Physical modifications of starches are changes in their properties caused by physical treatments without any chemical changes to the starch molecule. These treatments can be divided into thermal and nonthermal, although some nonthermal treatments may have a thermal component.
Thermal Treatments
Pregelatinized Starch
Pregelatinized starch is a type of starch that has been pre-cooked and then dried to form a powder. This process gelatinizes the starch, which makes it easier to dissolve in water and improves its stability in food and other applications.
Granular Cold-Water Swelling Starch
Granular Cold-Water Swelling Starch is a type of starch that has the ability to rapidly absorb cold water, swelling and forming a gel in a short period of time, without the need for heat treatment. It is often used as a thickener or binder in food and industrial applications.
Heat-Moisture Treatment
Heat-Moisture Treatment is a process that involves heating and moisturizing of starch to modify its properties for use in various food and industrial applications. It results in changes in the physical and chemical properties of the starch, such as increased solubility, stability, and viscosity. This process is used to improve the functional properties of starch, making it more suitable for use in a variety of applications.
Annealing
Annealing is a process of heating and cooling a material to change its properties, such as increasing its ductility and reducing brittleness. It is commonly used in metallurgy and materials science to improve the workability and structural integrity of metals, alloys, and certain polymers.
Heating Dry Starch
Heating dry starch is a patented process that changes its properties. It’s done by heating starch with less than 15% moisture to a temperature between 100°C and the temperature where it starts to break down. This makes the starch more resistant to acid, shear, and temperature. Low moisture and alkalinity make the transformation easier. Another way to heat starch is using a fluidized bed, but this method has only been tested using amaranth flour.
“Osmotic Pressure Treatment”
BeMiller and Huber (2015) analyzed the results of the three studies supposedly reporting changes in starch properties effected by osmotic pressure treatment (OPT) and concluded that the changes were the result of heating the starch in a kosmotropic solution which restricted granule swelling and gelatinization, so OPT is actually another type of hydrothermal treatment.
“Nonthermal” Treatments
BeMiller and Huber (2015) pointed out that, in the treatments categorized as being nonthermal because heat is not applied intentionally, the force applied may often generate intense heat in local areas that can heat the entire system.
Ultrasonic Treatment
Ultrasound treatment of starch involves heating and high-shear stresses in aqueous systems. This process can be used in food processing and can be affected by variables such as temperature, treatment time, starch concentration, power, frequency, and amplitude of the ultrasound.
Milling
Ball milling of starch is a process in which starch particles are subjected to mechanical stress using a ball mill machine. The mechanical force created by the rotating balls leads to the disruption and fragmentation of the starch granules. This process results in the modification of the starch properties and can alter its functionality, for example, changing its solubility, gelation, and viscosity characteristics. Ball milling is commonly used in the food industry to improve the functional properties of starches for specific applications.
High-Pressure Treatment
High-pressure treatment has two types: ultrahigh-pressure (UHP) and using homogenizers. UHP is a static type used for food processing. Homogenizers create turbulence, high shear, and cavitation by forcing a starch slurry through an orifice under high pressure. These treatments have different effects on starch.
Pulsed Electric Field (PEF)
Pulsed Electric Field (PEF) is a technology used in food processing that has benefits such as low processing temperature, continuous processing, short treatment time and uniform treatment intensity. It has been successfully used for the non-thermal pasteurization of liquids.
Freezing and Thawing and Freeze-Drying
Szymonska and Krok (2003) and Szymonska and Wodnicka (2005) found that freezing and thawing potato starch granules with 13% moisture caused changes in the starch, such as surface erosion and increased pore size, as found by Szymonska and Krok (2003) and Szymonska and Wodnicka (2005).
Physical Treatments That Produce Chemical Changes
These treatments are physical treatments and do not involve added reagents, but this author does not consider that they produce physically modified starch because the chemical structures of the starch polysaccharide molecules are changed (BeMiller and Huber, 2015). Gamma irradiation produces low-molecular-weight carbonyl compounds and organic acids via generation of free radicals, so the starch polysaccharides are definitely degraded. Ultraviolet irradiation effects cross-linking, oxidative photodegradation (in the presence of air), and depolymerization via generation of free radicals. Cold plasma (glow discharge plasma, low-temperature plasma) also generates free radicals on starch polysaccharide molecules and may produce some cross-linking.