Avocados

The avocado is from an evergreen tree of the Laurel family of plants. Other familiar members, which are mainly indigenous to the tropics, are camphor and cinnamon trees; but the avocado tree is the only fruit-bearing species of the family. The large avocado tree can reach heights of sixty-five feet in the wild, but less than half that in cultivation. It takes four to seven years for it to produce its first fruits, which grow on long stalks and do not ripen on the tree. The fruit is harvested when unripe and still quite hard. The avocado almost defies classification. Although it is botanically a fruit, it is usually prepared as a vegetable. It originated in tropical and subtropical Central America, where it remains one of their most important foods.

Avocados are highly nutritious, containing potassium, calcium, folate, fiber, vitamin C, vitamin E, riboflavin, vitamin B6, and polyunsaturated fatty acids. Depending on the season, location, and climate, the average total oil content of an avocado is 16% to 20%, and almost half of that is oleic acid. A staple food for vegetarians, an avocado is also an internal lubricator and is good for healing ulcers. The fruit is high in lecithin, which is a natural “brain food” and an easily digested fat. It is also made up of 2% proteins, 6-9% carbohydrates and sugars (glucose, fructose, D-mannoheptulose, taloheptulose, and an alloheptulose), plus two bitter substances and vitamins and minerals, including potassium and Vitamin D in higher amounts than that of eggs or butter. Although high in the sugars, avocados are beneficial for those with hypoglycemia (low blood sugar) as they contain ‘manoheptulose’, a special type of sugar which depresses the secretion of insulin. For this reason, despite its high fat content, avocados can be a valuable contributor to a weight loss program by helping to satisfy hunger for longer periods of time. Another interesting component (C17) has been isolated from the pulp and seed, and found to be an excellent bactericidal agent proven effective against Gram-positive bacteria, especially S. aureus.

The first written mention of the avocado dates from around 300 BCE, but it is known to have been cultivated for over 7,000 years. The fruit first reached European shores in the 16th century with the Spanish conquistadors. Although the avocado was a dietary staple of Central American people for centuries, it was not cultivated in North America until 1833, when Henry Perrine established extensive avocado groves in Florida. In 1873, the first avocado orchards were planted in California near Santa Barbara. In both cases, the thin-skinned Mexican variety was used. Today, in addition to its native Mexico, the main avocado producers are the US, Brazil, the West Indies, Peru, Kenya, Australia, South Africa, Indonesia, Israel, and Spain. It is estimated that there are between 500 and 1000 varieties, but all are believed to have come from three basic types: Guatemalan, Mexican, and West Indian. Guatemalan fruits are large, with warty skins; while Mexican ones can be both small and large. The smooth-skinned ones come from the West Indies. Size varies from the mini or cocktail avocados, which grow to the size of plums to others which attain weights of over four pounds. However, fruits weighing five to fourteen ounces are the ones most cultivated and exported.

Scientists have determined that there is enough evidence to show that the avocado did originate in south central Mexico, or nearby. The Aztecs knew it well, and called the fruit aoacatl. Transliterated into the language of today, the original Aztec name for the avocado is ahuacatl. This name is still used in parts of Mexico where the Aztec language has not been entirely replaced by Spanish word, quahuitl. Thus, the avocado became ahuacaquahuitl. Understandably, nearly all of the early explorers choked on the Aztec name, and it soon was changed to something easier to handle by the Spaniards – aguacate ( pronounced ah-wah-cot-tay). When Martin Fernandez de Encisco wrote about this language in 1519, Florida and California were still unknown to the Europeans. The first European to give a name to the fruit appears to have been Pedro do Cieza de Leon, writing between 1532 and 1550. He referred to it under the names “aguacate” and “palta,” a name for the fruit used by the Incas who had only recently discovered it when they conquered an area around 1450-1475, called Palta. An English merchant published his travels in Mexico in 1589 and mentioned this fruit; but he did not know how to spell, it became alvacata. This appears to be the first mention of the fruit in any English publication. When the fruit appeared in the West Indies, new varieties were quickly developed. It was here that the fruit was first encountered by many travelers, including George Washington, who wrote in 1751 that the agovago pears were abundant and popular in the Barbados. The name we know today as avocado was given by Sir Hans Sloane, a distinguished naturalist, who published a catalogue of Jamaican plants in 1696 and stating, at that time, there were over forty different names for the fruit.

Depending on the variety, avocados are about five inches long and generally pear-shaped; but they can also be round or elongated. The skin varies in colour, ranging from light and dark green to purple and black, and may be thin, thick, rough, or smooth. The delicate green to yellowish creamy flesh surrounds a large inedible pit. Black spots that appear in the flesh are caused by storage at cold temperatures. Avocados should be ripened at room temperature. To hasten the ripening process, they can be put into a brown paper bag with a piece of apple and left in a warmer part of the kitchen. When storing half an avocado, leave the pit in and brush a layer of lemon juice over top and cover tightly, then use within twenty-four hours. When an avocado is peeled or sliced, the cell walls are torn, releasing polyphenoloxidase, an enzyme that converts phenols to brownish compounds that darken the bright green flesh. This reaction can be slowed significantly with the addition of lemon.

Avocados are sometimes propgated from seed, but more reliable results are obtained professionally by grafting named cultivars onto disease-resistant root stalks. Grafted plants normally produce fruit within one to two years, compared to up to twenty years for seedlings. Avocados do well in the mild-winter areas and at some distance from the ocean, but not in the desert interior. West Indian varieties thrive in humid, tropical climates and freeze at or near 0°C (32° F). Guatemalan types are native to cool, high-altitude tropics. Mexican types are native to dry subtropical plateaus and thrive in a Mediterranean climate of about -6°C (19° F). Dwarf forms are suitable for growing in containers. Mini avocados are small, elongated fruits that contain no pits and grow without fertilization. They look somewhat like tiny, smooth-skinned, dark green cucumbers.

Avocado trees are usually fast growing and capable of reaching eighty feet and broadening out. The trees need some protection from high winds which may break the branches. The leaves normally remain on the tree for two to three years, but they also shed many of them in the spring. The leaves of West Indian varieties are odourless, but the Guatemalan types have a mild anise-scent and are used for medicines. The leaves of Mexican types have a strong anise scent when crushed. The leaves are high in oils and slow to compost, so may collect in mounds beneath trees. Mexican type fruits ripen in six to eight months from bloom, while Guatemalan types usually take twelve to eighteen months. Fruits may continue to grow on the tree even after maturity. Guatemalan types can be stored firm for up to six weeks. Mexican types discolor quickly and need to be eaten quickly. As for US varieties, Florida avocados tend to be larger than the California ones and contain less fat, but also lack the rich texture of the California types. West Indian avocados produce enormous, smooth, round, glossy green fruits that are low in oil and weigh up to two pounds each. Guatemalan types produce medium oval or pear-shaped, pebbled, green fruits that turn blackish-green when ripe. The fruit of Mexican varieties are small, about one-half pound, with paper-thin skins that turn glossy green or black when ripe. The flesh of the avocado is deep green near the skin, becoming yellowish nearer the single, large seed. The flesh is hard when harvested, but softens to a buttery, spreadable texture. High in monosaturates, the oil content of avocados is second only to olives among the fruits.

Avocado flowers appear in late winter before the first seasonal growth in groups of 200-300 small yellow-green blooms, but each panicle (flower cluster) will produce only one to three fruits. The flowers are either receptive to pollen in the morning and shed pollen the following afternoon (type A), or are receptive to pollen in the afternoon and shed pollen the following morning (type B). About 5% of flowers will be defective in form and, therfore, sterile. Production of the fruit is best when cross-pollination occurs between types A and B. The flowers attract bees and butterflies, and pollination is usually good, except during cool weather. Off-season blooms may appear during the year and often produce fruit. Some blooms produce fruit in alternate years. Avocados are often in bloom at the time of frost, and the flowers are often killed; but the tree tends to rebloom. This is especially true of Mexican types.

Warning: Avocadoes can interfere with the action of some drugs, especially with those people taking MAO inhibitors (monoamine oxidase), which are used as antidepressants or antihypertensives. They inhibit the action of enzymes that break down the amino acid tyramine so it can be eliminated from the body. Tyramine is a pressor amine, a chemical that constricts blood vessels and raises blood pressure. By eating such a food as an avocado that contains tyramine while taking an MAO inhibitor, the pressor amine cannot be eliminated. The result can be abnormally high blood pressure or a hypertensive crisis.

Avocadoes can also create a false-positive for carcinoid tumors which can arise from tissues in the endocrine system, the intestines, or the lungs. These tumors secrete serotonin, a natural chemical that makes blood vessels expand or contract. Because seratonin is excreted in the urine, these tumors are diagnosed by measuring the levels of seratonin by-products in the urine. Avocadoes contain large amounts of seratonin, and eating them three days before an endocrine tumor test can produce a false-positive result that will suggest the presence of a tumor that is really not there. Other such foods that can create a similar false-positive tumor test are bananas, eggplant, pineapples, plums, tomatoes, and walnuts.

Some varieties of avocados include the following:
Bacon has smooth green skin and is the variety most widely grown in Spain.
Benik is a variety from Israel and one whose skin turns dark when ripe – which, in some other varieties, is an indication of spoilage.
California Haas is a Guatemalan variety that is pear-shaped, with a thick, bumpy skin that ranges in colour from dark green to purplish black. The flesh is oily, with a buttery taste.
Edranol is one of the Guatemalan varieties extensively grown in South Africa.
Ettinger is a pear-shaped Mexican and Guatemalan mix variety that produces oblong fruit, with bright green, shiny skin. It has an excellent flavour and is exported by Israel.
Fuerte is the most frequently cultivated and most popular variety. Despite its name, the Fuerte (means ‘strong’ in Spanish) has a thin, green, textured skin, even when ripe, and a milder flavour. The name likely stems from its particularly aromatic scent. It also has a more pronounced pear shape than other varieties. It is a Mexican/Guatemalan mix that produces large fruits, with some weighing as much as a pound. Fuerte has its origin in Atlixco, Mexico, and tends to bear fruit in alternate years, but does not produce near the coast or in north. The fruit contains about 18% oil and it has a medium-sized seed.
Hass is a prized small variety with pale green flesh, dark wrinkled skin, and a nutty flavour.
Murrieta Green is a hybrid and has its origin in Colima. It is large, weighing more than a pound, and resembles the Fuerte. The flesh is exceptional and has an oil content of about 18%.
Nabal is almost spherical, smooth-skinned, with the lowest fat content, and grown in Israel.
Pinkerton is a lesser variety from Israel that can be recognized by its slender shape and elongated neck and rough skin.
Puebla also has its origin Atlixco, like the Fuerte. The fruit is medium to large and can weigh more than a pound. The skin is thin and looks like a lacquered maroon-purple. The flesh is very tasty, with an oil content of about 20%. It is the least hardy of the Mexican types so does not grow well in colder areas.
Reed is a late Guatemalan variety, but is very high-yielding and has been cultivated for some time in Israel. The thick-skinned, roundish oval fruit has dark yellow, highly aromatic flesh and weighs about eleven ounces.
Ryan is a rough-skinned variety widely grown in South Africa.
Wurtz is a slender pear-shaped variety grown in Australia and Israel. It has yellow flesh and a large, slightly tapering pit.
Zutano is yellow-skinned with a smooth, shiny surface.