The process by which starch granules swell, rupture, and form a homogeneous paste-like solution in water at an appropriate temperature (which varies depending on the starch source, typically ranging from 60°C to 80°C) is known as gelatinization. The essence of gelatinization lies in the rupture of hydrogen bonds between the ordered and disordered (crystalline and amorphous) starch molecules within the granules, causing them to disperse in water and form a colloidal solution.
The process of gelatinization can be divided into three stages:
(1) The reversible water absorption stage: Water enters the amorphous regions of the starch granules, causing a slight increase in volume. If cooled and dried at this point, the granules can revert to their original state, and their birefringence remains unchanged.
(2) The irreversible water absorption stage: As the temperature rises, water penetrates the interstitial spaces between the starch crystallites, leading to substantial and irreversible water uptake. The phenomenon of birefringence gradually diminishes until it disappears completely-a process also referred to as the "dissolution" of crystallinity-and the starch granules swell to 50 to 100 times their original volume.
(3) The final disintegration of the starch granules, wherein all starch molecules disperse fully into the solution.
Starch that has undergone gelatinization is also referred to as "alpha-starch" (α-starch). By dehydrating and drying a freshly prepared slurry of gelatinized starch, one can obtain an amorphous powder that disperses readily in cold water; this product is known as "soluble alpha-starch."
Methods for Determining Starch Gelatinization:
These include optical microscopy, electron microscopy, light transmission analysis, viscometry, determination of swelling power and solubility, enzymatic analysis, nuclear magnetic resonance (NMR), laser light scattering, and others. In industrial settings, viscometry and the determination of swelling power and solubility are the most commonly employed methods.
