When starch granules are heated in excess water, hydrogen bonds in the crystalline regions disrupt, causing water uptake, rapid swelling, and irreversible loss of the characteristic 'Maltese cross' polarization pattern (loss of optical birefringence). The temperature range where this transition occurs is defined as the gelatinization temperature (typically $60 - 75^\circ\text{C}$ for cereal starches).

Option analysis:

• Retrogradation temperature: Re-association and crystallization of amylose chains upon cooling.
• Gelatinization temperature: Correct, temperature at which crystalline order collapses and granules swell with loss of birefringence.
• Cooking temperature: General non-scientific operational term.
• Boiling temperature: Temperature at which liquid vapor pressure equals atmospheric pressure ($100^\circ\text{C}$).