The tropical fruits readily available in supermarkets year round include bananas, pineapples, tangerines, avocados and coffee (coffee beans are actually seeds that comprise the bulk of the coffee fruit). Temperate fruits include those from trees (apples, peaches, apricots, pears and plums, as well as olives) and vine and bush fruits like grapes, raspberries and blueberries. There are a number of factors dictating the differences between tropical versus temperate fruits, including environmental characteristics.
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Thickness of Skin
Generally, fruits from tropical and semi-tropical climates such as the equatorial region will have thick husk or shell; in the case of coconuts and bael (or wood apple), the skins are hard and wood-like. Mangos and papayas have relatively thin skin, but it is still much thicker than apples or pears. Climate influences skin thickness in tropical fruits, which need an ability to retain water in periods of prolonged heat. Temperate fruits, which grow best north of the tropic of Cancer and south of the Tropic of Capricorn, have fewer heat and evaporative stresses while growing so they do not require heavy skin.
Edible vs. Non-edible Skin
Most tropical fruits have inedible skin. Bananas have extremely bitter skin, as do almost all citrus fruits (kumquats are a rare and puzzling exception to this rule). Avocados have leathery skin, which is both difficult to chew and indigestible. Tropical climates are more likely to have large colonies of predatory and effective tree climbers like monkeys as well as sharp-beaked birds like parrots. The inedible skin protects the fruit from these predators. In temperate climates, the bird predators with ripping beaks are usually carnivores, not fruit eaters, and good climbers are limited in numbers or not inclined to eat fruit.
Fruit Flesh Composition
The composition of fruit flesh is dictated primarily by what the seeds need: protection, mobility and nutrition. The citric acid volume in tropical citrus fruits exists in response to environmental factors such as the pH value of the soil where citrus trees grow. Temperate fruits like apples or papayas tend to have firm, juicy and sweet (high sugar content) flesh that supports seed growth, but more importantly attracts animal predation so the seeds will travel inside the animal until they are passed and can sprout to expand their species’ territory.