Carbohydrate Analysis

This chapter covers the principles, procedures, and applications of carbohydrates analysis commonly used for nutrition labeling, quality assurance, or research for food ingredients and/or products. While chromatographic methods have largely replaced many older methods, some older methods continue to be commonly used for research and quality assurance [e.g., colorimetric methods for total carbohydrate (phenol-sulfuric acid method), various reducing sugar methods (e.g., Somogyi-Nelson method), and physical measurements (based on specific gravity or refractive index)]. Chromatographic methods (high-performance liquid chromatography and gas chromatography) separate mixtures into their component sugars, identify each component by retention time, and provide a measurement of the quantity of each component. Enzymatic methods are specific and sensitive, but seldom, except in the case of starch, is determination of only a single component desired. In the absence of a universal procedure for analysis of most polysaccharides, their analysis generally involves isolation followed by identification based on hydrolysis to constituent monosaccharides and their determination. An exception is starch, which can be measured specifically by digestion to glucose using specific enzymes (amylases), followed by measurement of the glucose released. Insoluble dietary fiber, soluble dietary fiber, and total dietary fiber are each composed primarily of non-starch polysaccharides. Methods for the determination of total dietary fiber and its components rely on removal of the digestible starch using amylases and removal of digestible protein with a protease, leaving a non-digestible residue. Improved methodologies for fiber analysis are closing the gap between prescribed, regulatory-based dietary fiber definitions and the previous inability to measure all designated fiber components.