Starch degradation mechanism

Starch degrades by two mechanisms photo- and bio-degradation. Eor this reason, most blends with synthetic resins will be sensitized by addition of organometallics — transition metal compounds. The rate of degradation is sensitive to temperature. 

In order to describe the kinetics of enzymatic starch depolymerization, information on reaction rate, reaction extent, and product distribution profiles are required. Traditional end-group analysis can be used to a limited extent in the first two areas, but will not provide information about the last important subject. Hence, SEC profiles can provide sufficient insight into the mechanism of starch degradation. 

The mechanism of starch degradation by the yeast Lipomyces starkeyi was studied in strain CBS 1807. It was shown that the amylolytic system is associated with cell walls. It is equally well induced by starch or maltose. The enzyme exhibits considerable a-amylase type activity and also liberates a small amount of D-glucose. Enzyme synthesis occurs during the exponential growth phase. The regulation of the synthesis of the enzyme is discussed. 

In general, dehydration and depolymerization have been considered as the two main processes associated with the degradation mechanism of polysaccharides [22], In the case of starch, ether bonds and unsaturated stmctures are formed via thermal condensation between hydroxyl groups of starch chains, which eliminates water and other small molecnles, and by dehydration of hydroxyl groups in the glucose ring. It was observed that water was the main prodnct of decomposition of modified starch at a temperatnre below 300°C, formed by inter-molecnlar or intramolecular condensation of starch hydroxyls [23,24],... 

Degradation mechanisms for polymers exposed to aquatic and terrestrial environments are presented and their significance is discussed in terms of current definitions, standards, polymer materials and biodegradation kinetics in model polymer-starch blends [1],... 

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