Amylopectin Structure and Starch Granule Behavior

Amylopectin Characteristics

Amylopectin:

• Branched chain links 1 to 4 and to 1-6.
• Generates a high viscosity due to its branching structure and high Polymerization Medium (PM).
• During cooking, it absorbs a lot of water, being largely responsible for the swelling of starch granules.
• Virtually no gels form; this takes a long time.
• Their solutions do not recrystallize, possessing a high water retention power.
• Almost no retrogradation, except in bread.
• Adsorbs only a small amount of iodine, producing a red complex.

Structure of Starch Granules

Structure of Starch Granules

They consist of several layers arranged around a central region called the nucleus. The molecules are arranged in a specific order. The reason for this structure is the presence of microcrystals formed by side chains of amylopectin. In its native form, it has a high density and a high degree of compaction, which causes mechanical stress support. It is practically insoluble in cold water.

Starch Granules and Heating

Starch Granules and Heating

If starch comes in contact with water and is heated, it produces water absorption and an increase in volume (swelling). This phase is reversible; it can dry out and return to its original size.

If the temperature increases, swelling continues, causing the crystals to "melt" and the starch to gel. A characteristic of this state is the increased viscosity of the starch suspension because the swollen granules adhere to each other.

If the treatment continues, the granules disintegrate, and the starch enters the solution; these last stages are irreversible.

Heating also produces a partial hydrolysis, and the viscosity decreases, leading to the almost total dissolution of starch.

The product resulting from this treatment may become dehydrated, obtaining an amorphous powder readily dispersible in cold water. This is the basis for the production of soluble starch and instant precooked cereal products (pregelatinized starch).

The gelatinized starch is more digestible by amylolytic enzymes.

Making Bread

Bread Making Process

The steps are: flour, water, NaCl, kneading, fermentation, rewinding, cutting, cooking, cooling, and yeast.

Kneading:

Gluten absorbs the added water. A structure with plastic properties is obtained. It can be shaped and increases in volume. The mass must also have good mechanical strength and elasticity to maintain its shape, volume, and porous texture. A network forms between proteins and glycolipids, surrounding the starch granules.

Additionally, polar lipids and triglycerides partially bind to gluten. The development of gluten extensibility and elasticity is due to disulfide bonds.

Fermentation:

Release of maltose by enzyme action. Degradation of glucose by yeast. Generation of CO2 and ethanol from glucose.

Cooking:

Increase in glycolipid-starch interactions (via hydrogen bonds). Partial gelatinization of starch. The yeasts die, and enzymes are inactivated. The proteins, especially albumin and globulins, coagulate. Water is lost.

Cooling:

Amylose extracted during kneading and baking crystallizes.