scavenging properties of plum fruits on harvest day. During storage at 18 °C, the ABTS●+ activity decreased about 15% to 19% (‘Čačanska Lepotica’), remained unchanged (‘Valjevka’, ‘Węgierka Zwykła’, and ‘Żółta Afaska’), or increased in a range from 16% to 101% (the remaining cultivars) with increasing fruit maturity.

3.6. Total Bioactive Compounds

The data obtained indicate that fruit storage at 18 °C for 3 days resulted in an increase in the concentration of total polyphenols (Table 2). The changes were accompanied by a concurrent increase in anthocyanins and proanthocyanins. In the majority of cases, the longer storage at 18 °C (up to 6 days) did not cause any further increase in the concentration of polyphenol compounds. The lowest concentrations of total polyphenols (67.7 to 116.6 mg 100 g−1 FW) were detected for ‘Amers’, whereas the highest (437.3 to 599.8 mg 100 g−1 FW) were detected for ‘Čačanska Najbolja’.
At harvest, the ‘Amers’ cultivar was characterized by presenting the lowest CIRG index and the lowest concentration of phenolic compounds. After 6 days of postharvest ripening, this cultivar exhibited the highest increase in the CIRG index and a high decrease in firmness. This resulted in the greatest increase of phenolic compounds (proanthocyanins and anthocyanins, especially) and antioxidant activity. On the other hand, the fruit from the ‘Čačanska Najbolja’ cultivar possessed the highest CIRG index and the highest polyphenols concentration at harvest day, but their firmness and soluble solids changed significantly during 6 days of storage and a very high increase in phenolic compounds concentration was also observed after 6 days of postharvest ripening. The late plum cultivars (‘Valjevka’, ‘Węgierka Zwykła’, and ‘Haganta’) demonstrated the lowest alteration of ripeness indexes, and at the same time, postharvest ripening had the lowest impact on their phenolic compounds concentration in comparison to the other studied plum cultivars. Díaz-Mula et al. [68] also observed a significant increase in total phenolic concentration in eight plum cultivars after 35 days of cold storage +4 days at 20 °C, as well as progressive increases of total polyphenols in eight plum cultivars throughout the ripening process on-tree [77]. Meanwhile, [10] saw significant increases in total phenolic content, antioxidant activity, and radical scavenging in autumn fruiting varieties upon cold storage (4 °C for 10 days) compared to fresh material analysis, but the same observations were not seen in summer fruiting varieties; in fact, small decreases in these metrics were observed upon cold storage for summer fruiting plums.

4. Conclusions

The results showed a significant effect of the degree of plum ripeness on the concentration of phenolic compounds. For most cultivars, fruit ripening during 6 days of storage at 18 °C resulted in a statistically significant increase in the CIRG index and polyphenol concentration (up to 76% more for proanthocyanidins and 133% for anthocyanins), as well as in higher antioxidant activity. The strongest impact of ripeness degree on phenolic compounds was observed for plums belonging to early and medium season cultivars. There were significant differences among the tested cultivars in terms of the concentration of phenolic compounds in fruit. The highest concentration of proanthocyanidins was found in ‘Čačanska Najbolja’ and ‘Čačanska Lepotica’, which also exhibited the highest antioxidant activities. The most abundant in anthocyanins were the cultivars ‘Čačanska Najbolja’ and ‘Valjevka’. Plums more advanced in ripening can have higher concentrations of phenolic compounds and higher antioxidant activity, besides being more visually attractive to the consumer. Short-term storage of plums (up to 3 days) at 18 °C does not have a detrimental effect on their quality.

Author Contributions

Conceptualization, M.M.-F.; methodology, M.M.-F. and D.K.; validation, M.M.-F.; formal analysis, M.M.-F. and D.K.; investigation, M.M.-F. and D.K.; resources, M.M.-F.; data curation, M.M.-F. and D.K.; writing—original draft preparation, M.M.-F. and N.J.D.; writing—review and editing, M.M.-F., N.J.D. and D.K.; visualization, M.M.-F. and N.J.D.; supervision, M.M.-F.; project administration, M.M.-F.; funding acquisition, M.M.-F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was carried out within the IUVENTUS PLUS Project (0263/P01/2010/70) funded by the Polish Ministry of Science and Higher Education.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors thank the staff of the Fruit and Vegetable Storage and Processing Department for their assistance.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agronomy 15 01351 g001
Figure 1. Total anthocyanin concentration (means with standard deviations) in the fruit of 10 plum cultivars stored for 0, 3, or 6 days at 18 °C. Columns marked by the same letter do not differ significantly at p = 0.05 (two-way ANOVA); * in statistical analysis means the factor is statistically significant.
Figure 1. Total anthocyanin concentration (means with standard deviations) in the fruit of 10 plum cultivars stored for 0, 3, or 6 days at 18 °C. Columns marked by the same letter do not differ significantly at p = 0.05 (two-way ANOVA); * in statistical analysis means the factor is statistically significant.
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Agronomy 15 01351 g002
Figure 2. Scatter plots for correlation between CIRG index and anthocyanidins content (A) and between polyphenols content and antioxidant activities (B) for plums during storage time (0, 3, and 6 days).
Figure 2. Scatter plots for correlation between CIRG index and anthocyanidins content (A) and between polyphenols content and antioxidant activities (B) for plums during storage time (0, 3, and 6 days).
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Table 1. Parameters of fruit ripeness: CIRG index, soluble solids concentration (SSC), and firmness (F) in the fruit of 10 plum cultivars stored at 18 °C.
Table 1. Parameters of fruit ripeness: CIRG index, soluble solids concentration (SSC), and firmness (F) in the fruit of 10 plum cultivars stored at 18 °C.
CultivarCIRGSSC (%)F (N)
Storage PeriodStorage PeriodStorage Period
0 Days3 Days6 Days0 Days3 Days6 Days0 Days3 Days6 Days
‘Diana’5.27 a6.42 b6.97 c13.0 a13.9 b13.9 b4.47 c3.74 b2.56 a
‘Węgierka Dąbrowicka’5.67 a6.99 b7.84 c13.8 a16.4 b18.0 c11.78 c5.49 b3.09 a
‘Čačanska Lepotica’6.08 a7.26 b8.72 c12.9 a13.8 ab13.9 b7.62 c3.77 b1.70 a
‘Haganta’5.95 a6.09 a6.41 a19.9 a20.3 b22.5 b10.44 c9.11 ab8.02 a
‘Valjevka’6.89 a7.48 ab7.72 b20.1 a21.9 b22.5 b13.64 c11.20 b8.51 a
‘Węgierka Zwykła’6.52 a6.88 a6.91 a20.7 a21.4 a21.7 a7.37 a8.79 a7.62 a
‘Jojo’7.12 a7.51 ab7.94 b16.2 a16.9 ab18.1 b11.02 b10.08 b7.96 a
‘Amers’3.68 a4.44 a6.03 b13.0 a13.5 a15.2 b8.59 b7.78 b4.62 a
‘Čačanska Najbolja’8.77 a9.18 a10.04 b15.1 a16.6 b18.9 c10.85 c7.95 b3.26 a
‘Żółta Afaska’1.05 a1.11 ab1.15 b14.9 a14.9 a15.7 a12.16 b10.69 b7.45 a
Means in the same line (within one parameter) marked by the same letter do not differ significantly at p = 0.05 (one-way ANOVA).
Table 2. Concentration (mg 100 g−1 FW) of phenolic compounds in the fruit of 10 plum cultivars stored for 0, 3, and 6 days at 18 °C.
Table 2. Concentration (mg 100 g−1 FW) of phenolic compounds in the fruit of 10 plum cultivars stored for 0, 3, and 6 days at 18 °C.
CultivarDays of StorageFlavan-3-olsPhenolic AcidsQuercetin GlycosideAnthocyaninsTotal Phenolics
CatDimPAntNeoChChloOtherC-glC-rP-glP-r
‘Diana’00.51 defn.d 73.8 efg4.31 a3.32 de3.75 d6.09 fg2.61 de7.06 bc0.30 cd1.58 cdef103.3 ± 4.3 de
30.54 defn.d91.7 ij6.63 ab5.21 g5.19 ghi6.31 ghi6.28 hi13.0 efgh0.49 eh2.23 fghi137.6 ± 2.3 hi
60.45 den.d91.3 ij6.44 ab4.84 fg5.39 hij6.09 fgh6.89 i14.1 fgh0.56 ijk2.50 ghij138.5 ± 3.4 hij
‘Węgierka Dabrowicka’00.34 bcd1.39 bc 81.5 ghi20.4 i3.00 d4.00 de5.27 def4.88 gh 11.9 efg0.27 bc0.56 ab133.5 ± 7.1 gh
30.32 bcd2.03 de101.8 j23.5 j3.26 de4.47 ef5.76 efh8.93 j18.7 i0.33 d0.75 b169.8 ± 5.1 m
60.14 abc1.73 cd 85.7 ghi20.5 i3.14 d3.56 cd7.78 jk12.8 l26.8 kl0.43 efh1.06 bcd163.7 ± 0.2 lm
‘Čačanska Lepotica’00.35 bce2.67 f233.3 k30.6 mn4.63 fg 5.54 hij3.95 bc4.88 gh8.5 cd0.61 kl2.00 efg296.9 ± 0.5 n
30.32 bcd2.29 ef256.5 l31.4 n5.22 g5.92 j4.92 de10.9 k 12.7 efgh1.00 o2.50 ghj333.7 ± 6.4 o
60.11 abc1.17 b258.6 l26.0 jk4.07 ef5.70 ij 6.24 fghi16.9 n14.5 fgh1.64 p3.17 k338.2 ± 5.3 o
‘Haganta’00.12 abcn.d 83.7 ghi27.6 kl2.97 d8.10 l7.88 jk2.57 de8.4 cd0.34 d0.96 bc142.6 ± 5.3 hijk
30.12 abcn.d90.7 ij 29.1 lmn3.34 de8.41 lm8.34 k3.51 efg10.5 de0.34 d1.07 bcd155.4 ± 2.7 jklm
60.10 abn.d88.0 hi 28.6 klm3.21 d8.15 l8.01 k3.57 efg10.7 de0.33 d1.19 bcd152.0 ± 2.7 ijl
‘Valjevka’0n.dn.d53.6 bc 9.88 cden.d3.50 cd5.93 fg3.23 def24.7 jk0.53 hij7.18 m108.6 ± 4.2 e
3n.dn.d49.4 b 7.90 bcdn.d 3.43 bcd6.61 hi4.42 fg28.5 l0.65 lm8.01 n108.9 ± 6.0 e
6n.dn.d57.8 b-d11.5 en.d3.66 d7.08 ij4.69 g35.6 n0.68 m9.87 o130.9 ± 5.2 fgh
‘Węgierka Zwykła’0n.dn.d58.2 bcd10.4 de1.55 bc2.61 a 5.86 efgh0.84 ab4.08 b0.46 ef 2.68 hijk86.7 ± 5.0 bcd
3n.dn.d77.9 fgh12.2 ef1.57 bc2.71 a5.95 fgh1.04 abc4.90 b 0.50 fghi3.13 jk109.9 ± 2.7 e
6n.dn.d65.1 cde7.49 bc1.61 bc2.83 ab 5.89 efgh0.81 ab4.00 b0.48 efh2.78 ijk91.0 ± 2.0 cd
‘Jojo’00.62 ef1.80 cd51.9 b55.4 r3.66 de 8.45 lm5.61 efg2.32 cde12.4 efh0.46 efg4.64 l147.2 ± 4.4 hijkl
3 0.58 def1.90 de 60.6 bcd53.2 r3.61 de9.18 n6.64 hi2.48 de15.0 h 0.48 efgh5.21 l158.9 ± 6.2 klm
6 0.34 bcde1.96 de53.2 bc50.3 p3.44 d 8.74 lmn 6.22 fghi1.99 bcd11.9 ef0.52 ghi6.68 m145.2 ± 3.5 hijk
‘Amers’0 0.30 bcdn.d29.7 a19.0 hi1.80 bc4.67 fg4.52 cd0.71 ab5.65 bc0.21 b1.20 bcd67.7 ± 3.4 a
3 0.38 cden.d36.7 a16.5 gh1.53 bc4.88 fgh3.88 bc0.56 a6.64 bc0.22 b1.67 def73.0 ± 0.9 ab
60.73 fn.d52.4 b 28.4 klm2.05 c5.90 j 5.75 efgh3.04 def15.0 gh0.43 e3.00 jk116.6 ± 1.6 efg
‘Čačanska Najbolja’01.99 g6.22 g327.8 m39.8 o10.1 h7.18 k 6.50 ghi12.2 kl23.5 j0.54 hij1.55 cde437.3 ± 7.1 p
32.84 h7.42 i452.8 o55.5 r15.0 i 8.56 lmn7.81 jk14.8 m31.9 m0.59 jkl 2.08 efgh599.4 ± 1.6 r
63.12 i6.91 h432.0 n54.1 r15.1 i 8.83 mn10.2 l23.9 o41.9 o0.83 n2.78 ijk599.8 ± 6.7 r
‘Żółta Afaska’0n.dn.d68.3 def6.80 ab1.28 bc2.56 a2.25 an.dn.dn.dn.d81.2 ± 1.8 abc
3n.dn.d56.9 bcd6.31 ab1.13 b2.56 a2.27 an.dn.dn.dn.d69.1 ± 0.4 a
6n.dn.d93.5 ij14.6 fg2.02 c2.97 abc3.12 abn.dn.dn.dn.d116.2 ± 1.0 ef
p-valueCv.0.0000.0000.0000.0000.0000.0000.0000.0000.0000.0000.0000.000
St.0.0000.0000.0000.0000.0000.0000.0000.0000.0000.0000.0000.000
Cv. × St.0.0000.0000.0000.0000.0000.0000.0000.0000.0000.0000.0000.000
Means in the column marked by the same letter do not differ significantly at p = 0.05; n.d = not detected. Cat = catechin, Dim = dimer of flavan-3-ols, PAnt = proanthocyanidin, NeoCh = neochlorogenic acid, Chlo = chlorogenic acid, C-gl = cyanidin-3-glucoside, C-r = cyanidin-3-rutinoside, P-gl = peonidin-3-glucoside, P-r = peonidin-3-rutinoside. Statistical parameters: Cv.—cultivar factor, St.—storage duration factor, Cv. × St.—cultivar × storage duration interaction (two-way ANOVA).
Table 3. Degree of polymerization of PAnt in the fruit of 10 plum cultivars stored at 18 °C.
Table 3. Degree of polymerization of PAnt in the fruit of 10 plum cultivars stored at 18 °C.
CultivarStorage Period
0 Days3 Days6 Days
‘Diana’7.5 a7.2 a7.5 a
‘Węgierka Dąbrowicka’9.9 b10.0 b10.0 b
‘Čačanska Lepotica’19.6 i19.7 i20.8 i
‘Haganta’12.0 cde12.1 cdef10.9 bcd
‘Valjevka’13.8 gh12.4 cdefg14.4 h
‘Węgierka Zwykła’13.0 efh13.8 gh13.8 fgh
‘Jojo’7.0 a7.1 a8.1 a
‘Amers’6.6 a6.9 a7.3 a
‘Čačanska Najbolja’10.8 bc10.8 bc10.0 b
‘Żółta Afaska’12.3 cdefg12.5 defg9.9 b
Means marked by the same letter do not differ significantly at p = 0.05 (two-way ANOVA). Statistical analysis: cultivar * (p < 0.05); storage (-) (p = 0.996); cultivar × storage * (p < 0.05).
Table 4. Antioxidant activity (mg Trolox g−1 FW) in the fruit of 10 plum cultivars stored at 18 °C (ABTS●+ method).
Table 4. Antioxidant activity (mg Trolox g−1 FW) in the fruit of 10 plum cultivars stored at 18 °C (ABTS●+ method).
Cultivars Period of Storage
0 Days 3 Days 6 Days
‘Diana’0.72 ab1.01 cd1.45 fg
‘Węgierka Dąbrowicka’0.86 bc1.00 cd1.14 de
‘Čačanska Lepotica’2.58 k2.09 j2.20 j
‘Haganta’1.46 fg1.60 gh1.70 hi
‘Valjevka’1.30 ef1.42 fg1.48 fg
‘Węgierka Zwykła’1.18 de1.29 ef1.17 de
‘Jojo’1.43 fg1.77 hi1.83 i
‘Amers’0.88 bc0.87 bc1.08 d
‘Čačanska Najbolja’4.27 l4.74 m5.87 n
‘Żółta Afaska’0.58 a0.53 a0.61 a
Means marked by the same letter do not differ significantly at p = 0.05 (two-way ANOVA). Statistical analysis: cultivar * (p < 0.05); storage * (p < 0.05); cultivar × storage * (p < 0.05).
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Mieszczakowska-Frąc, M.; Dickinson, N.J.; Konopacka, D. Effect of Postharvest Ripening on the Phytochemical Composition and Antioxidant Properties of Fruits from Ten Plum (Prunus domestica L.) Cultivars. Agronomy 2025, 15, 1351. https://doi.org/10.3390/agronomy15061351

AMA Style

Mieszczakowska-Frąc M, Dickinson NJ, Konopacka D. Effect of Postharvest Ripening on the Phytochemical Composition and Antioxidant Properties of Fruits from Ten Plum (Prunus domestica L.) Cultivars. Agronomy. 2025; 15(6):1351. https://doi.org/10.3390/agronomy15061351

Chicago/Turabian Style

Mieszczakowska-Frąc, Monika, Niall John Dickinson, and Dorota Konopacka. 2025. "Effect of Postharvest Ripening on the Phytochemical Composition and Antioxidant Properties of Fruits from Ten Plum (Prunus domestica L.) Cultivars" Agronomy 15, no. 6: 1351. https://doi.org/10.3390/agronomy15061351

APA Style

Mieszczakowska-Frąc, M., Dickinson, N. J., & Konopacka, D. (2025). Effect of Postharvest Ripening on the Phytochemical Composition and Antioxidant Properties of Fruits from Ten Plum (Prunus domestica L.) Cultivars. Agronomy, 15(6), 1351. https://doi.org/10.3390/agronomy15061351

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