Avocados are commercially valuable, and are cultivated in tropical and Mediterranean climates throughout the world, producing a green-skinned, pear-shaped fruit that ripens after harvesting. Trees are partially self-pollinating and often are propagated through grafting to maintain a predictable quality and quantity of the fruit.
Persea americana, or the avocado, originated in the state of Puebla, Mexico. The native, undomesticated variety is known as a criollo, and is small, with dark black skin, and contains a large seed. The oldest evidence of avocado use was found in a cave located in Coxcatlán, Puebla, Mexico, that dates to around 10,000 BC. The avocado tree also has a long history of cultivation in Central and South America; a water jar shaped like an avocado, dating to AD 900, was discovered in the pre-Incan city of Chan Chan. The earliest known written account of the avocado in Europe is that of Martín Fernández de Enciso (c.1470–c.1528) in 1518 or 1519 in his book, Suma De Geographia Que Trata De Todas Las Partidas Y Provincias Del Mundo. The first written record in English of the use of the word 'avocado' was by Hans Sloane in a 1696 index of Jamaican plants. The plant was introduced to Indonesia in 1750, Brazil in 1809, the Levant in 1908, and South Africa and Australia in the late 19th century.
The tree grows to 20 m (69 ft), with alternately arranged leaves 12 centimeters (4.7 in) – 25 centimeters (9.8 in) long. The flowers are inconspicuous, greenish-yellow, 5 millimeters (0.2 in) – 10 millimeters (0.4 in) wide. The pear-shaped fruit is 7 centimeters (2.8 in) – 20 centimeters (7.9 in) long, weighs between 100 grams (3.5 oz) – 1,000 grams (35 oz), and has a large central seed, 5 centimeters (2.0 in) – 6.4 centimeters (2.5 in) long.
The subtropical species needs a climate without frost and with little wind. High winds reduce the humidity, dehydrate the flowers, and affect pollination. When even a mild frost occurs, premature fruit drop may occur, although the Hass cultivar can tolerate temperatures down to −1°C. The trees also need well-aerated soils, ideally more than 1 m deep. Yield is reduced when the irrigation water is highly saline. These soil and climate conditions are available only in a few areas of the world, particularly in southern Spain, Portugal, Morocco, Crete, the Levant, South Africa, Colombia, Peru, parts of central and northern Chile, Vietnam, Indonesia, parts of southern India, Sri Lanka, Australia, New Zealand, the Philippines, Malaysia, Central America, the Caribbean, Mexico, California, Arizona, New Mexico, Texas, Florida, Hawaii, and Ecuador. Each region has different types of cultivars.
An average avocado tree produces about 500 avocados annually. Commercial orchards produce an average of seven tonnes per hectare each year, with some orchards achieving 20 tonnes per hectare. Biennial bearing can be a problem, with heavy crops in one year being followed by poor yields the next. The avocado tree does not tolerate freezing temperatures, and can be grown only in subtropical or tropical climates.
The avocado is a climacteric fruit (the banana is another), which means it matures on the tree, but ripens off the tree. Avocados used in commerce are picked hard and green and kept in coolers at 3.3 to 5.6°C (38 to 42°F) until they reach their final destination. Avocados must be mature to ripen properly. Avocados that fall off the tree ripen on the ground. Generally, the fruit is picked once it reaches maturity; Mexican growers pick Hass-variety avocados when they have more than 23% dry matter, and other producing countries have similar standards. Once picked, avocados ripen in a few days at room temperature (faster if stored with other fruits such as apples or bananas, because of the influence of ethylene gas). Some supermarkets sell pre-ripened avocados which have been treated with synthetic ethylene to hasten ripening. In some cases avocados can be left on the tree for several months, which is an advantage to commercial growers who seek the greatest return for their crop; but if the fruit remains unpicked for too long it falls to the ground.
The fruit of horticultural cultivars has a markedly higher fat content than most other fruit, mostly monounsaturated fat, and as such serves as an important staple in the diet of various groups where access to other fatty foods (high-fat meats and fish, dairy, etc.) is limited.
A ripe avocado yields to gentle pressure when held in the palm of the hand and squeezed. The flesh is prone to enzymatic browning; it turns brown quickly after exposure to air. To prevent this, lime or lemon juice can be added to avocados after they are peeled.
Indonesian-style avocado milkshake with chocolate syrup
The fruit is not sweet, but fatty, and distinctly yet subtly flavored, and of smooth, almost creamy texture. It is used in both savory and sweet dishes, though in many countries not for both. The avocado is very popular in vegetarian cuisine, as substitute for meats in sandwiches and salads because of its high fat content.
Generally, avocado is served raw, though some cultivars, including the common Hass, can be cooked for a short time without becoming bitter. Caution should be used when cooking with untested cultivars; the flesh of some avocados may be rendered inedible by heat. Prolonged cooking induces this chemical reaction in all cultivars.
It is used as the base for the Mexican dip known as guacamole, as well as a spread on corn tortillas or toast, served with spices.
Avocados have diverse fats. For a typical avocado:
About 75% of an avocado's calories come from fat, most of which is monounsaturated fat.
On a 100 g basis, avocados have 35% more potassium (485 mg) than bananas (358 mg). They are rich in B vitamins, as well as vitamin E and vitamin K.
Avocados have a high fiber content of 75% insoluble and 25% soluble fiber.
High avocado intake was shown in one preliminary study to lower blood cholesterol levels. Specifically, after a seven-day diet rich in avocados, mild hypercholesterolemia patients showed a 17% decrease in total serum cholesterol levels. These subjects also showed a 22% decrease in both LDL (harmful cholesterol) and triglyceride levels and 11% increase in HDL (helpful cholesterol) levels. Additionally a Japanese team synthesised the four chiral components, and identified (2R, 4R)-16-heptadecene-1, 2, 4-triol as a natural antibacterial component.
Due to a combination of specific aliphatic acetogenins, avocado is under preliminary research for potential anti-cancer activity.
Extracts of P. americana have been used in laboratory research to study potential use for treating hypertension or diabetes mellitus.
No comments:
Post a Comment