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By Mark Anthony, Ph.D., Technical Editor | 03/27/2012
More than 40 years ago, Denis Burkitt, M.D., proposed that the Western world suffered from a deficiency of cereal fiber that led to a number of diseases including diverticulosis and colon cancer. He postulated that the western diet was too rich in protein, fat, and refined carbohydrates, and suggested increasing dietary fiber would increase bulk and reduce transit time as digested food passed through the large intestine. This would in turn reduce exposure of carcinogens to the wall of the large bowl and reduce intestinal pressure.
Burkitt brought the story of fiber to the attention of the world and the resultant book, "Don't Forget Fibre in Your Diet," published in 1979, was a best seller.
We've learned a lot about the composition of different dietary fibers since then, and while the promise of preventing colon cancer by increased dietary fiber did not happen as Burkitt suggested, dietary fiber does in fact reduce the risk of diseases like diverticulosis and diverticulitis, and it lowers cholesterol, depending upon the fiber. Reduction of transit time is the property we associate with cereal fiber, generally the bran of wheat, which is mostly insoluble fiber.
Wheat bran, an important byproduct (along with wheat germ) of white flour production, found a home in many popular cereals promising to keep patrons regular. There are many forms of bran, each with a different composition and potentially different benefits both to the consumer as a functional food and the processor as a useful ingredient.
Bran is the hard protective outer layer of the grain composed of the aleurone — which contains about a third of the grain's protein — and the pericarp, the coating of the embryo. The aleurone layer can extend to a sublayer that merges into the endosperm. (Bran is not the same thing as chaff, a tough inedible scaly material that surrounds the grain. The chaff must be separated for the grain to be utilized as food.)
The bran and the germ, the growth center of the seed, are the integral parts of whole grains lost to conventional milling. Milling improves shelf life because the germ and bran contain essential fatty acids that can go rancid with time. But is a high price to pay in terms of nutrition.
The consumer preference for white flour consequently rendered the bran and germ popular dietary supplements. Bran is milled from a number of cereal grains, including wheat, rice, corn (maize), oats, barley and even millet. And each form of bran is distinct in composition, depending upon the properties of the grain itself and how deeply into the grain the milling process cuts.
All forms of bran are particularly rich in dietary fiber and essential fatty acids. They also can contain significant quantities of starch and protein, vitamins and minerals. The type of fiber can vary significantly with different grains. Consumers are most familiar with wheat bran, which is mostly insoluble fiber, a very potent substrate for reducing transit time of food in the colon as Burkitt suspected.
"Oat bran has become popular because of its content of soluble fiber in the form of beta-glucans," says Darren Shubert, sales manager for Grain Millers (www.grainmillers.com), Eugene, Ore. Beta-glucans are carbohydrates similar to cellulose, chains of glucose sugars that our digestive enzymes cannot handle, making it a valuable fiber.
Soluble fibers trap bile, which is released into the small intestine from the gall bladder where it is stored until we eat fat. Bile, made by the liver from cholesterol, helps to emulsify fat. When the bile is trapped by soluble fiber, it can't be recycled. This forces the liver to pull cholesterol out of the blood to make more bile, thus lowering LDL cholesterol.
"What most people don't know is that barley has a greater concentration of beta-glucans than oats," adds Shubert. "That makes barley bran an equally important form of fiber. In fact, whole grain barley itself is highly valuable as a source of fiber because the beta-glucans are buried more deeply into the endosperm than in most grains."
But grains aren't alone in providing healthful bran. Soak a raw almond in water for about six hours and you can easily peel off the skin. Although not a true bran as with a grain, the resultant product is a functional ingredient with most of the properties of grain-derived bran, plus some unique ones of its own.
"Almond bran is created from the brown outer skin of an almond removed during the almond blanching process," explains Robert Miltner, vice president of business development for Nut-trition Inc. (www.nut-trition.com), Hughson, Calif.
Nut-trition developed the technology to separate, dry and size the raw almond skins into a variety of flakes and powders. "We use the term bran because that term is so well understood as a functional ingredient," says Miltner. Of all the nuts, only almonds are blanched in great enough quantity to be marketed as an ingredient for the food industry.
Almond bran contains mainly cellulose as a fiber source, and is a rich source of minerals, polyphenols (antioxidants), plant sterols (which can lower LDL cholesterol) and even low-molecular-weight pectin, a soluble fiber. "Almonds have been approved by FDA as a part of a heart-healthy diet, much of which seems to derive from these compounds and minerals in the outer covering," Miltner adds. "In applications, it adds a mild nutty flavor and texture, plus it can be used as a 1:1 replacement for wheat bran in baked recipes. Almond Bran easily mixes with other ingredients commonly used in baked goods and confectionary products."
Bran is not a monolithic ingredient, but rather the highly variable outer layer of a seed rich in valuable properties that range in fiber content, fiber composition and nutrient content — components as varied as the seeds from which the bran is derived. It can enhance the texture of the product and the nutrient value to the consumer.