Starch Complexes with Macromolecules

XI. Starch Complexes with Macromolecules 1. Starch-Protein Complexes... 

To standardize how enzyme activities are expressed, the Enzyme Commission of the lUB proposed that the unit of enzyme activity be defined as the quantity of enzyme that catalyzes the reaction of 1 pmol of substrate per minute and that this unit be termed the international unit (U). Catalytic concentration is to be expressed in terms of U/L or kU/L, whichever gives the more convenient numerical value. In this chapter, the symbol U is used to denote the international unit. In those instances in which there is some uncertainty about the exact nature of the substrate or when there is difficulty in calculating the number of micromoles reacting (as with macromolecules such as starch, protein, and complex lipids), the unit is to be expressed in terms of the chemical group or residue measured in following the reaction (e.g., glucose units, or amino acid units formed). 

Novamont s Mater-Bi starch-based technology implies processing conditions able to destroy the crystallinity of amylose and amylopectin, in the presence of macromolecules, such as specific polyesters, which are able to form a complex with amylose. They can be of natural or synthetic origin. The specification of the starch, that is, the ratio between amylose and amylopectin, the nature of the additives, the processing conditions and the nature of the complexing agents allow engineering of various supramolecular structures with very different properties. 

The complexation of starch by macromolecules can give rise to even more stable complexes which play an important role on the final properties of the starch-based polymer. Unlike amylose, the majority of amylopectin does not interact with the complexing agent and remains in its amorphous state. In the following paragraphs, a summary of the state of the art related to starch destructurisation with synthetic polymers will be made. 

It is now more or less believed that the iodine is held as an absorption complex within the helical chain of the macromolecule f3-amylose i.e., a component of most starches. However, another component, a-amylose, is undesirable because it produces a red-colouration with iodine which is not readily reversible, and... 

These basic organic molecules can react with each other to form larger, more complex macromolecules. Amino acids can combine to form larger peptide chains, which in turn can combine to form protein molecules. Likewise, simple sugar molecules can combine to form polysaccharide molecules that combine to form starches and cellulose. 

Calculations of the distribution functions of sizes of relaxed structures (Figure 5.11b) show that the starch/silica hydrogel at ft=2.34 g/g is characterized by narrower molecular pockets than that at ft =17.9 g/g. The narrowest pockets (nanopores) are found for hydrogel with gelatinized starch alone. Notice that all distributions show complex structures of pockets (voids) between/inside starch molecules that are in agreement with complex structure of unfolding starch macromolecules. 

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