Black Chokeberry Aronia Melanocarpa L.—A Qualitative Composition, Phenolic Profile and Antioxidant Potential

Black chokeberry (Aronia melnocarpa) is a source of many bioactive compounds with a wide spectrum of health-promoting properties. Fresh, unprocessed chokeberry fruits are rarely consumed due to their astringent taste, but they are used in the food industry for the production of juices, nectars, syrups, jams, preserves, wines, tinctures, fruit desserts, jellies, fruit teas and dietary supplements. Polyphenols are biofactors that determine the high bioactivity of chokeberries, some of the richest sources of polyphenols, which include anthocyanins, proanthocyanidins, flavonols, flavanols, proanthocyanidins, and phenolic acids. Chokeberry fruit and products have great antioxidant and health-promoting potential as they reduce the occurrence of free radicals. This publication reviewed the scientific research regarding the phenolic compounds and the antioxidant potential of chokeberry fruits, products and isolated compounds. These findings may be crucial in future research concerning chokeberry based functional food products. Chokeberry fruits can be considered as promising component of designed food with enhanced antioxidant potential. However, like other plants and medicinal products of natural origin, black chokeberry requires extensive studies to determine its antioxidant potential, safety and mechanisms of action.

The degree of proanthocyanidin polymerisation is DP > 10, which translates to the mean procyanidin polymerisation degree (mDP). The mDP of proanthocyanidin in fruits was 19-59; in juice it was 12-52 and in pomace it was 18-34 [11,13,40,45,53,65]. Hellström et al. [66] observed an exceptionally high degree of proanthocyanidin polymerisation in chokeberry juice and extract (mDP > 100). In chemical terms, proanthocyanidins are oligomers and polymers of flavan-3-ol, linked by B-type and A-type bonds. Therefore, the results of many studies have confirmed that the biological and chemical properties of proanthocyanidins depend on their structure, and in particular the molecular weight also expressed as the degree of polymerisation (DP). Part of (−)-epicatechin in chokeberry fruit has the form of monomers [53,59,67], while powders and chokeberry juice epicatechin can be found in combination with cyanidin glycosides [33].

Antioxidative Activity
Chokeberry fruits have high antioxidative potential, usually higher than other plant materials tested. The antioxidative activity of chokeberries was confirmed in various radical scavenging assays, the effects of transition metals on changes in the state of oxidation, and the ability to inhibit lipid peroxidation in a variety of model systems (Table 3). Tarko et al. [110] studied chokeberries, apples, plums, pears, bananas and melons. They found that chokeberry fruit components were the most active scavengers of the ABTS radical cation. The analysis of blackberry, blackcurrant, chokeberry, raspberry and redcurrant antioxidants (DPPH • ) indicated a relatively high potential of chokeberries and selected blackcurrant varieties [120]. Nakajima, Tanaka, Seo, Yamazaki, and Saito [121] confirmed the DPPH radical scavenging ability using ethanol extracts of five berries, which were rich in anthocyanins: blackberries, black chokeberries, blackcurrants, bilberries and elderberries. The antioxidative activity of the chokeberry extract at the highest concentration (2 mg/mL) was lower than that of the other extracts, except the elderberry extract. Other studies tested the potential of 26 fruits to scavenge superoxide radicals (ROO • ) in the ORAC assay. Chokeberry fruits were less active than elderberries and wild roses-their values amounted to 160.8, 205.4 and 201.1 µmol TE/g FW, respectively. The antiradical activity of the other fruits ranged from 2.3 to 98.9 µmol TE/g FW [36]. Wu et al. [59] evaluated the antioxidative potential of different fruits using ORAC for hydrophilic (H-ORAC) and lipophilic compounds (L-ORAC). Among 15 fruit samples, chokeberries and blackberries exhibited the highest antiradical activity. The H-ORAC values noted for chokeberries were many times greater than the L-ORAC values, i.e., 158.2 and 2.42 µmol TE/g FW, respectively.
The high antioxidative potential of chokeberry fruit was confirmed using ORAC, TRAP, hydroxyl radical (HO • ) and nitric oxide (NO) assay. The ability of chokeberry extract to scavenge radicals (ROO • ) in the ORAC assay amounted to 5165 µmol TE/g of the extract and it was only 10.7% lower than that of the elderberry extract. The TRAP assay showed that the ROO • radical was more effectively scavenged by the chokeberry extract (4051 µmol TE/g extract) than the elderberry fruit extract (3230 µmol TE/g extract). The antiradical activity of the chokeberry, black elderberry and bilberry extracts against the hydroxyl radical HO • did not differ significantly (1264-1293 µmol GAE/g extract).
The chokeberry extract exhibited high nitrogen oxide (NO) scavenging capacity and inhibited the oxidation of α-linolenic acid [36]. The chokeberry fruits also inhibited liposomal oxidation effectively, exhibiting superior antioxidative properties to blackcurrants, rosehips and hawthorns [113].    blackcurrant> rowanberry> blueberry > chokeberry > rosehip > hawthorn autoxidation of linoleic acid was effectively inhibited by blueberry, rowanberry and blackcurrant extracts at the end of the first day of storage. The inhibition of hydroperoxide formation by these fruits and, in addition by chokeberry, was observed also after the third day of linoleic acid autoxidation (less than 50% of control). Finally, hydroperoxide formation was inhibited to more than 50% of the control value by all extracts analysed after 6 days of linoleic acid autoxidation. Extract from blueberry was the most effective as it diminished the hydroperoxides to 8% of control value.          Najda and Łabuda [73] investigated the antioxidative activity of different fruits and found that chokeberry fruits exhibited higher antioxidative activity than the other eight fruits. The activity was measured by determining the ability to reduce Fe in the FRAP assay and to scavenge the DPPH radical. The ABTS cation was effectively scavenged only by the ingredients of 'Titania' blackcurrants. The chokeberry fruit extracts exhibited antioxidative activity in DPPH, hydroxyl (HO•), superoxide anion (O 2 • − ), and nitric oxide (NO) assay, and inhibited lipid oxidation. The 'Viking' and 'Nero' varieties had the greatest antioxidative potential, whereas the 'Fertödi' and 'Aron' cultivars exhibited the lowest potential [3]. Viskelis et al. [129] compared the antioxidative activity of different fruit varieties of chokeberries, raspberries and elderberries. The chokeberry extracts showed the highest antioxidative potential, where the 'Viking', 'Aron' and 'Cleata' varieties scavenged the DPPH radical comparably.
Apart from chokeberry fruit, fruit products and post-production waste also exhibit the antioxidative potential. The analysis of the antiradical activity of chokeberry fruit, juice and pomace against ABTS •+ and DPPH • indicated the highest activity of the pomace, followed by the fruit and juice. The antiradical activity was correlated with the polyphenol content in the analysed material [53]. The antioxidative potential of fruit juices was tested. The chokeberry juice had the greatest ability to scavenge the DPPH radical (72.44 µmol TE/mL). The elderberry fruit juice exhibited high activity (62.14 µmol TE/mL), while the activity of other juices was at least 50% lower (4-30 µmol TE/mL) [74]. The ORAC assay confirmed the high antiradical activity of chokeberry juice, which was greater than the activity of 14 other juices [126]. The chokeberry juice concentrate also exhibited the highest antiradical activity, as it scavenged the radicals more effectively than the other fruit juice concentrates [87].
The chokeberry pomace scavenged DPPH radicals and reduced Fe in the FRAP assay much more than the honeysuckle, Japanese quince, blackcurrant and strawberry pomaces. In comparison with the other pomaces the chokeberry pomace exhibited moderate activity in the ABTS •+ assay [119]. According to Pieszka et al. [16] dried chokeberry pomace exhibited better antioxidative properties (TRAP) than apple, blackcurrant, strawberry and carrot pomaces. Chokeberry groups differ in their antioxidative activity considerably [45]. Sosnowska et al. [40] studied the antioxidative activity of juices and observed that the results differed about 5 times in ABTS, FRAP and DPPH assays, while chokeberry teas differed 1.1, 1.3, 6.6 and 36.1 times in FRAP, DPPH, reducing power and ABTS assays [108]. There were also differences in the antioxidative activity of dried chokeberry fruits, powders, capsules, and jams [7,34].
The analysis of the results of studies on chokeberry juice shows that the antioxidative potential of chokeberry products depends on the period and the year of raw material harvesting [5,41]. However, the main factor affecting the antioxidative properties of the products that needs to be considered is the technological production processes. The antioxidative activity is influenced by crushed raw material used for the production of juices and chokeberry powders [33], the method and drying parameters during the production of dried fruit and powder extracts [58,88], as well as the extraction solvent and temperature [89,125]. The antioxidative potential of chokeberry fruit and products is mainly attributed to polyphenols. The activity of individual chokeberry polyphenols: anthocyanins, proanthocyanidins, phenolic acids and flavonols was also determined. The major contributor to DPPH radical scavenging values was the anthocyanin fraction (66.7%), followed by the proanthocyanidin fractions (25.1%), flavonols and phenolic acids (8.2% of the total activity) [74,114]. Zheng and Wang [130] assessed the antioxidative activity of chokeberry in the ORAC assay and found that it resulted from anthocyanins (53.1%), phenolic acids (38.2%) and flavonols (8.7%). Proanthocyanidin was not included in the study.

Conclusions
Black chokeberry (Aronia melnocarpa) is a source of many bioactive compounds with a wide spectrum of antioxidant and health-promoting properties. Like other berries, chokeberry is a source of polyphenols, which exhibit the antioxidant potential, demonstrated in numerous in vitro and in vivo experiments. Black chokeberry has the potential to inhibit the activity of various types of radicals, through different mechanisms of action. Fresh, unprocessed black chokeberry fruits are used in the food production, e.g., juices, syrups, wines, preserves, various dietary supplements, and natural dyes. However, they are rarely consumed due to their bitter taste, resulting from the presence of polyphenols. Black chokeberry fruits and flowers are used as traditional remedies based on the health-promoting actions against influenza and immunity enhancer. Numerous studies confirmed the beneficial effects of Aronia melanocarpa L. varieties consumption on hypertension, glucose metabolism disorders, dyslipidaemia, proinflammatory conditions, and reducing the risk factors of the metabolic syndrome. Results also showed the probable potential of black chokeberry to inhibit the development of some types of cancers.
Further research is necessary to understand the interactions with other compounds which may affect the activity of chokeberry components. The antioxidant potential of chokeberry fruit and its products indicates that all fractions could be utilized as a source of antioxidants and valuable nutrients with potential applications in food industry. So far the literature has not provided clear answers to questions concerning the mechanism of interaction between chokeberry components and their stability in complex systems, e.g., in food. Studies conducted to date have indicated numerous benefits resulting from chokeberry and its polyphenolic compounds inclusion in a daily diet. Like other plants and medicinal products of natural origin, chokeberry requires extensive studies on humans to determine its efficacy, safety and mechanisms of action.