A Tasting of Culinary Science—Starch

Summary

This video explores the fascinating role of starch in cooking and its chemical properties. It explains how starch, a polymer of glucose, is stored in plants and undergoes gelatinization when heated with water. The process involves swelling, the breaking of hydrogen bonds, and thickening of the solution. It also covers retrogradation, where the starch molecules rebind upon cooling, causing water to escape and affect texture. The video highlights how these properties impact the making of sauces, gels, and baked goods, and provides insights into the behavior of amalopectin and amalos in cooking.

Takeaways

• 😀 Sunlight powers life on Earth through photosynthesis, where plants use sunlight and carbon dioxide to create sugars in their leaves.
• 😀 Plants store sugars as starch in their roots, which we can utilize in cooking due to its properties.
• 😀 Starch is a polymer of glucose and comes in two forms: linear amylose and branched amylopectin.
• 😀 Starch is stored in granules inside plant tissues, which expand when heated with water during a process called gelatinization.
• 😀 Gelatinization occurs when starch granules absorb water, swell, and break their hydrogen bonds, forming new bonds with water.
• 😀 Amylose, being linear, leaches out of the granules and helps thicken the starch solution when sheer force is applied.
• 😀 The expansion of starch granules and the release of amylose create a thickened solution by forming a tangled meshwork that slows water movement.
• 😀 If this meshwork is strong enough, it can immobilize water and form a gel, such as in gelled desserts.
• 😀 Retrogradation occurs as gelatinized starch cools, causing starch molecules to reform hydrogen bonds, firming the gel texture and releasing water (syneresis).
• 😀 Amylose is more prone to retrogradation due to its linear structure, whereas amylopectin resists retrogradation due to its branched structure.
• 😀 Retrogradation is responsible for the staling of bread and the liquid leakage from starch-thickened sauces, but it can be reversed by reheating the gel.

Q & A

What is photosynthesis and how does it relate to starch production in plants?

Photosynthesis is the process by which plants use sunlight and carbon dioxide to produce sugars, which they store as starch in their roots. This starch is a key source of energy for plants and also plays an important role in cooking, as it has properties that can be used to thicken sauces and create textures in food.

What are the two forms of starch found in plants?

The two forms of starch are amylose, which is linear, and amylopectin, which is branched. These forms of starch behave differently during cooking and contribute to the texture of food.

How does starch gelatinization occur?

Gelatinization happens when starch is heated in the presence of water. The starch granules absorb water, causing them to swell and break the hydrogen bonds between starch molecules. This process thickens the solution as the starch molecules separate and form new bonds with the water.

What happens to starch granules when heated in water?

When starch granules are heated in water, they absorb the water and swell to many times their original size. The granules rupture and release their starch content, thickening the solution.

Why does the solution thicken during starch gelatinization?

The thickening occurs because the swollen starch granules form a tangled meshwork that binds to water molecules, slowing their movement and increasing the viscosity of the solution.

What is retrogradation in starch, and how does it affect the texture of food?

Retrogradation occurs when a starch-thickened solution cools. The starch molecules form hydrogen bonds with each other, making the texture firmer and displacing the water that was surrounding the starch molecules. This process can result in the weeping of water from gels, such as in puddings or sauces.

Why is amylose more prone to retrogradation than amylopectin?

Amylose is more prone to retrogradation because it is linear, allowing it to stack closely together and form many hydrogen bonds with neighboring starch molecules. Amylopectin, being branched, does not easily line up with other molecules, which reduces its tendency to retrograde.

What is cineresis, and how does it relate to starch retrogradation?

Cineresis refers to the liquid that escapes from a gel, such as a starch-thickened sauce or dessert. It occurs as a result of retrogradation, when starch molecules bond together, forcing out the water trapped within the gel.

How does retrogradation affect the texture of bread?

Retrogradation in bread occurs when the starch molecules rebond during cooling, causing the bread's texture to firm up. This process contributes to the staling of bread, making it less soft and more rigid.

Can retrogradation be reversed, and if so, how?

Yes, retrogradation can be reversed by reheating the starch-thickened product. This breaks the starch-starch hydrogen bonds and allows water molecules to re-establish bonds with the starch, temporarily softening the texture before the retrogradation process occurs again upon cooling.