Purple Mangosteen - Tree & Fruit

Tree & Fruit

A tropical tree, the mangosteen must be grown in consistently warm conditions, as exposure to temperatures below 0°C (32°F) for prolonged periods will generally kill a mature plant. They are known to recover from brief cold spells rather well, often with damage only to young growth. Experienced horticulturists have grown this species outdoors, and brought them to fruit in extreme South Florida.

The juvenile mangosteen fruit, which does not require fertilisation to form (see agamospermy), first appears as pale green or almost white in the shade of the canopy. As the fruit enlarges over the next two to three months, the exocarp colour deepens to darker green. During this period, the fruit increases in size until its exocarp is 6–8 centimeters in outside diameter, remaining hard until a final, abrupt ripening stage.

The subsurface chemistry of the mangosteen exocarp comprises an array of polyphenols, including xanthones and tannins that assure astringency which discourages infestation by insects, fungi, plant viruses, bacteria and animal predation while the fruit is immature. Colour changes and softening of the exocarp are natural processes of ripening that indicates the fruit can be eaten and the seeds have finished developing.

Mangosteen produces a recalcitrant seed and must be kept moist to remain viable until germination. Mangosteen seeds are nucellar in origin and not the result of fertilisation; they germinate as soon as they are removed from the fruit and die quickly if allowed to dry.

Once the developing mangosteen fruit has stopped expanding, chlorophyll synthesis slows as the next colour phase begins. Initially streaked with red, the exocarp pigmentation transitions from green to red to dark purple, indicating a final ripening stage. This entire process takes place over a period of ten days as the edible quality of the fruit peaks.

Over the days following the removal from the tree, the exocarp hardens to an extent depending upon postharvest handling and ambient storage conditions, especially relative humidity levels. If the ambient humidity is high, exocarp hardening may take a week or longer when the aril quality is peaking and excellent for consumption. However, after several additional days of storage, especially if unrefrigerated, the arils inside the fruit might spoil without any obvious external indications. Using the hardness of the rind as an indicator of freshness for the first two weeks following harvest is therefore unreliable because the rind does not accurately reveal the interior condition of the arils. If the exocarp is soft and yielding as it is when ripe and fresh from the tree, the fruit is usually good.

The edible endocarp of the mangosteen is botanically defined as an aril with the same shape and size as a tangerine 4–6 centimetres in diameter, but is white. The circle of wedge-shaped arils contains 4–8 segments, the larger ones harbouring apomictic seeds that are unpalatable unless roasted.

Often described as a subtle delicacy, the arils bear an exceptionally mild aroma, quantitatively having about 1/400th of the chemical constituents of fragrant fruits, explaining its relative mildness. The main volatile components having caramel, grass and butter notes as part of the mangosteen fragrance are hexyl acetate, hexenol and α-copaene.

On the bottom of the exocarp, raised ridges (remnants of the stigma), arranged like spokes of a wheel, correspond to the number of aril sections. Mangosteens reach fruit-bearing in as little as 5–6 years, but more typically require 8–10 years.