Starch chemical modification

Table 10.8 Some common starch chemical modification reactions...

Evidence of starch chemical modification was confirmed by FTIR spectroscopy and X-ray diffraction methods. Compared to starch crystals [68-70], which can be destroyed by using high processing temperature value, CStM is not gelatinized during the processing of the composite film, therefore organic acid modified corn starch can be conveniently used as a filler for plasticized corn starch polymer matrix. 

The major limitation in developing applications, representing an obstacle to be overcome, is the hydrophilicity of starch, which leads to water sensitivity in physical properties. Strategies for decreasing sensitivity to water include derivitization. For example, acetylation at a degree of substitution greater than 1.5 of the three hydroxyl groups per monomer (6) leads to water-resistant hydrophobic starch. Chemical modifications often increase water resistance without... 

Due to the lack of a commercial supply, as well as their usually low molecular weight and poor solubility, xylans have found little industrial utility and interest in their modification has been rather low in comparison to commercially available polysaccharides such as cellulose or starch. With the aim of improving the functional properties of xylans and/or imparting new functionalities to them, various chemical modifications have been investigated during the past decade. Most of them were presented in recent reviews [3,399]. 

Dzulkefly, K Koon, S. Y. Kassim, A. Sharif, A. and Abdullah, A. H. (2007). Chemical modification of SAGO starch by solventless esterification with fatty acid chlorides. The Malaysian. Analy. Set, 11,395-399. 

Choi, S.-G. and Kerr, W.L. 2003b. Effect of chemical modification of wheat starch on molecular mobility as studied by pulsed H-1 NMR. Lebensm. If/vv. Technol. Food Sci. Technol. 36, 105-112. 

A specialty starch is defined as one where some form of chemical modification takes place to give properties to the starch that are lacking in the native product. The remainder of this paper will discuss the chemistry of modification and the chemical and physical reasons for the use of specialty starches in treating paper. 

This paper will also assume that the reader has basic starch and cellulose knowledge and that it is not necessary to review the structure of the molecules. It is, however, important to know that starch from native, non-genetically selected sources, is a mixture of two molecules and not simply one compound. Amylose is an essentially linear molecule and differs from amylopectin, which has about 4-6%oC-(l—>6) branches, even though both molecules are mainly o4 -(1—>4) linked D -glucose. The differences in these two molecules and their chemical modifications are the basis of application technology and the reason for the growing importance of specialty starches. 

Starch is one of the most abundantly produced carbon sources to be renewable on an annual basis. The chemistry of glucose and the possibility of having starch be the raw material of choice for synthetics has attracted researchers for many years. Fermentation reactions as well as chemical modification continue to be attractive. Economics has been the principal reason for lack of progress in using starch as a carbon source. However, as supplies of natural gas and petroleum decrease, new interest in starch will be found. 

Cyclodextrins, products of the degradation of starch by an amylase of Bacillus macerans(1), have been studied in terms of chemical modifications, mainly for the purpose of developing efficient enzyme mimics(2). Not only their unique cyclic structures, but also their ability to form Inclusion complexes with suitable organic molecules, led us to Investigate the total synthesis of this class of molecules(3) We describe here an approach to a total synthesis of alpha(l), gamma(2), and "iso-alpha" cyclodextrin (3). 

Hoover, R. and Sosulski, E. W. (1991). Composition, structure, functionality, and chemical modification of legume starches— A review. Can. ]. Physiol. Pharmacol. 69, 79-92. 

Wolf, W. B., Bauer, L. L., Fahey, G. C. Jr. (1999). Effects of chemical modification in vitro rate and extent of food starch digestion An attempt to discover a slowly digested starch. J. FoodAgric. Chem., 47, 4178 183. 

Starch (amylose and amylopectin) hydrolysis along with ester-fication, etherification or oxidation have been previously discussed as available methods for producing starch derivatives with improved water dispersibilities and reduced retrogradation potential (, ). Since oxidative and hydrolytic reactions are simple, easily controlled chemical modifications, starch-derived polymers made by hydrolysis alone or oxidative and hydrolytic processes were developed and tested. 

Individual flavor components are subjected to losses through distillation, flavor binding by starches and proteins, and chemical degradation during the microwave process. Specific data on flavor loss by distillation as affected by the various media and chemical modification of flavor precursors is presented in this paper. Data on flavor binding during microwave processing is addressed in a subsequent paper. 

The performance and quality of starch can be improved through chemical modification (see Chapter 17). Chemical modifications provide processed foods, such as frozen, instant, dehydrated, encapsulated and heat-and-serve products, the appropriate texture, quality and shelf life (see Chapter 21), and improved processing condition tolerance, such as improved heat, shear and acid stability. Modification also allows starches to be used in the paper industry (see Chapter 19) as wet-end additives, sizing agents, coating binders, and adhesives and as textile sizes. 

As indicated in Table 4.12, four regions which constitute the catalytic regions of amylolytic enzymes are conserved in the starch-branching isoenzymes of maize endosperm, rice seed and potato tuber, and the glycogen-branching enzymes of E. coli.286,281 It would be of interest to know whether the seven highly conserved amino acid residues of the a-amylase family listed in bold letters in Table 4.12 are also functional in branching enzyme catalysis. Further experiments, such as chemical modification and analysis of the three-dimensional structure of the BEs, would be needed to determine the nature of its catalytic residues and mechanism. 

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