Starch ester/ether substitution

Starches have been chemically modified to improve their solution and gelling characteristics for food applications. Common modifications involve the cross linking of the starch chains, formation of esters and ethers, and partial depolymerization. Chemical modifications that have been approved in the United States for food use, involve esterification with acetic anhydride, succinic anhydride, mixed acid anhydrides of acetic and adipic acids, and 1-octenylsuccinic anhydride to give low degrees of substitution (d.s.), such as 0.09 [31]. Phosphate starch esters have been prepared by reaction with phosphorus oxychloride, sodium trimetaphosphate, and sodium tripolyphosphate the maximum phosphate d.s. permitted in the US is 0.002. Starch ethers, approved for food use, have been prepared by reaction with propylene oxide to give hydroxypropyl derivatives [31]. 

Our objective was to prepare more hydrophobic starches to incorporate them in latex preparation for decorative paints so that substrates derived from fossil fuel can be replaced by modified starches derived from renewable resources. Partial substitution of starch with acetate, hydroxypropyl, alkylsiliconate or fatty-acid ester groups was described in the literature for the synthesis of more hydrophobic starch. An alternative route was employed consisting of grafting octadienyl chains by butadiene telomerization (8,9). This reaction (Figure 4) was catalyzed by hydrosoluble palladium-catalytic systems prepared from palladium diacetate and trisodium tris(m-sulfonatophenyOphosphine (TPPTS). Starch octadienyl ethers are expected to be much less sensitive towards hydrolysis compared to the esterified starches. 

Substituted products of starch are the esters and ethers of starch which prevent the formation of ordered structures in a starch paste and retard retrogradation. 

If the substituents are not stable during acid hydrolysis or methanolysis, the complementary substitution pattern can be determined after permethylation, as already noted. Examples are organic (acetates) and inorganic esters (sulfates), and benzyl and silyl ethers. " Such an approach was applied as early as 1964 to vinyl starches."" In contrast to the direct determination of the substituent pattern, incomplete methylation and consequently erroneous evaluations cannot be recognized from the product pattern obtained in the indirect methods. If the average DS is known from an independent determination, it allows at least a certain control. Therefore, the absence of OH absorption should be carefully monitored by IR spectroscopy. 

Chemical modifications may also include the derivatization of starch by reaction of its hydroxyl groups with alkylene oxides. Other suitable substances are such that form ether linkages, ester linkages, urethane linkages, carbamate linkages, or isocyanate linkages. The degree of substitution of the chemically modified starch varies from 0.05 to 0.2. 

For these and a variety of special non-food purposes esters with higher fatty acids, succinic, adipic and citric acids and carbamates (reaction products with urea), have also been prepared. Examples of starch ethers are 2-hydroxyethyl and 2-hydroxypropyl starches prepared by reaction of starch with oxirane (ethylene oxide) and methyloxirane (propylene-l,2-oxide). The reaction occurs preferentially at the secondary hydroxyl groups at C-2, with less on the C-3 and C-6 hydroxyl groups. The most common products are those shown in Figure 4.15. The degree of substitution tends to be <0.2. According to the reaction conditions, polyoxaalkyl starches ... 

Starch-based products suffer from water sensibility, brittleness, and poor mechanical properties. To solve these problems, various approaches are possible. In order to improve the mechanical properties of starch, modification by acetylation, grafting of monomers like styrene and methylmethacrylate, or blending with other polymers are the strategies to be pursued (Lawton and Fanta, 1994 Wang et al., 2003]. Chemical modification (e.g., hydroxylation (Chaudhary et al., 2008] and acetylation (Volkert et al., 2010] of starch by substituting ester or ether groups for... 

E amidon transform hydrophobique Granular starch can be chemically modified by substitution of the hydroxyl groups with hydrophobic substituents in the usual way as esters and ethers. The substituent acid anhydrides or halogen-ides and epoxides are containing usually allQrl, aryl- and aralkyl-groups with 8 or 10 or more C-atoms ... 

S. are chemically - modified starches, where the primary/secondary OH-groups are substituted in part or entirely by ether and/or ester groups. 

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