Enzymically depolymerized starches

Converted starches, also called thin-boiling starches, are produced by degradation of the starch chains into small segments. They can be cooked in water at higher concentrations than native starches. Low-viscosity starches are needed in applications where a high solid starch paste with a pumpable and workable viscosity is required. There are four classes of commercial converted starches dextrins (hydrolysis in solid-state) acid-modified starches (hydrolysis in a slurry) oxidized starches and enzymically depolymerized starches. 

Depolymerizing modification of starch usually involves the use of enzymes, acid- (and less frequently base-) catalyzed hydrolysis, and thermolysis alone and thermolysis combined with acid-catalyzed hydrolysis (see a recent survey in this Series2). Despite several studies, the physical treatment of starch has not yet resulted in major practical applications. The aim of this Chapter is to review physical methods as tools for the treatment of starch which deliver amounts of energy suitable for depolymerizing starch to target products. It should be noted that the duration of such processes does not need to exceed that for conventional, namely enzymic, chemical, and thermal modifications. Moreover, a potential advantage of nonconventional physical treatments is the fact that they generate no waste products. 

Preiss, J., and Boyer, C. D. 1980. Evidence of independent control of the multiple forms of maize endosperm branching enzymes and starch synthases. In Mechanisms of Saccharide Polymerization and Depolymerization (J. J. Marshall, ed,), pp. 161-174. Academic Press, New York. 

The use of alpha amylase on starch produces a depolymerized starch. The enzyme, cycloamylose gluconotransferase, is responsible for production of cycloamyloses. Biological modification is advantageous as enzyme reactions are often very specific, recognizing subtle variations in the polymer such as a particular monomer linkage or an or conformation. 

Starch can be hydrolyzed efiiciendy by acid treatment or by the use of enzymes yielding depolymerized starches with increased water solubility compared to the native starch. 

Degradation of starches with malt diastatic enzymes (which contain a-and )S-amylase) depolymerize starch to give soluble starch . "Thin-boiling starches are produced by mild acid hydrolysis of starch. D-Glucose is produced commercially by the total acidic hydrolysis of starch. 

Enzymes are specific, however. For example, starch is depolymerized using enzymes to D-glucose (dextrose). The solution of glucose is then treated with glucose isomerase [9055-00-9] to give D-fmctose in about 42% yield. No D-mannose is formed. Addition of isolated D-fmctose to this solution gives the common 55% high fmctose com symp (HFCS) so widely used in soft drinks in the United States. HFCS is about 1.5 times as sweet as sucrose. 

D-Glucose is produced by complete depolymerization of starch with enzymes that catalyze the hydrolysis of both its (1 — 4) and (1 — 6) linkages. Crystalline a-D-glucopyranose is generally sold as dextrose. Glucose is also isomerized to D-fmctose to produce high fmctose com symp (HFCS). 

While starches are commonly used, they are relatively poor viscosifiers. Acids and bacterial enzymes readily attack the acetal linkages resulting in facile depolymerization. Both formaldehyde and isothiazolones have been used as starch biocides (17). Development of improved high temperature water viscosifiers for drilling and other oil field applications is underway. For the... 

Gums are tasteless, odorless, colorless, and nontoxic. None, except the starches and starch derivatives, are broken down by human digestive enzymes. All are subject to microbiological attack. All can be depolymerized by acid- and enzyme-catalyzed hydrolysis of the glycosidic (acetal) linkages joining the monomeric (saccharide) units. 

Many kinds of native and modified starches are being used on the size press.207 The governing factors are dispersion viscosity, film formation and resistance to retrogra-dation. For low-cost applications, native corn starch is depolymerized in the paper mill by enzymic or thermal-chemical conversion. In-plant converted starches are... 

Depolymerization of hemicellulosic structure is still being developed. Because of its more complicated structure involving several kinds of sugar units in variously linked conformations, more than one specific enzyme is needed. More simple plant starches can be effectively broken down to sugars with combinations of enzymes, including amylases and glucoamylases. 

The properties and general specificity of aZpha-amylase are well established. There are slight differences in the properties of the enzymes from different sources, but all hydrolytically depolymerize the starch-type polysaccharides in an essentially random manner (at least... 

Inventory as siloxane and silicone, silsesquioxane, a protein (albumin, casein, gelatin, gluten, hemoglobin), an enzyme, a polysaccharide (starch, cellulose, gum), rubber, or lignin. This exclusion does not apply to a polymeric substance that has been hydrolyzed, depolymerized, or otherwise chemically modified, except in cases where the intended product of this reaction is totally polymeric in structure. ... 

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