Starch rapidly hydrolysed

The accessibility of the polymer to water-borne enzyme systems is vitally important because the first step in the biodegradation of plastics usually involves the action of extracellular enzymes which break down the polymer into products small enough to be assimilated. Therefore, the physical state of the plastic and the surface offered for attack, are important factors. Biodegradability is usually also affected by the hydrophilic nature (wettability) and the crystallinity of the polymer. A semicrystalline nature tends to limit the accessibility, effectively confining the degradation to the amorphous regions of the polymer. However, contradictory results have been reported. For example, highly crystalline starch materials and bacterial polyesters are rapidly hydrolysed. 

Table X 4 summarizes similar data for the hydrolysis by maltase-free malt alpha amylase of beta dextrins obtained from arrowroot starch by the action of beta amylase. The beta dextrins were precipitated with alcohol from the reaction mixture of arrowroot starch after it had reached a limit in the hydrolysis at 60% theoretical maltose. The beta dextrins were hydrolyzed extensively by malt alpha amylase. Glucose was liberated in very small amounts even in the later stages of the hydrolysis of these beta dextrins maltose was liberated in appreciable amounts and, at equivalent hydrolyses, appeared to be formed somewhat more rapidly from the beta dextrins (Table X) than from the untreated starch (Table IX). Upon hydrolysis with malt alpha amylase the molecular weights of the beta dextrins dropped appreciably but not as extensively as when arrowroot starch was hydrolyzed directly by malt alpha amylase.

Each of these amylases causes a rapid decrease in the viscosity of starch pastes and the rapid disappearance from its reaction mixtures of products that give color with iodine. During the early stages of the hydrolysis of starch, the relative decrease in the viscosity of the substrates for hydrolysates of equivalent reducing value is most marked... 

The AKD and ASA particles are cationic in nature and covered (see Fig. 5.7) by a layer of colloid (starch or polymer) which protects them from the harsh realities of hot stock conditions. As long as the protective layer is not broken and the particles are still firmly fixed to the fibres/fines, they will remain unaffected. However, at temperatures above 60-70 C the particles begin to lose stability. For AKD, this is above its melting range of45-60 C, and similarly for ASA, where the ASA begins to become more mobile within its particle. If the particles break, then the AKD and ASA are exposed to heat and water at alkaline pH, which hydrolyses them extremely rapidly - ASA more rapidly than AKD. 

Naltotriose-producing Amylases. Amylases that produce maltotriose from starch as the major end-product have not been reported commonly. Indeed the only enzyme in this category is the enzyme from Streptomyces griseus (24). This is an exo-acting enzyme that hydrolyses its substrate from the non-reducing end to produce maltotriose in the a-configuration (31). The enzyme hydrolyses short chain amylose completely but the extent of hydrolysis with starch and waxy maize starch as substrate is 55 and 51% respectively. The optimum pH for activity is 5.6-6.0 and the enzyme is stable up to 40 C but rapidly denatured at temperatures above 45 C. 

A. Spray with 0.5 N sodium hydroxide then, after an interval of 10-15 min to allow partial drying, it is further sprayed with a reagent composed of a mixture of 1% aq. starch, glacial acetic acid and 0.1 N iodine in 4% potassium iodide soln. (50 3 1). Decolorization of the iodine reagent by the hydrolysed penicillins is fairly rapid, yielding a maximum contrast after 5-10 min... 

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