Chemistry and physics

The composition of baked goods, for example potatoes, can be delineated into five major components, which are lipids, sugar, water, hydrophilic macro molecules such as proteins, and starch granules. The potential interaction of these species with each other is what defines the characteristics of a baked potato. One method to characterize the kinetics of the baking process for a potato is through examining the physiochemical properties of the starch granule.[4]

Composition of a Starch Granule
Amylose 23%
Lipids 0.09%
Protein 0.05%
Phosphorous 0.04%
Ash 0.3%
Amylopectin 76.52%

As the chart above shows a starch granule is mainly composed of amylose (long straight chains of glucose units joined by a 1,4-glycosidic linkage) and amylopectin (a branched molecule of many glucose units). Prior to cooking the amylopectin is in a co-crystalline complex with the amylose. During baking, which can be thought of as a melting phase transition for the starch granule, the starch goes through three structural changes, the starch swells by absorbing water and increases its volume, the crystalline structure melts, and the granule is disrupted releasing the amylose.[4]

This releasing of amylose is important because it reacts with iodine. This can be used to show the extent of the reaction, because iodine forms a blue complex with the free amorphous amylose. Looking at a cross section of a potato then one can see the region, which has started this gelatinization process and the untransformed region. From this the kinetics of the conversion can be examined.