A walnut is the edible seed of any tree of the genus Juglans (family Juglandaceae), particularly the Persian or English walnut, Juglans regia . They are accessory fruit because the outer covering of the fruit is technically an involucre and thus not morphologically part of the carpel; this means it cannot be a drupe but is instead a drupe-like nut.
After full ripening, the shell is discarded, and the kernel is eaten. Nuts of the eastern black walnut ( Juglans nigra ) and butternuts ( Juglans cinerea ) are less commonly consumed.
Walnuts are the round, single-seed stone fruits of the walnut tree. They ripen between September and November in the northern hemisphere. The brown, wrinkly walnut shell is enclosed in a husk. [1] Shells of walnuts available in commerce usually have two segments (but three or four-segment shells can also form). During the ripening process, the husk becomes brittle and the shell hard. The shell encloses the kernel or meat, which is usually in two halves separated by a membranous partition. [1] 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, preventing rancidity. [2]
Walnut trees are late to grow leaves, typically not doing so until more than halfway through the spring.
Walnut hulls contain diverse phytochemicals, such as 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 had concentrations of 2-4% fresh weight. [3]
Walnuts also contain the ellagitannin, pedunculagin. [4] Regiolone has been isolated with juglone, betulinic acid and sitosterol from the stem bark of J. regia. [5]
The fruits of trees in the family Juglandaceae are often confused with drupes.[ clarification needed ]
The three species of walnuts most commonly grown for their seeds are the Persian (or English) walnut ( J. regia ), originating from Iran, the black walnut ( J. nigra ) – native to eastern North America – and the Japanese walnut, also known as the heartnut ( J. ailantifolia ). [6] Other species include J. californica , the California black walnut (often used as a rootstock for commercial propagation 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).[ citation needed ]
Numerous walnut cultivars have been developed commercially, which are nearly all hybrids of the English walnut. [7]
The black walnut is of strong flavor, but due to its hard shell and poor hulling characteristics, it is not commercially cultivated in orchards.[ citation needed ]
Country | Production (millions of tonnes) |
---|---|
China | 1.10 |
United States | 0.66 |
Iran | 0.39 |
Turkey | 0.33 |
Mexico | 0.14 |
World | 3.50 |
Source: FAOSTAT of the United Nations [8] |
In 2021, world production of walnuts (in shell) was 3.5 million tonnes, with China contributing 31% of the total (table). Other major producers (in the order of decreasing harvest) were the United States, Iran, and Turkey. [8]
During the Byzantine era, the walnut was also known by the name "royal nut". [9] An article on walnut tree cultivation in Spain is included in Ibn al-'Awwam's 12th-century Book on Agriculture. [10] The wal element in the name is Germanic and means foreign, especially in the sense of Latin or non-Germanic. Compare, for example, Wales, Walloons, Wallachia. The wal element is present in other Germanic-language words for the same nut, such as: German Walnuss, Dutch walnoot, Danish valnød, and Swedish valnöt.
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 batch that contains mold-infested walnuts should be entirely discarded. [2]
The ideal temperature for the extended storage of walnuts is −3 to 0 °C (27 to 32 °F) with low humidity for industrial and home storage. However, such refrigeration technologies are unavailable in developing countries where walnuts are produced in large quantities; walnuts are best stored below 25 °C (77 °F) with low humidity. Temperatures above 30 °C (86 °F) and humidity levels above 70 percent can lead to rapid and high spoilage losses. Above 75 percent humidity threshold, fungal molds that release dangerous aflatoxin can form. [2] [11]
Walnut meats are available in two forms: in their shells or de-shelled. Due to processing, the meats may be whole, halved, or in smaller portions. 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: e.g. walnut soup, walnut pie, walnut coffee cake, banana cake, brownie, fudge. Walnuts are often candied or pickled. Pickled walnuts that are the whole fruit can be savory or sweet depending on the preserving solution.
Walnuts may be used as an ingredient in other foodstuffs. Walnut is an important ingredient in baklava, Circassian chicken, chicken in walnut sauce, tarator (a summer soup in Bulgarian cuisine), and poultry or meat ball stew from Iranian cuisine.
Walnuts are also popular as an ice cream topping, and walnut pieces are used as a garnish on some foods. [16]
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. [17] [18]
Nutritional value per 100 grams | |
---|---|
Energy | 2,738 kJ (654 kcal) |
13.71 g | |
Starch | 0.06 g |
Sugars | 2.61 g |
Dietary fiber | 6.7 g |
65.21 g | |
Saturated | 6.126 g |
Monounsaturated | 8.933 g |
Polyunsaturated | 47.174 g 9 g 38 g |
15.23 g | |
Vitamins | Quantity %DV† |
Vitamin A equiv. | 0% 1 μg0% 12 μg9 μg |
Vitamin A | 20 IU |
Thiamine (B1) | 30% 0.341 mg |
Riboflavin (B2) | 13% 0.15 mg |
Niacin (B3) | 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 | Quantity %DV† |
Calcium | 10% 98 mg |
Iron | 22% 2.91 mg |
Magnesium | 45% 158 mg |
Manganese | 163% 3.414 mg |
Phosphorus | 49% 346 mg |
Potassium | 15% 441 mg |
Sodium | 0% 2 mg |
Zinc | 33% 3.09 mg |
Other constituents | Quantity |
Water | 4.07 g |
| |
†Percentages are roughly approximated using US recommendations for adults. Source: USDA FoodData Central |
Walnuts without shells are 4% water, 15% protein, 65% fat, and 14% carbohydrates, including 7% dietary fiber. In a 100-gram reference serving, walnuts provide 2,740 kilojoules (654 kcal) and "rich" amounts (20% or more of the Daily Value or DV) of several dietary minerals, particularly manganese at 163% DV; along with significant amounts of B vitamins. [19]
While English walnuts are the most commonly consumed, their nutrient density and profile are generally similar to those of black walnuts. [20] [21]
Unlike most nuts, which 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. [20]
In 2004, 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 (43 g) 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." [22] At the same time, the agency refused to authorize the claim that "Diets including walnuts can reduce the risk of heart disease" [23] and in 2010, it sent a warning letter to Diamond Foods stating there is "not sufficient evidence to identify a biologically active substance in walnuts that reduces the risk of coronary heart disease." [24]
In 2011, a scientific panel for the European Food Safety Authority recommended a health claim that "Walnuts contribute to the improvement of endothelium-dependent vasodilation" at a daily intake of 30 grams (1.1 oz); it also found that a cause and effect relationship did not exist between consuming walnuts and reduction of blood LDL-cholesterol levels. [25] The recommended health claim was later authorized by the European Commission. [26]
A 2020 systematic review assessing the effect of walnut supplementation on blood pressure (BP) found insufficient evidence to support walnut consumption as a BP-lowering strategy. [27]
As of 2021 [update] , the relationship between walnut consumption and cognitive health is inconclusive. [28]
Walnut husks can be used to make durable ink for writing and drawing. It is thought to have been used by artists including Leonardo da Vinci and Rembrandt. [29]
Walnut husk pigments are used as a brown dye for fabric [30] and were used in classical Rome and medieval Europe for dyeing hair. [31]
The fine, straight-grained wood of the black walnut is highly valued for furniture, wall paneling, automobile interiors, and gunstocks. [32]
The US Army once used ground walnut shells for abrasive blasting to clean aviation parts because of low cost and low abrasive qualities. However, an investigation of a fatal Boeing CH-47 Chinook helicopter crash (11 September 1982, in Mannheim, Germany) revealed that walnut shell grit had clogged an oil port, leading to the accident and the discontinuation of walnut shells as a cleaning agent. [33]
Commercially, crushed walnut shells are still used outside of aviation for low-abrasive, less-toxic cleaning and blasting applications. [34] In the oil and gas industry, deep bed filters of ground walnut shell are used for "polishing" (filtering) oily contaminates from water. [35]
At least two companies, LitterMaid and Naturally Fresh, make cat litter from ground walnut shells. [36] [37] Advantages cited over conventional clay litter include environmental sustainability of using what would otherwise be a waste product, superior natural biodegradability, and odor control as good or better than clay litter. [38] Disadvantages include the possibility of allergic reactions among humans and cats. [39]
Walnuts have been listed as one of the 38 substances used to prepare Bach flower remedies, [40] a herbal remedy 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". [41]
Large, symmetrically shaped, and sometimes intricately carved walnut shells (mainly from J. hopeiensis ) are valued collectibles in China where they are rotated in hand as a plaything or as decoration. They are also an investment and status symbol, with some carvings having high monetary value if unique. [42] Pairs of walnuts are sometimes sold in their green husks for a form of gambling known as du qing pi. [43]
The pistachio, a member of the cashew family, is a small tree originating in Persia. The tree produces seeds that are widely consumed as food. The word can be countable or uncountable, meaning its plural is with or without an 's'. The word can be countable or uncountable.
Walnut trees are any species of tree in the plant genus Juglans, the type genus of the family Juglandaceae, the seeds of which are referred to as walnuts. All species are deciduous trees, 10–40 metres (33–131 ft) tall, with pinnate leaves 200–900 millimetres (7.9–35.4 in), with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts (Pterocarya), but not the hickories (Carya) in the same family.
The pecan is a species of hickory native to the southern United States and northern Mexico in the region of the Mississippi River.
A food pyramid is a representation of the optimal number of servings to be eaten each day from each of the basic food groups. The first pyramid was published in Sweden in 1974. The 1992 pyramid introduced by the United States Department of Agriculture (USDA) was called the "Food Guide Pyramid" or "Eating Right Pyramid". It was updated in 2005 to "MyPyramid", and then it was replaced by "MyPlate" in 2011.
A nut is a fruit consisting of a hard or tough nutshell protecting a kernel which is usually edible. In general usage and in a culinary sense, a wide variety of dry seeds are called nuts, but in a botanical context "nut" implies that the shell does not open to release the seed (indehiscent).
Corylus avellana, the common hazel, is a species of flowering plant in the birch family Betulaceae, native to Europe and Western Asia. It is an important component of the hedgerows that were, historically, used as property and field boundaries in lowland England. The wood was traditionally grown as coppice, with the poles cut being used for wattle-and-daub building, and agricultural fencing.
Juglans nigra, the eastern American black walnut, is a species of deciduous tree in the walnut family, Juglandaceae, native to North America. It grows mostly in riparian zones, from southern Ontario, west to southeast South Dakota, south to Georgia, northern Florida and southwest to central Texas. Wild trees in the upper Ottawa Valley may be an isolated native population or may have derived from planted trees.
Juglans cinerea, commonly known as butternut or white walnut, is a species of walnut native to the eastern United States and southeast Canada.
Juglans regia, the Persian walnut, English walnut, Carpathian walnut, Madeira walnut, or, especially in Great Britain, common walnut, is an Old World walnut tree species native to the region stretching from the Balkans eastward to the Himalayas and southwest China. It is widely cultivated across Europe and the Caucasus.
Juglans ailantifolia, the Japanese walnut, is a species of walnut native to Japan and Sakhalin. It is a deciduous tree growing to 20 m (66 ft) tall, rarely 30 m (98 ft), and 40–80 cm (16–31 in) stem diameter, with light grey bark. The leaves are pinnate, 50–90 cm (20–35 in) long, with 11–17 leaflets, each leaflet 7–16 cm (2.8–6.3 in) long and 3–5 cm (1.2–2.0 in) broad. The whole leaf is downy-pubescent, and a somewhat brighter, yellower green than many other tree leaves. The male flowers are inconspicuous yellow-green catkins produced in spring at the same time as the new leaves appear. The female flowers have pink/red pistils. The fruit is a nut, produced in bunches of 4–10 together; the nut is spherical, 3–5 cm long and broad, surrounded by a green husk before maturity in mid autumn.
The fox squirrel, also known as the eastern fox squirrel or Bryant's fox squirrel, is the largest species of tree squirrel native to North America. Despite the differences in size and coloration, it is sometimes mistaken for American red squirrels or eastern gray squirrels in areas where the species co-exist.
Juglone, also called 5-hydroxy-1,4-naphthalenedione (IUPAC) is an organic compound with the molecular formula C10H6O3. In the food industry, juglone is also known as C.I. Natural Brown 7 and C.I. 75500. It is insoluble in benzene but soluble in dioxane, from which it crystallizes as yellow needles. It is an isomer of lawsone, which is the active dye compound in the henna leaf.
Juglans californica, the California black walnut, also called the California walnut, or the Southern California black walnut, is a large shrub or small tree of the walnut family, Juglandaceae, endemic to the Central Valley and the Coast Range valleys from Northern to Southern California.
Juglans australis, the nogal criollo, is a species of plant in the Juglandaceae family. This large, fast-growing tree can grow to 20 m (66 ft) tall at elevations of 0.5—1.5 km in the Southern Andean Yungas, montane cloud forests on the eastern slopes of the Andes in Tucumán, Salta, and Jujuy provinces of Argentina and Tarija and Chuquisaca departments of Bolivia. It is threatened by habitat loss.
Juglans neotropica is a species of plant in the Juglandaceae family. It is found in Colombia, Ecuador, and Peru. It is threatened by habitat loss. Common names include Colombian walnut, Ecuadorian walnut, Andean walnut, nogal, cedro negro, cedro nogal, and nogal Bogotano.
Juglans mandshurica, also known as monkey nuts, or tigernut, is a species of deciduous tree in the walnut family Juglandacea, native to the Eastern Asiatic Region. It grows to about 25 m.
Macadamia tetraphylla is a tree in the family Proteaceae, native to southern Queensland and northern New South Wales in Australia. Common names include macadamia nut, bauple nut, prickly macadamia, Queensland nut, rough-shelled bush nut and rough-shelled Queensland nut.
Juglans hindsii, commonly called the Northern California black walnut and Hinds's black walnut, is a species of walnut tree native to the western United States. It is commonly called claro walnut by the lumber industry and woodworkers, and is the subject of some confusion over its being the root stock for English walnut orchard stock.
Husk in botany is the outer shell or coating of a seed. In the United States, the term husk often refers to the leafy outer covering of an ear of maize (corn) as it grows on the plant. Literally, a husk or hull includes the protective outer covering of a seed, fruit, or vegetable.
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
walnut.