Fiber in Animal Nutrition

13 Conclusion (Englyst et al.) in two food materials. Due to the strong extraction NDF and ADF had to lowest values, the enzymatic-gravimetric method has higher values than the enzymatic -chromatographic because in the former lignin and ash are included. With respect to human nutrition the authors concluded, that the AOAC (TDF) and Englyst method should be preferred, because they make a detailed description of single fiber components possible. They seem well suited for routine analysis of dietary fiber because the methods are relatively rapid and no sophisticated equipment is needed. The AOAC and Englyst method have signi- ficant differences concerning the quantities of soluble and insoluble fibers. This may be caused by the different reaction conditions during the separation process. 1.2.5 New aspects in animal nutrition due to increase in understanding of its physiological effects An important effect which is connected with dietary fiber, however cannot fully be described with the analytical methods, is the water holding capacity. Dietary fiber swells to a variable extent in water. The water holding capacity is determined by the physicochemical structure of the molecule, and also by the pH and electrolyte concentration of the surrounding f luid; thus during the passage through the gut, dietary fiber must swell to a very variable extent. There are several different methods of measuring the water holding capacity of dietary fiber (centrifugation, dialysis bags, filtration) each leading to different results. Furthermore the particle size and method of preparation of samples are important determinants of water-holding capacity, as measured in the laboratory (Lov, 1993). With respect to human nutrition Englyst et al. (2007) pointed out that physiological and health effects of carbohydrates are dependent not only on thei r primar y chemical form but also on their physical properties, which include water solubility, gel formation, crystallization, association with other molecules and aggregation into the complex structures of the plant cell wall. With respect to the analytical methods they stated, that there should be a commitment to move away from empirical based methods that measured unspecified materials towards rational methods providing direct and specif ic measurement of different types and categories of carbohydrates as their chemically identified components. 1.3 Conclusion Dietary fiber is defined variably depending on nutritional and physiological aspects.Thereby the definition is closely related to different analytical methods. Common acknowledged methods define crude fiber, detergent fiber, total dietary fiber or non starch polysaccha- rides. Nowadays a better understanding of the physiological effects of fiber in animal nutrition opens new aspects for evaluati- on. Therefore in the future more attention should be paid to fiber characteristics like water solubility, water holding capacity or gel formation in order to define dietary fiber more specifically. © ERLING Verlag