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Bran, also known asmiller's bran, is the component of acereal grain consisting of the hard layers – the combinedaleurone andpericarp – surrounding theendosperm.Corn (maize) bran also includes the pedicel (tip cap).[1] Along with thegerm, it is an integral part ofwhole grains, and is often produced as abyproduct ofmilling in the production ofrefined grains. Bran is highly nutritious, but is difficult to digest due to its high fiber content; its high fat content also reduces its shelf life as the oils/fats are prone to becoming rancid. As such, it is typically removed from whole grain during therefining process – e.g. in processing wheat grain into white flour, or refining brown rice into white rice.
Bran is present in cereal grain, includingrice,corn (maize),wheat,oats,barley,rye, andmillet. Bran is not the same aschaff, which is a coarser, scaly material surrounding the grain and is indigestible by humans.[2]
Bran is particularly rich indietary fiber andessential fatty acids, and contains significant quantities ofstarch,protein,vitamins, anddietary minerals. It is also a source ofphytic acid, anantinutrient that prevents nutrient absorption.
The high oil content of bran makes it subject torancidification, one of the reasons that it is often separated from the grain before storage or further processing. Bran is often heat-treated to increase its shelf life.
| Nutrients (%) | Wheat | Rye | Oat | Rice | Barley |
|---|---|---|---|---|---|
| Carbohydrates (excluding starch) | 45–50 | 50–70 | 16–34 | 18–23 | 70–80 |
| Starch | 13–18 | 12–15 | 18–45 | 18–30 | 8–11 |
| Proteins | 15–18 | 8–9 | 13–20 | 15–18 | 11–15 |
| Fats | 4–5 | 4–5 | 6–11 | 18–23 | 1–2 |
Rice bran is a byproduct of therice-milling process (the conversion ofbrown rice towhite rice), and it contains variousantioxidants. A major rice bran fraction contains 12%–13% oil and highlyunsaponifiable components (4.3%).[citation needed] This fraction containstocotrienols (a form ofvitamin E),gamma-oryzanol, andbeta-sitosterol; all these constituents may contribute to the lowering of the plasma levels of the various parameters of the lipid profile. Rice bran also contains a high level of dietary fiber (beta-glucan,pectin, and gum). It also containsferulic acid, which is also a component of the structure of nonlignifiedcell walls. Some research suggests, though, inorganicarsenic is present at some level in rice bran. One study found the levels to be 20% higher than in contaminated drinking water.[3]
Bran is often used to enrichbreads (notablymuffins) andbreakfast cereals, especially for the benefit of those wishing to increase their intake ofdietary fiber. Bran may also be used forpickling (nukazuke) as in thetsukemono ofJapan, as well as in the production of East Asianblack vinegars.
Rice bran in particular finds many uses in Japan, where it is known asnuka (糠;ぬか). Besides using it for pickling, Japanese people add it to thewater whenboilingbamboo shoots, and use it fordish washing. InKitakyushu City, it is calledjinda and used for stewing fish, such assardines.
Wheat bran is useful asfeed forpoultry and otherlivestock, as part of a balanced ration with other inputs. Wheatings, a milling byproduct comprising mostly bran with some pieces ofendosperm also left over, are included in this category.
Bran oil may be also extracted for use by itself for industrial purposes (such as in the paint industry), or as acooking oil, such asrice bran oil.
Bran was found to be the most successful slug deterrent by BBC's TV programmeGardeners' World. It is a common substrate and food source used for feeder insects, such asmealworms andwaxworms. Wheat bran has also been used for tanning leather since at least the 16th century.[4]
As with cereal fibers andwhole grain consumption, bran is under preliminary research for the potential to improve nutrition and affect chronic diseases.[5][6]
Commonly, bran is heat-treated with the intention of slowing undesirable rancidification, but a 2003 study of heat-treatment of oat bran found a complex pattern whereby increasingly intense heat treatment reduced the development of hydrolytic rancidity and bitterness with time, but increased oxidative rancidity. The authors recommended that heat treatment should be sufficient to achieve selective lipase inactivation, but not so much as to render the polar lipids oxidizable upon prolonged storage.[7]
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