Modified Starches and the Chemical Treatments of Native Starches

Starch is a complex carbohydrate that is composed of two main polysaccharides, amylose and/or amylopectin. These polysaccharides contain various amounts of naturally bound phosphate esters and counter ions. Amylose is a predominantly linear molecule of α-D-glucopyranosyl units linked by (1-4)-α-linkages. Amylopectin is a highly-branched polymer of α-D-glucopyranosyl units linked by (1-4)-α-linkages and by (1-6)-α-linkages that constitute the branch points. Each glucose unit possesses a maximum of three hydroxyls that can undergo chemical substitution.

Native starches can be physically and/or chemically modified for improved functionality. The most common sources of native starch used in these modifications are various roots, tubers, cereals, and legumes. Modified starches are used in applications requiring special properties not manifested by native starches.

Chemical modifications of food starches are often performed, in an aqueous suspension under controlled conditions of pH, time, and temperature.

After sufficient reaction time, the modified starch is recovered by filtration or centrifugation, washed with water, dried and packaged.

The relevant modification reactions can be, separately or in combination, fragmentations (hydrolysis, oxidation, enzymatic), bleaching, oxidation, esterification, etherification or phosphorylation of one or more of the hydroxyl groups of the α-D-glucopyranosyl units or cross-linking using polyfunctional agents.

Starches modified by fragmentation

Starches modified by fragmentation are food starches that have been treated using various methods to alter their molecular structure and physical properties. This treatment results in products containing polymers with a lower average molecular weight and reduced viscosity compared to native starches.

Examples of starches modified by fragmentation include:

The properties of the modified starches obtained by fragmentation vary depending on the source of the starch, reaction conditions (pH, time, temperature, reagents etc.). They are commonly used in applications that require reduced viscosity in hot solutions and/or use high levels of modified starches.

Bleached starch

The process of bleaching starch applies to Bleached starch (INS 1403), and all modified starches that are bleached.

Bleached starches are starches that have been treated with chemicals to improve their appearance. The process of bleaching involves the use of peracetic acid and/or hydrogen peroxide, sodium hypochlorite, sodium chlorite, sulfur dioxide, alternative forms of sulfites, potassium permanganate, or ammonium persulfate. The purpose of bleaching is to remove color due to the oxidation of trace pigments, such as phenolic compounds, carotenoids, and xanthophylls. The bleaching process is intended only to change the color and residual chemicals are either removed or limited to unavoidable levels.

Starches esterified and/or cross-linked with phosphorus-containing compounds

Starch Esterification and Cross-linking with Phosphorus-Containing Compounds

The following starches are included in this category:

Treatment Method: The process of esterification and cross-linking is achieved using phosphorus-containing compounds such as ortho-phosphoric acid, sodium or potassium ortho-phosphate, and sodium tripolyphosphate for esterification, and sodium trimetaphosphate or phosphorus oxychloride for cross-linking.

  • Monostarch phosphate (INS 1410) is created through the esterification of starch using ortho-phosphoric acid, sodium or potassium ortho-phosphate, or sodium tripolyphosphate.
  • Distarch phosphate (INS 1412) is obtained by cross-linking starch using sodium trimetaphosphate or phosphorus oxychloride.
  • Phosphated distarch phosphate (INS 1413) is produced by combining the processes of cross-linking and esterification, using sodium trimetaphosphate or phosphorus oxychloride for cross-linking and ortho-phosphoric acid, sodium or potassium ortho-phosphate, or sodium tripolyphosphate for esterification.
  • Acetylated distarch phosphate (INS 1414) is created by combining cross-linking and esterification, using sodium trimetaphosphate or phosphorus oxychloride for crosslinking and acetic anhydride or vinyl acetate for esterification.
  • Hydroxypropyl distarch phosphate (INS 1442) is produced by combining cross-linking and etherification, using sodium trimetaphosphate or phosphorus oxychloride for cross-linking and propylene oxide for etherification.

Phosphorylation partially substitutes the 2, 3, or 6 position of the anhydro glucose unit, unless the 6 position is occupied by branching. Crosslinking involves the use of a polyfunctional substituting agent, such as phosphorus oxychloride, to connect two chains. The structure can be represented as follows: Starch-O-R-O-Starch, where R represents the crosslinking group, and “starch” refers to the linear and/or branched structure.

Acetylated starches

Acetylated starches include:

This type of modified starch is obtained by esterification with acetic anhydride or vinyl acetate. The process results in the substitution of hydroxyl groups with acetyl esters.

  • Acetylated distarch phosphate (INS 1414) is obtained by first reacting starch with sodium trimetaphosphate or phosphorus oxychloride, followed by esterification with acetic anhydride or vinyl acetate.
  • Starch acetate (INS 1420) is obtained by directly esterifying starches with acetic anhydride or vinyl acetate.
  • Acetylated distarch adipate (INS 1422) is obtained by esterifying starch with acetic anhydride and then esterifying/cross-linking with adipic anhydride.
  • Acetylated oxidized starch (INS 1451) is obtained by treating starch with sodium hypochlorite and then esterifying it with acetic anhydride.

Starches subjected to oxidation

The specific types of modified starches that are the result of an oxidation treatment:

  • Oxidized Starch (INS 1404)
  • Acetylated Oxidized Starch (INS 1451)

PROCESS

  • Oxidized Starch (INS 1404) is obtained by treating starch with sodium hypochlorite, a process that results in the deliberate creation of carboxyl groups.
  • Acetylated Oxidized Starch (INS 1451) is obtained by treating starch with sodium hypochlorite and then esterifying the modified starch with acetic anhydride.

Starches esterified with octenyl-succinic anhydride

The treatment applies to starch sodium octenyl succinate (INS 1450). Starch is esterified with octenyl-succinic anhydride and neutralized using sodium hydroxide or sodium carbonate as a pH buffer.

Starches etherified with propylene oxide

The treatment of starches that are etherified with propylene oxide applies to two specific types of starches: Hydroxypropyl starch (INS No. 1440) and Hydroxypropyl distarch phosphate (INS No. 1442).

The process of etherification with propylene oxide is called hydroxypropylation and results in the substitution of hydroxyl groups with 2-hydroxypropyl ether.

Starches cross-linked with Adipic Anhydride

Acetylated distarch adipate (INS No. 1422) is produced by cross-linking starch with a reagent made by combining adipic acid and acetic anhydride. The starch is then acetylated through the esterification process using acetic anhydride. The final product consists of starch that has been both cross-linked and acetylated. The structure of the cross-link, which is created by adipic anhydride connecting two starch chains, can be represented as: Starch-O-R-O-Starch, where R = CO-(CH2)4-CO and starch refers to the linear and/or branched structure.

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