Carbohydrate and Fiber Degradation Products of Bran Phytate Formed during Digestion in the Human Small Intestine: Effect of Extrusion Cooking on Digestibility1 ANN-SOFIE SANDBERG, HENRIK ANDERSSON,* NILS-GUNNAR CARLSSON AND BRITTMARIE SANDSTRÖM* Department of Food Science, Chalmers university of Technology, S-402 29 Göteborg,Sweden and 'Department of Clinical nutrition, University of Göteborg,S-413 45 Göteborg,Sweden ABSTRACT To investigate the digestion of phytate in the stomach and small intestine in humans, studies were performed in subjects with established ileostomy. A re cently developed high performance liquid chromatography method made it possible to analyze phytate and its deg radation products in food and digesta. The digestibility of phytate in raw bran and extruded bran was investigated in seven ileostomy patients. Each subject was studied for two 4-d periods while consuming a constant low fiber diet with the addition of either 54 g/d of a bran-gluten-starch mixture or the corresponding extruded product. During passage through the subject's stomach and small intestine 58%, on average, of the phytate in unprocessed bran was hy- drolyzed to inositol penta-, tetra- and triphosphates. When bran was subjected to extrusion cooking, 25% of the in ositol hexaphosphate was hydrotyzed to penta- and tetra- phosphate and the phytase activity ceased. Essentially no phytate digestion occurred when the ileostomy subjects consumed the extruded product. The reduced digestibility might be due to the lost phytase activity or to formation of indigestible phytate complexes during extrusion cook ing. J. Nutr. 117: 2061-2065, 1987. INDEXING KEY WORDS: •phytate • inositol phosphates •digestion •extrusion cooking •bran • ileostomy subjects The role of phytate (inositol hexaphosphate) in hu man nutrition is due to its mineral-binding capacity, which limits the availability of essential dietary min erals. If the phytate is digested it may also serve as a source of phosphorus (1). In mature plant seeds the inositol phosphates occur mainly as hexaphosphate (2), but during food processing and digestion in the human gut it is most likely that other inositol phosphates are formed. These compounds may differ markedly from phytate with regard to their physiological and antago nistic properties. The degree of phytate degradation 0022-3166/87 $3.00 ©1987American Institute of Nutrition. Received 8 April 1987. Accepted 31 August 1987. 2061 and the site where it occurs therefore seem to be of importance for the absorption of minerals. Extrusion cooking is generally a high temperature, short-time process using high shear at elevated pressure and can be used to give texture to a wide variety of foods such as vegetable proteins, breakfast cereals, weaning foods, crispbread, snacks and sweets. Modi fications of the constituents during extrusion cooking may affect the nutritional value (3). Because several of these products contain appreciable amounts of phytate, the effect of extrusion on phytate and mineral availa bility should be considered. We have previously found through measurements using an iron precipitation method that extrusion cooking affects the digestibility of phytate (4). However, such a method lacks the spec ificity to distinguish between the fully substituted (hexa) inositol phosphate and its partially dephosphorylated analogues. The aim of the present investigation was to deter mine by means of a more specific method the extent of degradation of bran phytate in the stomach and small intestine in humans and also which degradation prod ucts were formed. For this purpose, analyses of food and ileostomy contents from the previous study (4) were performed with a recently developed high performance liquid chromatography (HPLC) method (5). The effect of extrusion cooking on the formation of dephosphor ylated analogues of phytate and their digestibility was also investigated. MATERIALS AND METHODS Subjects. Four men and three women volunteered for the study. Sex, age and diagnosis have been de- 'This work was supported by the Swedish Council for Forestry and Agricultural Research (Project No. 606/84 DL 12). by guest on July 10, 2011 jn.nutrition.org Downloaded from