Sosulski, F.

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Dietary fiber in oat hulls, flakes, and bran

University of Saskatchewan Research Archive

Dietary Fiber in Oat Hulls , Flakes and Bran Prank Sosulski Departaent of Crop Science and Plant Ecology University of Saskatchewan, Saskatoon During the past two decades there has been a ~owin~ interest in hi~h fiber foods and their role in hu.an nutrition and health. The initial evidence of the iaportance ot dietary fiber was drawn froa population studies which linked the lack of fiber in the diet to chronic bowel-related diseases prevalent in Western and industrialized countries, especially constipation, diverticulosis and cancer of the laree bowel. More recently, other diet-related disorders, includine obesity, cardiovascular disease and diabetes, have been associated with low-tiber diets . Due to the iaportance of these disease probleas and the wealth of inforaation available to the public on food fiber, there is considerable self-aedication and experiaentation being conducted by consu.ers . Since oat fiber has becoae the latest food fad, it is appropriate to review the characteristics of oat fiber in relation to those of other tiber sources . Most plant fibers are structural polysaccharides associated with cell walls and the vascular systea ot plants. Cellulose is the aain structural coaponent in plants which is lareely insoluble in the dieestive tract and resistant to enzyaatic hydrolysis . The liiUified cell walla of the bran and hulls in cereals and lecuae seeds would be lareely insoluble dietary fiber . Interior tisauea of seeds have soluble dietary fiber associated with the cellulosic cell walls · (beaicellulose and pectin) or cell secretions (guas and aucilages). Soluble and insoluble fibers are both beneficial to health , but they act in different ways . Water-insoluble tiber passes through the dieestive systea in a hiibly hydrated fora . It provides the bulk which pushes the food rapidly through the saall and laree intestine , thus relieving constipation. Alpha-cellulose (usually extracted fro• wood by-products),corn bran and wheat bran are typical bulking agents which decrease the degree · or food digestion and absorption of nutrients in general . High levels of insoluble fiber are often found in plant •aterials that have been traditionally used as aniaal feeds or agricultural w~ste~. Tbe outer cov~rings of seeds, fruits and vegetables may be contaainated with bacteria, yeasts or aolds as well as pesticides and other foreien aaterials . It is iaportant that the primary plant aaterial is sanitary and that food-grade processes are eaployed in the separation or extraction of the fiber source . Tbe physical fora of the insoluble food fiber is also i aportant. Some tiber-rich aaterials disintegrate into sharp , needle-like particles upon grinding . Oat hulls, unlike cereal brans and leguae hulls, contain spiculatua that are relatively hard and aight cause irritation or physical daaage to the aliaentary tract . Hulls are normally removed in aaking huaan oat foods , and only the clean groat with its coaponent bran, endospera and gera are consuaed. Water-soluble fiber is found in oat products, beans and other legumes, raw vegetables and fruits in relatively high concentration. These noncellulosic polysaccharides reduce plas•a-cholesterol levels and •ay increase the high density:low density lipid ratio which i s desired in - 544 -hypercholesterole•ic individuals . Researchers su~est that the soluble fiber ~baorbs aoisture like the insoluble fiber but , in the process , foras a gel ~hich traps the bile acids and prevents their reabsorption in the saall i ntestine. Soluble fiber is di~ested by bacteria in the lar~e intestine but the cholesterol is not absorbed at this sta~e . Methods tor analysis ot dietary tiber coaponents have under~one a rapid evolution in atteapta to obtain quantitative values that will predict the physiolo~ical response to the diet . Also it is very desirable tbat aeaninetul labels and coapositiona can be provided on hilb-tiber food packaees. The problea is aaply illustrated in the collaborative study conducted by Prosky et al. (1984). Analyses by over 30 laboratories deaonstrated that corn bran was exceptionally hieh in total dietary tiber , 89 . ~. as coapared to the aost coaaon fiber suppleaent , wheat bran , which had only 42 . 3• fiber . Whole wheat flour and quick-cookine oats contained only 12 . 8-13 . 0• of dietary tiber in this survey. However , studies conducted by Anderson and Chen (1983) showed that cellulose and wheat bran did not have a sieniticant effect on plasaa cholesterol levels whereas whole oats and oat bran decreased cholesterol-rich lipoproteins by 11' and 17,, respectively. Recent aedical investieations at the Northwest School of Medicine showed that the consuaption of 2 ounces of oats or oat bran daily resulted in decreases in blood cholesterol levels by nearly 8• within a few weeks (Van Hornet al., 1986). It is apparent that total dietary tiber analysis does not adequately characterize the differential effects of tiber sources in the huaan dieestive aystea. One of the advantaees of consuain~ whole ~rain cereals like oat flakes is that the tiber concentration is insufficient to cause any di~estive probleas. The intake of laree quantities of wheat bran or dry hydrocolloids like ~ar ~ or paylliua at a sinele sittin~ •ay result in excessive hydration and swellin~ at one re~ion in the ,_strointestinal tract. This can be painful, and there is risk of blockaee in extreae cases. Por a healthy diet, one should consuae a wide variety of hilh fiber, low fat foods that include oat•eal or flakes , whole erain_ breads and cereals, leeuaes , fruits and ve~etables, and avoid the concentrated tiber-rich laxatives which are offered as a panacea for an overly-refined diet. References Cited Anderson, J.W. and Chen, W.L. 1983. Leeuaes and their soluble fiber: Effect on cholesterol-rich lipoproteins . In "Unconventional Sources of Dietary Fiber, " I. Furda (ed.) p. 49, ACS Syaposiua Series. Prosky, L., Asp, M.G . . Furda, I .• DeVries , J.W., Schweizer. T. P. and Harland, B.P. 1984. Deter.ination of total dietary fiber in foods, food products. and total diets: Interlaboratory study . J . Assoc . Ott . Anal. Chea. 67 : 1044. VanHorn, L. et al . 1986. Serua lipid response to oat product intake with tat aoditied diet . J . Aaer. Diet. Assoc . 86 : 789. - 545 -

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Dietary fiber in oat hulls, flakes, and bran

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