VALUE-ADDED PRODUCTS FROM COTTONSEED
Location: Commodity Utilization Research
Title: Solution NMR spectroscopy of food polysaccharides
Submitted to: Review Article
Publication Type: Review Article
Publication Acceptance Date: January 25, 2012
Publication Date: May 8, 2012
Citation: Cheng, H.N., Neiss, T.G. 2012. Solution NMR spectroscopy of food polysaccharides. Polymer Reviews. 52(2):81-114.
Interpretive Summary: Polysaccharides are major agricultural products that include such common materials as starch, cellulose, agar, and pectin. Some of them are important items for direct food consumption, and others are food additives. They are also useful starting materials for renewable, biobased materials and biofuels. Notwithstanding their importance and utility, many polysaccharides have complex chemical structures. Thus, there are many different monosaccharides in nature; the monosaccharides can form five- or six-membered rings; they can be joined together at different locations or with different configurations (a or ß). Some polysaccharides are mixtures or heterogeneous in composition. Furthermore, when substituents are placed on hydroxy groups, there can be different degrees of substitution, positions of substitution, and sequence distributions along the polysaccharide chains.
Solution NMR spectroscopy has been shown to be an excellent technique to determine the chemical structures of polysaccharides. This technique has also benefitted from new and improved NMR methodologies and enhanced instrumentation over the years. The concurrent use of other analytical techniques has broadened the range of capabilities, so that even many complex polysaccharide structures can now be deciphered. The purpose of this article is to review the literature of NMR of food polysaccharide in the past 20 years. In this way, a prospective user interested in applying NMR to investigate food polysaccharides would know the major developments and the relevant literature references.
Many polysaccharides are allowed for direct food use, where they serve a number of useful functions. In addition to possibly being a source of calories, a food polysaccharide may be a dietary fiber, bulking agent, crystallization inhibitor, thickener, encapsulant, gelling agent, foam and emulsion stabilizer, protective colloid, emulsifier and suspending agent, adhesive and binder, flocculant, swelling agent, film/coat former, or syneresis inhibitor. Many of these polysaccharides have complex structures. Some materials are mixtures containing different polysaccharide components. Over the years, NMR has been a premiere technique to characterize these materials. NMR characterization can help identify the materials in question, quantify the different functional groups present, and detect minor components and impurities. Above all, the high resolution achieved in solution NMR can provide detailed structural information on composition, sequence distribution, substitution pattern, and molecular weight (in some cases) for individual polysaccharides. The widespread use of multidimensional NMR has been helpful in achieving improved understanding of structure-spectra relationships. Concurrent application of other analytical techniques, such as methylation, esterification, fractionation, mass spectrometry, and chromatographic methods, has enabled structural information on even complex polysaccharides or mixtures to be obtained. In this article a review is given of the solution NMR of food polysaccharides, with emphasis on papers published in the past 20 years. Included in the review is a survey of 21 common food polysaccharides, the current understanding of their structures, and the techniques used for their determination.