Native starches are structurally too weak and limited functions for application in pharmaceutical, food and non-food technologies due to its inherent weakness of hydration, swelling and structural organization. Unprocessed starches produce weak-bodied, cohesive rubbery pastes when cooked and undesirable gels when the pastes are cooled. To enhance viscosity, texture, stability among many desired functional properties desired, starch and their derivatives are modified by chemical, physical, and enzymatic methods. Modifications are necessary to create a range of functionality.
Starch modification can be introduced by altering the structure and affecting the structure including the hydrogen bonding in a controlled manner to enhance and extend their application in industrial prospective. This modification includes esterification, etherification, cross linking, acid hydrolysis, enzymatic hydrolysis heat treatment and grafting of starch. Modified starches can be found applicable practices in food industry and non-food industry.
Various types of modified starches for wide applications in many industries
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It is the simplest starch modification, prepared by cooking. It maintains starch integrity while providing cold water thickening which is a process that breaks down the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites (the hydroxyl hydrogen and oxygen) to engage more water.
Cross linking is the most important modified form that used in the food industry. It involves replacement of hydrogen bond present between starch chains by stronger, permanent covalent bonds. Distarch phosphate or, adipate are commonly used in cross-linked starch. Cross-linked starches offer acid, heat and shear stability over the native starch. Food with this type of starch processing tends to have longer shelf life.
The processing includes reaction with oxidizing agent such as sodium hypochlorite or peroxide. This type of starch is mainly used as surface sizing agent or coating binder and available in different viscosity grade. Oxidized starches have shorter chain lengths than native starches. It improves whiteness and reduces microbiological content. Oxidized starches are the best thickener for applications requiring gels of low rigidity. This improves adhesion in batters and breading.
Cationic starches are produced by reacting native starches with tertiary
or, quaternary amines, using wet or dry production processes. They are mainly used in
paper forming process. Cationic starch represents high performance starch derivatives widely used by paper manufactures to increase strength and retention. Cationic starches carry a formal positive charge over the entire pH range creating their affinity towards negatively charged substrates, such as cellulose, pulp and some synthetic fibres, aqueous suspensions of minerals and slimes and biologically active macromolecules. Cationic starch is also added at the beater to improve drainage on the wire, better sheet formation, and enhancement of the sizing efficiency of an alum-rosin size.
Anionic starches are prepared by reaction with phosphoric acid and
alkali metal phosphates or by making derivative with carboxymethyl group.
These are produced through depolymerisation reaction by hydrochloric acid or other acids. Unmodified starches are treated with a mineral acid at temperature lower than gelatinization and results in partially hydrolyzed starch molecules. This cleaves the chain length and lower viscosity. It increases the tendency to retro gradation. The lower viscosity permits higher concentrations to be used forming rigid gels in gums pastilles and jellies. In these applications, increased set-back leading to the formation of strong gels gives these starches significant advantages over native starches. Extended applications in food industry are found by acid-thinned starch in conjunction with esterification and etherification reaction.
Acetylated starch (E1420) esterification with acetic anhydride Starch after treatment with acetic anhydride produces starch esters which are useful in biodegradable applications. In particular, high starch acetates provide thermo plasticity, hydrophobicity and compatibility with other additives. The result of this treatment is a stability starch which will produce pastes that will withstand several freeze-thaw cycles and prevent syneresis (weeping) occurs. Wide applications are in foods as texturing agent and provide good freeze-thaw stability. Extended applications in food industry are found by acetylated starch in conjunction with cross-linked starch.
Dextrin (E1400) is formed by roasting the starch with hydrochloric acid. Dextrination is the heating of powdered starch, mostly in the presence of small amounts of acids, at different temperatures and with different reaction times. Dextrin is used as adhesives in paper and textile based industry.
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Grafted starches are produced by free radical copolymerization with
ethylenically unsaturated monomers. Starch grafted with synthetic polymers is most
utilized starches from different botanical origins were grafted with 1, 3 butadiene, styrene,
acrylamide, acrylonitrile and Meth acrylic acid using free redox reaction.
Starch ethers are produced by a nucleophilic substitution reaction with an ethylenically unsaturated monomer, followed by acid-catalyzed hydrolysis for viscosity adjustment.
Physically modified starch
Native starch can be modified with mechanical treatment, using spray drying technique, annealing technique
Enzyme modified starch
Enzyme-treated starch which includes maltodextrin, cyclodextrin Starch modified with amylase enzyme produces derivative with good adhesion property and mainly used in coating the food with colorant.
APPLICATION IN FOOD INDSUSTRY
To stabilize the food products starches are used in frozen bottle foods to provide freeze-thaw stability and retrogradation.
Modified starches are used to encapsulate or, preserve the flavour of the food products. Octenylsuccinylated derivatives and other starch hydrolyzates are used as flavour encapsulation.
Modified starches are used in a wider way to the dairy products; it provides variety of effects, including enhanced viscosity, cut ability, mouth feel and stability. In puddings, starch is used to enhance viscosity and smoothness. Starches are used in yogurts and sour cream to control syneresis and enhance thickness.
Canning process preserves food for up to several years by achieving a temperature sufficient to destroy or inactivate food poisoning or spoilage microbes. Starch is most commonly used to thicken, stabilize and enhance the mouth feel of canned foods such as puddings, pie- fillings, soups, sauces and gravies. Highly cross-linked starches are used for this purpose.