Fiber in Animal Nutrition

11 Analytical Methods 1.2.3 Total dietary fiber In human nutrition but also in pet nutrition the total dietary fiber plays an important role. This fraction is an enzymatic gravimetric method dated back to the 19 th century. In the 1930s total unavailable carbohydrates were measured in fruits, nuts and vegetables by determining the residue insoluble in 80% ethanol. This was corrected for starch measured after enzymatic hydrolysis and for protein. Prosky et al. (1985) published a collabo- rative study for the determination of total dietary fiber in food and food products as a combination of enzymatic and gravi- metric procedures. Later on Prosky et al. (1992) validated a modified AOAC method (985.29) and extended the method for the determination of insoluble and soluble dietary fiber. For the insoluble fraction it was argued that it was not or poorly fermentable, whereas the soluble fraction was fermentable. Dietary fibers are associated with physiologic actions in the small intestine and large intestine that have important metabolic implications. In the small intestine, fibers can affect the physical characteristics of the gut content and have influence on nutrient absorption. The ability of the fiber will directly affect the viscosity of the small intestine contents (Golz and Tungland, 2002). Although solubility and fermentability of this fiber fraction do not correspond in every case. Just because a fiber is determined to be soluble by the analytical method used to classify, it does not mean that it will be highly fermentable. For example carob bean gum is highly soluble by the analytical method but is only moderately fermentable (De Vries and Rader, 2005). Similar as in human nutrition, soluble fiber, especially some hydrolytic products are of special interest due to their physiological action also in pets, for example the glycemic response (De Godoy et al., 2014). In a study with pet rabbit diets a significant correlation between crude fiber and total dietary fiber could be found. On average total dietary fiber was two times higher than the crude fiber content (Molina et al., 2015). 1.2.4 Non starch polysaccharides A further group of analytical procedures are a combination of enzymatic treatment with a chromatographic detection of sugars after hydrolysis of poly- and oligosaccharides. Following starch removal (by enzymatic hydrolysis) the residue in the sample is separated into cel lulose, non cel lulosic polysaccharides and lignin, followed by acid hydrolysis and colorimetric measurement of the component sugars (Southgate 1969, 2001). A modified version of this procedure in which alditol acetate derivates of the sugars are measured by gas-liquid chromatography was developed by Englyst et al. (1982). Englyst and Cummings (1988) further improved the method for measurement of dietary fiber as non-starch polysaccharides (NSP), i.e. non- α -glucan polysaccharides in plant material. In an overwiew upon principles of carbo- hydrate measurement, Englyst et al. (2007) characterized NSP as a grouping of several types of polysaccharides that do not have the α 1-4 glucosidic linkage characteristic of starch. The intrinsic plant cell wall NSP were defined as dietary fiber as it consistently reflects the health benefits of plant rich diets. NSP is isolated by the dispersion and enzymatic hydrolysis of starch, which is then removed along with sugars by precipitating the NSP in 80% alcohol. Following acid hydrolysis NSP constituent sugars are determined in- © ERLING Verlag