The key difference between gelatinization and retrogradation is that gelatinization refers to the act of making or becoming gelatinous, whereas retrogradation refers to the motion in a retrograde manner.
The terms gelatinization and retrogradation describe the properties of starch. Starch is a polymeric carbohydrate that consists of numerous glucose units that are joined by glycosidic bonds. It is a polysaccharide that is produced by most of the green plants as an energy-storing substance.
CONTENTS
1. Overview and Key Difference
2. What is Gelatinization
3. What is Retrogradation
4. Side by Side Comparison – Gelatinization vs Retrogradation in Tabular Form
5. Summary
What is Gelatinization?
Gelatinization is the breaking down of intermolecular bonds between starch molecules, allowing the hydrogen bonding sites to engage more water molecules. Generally, we use this term to describe starch, so it’s normally known as starch gelatinization. When there are water and heat, the intermolecular bonds between starch molecules tend to breakdown and, the hydrogen bonding sites gain the ability to hold more water molecules in these sites. Then, the starch granules become dissolved in water irreversibly and act as a plasticizer.
Figure 01: Rice Starch seen on Light Microscope
The process of gelatinization occurs in three steps: starch granule swelling, melting, and amylose leaching. When we heat the starch sample, swelling occurs due to the absorption of water into the amorphous space of starch. Thereafter, the water enters the tightly bound areas of starch granules, which contain helical structures of amylopectin. Normally, water cannot enter this region, but heating allows this to occur. Then the penetration of water increases the randomness of starch granules, which leads to the disintegration of starch.
There are some factors that affect the gelatinization process including the type of plant from which the starch is obtained, amount of water present in the medium, pH, concentration of salt in medium, sugar, proteins and fat content.
What is Retrogradation?
Retrogradation is a chemical reaction that takes place when amylose and amylopectin chains in cooked gelatinized starch realign themselves when cooling the starch sample. In other words, it is the motion of these polymer chains in a retrograde manner.
If we heat starch and dissolve it in water, it causes the destruction of the crystalline structure of amylose and amylopectin molecules, which leads to hydration and forms a viscous solution. If we cool this viscous solution or leave it in a low temperature, the linear molecules (amylose) and the linear parts of amylopectin molecules tend to retrograde and rearrange themselves again, forming a more crystalline structure. The linear parts of the molecules tend to place themselves in a parallel manner, forming hydrogen bridges. In this process, we can observe that the amylose crystallization is faster than the amylopectin crystallization.
Furthermore, retrogradation can cause the expel of water from the polymer network. This process is called syneresis. However, we can observe a small amount of water on the top of the gel. This retrogradation process is directly related to staling or ageing of bread. Moreover, retrograded starch is less digestible. However, the chemical modification of starch can lead to the reduction or enhancement of the retrogradation process. Additives such as fat, glucose, sodium nitrate, etc. can reduce the retrogradation process of starch.
What is the Difference Between Gelatinization and Retrogradation?
Gelatinization and retrogradation are properties of starch that vary with heat. Gelatinization is the breaking down of intermolecular bonds between starch molecules, allowing the hydrogen bonding sites to engage more water molecules. Retrogradation, on the other hand, is a chemical reaction that takes place when amylose and amylopectin chains in cooked, gelatinized starch realign themselves when cooling the starch sample. The key difference between gelatinization and retrogradation is that gelatinization refers to the act of making or becoming gelatinous, whereas retrogradation refers to the motion in a retrograde manner.
Below infographic tabulates more differences between gelatinization and retrogradation.
Summary – Gelatinization vs Retrogradation
Gelatinization and retrogradation are properties of starch that very with heat. The key difference between gelatinization and retrogradation is that gelatinization refers to the act of making or becoming gelatinous, whereas retrogradation refers to the motion in a retrograde manner.
Reference:
1. “Retrogradation (Starch).” Wikipedia. 10 Sept. 2020, Available here.
Image Courtesy:
1. “Rice starch – microscopy” By MKD – Own work (CC BY-SA 3.0) via Commons Wikimedia