kiwifruit

Kiwivegetable

The kiwifruit, often shortened to kiwi in many parts of the world, is the edible berry of a cultivar group of the woody vine Actinidia deliciosa and hybrids between this and other species in the genus Actinidia.

The most common cultivars of kiwifruit are oval, about the size of a large hen's egg (5–8 cm / 2–3 in long and 4.5–5.5 cm / 1¾–2 in diameter). It has a fibrous, dull brown-green skin and bright green or golden flesh with rows of tiny, black, edible seeds. The fruit has a soft texture and a sweet but unique flavor, and today is a commercial crop in several countries, such as Italy, New Zealand, Chile, Greece and France.

Names

Kiwifruit jam from Lebanon

Also known as the Chinese gooseberry,^[1] the fruit was renamed for export marketing reasons in the 1950s; briefly to melonette, and then later by New Zealand exporters to kiwifruit. The name "kiwifruit" comes from the kiwi — a brown flightless bird and New Zealand's national symbol. Kiwi is also a colloquial name for the New Zealand people.

The importer in the US, Ziel & Co in San Francisco suggested the old name of Chinese gooseberry was unsuitable, recommending instead a short, Maori name. Jack Turner initiated the name "kiwifruit" around 1962^[2] as part of Turners & Growers marketing response to this feedback, and the name became a global brand. The trademark was not registered internationally, however. To distinguish 'Kiwi kiwifruit', the trademark Zespri was registered in 1997.

The fruit had a long history before it was commercialized as kiwifruit, and therefore had many other names.

In Chinese:^[3]

• Macaque peach (獼猴桃 Pinyin: míhóu táo): the most common name
• Macaque pear (獼猴梨 míhóu lí)
• Vine pear (藤梨 téng lí)
• Sunny peach (陽桃 yáng táo), a name originally referring to the kiwifruit, but often refers to the starfruit
• Wood berry (木子 mù zi)
• Hairy bush fruit (毛木果 máo mù guǒ)
• Unusual fruit or wonder fruit (奇異果 Pinyin: qíyì guǒ, Jyutping: kei4 ji6 gwo2): the most common name in Taiwan and Hong Kong, a quasi-transliteration of "kiwifruit", literally "strange fruit"

History

Kiwifruit output in 2005

Actinidia deliciosa is native to southern China. Originally known as yang tao,^[4] it is declared as the "National Fruit" of the People's Republic of China.^[5] Other species of Actinidia are native to India and Japan and southeastern Siberia. Cultivation spread from China in the early 20th century, when seeds were introduced to New Zealand by Mary Isabel Fraser, the principal of Wanganui Girls' College, who had been visiting mission schools in Yichang, China.^[6] The seeds were planted in 1906 by a Wanganui nurseryman, Alexander Allison, with the vines first fruiting in 1910.

The familiar cultivar Actinidia deliciosa 'Hayward' was developed by Hayward Wright in Avondale, New Zealand around 1924. It was initially grown in domestic gardens, but commercial planting began in the 1940s. Export markets opened up after World War II thanks to pioneering research into the transportability of the fruit by John Pilkington Hudson and others at the agriculture department in Wellington. Italy is now the leading producer of kiwifruit in the world, followed by New Zealand, Chile, France, Greece, Japan and the United States. In China, kiwifruit was traditionally collected from the wild, but until recently China was not a major producing country.^[7] In China, it is grown mainly in the mountainous area upstream of the Yangtze River. It is also grown in other areas of China, including Sichuan.^[8]

Cultivars

Almost all kiwifruit in commerce belong to a few cultivars of Actinidia deliciosa: 'Hayward', 'Chico', and 'Saanichton 12'. The fruit of these cultivars are practically indistinguishable from each other and match the description of a standard kiwifruit given at the head of this article.

Sliced golden kiwifruit

A close up view of kiwifruit skin

By contrast, a distinct species, gold kiwifruit (Actinidia chinensis) has a smooth bronze skin, a beak shape at the stem attachment, and golden yellow flesh with less tart and more tropical flavour than green kiwifruit. It is a new cultivar developed in New Zealand named Zespri® Gold,^[9] now marketed worldwide in increasing volumes. The yellow fruit fetches a higher market price and, being less hairy than green kiwifruit, is more palatable whole.

In 2010, Turners and Growers revealed their new "ENZARed" variety, a cultivar of the Chinese "hong yang" variety.^[10] Initially grown in China, the EnzaRed is now being developed globally,^[11] but its short storage life may limit its commercial potential.

Nutrition

Kiwifruit is a rich source of vitamin C, 1.5 times the DRI scale in the U.S. per 100 grams. Its potassium content by weight is slightly less than that of a banana. It also contains vitamin E,^[12] and a small amount of vitamin A.^[12][13] The skin is a good source of flavonoid antioxidants (though it may also retain agricultural pesticides^[14]). The kiwifruit seed oil contains on average 62% alpha-linolenic acid, an omega-3 fatty acid.^[15] Usually a medium size kiwifruit contains about 46 calories,^[16] 0.3 g fat, 1 g protein, 11 g carbohydrates, and 2.6 g dietary fiber found partly in the edible skin.^[17] Kiwifruit is often reported to have mild laxative effects, due to its significant level of dietary fiber.^[18]

Raw kiwifruit is also rich in the protein-dissolving enzyme actinidin, (in the same family of thiol proteases as papain), which is commercially useful as a meat tenderizer, but can be an allergen for some individuals. Specifically, people allergic to latex, papayas or pineapples are likely to also be allergic to kiwifruit. The fruit also contains calcium oxalate crystals in the form of raphides. Reactions to these chemicals include sweating, tingling and sore mouth or throat; swelling of the lips, tongue and face; rash; vomiting and abdominal pain, heartburn; and, in the most severe cases, breathing difficulties, wheezing and collapse. The most common symptoms are unpleasant itching and soreness of the mouth, with the most common severe symptom being wheezing. Severe symptoms are most likely to occur in young children.

Actinidin also makes raw kiwifruit unsuitable for use in desserts containing milk or any other dairy products which are not going to be served within hours, because the enzyme soon begins to digest milk proteins. This applies to gelatin-based desserts as well, as the actinidin will dissolve the collagen proteins in gelatin very quickly, either liquifying the dessert, or preventing it from solidifying. However, the U.S. Department of Agriculture suggests cooking the fruit for a few minutes before adding it to the gelatin to overcome this effect.^[19] Sliced kiwifruit has long been regularly used as a garnish atop whipped cream on New Zealand's national dessert, the pavlova. It can also be used in curry.^[20]

Kiwifruit components, possibly involving vitamin E and omega-3 fatty acids from its numerous edible seeds, have potential properties of a natural blood thinner. A study performed at the University of Oslo in Norway reported consuming two to three kiwifruit daily for 28 days significantly reduced platelet aggregation and blood triglyceride levels (similar to popular mainstream aspirin therapy), potentially reducing the risk of blood clots.^[21]

Kiwifruit is a natural source of carotenoids, such as provitamin A beta-carotene,^[22] lutein and zeaxanthin.^[23]

Cultivation

Top kiwifruit producers - 2007
(thousand metric tons)

Italy	410
New Zealand	360
Chile	170
France	80
Greece	40
Japan	40
Iran	20
United States	20
Canada	10
Cambodia	10
World Total	1,160
Source: UN Food and Agriculture Organization (FAO)[24]

Kiwifruit can be grown in most temperate climates with adequate summer heat. Whereas Actinidia deliciosa is not hardy, other species can be grown as substitutes.

Kiwifruit is commercially grown on sturdy support structures, as it can produce several tonnes per hectare, more than the rather weak vines can support. These are generally equipped with a watering system for irrigation and frost protection in the spring.

Kiwifruit vines

Kiwifruit vines require vigorous pruning, similar to that of grapevines. Fruit is borne on one-year-old and older canes, but production declines as each cane ages. Canes should be pruned off and replaced after their third year.

The plants are normally dioecious, meaning individual plants are either male or female. Only female plants bear fruit, and only when pollenized by a male plant. One male pollenizer is required for each three to eight female vines. An exception is the cultivar 'Issai', a hybrid (Actinidia arguta x polygama) from Japan, which produces perfect flowers and can self-pollinate; unfortunately it lacks vigour, is less hardy than most A. arguta forms and is not a large producer.

Kiwifruit growing on supported vine

Kiwifruit is notoriously difficult to pollinate, because the flowers are not very attractive to bees. Some producers blow collected pollen over the female flowers. Generally, the most successful approach, though, is saturation pollination, where the bee populations are made so large (by placing hives in the orchards) that bees are forced to use this flower because of intense competition for all flowers within flight distance.

Storage

Firm kiwifruit ripen after a few days to a week when stored at room temperature, but should not be kept in direct sunlight. Faster ripening occurs when placed in a paper bag with an apple, pear, or banana.^[25] Once a kiwifruit is ripe, however, it is preserved optimally when stored far from other fruits, as it is very sensitive to the ethylene gas they may emit, thereby tending to over-ripen even in the refrigerator.^[25] If stored appropriately, ripe kiwifruit normally keep for about one to two weeks.^[25]

See also

• Actinidia deliciosa
• Kiwifruit industry in New Zealand
• Pseudomonas syringaevar. actinidiae, a bacterium that attacks kiwifruit vines

References

Further reading

Books

• Neubauer, H. / Vorbeck, W. (2008). Kiwifruit: from the seed to your plate. NZVP Books. ISBN 9781877339110
• Qian, M.C. / Rimando, A.M. (eds. 2010). Flavor and Health Benefits of Small Fruits. American Chemical Society. ISBN 9780841225497

External links

Wikimedia Commons has media related to: Kiwifruit

Wikispecies has information related to: Actinidia deliciosa

• How to grow kiwifruit vines and nutritional data
• Kiwifruit at the Center for New Crops & Plant Products at Purdue University
• "What is the history of the kiwifruit?". Oregon State University. http://food.oregonstate.edu/faq/kiwi/faq_kiwi4.html.