Starch: a natural polysaccharide for the design of innovative materials

Starch in its native structure, is the largest energy source in human and animal diet; moreover it is capturing growing attention as a renewable natural resource in material science. Indeed by chemical, physical or enzymatic modification, it can change its physio-chemical properties and becomes suitable in the food industry as densifier or in packaging as biodegradable plastic (1). This work aims at studying different strategies for the modification of starch in order to introduce a photoresponsive behavior by a cinnamyl group. The photoreversible functionality may allow the cross-linking of starch with other (Bio)(macro)molecules, including inorganic matrices for the design of hybrid materials (see Orsini abstract). Modification of starch was accomplished by different chemistries (i.e. etherification, esterification) in order to optimize the degree of substitution, which is fundamental in determining the subsequent photoreactive process. The experimental determination of the degree of substitution (DS), defined as the average number of functional groups introduced in the anhydro glucose unit (AGU), is a key parameter. In order to properly quantify the degree of substitution DS the 1H-NMR technique is preferred to titration, since titration suffers from lack of accuracy and reproducibility (2). In the 1H-NMR analysis the dissolution of the sample is a key issue for the quantitative estimation of DS. However, dissolution of starch and its derivatives is not trivial (3).