Walnut

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The common walnut in growth.

A walnut is the nut of any tree of the genus Juglans (Family Juglandaceae), particularly the Persian or English walnut, Juglans regia. Technically a walnut is the seed of a drupe or drupaceous nut, and thus not a true botanical nut. It is used for food after being processed while green for pickled walnuts or after full ripening for its nutmeat. Nutmeat of the eastern black walnut from the Juglans nigra is less commercially available, as are butternut nutmeats from Juglans cinerea. The walnut is nutrient-dense with protein and essential fatty acids.

Inside of a walnut in growth
Walnut shell inside its green husk

Characteristics[edit]

Walnuts are rounded, single-seeded stone fruits of the walnut tree commonly used for the meat after fully ripening. Following full ripening, the removal of the husk reveals the wrinkly walnut shell, which is usually commercially found in two segments (three-segment shells can also form). During the ripening process, the husk will become brittle and the shell hard. The shell encloses the kernel or meat, which is usually made up of two halves separated by a partition. The seed kernels – commonly available as shelled walnuts – are enclosed in a brown seed coat which contains antioxidants. The antioxidants protect the oil-rich seed from atmospheric oxygen, thereby preventing rancidity.[1]

Walnuts are late to grow leaves, typically not until more than halfway through the spring. They secrete chemicals into the soil to prevent competing vegetation from growing. Because of this, flowers or vegetable gardens should not be planted close to them.

Types[edit]

The two most common major species of walnuts are grown for their seeds – the Persian or English walnut and the black walnut. The English walnut (J. regia) originated in Persia, and the black walnut (J. nigra) is native to eastern North America. The black walnut is of high flavor, but due to its hard shell and poor hulling characteristics it is not grown commercially for nut production. Numerous walnut cultivars have been developed commercially, which are nearly all hybrids of the English walnut.[2]

Other species include J. californica, the California black walnut (often used as a root stock for commercial breeding of J. regia), J. cinerea (butternuts), and J. major, the Arizona walnut. Other sources list J. californica californica as native to southern California, and Juglans californica hindsii, or just J. hindsii, as native to northern California; in at least one case these are given as "geographic variants" instead of subspecies (Botanica).

Walnut Production – 2014[3]
Country Production
(millions of tonnes)
 China
1.60
 United States
0.52
 Iran
0.45
 Turkey
0.18
 Mexico
0.13
World
3.46

Production[edit]

In 2014, worldwide production of walnuts (in shell) was 3.46 million tonnes, with China contributing 46% of the world total (table).[3] Other major producers were (in the order of decreasing harvest): United States, Iran, Turkey and Mexico.

The average worldwide walnut yield was about 3.5 tonnes per hectare in 2014.[3] Eastern European countries had the highest yield, with Slovenia and Romania each harvesting about 19 tonnes per hectare.[3]

In 2014, the United States was the world's largest exporter of walnuts, followed by Turkey.[4] The Central Valley of California produces 99 percent of total United States commerce in English walnuts.[5]

Storage[edit]

Walnuts, like other tree nuts, must be processed and stored properly. Poor storage makes walnuts susceptible to insect and fungal mold infestations; the latter produces aflatoxin – a potent carcinogen. A mold-infested walnut batch should be entirely discarded.[1]

The ideal temperature for longest possible storage of walnuts is in the −3 to 0 °C (27 to 32 °F) and low humidity – for industrial and home storage. However, such refrigeration technologies are unavailable in developing countries where walnuts are produced in large quantities; there, walnuts are best stored below 25 °C (77 °F) and low humidity. Temperatures above 30 °C (86 °F), and humidities above 70 percent can lead to rapid and high spoilage losses. Above 75 percent humidity threshold, fungal molds that release dangerous aflatoxin can form.[1][6]

Food use[edit]

Walnut meats are available in two forms; in their shells or shelled. The meats can be as large as halves or any smaller portions that may happen during processing, candied or as an ingredient in other foodstuffs. Pickled walnuts that are the whole fruit can be savory or sweet depending on the preserving solution. Walnut butters can be homemade or purchased in both raw and roasted forms. All walnuts can be eaten on their own (raw, toasted or pickled) or as part of a mix such as muesli, or as an ingredient of a dish. For example, walnut soup and walnut pie are prepared using walnuts as a main ingredient. Walnut Whip, coffee and walnut cake, and pickled walnuts are more examples.

Walnut is the main ingredient of Fesenjan, a khoresh (stew) in Iranian cuisine. Walnuts are also popular in brownie recipes, as ice cream toppings, and walnut pieces are used as a garnish on some foods.[7] Nocino is a liqueur made from unripe green walnuts steeped in alcohol with syrup added.

Walnut oil is available commercially and is chiefly used as a food ingredient particularly in salad dressings. It has a low smoke point, which limits its use for frying.[8][9]

Nutritional value[edit]

Walnut, English
Whole Walnut Kernel.jpg
Walnut kernel, halves
Nutritional value per 100 grams
Energy 2,738 kJ (654 kcal)
13.71
Starch 0.06
Sugars 2.61
Dietary fiber 6.7
65.21
Saturated 6.126
Monounsaturated 8.933
Polyunsaturated 47.174
15.23
Vitamins
Vitamin A equiv.
(0%)
1 μg
(0%)
12 μg
9 μg
Vitamin A 20 IU
Thiamine (B1)
(30%)
0.341 mg
Riboflavin (B2)
(13%)
0.15 mg
Niacin (B3)
(8%)
1.125 mg
Pantothenic acid (B5)
(11%)
0.570 mg
Vitamin B6
(41%)
0.537 mg
Folate (B9)
(25%)
98 μg
Vitamin B12
(0%)
0 μg
Vitamin C
(2%)
1.3 mg
Vitamin E
(5%)
0.7 mg
Vitamin K
(3%)
2.7 μg
Minerals
Calcium
(10%)
98 mg
Iron
(22%)
2.91 mg
Magnesium
(45%)
158 mg
Manganese
(163%)
3.414 mg
Phosphorus
(49%)
346 mg
Potassium
(9%)
441 mg
Sodium
(0%)
2 mg
Zinc
(33%)
3.09 mg
Other constituents
Water 4.07 g

Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database

Walnuts without shells are 4% water, 15% protein, 65% fat, and 14% carbohydrates, including 7% dietary fiber (table).

In a 100-gram serving, walnuts provide 2,740 kilojoules (654 kcal) and rich content (more than 19% of the Daily Value or DV) of several dietary minerals, particularly manganese at 163% DV, and B vitamins (table).

While English walnuts are the most commonly consumed, their nutrient density and profile are generally similar to those of black walnuts.[10][11]

Unlike most nuts that are high in monounsaturated fatty acids, walnut oil is composed largely of polyunsaturated fatty acids (72% of total fats), particularly alpha-linolenic acid (14%) and linoleic acid (58%), although it does contain oleic acid as 13% of total fats.[10]

Health claims[edit]

In 2016, the US Food and Drug Administration (FDA) provided a Qualified Health Claim allowing products containing walnuts to state: "Supportive but not conclusive research shows that eating 1.5 ounces per day of walnuts, as part of a low saturated fat and low cholesterol diet and not resulting in increased caloric intake, may reduce the risk of coronary heart disease."[12] The FDA had, in 2004, refused to authorise the claim that "Diets including walnuts can reduce the risk of heart disease"[13] and had sent an FDA Warning Letter to Diamond Foods in 2010 stating "not sufficient evidence to identify a biologically active substance in walnuts that reduces the risk of coronary heart disease."[14]

Non-food applications[edit]

Folk medicine[edit]

Walnuts have been listed as one of the 38 substances used to prepare Bach flower remedies,[15] a pseudomedicine promoted in folk medicine practices for its supposed effect on health. According to Cancer Research UK, "there is no scientific evidence to prove that flower remedies can control, cure or prevent any type of disease, including cancer".[16]

Inks and dyes[edit]

Walnut husks can be used to make a durable ink for writing and drawing. It is thought to have been used by artists including Leonardo da Vinci and Rembrandt.[17]

Walnut husk pigments are used as a brown dye for fabric[18] as once applied in classical Rome and medieval Europe for dyeing hair.[19]

Cleaning[edit]

The United States Army once used ground walnut shells for the cleaning of aviation parts because of low cost and non-abrasive qualities. However, an investigation of a fatal Boeing CH-47 Chinook helicopter crash (September 11, 1982, in Mannheim, Germany) revealed that walnut grit clogged an oil port, leading to the accident and the discontinuation of walnut shells as a cleaning agent.[20]

A three-segment shell which occurs rarely.

Chemical analysis[edit]

Walnut hulls contain polyphenols that stain hands and can cause skin irritation. Seven phenolic compounds, including ferulic acid, vanillic acid, coumaric acid, syringic acid, myricetin, and juglone were identified in walnut husks. Juglone, the predominant phenolic, was found in concentrations of 2-4% fresh weight.[21]

Walnuts also contain the ellagitannin pedunculagin.[22] Regiolone has been isolated with juglone, betulinic acid and sitosterol from the stem bark of J. regia.[23]

Uses in Chinese culture[edit]

In China, pairs of walnuts have traditionally been rotated and played with in the palm of the hand, both as a means to stimulate blood circulation and as a status symbol. Individual and pairs of large, old, symmetrically shaped, and sometimes intricately carved walnuts are valued highly and have recently been used as an investment, with some of them fetching tens of thousands of dollars.[24] Pairs of walnuts are sometimes sold in their green husks for a form of gambling known as du he tao.[25]

Cultivars[edit]

  • Ashley
  • Chandler
  • Feradam
  • Ferbel
  • Ferjean
  • Fernette
  • Fernor
  • Ferouette
  • Franquette
  • Grandjean[26]
  • Germisara
  • Hansen
  • Hartley
  • Howard
  • Ivanhoe[27]
  • Jupanesti
  • Lara
  • Livermore
  • Marbot
  • Mayette[28]
  • Meylanaise[28]
  • Paradox
  • Parisienne
  • Payne
  • Rita
  • Ronde de Montignac
  • Royal
  • Serr[29]
  • Tulare
  • Valcor
  • Vina
  • Wilson's Wonder
  • Yolo

See also[edit]

References[edit]

  1. ^ a b c "Walnut; Agriculture – Transport Information Service". Association for German Insurance. 2010. 
  2. ^ "Commodity Profile: English Walnuts" (PDF). AgMRC, University of California. 2006. 
  3. ^ a b c d "Production of walnut with shell by countries; Browse data, World, 2014". UN Food & Agriculture Organization, Statistics Division (FAOSTAT). 13 February 2017. Retrieved 21 April 2017. 
  4. ^ "Major Exporting Countries of Walnuts, 2014". Agri Exchange. 2015. Retrieved 29 September 2016. 
  5. ^ "California Walnut Industry". California Walnut Board. 2016. Retrieved 29 September 2016. 
  6. ^ "Food, Nutrition & Agriculture – Prevention of aflatoxin". FAO, United Nations. 1998. 
  7. ^ Forsberg, B.; Joan Clark-Warner, M.S.R.D.C.D.E.; Beale, L. (2004). The Complete Idiot's Guide to Terrific Diabetic Meals. DK Publishing. p. 98. ISBN 978-1-61564-486-5. Retrieved May 27, 2017. 
  8. ^ "Walnut oil recipes". BBC. Retrieved 3 July 2014. 
  9. ^ Turner, Lisa. "Oil Change". Better Nutrition. Retrieved 5 July 2014. 
  10. ^ a b "Nutrition facts: Nuts, walnuts, English dried per 100 g". Condé Nast. Retrieved 4 July 2014. 
  11. ^ "Nutrition facts: Nuts, walnuts, black, dried per 100 g". Condé Nast. Retrieved 4 July 2014. 
  12. ^ "Qualified Claims About Cardiovascular Disease Risk: Walnuts & Heart Disease Docket No. 02P-0292". US Food and Drug Administration,. 9 March 2004. Retrieved 1 November 2016. 
  13. ^ Laura M. Tarantino (9 March 2004). "Qualified Health Claims: Letter of Enforcement Discretion - Walnuts and Coronary Heart Disease (Docket No 02P-0292)". US Food and Drug Administration, Labeling and Nutrition. Retrieved 30 April 2017. 
  14. ^ Wagner, Roberta (22 February 2010). "FDA Warning Letter to Diamond Food, Inc". US Food and Drug Administration, Inspections, Compliance, Enforcement, and Criminal Investigations. Retrieved 1 November 2016. the evidence supporting a relationship between walnuts and coronary heart disease is related to the omega-3 fatty acid content of walnuts. There is not sufficient evidence to identify a biologically active substance in walnuts that reduces the risk of coronary heart disease. Therefore, the above statement is an unauthorized health claim 
  15. ^ D. S. Vohra (1 June 2004). Bach Flower Remedies: A Comprehensive Study. B. Jain Publishers. p. 3. ISBN 978-81-7021-271-3. Retrieved 2 September 2013. 
  16. ^ "Flower remedies". Cancer Research UK. 26 January 2015. Retrieved 1 September 2013. 
  17. ^ "Black Walnut Ink Workshop". Guild of Natural Science Illustrators. October 2002. Retrieved 3 July 2014. 
  18. ^ "The Colors of Invention – How to Dye Fibers Naturally". Smithsonian Museum. November 13–16, 1997. Retrieved 3 July 2014. 
  19. ^ Sherrow, Victoria (2006). Encyclopedia of Hair: A Cultural History. Greenwood Publishing Group. pp. 267, 355. ISBN 9780313331459. Retrieved 3 July 2014. 
  20. ^ "In Re Air Crash Disaster at Mannheim Germany on 9/11/82. Ursula J. Schoenborn, As Executrix of the Estate of Leonedward Schoenborn, Deceased, v. the Boeing Company. Appeal of the Boeing Company. United States Court of Appeals, Third Circuit. 769 F.2d 115". Justia. 1985. Retrieved 10 April 2014. 
  21. ^ Cosmulescu, Sina Niculina; Trandafir, Ion; Achim, Gheorghe; Botu, Mihai; Baciu, Adrian; Gruia, Marius (15 June 2010). "Phenolics of Green Husk in Mature Walnut Fruits". Notulae Botanicae Horti Agrobotanici Cluj-Napoca. 38 (1): 53–56. doi:10.15835/nbha3814624. ISSN 1842-4309. Retrieved 11 October 2016. 
  22. ^ Metabolism of Antioxidant and Chemopreventive Ellagitannins from Strawberries, Raspberries, Walnuts, and Oak-Aged Wine in Humans: Identification of Biomarkers and Individual Variability. Begoña Cerdá, Francisco A. Tomás-Barberán, and Juan Carlos Espín, J. Agric. Food Chem., 2005, 53 (2), pages 227–235, doi:10.1021/jf049144d
  23. ^ (−)-Regiolone, an α-tetralone from Juglans regia: structure, stereochemistry and conformation. Sunil K. Talapatra, Bimala Karmacharya, Shambhu C. De and Bani Talapatra, Phytochemistry, Volume 27, Issue 12, 1988, pages 3929–3932, doi:10.1016/0031-9422(88)83047-4
  24. ^ "Status-conscious investors shell out on great walnuts of China". Reuters. Aug 28, 2012. 
  25. ^ "Game of clones". Global Times. 16 October 2012. 
  26. ^ Le Verger Francais tomme II Chapitre I Fruits Locaux & Regionaux 1948
  27. ^ "Walnut tree named ‘Ivanhoe’. Google.com
  28. ^ a b Le Verger Francais, Tome 1 catalogue descriptif des Fruits adoptes 1947
  29. ^ The Walnut Germplasm Collection of the University of California, Davis report No. 13 july 1994

Further reading[edit]

External links[edit]