Starch ester forming

Starches may be used directly as feedstocks, or in more technical uses in modified form (typically as starch esters and ethers), or simply converted to glucose syrups for use in industrial fermentation processes or for onward conversion to isoglucose (fructose). After use of unmodified starches in ethanol production, the largest industrial user of both unmodified and modified starches is the papermaking... 

Much helpful information on starch esterification methods and on the probable properties of starch esters may be obtained by examining similar reactions and esters in the cellulose field. This is because both starch and cellulose consist of polymerized glucose units capable of esterification to the triester stage, and because the superior ability of the cellulose esters to form plastics, films, fibers, and lacquers has promoted an accumulation of information on cellulose esters which far exceeds the present knowledge of starch esters. 

Common starch esters include the acetates. High d.s. starch acetates have been formed by using acetic anhydride with either sodium acetate or pyridine catalysts at 90-100 °C [158,159,160]. The major use of starch acetates have been in the study of the stmctures of amylose and amylopectin after acid hydrolysis. Acetylation of granular starch in aqueous suspension by acetic anhydride at pH 10-11 is used to produce low d.s. starch acetates that are primarily used for the stabilization of their viscosity and for their water-soluble clarity. The acetylation decreases the hydrophilic character and increases the hydrophobic character of starch. The major uses of starch acetates is in the paper industry for surface sizing to give improved print quality, uniform porosity, surface strength, and resistance to various solvents [161]. 

Starch, often in its degraded form dextrin, and starch esters have long found application in general emulsion and dispersion technology, mainly in adhesives, construction materials or in pharmaceuticals for example, as aqueous coating material for controlled-release products [106]. 

Succinic anhydride reacts directly with starch to form a half-ester called starch succinate. Starch can also react with alkyl or alkenyl derivatives of succinic anhydride to form the corresponding succinates, among which one of the most used is starch sodium octenylsuccinate. Due to the presence of hydrophobic and hydrophilic groups, this product has interfacial activity and emulsif5ung properties. Alkenylsuccinates are used in food, pharmaceutical and industrial applications [39]. 

The complex formed by amylose with the complexing agent is usually crystalline, characterized by an amylose single helix around the complexing pol3mer [32]. Amylopectin does not interact with the complexing polymer, remaining in the amorphous phase. Starch can also be blended with polyvinyl alcohol (PVOH), for the production of foamed products, such as trays for food. Starch esters reinforced with natural fibers exhibit properties similar to those of polystyrene (PS). 

Starch esters are chemically modified starch preparations that are the most extensively applied in the food industry. When starch reacts with esteril g agents, acidic groups forming the so-called starch esters may be incorporated into both amylose and amylopectin [84]. 

It is industrially produced by the acid-catalysed hydrolysis of carbohydrates such as cellulose or starch. The global production of levulinic aid is very small (<3,000 t/a), the acid is used as a solvent in the ethyl ester form and in small niche markets [16]. 

Modification of the starch -OH groups by esterification chemistry to form starch esters of appropriate degree of substitution (1.5 to 3.0 ds) imparts thermoplasticity and water resistance (20). Unmodified starch shows no thermal transitions except the onset of thermal degradation at around 260 C. Starch... 

The reaction can be performed in a belt dryer, by spray-drying or by extrusion. The esters formed with a low DS (<0.1) belong to the - anionic starches. They exhibit enhanced paste viscosity, clarity, freeze-thaw reversibility and reduced - ret-rogradation. The pastes are c stically thinned at acidic pH, in the presence of salts and high cooking temperatures. Stabilization is achieved by crosslinking. 

---