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A walnut is the nut of any tree of the genus Juglans (Family Juglandaceae), particularly the Persian or English walnut, Juglans regia. 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. Characteristics. 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. Types. 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. The commercially produced walnut varieties are nearly all hybrids of the English walnut. 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. Walnuts are late to grow leaves, typically not until more than halfway through the spring. They also secrete chemicals into the soil to prevent competing vegetation from growing. Because of this, flowers or vegetable gardens should not be planted too close to them. Production. The worldwide production of walnuts has been increasing rapidly in recent years, with the largest increase coming from Asia. The world produced a total of 2.55 million metric tonnes of walnuts in 2010; China was the world's largest producer of walnuts, with a total harvest of 1.06 million metric tonnes. The other major producers of walnuts were (in the order of decreasing harvest): Iran, United States, Turkey, Ukraine, Mexico, Romania, India, France and Chile. The average worldwide walnut yield was about 3 metric tonnes per hectare, in 2010. Among the major producers, eastern European countries have the highest yield. According to the FAO, the most productive walnut farms in 2010 were in Romania, with yields above 23 metric tonnes per hectare. The United States is the world's largest exporter of walnuts. The Sacramento and San Joaquin valleys of California produce 99 percent of the nation’s commercial English walnuts. Top 10 Walnut Producing Countries - 2012 1  China 1,700,000 2  Iran   450,000 3  United States 425,820 4  Turkey 194,298 5  Mexico 110,605 6  Ukraine 96,900 7  India 40,000 8  Chile 38,000 9  France 36,425 10  Romania 30,546        World 3,282,398 Storage. 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. The ideal temperature for longest possible storage of walnuts is in the -3 to 0° C 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 and low humidity. Temperatures above 30° C, 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. Freshly harvested raw walnuts offer the best color, flavor and nutrient density when with water content between 2 to 8 percent. Food use. 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. Walnut Whip, coffee and walnut cake and pickled walnuts are three disparate examples. 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. Nutritional value. Walnuts are a nutrient-dense food: 100 grams of walnuts contain 15.2 grams of protein, 65.2 grams of fat, and 6.7 grams of dietary fiber. The protein in walnuts provides many essential amino acids. While English walnuts are the most common, their nutrient density and profile are significantly different from those of black walnuts. For example, the Omega-3 fatty acid content of English walnuts is approximately 4.5 times that of black walnuts. Unlike most nuts that are high in monounsaturated fatty acids, walnut oil is composed largely of polyunsaturated fatty acids (47.2%), particularly alpha-linolenic acid (18:3n - 3; 9.1%) and linoleic acid (18:2n - 6; 38.1%). The beneficial effects of this unique fatty acid profile have been a subject of many studies and discussions. Banel and Hu concluded in 2009 that while walnut-enhanced diets are promising in short term studies, longer term studies are needed to ascertain better insights.
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