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Bran, also known as miller's bran, is the component of a cereal grain consisting of the hard layers - the combined aleurone and pericarp - surrounding the endosperm. Corn (maize) bran also includes the pedicel (tip cap).^[1] Along with the germ, it is an integral part of whole grains, and is often produced as a byproduct of milling in the production of refined 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 the refining process - e.g. in processing wheat grain into white flour, or refining brown rice into white rice.

Bran is present in cereal grain, including rice, corn (maize), wheat, oats, barley, rye, and millet. Bran is not the same as chaff, which is a coarser, scaly material surrounding the grain, but does not form part of the grain itself, and which is indigestible by humans.^[2]

Composition

Bran is particularly rich in dietary fiber and essential fatty acids, and contains significant quantities of starch, protein, vitamins, and dietary minerals. It is also a source of phytic acid, an antinutrient that prevents nutrient absorption.

The high oil content of bran makes it subject to rancidification, 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

Rice bran is a byproduct of the rice-milling process (the conversion of brown rice to white rice), and it contains various antioxidants. A major rice bran fraction contains 12%–13% oil and highly unsaponifiable components (4.3%).^{[citation needed]} This fraction contains tocotrienols (a form of vitamin E), gamma-oryzanol, and beta-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 contains ferulic acid, which is also a component of the structure of nonlignified cell walls. Some research suggests, though, inorganic arsenic is present at some level in rice bran. One study found the levels to be 20% higher than in contaminated drinking water.^[3]

Uses

Bran is often used to enrich breads (notably muffins) and breakfast cereals, especially for the benefit of those wishing to increase their intake of dietary fiber. Bran may also be used for pickling (nukazuke) as in the tsukemono of Japan. Rice bran in particular finds many uses in Japan, where it is known as nuka (糠; ぬか). Besides using it for pickling, Japanese people add it to the water when boiling bamboo shoots, and use it for dish washing. In Kitakyushu City, it is called jinda and used for stewing fish, such as sardines.

Bran oil may be also extracted for use by itself for industrial purposes (such as in the paint industry), or as a cooking oil, such as rice bran oil.

Wheat bran is useful as feed for poultry and other livestock, as part of a balanced ration with other inputs. Wheatings, a milling byproduct comprising mostly bran with some pieces of endosperm also left over, are included in this category.

Bran was found to be the most successful slug deterrent by BBC's TV programme Gardeners' World. It is a common substrate and food source used for feeder insects, such as mealworms and waxworms. Wheat bran has also been used for tanning leather since at least the 16th century.^[4]

Research

As with cereal fibers and whole grain consumption, bran is under preliminary research for the potential to improve nutrition and affect chronic diseases.^[5]^[6]

Stability

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]

References

^ Corn Chemistry and Technology Watson and Ramstad 1987 p. 69
^ Catsberg, C. M. E. (1990). Food Handbook. Dordrecht: Springer Netherlands. doi:10.1007/978-94-009-0445-3_15. ISBN 978-94-009-0445-3. "chaff, which is indigestible for humans"
^ Sun, Guo-Xin; Williams, Paul N.; Carey, Anne-Marie; Zhu, Yong-Guan; Deacon, Claire; Raab, Andrea; Feldmann, Joerg; Islam, Rafiqul M.; Meharg, Andrew A. (2008). "Inorganic Arsenic in Rice Bran and Its Products Are an Order of Magnitude Higher than in Bulk Grain". Environmental Science & Technology. 42 (19): 7542–7546. Bibcode:2008EnST...42.7542S. doi:10.1021/es801238p. PMID 18939599.
^ Rossetti, Gioanventura (1969). the plictho. Massachusetts: The Massachusetts Institute of Technology. pp. 159–160. ISBN 978-0262180306.
^ Barrett EM, Batterham MJ, Ray S, Beck EJ. (2019). "Whole grain, bran and cereal fibre consumption and CVD: a systematic review". British Journal of Nutrition. 121 (8): 914–937. doi:10.1017/S000711451900031X. PMID 30761962. S2CID 73449809.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Jefferson, A., & Adolphus, K. (2020). "The Effects of Increasing Intake of Intact Wheat Fibre or Wheat Bran on Gut Microbiota Diversity: A Systematic Review". Proceedings of the Nutrition Society. 79 (OCE2): E531. doi:10.1017/S0029665120004802.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Lehtinen, Pekka; Kiiliäinen, Katja; Lehtomäki, Ilkka; Laakso, Simo (2003). "Effect of Heat Treatment on Lipid Stability in Processed Oats". Journal of Cereal Science. 37 (2): 215–221. doi:10.1006/jcrs.2002.0496. ISSN 0733-5210. See figure 1 in particular