Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/21/2005
Publication Date: 7/23/2005
Citation: Hall, M. B. 2005. Starches and sugars: conceptual and analytical challenges [abstract]. Journal of Dairy Science 88 (Suppl. 1): 347.
Technical Abstract: For use in diet formulation, partitioning of carbohydrates should reflect differences in digestion and fermentation characteristics and effects on animal performance. Indices of digestibility would be useful. Partitioning of NFC has been problematic in terms of designating fractions based upon nutritional characteristics, and selecting analytical methods to separate them. The relative dearth of information on digestion characteristics of various NFC and their interactions in diets means that fractions will not soon be perfectly established. Starch and sugars are fractions for which there is some consensus. Native starch is an alpha -(1-4)-linked-glucan with alpha-(1-6) linked branch points. In feedstuffs, it can be analyzed by specific enzymatic hydrolysis and detection of glucose, or by polarimetry, though sugars can interfere with both analyses. Key challenges with starch analysis include reliability of estimates (varies by lab and method) and description of digestibility; the latter is greatly affected by processing and source. "Sugars"are an ill-defined fraction. They may include mono-. di-, and oligosaccharides (80% ethanol- and water-soluble) and water-soluble polysaccharides such as fructans. The nutritional equivalence of fructans, sucrose, glucose, and fructose has not been well explored. Resolution is needed as to which carbohydrates comprise sugars before a definitive analytical method can be chosen. Another challenge when dealing with carbohydrates that vary greatly in molecular weight is the basis on which to express them to reflect their value to animal and microbes. The greater the degree of polymerization, the greater the proportional content of hexose after accounting for water incorporated for hydrolysis. For example, 1 kg of glucose (monosaccharide) = 1 kg of hexose, whereas 1 kg of sucrose (disaccharide) or starch (polysaccharide) yield 1.05 and 1.11 kg of hexoses released upon hydrolysis, respectively. Expressing carbohydrates on a hexose basis would seem to be more reflective of equivalence than is current practice. Improved methods and nutritionally relevant definitions will improve the utility of these carbohydrate fractions in ruminant nutrition. Key Words: Sugar, Starch, Analysis