Starch is one of the most abundant biopolymers and serves as energy reserve in many plants including cereals, tubers, roots, fruits and seeds. Due to their poor shear and thermal stability and high degree of retrogradation, starch does not have physical and chemical properties suitable for certain type of processing in its native form. Furthermore, native starches can easily undergo syneresis besides the gelling tendency of the pastes. In order to promote and enhance specific functional properties, starches are frequently modified by physical, chemical and enzymatic processes.
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Starches have been modified by adopting various methods of modification in order to acquire the desired industrial applications. Generally, there are four basic broad kinds of starch modifications: physical, chemical, enzymatic and genetic. We mainly focus on the first two methods.
Physical modification of starch can be safely used in food products and can be achieved through alcoholic-alkaline, micronization and drum drying. Some of the new physical methods used for starch modification that have been developed over the past few years are listed below.
Pre-gelatinized starch (PGS)
Pre-gelatinized starches also called as instant starches are pre-cooked and dried with the help of a drum that enable the products to form moderate stable type of suspension that disperse in cold water.
Hydrothermal modification
Annealing (ANN) and high moisture treatment (HMT) are the two most widely accepted hydrothermal treatments used to modify the starches without losing the integrity of the granules.
Non-thermal physical modification
Non-thermal treatments (such as ultrasound effect, high hydrostatic pressure and microwave treatment) can be used to preserve color, texture, taste, nutrients and other components as compared to the traditional thermal processes.
Chemical modification is carried out by introducing a functional group into the polymer molecule of the starch granule in its native form that brings about distinctive changes in the physicochemical properties of starch molecule.
Acetylated (Ac) starch
Acetylation of starch is a common chemical modification method during which part of the hydroxyl groups of glucose molecule is replaced by acetyl group resulted into modified molecular structure of the starch.
Cationic starch
Cationic starches are vital industrial derivatives produced by introducing a positive ionic charge with the help of functional groups such as ammonium, imino, amino, sulfonium or phosphonium.
Cross-linked starch
Cross linking is a chemical modification method during which the native starches are chemically modified using different cross linking agents like sodium trimetaphosphate (STMP), sodium tripolyphosphate (STPP), epichlorohydrin (ECH) and phosphoryl chloride (POCl3).
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