Starch gelatinization is a stage in the cooking or baking process where the starch granule swells and absorbs water and becomes functional.

Starch Gelatinization


What is Starch Gelatinization?

Starch gelatinization is a stage in the cooking or baking process where the starch granule swells and absorbs water, becoming functional. When starch is placed into a solution, it turns the solution from a thin and runny to a thick and viscous solution.

Starch gelatinization is the collapse (disruption) of molecular orders within the starch granule manifested in irreversible changes in properties such as granular swelling, native crystalline melting, loss of birefringence and starch solubilization.2

Function

Starch is the main component in grain-based flour. In wheat, it can consist of as high as 75% of the flour.1 This makes it an important component of the baked product, functionally and nutritionally. Starch gelatinization is a stage in the cooking or baking process where the starch granule swells and absorbs water and becomes functional, causing an increase in viscosity (pasting) of the batter or the dough. The gelatinization and pasting of starch during baking is controlled not only by temperature, but also by the availability of water.5 Available water may be limited by the presence of ingredients such as proteins, pentosans, sugar and shortening in the formula.5

When viewed in polarized light, native starch show birefringence in the shape of a ‘maltese cross’(Fig. 1).  Once starch gelatinization occurs, this birefringence is lost. The starch granule swells and becomes less crystalline. Understanding when starch gelatinization occurs during the baking process will assist in the thermal profile and the quality assurance of a baked product.

Fig 1: Starch under polarized light showing birefringence.6

Fig 1: Starch under polarized light showing birefringence.6

Application

Starch gelatinization plays an important role in the textural quality of freshly baked products and may influence the shelf life of the products.5

The availability of water affects the temperature at which wheat starch gelatinizes. Literature states that wheat starch gelatinization starts occurring about 60°C (140°F) to 70°C (158°F).3 It is general knowledge in the profiling of dough and bread products that starch gelatinization be targeted at a temperature of 75°C (167°F) in baking pan bread.4 Starch gelatinization in bread should be targeted by 60% of the bake time. This can be read by a thermal profiling instrument. As temperature increases from crust to the crumb region of bread similarly, starch gelatinization also progresses from crust to the crumb region.7

The extent of gelatinization and pasting, and the subsequent proportion of folded or collapsed granules, varied from relatively little in pie crust and sugar cookies to nearly 100% in angel food cake (Table 1).

Microscopic Methods
Scanning Electron Light
Baked Product Degree of deformation and folding % Loss of birefringence
(Values are given as total starch)
Angel Food Cake Very High 100
White Bread High 100
Cake Doughnuts Intermediate 98
Cinnamon Roll Intermediate 98
Pie Crust Low 50
Sugar Cookie Low 9

Table 1: Extent of gelatinization of starch in baked products.5

References

  1. Watt, B., and A. L. Merrill. “Composition of Foods – Raw, Processed, Prepared.” USDA Handbook. Revised Edition 8 (1963)
  2. Lim, S. T., T. Kasemsuwan, and J. Jane. “Characterization of Phosphorus in Starch by P-nuclear Magnetic Resonance Spectroscopy.” Cereal Chemistry 71 (1994): 488.
  3. Mathewson, P. R. “Enzymatic Activity during Bread Baking.” Cereal Foods World 45.3 (2000): 98.
  4. Sikora, Marek, Stanislaw Kowalski, Magdalena Krystyjan, Rafal Ziobro, Paulina Wrona, Duska Curic, and Alain Lebail. “Starch Gelatinization as Measured by Rheological Properties of the Dough.” Journal of Food Engineering 96.4 (2010): 505-09.
  5. Lineback, D. R., and E. Wongsrikasem. “Gelatinization Of Starch In Baked Products.” Journal of Food Science 45.1 (1980).
  6. Chung, H. J., and Liu, Q.  “Effect of Gamma Irradiation on Molecular Structure and Physiochemical Properties of Corn Starch.” Journal of Food Science, 2009 Jun;74(5):C353-61. doi: 10.1111/j.1750-3841.2009.01159.x.
  7. Chhanwal, Narayansing, and Chinnaswamy Anandharamakrishnan. “Temperature‐ and Moisture‐Based Modeling for Prediction of Starch Gelatinization and Crumb Softness during Bread‐Baking Process.” Journal of Texture Studies 45.6 (2014): 462-476.