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Aronia, the chokeberries, are two to three species of deciduous shrubs in the family Rosaceae, native to eastern North America. One species is naturalized in Europe. They are most commonly found in wet woods and swamps. Chokeberries are cultivated as ornamental plants and also because they are very high in antioxidant pigment compounds, such as anthocyanins. The name "chokeberry" comes from the astringency of the fruits, which are inedible when raw. The berries can be used to make wine, jam, syrup, juice, soft spreads, tea and tinctures. The fruits are eaten by birds, which then disperse the seeds in their droppings; birds do not taste astringency and feed on them freely.
The chokeberries are often mistakenly called chokecherries, which is the common name for Prunus virginiana. Further adding to the ambiguity, there is a cultivar of Prunus virginiana named 'Melanocarpa', easily confused with Aronia melanocarpa. Chokecherries are also high in antioxidant pigment compounds, like anthocyanins, further contributing to confusion. In fact, the two plants are only distantly related within the Rosaceae.
Identification and taxonomy
The leaves are alternate, simple, and oblanceolate with crenate margins and pinnate venation; in autumn the leaves turn a bold red color. Dark trichomes are present on the upper midrib surface. The flowers are small, with 5 petals and 5 sepals, and produced in corymbs of 10-25 together. Hypanthium is urn-shaped. The fruit is a small pome, with a very astringent flavor.
Aronia has been thought to be closely related to Photinia, and has been included in that genus in some classifications, but botanist Cornelis Kalkman observed that a combined genus should be under the older name Aronia. The combined genus contains about 65 species. In 2004, Kalkman expressed doubt about the monophyly of the combined group, and new molecular studies confirm this. They do not place these two genera together or even near one another.
In eastern North America, there are two well-known species, named after their fruit color, red chokeberry and black chokeberry, plus a purple chokeberry whose origin is a natural hybrid of the two.
Red chokeberry, Aronia arbutifolia (Photinia pyrifolia), grows to 2–4m tall, rarely up to 6 m. Leaves are 5–8 cm wide and densely pubescent on the underside. The flowers are white or pale pink, 1 cm wide, with glandular sepals. The fruit is red, 4–10mm wide, persisting into winter.
Black chokeberry, Aronia melanocarpa (Photinia melanocarpa), tends to be smaller, rarely exceeding 1m tall, rarely 3 m, and spreads readily by root sprouts. The leaves are smaller, not more than 6-cm wide, with terminal glands on leaf teeth and a glabrous underside. The flowers are white, 1.5 cm wide, with glabrous sepals. The fruit is black, 6–9mm wide, not persisting into winter.
The Purple chokeberry, Aronia prunifolia (Photinia floribunda) apparently originated as a hybrid of the black and red chokeberries but might be more accurately considered a distinct species than a hybrid (see also nothospecies). Leaves are moderately pubescent on the underside. Few to no glands are present on the sepal surface. The fruit is dark purple to black, 7–10mm in width, not persisting into winter. There are purple chokeberry populations which seem to be self-sustaining independent of the two parent species – including an introduced one in northern Germany where neither parent species occurs –, leading botanist Alan Weakley to consider it a full species rather than a hybrid. The range of the purple chokeberry is roughly that of the black chokeberry; it is found in areas (such as Michigan and Missouri) where the red chokeberry is not.
Products and uses
The chokeberries are attractive ornamental plants for gardens. They are naturally understory and woodland edge plants, and grow well when planted under trees. Chokeberries are resistant to drought, insects, pollution, and disease. Several cultivars have been developed for garden planting, including A. arbutifolia 'Brilliant', selected for its striking fall leaf color. A. melanocarpa 'Viking' and 'Nero' were selected for larger fruit suitable for jam-making, and because they are self-fertile only one plant is needed to produce fruit.
Juice from these berries is astringent and not sweet, but high in vitamin C and antioxidants. The berries can be used to make wine, jam, syrup, juice, soft spreads, and tea. In the U.S., aronia berries are used in mass-marketed juice blends for color and marketed for their antioxidant properties. The Voruta label exports a Chokeberry wine from Lithuania. In Poland they are dried to make an herbal tea. The tea is usually a blend with other more flavorful ingredients including blackcurrant. Aronia is also used as a flavoring or colorant for beverages or yogurts.
The red chokeberry's fruit is more palatable and can be eaten raw. It has a sweeter flavor than the black species and is used to make jam or pemmican.
Aronia melanocarpa (black chokeberry) has attracted scientific interest due to its deep purple, almost black pigmentation that arises from dense contents of phenolic phytochemicals, especially anthocyanins. Total anthocyanin content in chokeberries is 1480 mg per 100 g of fresh berries, and proanthocyanidin concentration is 664 mg per 100 g. Both values are among the highest measured in plants to date.
The plant produces these pigments mainly in the skin of the berries to protect the pulp and seeds from constant exposure to ultraviolet radiation. By absorbing UV rays in the blue-purple spectrum, pigments filter intense sunlight and thereby have a role assuring regeneration of the species. Brightly colorful pigmentation also attracts birds and other animals to consume the fruit and disperse the seeds in their droppings.
Anthocyanins not only contribute toward chokeberry's astringent property (that would deter pests and infections) but also give Aronia melanocarpa extraordinary antioxidant strength that combats oxidative stress in the fruit during photosynthesis.
A test tube measurement of antioxidant strength, the oxygen radical absorbance capacity or ORAC, demonstrates chokeberry with one of the highest values yet recorded—16,062 micromoles of Trolox Eq. per 100 g (see this ORAC reference for antioxidant scores for 277 common foods).
There is growing appreciation for consumers to increase their intake of antioxidant-rich plant foods from colorful sources like berries, tree or citrus fruits, vegetables, grains, and spices. Accordingly, a deep blue food source such as chokeberry yields anthocyanins in high concentrations per serving, indicating potential value as a functional food or nutraceutical.
Analysis of anthocyanins in chokeberries has identified the following individual chemicals (among hundreds known to exist in the plant kingdom): cyanidin-3-galactoside, epicatechin, caffeic acid, quercetin, delphinidin, petunidin, pelargonidin, peonidin, and malvidin. All these except caffeic acid are members of the flavonoid category of antioxidant phenolics.
For reference to phenolics, flavonoids, anthocyanins, and similar plant-derived antioxidants, Wikipedia has a list of phytochemicals and foods in which they are prominent.
Efficacy in disease models
Chokeberries' rich antioxidant content may be beneficial as a dietary preventative for reducing the risk of diseases caused by oxidative stress. Among the models under evaluation where preliminary results show benefits of chokeberry anthocyanins are colorectal cancer, cardiovascular disease, chronic inflammation, gastric mucosal disorders (peptic ulcer), eye inflammation (uveitis) and liver failure.
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